So I decided to buy a Predator so I could fix my Speed-O because I changed my Diff and Tires. Well it showed up yesterday and I went right out to my truck to program. Thats when I found out the Predator dos'nt support my Gears. I put 4.88's in my truck. The programer goes from 4.55 then jumps to 5.05 or something like that. Why did they skip 4.88? Well I decided to send them an email figuring they would have a soultion. WRONG! Instead they told me to play around with the gears and tire settings untill I get the problem corrected. What kind of crap answer is that!

So now I turn to the wisdom of the fourm. Does anyone know of a calculation I could use to figure out what settings I should set in the Predator to fix my speed-o? I have 4.88's and the tires measure 33.25 inches from ground to top of tire.

 

Basically all you need to do is find out what percentage difference you're dealing with from a 4.55 to your 4.88s. Then take that difference and subtract it from your tire. I think the predator uses revs per mile? It should be close to take the difference out of your actual revs per mile. I'm not sure if this is correct, but the difference in gearing looks to be 9.3%. Just for explanation sake, lets say your tires have a 650 revs/mile. Deduct 9.3% from that, you get 589. See if you can select a revs/mile on the Predator that's close to that. Then go out with a friend in another car with an accurate speedo to compare.

 

What size was the original rubber, and what gear ratio was the original?

Givr me the new size rubber, and knowing you now have a 4.88, I can probably come up with a setup that will work within the programmer limits.

 

UPDATE: I have checked tire sizes and gearing ratios, and have found this.


A 4.55 rear with 31.3 to 31.5 combination has the same road speed as a 4.88 with a 33.25.


The LT275.70R X 16 is 31.3 in. and 665 revs per mile. With a 4.55 rear it calculates the same road speed as the 4.88 and 33.25 size you now have.



I hope this helps. If you need more info, just post.

 

What the? Robert & Yardbird you gave me a headache, hehe, jk... don't know if this would help too but I found a tire size calculator on this website... tells you how many revs per mile just by putting in your tire size.

http://www.miata.net/garage/tirecalc.html

Hope this helps

 

The stock axel was 3.55 and the tires were p265/60r18.

The new axel is 4.88 and tires are 35x12.50r17. The actual height is 33-1/4 from ground to top of tire. I am not sure what tire number would give a better reading.

 

Thanks Yardbird, I will give this a try. Do you think I should use 35 since its a 35" tire or 33.25. or bettrer yet should I measure the circumfernce of the tire?

How did you make the calculation?

 

Since the programmer only gives you the option of the 4.55 or 5.05 rear, you have to find a tire size that will calculate the same road speed as your present setup, but using one of their default rear ratios.

That setup is:

4.55 rear and 31.3 tire height.
which equals same road speed as,
4.88 rear and 33.25 tire height.

Same final speed numbers. Just able to achieve it using the limited choices in the programmer.

I went to the BF Goodrigh site and found the tire size specs. Most tire companies list the revs per mile and tire height on their sites. I then used a road speed calculator to find combos that achieved the same speed as your size.

 

Yardbird, Where did you get the road speed calculator?

 

Road Speed Calculator:

http://www.free-online-calculator.co...lculator.shtml


Hope this helps you.

 

It just keeps getting better .

After everyones help I have found out that ne matter what I do The speed-o numbers ar'nt changing. I went from one end of the settings to the other and nothing happens.

Has anyone tried changing axel and tires and been successful?

 

Will these reprogrammers (the Diablo and Superchip) work with a 3.55 limited slip axle? The first person (rhicks_all_taken) said it goes from 4.55 to 5.05. What about people who have lower numbered axle gears?

 

YouAll gave me A HEADACK @ Im good with math !!

 

Isn't that a solution? Seriously, they should add it, but by using the tire sizing allows you to calibrate for any gear change. They include the most common gear ratios by default.

I believe http://www.onlineconversion.com has calculators to help with this.

 

When I said they go from 4.55 to 5. 04 I ment they skipped 4.88 Gears. The full Range of the programmer is from 3.07 to 5.13

These are the gears supported: 3.07, 3.26, 3.54, 3.73, 3.90, 4.09, 4.30, 4.55, 5.13.

I dont know why they use these numbers 3.54 SB 3.55, 4.30 SB 4.33. It seems like they didnt do their homework to see what gears are actually avalable for the trucks.

The other funny thing is that tire rev per mile goes from 500 to 2000. I have never seen a truck with a 11 inch tire 20168/11= Rev per mile.