I installed some z06 wheels on my car the other day with 2" spacers in the front now my car is sketchy when driving straight. Its fine as soon as you start turning but staying in a straight line is impossible. I have change the alignment twice.


first camber -.8 caster 4.2/4.5
Second Camber +.6 caster 3/3.4


Neither made much difference. My front end is al tight also. steering box has a little slop but should be ok.


Only thing I could think of is wit the 2" spacer it messed up the sai.


Any suggestions. Thanks in advance

 

How is the road you are driving on? I know wider tires will tend to pull more, depending on road conditions, may pull even more/harder.

 

When on a flat smooth road it is ok. But if there is a slight camber or bumpy the car goes nuts. Like changing lane on highway its very scarry

 

Maybe just to be certain, pull the 2" spacers and see what the car does. That's what I'd do. The tread on the tire looks good? No bulges or any flaws or cords torn? Inspect 100% of the tire...

 

Where is the toe set?
spacers have nothing to do with sai angle

 

Sounds like you increased the scrub radius. That is, the center line of the tire is further out then the previous tires. This gives the tire more leverage against the steering linkage.

Makes for a wild time when changing lanes, car has a mind of it's own.

RBob.

 

yes! scrub radius not sai. So Is there any remedy for this. I know a lot of people run zo6 rims with 2" spacer. I thought I read somewhere changing the sai can change the scrub radius. should be 3/8" to 2" is what I read


"tires are new nitto NT555s so shouldn't have a prob there"

 

SR is the distance between center of rim and where KingPinAnge hits the ground. but if the 2" spacer makes up for z06 offset it shouldn't have changed correct?

 

here is what I found but this is NOT for a McPherson susp.


KPA affects scrub radius, more KPA reduces the amount of scrub radius so sometimes this is a good way to decrease scrub due to offset changes. Generally if you have a race car with adjustable KPA you usually set the car up with a couple of degrees less KPA than positive caster so you end up with a good but not excessive amount of negative camber gain with turn in. This way you might be able to get away with less static negative camber. In some cases you may want the KPA to equal the caster. KPA affects the scrub radius so sometimes you end up balancing caster, KPA and scrub to get the car to handle in a desirable way.

 

Possibly the wider track and tires are just emphasizing an existing front end problem? You are putting more leverage on ball joints and the rest of the front end.

 

I have the exact issue with my iroc. I just rebuilt everything...control arm bushing, hd ball joints, struts, springs, sway bar links, upper strut mounts, all steering linkage (except steering box). And with my stock Iroc wheels...it drives like new, as soon as I put my adapters on and my C6 wheels it's all over the place any speed 50mph and up (on not perfect pavement). I do not have hub centric spacers on my car. I thought about buying some and see if it helps. But I'm just about done with these C6 wheels. I'm about to go full ****** and get some black D-hole rims and put yellow letter tires on it and make it look like a stock car. LOL!

 

What size spacer did you use

 

I'll have to check tomorrow. It's been so long. But I thought 1.25 on front with stock brakes, and 2.25 on back with stock axle. I don't feel the pull in my steering wheel either. It acts just like I'm driving with really big gust of wind hitting at the side while driving.
I think I'm going to put my stockers back on anyways. After I lowered it I'm having issues with slight rubbing on the inside edge of the outer back passengers wheel well. And I have my adjustable panhard bar adjusted to actually set the axle more to the drivers side until I can find a fender roller.

 

[QUOTE=closer;5955350] It acts just like I'm driving with really big gust of wind hitting at the side while driving.
QUOTE]

Yep.


I have 2" on front

 

This is exactly what others here have described. it is a scrub radius problem. These cars are not engineered with the geometry to put a wider tire on the car. It is why I always left an 8" wide front wheels on my car.

The Steering Angle Inclination of the 3rd gen suspension is designed for an 8" wide wheel when pertaining to scrub radius. There are two ways this can be changed, but both are expensive and complicated. 1) is to lengthen the a arms and hope the spring does not misalign in the spring pocket/can. Then with this you can run the wheel with more offset (less spacer width) and put it deeper over the brake components towards the centerline of the vehicle. THis allows the tread to hit more center with the SAI. Note that SAI is measured with the camber at 0. When you include negative camber, this is called Included Angle (IA). This will change scrub radius with more or less IA because solely on the portion of contact patch that touches the ground in straight line steering angle zero. The scrub moves with the SAI, but the outer poortion of tread lifting off the ground with neg camber will cause a change in scrub...ONLY UNTIL a bump is hit with the outer portion of the tread and the car will yank in that direction.

2) The SAI can be "fudged". What this means is when you tighten the two bolts holding the strut to the spindle- they have a little bit of play to force them one way to increase SAI upon tightening. What this DOES however is it will decrease te ability to gain negatve camber. The higher the ride height the worse this effect will have. A lowered car (not taking into account for a heightened strut mount) will have a shorter overall balljoint to strut mount distance and thus will have more potential static negative camber adjustments. The expensive part of this is the process of lowering the car with the proper components both front and rear. If this is already done to a vehicle then this step is easiest to take of the two.

Note that an increase of SAI has the same effect on steering and chassis geometry as does positive caster.

Dean

 

I seen moog sells a cam bolt that adjust where the strut mounts to the spindle but like STG said I will loose my camber adjustability. . . And I just replaced my springs and struts so I really don't want to lower the car

 

I was wrong on my spacers. 2" up front and 2 1/2" on back. I wonder why it doesn't seem like everyone with the other style corvette wheels have any issues? Oh, well... for now I'll just put up with it. I'm going to research more about the "Scrub" angle and try to understand it better.

 

That is the problem with these forums with all the internet racers and car builder's: People DO have these issues and never admit to it. It is why I put myself out there and am known locally to back what i say and put my money where my mouth is. I put So Calif in check years ago. There is always someone new that comes along trying to claim what they have is the cat's meow...a few of us know differently.

 

I already sold my old rims and just spent 700 in tires for these so I guess im gunna get the camber bolts and adjustable strut mounts and see what I can come up with to at least get it drivable.

 

No matter what it's still not as bad to drive as my old '78 f250 with 44inch bias ply swampers at highway speeds. LOL! I'm sure my front tires(even though almost 70%) still aren't helping. Bridgestone doesn't have the best reviews. But for $45 for the pair I'll wait until they're toast.

 

Sorry for the question, but... does "long course" and "short course" mean whether you drive the car mostly in the city (short distances) or on the fast lane for longer distances?

And do the values mean that this adds to the normal setting or is this the total setting?

Thanks,
Thomas

 

You may have replied to the wrong thread, Thomas Stahel. Not sure what thread you were replying to, but short course usually means autocross racing (tight corners, slow speed), and long course usually means road racing (much higher speeds).

 

Yeah, it's strange. I actually was in another thread while writing but after I had sent the reply I got into another thread. I'm confused. But the subject was just steering geometry. So your answer is helpful. I saw that table copied below which gives the values for camber, caster and toe for different usages. I'm not sure whether the additional values for "toe" only refer to the "road racing" part and whether the value has to be added / subtracted somehow to / from the "normal" toe value.

 

Those are suggested toe settings for two different situations. Some toe out will make the car dart into a turn. But you don't want that much sensitivity when turning into a corner at high speed, so some toe in will make the car not turn in so quick and feel more predictable.

 

Okay, so these two different settings only refer to the "Road racing" usage. I got it :-)