AJI Posted May 18, 2002 Share Posted May 18, 2002 When upgrading from 17" to 18" tyres do you or do you not need to drop down a profile height to maintain the same rolling radius? Am I right in thinking that the speedo and odometer run from the front wheels? Cheers for any replies. AJI Quote Link to comment Share on other sites More sharing options...
Guest Martin F Posted May 18, 2002 Share Posted May 18, 2002 The odo and speedo run from a sensor on the back of the box, auto or manual. As for rolling radius, you will need to drop the profile if you want to keep some speedo accuracy but i'm not sure what the figures are off the top of my head. Quote Link to comment Share on other sites More sharing options...
Terminator Posted May 18, 2002 Share Posted May 18, 2002 If you have an accurate speedo reading with the stock 17's ie 255,40,17, then fitting 275, 35, 18 will give you a 1 mile an hour error at 60, your speedo will read 60 but you will be travelling at 61. If you go to 285, 30, 18 you will be 1 mile per hour out but the other way, at 60 mph on your speedo you will be travelling at 59. Both of these are very close and should not cause a problem. Quote Link to comment Share on other sites More sharing options...
AJI Posted May 19, 2002 Author Share Posted May 19, 2002 So the speedo runs from the rear wheels then? I'm planning on getting 285/35/18 for the rear in that case. I just thought that if the speedo runs from the front wheels then it woulnd't matter what profile height I chose so long as it fit within the rear arch. But if the speedo is working from the rear wheel speed then it's a different story as you have mentioned. Cheers. Quote Link to comment Share on other sites More sharing options...
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