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Tech Information => Aerodynamics => Topic started by: speedrattle on July 29, 2018, 07:32:35 PM

Title: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on July 29, 2018, 07:32:35 PM
hey folks

i lurk here a lot but haven't posted. i'm looking for any and all suggestions on improving the aerodynamics of a naked 650 triumph i run in M/PG 650/4. we just got back from loring where the machine did extremely well, bumping the mile and the one-and-a-half mile record held by a good friend of mine to 130.935 and 134.287. we're going back in a month with some tweaked gearing and ignition timing to see if we can get 131 and 135.

all of the top three old british machines in this class are within about two miles an hour of each other, and we're not really looking at much more horsepower before we start blowing them up. so i'm looking for aero alternatives. my bike is a 1965 triumph bonneville, sort of, with a 1970 motor, sort of. i can't use any streamlining in front of the rider, although a 180-degree front fender is permitted. i'm allowed to use a seat with an aero shape behind my butt, so long as it doesn't go more than 3 inches back from the tire. here's what the machine looks like at the moment:

(https://i.imgur.com/ph1dHWll.png)
(https://i.imgur.com/94MALVkl.jpg)

right now i lie down with my chest on the top frame tube, with my head to the left and below the top triple clamp, level with the tanks. this gets my back down as low as i can, but i'm wondering if there are other things i might be thinking about.


Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: 55chevr on July 29, 2018, 08:09:15 PM
Tiger Racing front fender ---
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: tortoise on July 29, 2018, 08:33:58 PM
A straight side view of rider in full tuck position would be useful.

The original Bonneville tank, with the tunnel modified to mount lower maybe, would have to be better than flat-fronted cylinders.

Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: ETM on July 29, 2018, 11:15:06 PM
The down tubes in your exhaust are pretty draggy just hanging in the wind like that.  Consider turning them
inboard then turn them down in the wind shadow of the front tire.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: sofadriver on July 29, 2018, 11:43:42 PM
you already mentioned the obvious - you need a tail section.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: JimL on August 02, 2018, 12:03:39 PM
3 spoke mag wheels with aero shape spokes.  Wire wheels are pretty draggy.

Raise your seat position to flatten your back line.  Don Sligger told me to "raise your butt" during Speedweek '69.  I picked up 3-4 mph on the next run.

Clean up all the details.  Everything air flows over has drag....wires, cables, anything at all.  Before I was finished I was running the bikes with no opening in the fairing ahead of the engine.  It was a lot less drag than flowing air over the parts!

Flat blade girder forks are a lot less drag than round tubes.

The tail is an "anything helps" deal.  My 650 pushrod twin (gas engine) ran 164 with the tail and fairing.  I dropped to 134 with the outer aero removed!

Hope this helps.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Rex Schimmer on August 02, 2018, 02:11:39 PM
My favorite Bonneville springer forks:


Rex
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Stan Back on August 02, 2018, 03:59:47 PM
Don Sliger?

Boy, you are old.  Maybe you can tell some of these young'uns what he did – and when.  Royal Enfield, really?
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: WOODY@DDLLC on August 02, 2018, 04:24:33 PM
http://www.landracing.com/index.php/component/content/article?id=271
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: JimL on August 02, 2018, 04:41:44 PM
I did not know him well, but he was really nice and helpful to me.  My favorite memory:  I was in staging right behind him and had been struggling to get my 450 Honda above 120.  He asked what I was doing and I told him I had just geared it "too high".  I told him, "Don, dont fall down out there because if I cant get past 120 this time,  I am going to keep right on going and ride home to Colorado!"

He laughed and said, "Jim, I am going to go real fast, and if I fall down, I'd appreciate it if you would run me over right away."

My favorite pic is him sitting under his parachute sun shade, working on the single engine bike (which put up a very solid fuel record the next day).  Some folks don't know how tough those records we made were, back then.  First, you ran as hard as you could to qualify...and first thing next morning you made two more runs, back to back, with no repair time in between.  There were bikes that qualified ok, but didnt survive the actual record runs.

It was sure different.

