hymer1942 Posted August 6, 2014 Author Share Posted August 6, 2014 All that you say is correct exept all those clever were designing a panel van, not a motorhome. Link to comment Share on other sites More sharing options...
StuartO Posted August 6, 2014 Share Posted August 6, 2014 A new tyre has a tread depth of 10mm and you can wear then down to 1.5mm can't you? So that's a reduction in diameter of (10mm -1.5mm) times two during the tyre's life, which (on my MH tyres) is equivalent to a 2.3% difference in circumference and therefore speedo reading. Given that all sppedos on UK vehicles over-read slightly amd many of them by 5-15%, that isn;t going to make that much difference. The size of your wheel arches might be a limiting factor in what you could fit but I suspect most MHs would be able to accept a larger tyre up to 2cm greater in diameter if you wanted to fit one, which would be like having another 10mm of tread added, so would reduce indicated speed by about 2.5%. So fitting a tyre of 2 cm larger diameter would slow the displayed speed, but not by enough to worry about. Going up another 2cm would do the same again, so a total change of 5% indicated speed. Larger diameter tyres would have the effect of increasing the gear ratios slightly, and that might be problematic if you are already limited on engine power to pull the weight up hills, which lots of MHs are. And anyway if you change from the manufacturer's specification you have to tell the insurer - and these days they do seem to want to charge extra premiu for any "modification" to your vehicle, even changing to winter tyres. Incidentally after a lot of head scratching I replaced my original Michelin XC Camping tyres with the current equivalent, Michelin Agilis Camping, and these are marked "M+S" (standing for mud plus snow) which means they count as winter tyres for purpose of visiting snowy countries, where winter tyres are compulsory. They cost me over £700 for five, but I'm now good for another eight or nine years and I got back over £100 by selling the old ones via EBay. Link to comment Share on other sites More sharing options...
hymer1942 Posted August 6, 2014 Author Share Posted August 6, 2014 Very interesting, but I have now changed the van from the Hymer S Class 650 to a HymerSL 660 Bestline which has 235/60/16sa lot bigger tyres. Barrie Link to comment Share on other sites More sharing options...
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