Author Topic: Motorcycle wheelbase, swing-arm length?  (Read 6613 times)

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Offline panic

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Motorcycle wheelbase, swing-arm length?
« on: August 27, 2005, 06:40:43 PM »
For Mod. class max WB is 68", yes?
Assuming that my stock WB is 54" and that I want to extend only the swing-arm, how to figure what length? Bike will only go 125-135.
Looks like longer = more stable but less traction?
Any site I should visit for ideas?

Offline Dakin Engineering

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longer swingarm
« Reply #1 on: August 28, 2005, 12:59:11 PM »
Yup, much more stable. It is in my case, anyway. And that little annoyance of lofting the front went away.
I don't think wheelspin will be a problem until you hit the "aero wall."
You can always drill and fill with lead shot later, if needed.

Sam
Turbo Sportsters since '97

Offline panic

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Motorcycle wheelbase, swing-arm length?
« Reply #2 on: August 28, 2005, 01:09:51 PM »
What's your old vs. new wheelbase?
How much added to the arm?
Any suspension mods to compensate for the diff in leverage against the shock, and weight dist. change?

Offline Dakin Engineering

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Motorcycle wheelbase, swing-arm length?
« Reply #3 on: August 28, 2005, 10:42:11 PM »
I added on 10 1/2 inches from a donor swingarm. Seems to be adjustable from 67 3/4 to 68 1/2 now. (wonder how that happened?) That left the shock mounts OEM (I use struts). And moved a lot of weight to the rear. Sorry, no numbers, but the lower-back-factor comfirms it.

Sam
Turbo Sportsters since '97

Offline John Noonan

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Motorcycle wheelbase, swing-arm length?
« Reply #4 on: August 29, 2005, 10:18:06 AM »
Unless the course is in great condition shocks may have better results than a rigid rear...

Offline panic

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Motorcycle wheelbase, swing-arm length?
« Reply #5 on: August 29, 2005, 12:07:59 PM »
Luckily (actually, some planning for a change) the swing-arm I'm using has parallel sections exactly 1" X 2" X .090"(? with paint), I'm going to patch in some 11 gauge (.110").
I assume it's good practice to close up the "nose" of the open area to about the same safe distance to the tire as stock (i.e., add 12", close off empty forward area by 12") to improve rigidity? Tire is about same OD as stock.
I'm going to retain the suspension - if my engineering/fabrication skills are up to it!
I see the small cross-section arms (like mine, as opposed to 'Busa, R1, etc.) generally have some bracing added both along the top or bottom and also in 3rd dimension above or below at the pivot.
Other than clearance to some part of the bike or surface, isn't a bottom brace stronger for the same amount of metal? IMHO if the welds are good a tube will be stiffer in tension (on the bottom, being stretched up) than compression (on the top, being "folded" in compression). Am I overlooking something?

Offline Dakin Engineering

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rough course
« Reply #6 on: August 29, 2005, 05:55:02 PM »
I wonder if history will repeat itself as in 2002.
Flooded in September and white concrete for the World Finals.

I'll be sure to bring my shocks next time, just in case.

Sam
Turbo Sportsters since '97

Offline John Noonan

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Motorcycle wheelbase, swing-arm length?
« Reply #7 on: August 29, 2005, 06:34:17 PM »
Yes white concrete would be nice..

Offline hawkwind

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Motorcycle wheelbase, swing-arm length?
« Reply #8 on: September 16, 2005, 07:03:21 AM »
Quote from: John Noonan
Yes white concrete would be nice..


 :lol: we have "white concrete " all the time,  only problem it only 100 miles long
slower than most

Offline firemanjim

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Motorcycle wheelbase, swing-arm length?
« Reply #9 on: September 16, 2005, 08:34:20 PM »
White concrete "only" 100 miles long---and that is a problem???? :D
Bonneville 2001,2002,2003,2004,and NO stinking 2005,DLRA 2006, next?
Well,sure can't complain about 2008--6 records over 200 and 5 hats from Bonneville,Bubs, and El Mirage for the team!

Offline John Noonan

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Motorcycle wheelbase, swing-arm length?
« Reply #10 on: September 17, 2005, 02:23:54 AM »
Quote from: hawkwind
Quote from: John Noonan
Yes white concrete would be nice..


 :lol: we have "white concrete " all the time,  only problem it only 100 miles long


No problem for us, we hope to see you next year in Oz... :wink: