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I'm trying to run oval against these modern cars. They are running mainly 2.4 trans. I've been running a RPM 2.65 (has 17t top gear). My buddy was running a 58/104 on his 2.4. I know there is a chart out there but what's a good starting point to run the RC10 against these cats?

104/58 = 1.93 x 2.40 = 4.62

102/58 = 1.76 x 2.65 = 4.66

100/57 = 1.75 x 2.65 = 4.65

The formula for calculating gear ratios looks like this:
(# Teeth on spur divided by # teeth on pinion) multiplied by Internal Gearbox Ratio = Gear Ratio

Gear ratios are most often quoted in the form “2.4 to 1”, this can be represented in writing as 2.4:1. This means that the motor must rotate 2.4 times for the car’s driven wheels to complete one full revolution. Most instruction manuals should tell you the internal ratio of your car’s gearbox (some gearboxes have it stamped on them).

I've already seen how gear ratios can be represented as numbers (e.g. 7.8:1). The tricky part is in describing ratio changes in general. If you put a bigger pinion on the car, the ratio will change to a small number (say 7.4:1). Whilst the numerical figure has become smaller, the actual gear ratio 7.4:1 is said to be a ‘higher’ ratio than ‘7.8:1’. Similarly, moving to a smaller pinion will produce a ‘lower’ ratio (say 8.2:1). Without wanting to confuse you, changing the spur gear has the opposite effect. A smaller spur gear will result in a ‘higher’ gear ratio, and a larger spur gear will give you a ‘lower’ gear ratio. Confused? Stay with me.

Gear ratio changes do a couple of things. Let’s look at both the ‘lower’ and ‘higher’ gear ratios separately to see what we find.

A lower gear ratio will mostly give you more run time and more acceleration. It’s also generally easier on your motor.

A higher gear ratio will generally give you more top speed, and less run time. It’s also tougher on your motor. Once you get to a certain ratio point (lets call it the ‘optimum ratio’) continuing to change to a higher ratio will do nothing but damage. It will result in your motor overheating and being damaged, and in extreme cases, your car may actually go slower.

How’s that. Did you understand it all? Have another read, and think about it carefully. Then look at this simple chart, which might help make things clearer.

Pinion----------Spur Gear----------Ratio----------Gearing----------Top Speed----------Acceleration----------Run Time----------Motor
bigger.................smaller...............higher................up....................more........................less........................less..................harder
smaller...............bigger.................lower...............down..................less........................more......................more.................better

I understand, but I knew there was a chart out there. We used to have one. The original goal was to find one to bounce off these other guys with their ratios. But I have downloaded the calculator and since then my ratio and roll out is about where it needs to be.

Here's a generic 64p chart so it doesn't have the FDR. You could simply finish the math according to what transmission ratio your'e using.
http://www.rctek.com/pdf/gearing_chart_64_pitch_electric.pdf

If you weren't using 64p, I'd tell you to go to http://www.gearmachine.net That site will actually calculate the FRD for whatever transmission you're running and produce a custom chart in the pinion and spur range you want.

What they said...or get your pinion gear to spin the same number of times around for every one rear tire revolution.

(assuming you guys are running similar tire and motor sizes)

If you have an IPhone you can download the GearIt app. Not sure what the app for android phones is called but I know there is an app for that platform too. You can even add cars to the list.

Even my motor guy uses the gear it app,

I have a gear app that figures that out and roll out.

You can use that to compare final drive ratios if you are looking to gear the same as them.

How about these?
From a small Reedy wallet-sized chart I found in my carp the other day.....

Alex

I didn't think you could fit anything larger than 84 on a stealth.

RC10th wrote:I didn't think you could fit anything larger than 84 on a stealth.

90 under stock gear cover, 93 under RPM covers

I don't remember that big but it has been a while. Handy to know as I have a white 87T gear I want to run on my OIN.

Crap - I rembered I ordered a VTS slipper so that idea is out the window unless I buy a Yokomo special gear which are white in color with the hex shaped pads.