Badger90 Posted March 10, 2009 Share Posted March 10, 2009 hi all.. am i right in saying that 235/85/16 tyres are 31"? 265/75s are 32"? and 285/75s are 33? im not entierly sure thats right but hey. i measured up my tyres 235/85 and was 31" and my brother has 265/75 and they where 32" so i a asume that the any bigger you need 16/8 rims or 15" rims? sorry it a stupid question lol cheers sam Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted March 10, 2009 Share Posted March 10, 2009 http://www.tyresave.co.uk/tyresize.html Enjoy Quote Link to comment Share on other sites More sharing options...
cipx2 Posted March 10, 2009 Share Posted March 10, 2009 Here's another one with conversion to inches: http://www.dakota-truck.net/TIRECALC/tirecalc.html Quote Link to comment Share on other sites More sharing options...
Chicken Drumstick Posted March 10, 2009 Share Posted March 10, 2009 hi all..am i right in saying that 235/85/16 tyres are 31"? 265/75s are 32"? and 285/75s are 33? im not entierly sure thats right but hey. i measured up my tyres 235/85 and was 31" and my brother has 265/75 and they where 32" so i a asume that the any bigger you need 16/8 rims or 15" rims? sorry it a stupid question lol cheers sam Sadly its not that easy. You can work it out this way. For a 235/85r16: Rim = 16" Width = 235mm Profile = 85% of the width (235/100) x 85 = 199.75mm You have two side walls, top and bottom so double it. 199.75 x 2 = 399.5mm Convert to inches (1" = 25.4mm) 399.5 / 25.4 = 15.73" Add the rim diameter 16 + 15.73 = 31.73" total tyre diameter. Saldy manufactures don't always measure the tyres in exactly the same way, so their specs may not reflect fully the physical size of the tyre. Big lugs are also not always accounted for very well. Tread width is also different to tyre width. A 265/75R16 should be about 31.65" tall, so slightly shorter than a 238/85R16 but wider. If you want bigger tyres you may or may not need bigger rims depending on what you have. In the tyre world there are more BIG tyres in 15", mostly because you want a big sidewall and most American 4x4's use 15" rims as stock. Land Rover have usually used 16" rims, so while you have less choice it is still a well supported rim size. As for width, well it depends. You can usually get away with mounting large profile tyres on narrowed than spec rims. A 33.12.50R15 requires a rim which is 10" wide (15x10) however on such a large profile you will have no trouble running them on an 8" wide rim (15x8). Things to watch for with bigger tyres, they reduce steering lock and will rub on full lock so you need rims with a different offset. However this can cause them to stick out from the body work which is illegal in the UK. Bigger tyres will also up your overall gearing and may hamper performance and braking ability. They are also heavier and more likely to brake stuff. Quote Link to comment Share on other sites More sharing options...
clbarclay Posted March 10, 2009 Share Posted March 10, 2009 Whether a tyre is new or a retread will also affect the size. Retreads are typically over sized, in the case of some extreme off road tyres this can be an inch or more bigger diameter. Some manufacturers publish a size and spec chart which lists actual size. For example However the accuracy of some of these can questioned (possibly due to design tolerances). Interco seem to have a reputation for their tyres coming slightly smaller diameter than claimed. I wrekon my LTBs when new would be pretty close to the 33.6" claimed, but that would only when inflated to maxium pressure. Quote Link to comment Share on other sites More sharing options...
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