MKIII rim width questions for 19" & 18" rear.

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MichaelB said:
Coco, My Combat has a Mk III swing arm with a 2.5 Excel with a 120/90/18 Metzler ME55A with a custom chain guard and a 530 chain.
No problems, but it's close. For various reasons I can't fit a stock chain guard, but it looks like it would be problem.

My Dreer has a 110/90/18 with the stock guard. I'll have to check the wheel size, but I think it is a 2.15. The front is a 90/90/19 with I think a 1.85. Again, I'll have to check.

The 100/90/19 barely clears the stock front fender. I don't know anyone who has put a 2.15/19 on the front. It may spread the tire enough to cause an interference. I'm not sure. Just be prepared for this.

Oh the joy of customization.
Click to expand...

Thanks Michael. I must have been measuring my stock rims wrong because they are 2.5" accross and not closer to 3" like I originally thought. Too much coffee perhaps?

I am going with a CNW front fender which can accept a 4.10 tire and a CNW chainguard will go on the back and it is narrower than the stock one, but notching it out to fit is no big deal.

Here is a link to the Buchanan rim chart. They list a WM4 as 2.5 which is what my stock rims are, unless the 2.5 number is not in inches, which would be the reason for my troubles as I assumed that number for rim width is indeed in inches???? If that is the case I am totally out to lunch, which I probably am.

I'm getting really confused.

Guys, I appreciate the help.

http://www.buchananspokes.com/Excel_shld.htm
 
Stock wheels are WM2 or 1.85. WM3 is 2.15, WM4 is 2.5

It is usually stamped on the wheel by the valve stem.
 
MichaelB said:
Stock wheels are WM2 or 1.85. WM3 is 2.15, WM4 is 2.5

It is usually stamped on the wheel by the valve stem.
Click to expand...

Contact! :D I was indeed sniffing glue and the 2.15, 2.5 ect is not a number in inches so I was out to lunch by measuring the outside width of the rim. My stock rims are both WM2 so I will go with a WM2 on front and WM3 on rear (hopefully). Thanks Michael, it is clear to me now.

I did not know the rim number was stamped on. All I saw was the Dunlop name stamped in there and did not look on the other side of the valve stem. I feel like a dumb-ass now. :oops:
 
MichaelB said:
Coco, My Combat has a Mk III swing arm with a 2.5 Excel with a 120/90/18 Metzler
Click to expand...

So you are indeed running a WM4 on the rear with no issues except cahin guard clearance. I was told they would not fit, but I guess yours did. I wonder if I can get away with WM3 front and back?

Michael, are you using the stock rear fender with that WM4?
 
Coco said:
I was indeed sniffing glue and the 2.15, 2.5 ect is not a number in inches so I was out to lunch by measuring.
Click to expand...


1.85 (WM2)-2.15 (WM3) are 'Inch' sizes but this is the *internal* dimension of the rim not the external dimension, after all that is what is important when selecting a suitable tyre/rim combination.
 
Coco, just to add a bit to the information pile:

1974 Commando
Front> Metzeler Lazertec 100/90-19, Akront 1.85 rim
Rear> Metzeler Lazertec 120/90-18, Akront 2.15 rim

Ron L is right, the rear tire is VERY clost to the chainguard, maybe an eight inch but it DOES clear without modification. I've never had any problems with this configuration and the bike handles and tracks nicely.
 
Coco said:
I think putting an 18" rear wheel and 120 tire is going to be more of a tricky situation than I originally expected. With that much offset to the right side a 120 raer tire will definitely not fit so I am unsure how others like Mick Hemmings have done it (maybe it was not on a MkIII). Might be safe to go with a 110 but I wanted to try a 120 on the back.
Click to expand...

From what I could read about Mick Hemmings' racers, I could take that he uses 'featherbed' (Dommie) frames and also offers wider swinging arms for these.