He didnt fall down (close to 200) and my bike ran 124.65.  That was the day Bert missed a shift and spun the windings on his Indian's mag.  He and another fellow and I started up the mountain to strip "bell wire" from a plane crash magneto, but my little street bike couldnt make it up the silt.  They rewound the mag that night and my Dad stayed up all night watching. 

That week was a great experience for my Dad and I.  I had arrived home from Nam on July 17th and all you salt flats people yanked me right out of the war mentality, and planted me on the path to a better life.  Don is a small piece of the memory, but he was the right guy to meet, at that important moment.

Sorry for the long ramble...we get that way when we finally grow up and old.

Jim
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Peter Jack on August 02, 2018, 04:56:18 PM
That's not a ramble. That's history and a truly great story.  :cheers: :cheers: :cheers:

Thank-you JimL!

Pete
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: maj on August 02, 2018, 04:57:05 PM
Jim ramblings like that are gold  :cheers:

We went half hearted searching for that wreck a few years ago when the salt was wet and we were bored in Wendover , think we were in the wrong area
crossed the saddle (dodgy when damp) and went left instead of i think  right ?
road on the far side was cut up from rain anyway and were lucky to actually make it back

Back to the subject
smaller rider ;)
all the above esp raising your back  and will add rear wheel discs
Friction reduction, ceramic bearings, brakes backed off , non o ring chain ,  
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 02, 2018, 05:11:26 PM
dang. been locked out of here for days. people, thank you for your replies. i'll try to take them one at a time.

A straight side view of rider in full tuck position would be useful.

The original Bonneville tank, with the tunnel modified to mount lower maybe, would have to be better than flat-fronted cylinders.


i was using an old trident tank at first, but it was so wide i couldn't get my head down, and had to just rest my chin on top. with the tube tanks set below the frame, i can bend down to where i'm level with the triples trees:

(https://i.imgur.com/CxQT4xXl.png)

(https://i.imgur.com/CedD4ncl.png)

forgot to tell my daughter about persepctive, so you can't really see the wind shadow on the straight-on photo. lol, she can't hold a camera level, either.

i don't kno whether the shape of the tanks is important, as they're pretty well masked by the tach and the front forks. i can't make them smaller because they have to hold five liters, and i'm right there.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 02, 2018, 05:29:28 PM
Tiger Racing front fender ---

i'm running in modified, so while i can use a front fender, even one that flares in the fork tubes, it might get questionable with any aero shapes molded in. airtech makes this busa fender, which is getting closer, but i'm running a 19-inch front wheel, 110/90-19

(https://i.imgur.com/AJvnMBVl.png)

i'm looking for something like that  that will fit bewteen the fork legs.

you already mentioned the obvious - you need a tail section.

i can legally add a kamm tail seat, and for later next year i'm seriously considering it. there's a guy running an 850 commando in MPS, who goes 150-plus with this gigantic box behind his butt:

(https://i.imgur.com/iYtLFnQl.jpg)

but i want to do everything i can with the machine before i start adding bodywork, mostly because i'm chasing a 139 mph 650 record set by a guy on gasoline at bonneville without any bodywork at all. i'd like to see if i can get there.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 02, 2018, 05:36:09 PM
The down tubes in your exhaust are pretty draggy just hanging in the wind like that.  Consider turning them
inboard then turn them down in the wind shadow of the front tire.

i stuck them way out that way from the head to clear the magneto, then kept them out to the sides so i could add a megaphone that would clear the footpegs.

but i'm not going to use a megaphone after all, so i'll take your advice and build a new set this winter. this motor runs best with the pipes 36-inches long, and that would truncate them right about at the same position, far enough in front of the rear tire not to annoy the safety guys.

not much room there between the magneto and the wheel, but i should be able to do something.

