Coker e70p/rim size question

[Dr. Stupid]

Hey guys, i have a question about tire/rim sizes on my CB360. I'm totally sold on on the Coker e70p tires, and planning to get MikesXS shouldered aluminum rims.

The 3.25 and 3.50x18" e70p's are recommended for use with 1.85-2.00" rims. The MikesXS rims only come in 1.85" and 2.15". If I went 2.15" front and rear, could I use the 3.25" and 3.50" e70p tires safely? Or would the rims spread the tires to where they're unsafe? Should I just use 1.85" rims front and rear, and deal with the narrower contact patch?

Sorry if this is a total noob question, but this is my first build, and I want to make sure I buy right the first time. Thanks in advance for any help!

 

[crazypj]

I have no idea what Coker e70 tyres are but they will be fine on 1.85 and 2.15 rims

 

[crazypj]

OK, I Google'd them. Looks like a copy of Dunlop K70 8)
Should work quite well and look way better than sidecar tyres people want to fit )Firestone)

 

[Dr. Stupid]

Thanks crazypj! I know you're the resident expert with the MikesXS rims, so I was hoping you'd chime in.

Just to be sure I understand, should I go with the 3.25 front and 3.5 rear, with a 1.85 front and a 2.15 rear rim? I was hoping to go 2.15 f/r, so if there's a better size combo you'd recommend, I'm all ears. I'm not familiar with the Dunlop K70, so pardon my ignorance. Just trying to go a smidge larger front and rear, and keep the ride safe and stable.

 

[jpmobius]

Those sizes should be fine. It is not the case that you can't fit a larger front rim, and practically any size tire can be physically mounted on any size rim (within reason). But just because you can physically mount the tires doesn't mean everything is ok. The shape of the tire is dramatically affected by the rim width. A skinny tire on a wide rim flattens the tread out into a more gradual arc and can make it easy to lean the bike over to the very edge of the tread. Too fat a tire on a skinny rim pulls the sides of the tread in to where you will never lean the bike over far enough to ever use edge. More importantly, either way the tire is not supported in the fashion the designer had in mind, and how that flexible air filled doughnut is attached to your bike is important. The right size rim with the right size tire. Too wide a rim and consequently bigger tire on the front (or rear) doesn't necessarily make a bike unsafe, but you don't have to deviate very far from stock to make very noticeable changes in how the bike drives. Heck, same size tires from different manufacturers can make a giant change. You had commented that you were concerned with the speed rating of the tire. Mass of the front end of your bike of which the tire is a large component thereof, is of far greater concern. The combination of tire flex and steering geometry make motorcycles inherently unstable. Adding mass to the front end lowers its natural frequency, which means a bike will tend to become more unstable at lower speeds the more mass that gets added to the front. Probably not a real issue with your 360, but lighter is still better, especially in the front.

 

[crazypj]

Use WM3 front and rear but stick with the smaller tyres.
The front will spread a little further but it will look and handle just fine.
You could fit a 3.50 front and 4.00 rear but steering will be very different