I was about to order a Procal the day I got my Duratracs put on the jeep. 285/70R17 up from 255/75R17. But I just got out the GPS, as well as followed my wife, and my speedo is still dead on. Something seems off, from what I read just about everyone at least needed a procal to adjust.

Any ideas?

 

Here's my idea - your original tires calculate out to 32.05 inches in diameter. Your new tires calculate out to 32.7 inches. Their actual diameter is likely smaller, maybe 32.3 or 32.4, so you would not notice any difference in the speedo. Have you actually measured the diameter?

 

I did, my stockers were at 30.4 and my new tires are at 32.3 with 35 PSI. I just figured close to 2" would make a difference.

 

Wow - that's odd. All I can say is maybe they're calibrated for 32's from the factory? Did you ever check in detail when you had the stockers on?

 

That, I did not do. Wish I had now, but as long as it is correct I guess it does not matter... Was just hoping that this huge MPG drop I saw from just 33s was more than reality...Oh well, I did not buy a Prius, and at least I do not need a ProCal!

For those of you with 3.73s and 35s, I do not know how you stand it. Stock power I guess I could get used to..Adding 33s makes it pretty bad, I bet 35s are horrible on 3.73s and an auto.

Still, something seems off. Going for a drive tomorrow and going to take both of our GPS units.

 

The speedo from the factory may not be dead on. From what I have seen it can vary 3 MPH, so maybe with your tires on now it is dead on?

 

Have any friends who are LEOs?

In the end, I suppose the only speedo that matters is a LEOs radar gun

 

i just had my 315/70r17 BFG A/T's installed today and with all the talk about 35's, 3.73's and autos i was expecting the worst but it drove just fine down the toll road at 70mph (65 on the speedo).

 

You actually get used to it. I have 32" Duratracs with 3.21's, and when I first got them installed it felt like a pig. I rev higher now and am pretty happy on and off road.

 

Are you near sea level? I do not think I could stand it. The jeep is pretty slow stock compared to the pickup trucks I have driven in the past, which is fine, I knew it going in. When I put on 33 Duratracs, it got worse. I can only imagine if they were 35 how bad it would be. I do not think I could do it without regearing immediately. I am actually a little disappointed that I do not need a ProCal, now I realize that it was actually as bad as I thought. For 2 days I was thinking that I was going 75 when it read 72 or so...