What's new
By:
Ram Heavy Duty Forum

Register a free account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

Tire size adjusted and off by 3-4 MPH

cquilichini

cquilichini

Member
Messages
85
Reaction score
70
Points
18
Good morning guys,

I adjusted the tire size on my truck to match the new tires circumference and the Speedometer is off by 3-4 MPH when compared to my speedometer app on the iPhone and Waze...

My new tires are Nitto RG 35 x 12.5 R20 and its diameter is 34.76" and when i converted to find the circumference in mm it brings me to 2773.7mm.

Any input is greatly appreciated.
 
If you plug your phone into Uconnect, it will use the GPS in the truck if equipped with NAV.

Checking GPS against speedo with phone it needs to be standalone.
 
Keep adjusting it until it’s correct.

I put different tires on for elk hunting, adjusted the speedo, and then when I went back to stock tires and the stock setting it was off by 2-3%. It wasn’t off before I changed it, and I’m not sure what was different.
 
Yep, been there done that.

Set you rear tire pressure at what you will normally be running.
Make a mark on the ground and on the tire. Move the truck so that the tire makes one complete revolution and mark the ground.
Measure the distance between the marks and convert it to MM.
Use that number for your tire size.
Only way to be accurate.
 
I live next to aev r and d and in fact they used my truck to sort out the procal snap and this how the inventor of the procal told me to do it measrure your front tire from center of hub to ground when parked on flat cement surface and times that number by 2. I have found that everybody i know he runs 35’s does get really close using 33.5 tho
 
MtnRider said:
You need to actually measure the tires then tweak from there. A 35 tire is never close to actually being 35".


.
Click to expand...

Most tire manufacturers list rev/mile, which can be converter to a rolling circumference. That's a great starting place too.
 
Not sure that works as it would have to be done at the pressure/load of the truck you are putting it on. That makes a difference of the actual rolling circumference.
 
jadmt said:
I live next to aev r and d and in fact they used my truck to sort out the procal snap and this how the inventor of the procal told me to do it measrure your front tire from center of hub to ground when parked on flat cement surface and times that number by 2. I have found that everybody i know he runs 35’s does get really close using 33.5 tho
Click to expand...
you were absolutely right, from the center of the hub to the floor there were 16.25", so it should be a circumference based of a 32.5" tire or 2594mm for that fact... Thanks a lot!!!
 
You must log in or register to reply here.
Back
Top