Getting new wheels, choosing correct size

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JimC said:
The weave has absolutely nothing to do with tire diameter. I’ve had the exact same issue, in reverse. Weave with a 19”, no weave with 18”. More likely a tire mounting issue.
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The 18" wheel was from my t140e and that didn't weave !!
It had a roadrunner tyre fitted but I can't remember the width it was maybe a 4.10 but as i said the bonnie never weaved when it was fitted
The wheel I fitted was a 19" CMA mag wheel ,as soon as I went out on it the difference was noticeable ,no weaving at all
I then took my original wheel an apprillia pegaso and had a 19" morrad rim laced to it and have never looked back ,
I can guarantee one thing all the tyres I fit are correctly fitted
The very worse the bike weaved was with the 17" X 130
 
baz said:
The 18" wheel was from my t140e and that didn't weave !!
It had a roadrunner tyre fitted but I can't remember the width it was maybe a 4.10 but as i said the bonnie never weaved when it was fitted
The wheel I fitted was a 19" CMA mag wheel ,as soon as I went out on it the difference was noticeable ,no weaving at all
I then took my original wheel an apprillia pegaso and had a 19" morrad rim laced to it and have never looked back ,
I can guarantee one thing all the tyres I fit are correctly fitted
The very worse the bike weaved was with the 17" X 130
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Not doubting you experiences, but as I commented earlier, I have had a weave with a 19” rear tire and no weave with a 18” rear. Considering there are many Commandos running a 18” rear I would say you experienced an anomaly. I seem to recall Matt Ranbow of CNW recommending a 18” rear. I do know an improperly mounted rear tire will create a weave at higher speeds. Weaving is not caused by tires having a different diameter . I do believe the isolatic suspension can exacerbate any tire or rim untrueness.
 
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I would say weave could be caused by a number of things, either separately or in combination. I run TT100's I spit in the face of weave
 
When you change the wheel size, you change the trail. Going from 19inch wheels to 18 inch on a Triton, makes the steering much less nimble - the bike tends to become more stable and run wide more in corners, rather than tighten it's line. If you are getting weave at speed you might be approaching a geometry where the steering can grab you by the throat. If the geometry and tyre sizes are correct, your bike should be rock-steady everywhere, regardless of whether it is quick or slow steering - no surprises. With a Commando, you also have the isolastics to consider.
 
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acotrel said:
When you change the wheel size, you change the trail. Going from 19inch wheels to 18 inch on a Triton, makes the steering much less nimble - the bike tends to become more stable and run wide more in corners, rather than tighten it's line. If you are getting weave at speed you might be approaching a geometry where the steering can grab you by the throat. If the geometry and tyre sizes are correct, your bike should be rock-steady everywhere, regardless of whether it is quick or slow steering - no surprises.
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While everything you said is true, the circumference of the 4.10-19 and a 120/90-18 are within a fraction of one another. I doubt you could tell the difference riding both unless you saw beforehand which was which.
 
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Peter Williams specified the steering geometry for the first Commandos . They crashed a few guys and were changed, so the second Commandos would have been more carefully tested. Whatever was specified for production after that, would probably be pretty good. So for wheel sizes and tyre sizes, I would go as close to standard as possible. Fat rear tyres on British bikes do not necessarily improve the handling if they change the rake on the steering head - thus alter the trail. Fat tyres on the rear of modern bikes have a lot to do with the way they handle heat. And in any case it is rare for a British bike to be spinning the rear wheel while cranked over in a turn. It is more normal to tip-toe around nimbly. I use 18 inch tyres - a 3.50 on the front of the Seeley with a 4.00 on the rear. As far as grip is concerned, I don't think width makes any difference. But grippy 19 inch tyres are not so easy to find in any width.
 
JimC said:
While everything you said is true, the circumference of the 4.10-19 and a 120/90-18 are within a fraction of one another. I doubt you could tell the difference riding both unless you saw beforehand which was which.
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I was very disappointed when I shortened the spokes of the wheels in my Triton and fitted 18 inch rims to fit better rubber. Where the bike was previously easy and nimble to ride fast around corners on Winton, It became heavy and exhausting and I was always dragging it away from the edge of the bitumen when coming out of corners. I used to get off the bike after racing on short circuits, feeling terrible. The return path to 19 inch wheels cost too much, however shortly afterwards decent 19 inch tyres became available. I sold the bike and built the Seeley. It is a totally different experience. - NO anxiety and it self-steers the right way in corners.

This is one of the things I never realised about steering geometry until very late in life, it takes virtually nothing to change it dramatically - very dangerous. Often all you need to do is wind the preload on the rear shocks up one notch and the handling changes.
 
The old guy who built my wheels has been at it forever and learned from his dad. He has had his fill with the poorer quality of the new Borani rims. He had to return most of the ones he took delivery of as woefully oblong and very poor seams.

I went with shouldered Excel WM3 and really like them.
 
Onder said:
I just had a 19" rear WM3 put on my Pender hub. SS Devon. Not the best choice in width probably but marginally better than WM2 and I wanted the utility of stainless. Devon (and nobody else as far as I know) doesnt do a WM4 or 5. You have to go alloy for that. And I really didnt want to get too involved in going non-stock for things like chain guards and mudguards.
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I did the same with my Mk3 rear hub - all stainless Devon WM3x18. In the front I junked the Norton hub and went with a KTM single disc hub, all stainless Devon WM2x18 (I really should have fitted WM3x18 in the front too). So, can you endorse the cushioned hub by Don Pender? It would be nice to read a review.

