V730 track tire wear

[uberchris]

I've been trying to figure out how to get the most out of the Kuhmo V730 tire. I like this tire because it's cheap, sorta fast, and supposedly long lived. I'm having trouble with the last point. I started running this tire last year, and after a few weekends began seeing cord on the outside edge:

So I added 1 more degree of camber, increased the spring rate, and ran another track day on a new set. I am concerned that even with the changes, I am headed towards the same fate. The front-right tire is noticeably rounded off at the outside edge. So I'm curious if anyone has been able to wear these tires evenly and get decent life out of them? If so, what is your setup?

My current setup is:

• Camber: -4.0 front, -3.0 rear
• Toe: 0.10 total front, 0.30 total rear
• Spring rates: 750 front, 850 rear
• Turner front bar: soft
• 265/35/18 tires on arc8 18x9.5 square
• MCS 2wnr dampers, GC plates/arms, 996 brakes, dtc60 pads
• Corner balanced, 3467 lbs total

A couple other details:

• I typically run at The Ridge at about a 1:56 pace.
• Yes, driving technique (or lack thereof) is certainly part of the problem. Is it the whole problem?
• Should I add even more camber? I could do so, at the cost of some caster.

Comparison of front tires after 1 day:

Front left:

Front right:

Bonus action shot:

[Obioban]

The recipe for better tire wear is the same for all tires:

Get something that measures tire temps (probe, IR).

Immediately after each session, measure the inside, outside, and middle.

If everything is the same, you're optimized setup wise (still might be over driving/over heating the tires and need to pull back to not melt them).
If the middle is hottest, decrease pressure.
If the middle is lowest, add pressure.
If the outside is hottest, add negative camber.
If the inside is hottest, add positive camber.

... and higher ride heights let you run less static camber (more camber gain under compression), which is generally good for tire wear. What's your ride height? the fact that you're already at -4° makes me suspect you're too low.

[Estoril]

-4.0 is a lot of neg camber - and that tire doesn't look like that number. Who is doing your alignments and are you sure the measurement is correct? Is that a CW or CCW track?

[uberchris]

The recipe for better tire wear is the same for all tires:

Get something that measures tire temps (probe, IR).

Immediately after each session, measure the inside, outside, and middle.

If everything is the same, you're optimized setup wise (still might be over driving/over heating the tires and need to pull back to not melt them).
If the middle is hottest, decrease pressure.
If the middle is lowest, add pressure.
If the outside is hottest, add negative camber.
If the inside is hottest, add positive camber.

Yeah that's the weird part. Using a probe-type pyrometer fresh off the track:

	Outside	Middle	Inside
Front Left	52	59	67
Front Right	69	70	70
Rear Right	61	71	72
Rear Left	56	65	71

Which should mean front-right is wearing evenly, but obviously that's not the case.

... and higher ride heights let you run less static camber (more camber gain under compression), which is generally good for tire wear. What's your ride height? the fact that you're already at -4° makes me suspect you're too low.

14.25 front, 13.75 rear; only 1/4 lowered from stock 😕

-4.0 is a lot of neg camber - and that tire doesn't look like that number. Who is doing your alignments and are you sure the measurement is correct? Is that a CW or CCW track?

I do my own alignments, which would be suspect, but I feel like camber is the one measurement that's pretty hard to mess up.

The Ridge is a CCW track and is pretty hard on front-right tires, but this still seems excessive.

[Estoril]

How did you end up cording it at one single contact patch?

[Pklauser]

You may be using the steering wheel to slow the car down instead of the brakes. I'm guilty of the same. Try more brake, and feed the wheel in slower.

[Chas3n]

I dont have the best data to compare with, as I had some wheel bearing/brake caliper seal failures that I think significantly aided in the heavy wear off the V730s.

That said, they did grip when warm in their window, but I have found they have a very narrow window of temperature, and degrade quickly when not there. -4 up front is definitely too high for these, also curious what your caster is? That could contribute to your driving styling being too quick to turn in. I think Ill go back to RS4's if I am honest, as these Kumho's just didn't feel right most of the time. Curious if anyone else that's run these notice they run a bit narrow/short on the sidewall, too?




I was at 26 psi cold and -3 camber. Arizona motorsports park was VERY old and abrasive. I attribute some of the accelerated wear to that.

[elbert]

A couple other details:

• Yes, driving technique (or lack thereof) is certainly part of the problem. Is it the whole problem?

Some questions:

Driving technique
- Are you trail braking? What does your instructor say? Do you have any data acquisition?
- As Pklauser said, try not to use understeer to slow a car down. It's a good skill to have in your bag of tricks, but it's not something you will want to do regularly
- Another possibility is you are trying to push through the understeer by overdriving (and cooking) the RF tire.


