Wheels upgrade - speedo

[Ron Burgundy]

If i swap my stock 18" SS wheels with 19" wheels (redline wheels) both with stock bridgestone tyres, will my speedo still be acurate ?

 

[Forg]

You can calculate the outside diameter of both, by getting the specs for both.
Pretty sure the outside diameter’s the same though, and that speedo calibration is the same ... but mebbe check it using aforementioned calcs, because I’m guessing not knowing.

 

[panhead]

Use something like this to calculate the rolling diameter of your existing rim and tyre package against your intended new package.


There are a million of these Tyre Comparison Calculators on the net.

https://tiresize.com/comparison/



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[Ron Burgundy]

Cheers guys

Front is the same...no difference in speedo

Rear is like 0.1% to 0.3% difference which is negligible

 

[cashie]

If i swap my stock 18" SS wheels with 19" wheels (redline wheels) both with stock bridgestone tyres, will my speedo still be acurate ?

Yes, mine is still reading 4km/h high at 100km/h after swapping redline wheels on.

 

[panhead]

As long as you understand the basic principle that an increase in rim size diameter requires a degrease in the tyre wall profile or a decrease in rim size diameter requires an increase in tyre wall profile to maintain similar overall diameters and you keep the change within about a 2% margin you'll be fine.

Be aware if you change the width of the tyre this will impact on the tyre wall profile as well.

A calculator will take all this into account when you enter the tyre specs and most will show a '+ or -' for the change in the speedo reading.

Also a tuner should be able to correct the speedo reading if you have concerns.


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[Ron Burgundy]

Yes, mine is still reading 4km/h high at 100km/h after swapping redline wheels on.

How do you know it's reading 4km/h high ? It should not be that much ...

 

[07GTS]

as long as the front to rear difference dosnt trip an error, they have a zero tolerance from factory unless u have factory staggered then there is a error value between front to rear that it has to be within, 4% fast is pretty normal, my VE is 2-3% most others vehicles can be 5-10% especially 4wd's

 

[cashie]

How do you know it's reading 4km/h high ? It should not be that much ...

GPS, pretty standard, original wheels were the same 4km out.

 

[panhead]

You’re speedo will be reading wrong from the manufacturer as almost all manufacturers intentionally build in an error where they read from 3 to 5 kilometres over the actual speed at about 100km/h.

It has often been said the reason is to ensure that drivers are under the speed limit so no class action can be taken against the manufacturer for speeding infringements.

This can make more sense when another factor comes into play and that is the wearing of tyres will cause the speedo reading to change, as will over inflation and the fitting of new tyres.

Deliberately calibrating the speedo to run high makes up for some of these fluctuations without the manufacturer running the risk of the vehicle actually travelling faster than the speedo reading.

Stick as closely as possible to the original diameter and you should be ok.

Changing the rim/tyre package's overall diameter will of course alter the speedo reading so if you have worries then use a GPS or have the speedo recalibrated.

Or change the tyres to a lower profile as the smaller overall diameter will cause the speedo to read higher than the true speed.

Same goes when changing diff ratios, the speedo will not be accurate unless recalibrated.




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