I purchased my '81 240D a little over a month ago. Today I was looking at it and the driver side rear(DSR) tire looked different that the rest of the tires. The DSR is a 175/70R14 the rest of the tires are 195/70R14. I am completely ignorant as to what the tire numbers mean.

What is the difference in the tires?
What problems, if any, can this cause to the cars rear end?

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1981 240D, Auto Trans, 160k miles -- CRASHED!

The first number is the tread width. In the case of the one tire, the 175 is narrower than the 195.

The second number, 70, is the profile height. The height of the tire from the tread to the rim, is 70% of the tread width.

The third number, 14, is the wheel diameter for mounting.

It's not a good idea to run different sized tires on the same axle. The vehicle is sitting low on the side with the smaller tire.

Probably should switch the small tire to the spare and use a proper 195 in place of it.

You should not use 2 different size tires on the back. It can cause excess friction, heat and wear in the differential. Somewhere on this board there is a thread about a guy who had to replace his diff because of this.

Put a matched pair on the back and move the odd tires to the front, smaller on the passenger side. Or even better buy a tire or possibly a whole set and have matching tires all around.

i am the person who wrote of the problem. it was not my car but a friends. his diff went out because the previous owner had run different sizes and it caused the differential to work constantly as it does normally only in a turn. this heated up the grease and probably liquified it and in turn burned out the bearings... so get the same sizes on the rear asap.

it is a bad idea to run different sizes on the front too... for a different reason. first it will probably not run straight with out pulling, and second under hard braking it will want to turn the car.

same size left to right on the front and same size side to side on the rear. large front to rear differentials will cause alignment problems, ie if very large sizes are run on the rear it will cause the front to lack the proper caster. this will cause the car not to be as stable in a straight line. it wont drive like a mercedes... more like an ordinary car. it will want to wander and wont hold its course in wind as well. also in a turn it will not return to straight as quickly.

of course some cars such as 911 porsches are designed to run different sizes and that is a different story.

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NO, smaller tire on the driver side because roads are usually sloped to the passenger side for water runoff.

I run different sizes on the front because I have a lot of different tires to use up and I haven't noticed any problems. But I always run same size tires on the rear (rear wheel drive).

P E H

That screws up steering geometry for the whole car.
Litigation on this topic is fierce and constant in US courts.
Look up the Verdicts on the net, it will scare you.

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I went back to Sears and told them they sold me the wrong size tire. They said that the OEM was the 175/70R14 even though they wrote on the sheet that the tires on the car were 195/70R14. Anyhow they replaced the tire.

The one that they took off, though smaller, had less than 1000 miles on it. I asked If I could purchase it to use as my spare. I was told no, that they could not sell me the tire now that it was used, they had to destroy it.

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1981 240D, Auto Trans, 160k miles -- CRASHED!

Just shows you the way Sears does business. Not in the business of used tires.
My indy tire guy hooked me up with a "pre-owned" Goodyear Wrangler tire for the back of the Dodge B-250. $25.00 mounted and balanced. I don't spend any more money on this van than I absolutely have to and this was a heck of a deal!! It almost matches the existing tire on the opposite side.