Author Topic: Motorcycle question from a newbie...  (Read 15221 times)

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Screwdriver

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Motorcycle question from a newbie...
« on: August 29, 2006, 04:52:22 PM »
Hi guys, I hope this is the right section of the forum and that this isn't too cheeky for a first post...

With regards to naked unfaired motorcycles and specifically those with upright handlebars:

Is it possible to ride such a machine with wide bars sitting upright at, say, 180mph?

How stable would the bike/rider system be?

Anyone here ridden a non-specialised roadbike at these sorts of speeds?

The question comes  from a road riding motorcycle forum (VisorDown.com) where many members are "streetfightering" their hyper-sports machines; stripping off the fairings and fitting wide upright handlebars. While that makes a fun machine, I am wondering just how safe and stable they would be at high speed.

Many thanks

Screwdriver.

landracing

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Motorcycle question from a newbie...
« Reply #1 on: August 29, 2006, 05:09:22 PM »
Well you may not find the right answer, because I dont think there are many who even consider riding that way at 180 mph.. I think it would be a little unstable... Most riders over 180 naked, tuck handlebars in...  

Wish I had an answer for you but im not crazy enough to try it to find the result.

Jon

Screwdriver

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Motorcycle question from a newbie...
« Reply #2 on: August 29, 2006, 05:12:47 PM »
That's an answer in itself thanks!

Personally I think modifying these super high speed motorcycles in that way is a recipie for disaster. The forces involved must be immense. Anywhere on this site with some tecchy numbers? Pounds per square inch wind pressure etc?

Screwd.

Offline PorkPie

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Motorcycle question from a newbie...
« Reply #3 on: August 29, 2006, 06:01:11 PM »
Is it possible to ride such a machine with wide bars sitting upright at, say, 180mph?


May be the bike could reach this speed :wink: .....but than, fore sure.....the rider will be not anymore sitting on bike....... :D

......if he is fast enough (walking) he will catch his bike 1/2 hour later :shock:
Pork Pie

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Screwdriver

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Motorcycle question from a newbie...
« Reply #4 on: August 29, 2006, 06:03:09 PM »
What sort of forces would be involved on an exposed torso? Is there a calculator?

Thanks for the replies.

Offline Glen

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motorcycle question
« Reply #5 on: August 29, 2006, 06:05:12 PM »
Try putting your hand out the window of a car at 80 mph and feel it slap the side of the car. The body has a lot more area to push on and as Pork Pie says it will take a while to catch up.
Glen
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Screwdriver

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Motorcycle question from a newbie...
« Reply #6 on: August 29, 2006, 06:18:14 PM »
Yes I've done that at 160+ on a bike, putting my hand up into the airflow. Almost ripped my arm off. There's a craze in the UK currently to strip perfectly good 180mph sportsbikes of their fairings and fit upright handlebars. Great fun but i'd like to get the hard facts and figures behind the bravado. I simply don't believe it would be possible to hang on to the bars at that speed, sitting upright.

If you have to get into a racing crouch, then there could be a product liability issue if the manufacturers ever produced a naked bike with that sort of awesome performance...

Screwd.

landracing

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Motorcycle question from a newbie...
« Reply #7 on: August 29, 2006, 06:26:28 PM »
There is alot to be said of Jason McVicar going 235 mph on a naked Suzuki Hayabusa turbo charged. He however was in a full tuck and arms weren't out in the wind. A nice tuck he had... I still dont think he knows how the hell he hung on for that ride... But as you stated arms out in the air and situp bike... Nahh ill pass...

Jon

Screwdriver

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Motorcycle question from a newbie...
« Reply #8 on: August 29, 2006, 06:57:04 PM »
Any good sources for facts and figures for aerodynamic forces? Specifically on the human toro (this is a long shot!)

Screwd.

Offline Freud

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Air at 180 MPH
« Reply #9 on: August 29, 2006, 07:34:53 PM »
The last pass I made on my TZ 750 was 180MPH. It had no front brake and since the back pads were dragging we bled off all the fluid to eliminate that problem. So the bike had no brakes.

As I exited the 3, I chopped the throttle, grabbed the clutch for a plug check and sat straight up. It took my breath away but I had no problem in staying on the bike. I wanted to see how quick I could get off the course so I didn't wait long and leaned it off to the right. That was when there was a single course and the return road was to the right. The road race slick jumped over the pressure ridges and the back end was pretty loose but manageable. I was at a dead stop, pointed back to the starting line at the 3 1/2. My pick up fellow waited at the 4 1/2 and I never got there so I sat on the bike for quite a while before he found me.

I hear people talking about hanging on to an open bike and just think about that experience. Somehow their imaginations don't match my experience.  

Scott has probably done it also, but he's smart enough to keep his mouth shut.  Jason talks Canadian and there is no way to translate his experiences. That's one of the problems with letting foreigners run with us.


FREUD
Since '63

Offline Nortonist 592

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Motorcycle question from a newbie...
« Reply #10 on: August 30, 2006, 12:08:20 AM »
I think you answered your own question when you wrote taking the fairing off of a 180 mph bike.  Remove the fairing lose the speed.  I think the bike may be stable but it seems like it would be very uncomfortable to be traveling at say 160 sitting bolt upright.
Get off the stove Grandad.  You're too old to be riding the range.

Offline JackD

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« Reply #11 on: August 30, 2006, 12:16:44 AM »
In 1979, I made over 30 passes at Bonneville in excess of 180 with
 a Z-1 Turbo street bike with the only aero changes made with the change to ATC-90 bars and no tuck in.
The luggage rack and turn signals were in place.
I think we used 12 gallons of gas that week.
In 78, AMA made us take the fairing off the Z1-R to run in production.
It was a blessing because the bike ran 4mph faster and handled better.
Some times a bad fairing can make things worse.
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Offline hawkwind

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Motorcycle question from a newbie...
« Reply #12 on: August 30, 2006, 01:32:42 AM »
A few years back ( lake Gairdner), a couple of members of a well known outlaw bike gang showed up with some hotrod big inch Harley's, complete with forward controlls and ape hanger bars ,they were not shy in informing all and sundry how they would be the fastest vehicles of the meet,as it turned out they posted the slowest speeds of the meet, one bloke actually took some advice about streamlining and returns each year with improved aero and increasing speeds ,the apehangers did not show again  :wink: ,hint ,human windsocks and high speeds are as rare as rocking horse shit
Gary
slower than most

Offline jimmy six

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Motorcycle question from a newbie...
« Reply #13 on: August 30, 2006, 01:38:56 AM »
Screw.....What are you bringing; A Big Dog Beach Cruiser???? Or maybe OC Choppers has group ready to come to B'ville...Now THAT would fun!!!!!
First GMC 6 powered Fuel roadster over 200, with 2 red hats. Pit crew for Patrick Tone's Super Stock #49 Camaro

Offline hotrod

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Motorcycle question from a newbie...
« Reply #14 on: August 30, 2006, 03:25:12 AM »
Quote
Any good sources for facts and figures for aerodynamic forces? Specifically on the human toro (this is a long shot!)


That info probably exists in the skydiving community. A simple way to look at it is the terminal velocity of a skydiver in the normal arched back posture is near 120 mph, if he weighs 200+ lbs (body weight plus weight of equipment) that implies 180-220 lbs of drag at 120 mph. Most of that drag would be off the upper body, so a good guess would be near 100 -140 lbs drag on the upper body at 100 -120 mph. If drag increases at the cube of the speed, 200+ mph would give a drag number of almost 4.5x that or something in the 800+ lbs  of air drag, trying to shuck you off the bike if you sat up suddenly.

Larry