Speedo and shift points adjustment

[7GHellboy]

I'm currently running 275/35/19 Fronts and 305/35/19 Rears but I have a set of 305/45/18 drag radials for the rear that I plan on using for the dragstrip. Given the height and circumference difference between the fronts and rears with the drag radials, should any adjustments need to be made to the calibration (speedometer, shift points, etc) to compensate for the different height and circumferences in order to have accurate speedometer readings and correct shift points?

It's a 2024 S650 GT and I have an MPVI3 if needed.

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[7GHellboy]

 

[Neggytive]

you can use any of the hundred or so online tire size calculators to see how much difference there is in diameter and that will give you a good approximation of how far off your speedo is going to be.

I'd be more concerned about how the ABS and other ADAS systems interpret the difference in wheel speed than the speedo and transmission shift points

 

[7GHellboy]

ABS and other driving aids are not relevant for the drag strip. Traction and stability control issues are "fixed" disabling AdvanceTrac. But i dont want overrevving or misshifting because the car "thinks" its going slower or at lower rpms than it is actually going.

~8% difference between front and rear exceeds maximun tolerances (approx 3%) that can be auto adjusted by the Ecu.

 

[Neggytive]

 

[Percys650DH]

Any pics with them installed? And are you on any lowering springs?

 

[A.alansari]

You can use @roket website to calculate for you what you need to change in forscan to let the car know what is the tire size you have

https://roketgamer.dev/mustangtools

 

[7GHellboy]

Any pics with them installed? And are you on any lowering springs?

Steeda Progressive Lowering Springs.

 

[Percys650DH]

Steeda Progressive Lowering Springs.

Looks perfect, no issues with the 305/45 with that drop? I’ve got the Steeda dual rate springs on mine and want to do a 305/45 instead of 305/40 but don’t want them to hit the fender or anything

 

[tj@steeda]

Steeda Progressive Lowering Springs.

Solid choice!

 

[7GHellboy]

Looks perfect, no issues with the 305/45 with that drop? I’ve got the Steeda dual rate springs on mine and want to do a 305/45 instead of 305/40 but don’t want them to hit the fender or anything

So far, zero issues.... I'll be doing further testing this weekend at the strip and I'll let you know if anything happens.... bit this combo hooks!!!

 

[Percys650DH]

So far, zero issues.... I'll be doing further testing this weekend at the strip and I'll let you know if anything happens.... bit this combo hooks!!!

Good to know! I bet it does, Would love an update after testing

 

[7GHellboy]

Here's the update: zero issues with this setup, everything works perfect. Even the speedo and shift points are fine after the Lund Tune!!!...

 

[Percys650DH]

Here's the update: zero issues with this setup, everything works perfect. Even the speedo and shift points are fine after the Lund Tune!!!...

That’s great!

 

[KarKy]

Hi! Im looking to add some drag wheel n tires to my performance package too!
What are the specs of your wheels?
Have you try other sizes?

BTW, Your setup look fucking nice!

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