wheel and tyre size

[Deleted]

Hi all, having failed the first IVA for a few minor things, one fail point was the speedo reading.
Mine was displaying 2mph under the speed of the rolling road, eg, speedo saying 58 when actually travelling 60. this is a fail as it must read the same or higher than the actual speed.

take a look at the tyre calculator on maita.net to check yours out, as i was supprised what difference a few mm in circumference would make.

www.miata.net/garage/tirecalc.html



old standard wheels for the retest!

[Andy888]

That is surprising right enough. I mean even the tread depth could be enough to throw it into a fail situation. I assume they used a gps to test it at IVA?

[Tim Kerr]

Andy, over here i wouldnt worry about it! They tested it in the rollers at the MOT station. He had me hold the car at 30, 40, 50 and then 60 mph on my speedo and then he read the actual speed of the screen. Mine was ok but to be honest he couldnt see my dash so i could have easily held it at 27, 37 etc!

Tim

[Andy888]

Ah nice to know Tim, cheers! We drilled lots of holes over the Easter break - you'd be proud lol

[fasteddie]

Hi Alex, your right, with new 15/ 195/50 my speedo at 60mph is actually 0.03% high so actual speed will be 59.8mph so I guess I should be okay, having the car put through an MOT on Saturday to check every thing out. Regards Ted