For the uninformed scrub radius is the difference between the center of the tire contact patch and the imaginary line from the center of the strut's upper mounting point (pivot point) through the ball joint rotation center (in other words steering axis, aka SAI). A positive scrub radius is where the SAI lies inside the center of the tire contact patch on the road, and vice versa is negative. A neutral or negative scrub radius is generally preffered over positive for reasons I'll explain later.

Scrub radius is already marginal on 3rd gens from the factory, and what that means when you have wider tires or wheelspacers (or both, in my case ) is a significantly worse scrub radius, even to the point of creating a potentially dangerous situation. If a calper freezes up and you brake the action with positive scrub radius is the wheel wrenching in the direction of the good caliper. A positive scrub radius will increase steering effort and cause the car to be sensitive to ruts and uneven road height. This adds to the mystery of why gm specified positive camber for these cars. It would seem that increasing camber would be counterintuitive for both handling characteristics and improving scrub radius.

It is however common and advantageous to widen the track and tires to improve handling. A positive scrub radius will however improve road feel, which is why it's preffered in racing. The remedy would be in part to increase camber further to bring the strut's upper pivot point inward, thereby increasing the SAI angle to reduce scrub radius. Increasing caster can also help stabilize steering. This is only a bandaid though and will bring up other issues that need to be addressed by redesigning the suspension geometry. My car has a full 4" of scrub radius with spacers and 225 tires! Compared to ~1.5" stock. It's very road sensitive and can wear you out over long trips, but rips up the track when I need it to.

 

Ok this all kinda lost me. But my car does tend to wander since I put the 17x9 4th gen wheels on with 2" spacers in the front. It didnt do this before I changed the wheels. What can be done to reemedy this? I am currently rebuilding the front suspension.

 

Relocating the lower control arm would be best to bring the lower ball joint out more and increase the SAI. You could also lengthen the strut to spindle bolt holes to bring the spindle more upright and maximize camber to increase SAI without getting too much negative camber. Otherwise just increase camber & caster. Particularily caster. This will make your steering more stable and improve wheel return. If you have a pre-'90 model upgrade to the redesigned camber/caster plates and lengthen the camber/caster slots in both the plate and car's body .4" twoards the rear (for caster) and inboard (for camber) to get more adjustment out of it. you may need to remove the strut dust shield or cut the body to make full use of it because it will contact the body at max camber/caster. I'd aim for -.5* camber, 5* caster and .05* toe. SAI should be close to 25*, but most importantly equal on both sides.

 

I've never noticed any difference between the strut/caster/camber plate mounts.....

 

The rearmost slot (or front?? I forget) is about a 1/4 inch more inboard. I found it's best to use the early lower bracket and bend it slightly to fit the later upper. Also has a bearing instead of solid mount like my originals.

 

I realy don't understand the purpose of this post. Are we talking about your car and what you intend to do try and correct improper wheel fitment?

You are also not considering the wider track width and the ackerman problems with the factory length steering linkage still in tact.

 

You problem can be siply the wheel bearing slop and/or you have play in the steering linkage (ie- bad tierods, etc..). The wider the tires, the more worn parts will show trouble.

 

Further more, SAI is a preset design and generally can not be changed. It is the design angle of the spindle. you would have to cast new spindles at a different degree. I noted in my "ultimate 3rrd gen suspension" post that a "fudge" can be made to this using the intrax camber bolt kit with elongated bolts to adjust and equalise the two sides evenly and closer towards zero- yet staying positve. Just like Camber and caster, too much positive SAI can hurt you. It can yank the steering wheel out of your hands in certain cases.

85bcl, If you are messing with SAI then you had better have access to an alignemt rack and lots of time to check and recheck these settings when playing with the strut to spindle bolts. Every time you jack the car and change the angle, you will need to pull the car off the rack and resetle the chassis prior to gauging measurement again. If you lived near me, I would let you come over and watch me setup a racecar and see just what is involed in changing chassis setups and completely squaring a chassis to full track width leverage, then making everything articulate within bump and roll range. Turnplates, scales, gauges, Tire diameters.

