Upgrading 15" wheels to 17"

[Supervinnie40]

I did some research before I decided to switch to a IPK with message center (and Klarzy dials), and I read that the Dutch law says that a speedo is still approved if the discrepency stays below 10%. So when I'm driving 100km/h it should never read more then 110 and never under 90. But mechanics and dealers do suggest that you get your equipment checked/replaced if it becomes that bad.

I've tested my current IPK, and when I do 120 km/h the GPS says I'm doing roughly 115km/h, so that's pretty close.

[hamster19]

Ride comfort beats appearance for me every time, hence I have the smaller wheels on mine, so I suppose for me to go for the bigger wheels would actually be 'downgrading'

[Supervinnie40]

Personally I find the difference very small, but that's just my opinion. I don't feel much difference between the 15" and the 18".

[David Lawrence]

Originally Posted by StephenEssex

I used to have 17" meteors on my last 75, didnt like them and slightly ruined the ride for me. Stuck 15" crowns on and it drifted along like the magic carpet.

They might look better in some peoples opinion, but not for me.

Same here. The meteors look great but are terribly hard over the bumps, crowns on mine also now.

[maxxpump]

I had 15" wheels on the car when I got it and now have 16" unions on it now. The ride is much better and I don't have to worry about catching speed bumps so often. Anyway the crowns which came with it were ugly! I know it is not a 17", but the same principle could be applied.

[Dallas]

Originally Posted by Supervinnie40

I did some research before I decided to switch to a IPK with message center (and Klarzy dials), and I read that the Dutch law says that a speedo is still approved if the discrepency stays below 10%. So when I'm driving 100km/h it should never read more then 110 and never under 90. But mechanics and dealers do suggest that you get your equipment checked/replaced if it becomes that bad.

I've tested my current IPK, and when I do 120 km/h the GPS says I'm doing roughly 115km/h, so that's pretty close.

Vinnie, vehicle speedometers have a standard set tolerances of 10% set by the manufacture, this is due to variations in tyre diameter, tyre wear, temperature, variants in tyre pressure, and vehicle load etc. Vehicle manufacturers will calibrate a speedo to read higher, to ensure their speedometers never indicate a lower speed than the actual speed of the vehicle.

GPS devices are more accurate, its a positional speedometer based on how far the receiver has moved since the last measurement. The speed calculations are not subject to the same sources of error as the vehicle's speedometer (wheel size, transmission/drive ratios etc).

Has anyone ever heard of a vehicle owner getting their speedo calibrated on a regular basis, I'm sure that will be the next test added to the MOT is due course.

As for the differences in the ride when using 15" or 18" wheels, I find there is a huge difference in comfort, handling and road noise.