speedo gear not quite right

DeftwillP · Oct 25, 2005

I finally put my 4.10s in to match up with my aw4 and 30's. It feels aaaawwesome.

But, I switched in a 40 tooth gear. According to gps, I am dead-on up to 50 mph. At 55, I'm around 56. At 60, I'm around 62. Around 62.5'ish, I'm at 65. At 65, I'm at 70ish.

I know that my speedo is by no means a precise device. But it doesn't seem to make any sense that its right down low, but increasinly off as speed increases.

Any ideas?

will

Kejtar · Oct 25, 2005

DeftwillP said:
I finally put my 4.10s in to match up with my aw4 and 30's. It feels aaaawwesome.

But, I switched in a 40 tooth gear. According to gps, I am dead-on up to 50 mph. At 55, I'm around 56. At 60, I'm around 62. Around 62.5'ish, I'm at 65. At 65, I'm at 70ish.

I know that my speedo is by no means a precise device. But it doesn't seem to make any sense that its right down low, but increasinly off as speed increases.

Any ideas?

will

Well I think that your eye to gps to speedo coordination might be a bit off, and to all that add the lag on the gps. Your best way to test the speedo is to look at the trip odometer and go about 10 ~ 15 miles and watch the mile markers.

edit: also according to my calculations you should be using a 37 tooth gear.

jrsxj98 · Oct 25, 2005

Actually a 39 tooth gear for 4.10's and 30's

http://go.jeep-xj.info/HowtoSpeedoGears.htm

Kejtar · Oct 25, 2005

jrsxj98 said:
Actually a 39 tooth gear for 4.10's and 30's

http://go.jeep-xj.info/HowtoSpeedoGears.htm

Well that depends on the base used for calculations and how true is the 30" measurement.

jrsxj98 · Oct 25, 2005

and if the moon is align with the planets........lol :cheers:

Kejtar · Oct 25, 2005

jrsxj98 said:
and if the moon is align with the planets........lol :cheers:

There you go

now you're getting the right idea.

fizassist · Oct 25, 2005

DeftwillP said:
I finally put my 4.10s in to match up with my aw4 and 30's. It feels aaaawwesome.

But, I switched in a 40 tooth gear. According to gps, I am dead-on up to 50 mph. At 55, I'm around 56. At 60, I'm around 62. Around 62.5'ish, I'm at 65. At 65, I'm at 70ish.

I know that my speedo is by no means a precise device. But it doesn't seem to make any sense that its right down low, but increasinly off as speed increases.

Any ideas?

will

Based on those measurements, no speedo gear is going to get you dead on through the driving range. They are not consistent with 0mph speedo == 0mph gps; you can't draw a straight line through those points. I would second the suggestion that there's a disconnect between what you're seeing on the GPS and your actual speed. It's a tricky measurement; you really have to be on a level road and keep the speed dead-nuts-stable.

fizassist · Oct 25, 2005

Odd...I'm logged in, but I don't have an "edit" button for my post. Anyway, here's the picture to illustrate what I'm talking about.

fizassist said:

DeftwillP · Oct 25, 2005

jrsxj98 said:
Actually a 39 tooth gear for 4.10's and 30's

http://go.jeep-xj.info/HowtoSpeedoGears.htm

39 tooth is what I planned on buying but had forgotten by the time I got to the dealership. There are 3 different tables with 3 different suggestions as to how many teeth it should have. 40 was one of them. I am going to try the 39 next.

As far measuring by distance: I show 9.5 miles to 10 miles of mile marker.

rokjeep · Nov 11, 2005

Ok, I have a headache trying to figure out mine. I have yet to find a graph that includes my setup......I'm running an auto with 5.38's and 38" SX's that measure 37.75". I know I've been eating retard sandwiches lately but any help would be appreciated. I'm guessing a 39 or 43 tooth gear. Any experts out there.

The first person that says search I'm going to punch in the baby maker.

I already searched.......

Gojeep · Nov 12, 2005

rokjeep said:
Ok, I have a headache trying to figure out mine. I have yet to find a graph that includes my setup......I'm running an auto with 5.38's and 38" SX's that measure 37.75". I know I've been eating retard sandwiches lately but any help would be appreciated. I'm guessing a 39 or 43 tooth gear. Any experts out there.

The first person that says search I'm going to punch in the baby maker.

I already searched.......

Ok I see what I can do.
My chart shows up to 4.88 and a 38" tyre ( taking into account that most are under ) and a 36 tooth gear. So if we add the % difference between the gears to that speedo gear you will get the new figure. 5.38 - 4.88 = 0.5 divide by 4.88 x 100 = 10.25%
So add that % to the speedo gear of 36 = 3.7 teeth so call it a 40 tooth gear.

rokjeep · Nov 12, 2005

Gojeep said:
Ok I see what I can do.
My chart shows up to 4.88 and a 38" tyre ( taking into account that most are under ) and a 36 tooth gear. So if we add the % difference between the gears to that speedo gear you will get the new figure. 5.38 - 4.88 = 0.5 divide by 4.88 x 100 = 10.25%
So add that % to the speedo gear of 36 = 3.7 teeth so call it a 40 tooth gear.

I went cross-eyed just reading that. Thank you, it will get me much closer than where I am at now at least, if not right on.

speedo gear not quite right

DeftwillP

NAXJA Forum User

Kejtar

PostMaster General

jrsxj98

DILIGAF

Kejtar

PostMaster General

jrsxj98

DILIGAF

Kejtar

PostMaster General

fizassist

NAXJA Member #1052

fizassist

NAXJA Member #1052

DeftwillP

NAXJA Forum User

rokjeep

NAXJA Forum User

Gojeep

NAXJA Forum User

rokjeep

NAXJA Forum User

Similar threads