I just went out to the truck to grab something and I could hear a tire leaking air.

I have to be at work for 7:00 AM so I dont have time to drive it to a shop.

So, I drop the spare and swap the tires. When I was throwing the original tire into the bed I noticed the spare is at least 2" shorter.


Is it okay to drive? I assumed the outside diameter would be the same.

The truck has 20" rims. I assumed that it came that way from the factory. Now I am wondering if it had 17" wheels and someone swapped them out but left the spare.

 

It's no worse then using a donut on a car.... Just like a donut i wouldn't use it for long distance or high speeds.

 

If the flat is on the rear and you have LSD, it won't be happy. The front won't be so bad. Perhaps you can get a used 17" tire with a larger diameter for the future.

 

I just need to get to work and to the tire shop. It's probably 15 to 20 miles of driving.

I assumed the rim would be smaller but I thought the tire diameter would be close.

 

Is LSD = Limited slip diff?
How can I tell if I have it?

What are the odds of causing long term damage?

It is the one day of the month I have to be in first thing in the morning.

 

Yes, LSD is Limited Slip Differential. There may be a sticker on the glove box door. If not, put one rear wheel on slippery and one on dry. Goose it (don't punch it). If it moves, it likely has LSD. If the "slippery" wheel just spins, it's a peg leg.

It's probably not a good idea to perform that experiment while the different-size tire is on there. Permanent damage? Probably not, but don't work it any harder than necessary.

 

Yeah, put the spare on the front and the current front time on the rear.

 

^^
I agree, use the spare tire on the from. if you have two different tire diameters on the rear and you have a lsd, it isn't going to play nice. the reason being is that the LSD will see two different rates of rotation (due to the different tire diameters) and try to apply the clutch packs and send more power to the slower (bigger) wheel. I would think that this could cause some unnecessary wear on the lsd clutch packs.

nateroach

 

A small drive of 20miles isn't gonna hurt anything, nor is 2,000miles. The LSD will be perfectly fine running a 30" diameter on one side and a 33" rim/tire on the other. That is what the LSD is designed to do, besides, the LSD won't lock unless there is negative pressure on the slipping axle therefore causing the spring to engage. The pressure is caused by spining motion(i.e.cetripetal force) which is NOT going to happen with 2 different diameter tires. it doesn't work like 4wd does where the diameter front-back needs to be the same. If one tire does slip and the carrier locks...it's meant to create slipping which is why there is no chirping going around turns...etc