Since many people asked me about the accuracy of the speedometer after installation of the new wheels and tyres, I append the below calculation for those who are interested.
FRONT
Current wheel/tyre size : 225/45/17
New wheel/tyre size : 225/40/18
Current Radius : 317.15mm
New Radius : 318.6mm
Current circumference : 1992.71mm
New circumference : 2001.82mm
Difference in circumference : 9.11mm or 0.46%
So when the speedometer reads 100km/h , I'm actually travelling at 100.5km/h
REAR
Current wheel/tyre size : 225/45/17
New wheel/tyre size : 255/35/18
Current Radius : 317.15mm
New Radius : 317.85mm
Current circumference : 1992.71mm
New circumference : 1997.11mm
Difference in circumference : 4.4mm or 0.22%
So when the speedometer reads 100km/h, I'm actually travelling at 100.2km/h
As you can see, the difference is really minimal. Thus for those ER34 owners out there that intends to up size their wheels, you can be assured to follow the size I had on mine.
Hope this helps!! :)
Thursday, May 31, 2007
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Unlike motorcycle, speed sensor in most car today is inserted into the gear box. So its neither front nor rear wheel.
ReplyDeleteIf its a rear wheel drive car like mine, I can do whatever I like to my front wheel and there'll not be any effect in the speedometer. Only my rear wheel height will affect my meter.
For a 4WD car, all 4 wheels dimensions are calibrated to spin together, at the identical "rpm" for both front and rear because its driven by the same gearbox. Altering either the front or rear wheel heights would result in the gearbox having to drive both front and rear wheel at different "rpm" I wonder it will harm the gearbox in the long run.. :O
I hope I'm wrong.. :(
Thanks astroboy! I better remove that line out. :P
ReplyDeleteYea I think you could be right on the Vehicle Speed Sensor (VSS) part.