I was clocking my speedometer the other day with my GPS (I have 31" tires
and 4.56 gears on my 98 TJ SE) and I found that the speedometer was reading
64mph at an actual speed of 60mph (on the GPS). The SE came with a 40 tooth
gear, so I calculated that I need a 42.666 tooth gear. ;) I figured I'd go
conservative at 42 teeth. I called Jeep parts at three different
dealerships and they all say that the gears go up to 41 teeth and that's it.
Does anyone know where I can get a 42 tooth gear? 41 is hardly worth the
money to put it in. That's around a 1.5 mph correction.
TIA
TJim

 

Just curious
What is the accuracy of a GPS?
I own a GPS And I think I remember reading that there is a tolerance.
+/- something.

TJim wrote:
> I was clocking my speedometer the other day with my GPS (I have 31" tires
> and 4.56 gears on my 98 TJ SE) and I found that the speedometer was reading
> 64mph at an actual speed of 60mph (on the GPS). The SE came with a 40 tooth
> gear, so I calculated that I need a 42.666 tooth gear. ;) I figured I'd go
> conservative at 42 teeth. I called Jeep parts at three different
> dealerships and they all say that the gears go up to 41 teeth and that's it.
> Does anyone know where I can get a 42 tooth gear? 41 is hardly worth the
> money to put it in. That's around a 1.5 mph correction.
> TIA
> TJim
>
>

 

*Everything* has a tolerance of +/- *something*...
;)

"FrankW" <fworm@norpak.ca> wrote in message
news:3F0B137D.1080905@norpak.ca...
> Just curious
> What is the accuracy of a GPS?
> I own a GPS And I think I remember reading that there is a tolerance.
> +/- something.
>
> TJim wrote:
> > I was clocking my speedometer the other day with my GPS (I have 31"
tires
> > and 4.56 gears on my 98 TJ SE) and I found that the speedometer was
reading
> > 64mph at an actual speed of 60mph (on the GPS). The SE came with a 40
tooth
> > gear, so I calculated that I need a 42.666 tooth gear. ;) I figured
I'd go
> > conservative at 42 teeth. I called Jeep parts at three different
> > dealerships and they all say that the gears go up to 41 teeth and that's
it.
> > Does anyone know where I can get a 42 tooth gear? 41 is hardly worth
the
> > money to put it in. That's around a 1.5 mph correction.
> > TIA
> > TJim
> >
> >
>

 

Hi Jim,
I think you be going the wrong direction. Two sites I use to
calculate the number of teeth agree, you should use 37 teeth on a 31"
tires and 4.56 gears: http://www.sierrajeep.com/speedome.htm
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

TJim wrote:
>
> I was clocking my speedometer the other day with my GPS (I have 31" tires
> and 4.56 gears on my 98 TJ SE) and I found that the speedometer was reading
> 64mph at an actual speed of 60mph (on the GPS). The SE came with a 40 tooth
> gear, so I calculated that I need a 42.666 tooth gear. ;) I figured I'd go
> conservative at 42 teeth. I called Jeep parts at three different
> dealerships and they all say that the gears go up to 41 teeth and that's it.
> Does anyone know where I can get a 42 tooth gear? 41 is hardly worth the
> money to put it in. That's around a 1.5 mph correction.
> TIA
> TJim

 

I know, Bill, but the chart is wrong for the SE as far as I know. My SE
came with 29" tires and 4:11 gears and had a 40 tooth gear in it. The chart
shows a 38 tooth.
If I'm reading 64mph at 60mph and I have a 40 tooth gear, The speedometer
cable is turning too fast and I need a larger gear. 40 * 64 / 60 = 42.67
teeth.
TJim

"L.W. (ßill) ------ III" <----------@***.net> wrote in message
news:3F0B1C88.4995BE02@***.net...
> Hi Jim,
> I think you be going the wrong direction. Two sites I use to
> calculate the number of teeth agree, you should use 37 teeth on a 31"
> tires and 4.56 gears: http://www.sierrajeep.com/speedome.htm
> God Bless America, ßill O|||||||O
> mailto:-------------------- http://www.----------.com/
>
> TJim wrote:
> >
> > I was clocking my speedometer the other day with my GPS (I have 31"
tires
> > and 4.56 gears on my 98 TJ SE) and I found that the speedometer was
reading
> > 64mph at an actual speed of 60mph (on the GPS). The SE came with a 40
tooth
> > gear, so I calculated that I need a 42.666 tooth gear. ;) I figured
I'd go
> > conservative at 42 teeth. I called Jeep parts at three different
> > dealerships and they all say that the gears go up to 41 teeth and that's
it.
> > Does anyone know where I can get a 42 tooth gear? 41 is hardly worth
the
> > money to put it in. That's around a 1.5 mph correction.
> > TIA
> > TJim

 

I corrected my reference site to:
http://go.jeep-xj.info/HowtoSpeedoGears.htm
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

TJim wrote:
>
> I know, Bill, but the chart is wrong for the SE as far as I know. My SE
> came with 29" tires and 4:11 gears and had a 40 tooth gear in it. The chart
> shows a 38 tooth.
> If I'm reading 64mph at 60mph and I have a 40 tooth gear, The speedometer
> cable is turning too fast and I need a larger gear. 40 * 64 / 60 = 42.67
> teeth.
> TJim

 

Looks good, Bill. The only thing I find distracting is the "Go Jeep" flag
on the mouse pointer, although, I never lost the pointer the whole time I
was checking out the page. ;)
So, it seams that, although I need a 42 tooth gear, the biggest one
available is 41 tooth, right?
Rats. Good thing I don't have bigger tires...
TJim

"L.W. (ßill) ------ III" <----------@***.net> wrote in message
news:3F0B3CF1.D8D5AD22@***.net...
> I corrected my reference site to:
> http://go.jeep-xj.info/HowtoSpeedoGears.htm
> God Bless America, ßill O|||||||O
> mailto:-------------------- http://www.----------.com/
>
> TJim wrote:
> >
> > I know, Bill, but the chart is wrong for the SE as far as I know. My SE
> > came with 29" tires and 4:11 gears and had a 40 tooth gear in it. The
chart
> > shows a 38 tooth.
> > If I'm reading 64mph at 60mph and I have a 40 tooth gear, The
speedometer
> > cable is turning too fast and I need a larger gear. 40 * 64 / 60 =
42.67
> > teeth.
> > TJim