Wheelbase alterd

[gnarshread]

Hi guys! We have all seen plenty of bikes with swing arm, fork, and wheel swaps. Now, a stock bike is designed with a purpose in mind. Be it Dual sport, Road race, touring, you get the picture. And the wheels and wheelbase is all part of that picture to make the bike handle in a specific manner. The other day I rode a 650 sport bike with one of those god awful chrome extended swing arms. Please don't judge. I had the opportunity and I thought why the hell not. I felt like I was riding a razor blade. It sucked. Which got me thinking.

What I am pondering is that when adding different size wheels to an older bike, especially modern ones, it changes the wheel base which makes the bike handle differently. So, to maximize performance, is it advisable to attempt to make the wheels the distance from each as the factory bike they came off of?

I know there are allot more factors in the equation than just this but I am interested to see what you guys come up with.

 

[SONICJK]

Wheelbase is measured from axle to axle, so changing the size/make of the wheels makes no difference at all as far as wheelbase is concerned.

If you change your forks or swing arm or steering stem angle then you have to worry about wheelbase. Adding longer or shorter shocks can also change it slightly

 

[gnarshread]

Ah OK. Apologies for incorrect terminology. I suppose what I mean is where the wheel actually comes in contact with the road in relation to the rest of the bike.

 

[Rich Ard]

Ah OK. Apologies for incorrect terminology. I suppose what I mean is where the wheel actually comes in contact with the road in relation to the rest of the bike.

think about which part of the wheel touches the ground...no matter how large or small the wheel, the distance between the points touching asphalt will not change.

 

[SONICJK]

Yup. Only touches directly under the axle.
Hence the wheelbase

 

[VonYinzer]

The difference you'll have in wheel swaps is contact patch (smaller or larger) but unless you go to an extreme its negligible.

 

[gnarshread]

What I'm getting at is (Purely hypothetical before we get into a styling argument) If I add the wheels from a modern sport bike with the wheelbase of 59 inches to a bike from 1970 which has a wheelbase of 55 inches. The modern wheels have been designed to work well at the 59" not 55" wheelbase. Would it be better to extend the swing arm that extra 4 inches to help the new wheels work better? Assuming they have been designed to work 59" instead of 55" away from each other?

 

[rockcitycafe]

the modern wheels don't care what wheelbase they're positioned at, the forces acting against the contact area of the tire are virtually identical over a very wide range of wheelbase. trail, wheelbase and contact patch width are going to be the things that will matter to you in this case

 

[nixon]

roc city is right..

Wheel diameter – smaller front wheel will decrease rake and trail, smaller rear wheel will increase rake and trail
Tyre thickness – same as the wheel diameter ( http://bikearama.com/theory/motorcycle-rake-trail-explained/ ))

what are the rim sizes of the old / new bike?

yeah, i just had a freak out moment as im changing from 23 inch to 19 inch rim on a xl 250...

now im seriously freaking the rake/ trail difference may be too much ! Guess i can always try lower rear an inch ..

 

[gnarshread]

Thanks Roc C! Now I can sleep at night until I get another harebrained question.

 

[Bert Jan]

roc city is right..

Wheel diameter – smaller front wheel will decrease rake and trail, smaller rear wheel will increase rake and trail
Tyre thickness – same as the wheel diameter ( http://bikearama.com/theory/motorcycle-rake-trail-explained/ ))

what are the rim sizes of the old / new bike?

yeah, i just had a freak out moment as im changing from 23 inch to 19 inch rim on a xl 250...

now im seriously freaking the rake/ trail difference may be too much ! Guess i can always try lower rear an inch ..

No worry, supermortards change from 21 to 17 or even 16 and they seem to go around pretty good

Smaller front wheel means better handling, in general. You'd have to go to extremes to make it unsafe and unridable.

 

[Bert Jan]

roc city is right..

Wheel diameter – smaller front wheel will decrease rake and trail, smaller rear wheel will increase rake and trail
Tyre thickness – same as the wheel diameter ( http://bikearama.com/theory/motorcycle-rake-trail-explained/ ))

what are the rim sizes of the old / new bike?

yeah, i just had a freak out moment as im changing from 23 inch to 19 inch rim on a xl 250...

now im seriously freaking the rake/ trail difference may be too much ! Guess i can always try lower rear an inch ..

And as an XL is pretty much leaning to the back anyway, a smaller front wheel will make the bike's wheelbase a little smaller, as you're changing the front wheel only, and thereby the angle of the forks aswell. She will ride better, trust me.

did you know that with an extra rear wheel you can do the whole conversion? You need, the extra rear rim, one sides of spokes and one sides of spokes from the old front wheel. They fit. Gotta Love Honda. I know because i did the swap once in a distant memory in my parents backyard one sunday afternoon. It's really easy.

 

[nixon]

bert, you just made my day!! Thanks for the assurance

No, no idea of that mod..Wish we had this discussion 3 weeks ago.. next time!

 

[o1marc]

Adding taller or shorter wheels and tire will effect the ride height slightly and probably not as noticeable as going to a modern tire that is a lot wider in turn in ability. If you go from an old spoke rim to a newer alloy rim the stiffness will be greater and may now notice more swing arm flex. Stiffen the swing arm and then you may notice more frame flex.