I have recently upgraded to 315/70/17's from my stock 255/75's and I wasn't planning on using ProCal to fix my speedo readings because I figured that the stock GPS would give me accurate readings. Well turns out that the speedo and gps speed readings match still after my tire upgade. So I am pretty sure that the readings are wrong and it is a little weird that I seem to be passing everyone while still doing the speed limit.

So is the GPS reading just repeating what the in dash speedo reads (need to buy procal)? I really thought that they were stand alone systems? BTW, if I had an auto transmission I would have already purchased the procal to change my shift points, but since it is a manual I haven't. Thanks in advance for any help.

Cody

 

yea the GPS mimics the speed o... I thought wow.. i am still dead on, even with the 4.88 and 35" tires.. thought some magic combination tires and gears fixed mine... but nope! put a regular GPS in there and found that i am about 5mph slower than what speedo says. Of course that varies with the speed, that is my max though. 70 i am at 75 and 80 is 86.

 

Thanks for confirmation man! Kinda disappointed in my GPS now though.