So I installed tires that are almost 34.5" tall which equates to roughly 10% taller than stock, but when I checked my speedo against my GPS, it's showing me being upwards of TWENTY PERCENT off, which makes no send unless the speedo was 10% slow with the stock tires.
Anybody else notice this, and/or happen to gps their speedo with the stock tires?
10% doesn't bug me. My last 3 trucks were in the same boat, and I was perfectly fine driving around accounting for the 10%.
20% is too much however, so now I gotta go buy a speedo calibrator(not gonna use the foreskin)

 

 

My concern was with 10% taller tires equating to a 20% speedo error, but I hooked up my old Garmin Nuvi and it showed only a 10% difference(not to mention the extreme unlikelihood of everyone on the freeway doing 80+mph) , so the GPS on my phone must simply be off.

 

I've found my stand alone GPS units a Garmin Nuvi and a 62st, more reliable than a cellphone based GPS. I did my correction with FORScan, simple easy and inexpensive. KM