Front Sprockets

As mentioned in the last post, I need to "gear up" the bike in order to see speeds over 52mph, the rating of the bike at 10,000rpm with stock tire and gearing. The slightly taller rear tire will help a little, but I knew I would need to make changes to the sprockets. In stock fashion, the bike uses a 14T front sprocket and a 40T rear sprocket, giving it a final drive of 2.85:1.

I began searching for bigger front sprockets, but found it difficult to find items marked for use on the C100/110 engine. Most sprockets are tagged for XR50s, or CT70s etc. I got lucky the other day and found a Honda Passport (C70) site that gave a listing of other Honda models that used the same sprockets. It included the C100, along with a dozen other small Hondas like the CL70, XR80, ATC70, S65 etc.

So, I started searching for sprockets for some of these other Honda models. I came across Beatrice Cycles ( http://dratv.com/index.html ) which happens to have an excellent breakdown of parts, categorized by model and major component. If you want electrical parts for your ATC110, they've got it. Likewise suspension parts for your Z50.

I searched around the C70 page, and found that they offered 15T, 16T, and 17T front sprockets. I bought one of each, along with a few extra tire tubes (for the red wheels.) Everything arrived at my door within 3 days. I quickly ran out to the garage and confirmed that yes, these sprockets do fit the early pushrod motors.


From L to R: 14T, 15T, 16T, 17T


Based on my gearing calculation spreadsheet, these sprockets should give me a range of speed from 55 to 67mph in 4th gear at 10,000rpm. I plan on building up both the C110 4-speed engine, as well as a 3-speed C100 engine, which has a slightly shorter top gear.

Perhaps I'm spending too much time worried about this one subject, but given the fact Bonneville is at much higher elevation, I wanted to have plenty of options for fiddling with gearing. A few hundred rpm could make a difference, especially when your only dealing with 5.5 to 6hp!

C'