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Discussion Starter · #1 ·
What's the best cold pressure of v710's in SS sizes for autocross? My car just had alignment, lowering, and corner weighting, and I've got new v710's on ccw's. Last year I ran old hoosiers.
 

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The best pressure will depend some on what kind of negative camber you have front and rear. A good starting point on the 710 would be 35psi in the front, and around 31psi in the rear. Then find someone with a tire pyrometer and fine tune from there. One more thing you need to keep in mind. With the rear being a 315 and if you are running max camber, you may never get the car using the very outer edge of the tire.
 

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31 in back seems a bit low to me. Like you said though, it all depends on the camber and toe settings. I hope you didn't lower your car all the way down!
 

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Actually, the V710 likes much less pressure than you might think.
I've settled at 29/27 to start and then bleeding back down to that level after runs. This is using 275 fronts and, of course, the 315 rears.
Others I'm running with go as low as 25 on the rears.
 

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tigerdrvr said:
Actually, the V710 likes much less pressure than you might think.
I've settled at 29/27 to start and then bleeding back down to that level after runs. This is using 275 fronts and, of course, the 315 rears.
Others I'm running with go as low as 25 on the rears.
For time trials or road racing I'd agree, but just for parking lot stuff, I would think you'd need to be at or around what my hot pressures are after 10-20 laps...which would be around 35 or so. I was also more referring to the difference in front vs the rear. For a road race, I generally start at around 24 in the left front and 23 for the rest of the tires. After a few hot laps, the front tires are generally only 1-2 higher than the back and it's pretty balanced. I would think that 35 in front and 31 in back would be awfully loose.
 

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Discussion Starter · #6 ·
Thanks for all the replies. FYI I lowered the car about 1" which allowed for 2.1deg camber front and 1.3 rear, with the crossweight right at 50%.
 

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jimshepp1 said:
Thanks for all the replies. FYI I lowered the car about 1" which allowed for 2.1deg camber front and 1.3 rear, with the crossweight right at 50%.
Unless you've done something radical to the shocks, your handling is now screwed up. You're bottoming out the shocks and have messed up the suspension geometry. I've posted on this several times.
 

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I agree that the shocks are going to need to be swapped, but it is worth mentioning that the top (National champ caliber) Z06's in SCCA SS class autocross all are lowered near to, if not as much as, what the factory bolt/bushings will allow.

Back to tire pressures, I suppose my mild camber settings
(-1.5f/-.6r) may need less tire pressure to be able to use the outside of the tread surface, but I see max'ed out camber Z06's still in the 29-31f/27-29r range, which isn't exactly a "hot" number, but is a starting number before each run, with finishing pressures only slightly higher.
 

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Discussion Starter · #9 ·
The guy who did my alignment also did the alignment for Pat Salerno's new Z06 (he won SS nat'ls in 03 and was 2nd in 04) and they lowered his car almost 2" and 2.5deg front / 2deg rear camber. That's close to the setup all the top SS drivers use, and there are some poor souls like me who do this without Penskes (yet).
 

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wtknght1 said:
Unless you've done something radical to the shocks, your handling is now screwed up. You're bottoming out the shocks and have messed up the suspension geometry. I've posted on this several times.
1" lowering is too much for stock shocks? Can you explain?
 

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Yep, you're bottoming out the shocks! I've posted this info several times so I won't take up another thread with the info. Suffice it to say though, that the Corvette suspension is very sensitive to changes like that. You've messed up the suspension geometry and bottomed out the shocks. That was worth about 2 seconds per lap for me once Phoenix set the suspension correctly (basically raised it to the stock ride height).
 

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1" lowering is too much for stock shocks? Can you explain?
This subject was the source of a big "discussion" between Joe Aquilante and I starting as early as the Nelson Ledges Natonal (May) and ended up at last year's Run Offs. Joe was trying to tell me that my car was too low; I thought he had rocks in his head (a race car too low? can't be!).

