Just got new tires and the hypertech max energy. I'm confused with all the info here on determining tire size. They are BFG KM2 35 x 12.5 R17. Looking them up on the BFG website shows overall diameter as 34.8. Is this the tire height that I should enter into the hypertech? If anyone has the same tires and has already done this, what height did you enter?

Thanks,

 

It programs in .25 inch increments, so you can start with 34.75....In reality it will probably be less, IMHO maybe even 34.25.
But you wont know for sure with out a gps to compare it with.


chuck

 

Yea, I am running 28psi and programmed 34.25, it seems to be right on at that setting..

 

The Hypertech instructions explain how to measure your tire size or you could measure your tire from the ground up to the top of the tread. That will give you your true tire height.

 

I measured the tire height as explained somewhere else on JK-Forum: From the ground to to top of the shoulder where it squares off--not to the height of the tire. It was almost 2" less than the 33" tires I have installed. The speedo has been verified against my son's truck (stock-size tires), against GPS, and against one of those speedometer things the police use to encourage folks to pay attention to the speed limit. It's darn close.

 

Typiically what you want is the ROLLING DIAMETER or ROLLING RADIUS, to compute the true height relative to the recalibration.....and then either use a gps, or, mile markers and a watch with a second hand, etc...to check your accuracy.

To use mile markers along the road, pick a nice straight, flat stretch of hwy/rd...that has mile markers along it....and pick a section long enough to get a nice consistant reading.

60 MPH = 1 minute per mile, or 60 seconds/mile.

So - drive 60 MPH on the nose, and see if it takes one minute/60 seconds to go from one mile marker to the next (Cruise control might help here...)

If it says you need LESS THAN 60 seconds to go a mile, you are going FASTER than 60 MPH, etc...and the tires are taller than you thought....

 

I have the same tires and i am running 30-32lbs and I programmed it for 34.5inches and my speed is dead on at 25/50/70 mph according to radar gun

 

You should also simply be able to mark off your trip odometer at one mile marker and see where its at when you hit the next mile marker.

 

LOL

I do not think this will work...as your trip odometer is going to be reading the same misinformation as your speedometer if the guesstimate was wrong, etc.

If the trip odometer worked, hell, you could just use your speedometer to see how fast you were going.


No, seriously...the trip odometer reads in 1/10's...on a one mile trip, you'd have to be off by ~ 10% or more to see a difference. Its better to use the speedometer in this case.

If going a long trip's worth of distance, and say comparing the Yahoo map miles to the odometer miles, etc, over a few hundered mile trip, then you'd have the resolution to see within a smaller percentage how far off you were, etc.

 

Thanks for the help. I set it for 34.5 tire height and it is dead on as checked by the GPS!