Ok I've read as many threads as I can till I'm blue in the face. I have a fairly simple question that I've not seen answered or I missed in all the threads.

16 C7 Z51 - I bought new wheels/tires and have the dreaded rub on the rears since most offsets on aftermarket wheels cause some tire poke. I can't change that now so I'm mitigating it as much as I can.

Wheel/tire combo is Forgestar CF5V - 19x9.5 - 50 and 20x11 - 71. Tires are 265/35-19 and 305/30-20 Eagle Supercar 3s. The reduced offset, wider wheel and slightly taller and wider tire has added up to fender rubbing in the back when two people are in the car and hitting expansion bumps. It's not severe but it's there. There appears to be no issue with the fronts as they don't poke out quite as much as the rears.

I currently have -1 degree negative camber all the way around. I had an alignment done 2 months ago and requested a more street oriented alignment. But now I've changed wheels/tires and am thinkin of changing it to help with the top side tire poke/rubbing.

I've already raised the back on the bolts almost all the way up which gave me about 1/2 inch of clearance. When 2 people sit in the car it sit's almost exactly level with the fronts and sits a little high when empty. So it really doesn't look bad at all.

So long story short. I want to bump my negative camber to 1.7-2.0 degrees negative front and rear to gain that extra .3-.4 inches of clearance on the top of the tire.

If I have a washer removed from the upper control arm bolts in the rear will the tech still be able to dial in that range and get the toe right? From my reading that much camber won't wear the tires out too fast as long as the toe is set right.

I know you can dial in that much camber without removing the upper washers but it seems that's not pulling the top of the tire in but pushing the bottom out. Wouldn't removing the upper washer slightly reduce the track up top and then you finish adjusting the camber settings with the lower eccentrics?

Again I'm pretty new to Vettes so I hope I'm not way off base. I just want to add a tiny bit more clearance as I believe I've already tackled the rubbing issue with 1 person in the car and just want to make sure it doesn't rub with 2 and some luggage.

Note once these tires wear out I'll either swap wheels to something with better offsets or go with a shorter tire combo front and rear. This is not a daily driver so mileage is around 5k year.

Thanks

 

In all of my years reading and playing with alignments, the camber at 1.5 and higher will eventually get you on the inside of your tires. Toe will make it eat the rubber off quicker if you don't get it correct. I try to get the opposite of you and go down to 0 (or as close as possible) to have the tires last longer. I understand your problem but you are flat stuck with the situation because of the offset. Short of getting new wheels with the proper offset, you're gonna be irritated with the tire fit and function.

Welp, that's my $.02.

Elmer

 

I hear you but there are a lot of threads on here that state that is not true, that incorrect toe is the culprit. In my situation I really don't care since we don't drive the car enough. If I wear out these tires in 5k miles then it will just accelerate my plan to fix the issue permanently. For now, I'm stuck. I can't afford to just switch to something else 3 weeks after such a large purchase. And I'm not risking damaging my fenders to save a few thousand miles of tread life on a consumable (ie tire).

So the question still remains. Will pulling a spacer up top allow you to still get below -2 camber and effectively reduce track width by that small margin? Can you adjust back out to -1.7 - 2.0 camber after removing the spacer and still get toe and caster all back in spec?

 

Where exactly is the tire rubbing? On the wheel liner or the actual plastic fender? What part of the tire is rubbing?

The Z51 should have 2 GM shims/spacers behind each upper control arm dog bone. Those spacers are ~ 2 mm thick. The GM track alignment TSB indicates one of the rear shims should be removed to get to -2.0 deg camber. Removing the shim may not get you to that point but there will be adjustment in the lca cams to push the bottom of the tire out far enough to get to -2.0 deg.

Depending on where the tire is rubbing 2 mm should be sufficient to clear whatever it is rubbing against. If you want to have a more street related negative camber the lca cams can be adjusted to move the bottom of the rear wheel inward as well.

Your tire is ~ 0.6 inches taller than the stock tire. With the added inch plus tire width and a change in offset, you may not be able to avoid rubbing even after an alignment change.

Bill

 

Bill, thank you. It's rubbing on the plastic fender. I have raised the back up just about as far as the bolts will adjust and it seems to have stopped it. But I want to go a little further by pulling the tires in via camber and track width reduction.

The car has -1.0 camber all the way around as it was aligned recently by a reputable tuner shop here. So it sounds like I am right that if I go to -2 neg camber by removing a top spacer then I will gain ~ 6-7mm of clearance up top from the -2mm of track width reduction and the added -1 degree of camber. That should do it. Once these tires wear out then I'll go to a shorter tire all around or get new wheels with better back spacing.

