How does wheel base effect handling?

[slowxr]

I changed gearing on my XR650R and my rear wheel is about 1/4 of an inch more forward then prior.

At speed, it seems to have a significant amount of head shake. Also, the forks seem less plush then prior to the change.

Would moving the wheel forward have these effects on the handling?

thanks

[dgcars]

Such a small amount of movement should not have a significant effect.

[ncmountainman]

Such a small amount of movement should not have a significant effect.

it surely does:bonk:

what you've done is put more wt on the front wheel,if possible slide the fork tubes down in the tripleclamps about 5mm (don't go less than flush with the top) if they're already flush you may be able to dial it out with more comp or spring preload....or you could add a link next time you get a chain,which may put you in the opposite direction...its all about balance and a mm or 2 can make big differences in how a bike handles:thumbsup:

[yam259]

it surely does:bonk:

what you've done is put more wt on the front wheel,if possible slide the fork tubes down in the tripleclamps about 5mm (don't go less than flush with the top) if they're already flush you may be able to dial it out with more comp or spring preload....or you could add a link next time you get a chain,which may put you in the opposite direction...its all about balance and a mm or 2 can make big differences in how a bike handles:thumbsup:

Actually, if he slid the rear wheel forward, he placed more weight on the rear. He did shorten the wheel base, but moved the center of gravity rearward.

[dgcars]

it surely does:bonk:

what you've done is put more wt on the front wheel,if possible slide the fork tubes down in the tripleclamps about 5mm (don't go less than flush with the top) if they're already flush you may be able to dial it out with more comp or spring preload....or you could add a link next time you get a chain,which may put you in the opposite direction...its all about balance and a mm or 2 can make big differences in how a bike handles:thumbsup:

As has been said....By moving the wheel forward there would be slightly less weight on the front. This may make the bike feel lighter at the front end. This, if it were the case, would allow the forks to ride higher in the stroke, so your suggestion of sliding the tubes down the clamps, would have a compound effect.

I'm still doubting whether or not moving the rear wheel 1/4" in any direction, other than sideways, would cause such a significant change in handling.

To the OP....Try shifting your weight slightly forward to see if this temporarily cures your problem. If it does, then I stand corrected.

[Sun Devil]

Also the wheel would have less leverage on the shock. Hence making the shock compress slower.

[slowxr]

Thanks alot! Yikes, it could be more complicated then I thought.

Lot's of variable in suspension and handling.

thanks

PS. Can staked master links be purchased? I've only seen the clip style for sale.

[vlad7890]

Less leverage on the shock => less rear sag => steeper fork rake, could lead to more weight on the front. Excellent candidate for headshake. Check your sag and fork position in the clamps.

[ncmountainman]

As has been said....By moving the wheel forward there would be slightly less weight on the front. This may make the bike feel lighter at the front end. This, if it were the case, would allow the forks to ride higher in the stroke, so your suggestion of sliding the tubes down the clamps, would have a compound effect.

I'm still doubting whether or not moving the rear wheel 1/4" in any direction, other than sideways, would cause such a significant change in handling.

To the OP....Try shifting your weight slightly forward to see if this temporarily cures your problem. If it does, then I stand corrected.

i know it seems counter intuitive but moving the rear wheel fwd puts more wt on the front.....just try sliding the tubes down and see what happens,it doesn't cost anything:ride:

[dgcars]

i know it seems counter intuitive but moving the rear wheel fwd puts more wt on the front.....just try sliding the tubes down and see what happens,it doesn't cost anything:ride:

Hmmm, i'm not saying you are wrong..I just don't agree

If we say that a bike weighs 250lbs. Depending on the balance point, there will be a percentage of that carried on both wheels. This is determined by the balance point. If it were possible, and we kept moving the rear wheel forwards and towards the 'balance' point, eventually the bike would balance on the rear wheel, and it would be supporting 100% of the weight of the bike, 250lbs. All the time, whilst moving the rear wheel forward, the front wheel gets lighter. ?

[ncmountainman]

Hmmm, i'm not saying you are wrong..I just don't agree

If we say that a bike weighs 250lbs. Depending on the balance point, there will be a percentage of that carried on both wheels. This is determined by the balance point. If it were possible, and we kept moving the rear wheel forwards and towards the 'balance' point, eventually the bike would balance on the rear wheel, and it would be supporting 100% of the weight of the bike, 250lbs. All the time, whilst moving the rear wheel forward, the front wheel gets lighter. ?

you might think so,but dirt bikes don't exactly comply with reason;i think it has more to do with pivot points on accel/decel. (ex; longer wheelbase = more traction) your theory might hold true if it just sat in the garage.

i'm not sure of the reason.....just sure of the results:p

[dgcars]

you might think so,but dirt bikes don't exactly comply with reason;i think it has more to do with pivot points on accel/decel. (ex; longer wheelbase = more traction) your theory might hold true if it just sat in the garage.

i'm not sure of the reason.....just sure of the results:p

Hmmm (again)....OK.

Your bike is travelling along at 30mph, constant speed. Hit the brakes. I don't think the position of the rear wheel will have any effect on the amount of weight acting on the front end.

