Spoked wheels for cafe-racer. Rims and spokes.

In customizing wheels command how the motorcycle  will look, and it requires experience and knowledge to hit the bull’ eye and get perfect wheels. Especially when it comes to making spoked wheels for bikes that never were intended to have ones. For the two decades with motorcycles I’ve got a pretty large luggage of knowledge and a lot of opportunities to hone my skills.

Tires dimensions are not the least thing in wheels. Range of suitable tires depends on rim size: diameter and width. One also has to remember that one couldn’t put a wide low profile tire on a narrow rim, as well as a narrow tire on a wide rim. Or, even if one managed to do such a thing, the result would be ridiculous. So, when one starts to build custom wheels for the project bike the most important thing is to have a clear idea about tires so the choice of rims could be done.

For example, when I was working on wheels for my own CB750 Seven fifty cafe-racer I wanted  wide and high profile 17″ tire for the rear wheel (160/70 is the maximum) while for the front wheel I planned 120/80-17″ tire. 160/70-17 tire means at least a 4.00″ wide rim, but I decided that it’s better to use a 4.25″  rim. For the front wheel I had additional restriction: I wanted to cut off possibility to install 120/70 tire. Thus I chose a 2.50″ rim which perfectly fits a 120/80 tire but is unsuitable for a low profile tire of the same width.

Another example will explain how rim diameter may affect wheel look. let’s compare two rims, 18×4.25 and 17×4.25. The widest applicable tire for 18×4.25 is 160/60×17″. Let’s choose a tire of the same width but of higher height for 17″ rim: an 160/70-17″ from the first example.

It’s well known that the number between / and X means height of tire counted in percents from its width.

Now let’s calculate the wheels’ actual diameters.

Rim diameters:  18″=457.2mm, 17″=431.8mm

Tire height for 160/60 it’s = 160*0.6 = 96mm while for 160/70 it’s = 160*0.7 = 112mm

Wheel diameter = rim diameter + 2*tire height

Thus 160/60-18 actual diameter would be 457.2+2*96=649.2mm

While 160/70-17 actual diameter would be 431.8+2*112=655.8mm

So 160/70-17″ wheel is actually bigger than 160/60-18″ wheel. Moreover, 17″  would look fatter as tire height is bigger while rim diameter  is smaller. Or in other words, 18″ wheel in comparison to a 17″ wheel will look like a ring in comparison to donut.

Thus, we discussed all these details with Kris (KrisBiker) when he was ordering from Gazzz-garage custom made spoked wheels for his Honda CB750 Spider cafe-racer. I consulted him on rims’ and tires’ sizes. To achieve the desirable effect I chose for him 17×3.00″ front rim (130/80-17″ tire), 17×4.25″ rear rim (160/70-17″ tire).

According to Kris’ plan rims had to be black, but freedom of manufacture choice was on me.  Sure, I chose Takasago Excel black anodized rims without any hesitation.

I ordered from  Excel black anodized rims and galvanized steel spokes from a renowned UK manufacturer in aforesaid dimensions drilled to fit my Comstar conversion hubs. Due to Covid quarantine in the UK fulfillment of the order took longer than usual. However when rims arrived, it was clear from the first sight that I made the pretty right choice.

Needless to say, that I calculated parameters of spokes as well. When spokes arrived, I found out that in my craving for ultimate precision I made them a bit too tight. They’d fit bare aluminum adapters OK, but hubs had to be black, so I faced the possibility of scratching the anodized surface of adapters in the process of installing spokes.

I didn’t like such an idea, so I reordered spokes of adjusted configuration.  And once I got spokes that fit hubs perfectly I was ready to wheels initial assembling.

To be continued.

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