Author Topic: motorcycle wheelbase  (Read 538 times)

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Offline jim reed

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motorcycle wheelbase
« on: August 22, 2019, 11:40:51 AM »
Are the rules for modified production bike wheelbase still a max of 60" for 250cc and under and 70" for bikes over 250cc ?

Offline trimmers

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Re: motorcycle wheelbase
« Reply #1 on: August 22, 2019, 12:54:17 PM »
Section 7.F on Modified Production  (M,MPS) in the 2019 rule book (page  142) states "A maximum wheelbase not to exceed the original OEM specification plus 10%.  Entrants shall provide acceptable documentation for record certification."   There is no engine size-based variance.

Jeff in Boise
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Offline panic

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Re: motorcycle wheelbase
« Reply #2 on: August 22, 2019, 02:02:24 PM »
Another example of a rule that appears obvious, but isn't.
Is that measurement for the actual position of the rear wheel "as raced"?
Or the farthest adjustment for the rear chain?

Offline salt27

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Re: motorcycle wheelbase
« Reply #3 on: August 22, 2019, 02:22:22 PM »
What I was told was the factory wheelbase is determined by the manufactures specification and your chain adjustment ABILITY cannot exceed that plus the 10 percent aloud in M/MPS.

So bring your documentation.

If anyone has different info, please speak up.

  Don

Offline jim reed

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Re: motorcycle wheelbase
« Reply #4 on: August 22, 2019, 04:04:24 PM »
Thanks everyone. I have an old rule book. The new rule is identical to the rule used at the AMA events. Nice to see they are in agreement so you can easily run with either organization.

Offline JimL

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Re: motorcycle wheelbase
« Reply #5 on: August 22, 2019, 06:22:59 PM »
What Don said and "be careful"! 

The manufacturer spec is often at standard ride height (swing arm might be angled down a little) and they often use the most forward axle position in deference to strange tax laws in other countries.  When you lower the bike (before adding onto the swing arm length) you may find the maximum rear axle position remarkably close to the "spec + 10%" number.

I caught myself screwing this up, one year, thankfully in time to fix it.  It was just a bummer cutting and welding on the swing arm twice, to get it right....once.