-Knut
 
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JimC said:
Why the negative for 18" rear rims?
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1. Central Wheel/stainless spokes supplied Akront 18" for my MKIII had a significant woop de do at the weld joint. This is about the time akront went out of business. Some may know those kind of warps can not be removed with spoke tweeks. I was not willing to go under the 25 ton press to try and straighten it. I used it for many years. (wheel for sale)
2. The final 18" wheel with tire felt very "heavy"
3. Now back to stock original steel type 3-1 nipple pattern. Feels nice on my daily driver.
4. 63 Atlas converted to 19" rear.
5. Many fatso rear wheel tire combos cause chain guard problems or for some???tweeking the wheel to the side to clear the chain guard???
For how much benefit beyond harley styling ego.
For a long time now (30 years?), I do all my own wheel building, and for NENO club member I teach spoked wheel building.
Future builds will prefer to be steel or Sun with precision machined accuracy.
 
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Tires of different sizes, widths, and weight will give a bike a slightly different feel, but there's no voodoo combination that does everything best, nor is there a voodoo combination that must be avoided.

I have an 110/90/18 rear tire that works great... (the 120/90/18 tire below came with the rim and I used it initially for mock up. It actually fit, but I didn't keep it)

Getting new wheels, choosing correct size


I also have a 100/90/19 that works great too... (this too was the original tire that was changed to an avon roadrider)

Getting new wheels, choosing correct size


Obviously, neither is a stock norton rim. (in fact the tires you see came with the rims and aren't the final tires which were switched to avon roadriders of the sizes mentioned above)

My point would be ALL tire choices have characteristics which are not always better (or worse) in every way.

A fatter tire is heavier so even though it may have more grip because of it's increased contact patch area, it also has a greater mass of unsprung weight so it transmits more force to the bike frame from the road.

A narrower front tire is lighter unsprung weight, more nimble, has a lighter feel at the handlebars, and is more precise. It has less contact patch area than a wider tire, so it has less grip.

There's a lot more of this kind of physics in tire choices, where each choice has advantages of one kind and disadvantages of another kind... That's pretty typical of physics... where a heavier rotating mass adds stability, but also upsets the bike more when it hits a bump in the road. The reverse is also true that a lighter rotating mass adds less stability, and upsets the bike's inertia less when it hits a bump in the road...

Depending on the kind of riding a person does, their "best" wheel set up could vary quite a bit... There are some given elements specific to commandos that constrain certain choices, but you can go in a lot of directions and get very good results... depending on knowing something about physics and where you want you bike's performance to be "best"
 
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I don’t recall the exact difference in tire circumference between a 4.10-19 and a 120/90-18, but it was less than ½ inch. That translates to 0.08 inch in ride height. There is 0.08 inch change between hot and cold tire, much less weight of load. This dog of weaving and big change in handling because of tire diameter 18” vs. 19” just won’t hunt. Hell, the difference in circumference with different brand of tires in the same size is probably greater than ½ inch
 
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Didn't see this come up when comparing 19" to 18" but unless the tires are the same manufacture and model there could very well be differences in construction and materials that could cause different ride characteristics.
 
o0norton0o said:
Tires of different sizes, widths, and weight will give a bike a slightly different feel, but there's no voodoo combination that does everything best, nor is there a voodoo combination that must be avoided.]

I disagree. Avon Roadriders in 100/90 x 19 on WM4 (2.5 inch) rims are the magic combination. Correct tyres on the correct rims. I wonder why Avon recommends this combo?
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o0norton0o said:
Tires of different sizes, widths, and weight will give a bike a slightly different feel, but there's no voodoo combination that does everything best, nor is there a voodoo combination that must be avoided.
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I disagree. Avon's recommendation gives light,precise steering and impeccable handling. 100/90 x 19 Roadriders on 2.5 inch rims at both ends.
 
Yup,100/90/19 Roadrider on a 2.50 rim in the front of mine too.

But I have a 4.00/18 on a 2.50 rim on the rear. Exactly the same rolling radius, but with 7.5mm tread depth instead of 5.6mm (what’s that, about 40% more?).

Very pleased with them.
 
Years ago I was running an Avon Super Venom, the then Avon bias ply tire, 100/90-19, with a WM2-19 rim on my 1972 Commando. The bike had a very pronounced weave somewhere around 90mph. I went through every suspension component on the bike. Bored the cradle, fitted an oversize spindle (interference fit), new cradle bushings honed to spindle size, new isos, new shocks, new wheel bearings, new headstock bearings. You name it, it was either new and/or checked out. Installed a steering dampener. Still had the weave. I just lived with it until the tire wore out. The replacement was the same Avon, same size. NO WEAVE! The original was mounted by a motorcycle shop (probably some drug addled kid on the tire machine), whereas the replacement was mounted by myself ( an addled quinquagenarian at the time). After the second Avon wore out I replaced the rim with a WM4-18 and a Dunlop bias ply D501?, 120/90-18. NO WEAVE! No perceivable difference in handling. About 3 times longer wear. The specifications of that 18" Dunlop had a circumference of less than 1/2 inch difference than the 19" Avon. That less than 1/2 inch circumference difference (<0.08 radius) does not affect trail, rake or any other measurable spec.
 
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