Worm A much better forum Silver Donating Members 3,808 Member For: 16y 4m 9d Gender: Male Location: Victoria Posted 24/01/12 01:38 PM Share Posted 24/01/12 01:38 PM Has to be within 3% tolerance... So yes... This size is fine... Link to comment Share on other sites More sharing options...
astroinc New Member 23 Member For: 20y 8m 25d Posted 24/01/12 10:43 PM Author Share Posted 24/01/12 10:43 PM Thankyou for the help I might get my tuner to take a look at the tyre calibration as well. Link to comment Share on other sites More sharing options...
arronm Dropping a turd Gold Donating Members 9,520 Member For: 17y 1m 5d Gender: Male Location: Perth Posted 25/01/12 12:15 AM Share Posted 25/01/12 12:15 AM (edited) 235 /40/ 18 is 645 mm OD 235/45/17 (std size on XR6) is 644mm OD so no difference. The difference between 245/40/18 and 235/40/18 is only 1.2 % so a difference of 1.2kph at 100. Speedos read 3-5 higher at 100 than your actual speed so yours will just be more correct. JUST BUY THEM. Edited 25/01/12 12:18 AM by arronm Link to comment Share on other sites More sharing options...
arronm Dropping a turd Gold Donating Members 9,520 Member For: 17y 1m 5d Gender: Male Location: Perth Posted 25/01/12 12:17 AM Share Posted 25/01/12 12:17 AM 235's will make the diameter smaller and hence you will be doing prob 94km/h when your speedo shows 100...235's will make the diameter smaller and hence you will be doing prob 94km/h when your speedo shows 100...I think you calculator is broken again. Link to comment Share on other sites More sharing options...
wodsy78 Member 3 Member For: 17y 7m 22d Posted 30/03/12 12:13 AM Share Posted 30/03/12 12:13 AM ive been using 235/40r18 in dunlop 3000a for the last 3 years because of the price difference, have done about 70000kms without any problems the only issue is that the narrower tyre provides less grip, and the diameter is the same so it wont affect your speedo Link to comment Share on other sites More sharing options...
winstor Member 611 Member For: 15y 9m 3d Posted 30/03/12 02:59 AM Share Posted 30/03/12 02:59 AM (edited) The diameter is NOT the same.It is simple maths. 235/40 means the sidewall height is the tyre width times 40% or 235x0.4, which quite clearly is not equal to 245x0.4.The difference in rolling circumference is 24.12mm and when your speedo shows 100km/h you will be doing roughly 98km/h. Edited 30/03/12 03:00 AM by winstor Link to comment Share on other sites More sharing options...
clevo400 Member 33 Member For: 13y 10m 8d Gender: Male Location: Townsville Posted 08/02/17 03:45 PM Share Posted 08/02/17 03:45 PM 5 years later and I'm still confused over why Ford did not choose to stick with the 235/40/18 when it's diameter is effectively the same as a 235/45/17 thus no need to change the computer. I think it was a ploy to sell 245/40/18 tyres by Dunslop and make people pay extra $$$'s for a tyre size only Ford use. I suppose Ford and the girls think 1 cm extra makes a big difference lol. I think the VE did the same and uses 245/45/18 tyres. Anyway has anyone used the Achillies 123S street legal semi slicks before and will 265/35/18 fit on the FG Snowflake rims on a BA turbo sedan. Only ask cos they are dirt cheap for me. Cheers. Link to comment Share on other sites More sharing options...
Lennox Member 2,586 Member For: 11y 9m 5d Gender: Male Location: Perth Posted 09/02/17 12:10 AM Share Posted 09/02/17 12:10 AM I use them. Great for the price they are dirt cheap. Plenty of grip in the dry. Will wear fast and are very noisy probably because of the tread pattern Link to comment Share on other sites More sharing options...
vegie New Member 8 Member For: 5y 4m 5d Posted 23/08/19 01:31 AM Share Posted 23/08/19 01:31 AM Sorry to bump an old thread. I recently purchased a BAII XR6T Magnet ute with the 18 inch rims. The tyre placard says 245/40/18, the tyres fitted were 235/40/18. I didn't think too much of it, but I then acquired another set of rims and tyres, but the tyres were 245/40. When I stacked the 'old' rims on top of one another, the rim edges bumped against each other - meaning they were 'exposed' the most - the tyres sat 'inbound' of the rim edge if that makes sense. When I stacked the 'new' rims (with 245/40) on top of one another, the tyres rested on each other, so the rim edges were sort of 'protected' as the tyres sat out further than the rim. It probably doesn't seem like much, but I can envisage far more rim damage with minor 'kerb incursions' with the 235's than the 245's. Link to comment Share on other sites More sharing options...
arronm Dropping a turd Gold Donating Members 9,520 Member For: 17y 1m 5d Gender: Male Location: Perth Posted 23/08/19 02:43 AM Share Posted 23/08/19 02:43 AM The load rating on the 235 will likely not meet the vehicle requirements Link to comment Share on other sites More sharing options...
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