So I am reading a number of opinions and thoughts on speedo recalibration.

My boys truck - is a 1998 Dakota - 2.5L - 5sp - 2 wheel drive.
Currently running 215/75/15 on cast iron wheels
Just picked up a set of aluminum wheels with 31x10.50x15 tires on them.
Since he is 15 1/2 I want to make the speedo correct for the obvious reasons.
Wanting clarification that the 1998 , 2.5L -5 sp manual is not a gear change but a computer change.

Also, what is the cheapest way to make that change to the new tire size if it is just a computer change. Suggestions on where to find gears to change out if it is a gear change.

Thanks in advance - new member - Chris

 

my 2001 dakota with a 8 1/4 rear end has a plate bolted to the ring gear. which means a rear gear change will NOT put the speedo off. i changed from a 4.55 to a 1.4 rear gear, speedo was still ok. mine had different tires than showed on the door plate. i took it to a transmission shop. he put his computer on my computer. and it showed the truck computer was adjusted to the tires that was on it. my GUESS is the factory had to use a different tires and readjusted the truck computer to match.

 

Im not sure what you are getting at in your response. I am not changing any gears or such, I am changing tire size from the 215/75/15 to the 31/10.50/15

My question is how do you do this with the 5 Speed trans - and what is the best way and how - see first post again.

Thanks - still curious
Chris

 

maybe i gave to much info. the bottom line is if you change tire diameter the speedo will off. but it seams like it can be fixed in the trucks computer. you may have to get a dealer to fix it.

 

First yes a computer programing change but why even do it I have the same exact 1998 truck with the 2.5 engine with taller tires I estimated my speedo now shows 4 mph slower than its going if I remember that correct!

So if it shows I’m going 50 mph I’m actually going about 54 mph I just remember that and don’t think about it.

By the way with the 2.5 engine I wouldn’t worry about that too much it’s not a V8.

One thing you may want to consider doing if going with a taller tire that is changing out the ring and pinion gears to a better set more like a 3.9 or a 4.11. Not cheap but helps with taller tires and a small 2.5 engine the gearing will depend on if he drives on the freeway everyday or one time a month because changing to these gears screws up that.

One more suggestion change out the throttle body with one from a Jeep 4.0 engine throttle body its a good improvement to engine performance and cheap and easy to do, do a google search on it you will see.

Some Jeeps have the same engine in it the AMC 2.5L and the best way to get any info on this engine is in Jeep forums not on this one.

Some links on this

http://www.jeepforum.com/forum/f12/2...y-swap-602123/

http://www.wranglerforum.com/f8/2-5-...lp-146533.html

 

Good information thanks! The speedo thing is probably something I still want to do. He is 15 1/2 and just got his temps and is a new driver and learning stick so I think Ill probably get that done. Just would like some tips or suggestions on how to do it. Need to find the correct diag tool I guess.

THe motor is totally rebuilt, magnaflux, 40 over, all redone by the previous owner who was a motor builder for high performance engines. This was his little garage project - still has break in oil in it - LOL.

The cast iron wheels and regular tires got swapped out today for the aluminum and 31x10.5x15 white letter, what a difference in this plain little truck. I have bucket seats for it that we are going to switch out once we bolster some of the padding - a cool article I found on how to do that - got the seats at a pick and pull for 30 bucks, nice seats, with console.

Anyhow, thanks for the information and if you have any more it is appreceated. Ironic that you replied, as I used the picture of your truck to show him what it could look like with some work and pieces here and there.

Thanks
Chris

 

Thanks for the information. The reason for wanting to correct the speedometer is that I failed to mention my son is 15 1/2 (temps) and just starting to drive. I think I want one less thing that he has to do while he is learning and when he is on his own starting to drive. By my calculations his speedo will show 53 when actually going 60. So I dont want him to have to calculate on the fly (might help with his math skills though - lol)

So any guidence on this is appreciated and thanks for the information. The throttle body thing might be something that we can do at some point. The motor is freshly rebuilt, magnaflux, 40 over, heads, all of the motor gone through. The guy we bought it from builds high performance motors and this was his " get out of the house and tinker" project. Matter of fact it is about 200 miles from needing the break in oil changed on it.

Thanks for the response - we added the wheels and tires ( since he cast iron with stock 215/75/15) and it already looks like a different truck. We are not puting a ton of money into it but it gives him something to learn to work on and gets him "vested" in taking care of it.

Ironic that you responded, as I used a picture of your truck (his is red as well) as what he can make his base model look like.

This is the second time I have typed this response out so hopefully it doesnt double post.

Stock Tire - 215/75R15 Tire 1 - 31x10.50R15
Section Width:8.46 in215 mm Section Width:10.51 in267 mm
Rim Diameter:15 in381 mm Rim Diameter:15 in381 mm
Rim Width Range:5.5 - 7.5 in Rim Width Range:7 - 9 in
Overall Diameter:27.69 in Overall Diameter:30.97 in
Sidewall Height:6.34 in Sidewall Height:7.98 in
Raidus: 13.84 in Radius:15.48 in
Circumference:86.99 in Circumference:97.29 in
Revs per Mile:751.1 Revs per Mile:671.6
Actual Speed:60 mph Speedometer:53.6 mph
Speedometer Difference: - Speedometer Difference: 11.83% slow
Diameter Difference: -Diameter Difference: 10.6%