Baystate Jeepers

So I just got my jeep regeared to 4.88 and now the speedometer is off which is to be expected. The question I have is kind of an odd one, I originally had 3.07s in the jeep at which time the speedo was off. When I put in Rubi axles with 4.10s and my 35" MTK/Kevlar the speedo was surprisingly spot on. Now I don't know what I have for a speedo gear in the jeep now (its a 97 sport TJ with 6cyl) but its likely I had a 31 tooth gear in. Its "Recommended" that I use a 39 tooth gear for the speedo gear but unless I had a 33 gear speedo in there before Im not sure a 39 tooth gear will make things right...

Anyone running 35" MTRs with 4.88s out there that can comment? Im not sure the Goodyear are a true 35" and i don't want to waste 40 bucks on the wrong gear.... (i know about the give a speedo take a speedo on JF but it doesnt seem there are many folks leaving the higher tooth count speedos).....

I have 4.88 with 35" MTRs, automatic with NP231 and 39 tooth gear. Speedometer is very close to the speed shown on my GPS. Hope this helps.

Jeff : I have a 56 tooth gear in mine with 35s. It really depends on the final drive more than anything else. I went from a three speed to a 4 speed tranny and from a d-20 to a d-300. With 32s.I had 3.73s and my speedo was slow because of the 32s.Now on 35 with 4.56s I keep breaking the cable as the speedo is off the charts ! So I pulled the 39 and went to a56, Ill let you know how close it is. I was told there is more to it than your axle ratio. One of the off road mags had a great explanation. FjR68

I think I have an excel spreadsheet I created to calc gear ratios... It may figure out speedo teeth too... If I can find it I'll email it to you.

JW

I have several speedo gears here, believe I have the correct one for you.

Little Napoleon wrote:I have several speedo gears here, believe I have the correct one for you.

that would be great if you do! Let me know Chris!

there is a chart for these things on quadratec and such but I dont know how many teeth my current one has, I only know the speedo shouldnt have been right with 35s and 4.10 given the standard factory tooth count is too low but it was...

I have 4.56 and 33's soon to be 35's and never corrected the speedo. I use my GPS when on the highway and otherwise don' care. Is that bad?

COH143 wrote:I have 4.56 and 33's soon to be 35's and never corrected the speedo. I use my GPS when on the highway and otherwise don' care. Is that bad?

Your speedo is required to be within 5% of actual speed, or else is a safety violation. Also keeps the odometer accurate.

JW

COH143 wrote:I have 4.56 and 33's soon to be 35's and never corrected the speedo. I use my GPS when on the highway and otherwise don' care. Is that bad?

I think a lot of people do the same thing. I live in a town that strictly enforces the speedlimit and drive thru a few to get to most trail heads so its just better for me to be accurate rather than hoping I remember my GPS. Technically if you dont correct the speedometer the odometer is not accurate and it needs to be disclosed when selling as well as what Jon said...