Speedometer off by almost 5Kmph after tire and wheel swap

[Bloodham25]

I did a tire and wheel swap to SVE 19×10 Wheels and 28535/R19 all around.

My digital speedometer now seems to be off by 4-5kmph in my 22 GT pp1 premium.

I've seen forums in 18+ cars it recalibrate, I have yet to seen that yet, wondering if anyone has anymore info.

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[Assh]

Forscan

 

[galaxy]

Wow, 4,000-5,000 mph is quite a bit. That’ll be tough to adjust out.




(Hey, someone had to do it! LOL)

 

[Onewolf]

What were the previous tires? Diameter/Circumference?

 

[Bloodham25]

What were the previous tires? Diameter/Circumference?

They we're 255/40/R19 Front and 275/40/R19 in the rear. Went from a staggered to square setup.

 

[Onewolf]

Tiresize.com says you went from:

Front Diameter 27.0", Revs/mile 746
Rear Diameter 27.7", Revs/mile 729

To:

Diameter 26.9", Revs/Mile 751

751/729 = 1.03, so your new rear tires rotate 3% more per mile which could explain the speedometer being off.

 

[Bloodham25]

Tiresize.com says you went from:

Front Diameter 27.0", Revs/mile 746
Rear Diameter 27.7", Revs/mile 729

To:

Diameter 26.9", Revs/Mile 751

751/729 = 1.03, so your new rear tires rotate 3% more per mile which could explain the speedometer being off.

Anyway to get that fixed beyond the Forscan etc? I am planning to tune the car through either Lund or a tuner close to me that's very reputable.

 

[GTP]

You'll need to change a parameter using Forscan.
Did you check your speedo using a GPS phone speed app?
After I reprogrammed, my dash and phone speeds match within 1mph at 70mph.

 

[Bloodham25]

You'll need to change a parameter using Forscan.
Did you check your speedo using a GPS phone speed app?
After I reprogrammed, my dash and phone speeds match within 1mph at 70mph.

Yea I did definitely 4-5 Km/h (Canadian) faster than what the speed actually is.

Just not sure how to do the Forscan stuff, like the numbers to change etc.

 

[GTP]

I bet your tuner could do it for you. But I would have researched which parameter gets changed first.
I can look up my notes tomorrow.

 

[2017GBGTPP]

Anyway to get that fixed beyond the Forscan etc? I am planning to tune the car through either Lund or a tuner close to me that's very reputable.

The tuner can adjust for that, just be sure to let them know the rear tire size.

 

[Bloodham25]

Just doing a check (I ordered a ForScan thing) and I'm going from:

So I'd enter that number into the area that needs to be changed.

I saw a guide, just unsure if this is the exact number AND for reference, it only goes by rear tires.

 

[WildHorse]

FORSCAN doesn't always work. And most times you'll get weird BCM codes when you try. If your local tuner uses SCT or Diablosport, use that tuner.

I had the same problem, 5 km/h out. just used my tuning device to input the REAR tire height, boom over 60km/h 2 km/h out, below that bang on. Good enough.

 

[Bloodham25]

FORSCAN doesn't always work. And most times you'll get weird BCM codes when you try. If your local tuner uses SCT or Diablosport, use that tuner.

I had the same problem, 5 km/h out. just used my tuning device to input the REAR tire height, boom over 60km/h 2 km/h out, below that bang on. Good enough.

Maybe I'll just order the Lund tune early even though I don't have the CAI I want installed yet.

 

[WildHorse]

Maybe I'll just order the Lund tune early even though I don't have the CAI I want installed yet.

You could get the RTD that LUND requires, but adjustability will be ZERO. Then you need a laptop to log, unless they figured out all that android BS.

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