(Tech) Tell me about camber

[golf4283]

If you put wider wheels/tires on your car do you have to change the camber settings to something outside of the specified stock range? This may be o/t but the reason I'm asking is I just put 17x8 rims with 225/45 tires on my daily '92 Olds Cutlass Ciera. They fit fine. It corners sharper but I notice bumpsteer alot more now. Overall, Id say the handling is alot better. (Its not your ordinary granny's cutty ) Its front wheel drive with struts and the stock wheels were 185/75-14". I had it aligned and told them to "factor in the larger wheels" into the alignment but I think they only used stock specs. The specified range is -0.5 to +0.5 degrees. It drives true but I'm not sure of the amount of tire wear I'll be having. So since these wheels are so much wider, should the camber be beyond stock? What kind of benefits/results/expectations should I expect if these adjustments were made? Any help is appreciated.

 

[67bluestang]

The larger tire/wheel combo shouldn't have any affect on the camber. Just because they're larger, the alignment should still stay within specs. Bumpsteer comes from toe in/out changes as the suspension goes up/down. It may be worth having another shop look at the alignment. If it is toed out, the car will tend to wander more on the road.

 

[Hack]

Also remember that wider tires in general tend to wander more. You will especially notice it if there are depressions in the road in the cars' tire tracks.

It's a good idea to have the alignment checked, but bump steer to me usually will be related to worn suspension parts. The shop should have told you if anything was worn out, however.

 

[Red Barchetta]

By changing the wheels, you may have affected the scrub radius due to the back spacing. This will make the car drive different than before.

 

[golf4283]

Thanks for the info guys. I had it aligned at Sears Auto center and I dont think they really check for worn suspension. ;-) As far as toe is concerned, the specified range is -0.1 to +0.1 degrees and its set within that for left and right. Oddly enough, the measurement from before the alignment was +0.2 degrees for both wheels. The car does seem to wander from time to time which it didnt do at all before the alignment.

 

[67coupe351w]

The problem with changing the back spacing on your wheels is that the suspension was designed with the stock back spacing and wheelk diameter in mind.

I just wrapped up a complete suspension design for my Mech engineering senior project a few weeks ago. I did quite a bit of research on the subject before starting my design.

One aspect of the geomety is the "Pivot Radius". If you were looking at your spindle from the front and drew a line through the upper and lower ball joints and continued the line to the ground and also drew a line verticaly on the tire's centerline to the ground there would be a distance along the ground between the intersection of the two line's and the ground. typicaly the distance in cars is anywhere from 0 - 2 inches. the greater the distance, the greater amount of bumpsteer that is produced. at zero inches there is zero bumpsteer produced but you will not "feel" the road at all.

So the moral of the story is if you change the position of the wheel (via diffrent backspacing or a bigger diameter) you will change the ammount of bumpsteer produced.

If you eyes are glazed over from my horrible communication skills maybe the attached picture will help.

 

[Red Barchetta]

The problem with changing the back spacing on your wheels is that the suspension was designed with the stock back spacing and wheelk diameter in mind.

I just wrapped up a complete suspension design for my Mech engineering senior project a few weeks ago. I did quite a bit of research on the subject before starting my design.

One aspect of the geomety is the "Pivot Radius". If you were looking at your spindle from the front and drew a line through the upper and lower ball joints and continued the line to the ground and also drew a line verticaly on the tire's centerline to the ground there would be a distance along the ground between the intersection of the two line's and the ground. typicaly the distance in cars is anywhere from 0 - 2 inches. the greater the distance, the greater amount of bumpsteer that is produced. at zero inches there is zero bumpsteer produced but you will not "feel" the road at all.

So the moral of the story is if you change the position of the wheel (via diffrent backspacing or a bigger diameter) you will change the ammount of bumpsteer produced.

If you eyes are glazed over from my horrible communication skills maybe the attached picture will help.

Like I said, scrub radius (except without the detailed definition and diagram)

 

[67bluestang]

The problem with changing the back spacing on your wheels is that the suspension was designed with the stock back spacing and wheelk diameter in mind.

I just wrapped up a complete suspension design for my Mech engineering senior project a few weeks ago. I did quite a bit of research on the subject before starting my design.

One aspect of the geomety is the "Pivot Radius". If you were looking at your spindle from the front and drew a line through the upper and lower ball joints and continued the line to the ground and also drew a line verticaly on the tire's centerline to the ground there would be a distance along the ground between the intersection of the two line's and the ground. typicaly the distance in cars is anywhere from 0 - 2 inches. the greater the distance, the greater amount of bumpsteer that is produced. at zero inches there is zero bumpsteer produced but you will not "feel" the road at all.

So the moral of the story is if you change the position of the wheel (via diffrent backspacing or a bigger diameter) you will change the ammount of bumpsteer produced.

If you eyes are glazed over from my horrible communication skills maybe the attached picture will help.

Did you do an actual on car study or computer theory? Just curious because bumpsteer is in relation to the rack versus the suspension movement. I am under the impression, if the rack and suspension have no bumpsteer, then a larger backspacing will not change this.
The reason i ask is because i played with bumpsteer on my race car. I had the coil's off the coil overs, no tire/wheel, measuring at hub and car set at ride height. I then attached the bumpsteer gauge and moved the suspension up/down and adjusted the rack/tie rod end mount point until i had zero bumpsteer. I then put the car together, set it up and measured at the tire and still had zero bumpsteer.
Just wondering.

 

[67coupe351w]

As soon as the brakes get plumbed the suspension will be tested! Im confident it will work out great (I hope)

Yeah, the rack in relation to the suspension movement is the biggest contributer to the bumpsteer problem. Espeacialy when there are large amounts of suspension travel. It can be minimzed by making sure the steering linkage is parrallel to your lower arm and by ensuring there is a point in the steering linkage in the plane of the frame side arm mounts that allows the linkage to articulate with the A-arms.

I'm by no means an expert in the area but if I had to guess I think the piviot radious effects the bumpsteer through some sort of dynamic loading. That is, you wouldnt beable to physicaly measure it with a guage while your car is up on jacks but rather it is a force produced when the car is moving and then things like inertia start to influence what we feel through the wheel. I pulled that diagram and much of my design criteria out of several diffrent suspension design books.