Hey all-
I recently acquired a new project that needs new tires. The problem I've run into is that the tires I currently have are R78-15. I'm not at all familiar with this sizing. I'm familiar with the "255/75/16" style sizing, and don't know how to convert the old sizes to the new sizes. Can anyone help me with this?

Thanks!

 

Here's one but it don't go high enough for you. I got some on paper at home I can look up later.

http://www.tirerack.com/tires/tirete...sionchart.html

 

One site I found said it was basically a 37x12.5-15. Is it a pretty big tire? Sound about right?

If correct, the metric sizing would be ~ 315/85-15 (the exact conversions was 318/88-15).

http://www.4crawler.com/Diesel/Tires.shtml

 

It is a big tire. It's actually on a 66 Merc passenger car, but since FTE is my web home, I'm asking around here. Some other guys said (in another thread) that there's probably a letter that should be infront of the R, so when I get a chance I'm going to check it out.

Thanks!

 

Yes,there will be another letter in front.Most likely a H or L for that size car.

 

Well, SRD, I wish you were right. That would make a lot of sense. The car's not local, so I had my uncle (mechanic that's currently rebuilding the engine for me) double check the tire size.

All there is on the rear tires is R/78/15. On the front tires: 1 is P/205/75R15 the other is P215/75B15. So I've got three radials, 2 R/78/15, and 1 205/75/15, and a bias ply 215/75/15. Now I'm really lost!

Anybody know of a way to figure out the original tire size requirement for a given car? I believe that this would change depending on the rear gear, so it would have to be vehicle specific.

The reason for all this, btw, is that the vehicle needs new rubber, and I'd like to get something that is going to make the speedo correct (as speedos go).

Thanks all!

James

 

What does the door sticker says?

 

Check the Read First: FAQ thread at the top of the 73-9 forum for tire size info.

https://www.ford-trucks.com/forums/1...ease-read.html

 

As mentioned,check the door if possible also double check that letter,to the best of my knowledge the highest letter code was "N".Most likely the "original" size will be numeric i.e. 7.60/15,8.15/15,etc.

 

Thanks for all your help fellas (and any ladies I'm unaware of), but I'm afraid I'm going to have to put this on hold. I can't get to the rig in person right now. It'll be a couple weeks--I'm in the midst of a condensed class right now, and then the regular semester will start, but once I've got everything sorted, I'll be able to make the 5hr drive to get there and check it over.

I'll let you know what I find out then.