Bigger Tire

Can I get a few MPH out of a bigger tire and will it fit?

Stock Tire, a spare rear rim and tire.

Trying a 2.5 inch tire:

Stock tire has a circumference of 58.25 inches. This tire has a circumference of 61.25 inches.

At 10,000 RPM the stock tire would give us:

38.79 MPH = 10,000 RPM * 58.25 / (14.220 overall engine gear ratio * 12 in/ft * 5280 ft/mile) * 60 minutes/hour

The bigger tire would give us

40.79 MPH = 10,000 RPM * 61.25 / (14.220 * 12 in/ft * 5280 ft/mile) * 60 minutes/hour

This tire would be good for roughly 2 MPH gain, assuming the motor has the power.

Tire is from Treatland.tv. 

Motion Pro spoons to put the tire on. These Moped tires are very easy to put on compared to changing dirt bike tires. I have even done them with my plastic bicycle spoons.

Mocking it up on a spare engine, it's really close.

Really have to think about where the magneto wires are going to run.

Looking at the scooter, I don't think it will work with the back fender on.

Back fender is already tight on the stock tire.

I did have to modify the rear fender a little bit. The back bracket was easy, I just bent it a little bit and bolted it down at a different angle. The front, I re-drilled the location of the bolt for the front bracket, to move the fender up and over one of the ridges on the motor. It clears the back tire, not by much, but it does clear.

Not a lot of room to spare, but after weeks of running this, it hasn't ripped the back fender off.

There was a big benefit. The Honda Express was really sketchy at 50 MPH (Yes, I have the poor little motor spinning over 13K, it's not making much power up there, but enough.) Putting the bigger back tire on it helped. The 2.5-14 tire only raises the back by about an inch, but I think that must put a little bit of pressure on the front wheel, since the stability at high speed improved significantly. This makes me want to find a shock with adjustable sag, that I can experiment with.

Also, some later Honda Express's came with a 40 MPH speedometer rather than a 30 MPH speedometer. This is a direct drop in replacement. With the bigger tire, the GPS and speedometer are pretty close. Even at speeds beyond 40 MPH, the speedometer seems behaved and you can tell whether if you are running 45 or 50.