A 100 tire will be a good fit on an 19" WM3 rim in the Commando's swinging arm, and so will a 110 on a 18" WM3 rim. A 120/90/18 tire will unduly "balloon" due to the narrow WM3 rim, ending up with almost 130 mm (or even more) width, an 18"/WM4 rim might help here. Actual tire width can greatly vary, depending on manufacturer and tire type. AVONS (Venoms), Bridgestones (BT45) as well as Michelin (Macadams) should be similar.
I used 110/80/18" Michelins on the rear in the eigthies and nineties on WM3 rims, and they showed approx. 1/4" clearance between tire and right-hand swinging arm leg. To do this, I had to discard the original chain guard, which I replaced with a lightweight, similar-looking one (of a Yamaha 125cc) that shielded the chain only on the outer and upper side. The clearance between chain and tire was then approx. 1/3". The disadvantage of this set-up was that the rear end was approx 1" lower, and thus affected steering geometry a bit (slower steering response), but not by much. Using a 120/90/18 would have corrected this, but that tire was simply too 'fat' .... :-)
If you want to retain both the original chainguard and steering geometry, it might be best to use a 19" on a 19"/WM3 rim on the rear with a 100/90/19 AVON (Venom) tire.

BTW, Commandoes can look (and feel!) also rather mis-aligned due to another reason: with adjustable (vernier) isolastics, you keep pulling the front ISO slightly towards the right, and the rear ISO towards the left every time you re-adjust (tighten) them.
 
Gene said:
Coco, just to add a bit to the information pile:

1974 Commando
Front> Metzeler Lazertec 100/90-19, Akront 1.85 rim
Rear> Metzeler Lazertec 120/90-18, Akront 2.15 rim

Ron L is right, the rear tire is VERY clost to the chainguard, maybe an eight inch but it DOES clear without modification. I've never had any problems with this configuration and the bike handles and tracks nicely.
Click to expand...

Excellent, thanks Gene. Are you experiencing any ballooning of the rear tire as brittwin suggests in the post above?
 
brittwin said:
Coco said:
I think putting an 18" rear wheel and 120 tire is going to be more of a tricky situation than I originally expected. With that much offset to the right side a 120 raer tire will definitely not fit so I am unsure how others like Mick Hemmings have done it (maybe it was not on a MkIII). Might be safe to go with a 110 but I wanted to try a 120 on the back.
Click to expand...

From what I could read about Mick Hemmings' racers, I could take that he uses 'featherbed' (Dommie) frames and also offers wider swinging arms for these.

A 100 tire will be a good fit on an 19" WM3 rim in the Commando's swinging arm, and so will a 110 on a 18" WM3 rim. A 120/90/18 tire will unduly "balloon" due to the narrow WM3 rim, ending up with almost 130 mm (or even more) width, an 18"/WM4 rim might help here. Actual tire width can greatly vary, depending on manufacturer and tire type. AVONS (Venoms), Bridgestones (BT45) as well as Michelin (Macadams) should be similar.
I used 110/80/18" Michelins on the rear in the eigthies and nineties on WM3 rims, and they showed approx. 1/4" clearance between tire and right-hand swinging arm leg. To do this, I had to discard the original chain guard, which I replaced with a lightweight, similar-looking one (of a Yamaha 125cc) that shielded the chain only on the outer and upper side. The clearance between chain and tire was then approx. 1/3". The disadvantage of this set-up was that the rear end was approx 1" lower, and thus affected steering geometry a bit (slower steering response), but not by much. Using a 120/90/18 would have corrected this, but that tire was simply too 'fat' .... :-)
If you want to retain both the original chainguard and steering geometry, it might be best to use a 19" on a 19"/WM3 rim on the rear with a 100/90/19 AVON (Venom) tire.

BTW, Commandoes can look (and feel!) also rather mis-aligned due to another reason: with adjustable (vernier) isolastics, you keep pulling the front ISO slightly towards the right, and the rear ISO towards the left every time you re-adjust (tighten) them.
Click to expand...

Thanks Brittwin. Isolastics are new and I will install a Dave Taylor head steady as well so everything should be nice in that respect.

Now I am very unsure if a WM4 will fit on the rear with a 120/90 - 18 tire as Iw as told by a few people and the people at RGM motors that it would not fit. My original plan was Wm3 up front and WM4 on the rear but I am getting some conflicting info here.

