Rim width vs tire size and style

lcrken said:

These pictures are from my Commando with 100/90-19 Roadrunners on stock WM2 rims front and rear. They handle really well, and both my grandson and I like the way it drops into turns so easily. As Fullauto said, you do end up with large chicken strips at the edge of the tire. These pics are from a bike that has ground the rubber off the ends of both footpegs, and that's as far as you can safely lean it. I thought about putting folding pegs on, but I like the idea of having a soft limiter like the rubber.

Ken

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So, in effect, you have an 80/90 Roadrider because of the unused portion of the tread? My point being that you lose the same amount by using a 120 section tyre on a too narrow rim, turning your 120 into a defacto 100!

Fullauto said:

Good question, Ed! Normally, I would get about 4000 miles out of the rear. But that's after it's already done the same mileage on the front. So, I go through one tyre in 4000 miles. My current tyres are over four and a half years old and are looking pretty good after 3500 miles. Maybe because of the age related hardness?

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That is about right.
I just did a 3026 mile trip on the Skyline PW, Blue Ridge PW , Smokey Mountain/ Deals Gap, Then down to Leeds Alabama to the Barber Motorsport Museum then came back a similar way. I put an old Super Venom on the rear just to use it up, as it was getting past its recommended service life. (a Bit) :roll: My rear tire is burnt out on the return to home. I personally think the AM26 are better but I did 6050 miles on a fresh tire to when it needed to be changed (for the rear tire). Another thread for the trip will follow. 8) I know it didn't happen if there are no picx.
Cheers,
Thomas
CNN

Fullauto said:

So, in effect, you have an 80/90 Roadrider because of the unused portion of the tread? My point being that you lose the same amount by using a 120 section tyre on a too narrow rim, turning your 120 into a defacto 100!

Click to expand...

I think that's probably correct. I think the tires would work best on wider rims, but they work so well on these rims that we didn't think it worth the expense of new rims and spokes. The bike was built from a basket case, and we tried to use up as many old parts as possible from the stuff I have accumulated over the years. I think we will eventually go to wider shouldered alloy rims with stainless spokes, but more for cosmetic reasons (meaning I like the way they look) than for performance. Once you're at the point of dragging the pegs, more tire isn't going to get you anything. And as long as Avon doesn't make a rear Roadrider in a 120-19, that's not an issue I have to be concerned about. On my other MK3, I will be using wider rims (3.00 rear and 2.50 front) to suit the available tires, but they don't have the same issue of tire availability, because they are 18".

Ken

The link I posted explained it pretty well. The point of having the recommended rim for a certain tire is so that the tire's designed profile shape is maintained so when the bike is leaned into a turn the contact patch area of the tire actually increases which gives you a better grip on the road. If the tire's profile is changed due to being mounted on a narrower rim, you probably lose some of the contact area, and some grip as well.

Although small, I think this picture gives a good visual explanation of the importance of maintaining tire profile shape.



I know which tire sizes I am going to buy now after reading this thread and doing some research... I can see that there's no point in mounting a 120 tire on my WM3 rear rim because I will only use 110 of it anyway, and also I will be diminishing the contact area by changing the 120 tire's intended profile by mounting it on a narrower rim.

So I am going:
Front WM2 - 100/90/19
Rear WM3- 110/90/18