Need help figuring out speed after regearing (1 Viewer)

[Panzer]

With the stock gears and 315's 65mph indicated was about 72mph actual.
Now I am running 4.88's and have no clue now of my speed.
I know the 4.88's underdrive me for the the tire size so I am guessing that 65 indicated now is about 60 mph.

Anyone know the real answer?

TIA,
CAS

 

[GXO]

Use a GPS

 

[Romer]

If I recall, the 4.88's and 315's are 8% slower than the odometer says you are going.

 

[landcrusher80]

Install a Yellow Box.

http://www.ih8mud.com/reviews/fzj80-yellowbox.php

LandCrusher80

 

[Mark W]

RPM multiplied by the overdrive ratio, divided by the differential ratio, multiplied by the actual tire diameter (in inches), multiplied b Pi, divided by 12 multiplied by 60 divided by 5280.

True mph.


Mark...

 

[MTNRAT]

Just get one of these http://www.sleeoffroad.com/products/products_speedo.htm from slee. The box, not the gear. I installed a truspeed calibrator, but this box looks way easier to install. Calibration is needed to correct shift points.

 

[landtank]

I used the 8% value when I originally adjusted my truespeed. 5 years later I checked it with my GPS and is was right on.

 

[Panzer]

8% SWAG is good enough for now.
thanks for the assistance