bought my 2004 hemi ram and put 33in tires from 31in tires. left the 3.55 gears in the back. went to go get my speedometer recal. heres the trippy part that 7 dodge experts and 4 dealers cant find the problem.

the computor shows 33in tires 3.55 gears and the right chrysler axle. the speedometer still reads slow.

now if you make the computor think it has a dana rear end it reads perfect but the cruise control doesnt work past 62mph.

had it on the dyno at 5 shops and top line mopar techys scratch there heads.

any ideas?

 

Screw the dealers. Have it put back to stock configuration. Buy a tuner (and get performance benefits as a bonus) which will let you recalibrate for tire size. Actually measure your tires (I'll bet they are not exactly 33") and enter into the tuner to the nearest 1/4". Axle Gear ration has no bearing on the speedo readout on a 3rd Gen Dodge.

My 35" tires actually measure to a shade under 34.5", and when set at that, my speedo is within 1 mph of the readout I get on my GPS...

 

The dealers aren't programming in the right size tire. As hammer mentioned, a 33" tire isn't really 33". You need to measure it and use the actual size.

 

I got to agree with those 2^^^^. When I had the dealer recalibrate mine I had the same problem as you with the cruise so I took it back to them and they got it a little closer and got the cruise to work. I just got a SC tuner and have finally gotten my speedo right. Get a tuner, you'll get your speedo right and there are alot of other +'s that come along with it.

 

the tires are 275/65r20s or something like that its what the comp reads to. it wouldn't read 10mph slower that way. im going once more to this guy that my whole valley recommends. i will put up info if the prob still don't get fixed. yea if you have 3.73 and the comp reads 3.55 it will throw off the speed. i have another dodge that i had that with.

 

Gears dont throw off the speedometer, not in these trucks, I went from 3.92's to 4.56's with my same tires (31.5" tall) and my speedometer is still running within a 1mph of the speed warning radars we have around here just like it was before the gears (I know not the most accurate but its give a an idea if something changed or not). Buy a tuner and measure the actual height of the wheel/tire combo like the others have mentioned above.

 

Well, if your tires are 275/65 r20s, and your SURE of that, thats a 34" tire man lol. Myabe thats the problem?

Or maybe you have 275/60 r20?

I had my trucks speedo/odo adjusted by dodge when I went from 245/70 16 to 265/75 16 on my dakota, and its seems to be near perfect. Not all tires of the same numeric sizing are the same size though.

 

Yep, gear ratio makes no difference since the speedo reads the speed of the ring gear sensor wheel and it doesn't change with gear changes, only tire diameters. Most older vehicles have the speedo sensor in the tailshaft of the transmission and gear ratio changes do alter the driveshaft speed, which would change the speedo reading.

 

yep, you need to physically measure your tire diameter. For example, Firestone's Destination M/T 285/70/17 is a true 33" tire where as the Destination A/T 285/70/17 is 32.2".

 

o crap my bad that was my ranger i had that problem with. i went to drop my dodge off to that guy but he was gone on sick leave. so i went and got a tuner, tried everything but still no results. i swear i get stuck with these stupid problems on every truck i own. i dropped of my ranger at a shop to install a jet speed recal box and they couldnt get it to work so then they got a superlift and it still didnt work. ended up making a new exciter ring with 14 more teeth. worked great. now i got this tweaker dodge!

ok i went from the stock 17 in rim tires on a 2004 dodge ram 2wd hemi slt. to the 20 dodge rims and 275/60r20s. thats it. im wondering if i have a tweaker computor. the guys at r&e racing were stupped and there well known for top line work. im gunu go in wed and let the guy do what he does. if i still have the same problem then i will post up everything he did in detail.