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s2per's Avatar
 
Join Date: Aug 2001
Location: Hernando Beach, FL
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Kumho Ecsta V700 pressures?

I've been very pleased using the Kumho track rubber on my SC and the Carrera before it. But the last event showed that I'm going to need higher tire pressures to fight the premature wear I've noticed, esp. on the rear.

In the "old days", we ran our beloved BFG Comp T/A R1s with 23-25 psi front and 26-28 rear. I've used 24/28 for a while on the lightened SC with the Kumhos and last event showed big-time outer tread wear on the rear.

What's everone else using?

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Timothy Stoops
86 911 Cab-'06 Cayman S-12 Cayenne
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Old 01-01-2004, 03:16 PM
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I shoot for 29/31 hot pressures on mine, but the car weighs 2100# wet. I generally recommend with Kumhos that you increase the tire pressure about 1psi hot for every 100 lbs of car weight above this.

When you say "outer tread wear" do you mean the edges of the tire rolling, both inside and outside and wearing the tread on the outside of both edges, or more wear on just the outside tread? The first would indicate you need more pressure, the second would indicate that you need more camber.

So a fwe more questions:

What size wheels and tires?
What car weight?
What camber are you running?

Have you done the "chalk test" and are you taking tread temps? If so, what did you see?
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Old 01-01-2004, 03:25 PM
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Chris, the tread wear was on the outside edge only and yes, it was after the latest "adjustments", namely lowering and setting rear camber at about 1-1/2 degrees (front is about 1-1/4).

Car weighs about 2480 wet; tire sizes are 205/50 x 15 on 15 x 7s and 225/45 x 15 on 15 x 8s.

And this weekend I plan to try the chalk test at Sebring. Don't have a tire thermometer but I might be able to borrow one.

How soon after coming into the pits do you check the hot pressure?
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Timothy Stoops
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Old 01-01-2004, 03:39 PM
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On my '72 911 with 8" & 10" X 17" wheels and 235/275 /40 Ecsta V700's and 2340# weight, I run 24/26 hot.
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Old 01-01-2004, 03:44 PM
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Their is a new compound for the V700 (K8A = old, K6A = new as seen on the tire sidewall). Which are you running?
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Last edited by Jim Smolka; 01-01-2004 at 04:12 PM..
Old 01-01-2004, 04:10 PM
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Well, this may make it even more interesting. The fronts are K6As, the new rears ("home" heat-cycled and not shaved) are K8As.

BTW, I'm not looking for that last .01 second/lap. This is an entertaining little DE car and I'd like to keep a good balance of track performance and tire life. TIA.
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Old 01-01-2004, 06:47 PM
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Well wear on the outer edge only means that (obviously) the inner and middle section of tire are not touching the ground as well.

This is not likely to be a pressure issue, otherwise you'd see wear in both outer edges or the center...

Now... the best answer would likely be more camber, to even out the patch while cornering, but unfortunately most 911's can't get more than 1.5-1.75 degrees of camber in the rear. So, you may be able to add a little more pressure to cange the tread shape of your tire. I don't get good wear on my inner edge, but get even on the middle and outside this way. (I can't get more than 1.5 camber on the rear)

Your front camber is low... I would suggest trying a bit more.

Hot tire pressures are taken AS SOON AS POSSIBLE when coming off the track, same with temperatures! I will pull into the pit, jump out, check, then proceed to the paddock.

I would also look at toe in the rear. Excessive toe-in might also contribute to this. Did you re-align the car when lowering? If not, you may have changed everything.

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2001 GT3 Cup - "Pepin"
1999 Spec Miata
1996 993 RS Replica
2010 Harley 48
2013 Honda 250 CRF
1971 Norton 750 Commando
Alcon Brake Kits
Old 01-02-2004, 08:57 AM
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