Thanx for the info. Those BFG G-Force Sports are certainly top notch rubber-just bought a set of 225/55/16 ZR's for my grand prix and have raced in the rain with those same tires at Skip Barber Racing. I have 255/45/17 Kuhmo Ecsta ZR's in the front of my 78. The easiest way to check the control arm bushings is to inspect the upper control arm bushings and the lower by looking at the bushing where the metal end cap bolts to the bushing-you may have to remove the end cap by unscrewing the bolt to expose the material. Poly is either black or often times red in color and is very hard-difficult to compress with a screw driver-rubber will deflect fairly easily with a screw driver. Someone may have a better idea identifying the material.

 

Sorry we call it ET, I think you guys call it wheel offset. It's the position of the hub mounting face in relation to the wheel rim.



Wheel offset is important because it interacts with scrub radius to effect your steering stability.

Scrub radius is the point where a theoretical line through the upper and lower ball joints intersects with a line draw through the centre of the wheel. These two lines should intersect in the centre of the tyre contact patch at ground level or fractionally below.

If you change the wheel offset you get uneven feedback and load across the tyre when you steer. Also when the tyre meets an uneven road surface the tyre contact patch is loaded unevenly causing the tyre to pull to one side. A bit like a shopping kart with a bent castor wheel.

(hope that makes sense)

 

Yikes! Yes, the C2/C3 rear alignment should have static toe in.

Given their attachment points and that everything outboard was designed to mate with a 15" wheel, there are problems at both ends of the C2/C3 A-arms which cannot be readily overcome by simply bolting on different bits.

Golden illustrated what is scrub radius sufficently.

The camber spec on your basic alignment sheet is only the static camber when the vehicle is at rest. When the suspension travels up and down, except in the case of equal-length/parallel control arms, camber changes in relation to the chassis. Just how camber changes (typically you gain negative camber in bump), in relation to this travel is the camber curve. For pretty much everything but drag racing - where you want the rear tires to stay square to the surface when the vehicle squats during launch - negative camber gain is usually a good thing, as the outside tires would otherwise lean into positive camber when the chassis rolls during cornering, but the C3 seems to have a tad too much for many modern tires (the C2 is even worse).

The angle of the camber struts in relation to the half-shafts determines how much or little negative camber is gained in bump or squat, and a good place to start is with the inner links 1/2" lower than their OEM hieght (as originally recommended by John Greenwood). IMCO, unless you have the equipment and ability to actually test other heights scientifically, I wouldn't recommend going lower; the exception, again, being when setting up for drag racing. Slick as the Smart Strut bracket may be, it makes it all too easy to screw this item up, and in any event, you don't want the inner camber strut links further down from the half-shafts than the outer links, as this would cause positive camber gain in bump.

Toe steer is a result of the half-shafts determining the track of the rear tires as it arcs thru its range of travel and of the C2/C3 TA's having a fixed pivot point (theoretically) where they attach into the frame. Thus, as the rear track changes during suspension travel, so does rear toe. The C4 addressed this with double trailing links from the frame to the upright (or hub carrier assembly) and employed a separate toe link to control toe-steer. On the C2/C3, the best we can do is set up the rear ride height to reduce the liklihood that the half-shafts will travel below level from the outer stubs to the inner yokes, and to consider stiffer springs/shocks. The former may involve raising the diff in the chassis on lowered cars, and the latter will affect handling balance and ride.

FWIW, I don't subscribe to using poly for strut (or TA) bushings, as their travel isn't limited to a single plane, preferring heim-jointed rod ends myself, but they're fine for control arms and anti-roll bars. For control arms, look for those with serrated sleeves if you're not in the habit of doing a routine periodic "nut & bolt". Hope that helps.

 

Almost new. Like 4,500 miles.

 

I'm sure you have something like these, but if not have a look. They suggest some different settings than you have on your car now....especially the toe and camber

http://www.guldstrand.com/alignment.asp

http://www.vbandp.com/instructions/h...ruct/align.htm

With both ends of your car having toe out will make it darty.....toe in slightly on both will make it track much straighter. Your camber is too much @ -3.0, Try -0.5 to -0.75 degrees.

 

No rear out tow. I read the report wrong. What is factory rim off set? I'll measure mine tomorrow. The vette came with factory 8" rims and I have 10" rims. 2" increase doesn't seam like much. Of course the side wall is hugely different from F70-15 vs. 245/45/17. I have a friend purchasing a 69 that I'll later see if i can swap rims for a day.

