speedometer upgrade

[troublemaker]

I have a 1970 Road Runner and would like to go to a 20" wheel on the rear axle, the problem is the speedometer. Has anybody done this, if so did you go to an electric speedometer, what did you use to convert the pulse. This is a 4 speed car.
Thanx
TroubleMaker

 

[wannadrag]

20" wheel on a 70 RR?Kidding right?

 

[440brew]

it is not the wheel size that matters it is the overal height of wheel/tire combo. with a taller wheel the tire is typically a lower profile so figure out your new tire height and compare to old tire height. It may not change much at all!

 

[troublemaker]

I just happened to come across a 1969 Road Runner at a dealership. Stunning, the tire wheel combo was; Front, 255/45R18, Back; 255/45R20, TOO COOL on Billet Rims. I don't know how I could keep an original Rallye
dash with an electronic speedo. Thanks for the info on overall height. Need to get away from the original 14" magnum wheels

 

[PurpleBeeper]

Hey Trouble, what 440brew says is correct... it's not the wheel size it is the overall tire height in back that matters. You can just install a new speedometer gear in your transmission & "voila!" your speedometer reads correctly again. You might check out Brewer's Performance.