Ok a bit more after reading your response. If I removed both shims to gain 4mm track width up top, can the lower eccentric then pull in the LCA enough to get back to -2? I'm really ok with running a fair amount of camber since the car is mainly driven in town on the street and not much highway droning. And I'll chalk this up to experience if it wears out the tires faster.

Thanks again.

 

I added a couple of things to my post. So take those into consideration when getting the changes done. Removing the rear shims can be challenging since the wheel liner gets in the way and you have to remove the bolt just far enough so only one shim falls off.

Bill

 

I know. My fault on all fronts for not doing a bit more research and measuring ahead of time. Raising the rear has helped as me and the wife drove it 2 nights ago for dinner and it did not rub and we hit a few bumps that would have before I raised it. I just want that extra margin of safety with the extra camber and thinking I'll like the handling, as well.

The shop I will take it to is well known for working on sports cars of all makes/models so I suspect they will be able to handle the shim removal. It may just cost me a little extra.

 

My recent experience w/ my C7 is that the shim washers are worth about .5deg each. So remove both washers will gain you 1deg camber. I just did this last week. get the rear of the car off the ground on stands. Put your floor jack under the lower ball joint and pump it up so it just barely moves the hub up. Now remove the two front or two rear bolts and let the washers fall to the floor. Whichever UCA mount you left the bolts in will keep the UCA from going very far. You may even need to loosen the other two bolts a turn or two so you can pull the UCA a little further from the frame. You can then install however many washers, or none, that you want between UCA and frame and re- install those two bolts but don't tighten them fully yet. Now move to the other UCA mount and do the same. When you have all your washers where you want them torque the bolts to 48#.

 

Thank you! I was looking for install info on how to remove the washers. I've decided to bite the bullet and get new tires in a 265/30 and 305/25 sizes which I should have done in the first place. That's a painful lesson I learned. But, I'm also going to have the car track aligned. We only drive it 5-6k miles a year so if we get 15k out of a set of tires that's 3+ years.

I'll sell these Eagle Supercars I bought. They are fantastic just too tall in the back and I can't just replace the backs because of the staggered height requirement. So new tires all the way around it is.

Thanks again.

 

What are you doing with the rear Caster ? Alignment machines cannot measure rear caster. When you change camber it will change caster. So you will need tools to adjust caster. A metal block and angle gauge. Rear Caster should be 0.

 

Take it back to the shop that did the first alignment.
They specialize in sports cars and exotics and I confirmed they had the tool previously.

 

A lot of people remove all of the shims. However, if you read the GM track alignment instructions they always leave one shim behind each dogbone. Not sure why they do that but they definitely make sure to tell you to leave one shim. Since they know the engineering of the car better than I do I always leave a shim between the frame and the dog bone. If it isn't the GM washer style shim it is a thin standard alignment shim.

Bill

 

My Zo6 only has one washer each UCA, I purchased the car Certified Used , wondering if someone removed some before or did some it come from BG with just one washer per? I am cording Pirelli scrubs (fronts) on out side edge after 13/14 30 minute sessions at Sebring. Alignment tech at local Chevy dealer says 1.7 negative camber is all he could get on OE eccentrics. I am doubtful of that statement.

 

So the machined bar is over $200 but the angle gauge is around $30 from my quick internet search.

Seems odd that bar is so expensive.

 

Yes, if you go with the GM Tool Machined bar. There are other ones available through Corvette Forum Members that are lower cost. Or you could make your own adapter.

Here is another gauge shown with a homemade adapter.


The bar is a steel bar that has been cut off from a stock piece, the two bolts are 1/4 inch bolts that have their threads removed. The bolts are inserted into the holes in the knuckles and the rubber bands hold the bar to the bolts. The rubber bands have to be heavy-duty strong bands that will hold the bar tight to the two bolts while the gauge is magnetically attached to it. Some people just use the two bolts and hold a smartphone with an angle gauge app against the bolts.

Bill

 

 

Just a quick update. I gave up on the 305/30-20 and this wheel combo (20x11 et71) since I want no part of damaging my rear fender.

I bit the bullet and swapped tires to Michelin PS4S in 255/295 combo. The 5mm of width and 2.5mm of height difference seems to have solve the issue. My wife and I took the car out to dinner and hit several spots on the highway where the old setup would rub and it did not have the issue.

My next step is to still add some more negative camber just to add a little more clearance and be able to lower that back down back to near stock. I figure -1.5 degrees will be a nice setup for street and track days without killing the tires too quickly. I currently have -1 degree so that will give me another 3-4mm of clearance up top.

In 2-3 years when these tires wear out I'll revisit swapping the wheels for something with better offsets.

Lesson learned. Do a little more research and measuring before clicking the submit order button.