Mega Posted October 5, 2011 Share Posted October 5, 2011 Hi Guys. I've got a set of Vredestein Wintrac Xtremes in 225/45/17 size fitment. If I put these straight onto a set of 17" ers (which should ideally take 225/50/17 and 235/50/17) then I'll be 3.4% out at the front (too fast, IE 60 will be 58 or so) and 4.9% out at the back (too fast again, IE 60 will be 57 or so) My average speed will be out by the mean of those numbers IE 4.15% 2 questions: Will a 225/45 go on the rear 17 do you think? I know front will not be a problem but not 100% about the rear. I've got a friendly tyre shop so can always just give it a try Also will the CC be OK with this kind of number? I'd really rather not buy new tyres. The alternative would be I guess to just buy rears and go for 245/50 which would be 1.6% too slow and therefore bring the overall speed difference back down to around 2% which I'm certain will be OK. Cheers chaps. I'd be inclined to just accept the Management light for the sake of safe driving over winter: Although I've heard if this is on too long then you get shunted into limp mode etc Quote Link to comment Share on other sites More sharing options...
Mega Posted October 5, 2011 Author Share Posted October 5, 2011 someone must know? Quote Link to comment Share on other sites More sharing options...
Chris`I Posted October 5, 2011 Share Posted October 5, 2011 You'll need something like 245/50/17 to keep TCS happy. Putting the same size on front and rear will send it into overdrive. That will also keep the speedo right I think too. Quote Link to comment Share on other sites More sharing options...
Mega Posted October 5, 2011 Author Share Posted October 5, 2011 245/50 on the rear then... Not too bad, I can get some of those khumo jobbers. Not quite as good as the vredesteins but I've heard very promising things about them nonetheless. So dooes anyone know what the "rules" are about the TCS/CC system and tyre choices? IE max % speed difference without error from spec, etc etc. Quote Link to comment Share on other sites More sharing options...
Ekona Posted October 5, 2011 Share Posted October 5, 2011 Without trying to sound like the proverbial broken record, surely winter time is the last time you would ever want to consider running mixed tyres? Certainly running same size all round is a recipe for disaster fella, do it properly and do it right Quote Link to comment Share on other sites More sharing options...
Lexx Posted October 5, 2011 Share Posted October 5, 2011 I can't add anything to the above as it has all been said. What I am curious about is your avatar and your sig......you have a Zed, you are on a Zed forum, you no longer have a BMW. So why the beemer in both pics? (This is just my curiosity, it's not against rules or anything) Quote Link to comment Share on other sites More sharing options...
Mega Posted October 6, 2011 Author Share Posted October 6, 2011 Because I can't be bothered to change it. Also I still own the BM not that I tend to drive it with the Zed sat around Quote Link to comment Share on other sites More sharing options...
Mega Posted October 6, 2011 Author Share Posted October 6, 2011 Sorry to hammer the point... but I still want to know what the allowable speed differential % is without kicking out the system front and back. I'll go 245/50 on the rear: That's fine. I just don't want to go to that and still have an issue :) Quote Link to comment Share on other sites More sharing options...
Chris`I Posted October 6, 2011 Share Posted October 6, 2011 Not sure there is a definitive answer, no one has put many tyres on to check how far you can go. 2 things I know for sure though: 1. Keeping the difference 2.5-3% between front and back (ie back ~3% bigger than front) the TC is happy 2. Run the same size front and rear and TC will not be happy at all. Remember this isnt a speed differential, its a rolling radius. If you run massive 20" 50 profiles, so long as the rear is 3% bigger than the front, the TCS will be happy as it expects to see that 3% difference in "speed" of the tyres. Equally, if you could fit low profile 15s on there, it would still be happy if the 3% difference is there. Sure in those two examples the speedo would be a fair bit out but as far as TCS is concerned it doesnt care so long as the front to rear stay within the limits of each other. Quote Link to comment Share on other sites More sharing options...
Mega Posted October 6, 2011 Author Share Posted October 6, 2011 Thanks Chris. That's exactly the answer I needed ps. sig changed. hehe. Quote Link to comment Share on other sites More sharing options...
Mega Posted October 6, 2011 Author Share Posted October 6, 2011 So then. I'm planning to run 225/45/17 on the front and 245/45/17 on the rear. This is a difference of 2.8%. The stock 18s I'm on now on the other hand are 225/45/18 and 245/45/18 which is 2.7% difference front to back. Should therefore be fine Many thanks for putting up with me as I flogged the dead horse back there, by the way. Quote Link to comment Share on other sites More sharing options...
Chris`I Posted October 6, 2011 Share Posted October 6, 2011 That should be fine. Remember the speedo will over-read the speed slightly and your ground clearance will be lowered a bit too. Quote Link to comment Share on other sites More sharing options...
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