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Monday, December 21, 2015

Figuring out the gearing

So I misspoke about the smaller engine sprocket helping to lower my highway rpm's. The smaller motor sprocket would help me get off the line, but raise my highway rpms.

So let's start back again with the long story of my gear ratios. (I'm using calculations and images from Bakers RPM Calculator.) This was my first build set-up. It worked fine, but I wanted to drop my 70 mph rpm just a bit.

I'm running a light rigid bike with 93 inch motor with T&O torque monster wheels.  Even with a high ratio FX first gear, I think I have plenty of torque to get going off the line with higher gearing overall.

This was my first plan. Drop the rear sprocket to 46 teeth and the rpm drops about 120.

But then when I was doing the swap over, Ed didn't like the condition of the 24 tooth sprocket I was running. The only sprocket available in town on Monday was a 23 tooth. So we did that and I was exactly where I started.

So now where am I going to be with a 39 out front? Way up to 2945 rpm. That's 80 higher than I was when I wanted to go down.

So let's look at a 24 or 25 on the transmission. I'm thinking the 25 is what I need. Usually, a sprocket that big could be a clearance issue but with the open belt set-up I'm running it should be fine.

1 comment:

  1. I run a 25 gearbox (trans) sprocket with 48 on the back and it is just right for one up riding
    longer legs throughout the gears and a great motorway speed (80+)
    first 40 second 60 third 90? 4th who knows.
    1340 shovel with a j grind cam