(https://i.imgur.com/kaxzpR8l.jpg)
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: stay`tee on August 02, 2018, 07:28:28 PM
JimL's ramblings about Don Slinger reminded me of when visiting the National Motorcycle Museum in Solihull UK, thay had Don's twin engine 1500cc Royal Enfield bike on display,, in 1970 at Bonneville the thing set a class record at 194.726,, apparently it was the "first" naked bike to exceed 200mph at 203.16  8-)
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 02, 2018, 07:45:03 PM
smaller rider ;)
all the above esp raising your back  and will add rear wheel discs
Friction reduction, ceramic bearings, brakes backed off , non o ring chain ,  

my number-one daughter weighs 107 pounds. we're going to start her on a 300 ninja next year, i hope. i'm likely going to switch to cast wheels sometime.

i know nothing about ceramic bearings. why are they better?

3 spoke mag wheels with aero shape spokes.  Wire wheels are pretty draggy.

Raise your seat position to flatten your back line.  Don Sligger told me to "raise your butt" during Speedweek '69.  I picked up 3-4 mph on the next run.

Clean up all the details.  Everything air flows over has drag....wires, cables, anything at all.  Before I was finished I was running the bikes with no opening in the fairing ahead of the engine.  It was a lot less drag than flowing air over the parts!

Flat blade girder forks are a lot less drag than round tubes.

The tail is an "anything helps" deal.  My 650 pushrod twin (gas engine) ran 164 with the tail and fairing.  I dropped to 134 with the outer aero removed!

Hope this helps.

thanks. everything helps.

i'm looking at cast wheels from something like a 300 ninja. they're 17 inches, which is good, and about the same width as the old dunlop rims i'm running now. i'd have to adapt a disc brake in the back, but i don't need a front brake at all.

i'll be messing with riding position next month. i reinforced the pegs so i can stand up on them, and i tried it out last month. i was messing with pipes, jets, and ignition timing at the same time, though, and didn't pay any attention as to whether it was any better. but i've heard that making a wind tunnel through your legs helps close up the turbulence behind the rider. is that true?

Quote
My 650 pushrod twin (gas engine) ran 164 with the tail and fairing.  I dropped to 134 . . .

i'm intrigued. what exactly was that? i know a guy who does 166 on his 650 BSA, but he uses a turbo to get there.



Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Stan Back on August 02, 2018, 08:00:13 PM
Thanx JimL for your comments!

"goes 150-plus with this gigantic tail section"  –  It's probably not as gigantic as yours.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 02, 2018, 08:22:36 PM
JimL's ramblings about Don Slinger reminded me of when visiting the National Motorcycle Museum in Solihull UK, thay had Don's twin engine 1500cc Royal Enfield bike on display,, in 1970 at Bonneville the thing set a class record at 194.726,, apparently it was the "first" naked bike to exceed 200mph at 203.16  8-)

that machine is famous. i didn't know it ended up in the UK. is it still there?

a friend of mine with the second-fastest 650 has also built this. he was first-fastest until last month, but is planning on coming back.

(https://i.imgur.com/kOjX6lAl.png)

it ran one time last summer, and then ate a crank seal and lost pressure on one motor. but he runs an oil gauge, unlike everybody else, so the rider shut it down without any damage. did 141 on its first and only run. i'm waiting to see it when they bring it back.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: JimL on August 02, 2018, 08:56:02 PM
Before I finished the hobby, I thought about building an "ultimate" open bike....just for the fun of the challenge.  My pushrod Honda V-twins were such a wide engine that I never went onward.

The whole idea was that EVERYTHING has to have air flow across it when you are going fast.  Even things that are out of the direct airflow are still creating some air drag that adds to the total.

Those notes on ceramic bearings and such are very good.  I did go with those on my bike, and every little thing helps.

One of the ideas I had, which would aid aero without adding out-of-rule items, was to install the battery/box as low as possible just ahead of the rear tire (inline mounted).  There is a hard, high pressure area in front of the tire because it drags air around with it....and throws it into the oncoming air ahead of that tire.  That concept is why so many modern cars have spats hanging down in front of the tires.  Aero drag improvements help the mpg ratings and the manufacturers use those details.

When we prepared the Bonneville Prius (in 2004) with Car & Driver, we were told by Toyota engineers to lower the car until the spats could just touch the ground.  They knew very well how much drag a tire can create. 

In the bar cables could reduce a little drag, especially it the bars are not round section.

