I have always been very curious about anything to do with tires. I am curious to a point that I have my own computer balancer and study about tires wherever I can find information.

This does not mean that I know everything there is to know about performance tires. Mostly I am interested in things that effect smoothness. lack of vibration and longevity.

I have never had any ultra low profile tires beyond 50's. I just put a set of Kumho Ecsta ASX 205/40 17's on a set of SLites to replace the Conty 175 65 15's on my MC.

I had been very impressed with the originals. They were pretty amazing for a skinny, high profile tire. They were very predictable, stuck like glue(once I got enough rear sway bar) and just impressive. That being the case I expected going to a 17 ultra low profile would REALLY give some handling improvement.

This particular tire has a higher load rating than others of this size, so it is only 25 pounds shy of the original tire load rating.

The tires balanced with minimal weight added and run extremely smooth at whatever speed I want. Amazingly they seem to ride every bit as softly as the 175's. More amazingly, they have more tread squirm than the 175's. There is so much tire squirm that the car actually seems to have understeer again. I had dialed out the understeer with an H Sport 19MM sway bar on the center setting.

Remember, I'm not an experienced ultra low profile tire user, but how can it be that these tires that look almost like band of rubber stretched around a wheel can have more squirm than a tire with probably twice as much vertical section?

I had read reviews of this tire indicating squirm, but I thought, "how could they squirm more than the 65 series tires?"

I am going to stiffen up the rear sway bar one notch and see how it feels. If I can't put that great neutral feeling that it had with the 175's, they will go back on there.

Life is a learning experience and not everything works out in practice like you thought that it would in theory. I am not totally disappointed because I have opened up a whole new element in my interest of tires.

 

 

I have a question about tires ... does more air pressure increase grip? it seems since i replaced the runflats with conventional tires, the ride is better but the cornering grip is gone a little.

does this have to do with the air pressure in the tires? as they are now a few psi less than the runflats.

 

Air pressure can increase grip if your tires are underinflated for the use you have in mind for them. Everything is relative. For autocross we use pressures that are much higher than normal street driving to get a desired effect.

If you are running the normal air pressure as recommended by MINI then you should get adequate grip to a point which is limited by your suspension setup, your tires, the surface you drive on, your driving style and the speed with which you are going.

Your runflats do have a stiffer ride with a moderate amount of grip. While not the "best" like an R compound tire for track use it is still not too bad. Your non runflat tire is a Toyo Proxes 4 which is a good street tire but not a true performance tire like the Goodyear Eagle F1 DS-G3 or Bridgestone Potenza Pole Position S-03.

Everything is a compromise, the Toyo Proxes 4 will wear longer than those performance tires and cost alot less. I would not be surprised if the Proxes 4 didn't perform quite as nicely for you as the runflats did but there are so many factors you have to really take both to the track to tell what is going on.

Whether your tires are runflats or not should not change the air pressure for your MINI.
If you were using 32-37 psi for your tire pressure on an MCS then you should keep it there.

 

Raising airpressure in this case changes the sidewall's ability roll over, hence the ultra high autocross pressures. Higher pressure less roll.

Now in water - higher pressures actually inprove your tire's hydroplaning resisance. In this case airpressure would controll grip, but its due to the tire's contact patch shape being better at pushing water aside.

Over inflated = a rounded tread shape, with less width and more length.

Alex

 

2 factors at play here.

Heat cycle -
Your Conti's have been used for a bit, each time you drive, and allow the tires to cool, its called heat cycleing. Heat cycle makes a tire's rubber feel firmer, as it breaks the weakist bonds, allowing them to recool and become stronger.

This makes tires handle very well, but there is a point when the tire has cycled SO many times it begins to become so firm it will no longer adhere to the pavement as well.

Your conti's are well heat cycled, your Kumho's in comparison are brand new.

Tread block flex -

The conti's have worn for a bit and their trad blocks individually are much shorter than when they were new. Your Kumho's still have tall tread blocks - so they naturally flex more.

Think of a pencil eraser - very easy to bend a flex when its new and tall. Ever tried to get the flex on an eracer in its last 1/2 of its life? - very little bend or flex.

Luckily tires wear the quickest they ever will in the 1st 10k. You decrease more measurable tread depth vs mileage at the highest wear rate the tire will EVER have.

The moral - Rotate often especially when new. Sit tight they will feel better soon!

Alex

 

Thanks Alex ... it seems then that increased air pressure is a good thing for all around street use as well ... or am I reading something wrong?

 

It can cause premature wear in the center section of the tire. On big trucks they call it "crowing" or "fawning". Watch your tire wear.

Alex

 

Alex,

Thanks for the great and detailed explanation. Since I like everything else about this tire/wheel combination, except for its increased weight compared to the skinny tires and light wheels I took off, I'll give them a little more time before I do anything drastic like taking them off.

BTW, the tires I took off only had about 1,700 miles on them.

Thanks again.

 

I've now had three more 40 mile runs through the twisting roads to town and back. I'm either getting used to the squirm or it is not as bad due to the heat cycling effect. Maybe it's a little of both.

Anyway I don't notice it, so driving the daylights out of the little toy car is enjoyable again.

 

I agree!

lets chat @ 750 miles

Alex