I feel the need to address the issue of speed rated tires and people that think they are certified tire specialists by reading articles on Tire Rack.

Basically the reason vehicle manufacture's go with certain speed rated tires is that the vehicle's suspension is designed to work with a certain rated tire. A higher speed rated tire has a stiffer sidewall and softer tread. When some people decide to get a set of tires they ask for the cheapest tire and expect the vehicle to perform the same way - this is not the case. For example a common problem we see every day is someone with a newer Honda Accord with a V rated tire from the factory. The first thing they say is "I'm not going to be going that fast what do I need that tire for?". The reason you need that tire is your vehicle was designed to work with that kind of tire. When you deside to buy a new set of tires that are S or T rated for a Honda Accord and then wonder why the vehicle does not handle the same way it did and you experience irregular tire wear this is because you decided to be cheap and not put the proper speed rated tire on your vehcile. We have had so many people come back and want their money back because of their stupidity of not listening to someone who works with the tires all day that we now make customers sign disclaimers that read: "Customer requested lower speed rated tire than OEM rating and is aware of the potential for irregular treadwear and adverse handling effects - warranty is void." On the Cobalt SS the absolute lowest speed rated tire that should be on the vehicle is a W rated tire regardless of how fast you will actually be going. With that being said some people can get away with going maybe one rating down and not have problems, but I still don't recommend it and the warranty will still be immediatly void at least from us.

Another issue that should be brought up is hign speed driving and proper inflation. Now, the Cobalt SS calls for 32psi in all 4 tires. The factory Pirelli's are W rated which is 168 miles and hour. In a situation where a vehicle is traveling 160 miles and hour with 32 psi in the tires is asking for disater. You have to realize when traveling at extremely high speeds extra air needs to be added to the tire. For example, I have BF Goodrich G-Force Sports on my car that are W rated. If I was going between the range of 149-168mph then I would need to inflate an extra 7.5psi in each tire to be able to support this speed and the heat generated in the tire by going this fast. 32psi+7.5psi= 39psi. In this tire for example air pressure adjustments are not needed until the speed of 124mph in which an extra 1.5psi should be inflated in each tire.

Thats about all the rambling I can do for now I am just pissed when people print **** off of a website and think they know more than someone certified in the field. If you are so f'in smart then you obviosuly wouldn't have purchased tires off the internet which would be the same price in the store and you would get free road hazard, free rotation and balance, and free flat repair dummy.

 

When I was on Pirelli's site our tires are rated Z for the SS\SC not w as you just mentioned. Is that just a typo?

 

A W rated tire is also Z rated if that makes any sense. It's just a type of Z rated tire.

 

No, not really.

 

ZR and a 2 digit number load code followed by another letter. This code was developed in Europe where they started having a large number of vehicles travelling at high speeds for longer lengths of time.

ZR indicates the tire has been tested to a MAXIMUM speed in excess of (I think) 149 MPH.

The second letter indicates the maximum certified speed of the tire.
W = 169
Y = 186
Z = 186+

The stock tires are only the ZR base rating, W speed code. 215/45 R18XLTL 93W according to Pirelli. MAX safe speed is 169 MPH.

- Solo

 

Good post. stealth. I wouldn't go as far as calling all who cheap out on tires dumb- some are just ignorant, lol. Still a good post, though.

 

Hey i tried!

Solo picked up the slack for my lazy ass. Thanks.

 

Good post. The owners manuals states to increase the tire pressure to 35 PSI if driving over 100 MPH for an extended period of time.

So what are the effects of going to a higher rated tire than OEM? Just curious since you stated the illeffects of going lower.

 

is there any type of an issue when going with a higher speed rated tire?....

besides shorter life length and possible noise?

 

I am not aware of any but I baby my tires. No burn offs, no smoking them at an intersection. I know that the tread life is shorter than stock but the tire itself will tell you expected tread life. With the softer compound at normal speeds I actually find them a little quieter than stock.

- Solo

 

to their credit chevy does say to raise the pressure in your tires a bit when your are going to be doing extended high speed driving

 

Sorry guys I haven't checked this thread in a week. There are no bad effects of going higher than your OEM rating. Usually in most cases you will see more rapid treadwear than on a lower speed rated tire. When going up in the speed rating the tread gets softer and the sidewall gets stiffer.