When do tire size differences cause problems?

[harringtondav]

I've been lucky and wear out tires four at a time. My two kids, not so lucky. Each have lost one tire from a set of half worn tires and replaced with a new tire.

My worry is rotating the newer tire to the drive axle and overworking the differential bevel pinions/shafts from two different size tires. Is this a problem?

 

[JoLin]

As long as the ruined tire is being replaced with one of the same brand, size and model... I don't see a concern. Tell 'em to stop running over pointy things :joyous:

 

[MTboatguy]

I've been lucky and wear out tires four at a time. My two kids, not so lucky. Each have lost one tire from a set of half worn tires and replaced with a new tire.

My worry is rotating the newer tire to the drive axle and overworking the differential bevel pinions/shafts from two different size tires. Is this a problem?

What kind of cars and what type of drivetrain do they have in them? I know in my wife's Subaru, the AWD system is not tolerant of different sized tires much because of the way the coupler in the system senses slippage.

 

[Scott Danforth]

AWD cars require the tires on all 4 corners to be the same with minimal difference.
4x4 vehicles with limited slip differentials or quaife differenteials require the 4 corners to be the same with minimal difference.

typical FWD and RWD cars without limited slip or quaife differentials do not care one way or another if any tire is different

two wheel drive cars with limited slip or quaife differentials do not care if the font is different than the back, however do need the right/left to be the same

 

[harringtondav]

What kind of cars and what type of drivetrain do they have in them? I know in my wife's Subaru, the AWD system is not tolerant of different sized tires much because of the way the coupler in the system senses slippage.

One is a Neon frt wheel drive 5 speed stick. Other is a Sebring frt wheel drive auto.

 

[Scott Danforth]

Both one-wheel wonders. no problem

 

[harringtondav]

Both one-wheel wonders. no problem

Yes Scott. But my concern is the side gear/pinion mesh is working 100% of the time vs. just in turns and curves. Not sure if it was designed to take that kind of use. Most auto diff. pinions and some side gears are compacted sintered powdered metal. Not cut gears but more like Cogswell cogs.

 

[Scott Danforth]

the difference between a new tire and a used tire or between two tires the same size and wear, however one 10 psi different from the other is what the differential is for

your over-thinking it in this case, especially with the sloppy diffs in the MOPAR front drivers.

I can tell you from personal experience for 100,000 miles I beat the manual trans on the PT cruiser (same as the Neon) and that included the occasional new tire to replace a damaged one. when I took the trans apart (part of the shift detent mechanism dropped and got pushed thru the case by the ring-gear), the diff was fine, I actually drove the car 20 miles without oil in the trans.

the diff is the low-point and fully oil-bathed. no problem with one new tire and one bad. however if it bothers you, put them on the back.