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Author Topic: looking for suggestions for improved aerodynamics on a naked motorcycle  (Read 2218 times)
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speedrattle
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« 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:




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.


« Last Edit: July 29, 2018, 07:39:07 PM by speedrattle » Logged
55chevr
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« Reply #1 on: July 29, 2018, 08:09:15 PM »

Tiger Racing front fender ---


* Tiger Racing.jpg (37.02 KB, 640x480 - viewed 48 times.)
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tortoise
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« Reply #2 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.

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ETM
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« Reply #3 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.
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sofadriver
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« Reply #4 on: July 29, 2018, 11:43:42 PM »

you already mentioned the obvious - you need a tail section.
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Mike in Tacoma

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JimL
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« Reply #5 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.
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Rex Schimmer
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« Reply #6 on: August 02, 2018, 02:11:39 PM »

My favorite Bonneville springer forks:


Rex


* 2879.JPG (463.69 KB, 1024x768 - viewed 87 times.)
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Rex

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Stan Back
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« Reply #7 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?
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WOODY@DDLLC
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« Reply #8 on: August 02, 2018, 04:24:33 PM »

http://www.landracing.com/index.php/component/content/article?id=271
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JimL
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« Reply #9 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
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Peter Jack
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« Reply #10 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
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maj
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« Reply #11 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 Wink
all the above esp raising your back  and will add rear wheel discs
Friction reduction, ceramic bearings, brakes backed off , non o ring chain ,  
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speedrattle
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« Reply #12 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:





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.
« Last Edit: August 02, 2018, 07:00:04 PM by speedrattle » Logged
speedrattle
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« Reply #13 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



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:



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.
« Last Edit: August 02, 2018, 08:15:42 PM by speedrattle » Logged
speedrattle
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« Reply #14 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.

« Last Edit: August 02, 2018, 07:16:20 PM by speedrattle » Logged
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