Old + new tire on front wheel drive... a no-no?

[zanzabar]

So, VW Jetta front wheel drive - just rotated tires. Passenger front is brand new replacement from a blow-out. Other three including drivers front are older (same size) and worn approx 75%. The difference in diameter is noticeable in that the car tracks slightly differently (more left biased than previously was to the right - by design, alignment is fresh) and when accellerating hard there is a noticeable pull to the left.

Owner is not interested in replacing tires, so should I leave it as is? Or should I have them mount the spare (full size and unused) on the front drivers side to match the diameter of the new tire?

 

[Loobed]

Both front tires should be the same size and type and have the same wear. This is with any vehicle. The front steers the car. The rear is not so important.

 

[Quattro Pete]

I would use the spare, but would mount it and the one new tire on the back. For an average driver, it's safer to have the better tires on the rear.

But really, sounds like 4 new tires is what this car needs.

 

[eljefino]

+2 the spare is a great idea.

Surprised it pulls, would be interested if another tire of the same make model lot number would make it stop or if it's a radial pull etc.

 

[Rand]

I would buy a second new tire and keep the 75% worn one for a spare incase you blow another one.

run the 2 new ones on the same axle.

 

[Rand]

I would buy a second new tire and keep the 75% worn one for a spare incase you blow another one.

run the 2 new ones on the same axle.

since they have 75% tread i think you would be ok with the 2 new ones on the front... and they will wear faster so they should all be even in tread in 10-15000 miles.

 

[The Critic]

It's funny that you posted this.

I just serviced a TSX last night that has a near-new YK580 on the left-front and a 50% worn YK520 on the RF.

The car pulls to the left...though I suspect the alignment is questionable as well.

 

[zanzabar]

Critic: that must be alignment - seems to me the larger diameter tire on the left would push the car to the right, makes no sense that it would pull left.

Rand: I should have made it clearer, but the three worn tires are down to about 25% of tread depth, not 75%. So they only have a short lifespan really, maybe another year and 15k miles. But we're in Cali where there's not much need for good tread year round (no snow, not much rain). I'm just looking for a temporary solution and I think I'll go with mounting the spare up front with the new tire.

Thanks for the knowledge all!

 

[default]

More wear on the differential. Ideally you would have the new one shaved to match, as you would on an AWD car.

 

[yonyon]

Originally Posted By: zanzabar
Critic: that must be alignment - seems to me the larger diameter tire on the left would push the car to the right, makes no sense that it would pull left.


It doesn't necessarily work that way. A FWD car with an open differential is potentially subject to torque pull. The smaller diameter tire will provide greater mechanical advantage and tend to turn faster than the other larger diameter tire. All else being equal (and when is all else ever equal) it should want to turn toward the larger tire except when decelerating without use of the brake.