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Discussion Starter · #1 ·
Warning Hybrid here!
This is a little off topic, but...Does anybody know what the correct measuring rim width is for a Dunlop SP8000 245/50/15 tire?
I'm having a heck of a time trying to find the correct info. The Dunlop site info can't be correct. It states it to be 7" ??? my SP5000 205/50/15's called for 6.5" I have the 205's mounted on a 8" wide rim and it gives me the least amount of sidewall flex and optimum contact patch. I'm trying to calculate the correct width rim to use with the 245's. Right now on the 8" wide rims there is too much side wall flex. (It looks mean though, with that rubber bulging out over the rim, but I want the car to handle and not get squirrelly with all the sidewall flex.)

Thanks,
Paul
1972 Toyota Celica with an 87 GN drive train.
canada
 

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7-8.5"
 

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it depends on how wide the actual tread surface is. the tire that you're looking at is rated at 245mm wide. that's total width (+or-), not contact patch width.
on the chance that you don't know how to read a tirer numbers, it goes like this.... the first number is with width in MMs (that's small portions of a meter, not the tasty candies :) ), the second number is the aspect ratio. that one can get a little confusing. so in your case you're looking at a 245/50-15. on paper that tire is 245mm wide and the side wall is (50% of the 245mm width) 122.5mm tall.
now for the fun part, the 245 isn't going to be exact and that's also not going to tell you exactly how wide the tread it.
Just about the only way to know for sure is to put your hands on a tire and take a measuring tape to it :)
have you been to www.tirerack.com yet? they have a chart with more exact sizes in specific tires. i think they sell dunlop too.
if i had to guess i'd say around 8" wide would be about right for a set of 245's.


end of book

Earl
 

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Rule of thumb says the wheel width should not be less that 70% of the tread width. In this case, that is 6.75" so I guess a 7" is OK. However, I would not go with less than 8" as it defeats the purpose of having a tire with a wide tread width.

Makes you wonder about all the TRs running 275 DRs on the stock 7" wheel. Must be that "stock-appearing" thing, but that is another story. This hybrid will never understand the obsession with stock-appearing. If you have a TR that runs 11s, what TR owner is going to believe that you are stock? No point in trying to fool non-TRs, they do not have a clue what they looking at when you pop the hood. So, what is the point. I once got a big giggle out of seeing a local GN with a fake battery and cables to hide the fact that the battery was relocated to the trunk. This GN was running 9s with a SII. Boy, it sure had me fooled :rolleyes:

Oops. Sorry Paul, got carried away there.
 

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Scottie-GNZ:
Must be that "stock-appearing" thing, but that is another story. This hybrid will never understand the obsession with stock-appearing. If you have a TR that runs 11s, what TR owner is going to believe that you are stock? No point in trying to fool non-TRs, they do not have a clue what they looking at when you pop the hood.
I thought I was the only one that thought like that. Although I have 275's on "stock" 8" wheels :)

Earl
 

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Discussion Starter · #6 ·
Thanks for all the replies guys.
In doing some calculations, I needed to get the measuring rim width so I could calculate the true section width.
Section width in mm = size/25.4... but for each 1/2" over/under measuring rim width you must add/subtract 0.2
So I have a 245/50/15. 245/25.4 = 9.6456692
If I use 6.75" as the MRW and go up to a 9" rim I need to add 0.9" to the SW to get true SW.
So I'm now at 10.545669.
Calculating section height = SW x aspect ratio%
10.545669 x 50% = 5.2728345
Calculating tire dia. = SH x 2 + wheel dia.
5.2728345 x 2 + 15 = 25.545669"

Far cry from the 24.645669 I get when using the MRW...That is almost an inch in overall tire diameter difference.

Paul
 
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