You are travelling at 10mph, constant speed. Accelerate hard. The front end gets light because the bike is trying to pivot on the rear axle. Move the rear axle forward, and the bike will, in theory and practice, pivot easier.

Result - lighter front end.

Hill climbers. Why do they extend the swinging arm. To move the rear wheel back. Why?...to keep more weight on the front end.

I'm going to convince you yet. ?

[ncmountainman]

Hmmm (again)....OK.

Your bike is travelling along at 30mph, constant speed. Hit the brakes. I don't think the position of the rear wheel will have any effect on the amount of weight acting on the front end.

You are travelling at 10mph, constant speed. Accelerate hard. The front end gets light because the bike is trying to pivot on the rear axle. Move the rear axle forward, and the bike will, in theory and practice, pivot easier.

Result - lighter front end.

Hill climbers. Why do they extend the swinging arm. To move the rear wheel back. Why?...to keep more weight on the front end.

I'm going to convince you yet. ?

good luck convincing me,the only thing i have to learn is why it happens;vlad mentioned decreased leverage ratio which in turn would mean you'd need a lighter rate rr spring to get the right sag...which in turn would be taking wt off the front. i guess that's why your hill climber bikes need to run much stiffer rr springs.

so drawing from my limited knowledge the only way i see to remedy this is with less shock preload or maybe even lighter spring(depending on current sag #'s,lowering the forks in the clamps,or lengthening the chain (which may overshoot into the other direction)

[dgcars]

good luck convincing me,the only thing i have to learn is why it happens;vlad mentioned decreased leverage ratio which in turn would mean you'd need a lighter rate rr spring to get the right sag...which in turn would be taking wt off the front. i guess that's why your hill climber bikes need to run much stiffer rr springs.?

Fair enough. Shall we just agree to disagree.......

[union7]

perhaps everything inanimate always complies with truth/laws of nature/science/ultimate laws of physics, but humans make reasoning errors from time to time

[ncmountainman]

all i can tell you from experience in the real world, moving the the rr wheel fwd on any given bike wts the front wheel......in a theoretical situation when designing a chassis it may just be as dgcars explains; but the op's problem lies within the realm of his XR not a theoretical one.

maybe someone who actually knows the physics behind it could enlighten us:thumbsup:

[union7]

all i can tell you from experience in the real world, moving the the rr wheel fwd on any given bike wts the front wheel......in a theoretical situation when designing a chassis it may just be as dgcars explains; but the op's problem lies within the realm of his XR not a theoretical one.

maybe someone who actually knows the physics behind it could enlighten us:thumbsup:

mountain man,

What specifically did you experience that leads you to believe more weight was placed on the front when you moved the rear wheel forward? I'm talking about your real experience, not a theoretical one. This is an honest,real question.

Your explanation may help me avoid breaking out the scales. ;-)

[ncmountainman]

mountain man,

What specifically did you experience that leads you to believe more weight was placed on the front when you moved the rear wheel forward? I'm talking about your real experience, not a theoretical one. This is an honest,real question.

Your explanation may help me avoid breaking out the scales. ;-)

well...... i like to keep a neutral handling bike and when i bought my SH500 which was built on a 08 crf250 chassis the bike had pronounced stink bug effect which i battled with to the point of insanity,one of the things i did was shorten the chain a link and a half thinking much like everyone else that it would put more wt on the rr... lost its balance even more to the fnt and just plain screwed it up. changed it back...it got better but i never got that bike balanced even with fact connection linkage,24mm offset triples,rr offset pegs,90/100 fnt tire,120/90 rr....

same thing with my ktm another stinkbug,but got that dialed out alot easier.....one day decided to go with a 48 sprocket instead of a 50 and it moved the wheel back a good bit made the bike handle like bubba's 450 (real low in the rr) couldn't get the proper sag back and had to shorten the chain which kinda overshot where it was in the 1st place and back came the stinkbug...fixed it by running the forks flush which were up 5mm to start with.

i don't know if whats happening will measure out on a set of scales or not,the more i think about it the more the reduced swingarm leverage makes sense.....think about it,i can make my bike fall on its face by opening up the fork comp clickers but that will not measure on a set of scales:ride:

[Dwight_Rudder]

Moving the wheel forward does not put more weight on front. I have seen them increase wheelbase to put more weight on front in a turn. I like the shorter wheelbase for quicker handling in the tight woods.

[dgcars]

Hmmm (again)....OK.

Your bike is travelling along at 30mph, constant speed. Hit the brakes. I don't think the position of the rear wheel will have any effect on the amount of weight acting on the front end.

You are travelling at 10mph, constant speed. Accelerate hard. The front end gets light because the bike is trying to pivot on the rear axle. Move the rear axle forward, and the bike will, in theory and practice, pivot easier.

Result - lighter front end.

Hill climbers. Why do they extend the swinging arm. To move the rear wheel back. Why?...to keep more weight on the front end.

I'm going to convince you yet. ?

This is, pretty much, the physics

maybe someone who actually knows the physics behind it could enlighten us:thumbsup:

Moving the wheel forward does not put more weight on front. I have seen them increase wheelbase to put more weight on front in a turn. I like the shorter wheelbase for quicker handling in the tight woods.

Spot on