How to calibrate 38” tires

[Odd Ball]

I’m looking for a tune of some sort to calibrate my 38 inch tires and if I could get some extra horsepower that wouldn’t be a bad thing… Does anybody know of which option might allow for 38 inch tires? And I need to pass California smog…

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[Brian_B]

Ford performance Tune is the only one I know of that’s CARB legal. That will get you another 10% or so.

All of the rest that I am aware of won’t make it though smog.

You may want to consider gearing down a bit - that will make it a bit easier running those bigger tires

 

[Squatch]

I agree with @Brian_B that gearing will give you the most "felt horsepower."

The FP tune says it compensates for 37 inch tires, though... When I installed it, however, the name Livernois came up and maybe you can get help to switch it to less than 579 revolutions per mile or maybe it won't matter that much unless you have a true 38 inch. At true diameters, it would be a 2.7% difference in circumference but also less than 579 revolutions per mile... maybe you know a good dealership that will do that for you or @NORCALGXP may.

 

[Brian_B]

Forscan will also let you calibrate the speedometer, but I don’t know if it has the same limit as the FPT tool.

I was able to dial in my 35s with just tire size, but that’s tame compared to 38s. Just do a run, compare GPS to speedometer and adjust until I got it dialed in. The final number was no where near what an online tire calculator said it should be (ECM requires tire size in rotations per mile, not inches or mm)- but it’s dead on whenever I pass one of those speed radar signs

https://www.bronco6g.com/forum/thre...eedometer-with-forscan-for-2021-bronco.23064/

 

[rtaylor]

I’m looking for a tune of some sort to calibrate my 38 inch tires and if I could get some extra horsepower that wouldn’t be a bad thing… Does anybody know of which option might allow for 38 inch tires? And I need to pass California smog…

Unless Ford changed something recently the bronco modules don't support 38", but you can use forscan and set it to the max supported "circumference" of ~2800mm (~37" tire) and live with the remaining speedo error. The Ford Performance Tune should also let you set near the max (it uses rev per mile instead of circumference units, but has the same limitation due to the modules).

https://www.bronco6g.com/forum/thre...th-forscan-for-2021-bronco.23064/post-1336626

 

[Los]

I love to read the blog of different Bronconians modifying their wheels to look more badass that what they already are. However it just sounds like a pain in the and hoping that such changes won't break the ride... kudos to you all. I am not planning on changing much on my WT ride for a very long time... (though I do think about how cool those 37" look over my 35"s, but for now I am happy)

 

[userdude]

Check the actual height, it's probably not a true 38 so doing the max in Ford ProCal would be close enough. I would think you'd measure at the psi you plan to run (say, 35psi).

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