Different size tires??

Would P215 75R15 studs on the front of a 97 Safari AWD van and P270 70R15 studs on back cause the rear end to go out ? If so , how long would you have to drive it after mounting to be able to tell there was a problem? A friend had this happen and company who rebuilt the rear end said that it was because there were 2 different size tires on it.

2 different tires on opposite sides of the differential will cause that. I wouldn't think it was cause much of a problem front to rear though, except for screwing up your ABS.

On AWD all 4 tires MUST be the same size, even better to be the same brand tire on all 4 corners. Different size tires will cause damage to the transfer case as well as the differentials, and also cause erratic operation of the ABS.

On AWD all 4 tires MUST be the same size, even better to be the same brand tire on all 4 corners. Different size tires can cause damage to the transfer case as well as the differentials, and also cause erratic operation of the ABS.


Old Master

What is rhw bether size and tires for the astro 97?

The owners manual, and also a sticker in the door jamb will tell the correct tire size for the vehicle.

What's the maximum size you would put on a 97 AWD, no lift?

What's the maximum size you would put on a 97 AWD, no lift?

What ever size the sticker in the door recommends.

What ever size the sticker in the door recommends.

So, what would say to a 'dear friend' that insists "235/75 won't make a bit of difference?"

Any help would be appreciated.

The wheel speed/vehicle speed sensors generate a pulsing AC voltage signal that the ECM, EBCM, and TCCM all monitor. The signal is usually around 740 pulses per mile, or PPM. Each module uses the information for different reasons. Each front wheel has a sensor, and there is a single sensor in the tail housing of the transmission that monitors both rear wheels simultaneously. If tire circumference changes, larger or smaller, the PPM changes. If tire size is different side to side, it will affect the ABS and cause premature damage to the differential. If tire size is different front to rear, ABS will be affected and the transfer case will wear prematurely. SO, by using a tire size different from the factory recommendation, the speedometer will be incorrect, the odometer will be incorrect, the ABS will be adversely affected, the differentials and transfer case could be affected if the tires are not the same size, and the 4WD might not engage. Bottom line... if you think you know more about it than the engineers that designed it.... go for it! But don't bother calling GM, I don't think they're hiring right now ;)

he is right as far as diff tires sizes go. I run 225/70R15 studded in winter & same but unstudded in summer. AWD comp will have to be reset to compensate for tire size change, but anything much bigger than a 235 rubs the fender wells & frame anyways. It is QUITE important though on AWD that they be the same size on all corners. He is 100% correct. Have a good day:iceslolan

I always assume(d) he's right. I needed more info because the people who talk to me about the van don't know that they are wrong. One says, "235 won't make a difference". Another says, "I've got some 31X10.50's you can have." Once Old Master says it's a matter of the light-truck transfer case, the subject is closed. (I needed help getting to the closed part.)

Of course I know that they have to be the same all around. I currently have 225/70's on it, and it doesn't seem to mind too much, except when we get the sticky snow which bogs down the flare kit-making it hard to steer. the 235/75's would only make this worse. But I have to convince these 'helpers' of what is help, and what is not. (Yes, the same helper who kept asking "3/4 or 13/16?" in wrenches.... :( I had already told him 'it is a metric vehicle!')

I used to have a 2001 AWD Safari van. As many certified mechanics will state, all tires on 4WD / AWD system and/or 2 WD with "stability track" systems must have the exact same size of tire. "Stock" tire size numbers can be found on the vehicle's door sticker or within its manual. As a general rule, only install stock size tires. If I remember correctly, my previous van has a factory door sticker of: P215 75R15 as well...

If, for some unique reason, you must use non-stock tires, all 4 tires must be the same size as well. And, they must be under 3% "variance from stock" - without impacting the vehicle's ABS or stability track systems. With this in mind, one can replace P215 75R15 with P225 70R15 tires. If wondering, 225 is slightly wider and 70 is slightly shorter. But being slightly wider surface, it makes the tires slightly taller. When "size" comparison numbers are crunched, both rubbers are under 3% of one another (yet, 225s have slighly more contact surface - which I wanted on my previous AWD van - that also had a 1" lift).

To compare numbers, use: http://www.miata.net/garage/tirecalc.html

If wondering, P225/70/15 tires worked great on my previous 2001 AWD van. Although, they were within 2.1% variance of factory specs.

But general rule is... All 4 tires must be same size on 4WD/AWD vehicle. And, same size rubber on 2WD with "4 wheel stability control" as well... Larger then 3% and its new technology computers start to screw up...

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