Different diameter tires - PeachParts Mercedes-Benz Forum

Graham · #1 09-22-2013, 07:59 PM

I pulled the spare out of my 85 300D today. It is likely quite old and doesn't look like it has ever been used. It is a Bridgestone and size is P195/70HR14 M&S.

What struck me, is that it looked much larger than my Kumho P195/70R14s. These have some wear and have done 20k miles. I measured overall diameter and Kumhos are about 1/2in smaller in diameter.

I have noticed this on speedo - it reads high.

Is it common for tires from different manufacturers to have different outside diameters?

jusme · #2 09-22-2013, 08:16 PM

From what I've heard, China sourced tires are actually sized on the small end of the scale.

Graham · #3 09-22-2013, 08:25 PM

I just noticed there is a separate forum to discuss tires. I will move thread over there!

t walgamuth · #4 09-22-2013, 09:58 PM

Same nominal size tires often are different if measured. Be sure to run it on the front. If you run different sizes on the rear you can boil your diff lube and ruin your bearings.

vstech · #5 09-22-2013, 10:15 PM

fwiw... tires 1/2" smaller in diameter will show higher speed than actually traveling...

Skippy · #6 09-23-2013, 12:37 AM

Quote:

Originally Posted by t walgamuth

Same nominal size tires often are different if measured. Be sure to run it on the front. If you run different sizes on the rear you can boil your diff lube and ruin your bearings.

Back when I was a broke teenager buying used tires, I had two different sized tires on the back of my '72 Mercury, like a 205 on one side and a 215 on the other with the same aspect ratio on both. It did just fine (didn't pull or anything), but that car had a 9" rear end. YMMV.

charmalu · #7 09-23-2013, 01:26 AM

+hen I was working and driving trucks with Dual Tires, they would match up same brand of tire together with ea set of Duals. Even though they were the same size, there was a difference between manufactures in the height of the tire. this way the taller tire was not taking on more weight.

With cars with single tires on each side, it is advisable to run the same brand size together, and to have the same amount of tread.

Graham, if that tire is the original from 1985, it should be replaced with a new tire. the rubber ages with time and looses it elasticity, hardens and there is a safety hazard. New tires have a life of 7 years I believe, there is a date code on the side wall.

Charlie

t walgamuth · #8 09-23-2013, 07:14 AM

Quote:

Originally Posted by Skippy

Back when I was a broke teenager buying used tires, I had two different sized tires on the back of my '72 Mercury, like a 205 on one side and a 215 on the other with the same aspect ratio on both. It did just fine (didn't pull or anything), but that car had a 9" rear end. YMMV.

One of the few failures on a mb rear end that I ever heard of was about 20 years ago. A friend of mine had a nice white 240D and had two different size tires on the rear. He fried the diff bearings after taking a long trip that way at highway speeds. (I was told).

If all your driving were around town probably never a problem.

Of course the ford 9" is one of the most durable rear ends ever built too.

The mb diff is a very tough cookie too!

t walgamuth · #9 09-23-2013, 07:16 AM

Quote:

Originally Posted by charmalu

+hen I was working and driving trucks with Dual Tires, they would match up same brand of tire together with ea set of Duals. Even though they were the same size, there was a difference between manufactures in the height of the tire. this way the taller tire was not taking on more weight.

With cars with single tires on each side, it is advisable to run the same brand size together, and to have the same amount of tread.

Graham, if that tire is the original from 1985, it should be replaced with a new tire. the rubber ages with time and looses it elasticity, hardens and there is a safety hazard. New tires have a life of 7 years I believe, there is a date code on the side wall.

Charlie

Being a bridgestone it is unlikely an original tire. There is a number on the side of the tire which contains the build date.

Graham · #10 09-23-2013, 10:33 AM

Quote:

Originally Posted by t walgamuth

Being a bridgestone it is unlikely an original tire. There is a number on the side of the tire which contains the build date.

You are right, it is unlikely original, but it is old. I have had car since 1990 and it was there when I bought it. I didn't understand the numbers on teh tire, but did see an 88.

I realize that tires have life of about 7 years when exposed to sunlight, ozone etc. Usually wear out by then anyways. But spares don't see that environment and would only be used in an emergency to get some place close where the flat tire could be repaired. Mostly a flat can be temporarily repaired using a can of puncture seal or a small portable pump. So, having not needed that spare for 23 years, I am not too worried by it's age. It actually looks like a new tire

BTW: Car we just sold and new one we are getting have no spare tires! Just a kit with pump and sealant.

Graham · #11 09-23-2013, 10:38 AM

Quote:

Originally Posted by vstech

fwiw... tires 1/2" smaller in diameter will show higher speed than actually traveling...

Isn't that what I said? My speedo reads high.

You can check this here:

Palo Alto Speedometer: Speedometer Calculator

vstech · #12 09-23-2013, 11:01 AM

Quote:

Originally Posted by Graham

You are right, it is unlikely original, but it is old. I have had car since 1990 and it was there when I bought it. I didn't understand the numbers on teh tire, but did see an 88.

I realize that tires have life of about 7 years when exposed to sunlight, ozone etc. Usually wear out by then anyways. But spares don't see that environment and would only be used in an emergency to get some place close where the flat tire could be repaired. Mostly a flat can be temporarily repaired using a can of puncture seal or a small portable pump. So, having not needed that spare for 23 years, I am not too worried by it's age. It actually looks like a new tire

BTW: Car we just sold and new one we are getting have no spare tires! Just a kit with pump and sealant.

I can assure you, that if the tire is 23 years old, it's not just sunlight that rots out a tire... it's oxygen. put that tire on the road, and it'll leave you stranded in short order.
trust me. I've seen it over and over with all the cars I have. NEW appearing tires are NOT!

t walgamuth · #13 09-23-2013, 11:25 AM

I agree with vs. I have tried those old spares and they look great but when put into service the belts will shift and you will be needing a spare. I've had it happen more than once.

charmalu · #14 09-23-2013, 11:49 AM

I bought a Light Alloy 5 1/2" spare out of a 80 240D in PNP. It had the original spare tire from the factory, still had the little nubbys from the mold and the white stuff that was on the rubber. even had a ridge molded on the sidewall, haven`t seen that in a long time. But I was excited to find an original never used light Alloy wheel.

PNP sold me the wheel for about $7, but charged me for a new tire, $17. I could bring it back for store credit, but would still have to pay a shop to remove the tire. I could also bring the tire back with in 3 days for a replacement. The closest PNP is 25 miles from here, such a deal.

There was no way I was going to use that old tire no matter how good looking it was. I don`t remember now, what the brand was on the tire that MB used back then.

Here is how to read the tire code:

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=11

Charlie

charmalu · #15 09-23-2013, 11:53 AM

Quote:

Originally Posted by t walgamuth

Being a bridgestone it is unlikely an original tire. There is a number on the side of the tire which contains the build date.

I wasn`t thinking of the brand of tire when I wrote that post. would it have been a Continental? I know VW used them on new cars, a 69 I bought new had them as I remember.

Charlie