Tire Question

[LS1 TA]

So the other day I purchased some new tires(Kuhmo excsta STP's). I did not have that much cash so I only got 2, which is where I believe the problem is. I placed the two tires on the back because I just got my new beltronics vector FX2 and I wanted to see what what my 1/4 mile times would be on good tires. The day after I got the tires I noticed the the back end was super squirley, scary squirley. Come to find out the tire guy put 55 psi in the tires. I let air out until I got it down to the factory specs on the car door and it did better. When I run the car at higher speeds now though it starts to feal squirley again. I was just wondering what causes this. I am assuming its besuase I only bought two, but I was just curious what the physics behind it is.

[ConElite]

At what Pressure are you running them? Does it Only feel like this when your at Highway speeds? What size are the new tires and the old ones.

[LS1 TA]

At what Pressure are you running them? Does it Only feel like this when your at Highway speeds? What size are the new tires and the old ones.

31 psi. And it only does it on smaller side roads, not the highway. 245/50/16 same as the old ones. Its like what ever is wrong is amplyfing any imperfection in the road I am on.

[ConElite]

31 psi. And it only does it on smaller side roads, not the highway. 245/50/16 same as the old ones. Its like what ever is wrong is amplyfing any imperfection in the road I am on.

Thats Rather Low no? I run Mine at 40 in the Front and 38 in back. They are rated for 44 psi Im sure. I doubt thats the problem though. I drop My PSI in the rear to about 20-25 when I go to the Track. Keep in mind I have 245's (baby tires). If your going to be testing your car, I would drop them about 25-30. You should be able to get a 2 second 60 foot.

[LS1 TA]

Thats Rather Low no? I run Mine at 40 in the Front and 38 in back. They are rated for 44 psi Im sure. I doubt thats the problem though. I drop My PSI in the rear to about 20-25 when I go to the Track. Keep in mind I have 245's (baby tires). If your going to be testing your car, I would drop them about 25-30. You should be able to get a 2 second 60 foot.

These tires are actually rated at 51psi which I thought was kind of high. the guy at the tire shop had them at 55psi and it was a scary ride. Whenever I switch lanes it felt like the back of the car was floating back and forth

[ConElite]

I'd Say run them at Around 38psi. By the way, What exact size are the tires and how much did you pay a pc.

[LS1 TA]

I'd Say run them at Around 38psi. By the way, What exact size are the tires and how much did you pay a pc.

245/50/16 and $120 each. good and sticky tires with good wet traction, just squirely for some reason now.

[raroZ28]

i had those tires, i think wolfman warned me about them being junk. sure enough they were. it was a terrible tire the entire life that i had them. mine acted funny and wore terrible.

I pulled them off after 15000 and put on Nitto's. Try taking them back.

[LS1 TA]

i had those tires, i think wolfman warned me about them being junk. sure enough they were. it was a terrible tire the entire life that i had them. mine acted funny and wore terrible.

I pulled them off after 15000 and put on Nitto's. Try taking them back.

Nice!!! thanks for the info.

[Injuneer]

No.... you so not want 40psi or 38psi in those tires for "normal" driving. The rating on the side of the tire is the pressure required to achieve the maximum load rating of the tire, which far exceeds the loading your 4th Gen puts on it. Ignore that label on the tire.

FOLLOW THE TIRE PRESSURE TAG ON THE CAR DOOR. If you got Z-rated tires, there is a secondary label showing the pressure required for running the tires at the speed level of the Z-rated tires (150+ MPH). Its OK to go +/- a couple psi on those ratings, but you don't need 38psi or 40psi for normal driving. As speeds increase, the temperature of the tire increases and the pressure in the tire increases. Over-inflate them cold, and they will just get worse as speed/temperature increases. Pretty soon you're riding only on the center of the tread and wearing it out prematurely.

Take the time to read the writeups on the Tire Rack page, and you will understand why you don't want the kind of numbers that are being recommended in the posts above.

http://www.tirerack.com/tires/tiretech/tiretech.jsp

Disadvantages of Overinflation

An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when encountering potholes or debris in the road, as well as experience irregular tread wear. Higher inflated tires cannot isolate road irregularities as well causing the vehicle to ride harsher and transmit more noise into its interior. However, higher inflation pressures reduce rolling resistance slightly and typically provide a slight improvement in steering response and cornering stability. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures.

[Shockwav86]

I have these tires on my bird on all four corners. They are a little wider at 275/40/17 but they have been great. When I got the car it had high end Pirelli's but they were pretty shot so it didnt really matter. I noticed a huge difference from the baloney skins to the kumhos of course. But I haven't had one problem with them and I even drove in some light snow up here @ school in connecticut. I have about 11k on these and still have plenty of tread left. I do drive pretty hard too. I inflated them to the door ratings but check them every now and then due to changing temp's. I did notice on thing that bothered me about the old Pirelli's that were on the front though. They only wore on the inside half of the tire, and you can't rotate them from side to side because they are unidirectional. I do have a 2" drop in the car which was already done when I bought the car. I don't know if they did and camber/caster adjustments but I had the car put on the rack to check the alignment and it was perfectly in spec. I also notice a pretty moderate vibration that starts around 85mph and gets worse. I can feel it in the steering wheel, the clutch, the gearshift and not as bad in the other pedals. Could this have any relation?

[LS1 TA]

To follow up and conclude this post, I took my car back to the place where I purchased the tires and they offered to make things right for my the next day. I took my car out on the highway and layed into it. I got the car up to about 125 and all was fine. I did this about three times and determined maybe it was not the tires, but just the road I was previously testing my car on. The road I was first testing my car on is not exactly a perfect road, but its paved, on private property, and no police and other traffic. The other tires I had on my car did not cause the rear end to "float" around like these do on this particular road, but then again this is not a prime road to run at these speeds. Assuming any track I am ever on will be state highway grade or better, I told the guys not to worry about replacing them, and thanks for the offer to replace them.