Speedometer Calibration after New Tires

[397STROKER]

I have 276/65/20 which are 34.1 and I am set to 33.5. I am less than 1 MPH off according the my satellite speed app on my phone. I have diablo sport I3 tuner to calibrate. all my sensors work.

 

[Louhound88]

I had mine recalibrated by a dealership and it didn't affect any parking sensors. Was $50 I believe, and speed matches GPS nearly perfectly. Shift points are much improved too from before I had it recalibrated for the larger tire.

 

[Shots]

Hi,
Thanks for the reply. I will have to investigate and see if it's possible to do this. Are 34s even a standard size tire tho? With smaller tires we are using a different format for the tire numbering ie the tire width in mm, the profile ratio then the internal diameter in inches (315/55/22) for example.

PS - I'm from the UK and we use miles on our roads not km

Man you Brits are a weird bunch, mixing Metric and SAE.

As for tire size, yeah, most of them are listed P-metric in the states too. I guess we're a bit weird as well.
There are some good 34" options depending on the wheel (aka rim) diameter. I personally like more side wall, so I always ditch the big wheels from something smaller. As a result I don't know what specific 34" sizes are available in the 20 or 22 inch wheels but I know they exist. Not as plentiful as 35's, but there are options out there.

Oh, I re-read what you said. So you're saying put the 35s on but re-calibrate to 34s and live with the slight error? Is that what you mean?

Yup you understand it correctly. That's the work around I was suggesting.

 

[JohnGow383]

Man you Brits are a weird bunch, mixing Metric and SAE.

As for tire size, yeah, most of them are listed P-metric in the states too. I guess we're a bit weird as well.
There are some good 34" options depending on the wheel (aka rim) diameter. I personally like more side wall, so I always ditch the big wheels from something smaller. As a result I don't know what specific 34" sizes are available in the 20 or 22 inch wheels but I know they exist. Not as plentiful as 35's, but there are options out there.


Yup you understand it correctly. That's the work around I was suggesting.

Haha, yup, the EU tried to fully metricate us and we kept missing the dead lines, so we are kinda half and half. Metric road signs are illegal in the UK, and if a bridge height for example has meters on it it must display feet and inches too. What's funny is the kids now get taught in cm but they think like everyone else in feet and inches.
I think a 34" option and set it to 33.75" might be the way to go. I my be crying in a few months after all this when I realize how much im spending on gas(7USD per Gal), but hey, I'd much prefer to have a bad *** looking truck than save on gas milage

 

[Shots]

LOL something tells me you're not alone on that. Many of the trucks on this forum are far from efficient, but man some of them look amazing.

 

[JohnGow383]

I'm going to speak to the dealer on Monday or Tuesday to confirm that firstly they are actually able to make adjustments and to ask what device they are using to make the adjustments.

From searching the internet it would appear that the maximum rolling circumference that can be entered is 2715mm which equates to a tire diameter of 34..02" and still retain the parking sensors. Assuming the parking sensors still work then so should the parking assist feature (it's more of a gimick I know but still cool to show off). As most 35s are actually closer to 34½" then the error when entering say 2710mm won't be that far out and I could live with it. Whether or not the parking assist feature will be safe to use and how accurate it is with the error and lift of the vehicle will be interesting to see.
When you think about it, as tires wear then the speedo reading will eventually get a slight error as the overall diamter is reduced slightly over time.

 

[Av1]

I'm going to speak to the dealer on Monday or Tuesday to confirm that firstly they are actually able to make adjustments and to ask what device they are using to make the adjustments.

From searching the internet it would appear that the maximum rolling circumference that can be entered is 2715mm which equates to a tire diameter of 34..02" and still retain the parking sensors. Assuming the parking sensors still work then so should the parking assist feature (it's more of a gimick I know but still cool to show off). As most 35s are actually closer to 34½" then the error when entering say 2710mm won't be that far out and I could live with it. Whether or not the parking assist feature will be safe to use and how accurate it is with the error and lift of the vehicle will be interesting to see.
When you think about it, as tires wear then the speedo reading will eventually get a slight error as the overall diamter is reduced slightly over time.

Just as a reference adding a little more information to my previous reply, my tire size is 295/65R20 which have an inflated overall diameter of 35.12" as per Nitto. My speed was dead accurate when I calibrated to 34" using Flashcal when checked against a gps speed app on my phone. But unfortunately, it caused errors when set to 34". When I set it to 33.75" everything works properly, and it is now less than 1 mph in error when checked against gps. The radar speed signs on the side of the road show it exactly correct, but I don't know how accurate those are.

An option (rather than visiting a dealer) would be to order a Superchips Flashcal or equivalent and do it yourself, so you could play with the different calibrations and see what works best for you. They are actually quite simple to use.

 

[JohnGow383]

Just as a reference adding a little more information to my previous reply, my tire size is 295/65R20 which have an inflated overall diameter of 35.12" as per Nitto. My speed was dead accurate when I calibrated to 34" using Flashcal when checked against a gps speed app on my phone. But unfortunately, it caused errors when set to 34". When I set it to 33.75" everything works properly, and it is now less than 1 mph in error when checked against gps. The radar speed signs on the side of the road show it exactly correct, but I don't know how accurate those are.

An option (rather than visiting a dealer) would be to order a Superchips Flashcal or equivalent and do it yourself, so you could play with the different calibrations and see what works best for you. They are actually quite simple to use.

So 33.75 is equivelent to 2693 right? And thanks, is this similar to something like Tazer or AlfaOBD?

 

[Av1]

So 33.75 is equivelent to 2693 right? And thanks, is this similar to something like Tazer or AlfaOBD?

So 33.75 is equivelent to 2693 right? And thanks, is this similar to something like Tazer or AlfaOBD?

Yes, 2693 is what I calculated too. Tazer or AlfaOBD will do MUCH more than Flashcal. A search of the forums show how much you can do with those two. It is a lot.

I ordered the Flashcal because at the time I was only interested in doing a quick speedometer calibration. It's not the only option by far, it's just the one I used, and it worked for me.

 

[Shots]

.....The radar speed signs on the side of the road show it exactly correct, but I don't know how accurate those are.

They are between +1 and -2. Meaning that it show +1 mph to -2 mph of your actual speed. So if the sign shows 50 mph, you are traveling 51 - 48. In other words, they're pretty close.