Anything that air flows across should have sharp rear corners (teardrop idea is great, but doesn't really work on a short bike).  Look at the new cars and you see more sharp corners at the back.  The whole principal of Kamm is a clean break.  As proof of little things adding up, look at the top of pickup tailgates, these days.  They all have added top width, sharp corner, and tuck-in for better air release of the high pressure stream that dives off the top of the roof.  Those folks are good engineers and we should all pay attention to what they are learning.  The latest Tacoma has air straighteners to keep airflow under the mirrors from tumbling through the front door handle.

Everything can make a small difference.  You could really have fun with your project and perhaps open a new chapter in un-streamlined bikes!

Good luck and success, while you go forward.

JimL
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 02, 2018, 10:07:45 PM
Everything can make a small difference.  You could really have fun with your project and perhaps open a new chapter in un-streamlined bikes!

i'll still be playing follow the leader for some time. i currently have the fastest production-framed triumph in the running, but there is a faster one running in altered that might be within reach before too long:

(https://i.imgur.com/DgCMf2sl.png)

^^^this 650 triumph went 139 on gasoline and 175 on nitromethane. 139 mph on any naked machine with a naturally-aspirated gas triumph motor is something to be proud of.

Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: stay`tee on August 03, 2018, 01:17:16 AM
It was 2010 when I was there, not sure if its still on display,, I have some photos that I tried putting up here but this site is telling me thay are too large at over 500kb  :|
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Frank06 on August 04, 2018, 07:19:06 AM
Re: riding position.  I would experiment a bit, try keeping your head centered (just make sure you can see where you're going!) then raising your back, etc.  Hopefully there will be no shortage of runs available to experiment.  Did you try a different helmet (one without the lip)?

I've been told that ceramic bearings make a difference at 200 mph, I imagine the impact would be more significant at lower speeds.  I don't know if anybody has ever made back-to-back runs in an effort to try to quantify.  Wheel bearings are an obvious choice but I've also heard of guys changing transmission bearings.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Stan Back on August 04, 2018, 11:04:59 AM
Seems like a clever guy could test helmet and riding positions and more at little or no expense with coast-down testing.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: JimL on August 04, 2018, 03:04:30 PM
Balanced aero on a motorcycle is more important than we think.  Anyone who has ridden in side winds notices that the bike loses a lot of power.  The reason goes back to the basic rule that:  HP = Torque x RPM divided by 5252.

If you have to lean the bike (even a little bit) to keep going straight, you must apply torque into the handlebars to counter the gyroscopic precession trying to turn the front wheel into the lean.  There is absolutely NO way to counter this effect if you are riding on a planet with gravity.

The amount of power absorption is pretty surprising, and explains why side-wind runs at Bonneville are really lousy for our bikes.

Let's imagine you are having to make a 5 pound push into the right bar (and a 5 pound pull on the left), to keep going straight while leaned.  If your bar length were 12" it means you are absorbing 10 lb-ft at the tire contact patch to hold your course.

If you have an engine that makes 50 lb-ft of torque at 5252 RPM, you just sucked up 10 horsepower with your handlebars, if that is the exact rpm you are riding.  I have had runs at Bonneville that I was pushing/pulling on the handlebar with a LOT of pressure, trying to hold my line.  The bike really slows down.....far enough that I have had to downshift to try to recover.  I have pushed the bars far enough to feel the front tire break loose and slide across the course.

That really ruins your run speed.

I had a couple years that the bike was always requiring handlebar pressure to run straight, in no wind conditions.  I reworked the fairing mounts to get both sides in balance....the bike was then easy to ride and went faster.