Well, in January I brought the car to Joe for a number of small items (a new crate motor!...yeah, right, small) and he set the suspension up the way HE wanted it.

Boy was I wrong!

The car now looks like a 4X4, but it sure does handle well.

Lesson: learn from those who know more than you. Ya think after 42 years I'd remember that one. :mah:
 

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Coming back to this rather late, but Solo II (topic of this thread) and road racing are different animals. For Solo II...slam it.
 

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As a reference point, since this thread started I've gone to a more aggressive alignment (-2.0f/-1.0r camber) and 295 fronts...I'm still right at 28-29f/26-27r (depending on asphalt or concrete and surface temp). This is, of course, for Solo II.
 

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My recommendations for Solo II National Tour and Pro Solo:

For SS: Lower to the max on stock bolts and shocks. Although the shocks are near bottoming out they won't be compromised in low speed Solo as the deflections won't be as great or as rapid as in high speed road course. The courses are much smoother with less undulations. Although the shocks may experience higher low speed and higher high speed shaft deflection; the deflections won't be as great.

For ASP and above classes: Lower to the max using longer Hardbar Titanium rear bolts and Hardbar SS front spring perch bolts with Delrin Bushings. You MUST use short shaft shocks such as Penske DA with Remote Reservoir Shocks for a maximally lowered car. As an option you can run VB&P Poly Graphite bushings and Extreme front spring. These have a better recurve, are lighter and much stiffer. These have less deflection than the OEM springs.
T1 Sway bars are also an option.
If you encounter excessive bump steer due to lowering this can be easily corrected with Baer adjustable pin hemi jointed spherical tie rod and steering rod bushings. These allow the tie & steering rods to be brought back to parallel on a lowered car to correct the suspension geometry. You may not find these necessary on low speed events but the bump steer may increase for high speed events.
Modified Billet Aluminum spindel/hub carriers are also available to aid lowering.
All this is done to lower the CG and roll center which improves handling immensely.
Lowering will also effect the Zero Scrub Radius by bringing it too positive. You can bring it back to Zero by using a wider tire and a positive offset (increasing the track).

You also need to decrease static & mid corner understeer, increase front grip and increase Turn In and Neutralize the handling. You can do this by increasing the front tire tread contact patch and decreasing the front aspect ratio of the tire.
I recommend 305/30x18 on 10.5x18 front and 315/35x17 on 11x17 rear. You need to run both front and rear with a +0.25" offset.

By using the above ASP recommendations you will have exceeded the capabilities of a T1 car and will be faster in high speed road courses as well. These recopmmendations are applicable to Solo I Time Trials and Hill Climbs as well. So if you are not bound by T1 rules you can exceed them and the OEM suspension limitations on a lowered car and have lower lap times.

I recommend for AutoX:
-2.4 deg. Front Camber
Max Positive Caster
1/16" Front Toe OUT each

-1.5 deg. Rear Camber
1/4" Rear Toe IN each

For high speed road course:
-1.8 deg Front Camber
Max positive Caster
0.0", Neutral Front Toe

-1.3 deg. Rear Camber
1/8" Rear Toe IN each

Bottom line is that you can only lower so far IF you are bound by T1 rules and using OEM stock parts. You can bottom out the stock shocks due to the long shafts, misalign the toe & steering rods out of parallel and get the Zero Scrub radius too positive.

You can however lower the car further thus lowering the CG and Roll Center and achieve better handling and faster lap speeds by using shorter shaft shocks, stiffer aftermarket springs, T1 sway bars, modified spindels, adjustable tie & steering rod and wider tires.
This will also neutralize the handling, increase front grip, reduce braking distance, increase turn in, decrease understeer and increase traction.

Remember T1 rules allow the car to run on the track safely in basically a stock class. The T1 rules however are a limiting specification.

The transition in suspension evolution is something like this:

Stock -> SS -> T1 -> ASP -> SM2/TimeTrials/GT1/HillClimb -> C5R/C6R
 
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