I Ordered some different Size Idler gears for the afx Chassis. What is stock ??? If I run a 20 tooth instead of a 26 would my car be better on take off and less top end or the other way around ?? I always get confused on this. Appreciate any input. Thanx guys.

I thought all the AFX idler gears were 14 tooth...
Unless you are refering to the 4 gear chassis.....
Other sizes will not work on a regular AFX...
You are talking about the middle gear on top right?
(The one under the clamp)
http://users.aol.com/hifisapien/private/afxtop.jpg

Not to be confused with a 4 gear chassis.
(which has two idler gears...)
http://users.aol.com/hifisapien/private/afxstop.jpg

yes, The middle gear on the top.They were described as 20 and 26 tooth gears for Aurora afx chassis. They are brass with large size holes. Guess I will see when they get here and will let you know. $2 for 8 of them. Thanx

[QUOTE=noddaz]I thought all the AFX idler gears were 14 tooth...
Unless you are refering to the 4 gear chassis.....


Noddaz, count the teeth of the gear pressed on to the arm of the reg afx. 14 teeth, right? seems kinda small for an idler gear. :wave:

Changing the idler gear on TJet/AFX (or both idler gears on a 4 gear chassis) would have absolutely no affect at all on the gear ratio between the armature pinion and the top gear on the cluster shaft. Idler gears never affect the gear ratio, they are used to change the direction of rotation or to deal with physical drivetrain offset issues. Incidentally, that's why they are called idler gears.

Makes sense to me! The pinion and top gear will always have 1 tooth engaged each into the idler gear. When the pinion gear moves 1 tooth, they all have to move 1 tooth down the line! The crown gear is a different animal all together. :)

For more on gears and how to calculate ratios for pancake chassis see:

http://virtualgarage.net/Automobilia/Miniatures/SlotCars/ModelMath.shtml

It's been up for years and no one has corrected my math yet.

Or you can do the math... say you had a pinion gear with 12 teeth, an idler gear with 24, and a drive gear with 36 teeth the total gear ratio is 12/24 x 24/36 = 1/3 which is exactly the same as the ratio would be without the idler gear 12/36 = 1/3. If you put in a 48 tooth idler gear and redo the math it is now 12/48 x 48/36 = 1/3 again. Put another way, the idler gear always cancels itself out because it divides the gear ratio on one side by the same amount that it multiplies the gear ratio on the other. It factors itself out.

You can change the crown gear on the rear axle of a magnatraction. I currently run 4 different gears in the back end, depending on the application. The standard crown gear in a magnatraction has 15 teeth on it. The hop up gear that was sold by AFX has 19 teeth. This creates a lower axle ratio for faster take off but less top end speed. Just like changing gears on a bicycle you start off in the easiest gear but that gear would not give you much top speed. I also use the 22 tooth gear from a Tomy Turbo, depending on the application and a 25 tooth gear from a G-Plus (with a little chassis cutting). The 25 tooth gear works great for my Quadralam armature that spins to 68,000 rpm but has low end power as a stock armature that spins slower but has more torque. By the end of my 16 foot track, the Quadralam is still accelerating while a stock-arm car has already topped out. I find that the mean green arms work best with the 19 or 22 tooth gears. The lower ratios also work well with the Truck/trailers as they give the trucks more launch and the lower top speed is negligible as they cant be driven that fast anyway. I find it useless to use the lower axles with the stock arms as they reach their lower top speed too soon and are out run by anything racing them. This is why the 4-gear specialty chassis are not as fast (top speed). The gearing is way lower due to the extra gearing. They take off ok but reach a lower top speed.

VirtualGarage.Net does a concise job of presenting the calculations. Maybe they can add the armature RPM calculation that was asked about on another thread.

Wasn't the specific question about the effect of changing the number of teeth on the idler gear? The answer is that it has absolutely no effect. If you're paying more money for "special high performance" idler gears that have more or fewer teeth you are getting ripped. The only performance improvements you can get from idler gears are 1) reduce the friction by improving the gear mesh, or 2) lighten the gear (drilling it out or change to a lighter material) which moves the chassis' center of mass lower and lightens the chassis.

Im not sure what chemical may have been in my body on the day I asked this question. In further correspondence with "GEARMAN" Ive found out that these are for the 4-gear chassis or specialty chassis as he called them. Anyway I replaced some worn ones and got a few extra. Thanks for that formula to figure ratio.

I have run everything from the stock 15 tooth crown gear up to a 25 tooth G plus gear shoe-horned into an AFX magnatraction. It depends on the arm and the magnets and of course the application. For short tracks, the bigger the crown gear the better. For long tracks you don't want it to top out too soon and feel flat so go with the smaller crown.
JL magnets are thick and don't allow room for a G-plus gear so you need strong AFX magnets.
A strong mean green arm and a 25 tooth G plus gear is great for sliding the back end out whenever you want in a curve, but in a long straight over 15 feet will top out.
The higher revving arms need the lower gears (bigger crown gears) to make use of the higher revs. The stock 19 tooth hop up is nowhere near enough for the quadralam even on a long track.
For the semi trucks, I use my old G Plus chassis that still have lots of torque but not as much top end which you can't use in them anyway. The front ends don't bounce up and down on take off with the G chassis like they do with a magnatraction.