Mac Posted January 13, 2013 Report Share Posted January 13, 2013 The stock tyre sizes on my M3 are 245x35 fronts and 255x35 rears, however I run 255x35 fronts and 265x35 rears. Mainly because it opens up the options on tyres and because the reviews I've read say these build tyres offer a more sure-footing and a better ride. I'm not convinced on this bit, but hey ho. What do I do with tyre pressures? On the stock tyres pressure is 2.3 fronts, 2.4 rears. Should I just stick with that or should I be running a different set up? Excerpt from the US manual: 245/35ZR19 for the rears is a well-known typo in the 2008 manual, should be 255x35. Anyways, they list 2.3/2.4 for up to 100Mph/160Kph which to be fair covers me. This raises to 2.8/3.0 if you go over that speed fully loaded. That's clear, the only query I have is the fact that I am using slightly wider tyres :confused: I've been running 2.4/2.5 and it seems fine, but just wondering really whether I should be carrying less/more pressure. What's TSN's opinion? Link to comment Share on other sites More sharing options...
patently Posted January 13, 2013 Report Share Posted January 13, 2013 Well, my approach during testing and practice is to vary them and see what happens. If you spin off, put them back to where they were before. I can see how that might not be helpful though Link to comment Share on other sites More sharing options...
garcon magnifique Posted January 13, 2013 Report Share Posted January 13, 2013 I can't see a tenth of a bar making much difference if I'm honest. I'd say it's more important to check and adjust regularly to whichever you choose than the difference between 2.3/2.4 and 2.4/2.5. For what it's worth I'd probably stick with the manufacturer's 2.3/2.4 although I can understand the logic of trying a tenth higher for the wider tyres. Link to comment Share on other sites More sharing options...
Mort Posted January 13, 2013 Report Share Posted January 13, 2013 With lower profiles (like 35s) the pressures need to kept up. Car Manufacturers deliberately state them low cos new buyers will notice the shitty ride and won't buy the car. The cost to the punter is piss poor tyre life and less poor performance than optimal.. I've mullered 2 sets not knowing this despite keeping an eye on pressures. My 2c... Keep the pressure high. It's how they were designed. Link to comment Share on other sites More sharing options...
Scotty Posted January 13, 2013 Report Share Posted January 13, 2013 I hope this doesn't sound wrong ... ... why not ask the people that recommended you change the size? If they can tell the difference in the size then I'm sure they can tell the difference in the pressures and what works best with them. Link to comment Share on other sites More sharing options...
garcon magnifique Posted January 13, 2013 Report Share Posted January 13, 2013 That's far too logical a suggestion for a Sunday. Link to comment Share on other sites More sharing options...
Scotty Posted January 13, 2013 Report Share Posted January 13, 2013 Fair point, well made. Link to comment Share on other sites More sharing options...
Andrew Posted January 13, 2013 Report Share Posted January 13, 2013 Now, I though standard widths were 245 front and 265 back; that is certainly what I've got and have seen on other model specific forums. Link to comment Share on other sites More sharing options...
Mac Posted January 13, 2013 Author Report Share Posted January 13, 2013 I hope this doesn't sound wrong ...... why not ask the people that recommended you change the size? If they can tell the difference in the size then I'm sure they can tell the difference in the pressures and what works best with them. Mainly because the opinion is very subjective matey. Also, most of where this is discussed is in the US, and they have very different roads to the UK. Now, I though standard widths were 245 front and 265 back; that is certainly what I've got and have seen on other model specific forums. Yes, you're quite right Andrew - Sunday morning typo on my part. Mine are now 255x35ZR19s and 275x35ZR19s, against stock 245/35 and 265/35. Link to comment Share on other sites More sharing options...
Tipex Posted January 13, 2013 Report Share Posted January 13, 2013 The standard manufacturers pressures should be fine. Link to comment Share on other sites More sharing options...
Calm Chris Posted January 13, 2013 Report Share Posted January 13, 2013 You might want to factor in the summer / winter bit. Cold air, cold roads need 0.2 bar more than summer pressure. It's a very subjective thing, how you drive, how far you drive, the types of road, the amount of passenger and luggage. Theres also that old fashioned thing, eyeball them and check wear. If its even then it should be right, if wear in the middle then they are over and if worn on the outside and inside they are under. I tend to go on the firm side, always have. Link to comment Share on other sites More sharing options...
Andrew Posted January 13, 2013 Report Share Posted January 13, 2013 Presumably Mac you have not done anything to your standard wheels to fit them; spacers or whatever? My rears will be due a change in a few months and I'm planning on trying the Pilot Super Sports. I run my pressures as per the sticker on the door. Link to comment Share on other sites More sharing options...
Mac Posted January 13, 2013 Author Report Share Posted January 13, 2013 No spacers needed. 265 - 275 is only 10mm wider, and 3.5mm more sidewall. Link to comment Share on other sites More sharing options...
Scotty Posted January 13, 2013 Report Share Posted January 13, 2013 Mainly because the opinion is very subjective matey. Also, most of where this is discussed is in the US, and they have very different roads to the UK. Yup and because of the roads they have different tyre compounds and maybe even pressures. I nearly said this when I saw the US manual extract. I'm not deliberately being picky I just don't understand why would go with their opinion on changing size but not about the pressures. Link to comment Share on other sites More sharing options...
Mac Posted January 13, 2013 Author Report Share Posted January 13, 2013 Simply because they're not related - by changing tyre sizes it opens up a whole range of tyres as opposed to being stuck with PS2s, PS2s, more PS2s or Cups. Link to comment Share on other sites More sharing options...
Scotty Posted January 13, 2013 Report Share Posted January 13, 2013 aha! Didn't appreciate quite how limiting it was. Link to comment Share on other sites More sharing options...
Rachel Posted January 14, 2013 Report Share Posted January 14, 2013 So by putting larger rubber on the rims, how much has it affected the accuracy of the speedometer 9given you have changed the rolling diameter of the wheels)? Link to comment Share on other sites More sharing options...
Mac Posted January 14, 2013 Author Report Share Posted January 14, 2013 (edited) Bugger all. 255/35=89.25mm sidewall against 245/35=85.75mm originals - so rolling radius of 2076mm against 2054mm so less than 1%. Reads go from 265/35 to 275/35 so 2098mm against 2120 so again less than 1%. For what it's worth, the speedo on the '3 is virtually bang on compared to the SatNav/TomTom speed - probably the most accurate I've had in any car. Edited January 14, 2013 by Mac Link to comment Share on other sites More sharing options...
Merlot Posted January 15, 2013 Report Share Posted January 15, 2013 I tend to run about 2psi over the stated figures, allows for some pressure loss and the need for more air in the winter. Always amazed when I come out of the tyre fitters how all over the place the pressures are FWIW. Link to comment Share on other sites More sharing options...
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