 

I went from big balloon 15 inch BFG tires we have all had or still have to Toyo T1R Ultra High Performance 285/40/18 on the back and 255/45/17 on the front.

Now I am speaking from something I have done and I have 15 years seat time in this car and have been driving it on the same roads for 15 years around my home.

What I expected was a much harsher ride due to thinner sidewall and sidewall stiffness but also expected better traction and cornering.

What I got was a smoother ride, that's right actually less harsh ride and a car that handled like a different car, like a sports-car should handle around corners.

No other changes, just wheel size and tires and the handling went from dump truck to sports car. The car does not wander just tracks where you steer it. Real world experience I am talking about here no theory involved, just the facts

 

Seems a ton of people have good luck with wide tires. I wish I had a pro to check things out. My local vette shops says it most likely due to a worn rear spring. However, it's not that old and looking at pics of everyone else's springs, mine sits the same. I guess I need to do the free stuff, swap rims and test drive. My front rims might have too much scrub, but then reading some, people say older cars had a lot of scrub. I don't know what to believe anymore. Although breaking into ruts is horridly scarry, it points to too much scrub from my readings.
What is factory scrub? 1", none, have no idea.
Will only swapping front tires prove anything or should both front and rear be changed at the same time?

 

Oya, steering does not want to self straighten at all. In parking lots, I have to manually return with effort.

 

I didn't see anyone discuss Caster in this string, might have missed it. My C-5 buddies get 7 degress of caster in their cars with 3 degrees of negative camber, (AutoX settings) I can only get 2.5 degress neg camber and 1.5 degress caster. Think of a shopping carts rear wheels. I believe the addition of wider wheels/stiffer tires (aspect ratio) and not much caster is the issue. After market upper A arms are suppoesed to allow much more caster and I would like to try it for a fix. You all should drive my car with 295/35/17 Hoosiers on the street. Better have both hands on the wheel. I have poly bushings and everything in my front and rear suspension has less than 3,000 miles on it.

 

I have 3 degress (maxed) of caster. I see several sets of aftermarket A arms that allow upto 6 degrees. That would be next IF after I test smaller tires, it still doesn't work.

How do I measure my scrub radius at home with common tools?

 

Well I learned some new things I didn't know before from this thread, but I have a question.

Here's the situation:
My Mom has a '93 vette that has 285/40/ZR17 rears and 255/45/ZR17 fronts and I have a '95 stang with 275/35/ZR18 front and rears...and on the same roads her vette doesn't wander nearly as bad as my stang does.

My stang is lowered 2" with Steeda suspension, her vette has Goodyear's tires and mine has Yokohamas, and seems the tread of the Goodyears is a bit thicker than mine, but both are cut in a V pattern.

So they are both somewhat similar, so what causes such a difference in wandering?

From a 35 to 40/45 sidewall does it make that much of a difference? Or does tread depth factor in as well? Or different compounds of the tire?

Thanks, just curious since were on this subject.

 

Castor is an oil, Caster is the angular displacement from verticle.

 

Wow....where did that come from
Its not like we went from 1 degree to 8 degrees...... more like 1* to 21/2*. Maybe you should email these guys and tell them they have it setup all wrong too

 

From your alignment specs, you have a lot of 'toe' adjustement in the front wheels (compared to mfg. specs). And, if your steering wheel doesn't straighten on it's own in a parking lot, that means the steering box is likely too tight. So, on an open highway, if the wheels need to re-center themselves, they [apparently] aren't. Can you free up the steering system at all?

 

It was a sad day when they went to those tires, I quit watching F1.

These guys are light years ahead of anyone and constantly trying to do things to go faster.

Many of their engineering improvements from safety to paddle shifters to brakes eventually gets into our modern cars. Then they make them run on snow tires

 

Where does this quote come from cos I can't see it anywhere in this thread?

 

Did GM change something in the later C-3's because I have not problem setting my 1979 to 3.96 degrees of caster.

Jim, I just got my front end back together with speed directs new shorter springs for QA-1 shocks. They have them in 50 pound increments from 500 - 1000 pounds. I just threw on the 600# to test. So far I'm very impressed

 

wonder or wander?

break or brake?

Its fun reading the forum.

 

Well...I wander about breaking all the time.