I have a 2006 MegaCab 5.7L Hemi and I am considering an axle ratio gear change. I don't have a tuner yet, but I was wondering if any, orall them allow speedometer corrections to compensate for differences in gearing.

Can anyone advise me on what their setup allows?

TIA!

 

Gear swap does not effect speedo, no change necessary. Only tire diameter changes require a speedo adjustment.

 

superchips will change your speedo

 

Not trying to be a smartass at all, but I think you're misinformed. A higher or lower gear ratio affects the distance that a vehicle will travel for the same amount of driveshaft revolutions, which is the same way that the tire's height/circumference affects the speedometer.

 

Thanks, good to know. I've been looking at that one, but I've also been waiting to see what the new Diablo has to offer before I purchase the Superchips.

 

I would definately watch that diablo first! It sounds like it will be great, i just wanna let a few other people buy it and see what its actually like. I do have the superchips and i love it, but i just want the best!

 

Then we need to straighten out the 4x4 shop that installed my gears who said that the swap would not effect my speedo, as well as my local dodge dealership who stated the same, and the dozens of responders on another forum who changed their gears and answered the same question I posted prior to getting my gears swapped,and lastly, GARMIN, whose GPS is obviously "mis-informed", because it said I was doing 65.1 mph when my speedo said 65mph, after the gear swap!
However, when I added the lift, and went to 35" tires, my speedo was 9 mph off, according to the GARMIN. I used my Superchips at that time to adjust my speedo, but did not use 35" (even though the tire manufacturer's specs said the tires were exactly 35") I used the GPS and found that the 34.75" setting was more exact. I then measured my tires and sure enough, they were just barely over 34 and 3 quarters inches.
Now I won't swear to GOD that I'm correct on this, and I've been wrong a good many times before, but after getting that much info on this matter when I changed my gears, I'm pretty darn sure...

I am not jumping on you and I thought the same thing, I could not see how it could not effect my speedo and I have a friend with a '94 Ford who it did make a difference with ( I got an expanation why from a user on the other forum when I posted the question, but I forget why), which is why after I was told by so many sources, I still had to check it for myself.

Here is a link to a thread on another Truck Forum I just found regarding this matter:
http://www.dodgetalk.com/forums/show...ghlight=speedo
The Defense Rests...

 

whoops, I guess THIS forum won't allow me to put a link to another forum on a post, but if you would like to read it, PM me, and I'll PM it to you...

 

HammerZ71, If the speedometer reads directly from a tire rotation standpoint, you are absolutely correct, and I am wrong.

But if the speedometer input comes from the driveline (i.e. transmission) then you are misinformed, and I am correct.

So thereal answer depends on where the gauge's input comes from. I am not familiar enough with my 2006 MegaCab's equipment to know exactly where the speedometer gets it's input, so it's very possible that I am incorrect.

As far as traditional driveline inputs are concerned, I have done the math, and the numbers don't lie.A 265/70/17 tire has an approximate height of 31.7 inches, which would give it a circumference of about 99.5 inches. To travel 1 mile (63,360 inches) would require the tire torotate 636.8 times.The 636.8 tire revolutions would requirethedriveshaft to rotate 2375.3 times if the rear gears were a 3.73 ratio. Conversely, a driveshaft connected to a differential equipped with a 4.10 ratio would require 2610.9 rotations to achieve the same 636.8 tire rotations necessary to move the vehicle that exact same mile. Therefore, more or less driveline rotations would indeed alter the reading indicated on the speedometer.

No hard feelings? I'm new to this board, and I'm not interested in forming any adversaries here. I'd like to learn as much as I can from other's experiences, and contribute what I can to the board.

Thanks.

 

No, thereare no hard feelings at all, it's just:
1) I don't want to see someone think they have to go and spend upwards of $500 on a tuner that he/she does not need for this (although there are many other reasons forsomeone to do so).
2) I went through this whole thing a year and a half ago, and I too believed that changing gears HAD to effect my speedo, to the point where, after being told by multilple, good sources that it didn't, I still had to check it for myself with my GPS.

I cannot give you the link here but this is a cut & paste of a thread on another forum, the poster is a technician at a 5 star Chrysler dealership:

"You don't need to reprogram anything for a gear change. The speed is read off the ring gear, so no change is necessary."

Again, if you'd like to read this thread, for your own info, PM me & I'll PM you with the address.

I have also read a response on the Superchips forum when the question was asked why some SC tuners allowed you to adjust for different gears while the '04-'07 Dodge Hemi Tuner did not. And the response from the SC was that it was not needed as gear changes do not effect the speedo on this particular model vehicle.
As further evidence to this point, I own a Superchips and have installed same on two other 3rd Gen Dodge Trucks, I have also installed a Hypertech on a '03 Hemi and have yet to see an option that has ANYTHING to do with gears...
PLUS... my GPS don't lie!!!

If you are still skeptical, go buy or borrow a GPS and see for yourself.

'Nuff said on this...