2009 Dodge Ram Gear Ratio Swap

[hispirish]

Hello,

I am having a shop change my ring and pinion from 3.21 to 3.90. The question I have is this:

Since there is no adjustment in the programmer for gear ratio, do I just adjust tire size accordingly? I have used a gear ratio calculator and know that in order to fool the computer, I need to drop the tire size from 31 to 25.5 to achieve a correct speedometer reading after the gear swap.

I don't understand why the tuner does not have this parameter. Seems like kind of a lame work around to do the tire thing.

Am I missing something?

Thanks.

Sean

[mikel]

The gears do not affect the speedo, there is no need to adjust the ratios in the tune.

[hispirish]

Ok, thanks a lot. Can you satisfy my inner gear head and explain this? I am not doubting you at all, I would just like to visualize how that works. If I changed to larger tires, I would need to calibrate for that wouldn't I? Isn't final drive final drive?

Thanks

Sean

[hispirish]

Maybe I just answered my own question. Is the speed sensor in the hubs?

[mikel]

Yes, the speed is read from the abs rings, thus the gear ratio has no effect, just the tire height. Vettes work in this same way as well....

[hispirish]

Thanks again.

[bighemitex]

the speed will remain the same but your shift points will probably be off a little bit now because the trans has it programmed to have 3.21s instead of 3.90s

[akatoad]

do the 2004 rams work the same way cause i have thought of swapping gears. I thought the 04 works off the reluctor ring in the rear end. is this correct?