Art Webb wrote on 04/22/15 at 20:50:26:


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.

It is a mistake I made on my first rear tire.  I followed the herd and installed a 130/70-18 tire on the 18x2.50 rear rim.  I wore out the center of the tread in 4,000 miles and there was tread wrapped over on the side of the tire I couldn't possible lean over far enough to use.  A 130/70-18 tire belongs on a 18x3.50 rim.

If you want a wider tire....you really need a wider rim to match.

Dave wrote on 04/23/15 at 08:29:58:

I wore out the center of the tread in 4,000 miles and there was tread wrapped over on the side of the tire I couldn't possible lean over far enough to use.

Also keep in mind that while modern sport bike tires use dual - or even triple - compounds (soft at the edge, hard in the center) to evenly distribute wear and improve handling at the limit; the tires available for for a stock S40 (15-inch rim) or even the cafe conversions (18-inch rim) are old-tech single compounds. Unless you spend a third of your time in left hand turns,  a third in right hand turns and a third in straight-line cruising - you'll never get even wear on a single compound tire.

The one advantage I can think of (if you like this characteristic) with a pinched tire is faster rotation from straight-up to leaned over due to the more rounded radius of the tire. This characteristic might be less desirable on an S40 then on a cafe racer.

As I gain confidence on my cafe racer I notice the chicken strips on my rear getting smaller and smaller.

I was not aware of the Pirelli Sport Demons or the Bridgestone Battlax BT45. It's nice to know there are options besides the Kendra 671's I got from RYCA.

Let us know what you think of the BT45's.