Car setup
- What were your original spring rates? Did changing springs help, make things worse, or about the same?
- Same questions with changing camber
- Did you adjust your dampers to compensate for your spring rate change?
- You need to be toe out with your front.
- Has your car ever had frame damage (is everything symmetrical)?
- You should also try to make one change at a time

Yeah that's the weird part. Using a probe-type pyrometer fresh off the track:

	Outside	Middle	Inside
Front Left	52	59	67
Front Right	69	70	70
Rear Right	61	71	72
Rear Left	56	65	71

Which should mean front-right is wearing evenly, but obviously that's not the case.

For the RF tire, my WAG is the camber is heating the inside portion, and your understeer/overdriving is heating the outer portion. You can see this by comparing the LF and RF heating pattern.

[BBRTuning]

I have found that the V730 (and other cheaper tires) don't wear as nicely as other higher end tires I have run, I suspect it's due to inferior carcass/construction. However, I haven't seen wear nearly this bad or asymmetric with this tire. My first guess is something mechanically is off with that corner, likely a bad wheel bearing, bent/worn suspension component, etc, where you're losing a lot of camber under load. I'd also suggest running a wider wheel, but the V730 does run a bit narrow so you can probably get away with it.

Also, regarding tire temps, this seems to confirm it, typically you want to aim for the inside to be slightly hotter especially on tracks with lots of straights - I've never run Ridge, it appears more dynamic, but still, with almost perfectly even tire temps on that corner this usually suggests you're loading the outside of the tire too much on cornering, as only the inside is heated during accel/braking as well as from radiant heat, especially if you're pulling into the hot pit and checking with a probe. If you're running CCW, your RR tire temp spread looks just about perfect.

I'd also suggest zero front toe or slight out, and possibly less rear toe-in, depending on driving style and preference. These cars are quite stable when set up properly.

[uberchris]

You may be using the steering wheel to slow the car down instead of the brakes. I'm guilty of the same. Try more brake, and feed the wheel in slower.

That's definitely true. I catch myself doing this at turn 6 often.

also curious what your caster is? That could contribute to your driving styling being too quick to turn in.

The caster is 6.9. I do have a habit of throwing the car into corners, which is a holdover from when I had the car setup for SCCA FS class and had lots of understeer. I need to work on that too.

I think Ill go back to RS4's if I am honest, as these Kumho's just didn't feel right most of the time.

I'm considering switching to these if I can't figure out the V730s. How much slower are they in your experience?

I was at 26 psi cold and -3 camber

What psi were you running hot? I landed at 35 hot, which seems much higher?

- Are you trail braking? What does your instructor say? Do you have any data acquisition?
- Another possibility is you are trying to push through the understeer by overdriving (and cooking) the RF tire.

I did grab an instructor for a couple laps, and they told me I need to be more patient with 15, so pretty much what you're saying.
I've got a garmin (https://youtu.be/6QJmwluw8fI?t=148), but obviously that's not really "data".

- You should also try to make one change at a time

Yeah I changed a bunch of stuff. And honestly I think all the car adjustments were improvements because the car felt great and I did get better laptimes.

I think the answer here is just drivermod. And if that doesn't happen before this set of tires is done I'll get RS4s since they can probably better deal with my nonsense.

[bigjae46]

Way too much toe. 0 toe in the front, .15 total toe in the rear...or maybe a little less.

The problem is as you add negative camber, you have to reduce the toe. You're concentrating more heat on a smaller section of the tire which overheats the tire and causes excessive wear.

My camber is -4.25 front and -3.25 rear and I run almost zero toe front and rear. 1mm toe in each side on a 17" wheel which is about 7' or 8' which is a little less than half of what the OEM specs are.

Some of the uneven wear between the left and right tire will be caused by the direction of the track. Swap tires left to right...two floor jacks makes life easier.

[Lavatoad]

I just went through a set of V730 on my cayman. Got 3 weekends out of them before the cords appeared. I was hoping for more; but given the price, I'm not too upset.

[L0okitzRaj]

Semi-thread jack; did you have these pre-heat-cycled?

I just saw that tire rack has that service

[PenguinScotty]

Based on just the difference in wear, i'll mirror what others said and say that there is something mechanically going on with that corner. Bushings bad, wheel bearing, anything that could cause a change in camber, and fairly significant at that. At -4 degrees and 35 psi hot, there should be no rolling over of the sidewalls.

A lot of us are running V730s in GLTC and they are extremely reliable and consistent, so i'm very surprised to hear people struggling with them longevity wise.
We ran 275s at 30-32psi hot (track dependent) on a 3440lbs car, square. Mild to no aero.


One thing that we found helps with sidewall stiffness, is a light stretch. What size wheel are you running? For reference, 275 on a 11" is what we ran. Regardless though, i maintain that there is a mechanical issue there causing this uneven wear.

[Lavatoad]

I was running 33 psi hot on a 3000lb car. All 4 tires showed similar wear. mine had been heat treated by tire rack.

One thing that may have contributed to my quick wear... I typically see ~8-10 psi increase over a 20 minute session. I allow 1 warm up laps, then start pushing. Its possible additional warm up time would improve tire life