What tires will fit my stock WM2 rims?

I have searched this forum and many others to try and find an answer to my question, so I wanted to get that out there before anyone decides to 'flame me' with nasty messages. There is a lot of conflicting information and stories about what will and won't fit on my rims.

I have a '75 MkIII with the original 19" WM2 rims front and back. I would like an alternative to the K81 tire- and don't want to change the rims. I definitely don't want to go to an 18" rear. Several say the AM26 RoadRider is too wide for the WM2 rim, but others say it's fine. I can't find another tire available in 100/90 or 4.10-19. In fact the RoadRider shows to be only available in 90/90 on the Avon website. The AM9 RoadRunner would've been my first choice but no one has it and it seems to be out of production. There seem to be some other tires that can be had in 100/90-19 like the Avon Cobra but they all have tread patterns that I think would look wrong on my 850 and none are available in that size as a rear tire.

This is awfully frustrating. I've got 2 of my own Commandos to get ready for spring and another two that belong to a friend....they all need new tires before we're going to ride them this year, and I have spent hours trying to figure out what choices I have outside the K81s. I don't mind those too much for the kind of riding I do, but my buddy hates them.

On my Mk3 I have a 325x19 Avon Roadrider on the front with a 100/90x19 Avon Roadrider on the back.

possm said:

On my Mk3 I have a 325x19 Avon Roadrider on the front with a 100/90x19 Avon Roadrider on the back.

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Are those on original WM2 rims? I'm reading that the 1.85" of these rims do not fit well with the 100/90x19 tire.....haven't seen it with my own eyes but there are many descriptions of the tire not looking right and the tread not completely touching ground because the rim is too narrow. This is what has me worried about trying to put them on the WM2 rims.

There are a gazzilion British bikes using the 100/90x19 Avon rear tyre on a WM2 rear rim without a problem. Ignore the naysayers. The Avons are great tyres on a Commando.

Just because its not on the Avon recommended list of WM's does not mean its going to fit, if that was so then my tyres have been on the wrong rims for 25 years.

Currently RR 90/90 19 front RR 100/90 19 on rear, have a set of RR2's with same numbers ready to go on as replacements.

This is for mine (19/18 combo) but may give you some leads.
Cheers

Roadrider II spec


For the 90/90 19

Rec rim MT2.15 alternate rim range 1.85-2.50

For the 100/90 - 19

Rec rim MT2.50 alternate rim range 2.15-2.75

'MT' equivalents of 'WM' are:- WM2 = (MT)1.85, WM3 = (MT)2.15, WM4 = (MT)2.5.

The skinny rim seems to me to make the tyre profile more round perhaps it will wear the centre off more quickly.
I ran a 4.10 Avon old style which was noticeably skinnier than the 4.10 Dunlop. But it handled the same and wore out the same. Factor in my advancing age and inability to tell good from bad at this point!
I put a WM3-19 on the back when I really should have gone for a 18 inch
rear rim. Much better tyre choices and dedicated rears last longer.
At this point it doesn't matter...

YellowPeril said:

Are those on original WM2 rims? I'm reading that the 1.85" of these rims do not fit well with the 100/90x19 tire.....haven't seen it with my own eyes but there are many descriptions of the tire not looking right and the tread not completely touching ground because the rim is too narrow. This is what has me worried about trying to put them on the WM2 rims.

Click to expand...

What you read it true, however your current tires are considered too large as well. I have no clue why Norton used WM2 front and rear. Many others used WM2 front and WM3 rear.

I use Avon RoadRider 90/90 x 19 or 3.25 x 19 on the front and 100/90 x 19 on the rear. Most others here do the same. - all on WM2 rims.

Many opinions are just oldschool hearsay. "You shouldn't do this or you shouldn't do that"

The physics of it has evolved... Modern tires have wide rims and a huge crown in the tire with very little sidewall. The wide rim makes the tire have much less lateral flex because it reduces the size of the "sidewall" of the tire. That allows the modern tire to have reasonably low inflation and still have a rigid tire. The inflation amount allows the tire to maximize it's contact patch area for a better grip and the tiny sidewall gives the tire rigidity and removes the lateral play that a larger sidewall imparts to a tire when the rider leans the bike over.....

SO,..... Norton WM2 rims are narrow. they are old school and any tire that will hold air when mounted on them will work,... But the wider the tire you put on those narrow rims, the more you will have a bulbous shape to your tire. That shape greatly increases the size of the tire's sidewall. In theory, you may get more surface area out of that wider tire, but you have to inflate the tire more to make the sidewall more rigid to eliminate some of the sidewall flex and that reduces the contact patch area. So in the end you can't maximize both contact patch area and sidewall rigidity without having a wider rim....

That means that you have to compromise in that regard

In other aspects, a narrow front tire steers more quickly and feels more precise than a wider front tire. The narrow front tire also wears out more quickly because there's less tire there. The effect of the narrow front tire is why choppers mount those ridiculously skinny front tires on them. They handle so poorly that the extra narrow tire helps them feel more manageable, so that's part of the effect of a narrow front tire.... A commando doesn't need that extremely narrow tire to handle well, so you can compromise and your front can last a little longer OR you can go super narrow if you like that very nimble feel...

Personally, I run a 100/90/19 on my WM2 front rim, and I run a 110/90/18 on my WM3 rear rim. I also run a little extra tire pressure since they are wide tires on narrow rims to offset the inherent sidewall flex from having wider tires on narrower rims..... I compromise.....

Here's one worth considering: https://www.accessnorton.com/Norton...r-tires-what-is-recommended.36694/post-651423

Someone might correct me but I think Jim Comstock uses these?
Cheers

EDIT - I was correct: https://www.accessnorton.com/NortonCommando/18-rear-wheel.33460/post-579861