Food for thought.....and sometimes you can make some decisions based on the NWS isobar map predictions for the day.  When the isobars for the salt flats area are wide, it is time to make your runs.  It seems like it is just impossible to cover all the bases, but you must keep thinking, "everything matters".
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: maj on August 04, 2018, 03:30:35 PM
 "everything matters"

Actually i just realised were all talking Bonneville and you run mile events
if you get the chance, go to the salt . A mile is not long enough to try body position changes and see a result
On the salt everything has a visible reaction, just watch the tach , it tells all
think small, knees in elbows in toes in , bum up , head down , can you creep your hands along the bars a little more , lots of time so test it all

I run turbo bikes, harder to tell this sort of stuff , but back in 05 a mate let me take his NA bike for a run , i learnt so much more on that 1 run than i would have in 3 or 4 years of wheelspinning and fishtailing the turbo
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 04, 2018, 11:20:11 PM
Re: riding position.  I would experiment a bit, try keeping your head centered (just make sure you can see where you're going!) then raising your back, etc.  Hopefully there will be no shortage of runs available to experiment.  Did you try a different helmet (one without the lip)?

centering my head means i have to rest my chin on the top tube, way above the triple tree in the wind. ducking down means my head creates a wind shadow that conceals some of the rest of my body. i've run older-style bell helmets that just bounced from side to side at speed. this one with the lip actually has no discernable buffetting, so i'm guessing they got it right. smooth as glass at speed, rather thnanknocking my head back and forth. the shoei helmets have a kamm profile, and i'm look at the budget for one of those. my bell is getting chewed up from grinding against the fork tubes.

Quote
I've been told that ceramic bearings make a difference at 200 mph, I imagine the impact would be more significant at lower speeds.  I don't know if anybody has ever made back-to-back runs in an effort to try to quantify.  Wheel bearings are an obvious choice but I've also heard of guys changing transmission bearings.

i'm looking at wheel bearings for the winter rebuild, along with all the other small increment stuff. dunno about transmission bearings. the layshaft runs in wet needles, so i'd only get to change out the mainshaft ball and roller. maybe it would be something.

did you run something up there last month? i was busy and didn't have much time to talk to people.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 04, 2018, 11:29:07 PM
Seems like a clever guy could test helmet and riding positions and more at little or no expense with coast-down testing.

i wish i could. appalachian ohio doesn't have a lot of sweeping downgrades.  that's the main obstacle. but maybe i could figure something out. the race bike isn't even barely street-legal, but i can fake head and tailights.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 04, 2018, 11:36:43 PM
Food for thought.....and sometimes you can make some decisions based on the NWS isobar map predictions for the day.  When the isobars for the salt flats area are wide, it is time to make your runs.  It seems like it is just impossible to cover all the bases, but you must keep thinking, "everything matters".

i run whenever i can, make notes of the conditions, and then try to make sense of it afterwards. the fastest runs at loring in july were the last day, when there was a seven mph tail wind and the relative air density was 105, highest of all four days. all our runs are in one direction, one time, so that really makes a difference. when the wind is in your face, everything sucks.

but at loring, we're looking at a 12,000-foot runway, the longest straight paved race course in the world. if the wind is right, and your machine is right, you can do very well.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 04, 2018, 11:42:52 PM
"everything matters"

Actually i just realised were all talking Bonneville and you run mile events
if you get the chance, go to the salt . A mile is not long enough to try body position changes and see a result
On the salt everything has a visible reaction, just watch the tach , it tells all
think small, knees in elbows in toes in , bum up , head down , can you creep your hands along the bars a little more , lots of time so test it all

I run turbo bikes, harder to tell this sort of stuff , but back in 05 a mate let me take his NA bike for a run , i learnt so much more on that 1 run than i would have in 3 or 4 years of wheelspinning and fishtailing the turbo

i'd love to do bonneville, but it's so expensive for me to get there-- 1920 miles-- that i want to do everything i can on the mile events in the east before i spend the money. i used to live in california, but that was a lifetime ago.

the difference with the short and long events is just as you say-- i don't have time to change things and watch the tach, i have to be right the first time or i'm slow. still, i have 1.5 miles to get up to speed, even though i don't get to run a flying mile at the end.