Does anyone here rotate their tires? I would think so. Getting into this technical of stuff, I would bet to think that anyone attempting this level of setup knows the diameter of each of his individual tires. Yes? No? What happens when you change tire brands and the diameters are slightly different and completely different as for each individual positioning on the chassis (ie- LF, RF, LF, RR) What if your LF was 85.5 and your RF was 85.2, and your new tires are lf 84.7 and rf at 85.6? what then. Lets back way up before you start messing with SAI and spend $$$$$$$ to get the worng offset tire to try and work on the wrong car. I think you'll be surpeised to see what difference you have in tire diameter on your 225's. They are not perfomance tires, they probably have poor tolerances when manufatured compared to a high dollar perfomance tire (ewven these will have tolerance variances I describe, but just not as much)

I'm going to stop. Its hard to write this stuff without getting the feeling you are going to think I am picking on you. I am just giving you food for though in a public forum you posted on. Its human nature to read your first post, then look at the car in question and see what mods have been done to it, then analyse why you are posting what you did. I am simply a guy that comes into here to read people questions and help answer things so people can buy and adjust things to the best of their hard earned dollars. I just do not agree with changing the SAI in your case. I am sorry to say this, but those are the wrong wheels for the car...period.

 

If your front steering and suspension is in good shape and you use the right backspaceing, offset, etc., with non-stock wheels there should be no problem with "wondering", unless you have done something wrong. If your wheels stick out too far and have the wrong backspacing this would make your bearings wear out and would most definitely change the steering of the car.

There are aftermarket parts you can change out to adjust caster/camber of our cars. I wouldn't change it any further than these limits unless you are going for a track car. Too extreme of an adjustment like this on a daily driver will result in horrible treadwear. What is the point unless it is a track car??

 

It's cool. I was hoping you'd chime in vetruck. I have yet to see an equal size set of tires, much less a round one, LOL. I have 15" venturas and 2 1/2" spacers to clear my LS1 brakes and equalize with the rear track (4th gen rear). I'm a tech and have acess to a rack any time I want . Everything's tight upfront and yes it is road sensitive with so much scrub. I keep my align pretty mild at -.5* camber, 4.5* caster and .05* toe. I'd have to rack it up to tell you what SAI's at (I'm at work, LOL). It's a compromise but I'm doing more suspension crap down the road. Right now the hybrid motor takes priority.

This thread is kinda a refresher on what wheels & spacers do.

 

I took a second look at these wheelspacers today since I need to lower the front end now with the new motor and correct me if I'm wrong, but it would appear that widening the track raises the roll center pushing it closer to the CG, which results in less body roll. Now I'm not saying this is a good idea, but if someone is dying to lower their car using dropsprings (or just cutting the stockers) widening the track proportionately along with adjusting the included angle via the strut bolts may help get your traction back by moving the roll center closer to stock while helping the scrub radius. On another note, does anyone still make longer balljoints?

 

I would never run wheel spacers and think they are a bad idea. Very unsafe IMO.

 

I thought the same thing myself at first, but after having them for a couple years on south denver streets I'm convinced they're fine.

 

I've seen those ball joint relocaters/spacers, but not a ball joint designed to be taller.

 

GM used spacers on some wheel options from the factory. Use your head when considering them and they'll give you no issues

 

well GM didnt want to make the right part so they made things fix. I just feel moving the wheels out with spacers is like putting a breaker bar on a bolt that you cant get lose. More likely to break. But please do as you think!

 

wheels spacers, mostly the slip on kind of various thicknesses are used on many race vehicle's for various reasons. there is NOTHING wrong with a wheel spacer when used with proper length, hardened wheels studs, and torque properly and re torqued as needed. (drag racing may be different, tracks may not allow them for other reasons, could be wrong)

bolt on spacers are the same way, a good billet aluminum spacer, with good lugs, torqued, and re-torqued after a few miles an so on, will be fine. they fail when they are improperly installed, and the lugs are not torqued/re-torqued properly.