Help me set up my formula for the Nurbrurgring Options

[phoenix64]

http://ls1tech.com/forums/suspension-brake...ml#post16397439
Long story of my experience so far.

Right now I'm leaning toward stock brakes or possibly putting the C5 brackets back on with 17in wheels and 315/35 tires.

I'm also tempted to stay with the 16in wheels, and get some 255 slicks, just cause the car steers/tracks/rides so well with the lighter 16in wheels.

Any thoughts? Is there a calculator some where that lets you compare grip with 255 vs 315 tires?

Also any suggestions on seats or steering wheels would be appreciated.

[Blainefab]

Nice read - Thanks for the all the detail, it helps figure out what advise to offer.

Tire pressures were way too high - the general rule of thumb is to lower pressure on the end that slides first. Start with 32F/32R on street tires, run a session, drop 2psi from the end that slides first. Evaluate your balance in steady state cornering, do not confuse balance with power on or trail braking oversteer. Your car will push (aka understeer = front slides first).

Check for bottoming in the rear - riding on the bump stops can cause oversteer. If you have bump stop extenders, toss them. Use the OEM bump stops, and adjust the rake for 1/2" higher in the rear than the front, measured at the LCA bolts. Use spacers on top of the rear spring perch to raise the rear.

Stick with street tires till you get proficient tuning and driving the car. You need to understand the cause and effect of changes in setup and technique before raising the grip level. A high performance summer tire will stay cooler than an all season.

245 is not enough rubber for our cars - I recommend 275 on 17x9.5" 01-04 Corvette Z06 front wheels, They ideal for the Fbody, are lightweight and inexpensive. Moderate spacers with ARP studs will get them off the fenderwells, you may need to roll the outer fenders. The Pontiac is wider here than the Chev.

Don't use 315s on 11 rims - you would need to do extensive fenderwell adjustments and relocate the bumpstops to fit them without rubbing, and upgrade your LCA/PH to rodends, or use a Watts. The 11's will hang up on the bump stops at full droop - this can happen when the car gets light - the last thing you want when you are flying over over a rise at 130mph is to have the rear wheels lock up on the bumps stops.

Get a spec alignment - With a stock front suspension you can get about -1deg camber, equal both sides, and as much caster as you can get, also equal both sides. Toe zero to 1/16" out. Find a shop that will align to your specs, not just light up the green lights.

The C5 brakes should be adequate, use a good pad and fluid. You'll want a medium grip pad front and rear - too much pad will overpower a street tire. Street pads can overheat quickly and fade. Finding the right pad compounds front and rear will be your biggest challenge.

[pharmd]

Nice read - Thanks for the all the detail, it helps figure out what advise to offer.

Tire pressures were way too high - the general rule of thumb is to lower pressure on the end that slides first. Start with 32F/32R on street tires, run a session, drop 2psi from the end that slides first. Evaluate your balance in steady state cornering, do not confuse balance with power on or trail braking oversteer. Your car will push (aka understeer = front slides first).

Check for bottoming in the rear - riding on the bump stops can cause oversteer. If you have bump stop extenders, toss them. Use the OEM bump stops, and adjust the rake for 1/2" higher in the rear than the front, measured at the LCA bolts. Use spacers on top of the rear spring perch to raise the rear.

Stick with street tires till you get proficient tuning and driving the car. You need to understand the cause and effect of changes in setup and technique before raising the grip level. A high performance summer tire will stay cooler than an all season.

245 is not enough rubber for our cars - I recommend 275 on 17x9.5" 01-04 Corvette Z06 front wheels, They ideal for the Fbody, are lightweight and inexpensive. Moderate spacers with ARP studs will get them off the fenderwells, you may need to roll the outer fenders. The Pontiac is wider here than the Chev.

Don't use 315s on 11 rims - you would need to do extensive fenderwell adjustments and relocate the bumpstops to fit them without rubbing, and upgrade your LCA/PH to rodends, or use a Watts. The 11's will hang up on the bump stops at full droop - this can happen when the car gets light - the last thing you want when you are flying over over a rise at 130mph is to have the rear wheels lock up on the bumps stops.

