PCA SDR

I just picked up a set of the 2nd generation Kumho v710 to try out in lieu of the V700 Victoracers I've been using on my race car. Hopefully, these won't fall apart like the 1st generation ones did. We'll see. The 710s are these ones:



Anyway- does anyone have any experience on the track with these tires on a lightweight, short wheelbase race car. Road race, not autocross.

In particular, I'm looking for advice on suggested hot pressures and temps they like best.

The car is approx 2030lbs loaded and is a '66 short wheelbase 2.0L vintage race car:



Thanks in advance!

JP

JP:

I run the Ecsta 700, a not-as-soft compound on a heavier car.
I have found that for longer sessions, they tend to heat up and
become a bit slippery. I was setting my cold pressure too high
(33-35) and they were going well over 40 hot (tire temp over
90°C/200°F). I started setting cold temp at 26psi, and they seem
to last longer, but I still can't get a full run session (20 minutes
instead of 30).

My tires are 225/45-15 rear, and 205/55-15 front on 8s and 7s
on a 2700lb car (with driver), biased about 60/40 to the rear.
I definitely could use a larger width tire, but I am trying to stay
within class boundaries. You didn't mention the tire size, but
bigger is better (up to a point).

I also found they really, really like smoothness instead of sliding
or too much drifting, as that heats them up too. I was told (by the
Kumho engineer) that the V710 is even more picky about driver
smoothness, and that it can withstand fewer heat cycles than
the V700 Ecsta (which can take even fewer than the VictorRacer).

Anyhow, as an educated guess, I'd think the V710 wants to see
temps about 85°C (190°F), and pressures in the mid-30s psi hot.
It will depend on size, though. Why not contact Kumho directly?
Also check out Tire-Rack's website, as they have a "care and
feeding" blurb on this tire.

Best,


Paul.

From what I've seen on the local tracks/Qualcomm the V710's are very sticky, and are loved by the drivers .... however they appear to last only a couple of race days, and with big power cars (GT-3) they cord very quickly at the A-X's with tough, tight turns and radical heat-cycling.

Ask the POC/TT boys about road-race reliability and durability for the big-track stuff. I know it's grossly different on the big tracks.

My 2 Cents

I just tried out my first set of V710's (245/35R18 and 285/30R18) on my 965 at the 3-day IRPCA Vegas DE and they were awesome. I ran them 33/35 hot. They wore beautifully. They squeal before they break grip, so they let you know when you are getting close. They are nice and sticky. The wear was even (though I was careful to not overcook entry speeds, so there was very little pushing). The Vegas (outside) track isn't particularly hard on tires, so it may not be the best proving ground. But I've got tons of tire left on the set and will be taking them to Buttonwillow in June to continue the evaluation.

Dan,

My experience has been that the V710 last a very long time on the GT2, Viper and Corvette. They don't seem to fall off too much due to heat cycles either -- I just won the Atwater Pro Solo in ASP on a set that had 3 heat cycles on them at the beginning of the weekend and were at 6 by the time I made my fastest runs on Sunday. Typically we are all seeing 100+ competitive runs on the tires, so I think the Kumho engineer was smoking something. This tire wears better than any Kumho I have used to date. Dente's rear tires started the weekend with more than a few runs on them prior to that weekend.

JP -- I would want to know tire sizes in order to really give you a good idea, but I shoot for around 32 to 36 psi depending on size and weight distribution, wear, etc. in a 911 application.

Thanks Everyone.

I ran them at BWRP this weekend racing with VARA and I thought they were great. They liked about the same pressures as the Victoracers. Maybe 1 lb lower. My best times came when they were about 32lbs front and 34lbs rear hot. Temps ranged from 145 to 180 degrees depending on tire and location. Got the little 2.0L down to 2:06.3 running the clockwise 13 configuration. Need to get in or below 2:05 to contend for the lead though. 2nd in class (C production) and 5th overall though.

Anyway- verdict on the tires is that I like 'em. Ran them in two races and two practice sessions. Will run the same set again for a full weekend at WSIR and see how thay last after that.

JP:

Good to hear of your experiences, and glad it went well. What sizes tires and wheels do you run?

pdy: I'm running 225-50x15 tires on 15x7 wheels. SWB car. With me in it and full fuel, oil, etc., she weighs in approx 2,030lbs.
30mm rear and 22mm front torsion bars (solid). 21mm front and rear sway bars (solid).

JP

Sounds like your pressures are about right. You may be able to go down a bit more and pick up some time, but only if you can be smooth.

I've been experimenting with the V710s this season on JGW's recommendation and I've got to say I am really impressed with them. I have only used them for autox so far, but I have found they like lower pressures than the V700. I have 35 runs on them now and have kept lowering the starting (cold) pressures and they keep getting faster, or maybe it's just that I am trusting their grip more, I don't know.

I am down to 24F and 25R starting pressures and end up at about 28F and 30R hot after 4 runs (with air fill, not nitrogen) with the 205/50-15s. They have shown excellent wear so far, and I still have not gotten enough rollover on the shoulders to reach the little triangle marker on the sidewall with my 2360 lb. SWB 911, so I may even be able to go lower. I used to run the V700s at 32F/34R when hot and they would rollover farther.

From what the Kumho engineer said at our tech session, heat management may be an issue with them in continuous lapping sessions, but I have been careful not to overdrive the car, keeping slip angles reasonable (most of the time, anyway. )

Like James says, try lowering them a few pounds and be smooth! Your car is lighter than mine, JP and you're running a bigger tire.

TT

We run as low as 24 PSI in the rear of the Vette with 335s, so I would think around 25 front and 28 rear (hot) would be pretty fast on that light little car. Keep lowering the pressures and keeping the wear about 1/4" from the edge of the triangles. Go down a couple of pounds at a time with a 3 psi split.

jgunn wrote: Keep lowering the pressures and keeping the wear about 1/4" from the edge of the triangles.

So you don't want the scuffing to go all the way down to the triangles, James? My wear goes right to where you said-- about 1/4" above them right now...

TT

From what the Kumho engineer said at our tech session, heat management may be an issue with them in continuous lapping sessions

So what is this about??? Is the 710 not a good track tire? Just autocross?