Putting new runflats on my 98 cp. Best to use factory specs ? Also saw a range of specs in a Vette brakes catalog. Any alignment pros out there ? Thanks :chevy

 

Not a pro, but have had tire wear with the OEM specs; too much camber for sraight line street driving. I would go with as close to 0 negative camber on the front tires as possible. Any good shop will have the GM specs, so you will have to tell them what you want. :smash: :yesnod: :)

 

Thanks for the reply. After 24K miles my runflats are worn and cupped on the inside of both front tires. Have a new set in the garage so want good handling and not the same wear problem. Always run 30 psi on cold tires. Anyone else ?? :)

 

Here's an old post I did a couple years ago and with over 20,000 miles on the tires now, they still look as even as new, tread just isn't quite as deep.

Here's my thoughts on alignment. I too had tire wear problems and was running on my third set of front tires by the time I acquired enough information about the C5 alignment to get things figured out, (I think). I set my own alignment in my home shop so I can try lots of settings with little expense.
First off, keep this in mind, you're driving a high performance car and a little aggressive tire wear is not out of line for a performance car running neg. camber, which is necessary to attain the cornering G-force ratings GM advertises.
According to GM document #776629, which gives alignment specs for the C5 & Z06, the (Preferred Front Camber is -.20 degree) for the C5 with FE1 & FE3 suspension. The (Camber Tolerance is +/- .50 degree). So if your front camber is anywhere between (-.70 degree to +.30 degree), you are within GM specs. You hardly need an alignment machine to get camber within that tolerance, that's easy hand level and eyeball range.
The Good Year run flat tires have a wide, square shoulder tread and a very hard sidewall which will put much more pressure on the edges of the tread, due to a small camber angle, and will result in what seems to be aggressive tread wear on the edges of the tread, usually the inside due to the neg. camber. Non-runflat tires have a much softer more compliant sidewall and is part of the reason the Z06 runs more negative camber.
The more square (0 degree camber) you set a wide tread tire, like the runflat, with the road, the less abnormal tread wear you will see.
I think it would be a wise move for GM to provide a set of "performance specifications" for aggressive driving, and another set of "touring specifications" for normal highway driving. They would need to provide a brief pro & con statement of the two specs and let the driver decide which way he wants his car set up.
So, back to the question as to what to use for good tire wear. Following is what I am currently running and with 11000 miles on the Stone RFT’s , there is no measurable wear variation in the tread.

Front
Camber: 0.0 degree, (error to the pos. side less than .05 degree if not exactly 0)
Caster: 5.0 degree, (steers a little easier and not nearly as important for street as it is for performance)
Total Toe: 0.1 degree pos.
Rear
Camber: 0.0 degree, (error to the neg. side less than .05 degree if not exactly 0)
Total Toe: 0.0 degree to neg. 0.1 degree

 

Hi,
I just changed to Z06 wheels and tires on my FRC so I took some time to look at the wear on the stock EMT’s.
The alignment was:
Front camber ~3/8 negative (0.38) on a –0.20 spec (-0.70 Z06)
Rear camber ~3/16 negative (0.19) on a –0.18 spec (-0.68 Z06)
The caster and toe were close to spec.
I have eight thousand miles, three drag strip days (~10 runs with short burnouts) and a track event at CA Speedway (10 laps) on these tires.

I used a tire depth gage I bought from a circle track store to check the wear. The front EMT’s were all within 0.010” of flat across the tread. I ran these at 32 psi hot (20-mile trip). This was slightly under inflated for the driving I was doing. There was a slight positive camber ground into the fronts. I wonder if this was mostly from the track event that I did last month.

The rear EMT’s are worn more in the centers by ~0.020”. I ran these at ~30 psi hot, which seems to be over inflated for these tires. At the drags I ran them down as far as 25 psi. There is a slight positive camber cut into the right tire only.

I am going to set my alignment to ~0 camber for the street and have a second setup for track days using Hardbars shims. You need something like –1.4/1.8 camber for track so this is not a good setup for just cruising around. If you run the track camber on the street, you will soon wear the tires close to this camber angle, which not only wears out your tires but also defeats the purpose of the big negative camber in the first place. Some racers cut their tires at an angle if the rules limit geometry changes. This gives them the desired effective camber on fresh rubber.

In terms of tire wear only, zero toe seems to be preferred. You will change the dynamics of you car when you change the toe, so you may want to do some reading before changing Chevy’s settings.

Another issue for those of us in CA is that most of the freeway on and off ramps are right hand turns (were you can nail it) so the street alignment may want to be asymmetric.

IMHO, it comes down to finding an alignment spec that will wear your tire evenly for the driving you do.

Good luck,
Steve

:steering:

 

Thanks for the informed replies. Anyone else ?? Thanks :)