Kuhmo 730s vs Supercar 3Rs

[SVO MkII]

I purchased a set of Kuhmo 730s to replace Supercar 3Rs on my track wheels. Nothing changed with my setup, other than the tires. I run a 305 square setup, and rotate after each event. I assumed that I would be giving up a little bit of grip, going from the 100 treadwear 3Rs to the 200 treadwear 730s, and that was certainly the case. But, I also expected better longevity from the tires. However, after half as many track days, one of the 730s (the one on the front left at the last event, i.e., most loaded) is showing threads on the inside shoulder. I find this to be very strange (and disappointing, to be honest). With approx. -2.5 deg camber up front, the 3Rs wore out much faster on the outside edge. This was not surprising, considering that most guys with dedicated track S550s seem to run -3.5 deg up-front (since this is a daily driver, I didn't want to go more than -2.5). I try to run the pressures in the mid 30s, hot (higher and there is no grip at all).

I'm curious if there is anyone else out there who has used both of these tires for HPDE, and what their experiences and/or observations are?

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[WItoTX]

Camber isn't usually the culprit as much as toe. When was the last alignment done? Did you clip a pothole somewhere possibly that might have knocked it out of alignment? Getting aggressive with the curbs? When was the tire last balanced? It's odd that just one spot is showing threads. And someone will come along shortly who can explain it better than me.

That tire looks cooked even without the threads though.

 

[SVO MkII]

Camber isn't usually the culprit as much as toe. When was the last alignment done? Did you clip a pothole somewhere possibly that might have knocked it out of alignment? Getting aggressive with the curbs? When was the tire last balanced? It's odd that just one spot is showing threads. And someone will come along shortly who can explain it better than me.

That tire looks cooked even without the threads though.

Threads are showing at several spots on the inside shoulder, that is just the largest spot. Might be toe, although I assume that would also cause similar wear on my street tires, which I am not seeing.

 

[VictorH]

That's a bummer, especially since tires are so expensive. When folks see wear like that the standard response, for some reason is, toe, toe, toe. Yes, too much toe out will cause that wear, however, for track use, if you've had a decent alignment, it's NOT the toe wearing out the inside shoulder. I run zero toe, all the time, track or street and my track tires always wear out the inside shoulder first. Now in an ideal world, I'd be measuring tire tread temps (below the tread surface with a probe) not surface temp with an IR gun, but my guess based on tire pressures and wear patterns is that my alignment is pretty good (I'm running -3.2 in front for track).
I'm willing to bet (maybe 5 cents) the inside shoulder wear is from braking! Just think you've got a ton+ of weight up front and if you're generating 1.3-1.5g of braking force (if you can trust the g-meter in the car) you are putting huge load on the front tire and with that much camber most of the load is in the insides of both front tires.

 

[SVO MkII]

That's a bummer, especially since tires are so expensive. When folks see wear like that the standard response, for some reason is, toe, toe, toe. Yes, too much toe out will cause that wear, however, for track use, if you've had a decent alignment, it's NOT the toe wearing out the inside shoulder. I run zero toe, all the time, track or street and my track tires always wear out the inside shoulder first. Now in an ideal world, I'd be measuring tire tread temps (below the tread surface with a probe) not surface temp with an IR gun, but my guess based on tire pressures and wear patterns is that my alignment is pretty good (I'm running -3.2 in front for track).
I'm willing to bet (maybe 5 cents) the inside shoulder wear is from braking! Just think you've got a ton+ of weight up front and if you're generating 1.3-1.5g of braking force (if you can trust the g-meter in the car) you are putting huge load on the front tire and with that much camber most of the load is in the insides of both front tires.

Could be braking. But I'm still confused why the softer Supercar 3Rs held up much better than the harder 730s. That is the real mystery to me.

 

[tosha]

maybe kumhos are too soft on the inside and it's specific to their construction versus 3R's being better designed and not prone to this.. that's just a guess. my friend had exact same issue on his Cup 2's, though completely different car.

 

[Egparson202]

Could be braking. But I'm still confused why the softer Supercar 3Rs held up much better than the harder 730s. That is the real mystery to me.

Dunno. Check the alignment. If it’s unchanged, buy more Goodyears. Maybe the 730’s just aren’t your jam.

 

[WItoTX]

Could be braking. But I'm still confused why the softer Supercar 3Rs held up much better than the harder 730s. That is the real mystery to me.

What does the other front tire look like?

 

[Egparson202]

What does the other front tire look like?

Smart question

 

[Dana Pants]

Alignment settings and air pressures are tire specific unfortunately.

The 730 is considered attractive for camber limited cars. So this outcome isn’t totally surprising.

If those tire require more slip-angle, it could also put things over the edge to killing insides of tires.

 

[SVO MkII]

What does the other front tire look like?

No threads yet, but I can't really tell how much rubber is left on the inside edges of the other three. Again, it's a square setup, so I rotate them after each event. The tire showing threads was the most heavily loaded at the last event. I suspect whatever tire I would put in the front left next time would start showing threads.

 

[SteveW]

Is Camber Thrust coming into play here along with variations in how different tires respond to that?

https://en.wikipedia.org/wiki/Camber_thrust

@SVO MkII On the street does the car tramline significantly with either of those track tires?

 

[mavisky]

The 730 is more suited to autocross in my opinion than track days. That's what I bought mine for and they seem to be working great so far. These cars have a lot of caster so any excessive toe out really gets exaggerated on the inside corner it seems leading to excessive tire wear on the extreme inner edge.

 

[NightmareMoon]

Tire pressures too low?

Whats the last time the alignment was checked?

Hubs, bushings all in good shape?

 

[tosha]

Tire pressures too low?

Whats the last time the alignment was checked?

Hubs, bushings all in good shape?

This may be counterintuitive, but can this actually be a result of too much pressure? I was thinking about it over weekend while rotating my tires. If you have track level camber (over -2.5 deg) and too much pressure, the tire could actually "ride" more on the inner side. With 0 camber, you would wear the middle part, but as you add more negative camber, that kinda shifts to inner side. Just my theory and thoughts so far, maybe I'm imagining things, but I got similar wear pattern after driving for 6 hours on a highway with overinflated wheels.

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