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Discussion Starter · #1 ·
My car(not mini) use to run on 195/60 R15 88H from the manufacturer. Now im on 205/40/17. i need to buy new rubber soon and considering getting 45 ratio for a smoother ride(to a degree)... Can someone explain to me how to read the ratios properly so that my overall diamter of wheel is close to that of the manufacturers? Also, couldyou tell me which one would be closer to stock tire's diameter, the 40 or 45s.

Thanks
Chosta
 

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Tire diameter calculations ...

205 * 40 / 100 * 2 / 25.4 + 17 = 23.46 [-3.1%]
195 * 60 / 100 * 2 / 25.4 + 15 = 24.21 <==== stock
205 * 45 / 100 * 2 / 25.4 + 17 = 24.26 [+0.2%]

Replacement tire size should be within ±3% of stock, so 40 series is marginal.

The 40 series will provide slightly better acceleration but 45 series will provide more speedo accuracy.

A good site to bookmark ...

http://www.miata.net/garage/tirecalc.html
 

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Discussion Starter · #3 ·
thanks maniac,

is it better to be under stock size or over? what are the advantages/disadvantages
 

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As stated in my previous post, being under the stock diameter size will provide [slightly] better acceleration.

In your case, I'd say you're better off with the 45 series tires, because the speedo readings will almost be identical to stock and the ride quality offered will be better than the 40 series. Also, the load index of some 40 series tires may not meet the manufacturers recommendation.
 
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