how bad will speedo be off?

[Mustang4119]

I have 295/35/18 in the rear and 3.73 gears. I am going back to stock, now I need a speedcal or something because Im not keeping the sct chip in. How bad will my speedo be off?

 

[Bolt on 5.0]

you can have it fixed at the dealer. I am not sure about the 18" wheels but theyll prob charge a hour labor to connect wds and recal the speedo. Make sure the chip is out first.

 

[Mr.~G]

At 2500 RPM with 26.75" tire hight.

RR end 3.73
1st 14.15
2nd 26.67
3rd 40.72
4th 53.34
5th 79.61


RR end 3.27
1st 16.14
2nd 30.42
3rd 46.44
4th 60.84
5th 90.81

 

[Bolt on 5.0]

mr g how did you calculate that, I would like to run that on my car. Super duty t5 with 295 first and 4.10 rear. Also 245/55r16 I think, stock tires

 

[Mr.~G]

file is rpms2.xls.doc
you must rename to rpms2.xls

There are several tabs at the bottom.
The yellow or green cells can be modified as input.
The last two tabs are just reference.

 

[Bolt on 5.0]

excelent thanks