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redrrover

Member

• Dec 4, 2013

• #1

hi i have just changed my wheels from 16 to 18 this puts my speedo readings out. can i change the abs ecu off the r/r with the 18 inch wheels to give the right readings . my r/r has no TC but the other has will this all work cheers Pete

 

M

markav8r

Member

• Dec 5, 2013

• #2

Have you checked your actual speed readings using a GPS.
You might find that the larger wheels actually make the speedo read more accurately! Generally most speedos overread, so the larger wheels will compensate some.

Cant see any reason why the ABS ECU needs altering.

 

Saint.V8

Dyed-in-the-wool 100% RR Junkie

Full Member

• Dec 5, 2013

• #3

The rolling radius should remain the same as the 18 rim tyres will have a lower profile to them to keep them within the required radius.....


And the Speed signal sent from the ECU cannot be changed.....check the handbook for the correct tyres for 18" rims if they are not the correct tyres, fit the correct tyres before you kill yourself or the car....

 

Datatek

Well-Known Member

• Dec 5, 2013

• #4

redrrover said:

hi i have just changed my wheels from 16 to 18 this puts my speedo readings out. can i change the abs ecu off the r/r with the 18 inch wheels to give the right readings . my r/r has no TC but the other has will this all work cheers Pete

Click to expand...

As the others have said, with the correct tyres, (see owners manual) the rolling radius of the 16" & 18" wheels are the same. I swap from 18" to 16" for winter, no difference to the speedo error compared to my GPS.

 

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redrrover

Member

• Dec 5, 2013

• #5

thanks for the info tyres size 255x60x16 to 255x55x18 not far off .abs sensors send 8000 pulses to abs ecu per mile and then to becm .i just thouht the one off the other r/r with 18 wheels would show right readings.my fuel readings have gone from av 25 to 21 miles per gallon thanks Pete

 

Saint.V8

Dyed-in-the-wool 100% RR Junkie

Full Member

• Dec 5, 2013

• #6

You'll find the ABS ECU's will be totally indentical regardless of tyre/rim size...the idea is to match the rolling radius of the original fitment, that way the pulses from the sensors to the ECU and subsequently to the Speedo will be correct...

Different P38's with different size tyres/rims to eachother will have the exact same identical ABS ECU as eachother....aslong as the radius's match you will have no issues...

 

wammers

No longer with us, RIP

Donater

• Dec 5, 2013

• #7

redrrover said:

thanks for the info tyres size 255x60x16 to 255x55x18 not far off .abs sensors send 8000 pulses to abs ecu per mile and then to becm .i just thouht the one off the other r/r with 18 wheels would show right readings.my fuel readings have gone from av 25 to 21 miles per gallon thanks Pete

Click to expand...

There is your problem, you have the wrong profile tyres on the 16s. They should be 255/65/16 not 255/60/16. The size/profile on the 18s is correct.

 

Datatek

Well-Known Member

• Dec 5, 2013

• #8

wammers said:

there is your problem, you have the wrong profile tyres on the 16s. They should be 255/65/16 not 255/60/16. The size/profile on the 18s is correct.

Click to expand...

+1

 

wammers

No longer with us, RIP

Donater

• Dec 5, 2013

• #9

Datatek said:

+1

Click to expand...

Yes the 16s gave an actual 29 MPH at an indicated 30 MPH. Whereas the 18s are correct. So if you want to improve fuel consumption, in the mind at least. Fitting smaller wheels with the wrong profile tyres would seem to be the answer.