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A while ago I won these 48 pitch gear sets made by trinity for the ultima & optima. I'm thinking of using one in my ultima runner but am having difficulties figuring out the gear ratio. Surely a gear ratio table existed but it didn't come with either set (which are still nip) and I couldn't find one online as well. I hope someone has the ratio sheet and can help me but failing that, is there a way to figure the final gear ratio if you know the gear's tooth number? (The problem is that the ultima still uses its original 32 pitch final pinion and diff gear).

The ratio on the 32 pitch version was 3.03:1. Then you had to multiply by your spur/pinion to get your final ratio. I would guess that the 48 pitch version would be close to the original.

(# diff gear teeth/ # top gear teeth) x (# large underdrive gear teeth/# small underdrive gear teeth) x (spur/pinion)

RichieRich wrote:I would guess that the 48 pitch version would be close to the original.

The counter gear in these sets are of different size so my guess (since these are overdrive & underdrive conversions) is that the final ratio will not be too close to the original.

RichieRich wrote:(# diff gear teeth/ # top gear teeth) x (# large underdrive gear teeth/# small underdrive gear teeth) x (spur/pinion)

Not sure I understand some of those definitions, so just to be clear:
(your definition=name in manual)
top gear=final pinion gear
large underdrive gear=counter gear (the gear mounted on the same shaft as the final pinion gear)
small underdrive gear=the small gear molded with the spur gear (center gear in manual)

did I get it right?

Snake Plissken wrote:...is there a way to figure the final gear ratio if you know the gear's tooth number? (The problem is that the ultima still uses its original 32 pitch final pinion and diff gear).

It's pretty easy, pitches don't matter: just count the number of teeth on the diff, than divide that by the number of teeth on the small gear which makes the diff turn. Multiply that by the nr of teeth on the same axle : on the outside. Divide this by the small gear nr on the back of the spur. Multiply that by the nr on the package 62, or 66. Now you got your gearbox ratio. You should divide it by the pinion count to get final drive ration, and don't forget, the larger the tires, the smaller the pinion you'll need

You could also mark your tires, roll the car fwd 1 turn of the wheels and count how many tours your pinion have made during this roll.
Just compare it to another car for which you know the ration is good and gear up or down accordingly. (I believe Kenooze has the ratio table for this gearbox by the way)


If you don't plan using both sets, I'd be happy to take either one from you.
Send me a PM.
eitherway: do me a favour and put up a picture of our Ultima, thanks in advance.

Mr. ED wrote: eitherway: do me a favour and put up a picture of our Ultima, thanks in advance.

A quick search of TC will find it
http://www.tamiyaclub.com/showroom_model.asp?cid=56960&sid=1147

Thanks Mr. Ed, I'll have a shot at calculating the gear ratio. Just to be on the safe side I'll try the stock gears first and see if I get a 3.03 ratio.
Regarding the gear sets: sorry, one goes to the Ultima and the other will go to my Optima Pro long term project (long term=parts sitting in a box waiting for me to finish other projects).
The link terry.sc provided is indeed of my Ultima, but the body doesn't look so new now and I also installed proline 2.2" tires for better grip on the local track (hard packed). There should be another vintage meeting within the next couple of weeks, I'll take some pics then and post them.

Snake Plissken wrote:

RichieRich wrote: top gear=final pinion gear
large underdrive gear=counter gear (the gear mounted on the same shaft as the final pinion gear)
small underdrive gear=the small gear molded with the spur gear (center gear in manual)

did I get it right?

Correct! Don't forget to count 2 or 3 times. I swear, my eyes start playing tricks on me when counting teeth. Did I start here? Did I already count that one?

Ah sorry I didn't realize this was Snake's car. I actually put the most recent comment aside it about 4 weeks ago LOL

Awesome body!

OK, I just spent 30 minutes counting gears and calculating ratios and thought I'll post my findings here in case someone else would need this info.

For the 62T underdrive set the ratio is 3.03 (same as stock)
For the 66T overdrive set the ratio is 2.53
in order to get the final gear ratios these number need to be multiplied by the spur (62T or 66T) and divided to the pinion teeth number.

Excellent! This is great info to have. I've always wondered about the gearing for the Ultima. To me, it always seemed kinda high so you'd have to run a really small pinion. I can't understand why anyone would want to run the overdrive gears (maybe for oval?). Think about it, a 2.53 tranny and a 66 tooth spur? Yikes, I smell burnt motor.

A larger spur allows you to use smaller pinions and still reach the spur. Doing so will bring the final ration for both closer agian, so that makes sense.
My guess: the overdrive kit was intended for stock moters.

I never had any issue with the gear ratio:

On one of mine I'm using the ultima pro 48dp spur, which admitted, is a little larger than the original 32dp, and yes; it has only about 12 teeth on the pinion... But hey that's a truck with massive wheels:
http://www.rc10talk.com/viewtopic.php?t=767&highlight=

My other truck:
http://www.rc10talk.com/viewtopic.php?t=663&highlight=
has the normal size truck tires, and a Tufnol 'overdrive' spur: bit smaller than normal. But it still works very well with a 14 teeth pinion.

If you use the typical winds of those days finding a small enough pinion should never be an issue with buggy tires.

(My trucks have a standard moter with 9.6 volt pack for the monster, and an 18 quad motor and 7.2 volts for the racing truck.)