michaelkrelina

A. With V710, 305/30-18 all around, what size of sway bars do you recommend.
b. Is there a major advantage in going to a wider rear tire?

M

Davinss

I've run with 305s all around and the car was VERY loose.

michaelkrelina

Was this in autocross or on the track?
What do you mean loose? Did it understeer .. Oversteer?
Did you use a stiffer than base sway bar?
Did you use r-compounds? .. What kind?
Do you recommend more rubber?

Bill Dearborn

I can't give you an answer for the size you mentioned but I have run 315/35/17s all the way round and the car sticks like glue with good tires. Have run this size with Kumho V700s and the 710. The 305 will have a little less tread width (1 cm less) but that shouldn't make that much difference. Usually loose conditions with these tires happen when the rubber has gone too many heat cycles or the tire pressure is too high. I usually set my cold tire pressure at 28 front and 26 rear for Xcross and a couple pounds lower for a road course.

Bill

michaelkrelina

What kind of sway bar and what wheels (ZR1 wheels?) do you use? Did you upgrade the shocks? Would you mind sharing?
Mike

EvilBoffin

Sorry that I can't address your particular question, as I run a C6 in SuperStock on stock wheels and 285f/315r Hoosiers. I can't change wheel sizes in this class, and the front 8.5-inch wide wheels can't handle tires any bigger, so my class is pretty much dictating what sizes I can run. I'll offer you some general info that might help, though...

First - "Loose" means oversteer, which would make sense when you run a 'square' setup like this (same size tires on all 4 corners) without making any other changes. This setup would typically increase front grip relative to the rear when compared to staggered tire sizes. In turn, that would cause the rear to seem to have LESS grip, introducing some oversteer.

You are right to ask what bars, shocks & wheel sizes to use with this particular tire combo, as ALL of these things are interdependent. It's not necessarily a bad setup - you just have to work towards your goal as a complete package. You can probably offset what oversteer you don't like by changing to a bigger FRONT swaybar, stiffer front shock settings and/or different alignment settings (more rear toe-in, less front camber, etc.). It will take some experimentation to get it right for YOUR particular driving style.

Just keep in mind that wheel sizes and other suspension changes will be dictated by the rules of the particular autocross class you intend to run in. Which class are you going to compete in?

michaelkrelina

Thanks for your response.

I have been participating only in local autocross events in Ottawa, Canada. In our classification, I am in "Class A", which is the top class, by virtue of driving a Z06. Additional mods do not change my class in this case. I'm trying to mod my car in a cost effective way, given resources that I already have, ie a set of 18x10.5 wheels.

With V710, 305/30-18 all around, I thought I would get a set of adjustable Pfaadt Street or Pfaadt Competition bars to be able to make adjustments in the relative firmness, front and back. I was hoping to delay a purchase of shocks until I see how the car behaves.
I understand that with stiffer bars I may have to stiffen the shocks to prevent pertubations from spreading from one side of the car to the other.
If I got Pfatty bars (~3x stock stiffness) do you think I'd have to upgrade the shocks at the same time to isolate the road irregularities to the each side of the car.
I think that I understand your points about the relative stiffness of bars and shocks and alignment changes as they impact on oversteer and understeer.

Mike

VetteDrmr

A. Can't really recommend any sway bars; I think that's at least as much affected by driving style as the physics involved.

B. On my C5 I've run 275s all around, 275/315, and 275/305 combinations. Running a square setup will typically have quite a bit of oversteer, especially under trail braking or powering out of a corner.

275/305 is much, much, better, almost neutral, tending towards a hint of oversteer on corner exit. 275/315 crosses the line towards understeer, especially on corner exit.

My experience has been that your tire selection has by far the biggest impact on your car's handling. I've recently bought 4 Z06 rear wheels (18x10.5") and I'm planning on trying maybe a 295/(305/315) combination once I run through my current inventory.

HTH, and have a good one,
Mike

96solo

Some true statements here, I've run many of combinations of tires, (size and brand), Shocks, and sway bars. L'tle Blu' has competed in National SCCA events in Superstock and A Street Prepared, and now in NASA TTS Time Trials.

Tires are first.. It's where your car meets the road. Depending on size allowed, as some are in stock classes, the best set up for stock Speedline wheels is 295/17 front and 315/18 rears in a Kumbo 710 or Hoosier. Speedlines is a very light weight wheel from the factory (19.5 and 21 lbs.) and do surprisingly well. If your class allows you to upgrade your wheel go to 18" wheels in a light weight CCW or Forgeline wheel. I prefer CCW and John will set you up right as he has much experience in Corvettes.

MAKE CHANGES ONE AT A TIME. This is the only way to know what changes have done to your car's handling.

Shocks second... The '04 Sachs shock is a great shock and does very well in rain conditions, but adjustable Koni 3013's I have found better in dry and better than the expensive Penskes. The Dyno proves that. See Sam Stanos for Konis. A fair and honest vendor, a F/S National Champion.

Sway Bars... Much testing has been done on this and talking to guys like Danny Popp and Jake Latham the T-1 is too stiff for autocross. Hotchkis is my setup for autocross, then Pfadt for anything more. Pfadt gives you adjustment under and over the Factory T-1 bar. The Pfadts are great people to work with, their stuff is a little pricey, IMHO, but always fits and is well designed and engineered.

I hope this helps!

