Jeep Wrangler Forum banner

1 - 19 of 19 Posts

·
Registered
Joined
·
147 Posts
Discussion Starter #1
I went from the stock Sahara rims/tires (255x70x18) to the BFG's(285x70x17). I bought a ProCal but I haven't used it yet. While on a road trip yesterday just for kicks & grins-I compared the digital speedo reading in the Jeep to the MPH reading on the GPS system. They were both dead on the same numbers. I varied my speed(between 55-60 MPH) and they still matched up. Should'nt they be off a little, say 1-3 MPH? The guy at the tire store where I had them mounted & balanced asked me if I wanted them to "flash" the new wheel/tire dimensions. I told him, "no" because I had the Procal on order and I would take care of it.
Is this just a fluke or is this OK? Thanks, Smitty
 

·
Registered
Joined
·
1,678 Posts
I think those overall diameters are super close, like 32.1 to 32.3 inches, might explain it.

EDIT: Looking at the wrong tire size.....I guess those are 33 inch....Oops!
 

·
Registered
Joined
·
1,492 Posts
Use a hand held GPS instead of the factory nav. The speedometer and the factory nav are tied together.
 

·
Super Moderator
Joined
·
14,588 Posts
Thanks, but I don't have a hand held GPS & I don't know anyone who does. Guess I better unpack the old ProCal & get busy.
There are bunch of GPS speedo's available for any smart phone. I use Speedometer Free on my iPhone.
 

·
Registered
Joined
·
48 Posts
There are bunch of GPS speedo's available for any smart phone. I use Speedometer Free on my iPhone.
I did the exact thing you have done except I went with Nitto's and my speedo did not need changed either. I have checked it with 2 different GPS Speedo apps and an old fasion Garmin GPS and its dead on..
 

·
Registered
Joined
·
8,968 Posts
It seems that JK's that have the UConnect 2, the speedo is tied to the nav. system through the head unit. I initially thought that it couldn't be but I wasn't differentiating between UConnect and UConnect 2. UConnect doesn't.
 

·
Registered
Joined
·
1,048 Posts
What is the difference between UConnect and UConnect2? How would I know which is in my 13' JK?

A quick google search indicates that UConnect2 is currently only available in the 2015 Dodge Ram so we wouldn't see that in any JK yet???
 

·
Registered
Joined
·
8,968 Posts
What is the difference between UConnect and UConnect2? How would I know which is in my 13' JK?

A quick google search indicates that UConnect2 is currently only available in the 2015 Dodge Ram so we wouldn't see that in any JK yet???
It seems like the JK's have enhanced Uconnect with the 730N package starting in 2013. The screen is smaller than the 8.4" UConnect 2.
 

·
Registered
Joined
·
565 Posts
I found that my speedometer was slightly fast with the stock tires and slightly slow with the 285/70-17's. Only about 3-4 % each way.
 

·
Registered
Joined
·
147 Posts
Discussion Starter #16
OK- I had a buddy download a GPS app to my Wife's phone. We took the Jeep out and the phone GPS was spot on with the digital speedo and the Jeep GPS. There may have been about a half second delay between the phone GPS and the other 2, but they all matched up. I still haven't used the procal yet. So I guess I'm ok on the speedo?
 

·
Registered
Joined
·
615 Posts
There isn't enough difference between those tire sizes to matter. When you get 40,000 miles on your new tires they will be the same size as the old tires when new.
 

·
Registered
Joined
·
141 Posts
My tires are just under 33" and I don't see a difference between the speedometer and my iPhone app either until I get over 60mph - then there is a 1 mph difference. For example when I'm traveling 70mph the speedo reads 69mph.
 

·
Premium Member
Joined
·
1,551 Posts
It's going to be a percentage based difference. That's why not noticing any difference until above 60mph. To give you an idea when I switched from stock Sahara tires to my Grabber AT2 I went from 255/70/18 to 275/70/18. That resulted in a 3.4% difference in measurements. So if I wanted to drive 100mph by speedo, I would actually be going 103.4... At 50mph, it's half that difference, or 51.7.
 
1 - 19 of 19 Posts
Top