Can SCT flash tuner correct speedo ?

[Whitey-AMG]

Chris / Theo

Do you know if the SCT handheld device can correct speedo error ?
GPS shows 100 - speedo on the GT shows 108.
Error varies from 5-8 klmh

There is a menu option in the SCT tuner for rear end ratio and revs per mile......would plugging in some data here fix the error or is the speed calculated from ABS sensor.

[Theo@BluePower]

The best way to fix it is to run the car on the dyno @ 100klph and work backwards to the tune to correct it. This way it will be right on 100..

I don't think user settings has the functions for you to change yourself..

[Whitey-AMG]

Originally Posted by Theo@BluePower

The best way to fix it is to run the car on the dyno @ 100klph and work backwards to the tune to correct it. This way it will be right on 100..

I don't think user settings has the functions for you to change yourself..

Thanks Guys
The SCT device allows for rear end ratio to be changed and also REVS per MILE input. I have put in the rear end ratio for the GT and also the REVS per MILE ( 783 ) based on the Tire calculator - here :
http://www.gordon-glasgow.org/tirecalc.html

I'm thinking maybe I should just reset the REVS per MILE back to factory setting ? I'm guessing it may not be correct as it may vary from tyre to tyre and how much air pressure and tread you have left ?

[Theo@BluePower]

Jim,

depending upon the strategy it can be as simple as changing user available options, We dont normally leave these unlocked, sometimes the VSS source code needs to be changed to get this to work.

Hope you've been well mate

Chris

[Whitey-AMG]

Thanks Guys.....all fixed now

I reset the axle ratio in the SCT to "STOCK" - which I think turns it off.....

I then measured the actual rolling diameter of my rear tyre. 1 complete rotation = 78.5 inches.

There are 63,360 inches in 1 mile
So 63,360 divide by 78.5 = 807
Therefore - it ends up being 807 revs per mile.

When I used the online calculator to get the REVS per Mile :
http://www.gordon-glasgow.org/tirecalc.html

It gave me 783 Revs per mile for a 245 / 35 / 19 tyre
So I think that's where the error was.

Driving to work this morning after the change - the Speedo now shows 80 and the GPS shows 79......much better. Previously - it was out by about 8klm/h at 90.

I wonder if the trans shift points are also altered by this ? If the car thought it was doing 80 - but it was actually only doing 72 - it would have been shifting early - right ?

[Bluepower]

Originally Posted by ESP

Thanks Guys.....all fixed now

I reset the axle ratio in the SCT to "STOCK" - which I think turns it off.....

I then measured the actual rolling diameter of my rear tyre. 1 complete rotation = 78.5 inches.

There are 63,360 inches in 1 mile
So 63,360 divide by 78.5 = 807
Therefore - it ends up being 807 revs per mile.

When I used the online calculator to get the REVS per Mile :
http://www.gordon-glasgow.org/tirecalc.html

It gave me 783 Revs per mile for a 245 / 35 / 19 tyre
So I think that's where the error was.

Driving to work this morning after the change - the Speedo now shows 80 and the GPS shows 79......much better. Previously - it was out by about 8klm/h at 90.

I wonder if the trans shift points are also altered by this ? If the car thought it was doing 80 - but it was actually only doing 72 - it would have been shifting early - right ?

Usually Jim it does, depends on where the VSS is set, if its default (and I think yours is) then it is indeed one of the primary protocols for VSS, therefore tailshaft rpm, therefore shift speed.

Chris