Which speedo gear?

[cactushorse]

I'm ordering some parts on monday and need to know which gear to get for my 33's Help a brother out

 

[Viperwolf1]

It depends on many factors. Best solution is to figure out how far off your speedo is off now (in percent) and see how many teeth you have on your current gear. Each additional tooth will be a 5-6% change so if you figure your speedo is 20% low you'll need about 4 fewer teeth on the gear.

 

[Broncobowsher]

I'm ordering some parts on monday and need to know which gear to get for my 33's Help a brother out

Since there are 2 different possible drive gear tooth counts, that would mean there could be 2 different driven gear choices. So just throwing a number out there, like 16, may or may not be right. Axle ratio is another consideration, that also has a huge influance. Then there are some combonations that you can't get the right number of teeth, they just don't make gears with that few (or in other cases that many) teeth on them.

You need to know the percentage error you have now and the current gear you have now. If you have no gear at all, you will need to find one and put it in and get a baseline. Once you have the % error and the number of driven teeth it is easy.

Example:
18 teeth
speedo reads 10% slower then actual.
Multiply the error (10% ) and the number of current teeth (18) and you get the number of teeth you need to change the gear (this case 1.8). you will have to round as you can't have a fraction of a tooth so we will call it 2 teeth.
To make the speedometer read faster, use fewer driven teeth
To make a speedometer read slower, use more.
We want faster, so subtract the 2 from the current 18 and you get a 16 tooth desired gear.

16 tooth is the smallest you can get, 22 or 23 is the largest. After that you are visiting your local speedo shop and getting a custom inline converter box.

 

[cactushorse]

Thanks for the info. I thought it would be as easy as "get xx gear" . Guess i will have to wait until it's back on the road.

 

[freeheelbillie]

I'm ordering some parts on monday and need to know which gear to get for my 33's Help a brother out

This takes the guess work out of it... http://www.corral.net/tech/gearcalc.html

 

[Broncobowsher]

This takes the guess work out of it... http://www.corral.net/tech/gearcalc.html

How does that take the guesswork out? That is a simple MPH/RPM/gear ratio calculater. Nothing to do with speedometer gears.

 

[needabronco]

I did the percentage method, and figured the percentage from a stock (28") tire to my newer 34" tires. With 34" measured tires an AOD, and 4.88's I ended up with the largest available gear, my speedo is off a max of 1-2 MPH depending on the speed I'm going. At 50 it's dead on, 70 it actually going 71, at 75 its dead on again. All GPS verified.

 

[freeheelbillie]

How does that take the guesswork out? That is a simple MPH/RPM/gear ratio calculator. Nothing to do with speedometer gears.

oops wrong one. I know the Jeff's Bronco Graveyard paper catalog has a formula in it, I assumed that was the link. Try this one http://www.wallaceracing.com/speedo-calculator.php

 

[Viperwolf1]

oops wrong one. I know the Jeff's Bronco Graveyard paper catalog has a formula in it, I assumed that was the link. Try this one http://www.wallaceracing.com/speedo-calculator.php

Still need to know the correct speedo drive gear tooth count which is difficult to determine without disassembling the tcase.

Best bet is to trust the math and measurements.

 

[DirtDonk]

...Guess i will have to wait until it's back on the road.

Well at least the good news is that it's only a 5 minute job after you figure out which one.
And even if you have to order it from someone through the mail, it's so light that shipping isn't (or shouldn't be) a big concern.

Paul

 

[freeheelbillie]

Still need to know the correct speedo drive gear tooth count which is difficult to determine without disassembling the tcase.

Best bet is to trust the math and measurements.

Old Tire diameter X Old speedo gear divided by New Tire Diameter = New Spedo gear.

 

[Broncobowsher]

Old Tire diameter X Old speedo gear divided by New Tire Diameter = New Spedo gear.

Providing the old was right to begin with

 

[freeheelbillie]

Providing the old was right to begin with

Well theres the tried and true, wait till you get a speeding ticket...
MPH provided by, Buford T. Justice = actual speed.