Art Webb wrote on 04/22/15 at 20:50:26:wonder what that corresponds to in metric sizing?
online converter says 104.5 mm, so probably 100/90/13 would be the modern equivalent
There are 25.4 mm in each inch.....so a 4.10 tire x 25.4 = 104.14 mm.
You need to be a little bit cautious about making those kind of conversions - you need to check the allowable rim width. The tire sizes shown in inches may be made for a different rim width than the equivalent metric tire. It is also important to check the rim width that a particular tire is made for. Most 150 width tires are made for a 3.50 rim and are not recommended for use on our 2.75 rear rim. Mounting a 150 on that rim will make a really arched tread....you will wear out the center too soon, and never be able to use the tread that is wrapped over on the side as a result of the tire being squeezed by the narrow rim.
I currently have a 90/90-18 tire on the front and a 110/80-18 rear tire on my Cafe' conversion.....and there is plenty of tire for the 30+ HP and torque. We currently are in a mindset of needing much wider tires than we really do......it's a visual thing induced by looking at custom cruisers and road racing 1,000cc superbikes......or 800 pound touring bikes.