Setting arbitrary tire sizes for speedometer calibration

Testing new functions
becausebear
Posts: 2
Joined: Thu Oct 11, 2018 7:07 pm
Vehicle: 2011 Escape XLT 3.0 AWD

Re: Setting arbitrary tire sizes for speedometer calibration

Post by becausebear » Fri Oct 12, 2018 5:43 pm

Can anyone confirm or deny that this method would work on an '11 escape? I've compared ABD with another escape with different stock tires and have found one bcm line change and four abs line changes, but not sure as to which one to alter.

using the excel calulator at the start of this thread results in a 225/65/17 showing as xxxx 0898 xxxx which i do not see in the bcm or abs lines

what i have found, in the pcm log in forscan, is that it has a listing of tire sizes and corresponding rpm. it shows my stock 225/65/17 as 731, which is off, as its 708 rpm. but factoring in a 98.65% conversion gets me 731 rpm.

Wonder if i could find a way to alter the pcm's tire rpm value.

Solved my own issue, for anyone who was curious this vehicle has it in the pcm, forscan is unable to change it beyond factory settings. Ended up using an sct tuner to adjust it.

ggandzz
Posts: 1
Joined: Tue Nov 06, 2018 3:09 am
Vehicle: Mustang2.3T-2015

Re: Setting arbitrary tire sizes for speedometer calibration

Post by ggandzz » Wed Nov 07, 2018 6:49 am

hi, I have a few questions to ask you. If you only change the tire size, can the relevant ABS or other safety aids work properly? For example, Mustang 2015-2.3T-255-40-19, according to your formula, the original value is 208 5, that is 0825. If I change to 275-35-20, will it become 2128, that is 0850? Is the power conversion factor calculated according to 96.7% or else? Please give me a hand.

Aussiejoe
Posts: 1
Joined: Mon Aug 21, 2017 5:55 am
Vehicle: Ford Transit VM t280 2.2 2008

Re: Setting arbitrary tire sizes for speedometer calibration

Post by Aussiejoe » Sat Dec 01, 2018 6:10 am

Does anyone know if it's possible to change tyre size on a 2008 transit van fwd 2.2? Thanks

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