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T-Series MG TD metric tire size

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Bob_Engelhardt

Freshman Member
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I am SO frickin' frustrated!! I have been all over the web (it seems) trying to find an answer to a really simple, common knowledge, question: what is the metric size for TD tires? _Including_ aspect ratio!

Not finding it, I measured my old style tires (5.50 x 15 Mich. XZX inflated to 18 psi). The section width is 162 +- 3 mm. The outside diameter is 645 +- 6 mm. The inside diameter is 381mm (i.e., 15 * 25.4).

Aspect ratio is defined as height/width. And height is (OD - ID)/2. So:
Aspect ratio = ((645+-6 - 381)/2) / 162+-3
= 81 +- 3

Then the TD metric tire size is .... (wait for it):

165/80R15 !!

Of course I could be wrong and I would welcome corrections. Otherwise let this be a defining post for anyone else seeking his metric tire size.

Bob
 
David_DuBois said:
I am running 165/80R15. The previous tyres were 165R15 - see my PM
Cheers,
Click to expand...

About the "165R15" size: I thought the aspect ratio was an integral part of the metric size. What does it mean when it's not specified? (Many sites require the a-r for their search.)

And what's a "PM"?

Thanks,
Bob
 
Go to tirerack.com and hit the chat box...they will explain everything to you.

On the other hand, I don't know too many people who know more about TD's than Dave, and his PM is likely the best advice you can get.

Good luck,
Bruce
 
FOLLOW UP:

I found this Moss page that has metric sizes for a bunch of old British sports cars and explains sizes and original-metric conversion:
https://www.mossmotors.com/graphics/products/PDF/Tire%20Sizes.pdf

It claims that the TD had 5.90-15, while TD Operation Manual says 5.50-15. And my old tires were 5.50-15. But neither 5.50 nor 5.90 convert to 165 (140 & 150 resp). And my tires measured 160 - 165. So there was something strange about the old tire width number.

Buying New Tires
There is not much available. I was looking for economy tires and found Nexen and Nankang. Kumho's were not available. Many places did not have any 165/80R15's (e.g., TireRack). I bought Nexen's from TireBuyer: $59 with free shipping. They arrived in 2 days.

Bob
 
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