interesting that you learnt as much as that on a slow bike. my machine is slow by modern standards-- 130 mph or so-- which means i live and die by the wind, not by horsepower. i'm barely accelerating at the mile, and pick up four mph by 1.5. at that point it's all wind.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Buamotorsport on August 05, 2018, 01:19:42 AM
1920 miles? Is that all......it’s around 6000 if not more for me. Fly London to LA ....then pick the car up and tow to Bonneville. Lol. It’s worth every cent.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: maj on August 05, 2018, 02:34:48 AM
And 8268.5 miles for me , made the trip for 10 yrs this season will be 11
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Koncretekid on August 05, 2018, 07:10:44 AM
Kevin,
Although there's no substitute for going to the Salt Flats during an event for new ideas, you can learn a lot just from the photos that are posted by Scooter Grubb (https://www.scootershoots.com/BUBMotorcycleSpeedTrials/2014-Bonneville-Motorcycle-Spe/) and Phil Hawkins (http://ishootfromthehip.com/contact.html) as well as the photo gallery on this site.
Tom
P.S. For example, Scooter's BMST photos, 2014, page 17, photo 337
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 05, 2018, 05:35:29 PM
And 8268.5 miles for me , made the trip for 10 yrs this season will be 11
1920 miles? Is that all......it’s around 6000 if not more for me. Fly London to LA ....then pick the car up and tow to Bonneville. Lol. It’s worth every cent.

it's worth it, but that's simply more money than i have, worth it or not. i've got two kids in college and three more headed in. but if i strike the lottery i'll be there.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Larry Forstall on August 05, 2018, 09:12:01 PM
The rules state that streamlining is anything IN FRONT of the Rider that acts to guide the air around the bike. How about a nice belly pan that goes from the front of the engine to the rear where a batwing guides the air around the tire ?  NASCAR teams had lots of neat ideas such as oval exhausts and very wide flat bottom oil pans. Rules now do not allow anything. Much more fun in the old days .   LSL
Title: Re: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: Frank06 on August 06, 2018, 04:22:24 AM
Re: riding position.  I would experiment a bit, try keeping your head centered (just make sure you can see where you're going!) then raising your back, etc.  Hopefully there will be no shortage of runs available to experiment.  Did you try a different helmet (one without the lip)?

centering my head means i have to rest my chin on the top tube, way above the triple tree in the wind. ducking down means my head creates a wind shadow that conceals some of the rest of my body. i've run older-style bell helmets that just bounced from side to side at speed. this one with the lip actually has no discernable buffetting, so i'm guessing they got it right. smooth as glass at speed, rather thnanknocking my head back and forth. the shoei helmets have a kamm profile, and i'm look at the budget for one of those. my bell is getting chewed up from grinding against the fork tubes.

Quote
I've been told that ceramic bearings make a difference at 200 mph, I imagine the impact would be more significant at lower speeds.  I don't know if anybody has ever made back-to-back runs in an effort to try to quantify.  Wheel bearings are an obvious choice but I've also heard of guys changing transmission bearings.

i'm looking at wheel bearings for the winter rebuild, along with all the other small increment stuff. dunno about transmission bearings. the layshaft runs in wet needles, so i'd only get to change out the mainshaft ball and roller. maybe it would be something.

did you run something up there last month? i was busy and didn't have much time to talk to people.
I guess my suggestion was that actually trying the alternative position would prove your assumption that your current position was better.  You know what they say about assumptions...  I ran the electric 'Busa.

Sent from my MotoE2(4G-LTE) using Tapatalk

Title: Re: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 06, 2018, 05:08:07 PM
I guess my suggestion was that actually trying the alternative position would prove your assumption that your current position was better.  You know what they say about assumptions...  I ran the electric 'Busa.

yo!

i talked with you on the line about the voltage you were running on your bike. wonderful machine.

on positions, i don't know what is better, or what is worse. have to look at the timing slips. i will test it.

currently broke-back-butt-in-the-air seems effective, just not aesthetic.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on August 06, 2018, 05:13:06 PM
The rules state that streamlining is anything IN FRONT of the Rider that acts to guide the air around the bike. How about a nice belly pan that goes from the front of the engine to the rear where a batwing guides the air around the tire ?  NASCAR teams had lots of neat ideas such as oval exhausts and very wide flat bottom oil pans. Rules now do not allow anything. Much more fun in the old days .   LSL

this next meet is where i see what i can do without bodywork.

for next time, i'll show up with a kamm boxx, a fender, a bellypan to test. . .

dunno.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on September 06, 2018, 05:02:31 PM
the totally naked machine did well.

