I was looking around the web when i came accross a tool/calculator that gives you a measurement in percentage to tell you what you should or shoulnt put on your car. Your tyre siezes from front to back have a difference in diameter and is measured in percentage and you shouldnt go above the recomended 2.5%.

Heres a couple of sizes and results that i was playing with.

225 35 18 rear 225 40 18 front = -3.45% rubbish result

265 35 18 rear 245 40 18 front = 1.56% rubbish but within the recomended perameter.

275 35 18 rear 245 40 18 front = 0.46% tonnes better and really low/good but then i got this next result,

265 35 18 rear 235 40 18 front = 0.31% This was best result i could get right accross the board. I was going for the 275 rersult but i belieave im only gaining 10mm on the rear tyres so i think im going to be getting 265 35 18 rear 235 40 18 front.

Out of curiosity, why do you opt for, or what are the reasons for running a lower/different profile tyre on the rear to that of the front?

Out of curiosity' date=' why do you opt for, or what are the reasons for running a lower/different profile tyre on the rear to that of the front?[/quote']

 

Staggered wheel widths, wider rear wheels mean wider rear tyres. If the rears are wider you need to run a lower profile to match the rolling radius. The 2.5% recommendation is so the speedo stays reasonably accurate.

Out of curiosity, why do you opt for, or what are the reasons for running a lower/different profile tyre on the rear to that of the front?

 

Tyre profile is a percentage of tyre width. So a narrower tyre needs a taller profile to keep the same overall diameter as a wider tyre.

 

You aim to keep the same overall diameter as stock to not affect vehicle gearing, and subsequent speedometer accuracy.

It's also worth noting that an average percentage of the front and rear is not necessarily accurate, you need to do them individually and get the front and rear as close as possible to each other whilst maintaining as close as possible to the design tolerances of the oem speedo.

Completley understand that, and with 4 wheel driven cars. I know a few Supra owners that run 18's on the front 19's on the back on the same profile tyre???.

I was looking around the web when i came accross a tool/calculator that gives you a measurement in percentage to tell you what you should or shoulnt put on your car. Your tyre siezes from front to back have a difference in diameter and is measured in percentage and you shouldnt go above the recomended 2.5%.Heres a couple of sizes and results that i was playing with.

225 35 18 rear 225 40 18 front = -3.45% rubbish result

265 35 18 rear 245 40 18 front = 1.56% rubbish but within the recomended perameter.

275 35 18 rear 245 40 18 front = 0.46% tonnes better and really low/good but then i got this next result,

265 35 18 rear 235 40 18 front = 0.31% This was best result i could get right accross the board. I was going for the 275 rersult but i belieave im only gaining 10mm on the rear tyres so i think im going to be getting 265 35 18 rear 235 40 18 front.

 

What i should have said was no more or less than 2.5% + or - 2.5%

I was looking around the web when i came accross a tool/calculator that gives you a measurement in percentage to tell you what you should or shoulnt put on your car. Your tyre siezes from front to back have a difference in diameter and is measured in percentage and you shouldnt go above the recomended 2.5%.

Heres a couple of sizes and results that i was playing with.

225 35 18 rear 225 40 18 front = -3.45% rubbish result

265 35 18 rear 245 40 18 front = 1.56% rubbish but within the recomended perameter.

275 35 18 rear 245 40 18 front = 0.46% tonnes better and really low/good but then i got this next result,

265 35 18 rear 235 40 18 front = 0.31% This was best result i could get right accross the board. I was going for the 275 rersult but i belieave im only gaining 10mm on the rear tyres so i think im going to be getting 265 35 18 rear 235 40 18 front.

 

That's the combi that many people on here run - I do myself - 265 rears are more than adequate width and it stops before tyre prices start getting silly!!

 

And Yowser explained the tyre profile/ration thing perfectly.... Nice one mate!!

 

Richard:thumbup1:

yeah ive got 265/35/18 at the rear and 225/40/18 up front.

yeah ive got 265/35/18 at the rear and 225/40/18 up front.

 

I never got round to putting your front size in ill find the site and come back with you percentage?

I never got round to putting your front size in ill find the site and come back with you percentage?

your size it says they are 0.94% about 6m dif, well within the perameter, but if you had put the same size at the front with say a profile of say 35 same as the rear you would been way outside the peramerters to plus 4.55%.

heres the tool i found. http://www.etyres.co.uk/tyre-size-calculator.htm