Plus sizing just rear tires?

If some is good, more is always better.

edward wrote in article ...

If you are talking about increasing the cross section while reducing the aspect ratio to retain the same OEM tire circumference, you SHOULD be okay.

But....if you plan to, let's say, replace a 215/70X15 with a 225/70X15 - which WILL change the tire circumference - then you just *might* be affecting various computerized functions such as ABS which sense wheel rotation differences front-to-rear in order to make logical decisions.

If the VSS says that the car is going "X" speed at the rear wheels, but the front wheel sensors disagree some sort of computer logic might attempt to "adjust" things - resulting in ???????

Bob Paulin - R.A.C.E. Chassis Analysis Services

I'd be comfortable with it if I liked the look and drove carefully. Any time you change the grippping surface on one corner or one axle, you will affect the braking and handling of the vehicle. If the difference in great enough that you can see it, the operating difference will be pronounced also. Considering ABS and just the proportioning valves on some vehicles, the braking might change noticeably. If you do make a change, test drive it in the parking lot making panic stops.

In most places it is against the law to run mis matched tires unless the vehicle calls for it.

Simply put, if you get into a fender bender and a cop notices you have the wrong tires on back, he will write you up as the 'at fault' driver no matter who hit who.

The rational is you maybe could have avoided the accident if your vehicle was properly equipped.

This can turn a bad 'accident' where someone gets killed into a vehicular homicide charge against you for driving an unsafe vehicle.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

edward wrote:

I thought this usually applied only to tires on the same axle - and then only in certain states. It's not the case in California, where periodic inspections aren't required. Many high-performance/exotic cars come with larger rear tires.

I haven't rotated my tires since I got a new set (about 20K miles). The fronts are ready to be replaced (I'm thinking of selling the car, a new owner could change the tire or tire/rim set). I brought the car in for a lifetime alignment, and there was a recommendation for new tires, including an estimate for some Bridgestones. The current tires are Dunlop SP Sport 9000s.

Again - the laws vary by state, and as far as I know, the most that can happen is the tires need to be matched only on the same axle. Some requirements I've seen only say that radial and bias ply tires shouldn't be mixed on the same axle.

Here's the tire part of the periodic inspection in Hawaii (I use Hawaii because I remember seeing biannual inspection stickers on my rental car):

"b. No certificate of inspection shall be issued if any of the following occurs:

1. Tires of different sizes or types are mix mounted on the same axle, disregarding brand name or tread design;"

I believe "types" refers to radial/bias ply, while only the size has to be the same on the same axle. Granted - I wouldn't recommend different tires of the same size on the same axle, because traction differences could cause strange things to happen.

This would give you more grip in the rear due to the larger footprint. Maybe a good thing in something like a corvette that oversteers. If your car understeers (like most of them do now) then you'll be making it worse.

If it's RWD you will throw your speedo off. If it's a newer car with ABS you may cause that system to malfunction. What are you trying to change? Handling? Gas mileage? Maybe you can get the same net result by changing tire pressure rather than tires.