133.002 in the standing start mile, and 135.259 in the standing start mile-and-a-half.

no aero aids on it all, except my fat butt stuck up in the air.

looking for three-spoke 17-inch cast wheels now.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on December 15, 2018, 09:39:37 AM
old GSX750 wheels. got two of them:

(https://i.imgur.com/osarMcdl.jpg)

the front will go in with just spacers.

17 x 3.00 inches. goodyear says their 2.5-inch frontrunners will fit just fine.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: donpearsall on December 15, 2018, 12:06:11 PM
That's a good find! Those spokes look like good aero. And being able to use an actual LSR tire is a plus.

Don
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on December 15, 2018, 06:43:19 PM
well, now i have a question.  i was planning on fitting these front and rear, but i just had a friend tell me that goodyear front runners aren't legal in SCTA for a drive tire.

is that correct?

alternatives in this size are hooziers and mickey thompsons, who i haven't spoken with. it has never occurred to me to ask about drive wheel applications for one of these. i'm not going to be putting more than 65 hp through it, and not more than 140mph, ever.

goodyear said that their 17x2.5-inch front runners aren't speed-rated (he said, we didn't bother . . . ), but the 17x4-inch tires are labelled for 300 mph.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: RidgeRunner on December 15, 2018, 07:48:07 PM
     Been my observation that the "Front Runner" term is loosely used when applied to the Goodyear tires.  My understanding that the same molds are used for Drag Fronts and LSR tires.  Internal construction is different between the two.   The actual tire model number is what counts when they are considered for specific applications, speeds, driven or not, etc.

                 Ed
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: maj on December 15, 2018, 09:06:18 PM
old GSX750 wheels. got two of them:

(https://i.imgur.com/osarMcdl.jpg)

the front will go in with just spacers.

17 x 3.00 inches. goodyear says their 2.5-inch frontrunners will fit just fine.

I wish they would say that to the SCTA  :-( 
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on December 15, 2018, 10:38:47 PM
well, looks like andy cox has them on his 68 norton atlas. 17 -inch wheels, with tubes, and he ran 154 on them.

(https://www.accessnorton.com/media/bonneville-2018.172/full)

clearly i need to make some telephone calls.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: panic on December 15, 2018, 10:47:24 PM
I agree, the teardrop requires greater transitional length to work.
IIRC the Kamm principle:
The rear extends back @ 14 degree angle until the X-area is 50% of the original cross section, then cut off flush. No radius, corner, reducing taper.
The flaw: Kamm uses the largest X-section of the car, not just the bike tail, so it can't be translated. If it work, it just reduces the drag of the tail, not the bike.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on December 16, 2018, 09:52:37 AM
I agree, the teardrop requires greater transitional length to work.
IIRC the Kamm principle:
The rear extends back @ 14 degree angle until the X-area is 50% of the original cross section, then cut off flush. No radius, corner, reducing taper.
The flaw: Kamm uses the largest X-section of the car, not just the bike tail, so it can't be translated. If it work, it just reduces the drag of the tail, not the bike.

that seems to make sense. on a tucked-in rider, the slipstream detaches right about the middle of the rider's back. for the kamm tail to work, the air would have to remain attached to the rider all the way back to where the tail begins, else you would fair in to the rider's butt. not impossible on a partial streamliner, but harder on a naked machine:

(https://i.imgur.com/vR3DoUnl.png)

https://www.youtube.com/watch?v=zG8Htax6_Og
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: tauruck on December 16, 2018, 04:00:55 PM
I did not know him well, but he was really nice and helpful to me.  My favorite memory:  I was in staging right behind him and had been struggling to get my 450 Honda above 120.  He asked what I was doing and I told him I had just geared it "too high".  I told him, "Don, dont fall down out there because if I cant get past 120 this time,  I am going to keep right on going and ride home to Colorado!"

He laughed and said, "Jim, I am going to go real fast, and if I fall down, I'd appreciate it if you would run me over right away."