P.S. Mike go with 315's around with your 18" wheels, then soften or stiffen shocks according to what the car needs. The 315's in front totally stop the low speed tight corner understeer.

D.J.

Bill Dearborn

Stock Sway Bars, stock shocks with 40K miles on them. ZR1 style wheels with Grand Sport offsets. With fresh tires it totally amazes the BMW club racers I have given rides to. They can't believe how it sticks.

Bill

VetteDrmr

Thanks for the suggestion. Right now I'm running '04 Sachs shocks, but running 315 square is something I'm considering. Nice to move tires to whatever corner you want for wear purposes (Yes, I'm cheap!)

Have a Merry Christmas and Happy New Year!
Mike

96solo

Thanks Mike! I hope you have a great Christmas too. I want L5 fenders under my tree with a new Hans Device.

The tires will work, If you're cheap, spend the money on the Koni 3013's. It's fun to beat the guys with $4,000 of Penskes.

michaelkrelina

I now have R888 295 front and 315 rears for the track. I will get two more 315 so that I can use 315 x 4 for autocross. I am a beginner and will work my way up to Kumho or Hoosier next year. I don't want to wear out expensive tires while learning the basics. I am thinking of Pfaadt street bars. The shocks I will probably decide a little later. Does anyone have experience with the Pfaadt double adjustable shocks?
Thanks for the comments and suggestions.
Merry X-mas
Mike

EvilBoffin

Mike -

Though I've autocrossed for many years on 'true' R-compound tires in SCCA stock classes, I started out running my '08 Corvette (my 1st Vette) on 275f/305r Toyo RA-1's, which are the same compound as R888's. I bought them to be used only for HPDE's, but ended up running them at about 7 autocrosses last year also (before I could afford dedicated auto-x wheels and Hoosiers). I actually found they offered a pretty well-balanced setup on my otherwise stock Z51 C6, and were quite fun and predictable on-course. But keep in mind that you have wider wheels then I do, so bigger fronts may still be the ticket for you.

R888's will certainly not be ultra-competitive against Hoosiers (everything else being equal), but they will be JUST FINE if you're starting out or only competing at the regional level. And they should last a lot longer, too.

However, be aware that dramatic changes to your suspension and a 315 square setup can be overwhelming for a beginner to dial in, since you are not really familiar with the car's balance in it's stock configuration on an autocross course.

I don't want this to sound too preachy, but to be honest, it's usually best to start a beginner out with a truly stock car, with a good performance alignment, and then work on the DRIVER instead of modding the car immediately. Many experienced competitors have found that having TOO much adjustability - too many variables - can just make you go SLOWER. If you're constantly worried about adjusting your shocks & bars & tire pressures & camber settings, etc., etc. between runs, then you're not concentrating on just learning to drive the car.

As for the Pfadt shocks, they are NOT true double-adjustables. There is ONE adjuster, that changes BOTH rebound and compression at the same time, at a 3:1 ratio. That is not to say that they don't work well for our cars... Forum members DaveOH32 and G.J.Dixon both have them and seem very satisfied by all reports.

Davinss

I couldn't agree more. Autocross is about the driver not the car. As a beginner all the mods in the world aren't going to make you any quicker. And going with an unusual setup like the 305s all around will likely slow you down as you spend a season trying to get it dialed in instead of focusing on your driving. If you're dead set on buying some parts and tires I would ONLY copy a proven formula. Anything else will be slower and more expensive in the long run...

TedDBere

I don't know of a single national level stock class C5 driver that uses a square set up. Hoosiers: 295/315; Kumho: 275/315. Much better car balance. FWIW

Good luck.

thehammer69

But Ted, it's kinda difficult to run "square" in the STOCK class considering the wheels are not "square". Sure, you could probably squeeze a 315/17 on the front if one really tried but the contact patch would probably be bad from having the sidewalls rolled inward so much.

Oh, and by no means assume I'm an advocate of running square because of what I just said. I may try it though in the ASP class with a Rear wheel used in the front.

TedDBere

It's not that uncommon for the ASP vettes to run a 315/18 on the fronts, but they match 'em up with the 335/17s on the rears. I believe this was Popp's national championship setup a few year's ago.

fej

I agree with the poster regarding lots of seat time before you get crazy with the mods, especially the adjustable variety (shocks, sways).

Get yourself an aggressive alignment and go drive the car on what you have to work with. It is a damn good package right out of the gate.

Driving style does have a fair amount to do with it as well IMO.

Alignment was the biggest change I have made with my car outside of Street tires vs "R" tires.

I do find it interesting that people are recommending the 275/315 combo for the 710's. I personally feel that it lacks turn in in this setup, but I am still working on improving the nut behind the wheel

G'luck
Fej

EvilBoffin

I think you can definitely take advantage of lots of front grip for autocross. Like Ted is saying, since you're class doesn't force the use of skinny front wheels, you could go with 295's or 305's, as long as the rear has enough tire width to maintain chassis balance without resorting to some weird alignment settings.

Also, 285/18 Hoosiers are actually the same width as 295's, so they both fit my narrow, 8.5-inch wide fronts equally well. The only difference is diameter and load rating, with the 295 being considerably taller and able to carry a lot more 'weight'. My theory is - the 285's will offer extremely quick turn-in and steering response, while the 295's will not overheat as quickly and will probably last longer.

That may not apply to Kumho's, though.

You'll have a lot more tire size options running 18-inch rear wheels then I do with the 19-inch C6 rears, too...
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