Procal Tire Size - Miscalculated?

[dman918]

Hi all,

I installed my calibration kit, and cycled through all the settings. Under the tire / gear settings, it showed 249 revolutions, 3.55 gear. Gearing is right, but I believe the tire revolutions are wrong. I have 265-35-20s on, which would leave me to believe the equation would be:

20850/(((2x265x35)/2540)+20) = 763.74 revs or 764. Is my math right or am I missing something? Just want to make sure it's right. Thanks for your help!

Mike

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[MROCGUY]

that's what i got on mine, same axle and tire size here

 

[dman918]

that's what i got on mine, same axle and tire size here

Great thanks.

 

[MROCGUY]

i had 764 before, but now looking at some online calculator...i'm seeing about 739
unless the first calculator i came across was wrong, now i am not sure

 

[MROCGUY]

3 different calculators point to 739...i guess my 764 was wrong, weird.

https://tiresize.com/tiresizes/265-35R20.htm

 

[dman918]

3 different calculators point to 739...i guess my 764 was wrong, weird.

https://tiresize.com/tiresizes/265-35R20.htm

I saw that the online calculators vary from the ford performance manual. See this thread:

https://www.mustang6g.com/forums/threads/procal-3-power-pack-and-tire-revolutions.158440/

 

[MROCGUY]

it's settled then..764 it is

 

[dman918]

it's settled then..764 it is

I guess let's hope! LOL!

 

[Tucker80]

It's varies by manufacturer, but the vast majority of manufacturers list the revs per mile in thier specs. Tirerack is a good source if you need it. I used the calculation 1st and was way off based on the manufacturer spec so I definitely wouldn't use the calculations.

 

[ice445]

It's varies by manufacturer, but the vast majority of manufacturers list the revs per mile in thier specs. Tirerack is a good source if you need it. I used the calculation 1st and was way off based on the manufacturer spec so I definitely wouldn't use the calculations.

Yep, tire manufacturer provided revs per mile is your best bet. That's what I use, and my speedo is dead nuts on.

The online calculators get you into the ballpark, but they make some assumptions that ignore real world effects. Calculating circumference is easy, but calculating it when there's load on the tire is much harder. That's why it's better to use what the manufacturer has determined.

 

[dman918]

Ok thank you both. I will take a look at manufacturer spec and adjust accordingly. I'll report back what I find.

 

[dman918]

Ok they are Nitto G2s, so tirerack says 760. Pretty darn close.

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