please help

[chass1971]

I just went from tire 14" to 15" and replaced rack and pinion and went from 3.45 to 3.73 now my speedo its like + 10-15mph off, I know that the gear that reads the speed ned to be replaced also, which one do i need??
my truck is a ranger 94 3.0 v6 auto a4ld tranny
thanks...

 

[metalmacguyver]

umm, the original tire size and the new tire size would make this alot easier.

 

[chass1971]

umm, the original tire size and the new tire size would make this alot easier.

uhh, what??

 

[Hardwareman]

Let's be a little bit clearer here.

1. You went from a 14" tire to 15" tire?

(Do you mean you went to a larger tire because what you said does'nt really make sense unless you changed wheels.)

2. You went from a 3.45 to a 3.73 gear ratio on your rack and pinion?

(Again, this makes no sense as the rack and pinion controls your steering. There are no gear ratios.)

3. If you replaced your rack and pinion because it was damaged and put bigger tires on your Ranger then yes, your speedometer will be off.


Just tell us what you did.




Allen

 

[chass1971]

Let's be a little bit clearer here.

1. You went from a 14" tire to 15" tire?

(Do you mean you went to a larger tire because what you said does'nt really make sense unless you changed wheels.)

2. You went from a 3.45 to a 3.73 gear ratio on your rack and pinion?

(Again, this makes no sense as the rack and pinion controls your steering. There are no gear ratios.)

3. If you replaced your rack and pinion because it was damaged and put bigger tires on your Ranger then yes, your speedometer will be off.


Just tell us what you did.




Allen

sorry I meant ring and pinion, I put bigger tires on my truck because I body lifted my truck

 

[Hardwareman]

Oh. Ok, well that makes A LOT more sense now.

Kind of weird that I did'nt figure that one out as I usually do....haha

What size tire did you have on there before and what size do you have on there now?

I went up to 31's on my Ranger and went with 4.56 gears. It's about 2 mph off. If I'm going 40 I'm actually going like 38, so it's not that bad.

You may have needed to go with deeper gears?




Allen

 

[chass1971]

before 225/70/R14
after 225/75/R15

 

[chass1971]

before 225/70/R14
after 225/75/R15

 

[chass1971]

anyone??

 

[metalmacguyver]

before = 82.94" tire circumference.

after = 88.86" tire circumference.




I did all the math and you speedometer should only be off by about 1%. That was a pretty good tire/gear combination that you chose.

You dont need to bother replacing the speedo drive gear or anything. It will be fine as is.

 

[Touring23]

*edit* Macguyver posted while I was typing this. I spent a farkin' long time on it, so I'm going to leave it. Maybe someone else can use it.
---
First, download this Acrobat file from FRPP.

Next, crawl under your truck, unbolt the speedo cable at the tranny, and determine what color speedo gear is in there now. This and the table will tell you whether you have a 6- or 7-tooth speedo drive gear.

Check my math: Your new tire diameter is 28.3", 713 Rev/mile.
Do the math at the bottom of the FRPP file.
Watch out for note (3) that says some gears have been discontinued.

 

[Hardwareman]

Sorry, that's why I did'nt respond back right away as well.

With the tire size difference and the lower gear ratio you chose, I don't see how it could be off by 10 mph.




Allen