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Discussion Starter #1
Seeing Wayne's post made me want to ask....

I need new tires, and I have 15" wheels. What's the accepted metric tire size to reach the correct (tire + wheel) radius for the speedo?
 

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I would go the other way. Find tire that fits and looks good then change seedometer gear at transmission to correct.
 

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Discussion Starter #3
swamper said:
I would go the other way. Find tire that fits and looks good then change seedometer gear at transmission to correct.
Well, sure Swamper, but that's not what I'm after here.

I'm the type of owner that doesn't change things for the sake of changing them. If "stock" looks good and performs adequately, I'm happy to stay stock.
 

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Let's see if my understanding and some math can do this for you (others please correct me!):
Stock = F70x14 = 70 profile, 7.5 inch tread, 14 inch dia. -> 24.5 inch height (diameter).
Assuming 205 tread width on new tires (common, roughly 8.07 inch tread):
(24.5-15)/2 = 4.75 inch sidewall
4.75/8.07 = 58.85% -> 60 profile

-> 205/60/15

How did I do? (Biggest question that I have is stock tread/tire diameter)
 

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http://www.geocities.com/MotorCity/2398/tires/tirediam.htm

not sure where that link came from.. but it has the tire diameters for most size tires out there. should help make it easier to choose a size that will keep the speedo readings about the same. i run 215 70 14s on my car... had E78 14s originally... its a lil off but not too bad
 

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Discussion Starter #6
That's a good link!

I also just remembered Coker Tire, which are expensive repros of the originals. According to their site, the Cougs came standard with F70-14, which have an overall diameter of 26.2". Interestingly, this contradicts the Tire Diameter link above, which claims F70-14 have a diameter of 24.8".

If Coker is right, what do y'all think about running 215/70R15s vs 205/70R15?

[Sorry that I can't format the following... please try to follow along]

Original 14" 215/70R15s 205/70R15
Diameter 26.2" 26.8" 26.3"
Treadwdth 6.7" 6.2" 6.8"
Cross Sec 8.3" 8.7" 8.2"

Just looking at this, I'd lean to the 205's, eventhough I'm losing 1/2" of tire-height-above rim, treadwidth is very slightly larger than the originals.
 

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Discussion Starter #7
Wow!

P205/70R15's are on, and alignment was made.... toe-in was WAY way off. What a difference! I feel like I'm going to be staying on the road now.
 
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