Steering and Handling Discussion.

[400exrider707]

Originally posted by Derrick Adams
Reading thru these definitions, would adding taller or shorter tires than stock contribute to bumpsteer, much like changing offsets of the rims?

I understand where your question is coming from, but no that wouldn't change bumpsteer. Bumpsteer is strictly controlled by the pivot point of the a-arms in realtionship to the pivot point of the tie-rod ends. If the tie-rod ends are at different pivot axis' than the a-arm pivots, when the arms cycle through their motions they all move at different rates. This is what causes bumpsteer.

Now as far as what is actually effected by the taller or shorter tire scenario, I need to think about this a bit before I leave an answer.

[Def-e-nition]

Originally posted by Derrick Adams
Reading thru these definitions, would adding taller or shorter tires than stock contribute to bumpsteer, much like changing offsets of the rims?

good question .

[Derrick Adams]

Originally posted by 400exrider707
I understand where your question is coming from, but no that wouldn't change bumpsteer. Bumpsteer is strictly controlled by the pivot point of the a-arms in realtionship to the pivot point of the tie-rod ends. If the tie-rod ends are at different pivot axis' than the a-arm pivots, when the arms cycle through their motions they all move at different rates. This is what causes bumpsteer.

I was under the impression that changing wheel offsets contributes to bumpsteer as well as pivot point locations. Would that be correct?

It seems that changing tire diameter would effectively change contact patch location, same as wheel offset.

Now the real question would be how much tire height effects contact patch location. Say if someone went from a 22" tire to a 19" tire. Is the stability two-fold because of reduced sidewall AND better steering geometry, due to a better contact patch location in relation to the spindle?

[400exrider707]

Originally posted by Derrick Adams
I was under the impression that changing wheel offsets contributes to bumpsteer as well as pivot point locations. Would that be correct?

No wheel offsets do not effect bumpsteer. Again it is strictly the pivot points. Taller or shorter tires also have no effect on bumpsteer

Originally posted by Derrick Adams
It seems that changing tire diameter would effectively change contact patch location, same as wheel offset.

Now the real question would be how much tire height effects contact patch location. Say if someone went from a 22" tire to a 19" tire. Is the stability two-fold because of reduced sidewall AND better steering geometry, due to a better contact patch location in relation to the spindle?

Of course diameter will effect the contact patch location, but I think the locational change as far as imaginary lines goes, between a 19" tire and a 22" tire is quite minimal. Also if you factor in most quads with aftermarket setups run some negative camber, you are putting the wheel/tire combination more parallel with that imaginary line running through the balljoints, so change would be even less between tire heights. Between two vast extremes as far as sport atv front tires go, 19" to 22" is only 1.5" on each side of the tire. That 1.5" of vertical distance equates to almost nothing in horizontal distance from that imaginary line to the center point of the tire. Though I can say that to your original question it doesn't effect bumpsteer, but what it does actually effect I don't think I know. I need to do more research on this, but thank you for bringing it up. I'm having a very hard time visualizing this all in my head, I think I need to go spend some time playing around with my quads front end in the garage.

[f1502nv]

anyone got anything on how to set the sag

i cant do a search cause the word sag isn't long enough

[LotusPosition]

Originally posted by f1502nv
anyone got anything on how to set the sag

i cant do a search cause the word sag isn't long enough

http://www.4strokes.com/tech/racesag.asp

[400exrider707]

Originally posted by f1502nv
anyone got anything on how to set the sag

i cant do a search cause the word sag isn't long enough

Here's one too, it's already been posted though...

http://www.gtthunder.com/SuspensionHome.htm

LotusPosition - great link!

[bradley300]

Originally posted by Derrick Adams
I was under the impression that changing wheel offsets contributes to bumpsteer as well as pivot point locations. Would that be correct?

"bumpsteer" can be a confusing term becasue its popular to call two different issues bumpsteer. the first is the toe change as the tire goes thru its travel, this is actually what bumpsteer is. the term gets confused because say you hit a rock with one tire and the bars steer that way. many people also cal this bumpsteer, but trail feed back thru the handlebars is a more accurate and less confusing term

to answer your question, yes wheel offsets will affect the trail feed back you feel thru the bars. the basic theory is the closer you can get the ball joints to the centerline of the wheels, the less feedback you will have. offsets do not effect actuall bumpsteer

[bradley300]

Originally posted by Derrick Adams

It seems that changing tire diameter would effectively change contact patch location, same as wheel offset.

Now the real question would be how much tire height effects contact patch location. Say if someone went from a 22" tire to a 19" tire. Is the stability two-fold because of reduced sidewall AND better steering geometry, due to a better contact patch location in relation to the spindle?

i'm not 100% sure, but i know the shorter tires will turn quicker, as well as transfer more feedback to the bars so its a compromise between a positive and a negative. given the same air pressure, i would say the bigger tires would have a larger contact patch for the sheer fact that they are bigger.like someone else said, the difference in extreme sizes are pretty close, so i would say that would be a minimal difference in contact patch. also, the taller tires will ride smoother, all with a sacrifice of center of gravity though.

will a bigger tire effect bumpsteer, if everything else is the same then i would say no, because you havent changed a pivot point. but say you have a bigger tire now, and adjust the shocks to keep the same ride hieght you had with the smaller tires. ( you would do this for a smoother ride, less twitchy steering, but maybe you dont want the higher ride hieght that comes with it) now you are going to run into some issues.

1. you have changed the length of the shocks (made them shorter for the lower ride hieght) so now, they will bottom out at a ground to frame clearance then the same ride height with the smaller tires. so you have taken away some of your suspension travel.

2. since the shocks are shorter, you have raised the position of the a-arms within thier travel. you have not added any bumpsteer, but now you will come to the max amount of bumpsteer thru the travel quicker.

ex. say at ride hieght, the quad has .175 inches of bumpsteer and an inch into the upstroke it has .190 inches and another inch it has .250 another inch it has .320. as you can see it gets progressivly worse as you go thru the travel.

since you have added bigger tires and lowered the ride height (raising the a-arms posistion in the travel) you are skipping the .175 inches of bumpsteer and you ride hieght now has .190 inches. now everytime you hit a 1 inch bump the bumpsteer increases .600 inches, if you left the ride hieght alone, it would only increase .150 inches if you hit that same 1 inch bump.

so you havent increased given the quad more bumpsteer, but you have changed how quicky the bumpsteer gets worse

[bradley300]

if you cant understand that, i'll try and re word it