Spare tire?

[BuckHunter]

Don't mean to beat a dead horse here. If so I'm sorry I have a 2002 Ranger 4x4 I bought new. So today I decided to check the spare after 20 years. Its dry rotted bad got to checking and its a 235 75 15 . The tires on the truck are 245 75 16. But have already dropped of my spare at the shop for replacement. So my question is would this difference hurt my drive train say I had a flat on the interstate. And would the difference be better on rear or front since it is a 4x4. Thanks

 

[superj]

Tire Size Calculator

thats a good amount of difference but if you are just using it to get to the house or tire place, it wouldn't hurt. it probably actually wouldn't hurt for longer either unless you have some type of locker because i see people driving on those little weenie spares for months but no reason to test that out.

and you see those jeep guys with 35s on the ground a stock 215/75/15 on the back, ha ha ha

 

[Curious Hound]

With open diffs, no big deal.

 

[Ranger850]

FYI a 235-85 15 is about the same size diameter and width of a 245-75 16.

Not sure how common or rare a 235-85r15 tire is.

 

[don4331]

FYI a 235-85 15 is about the same size diameter and width of a 245-75 16.

Not sure how common or rare a 235-85r15 tire is.

I'm not sure a 235/85R15 even exists

10.5x31R15 is almost exactly same diameter as 245/75R16, so that is what I would order for spare.

10.5x31R15 is really identical to 265/70R16, so a little wider than 245/75R16.​

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Putting a 235/75R15 on one side with 245/75R16 on the other on a limited slip axle will destroy a clutch type differential within about 20 miles. After which you will have an open axle until you replace the clutches. You would also have a large amount of abrasive in the oil.

If you have a Torsen or other gear differential, they will accommodate the difference in size, with just a lot of motions = heat/wear - drive slow and replace as soon as possible

For an open axle, not much of an issue, other than the differential gears would be spinning at much higher rate than normal - heed the compact spare rule and drive slow 80km/h or less until replaced.

In 4x4, you will get severe binding between front and rear axle (like turning a sharp corner). It will work to get you along in poor tractions situation, but don't do it on pavement.

I recommend 10.5x31R15 spare or get a 16" rim and same tires as you're running.

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[Curious Hound]

The only differential gears turning in relation to each other in this case are the side gears and spider gears. If driving in a perfectly straight line with equal diameter tires, they don't turn against each other at all. When turning. Or with a slight difference in ture diameter, they begin to turn against each other very slowly.

The tire size issue would have no effect on ring and pinion gears.

I do agree that equal size tires are best and in 4x4 and/ or with lockers or limited slip, it becomes more important.

 

[Ranger850]

I'm not sure a 235/85R15 even exists

I was just playing around with the tire size calculator to see what would match outer diameter.

 

[superj]

i always do that on that web page

 

[BuckHunter]

Thanks guys for the replies. I have been investigating this today because I sure don't won't to mess anything up. I have a 8.8 open with 4 10 gears my axle code is 97. So I'm assuming I have a open differential. I would never use the 4x4 with the spare and get it off as soon as possible so I'm hoping I will be ok. It would be emergency situations only.

 

[Lefty]

I asked the same question at the tire store. They said no problem. My tire size is 255-70-r15, a lot wider and a little more in diameter. My spare is stock.

 

[19Walt93]

My 2004 came with 245/75r16's on the ground and a 235/75r 15 spare. My 2011 had 235/75ra5's on the ground and a 16" spare. Compared to the Focus customers who got a little compressor and a can of fix a flat instead of a spare tire, I guess we won.

 

[Lefty]

TBH I can't remember the last time I had a flat.

 

[BuckHunter]

Yeah I guess I need to be glad I even got a spare when I bought the truck.

 

[Lefty]

I got an extra if anyone wants one. Come on by. I live in Saint Paul.

 

[19Walt93]

TBH I can't remember the last time I had a flat.

Never say that out loud, it's just like saying "this job won't take long".