View Full Version : 84 pitch pinions and spurs

November 7th, 2014, 02:38 PM
In preparation to start designing the 84 pitch pinion trees, I bought a few extra "oval racer sized" sets and put them in our web store.

http://www.mcpappyracing.com/store/product_images/f/685/IMG_5129m__22900_std.jpg (http://www.mcpappyracing.com/store/product_images/k/967/IMG_5129m__98908_zoom.jpg)
http://www.mcpappyracing.com/store/product_images/l/240/IMG_5131m__54036_thumb.jpg (http://www.mcpappyracing.com/store/product_images/e/704/IMG_5131m__50542_zoom.jpg)

84 pitch (84P) pinion/spur gears were released last year, but this is the first time they've been available large enough for oval racers. 84 pitch gears provide 2 slight advantages over 64P gears:

They are a little more efficient due to the decreased angle of attack on the teeth. You can feel the difference when comparing rolling 84P gears together versus 64P gears. The 84P gears are much smoother.
Secondly, when you make a single tooth pinion change, it's a smaller rollout change. This let's you fine tune the rollout a little better.

These are surprisingly less prone to stripping than you'd think because there are 2-3 teeth touching at all times. At IIC in Las Vegas this year, even some 1/12th open mod cars were using them, so they can handle the powerful motors.
The pinion gear set (http://www.mcpappyracing.com/store/products/84-Pitch-Pinion-Gear-Set.html) is a set of 19 pinions: 74T-92T (55-68T 64P equivalent)

The spur gears (http://www.mcpappyracing.com/store/products/84-Pitch-Spur-Gear.html) are:
148T (approximately 112T 64P equivalent)
150T (approximately 114T 64P equivalent)
152T (approximately 115T 64P equivalent)
154T (approximately 117T 64P equivalent)

February 19th, 2015, 02:21 PM
Could you please tell me how to calculate rollout on the 84 pitch gears. Most of the rollout numbers I run at local tracks vary from 3.71 to 4.24 with 64 pitch gears. I want to order 84 pitch gears and want to make sure the gears I am getting are relatively close to those rollout nos. Thanx and God Bless.

February 19th, 2015, 02:43 PM
It's the same formula as before. Nothing changes.
Tire Diameter x 3.14 x pinion / spur

To find the equivalent 84 pitch gear to a known 64 pitch gear:
There are approximately 32% more teeth on 84 pitch. So a quick and easy way is to multiply your 64P gear times 1.32.

Example, if you have a 112T 64P spur, and you want the 84P equivalent.
112 x 1.32 = 148

February 19th, 2015, 03:20 PM
Cool. Thanx for the quick response. Have a great day!!!!

February 23rd, 2015, 07:09 AM
Is there anything special I would need to do to get these big of gears to fit in my car? I have a problem fitting anything over a 60 tooth with a 96 spur gear (64 pitch) in my mcdominator. God Bless.

February 23rd, 2015, 02:00 PM
Sounds like you choose the wrong motor screw hole selections because our cars can fit huge gears. With that 96 spur, you can fit 80T pinion (64p). I recommend one motor screw on top, one on the bottom. For D3.5 motors, I take the apart and rotate the front 1/3 clockwise. Then in the car, I use diagonal motor screw selection. This allows the wiring tabs to be straight up and down.

February 23rd, 2015, 04:22 PM
You know your car best. I was using two screws in the bottom. Shouldn't be a problem now. Thanx James.