DadsCJ

Florida is downhill both ways, look at the map.....

redrubiconunlimited

My UL Rub speedo is 6 Kilometers Per Hour slow on stock tires. Checking with my gps.

So keep that in mind, yours may not have been bang-on from the factory either.

darkrambler

I found the best way to check speedo error is to find a straight stretch of interstate highway, pull over at a mile marker, reset your tripmeter to 0, and travel 5 (or better 10) mile markers. Pull over at last mile marker and record your tripmeter reading.

If you travelled a true 10 miles, but your tripmeter says 9 miles, then your speedo is off by 10%. 9 / 10 = .90 or your speedo is 90% of actual.

I don't know if the Yellow Box speedo calibrator can be used on our jeeps (I have 33" tires and had the computer reprogrammed to the largest size) but I have a Yellow Box on my sportbike and its a great device. Sportbike speedos are historically very optimistic, so I got one of these for true high speed bragging rights... "yes dear, we really were doing 160 back there!":toung:

Here's a link to Yellow Box website:

http://www.blackrobotics.com/

For my sportbike, a ZX9R, all I had to do was splice into the speedo sensor harness for the install. I mounted it under the seat so I could change the setting when I changed the sprockets to different sizes. I would think this device would be great for anyone who has larger than 33" tires if it can be adapted to our JK's.

DebnJohn

I'd be willing to bet each jeep off of the assembly line has it's speedo programmed with whatever tire size is put on it there. For example, my basic X c-pkg, 225x75x16 tires was dead nuts with the original tires. When I upgraded to 265x75x16's it is now 5mph off at 60mph as measured with gps.

Does anyone know if this affects other ecm performance issues like auto trans shift points etc?

moabmike

So true!! All tires sizes are not created equal. But measure your diameters off the vehicle with no load on them. But depenping on width, I 'm willing to bet your 33' just aren't that tall. BFG"S tend to run small...The only true indicater is a tape measure.. having said that..remember how much you lose once you air down. Historically most jeep speeds are wrong from the factory. Use a Gps to get a good speed reading.

mytjjeep

I emailed AEV and they will have a reprogrammer out this summer sometime. It will adjust the speedometer and he thought maybe some other stuff but didn't have details yet. He also said they would have one at the Moab EJS and they would do the reprogram for free out there but I just can't make it. Didn't sound like it would be price to bad either. Dave Harrington is the gentleman that I spoke with at AEV, he was very helpful and super fast on his email communication. Great customer service so far.

LinkSync

There are replacement resolver gers that can be be put in to get back to true readings, assuming you had true readings once.
The difference in tire diameter needs to be known and also the gear ratio and then they can calculate which one is needed.
I haven't as yet seen any specificaly claiming JK compatability but I'm sure they won't be far off.
Note that this option would require advanced mechanical abilities as they have to get put down inside someplace mystierious and unkown by your humble reporter, as they replace the factory one.
It looks like a lil gear on a wire and I suppose it spins against something that "reads" it. If u make it bigger it spins more and smaller less etc.
Maybe?

pmergler

x2.....was just about to recommend the same thing

LinkSync

I was told today by the Dealer that they can mod the computer to any size as what they do is tell it how many revelutions = 1 mile.
He wasnt clear as to it's effect on spedometer real time readings but he was SURE it made the odometer reading correct...

So i'll tell the cops I only went 5.3 miles at some speed closely associated with "Too Fast" but I duno.....

Rubidozer

Those devices only work on gear-driven speed-sensor-rings that are mounted just inside of the transfer cases, similar to chevy new venture cases. The device used to correct the original signal is attached just outside the case where the revolving-wire is fed in and the new speed-sensor ring accentuates the original ring output, thus the revolving-wire spins at the corrected rate. I learned how to make them from a buddy that ran a 'Tachometer/Speedometer Shop' where we did high performance tuning on racecars and speedboats. I built my first one for my Chevy Pickup with 36" tires.
The JK is an electronic-speed-sensor which uses a magnet to read another magnet that spins in the transfer case. Very similar to the TJs, if not the same setup. This magnet-to-magnet design is also what ABS systems have been using for many years.
The Superlift Speedo-Corrector just takes the reading and corrects it by varying the timing of the signal sent into the box and delaying or increasing the timing of the signal sent to the ECM.