My favorite pic is him sitting under his parachute sun shade, working on the single engine bike (which put up a very solid fuel record the next day).  Some folks don't know how tough those records we made were, back then.  First, you ran as hard as you could to qualify...and first thing next morning you made two more runs, back to back, with no repair time in between.  There were bikes that qualified ok, but didnt survive the actual record runs.

It was sure different.

He didnt fall down (close to 200) and my bike ran 124.65.  That was the day Bert missed a shift and spun the windings on his Indian's mag.  He and another fellow and I started up the mountain to strip "bell wire" from a plane crash magneto, but my little street bike couldnt make it up the silt.  They rewound the mag that night and my Dad stayed up all night watching. 

That week was a great experience for my Dad and I.  I had arrived home from Nam on July 17th and all you salt flats people yanked me right out of the war mentality, and planted me on the path to a better life.  Don is a small piece of the memory, but he was the right guy to meet, at that important moment.

Sorry for the long ramble...we get that way when we finally grow up and old.

Jim
👍👍👍👍👍
Great story. Thanks Jim.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: gowing on December 16, 2018, 04:58:40 PM
Being a noob to LSR aero, but not totally lacking in analytical thinking,
I have a question:

In the Kolb 125 video, it looks to me like the helmet sticking up above the fairing is increasing turbulence.
wouldn't it be better to be tucked completely behind the windscreen?
would a taller hump on the leathers be a benefit?

If so..... why wouldn't they just build the bodywork tall enough to hide behind?
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: gowing on December 16, 2018, 05:42:21 PM
The rules state that streamlining is anything IN FRONT of the Rider that acts to guide the air around the bike. How about a nice belly pan that goes from the front of the engine to the rear where a batwing guides the air around the tire ?  NASCAR teams had lots of neat ideas such as oval exhausts and very wide flat bottom oil pans. Rules now do not allow anything. Much more fun in the old days .   LSL

I was wondering about rear wheel covers, do you think they might work better than 3 spoke?
I know that Ducati, and the World Superbike series have been testing them.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on December 16, 2018, 09:13:40 PM
I was wondering about rear wheel covers, do you think they might work better than 3 spoke?
I know that Ducati, and the World Superbike series have been testing them.

some people running machines like mine use them

(https://i.imgur.com/CJJhkTfl.png)

complete covers are legal for the rear, in front they have to leave 20 percent empty, i think

would be easy to adapt to the cast wheels, once they're fitted.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on December 16, 2018, 09:17:00 PM
Being a noob to LSR aero, but not totally lacking in analytical thinking,
I have a question:

In the Kolb 125 video, it looks to me like the helmet sticking up above the fairing is increasing turbulence.
wouldn't it be better to be tucked completely behind the windscreen?
would a taller hump on the leathers be a benefit?

If so..... why wouldn't they just build the bodywork tall enough to hide behind?

i don't know why they left the helmet sticking up. if you look at the kolb video, there's quite a bit of turbulence all over close to the rider, maybe four inches everywhere. if they made the cutouts smaller all around there would be less of that. this 1950's triumph 650 goes 180, so far, and the rider is completely shielded when he's in position:

(https://i.imgur.com/ra0rz50l.png)
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: speedrattle on July 02, 2019, 04:27:00 PM
well, we'll see what the brandy-new aero wheels do in about a week, in loring, maine.

(https://i.imgur.com/vDS8gZCl.jpg)

these are both front wheels off a 1990 GSX 750 suzuki, that came with dual disc brakes in the front. i have the front wheel mounted to mongrel triumph forks without a brake, and the rear wheel has a stock suzuki disc on one side and a sprocket bolted to the disc mounting bolts on the other.

the 17-inch suzuki wheels and goodyear front runner tires are set up to give a couple of inches of ground clearance at full bump, so frontal area is down a bit. the 2.5-inch tires also reduce the contact patch. dunno what effect the reduced volume under the chassis might have.

didn't have time to change the pipes. i'll make new ones for autumn that curve in and go under the motor.
Title: Re: looking for suggestions for improved aerodynamics on a naked motorcycle
Post by: drc42 on July 27, 2019, 09:52:39 AM
well, we'll see what the brandy-new aero wheels do in about a week, in loring, maine.

And the results are????