Get a spec alignment - With a stock front suspension you can get about -1deg camber, equal both sides, and as much caster as you can get, also equal both sides. Toe zero to 1/16" out. Find a shop that will align to your specs, not just light up the green lights.

The C5 brakes should be adequate, use a good pad and fluid. You'll want a medium grip pad front and rear - too much pad will overpower a street tire. Street pads can overheat quickly and fade. Finding the right pad compounds front and rear will be your biggest challenge.

Alan, do you recommend no 315 rear as a general rule? Alot of folks including some hard core racers are running this setup, so I wonder if their is an amiable solution that allows us to run it (via modification). Would going with a more custom wheel with correct offset avoid this issue (what backpacking would u recommend)?

[Blainefab]

Nice read - Thanks for the all the detail, it helps figure out what advise to offer.


Don't use 315s on 11 rims - you would need to do extensive fenderwell adjustments and relocate the bumpstops to fit them without rubbing, and upgrade your LCA/PH to rodends, or use a Watts. The 11's will hang up on the bump stops at full droop - this can happen when the car gets light - the last thing you want when you are flying over over a rise at 130mph is to have the rear wheels lock up on the bumps stops.

Alan, do you recommend no 315 rear as a general rule? Alot of folks including some hard core racers are running this setup, so I wonder if their is an amiable solution that allows us to run it (via modification). Would going with a more custom wheel with correct offset avoid this issue (what backpacking would u recommend)?

No, for general autox and track duty 315's all around are great, once the proper fitment techniques are used.

That was a caution specific to the OP's usage, for the reason stated. Running at top speed on the Ring is different than any of our tracks, From his excellent description of how the car is working (ie not working), he has a setup issue that needs to be fixed, and I sense that he is new to the Fbody or car setup in general, and has not done the typical suspension improvements that are prerequisites to using fatties. Just putting 315's on an otherwise stock car could be disastrous. Cutting a tire or grounding the rim to the frame at top speed carries a big penalty.

[phoenix64]

No, for general autox and track duty 315's all around are great, once the proper fitment techniques are used.

That was a caution specific to the OP's usage, for the reason stated. Running at top speed on the Ring is different than any of our tracks, From his excellent description of how the car is working (ie not working), he has a setup issue that needs to be fixed, and I sense that he is new to the Fbody or car setup in general, and has not done the typical suspension improvements that are prerequisites to using fatties. Just putting 315's on an otherwise stock car could be disastrous. Cutting a tire or grounding the rim to the frame at top speed carries a big penalty.

This is a major concern of mine. Until you've run it, you can imagine the amount of vertical load that a car experiences on the ring. I was getting airborne at 3 different points on the track, you get probably 2-3+vertical G's, at which point the car weighs in the range of 6-9,000lbs, and the suspension is still having to absorb massive bumps,and cornering forces.
Not to mention the Carousel that loads up the suspension then beats the hell out of the car.

So what are some possible solutions for getting the rear planted under trail braking, or curing the lift-off over-steer?

[phoenix64]

I also wonder if its a weight balance issue?

When I was swapping out my old tranny, I drove a few twisty roads with the new one in the trunk, and it made a huge difference in how the rear end of the car felt especially under braking. It was more planted and confidence inspiring.

But I really don't want to add 150lbs of ballast to the trunk.

[Blainefab]

So what are some possible solutions for getting the rear planted under trail braking, or curing the lift-off over-steer?

Check the stuff I mentioned, and let us know here what non stock parts you have on the car now.

[Jeff94TA]

Everything Alan mentions is spot on as always. I ran the Strano setup that you have for years on some challenging tracks and never had the oversteer issues your describing. I'm talking about tracks like Sebring, which is very rough, Daytona, transitioning on and off the banks, and Road Atlanta which has tremendous elevation change. The only difference with mine from yours was an aggressive alignment and good tires in at least a 275 section width.

Get it aligned, pick up some 17" wheels w/ 275's and put on the C5 brakes. Alan pretty much said the same thing but I wanted to add my personal experience.

[dailydriver]

Hasen't roy run the Nordschleife??

Maybe he can chime in with a few suggestions/recommendations. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/wink.gif)