Tire Help..

[PathfinderGuy]

Hey guys.. got a question a friend is wanting me to ask/answer..

He has a pathfinder like i do, with stock rims. Size of tires/rims are 265 70 R15. He is looking to put some new tires, but he doesnt have the money to put new rims. I know that changing the stock tire/size without knowing what you are doing can cause the speedometer to incorrectly read out ur speed (atleast according to www.tirerack.com)

He wants to know what size tire he can put on there without having any negative effects on the vehicle.

any adivce?

[Guess My Name]

I will give the easy answer: the same size LOL

But seriously:

What he needs to do is get the outside diameter or circumferance of the original tires and put tires on with the same to ensure the speedo works correctly.

[PathfinderGuy]

???

which of the numbers from:

265 70 R 15 is the circumference?

[Guess My Name]

None:
265 is the tread width in milimeters.
70 is the aspect ratio of the sidewall as compared to the tread width.
15 is rim diameter in inches.

I guesstimate the OD to be 29.61 inches.

I think tire rack lists OD's for tires.

What he will need is for a wider tire with lower aspect ratio...problem may be in tire clearances with the fender wells and stuff.

For a 60 ratio tire the tread width would need to be about 310 if they make such a tire.....

Check with a tire guy and see what he says.

[Meguiar]

http://www.discounttire.com/dtc/home.jsp

this site is very helpful. It will give you a variety of tires sizes that fit your car without any negative results.

Good luck.

[Ken E.]

Check out this site. http://www.miata.net/garage/tirecalc.html Very helpful to determine correct tire/wheel size and the effect it will have on the speedo. A small 1-2% change is nothing to worry about. Sometimes it is difficult to have 0% change when plus sizing.

[TBird]

Some SUV's have a computer module that can be adjusted to account for different sized tires so things like the speedo, odo and antilocks don't get screwed up by a different sized tire. Check that out with a tech and he may be able to get anything he wants.

[laynlow]

Not only will changing tire size throw the speedometer out of calibration, it will also cause problems with the anti-lock breaking system.

Changing tire size changes the rpm of the wheel in proportion to the speed of the vehicle. That's why the speedo gets knocked out of wack. The anti-lock system has the same problem because the wheel speed sensors will read an improper wheel speed with an non-factory tire size. The result is reduced braking performance! :scared

Imagine you are making an emergency stop on dry pavement to avoid a rear-ender. Your wheel speed sensors incorrectly determine a wheel is close to lock-up, so they reduce braking pressure to that wheel.....bang!

[Huy]

Laynlow, I disagree.

Yes, changing tire size will throw your speedo off calibration if you poorly select the tire size. There is "PLUS" concept out there if you guys haven't heard. That's when you increase your rim diamater by one inch, or "plus 1". You obviously need bigger tires right? Yes, well, you select tires that will presever the overall same size as the original size. In effect, you are preserving the original size but increasing the innner diameter (and therefore reducing the aspect ratio). This gives you that cool 'low profile' look on race cars. Choosing the right size when going +1 or +2 will only throw off your speedo slightly. There are various tire calculators out there that will show how much your speedo accuracy has changed. Staying within 1-3 percent is fine. And so, in keeping with this constant overall diameter, your ABS system will still work fine.

Huy

[laynlow]

If you read the original post, you will see that it states that rim's are not being changed. Thus, if he changes tire size, he IS changing the OD of the wheel/rim assembly. There is always a workaround in the aftermarket world, but most guys just say "gimmie the biggest tire that will fit" and are done with it. These people should be warned.

I have a friend who put oversized tires on an otherwise stock explorer. The tires were large enough that they rubbed the body if the wheel was cranked too far. Dangerous IMO.

[Huy]

Laynlow, my bad...I didn't know he was sticking with stockers...