giddyup Posted March 5, 2016 Share Posted March 5, 2016 At present my Triton has 245/70/R16 tyres, obviously on 16" rims. Now if I want to increase my rim size to 18" what size tyres will I need so I don't affect speedo accuracy, handling etc. Obviously the tyre radius has to decrease by 2" to remain the same, so what low profile tyre size is it? I believe there is a formula that tells you, but maths was never my strong point. Link to comment Share on other sites More sharing options...
JoeW Posted March 5, 2016 Share Posted March 5, 2016 265/60/18 or 255/60/18 will fit without problems. Link to comment Share on other sites More sharing options...
giddyup Posted March 5, 2016 Author Share Posted March 5, 2016 265/60/18 or 255/60/18 will fit without problems. Thanks. Link to comment Share on other sites More sharing options...
cumgranosalum Posted March 5, 2016 Share Posted March 5, 2016 (edited) 16 inch is the diameter, not the radius This is a calculation that could involve π - but this is no problem as there are LOADS of web sites that do these sort of calculations Here is just an example.... http://www.willtheyfit.com If you increase the width or diameter of the whole wheel you need to check for body clearance. you might need to take into account the effect of "offsets" this site explains that pretty clearly.... http://www.wheel-size.com/calc/?wheel1=205-55-16X6.5ET45&wheel2=225-45-17X7.5ET40&fcl=50mm&wcl=30mm&scl=50mm Edited March 5, 2016 by cumgranosalum Link to comment Share on other sites More sharing options...
giddyup Posted March 5, 2016 Author Share Posted March 5, 2016 (edited) 16 inch is the diameter, not the radius This is a calculation that could involve π - but this is no problem as there are LOADS of web sites that do these sort of calculations Here is just an example.... http://www.willtheyfit.com If you increase the width or diameter of the whole wheel you need to check for body clearance. you might need to take into account the effect of "offsets" this site explains that pretty clearly.... http://www.wheel-size.com/calc/?wheel1=205-55-16X6.5ET45&wheel2=225-45-17X7.5ET40&fcl=50mm&wcl=30mm&scl=50mm Thanks, but I don't think an extra 2" is going to be a problem with clearance, especially on a pickup. You're correct, I meant diameter, not radius. Edited March 5, 2016 by giddyup Link to comment Share on other sites More sharing options...
cumgranosalum Posted March 5, 2016 Share Posted March 5, 2016 (edited) 16 inch is the diameter, not the radius This is a calculation that could involve π - but this is no problem as there are LOADS of web sites that do these sort of calculations Here is just an example.... http://www.willtheyfit.com If you increase the width or diameter of the whole wheel you need to check for body clearance. you might need to take into account the effect of "offsets" this site explains that pretty clearly.... http://www.wheel-size.com/calc/?wheel1=205-55-16X6.5ET45&wheel2=225-45-17X7.5ET40&fcl=50mm&wcl=30mm&scl=50mm Thanks, but I don't think an extra 2" is going to be a problem with clearance, especially on a pickup. You're correct, I meant diameter, not radius. I've seen Mitsus with fairly large wheel/tyre combos but if the wheels are a lot wider, the problem comes with front wheels and steering lock to lock. If the overall wheel/tyre diameter is increased, that too can cause problems. I've found that the average customer wheel/tyre salesperson's primary objective is to sell you something and they often don't know or care whether it's suitable for your vehicle - so I'd spend a bit of time researching those sites before you get involved with a vendor. However that's not to say that some companies actually have the experience and knowledge to do it right. I'd also recommend that you check out other vehicles - e.g. if you see a Triton in a car park with interesting rims/tyres, check out the tyre size etc.... If you do end up changing the overall diameter, some of these sites have a table that will convert your speedo readings to actual speed too...... ! got a variation of 11% on one of mine! Edited March 5, 2016 by cumgranosalum Link to comment Share on other sites More sharing options...
Kwasaki Posted March 5, 2016 Share Posted March 5, 2016 Go to any tyre manufactures Internet site and usually all measurements can be found. With most rides there is tyre clearance built in that can be used.. What about the psi. whoops !!! Link to comment Share on other sites More sharing options...
Don Mega Posted March 5, 2016 Share Posted March 5, 2016 What rim width are you looking at ? Link to comment Share on other sites More sharing options...
Singhajon Posted March 5, 2016 Share Posted March 5, 2016 If you stay with 245 width tyre on a 18 inch rim you would need to go for 245/50/18 this would keep the speedo correct. Link to comment Share on other sites More sharing options...
giddyup Posted March 5, 2016 Author Share Posted March 5, 2016 What rim width are you looking at ? Stay with 245. Link to comment Share on other sites More sharing options...
cumgranosalum Posted March 5, 2016 Share Posted March 5, 2016 What rim width are you looking at ? Stay with 245. That's actually the tire width.....but same anyway. The other factor could be "offset"...... a wider track reduces steering clearance. Link to comment Share on other sites More sharing options...
MartinL Posted March 5, 2016 Share Posted March 5, 2016 (edited) This is a handy little tool I've had sitting around for ages. http://www.club80-90syncro.co.uk/Syncro_website/TechnicalPages/TRC%20calculator.htm Enter your original tyre dims. then slot in dims. for your preferred tyre options and find one that gives zero (or as little as possible) speedo. deviation in the yellow panel. It's been pretty accurate for bike tyres and I suppose it'd be the same for cars. Edited March 5, 2016 by MartinL Link to comment Share on other sites More sharing options...
giddyup Posted March 5, 2016 Author Share Posted March 5, 2016 Thanks for all the good advice. Link to comment Share on other sites More sharing options...
Don Mega Posted March 5, 2016 Share Posted March 5, 2016 What rim width are you looking at ? Stay with 245. 245 is a tad over 9.5 inches.... you do not have a rim that wide currently and a doubt you will be changing to them either. Link to comment Share on other sites More sharing options...
cumgranosalum Posted March 5, 2016 Share Posted March 5, 2016 What rim width are you looking at ? Stay with 245. 245 is a tad over 9.5 inches.... you do not have a rim that wide currently and a doubt you will be changing to them either. I don't understand your comment - the OP states - "At present my Triton has 245/70/R16 tyres," - So the width is the same? (unless a lower profile requires a broader rim? Link to comment Share on other sites More sharing options...
JoeW Posted March 5, 2016 Share Posted March 5, 2016 For a Triton or PJS (old) changing to 265 does not affect the car much. You can still turn lock to lock no problems. My PJS has 255/50/20 which is overall similar in dimension as the original 265/65/17 that were on it. Anyway FYI: 265/60/18 will increase the total diameter with 3% 255/60/18 will increase the total diameter with around 2% If you want to keep the exact same ratio you need to stick with 245/60/18 tires The op will be changing the rims anyway so any experienced shop will set the offset correctly if asked. Link to comment Share on other sites More sharing options...
Don Mega Posted March 6, 2016 Share Posted March 6, 2016 What rim width are you looking at ? Stay with 245. 245 is a tad over 9.5 inches.... you do not have a rim that wide currently and a doubt you will be changing to them either. I don't understand your comment - the OP states - "At present my Triton has 245/70/R16 tyres," - So the width is the same? (unless a lower profile requires a broader rim? I asked rim width, not tyre. Link to comment Share on other sites More sharing options...
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