MichaelB on the forum here mentioned his rear is in fact a WM4 with a 120 tire and he says it fits so now things are up in the air again.
 
brittwin said:
From what I could read about Mick Hemmings' racers, I could take that he uses 'featherbed' (Dommie) frames and also offers wider swinging arms for these.
Click to expand...


Mick Hemmings generally races (and specialises in) Commandos, but not exclusively though, and has raced various machines and supplied standard Norton and Norvil (Hemmings Norvil) parts for some years.

http://homepage.mac.com/pierregabriele/ ... ings35.jpg

http://www.tr3oc.co.uk/bz13ww5.html

http://www.norton.norvil.net/mickh.htm
 
Excellent, thanks Gene. Are you experiencing any ballooning of the rear tire as brittwin suggests in the post above?[/quote]

You're welcome. By "balooning" I'm guessing he means inflation(?). If that's correct, at 32psi there's an eight inch clearance with the stock chainguard.
 
Gene said:
If that's correct, at 32psi there's an eight inch clearance with the stock chainguard.
Click to expand...

Should that read: "an eighth of an inch" ?
 
L.A.B. said:
Gene said:
If that's correct, at 32psi there's an eight inch clearance with the stock chainguard.
Click to expand...

Should that read: "an eighth of an inch" ?
Click to expand...

Haha. I assumed he meant 1/8" unless Gene is running car tires in the back with a modded rear end. Drag bike? :D
 
Gene said:
Excellent, thanks Gene. Are you experiencing any ballooning of the rear tire as brittwin suggests in the post above?
Click to expand...

You're welcome. By "balooning" I'm guessing he means inflation(?). If that's correct, at 32psi there's an eight inch clearance with the stock chainguard.[/quote]

I assume by ballooning he meant a grossly oversized tire compared to rim width so the side walls would be very round.
 
Coco said:
Isolastics are new and I will install a Dave Taylor head steady as well so everything should be nice in that respect.
Click to expand...
I am afraid said head steady (and any other H/S types) will not prevent the mis-alignment of the isolastic-mounted sub-frame as a whole that increases with time due to the adjustments made. This does of course not change the rear wheel's position within the swinging arm, but pulls the whole subframe out of line - front to the right, rear to the left. In consequence, the swinging arm and thus the rear wheel become angled out to the left (top view).

Coco said:
Now I am very unsure if a WM4 will fit on the rear with a 120/90 - 18 tire as Iw as told by a few people and the people at RGM motors that it would not fit. My original plan was Wm3 up front and WM4 on the rear but I am getting some conflicting info here.
Click to expand...
A rear WM4 rim will actually see to that the tire's width is kept to it's nominal max, and not "balloon" it beyond llike a WM3. However, you may not find correctly drilled WM4 rims for the Commando, so youl'll need a wheelmaker to let him do this work for you. He can use your original rim to copy it's spoke hole pattern in order to make a correctly drilled rim with appropriate spokes.
There's no need to use a WM3 rim for the front side, WM2 rims are OK with 90/90/19 or 100/90/19 tires.

Coco said:
MichaelB on the forum here mentioned his rear is in fact a WM4 with a 120 tire and he says it fits so now things are up in the air again.
Click to expand...
He's right. A WM4 rim is only marginally wider than a WM3, it is the standard rim size for a 120/90/18, and will keep this tire's cross-sectional shape within it's correct specs.
 
I broke down and called Matt Rambo at Colorado Norton Works. His work has been a huge influence on the kind of machine I want to turn my MkIII into so I asked him about what type of rim/tire sizes they use.

He told me a 100/90-19 & WM3 on the front and a 120/90-18 & WM4 combo on the rear will work just fine with no adverse affects and in his opinion will handle just dandy.

The 120/90-18 Bridgestone BT45 are a tad narrower than the Avons so I'll go that route just in case but I am going to go with my initial plan with those rim sizes in Excel rims. Thanks to any and all who have contributed to this thread with thoughts and information.
 
Of course, 1/8", not 8". Thinking one thing and writing another. Sorry for any confusion
 
Before this thread becomes too distant, I wanted to ask about the general consensus and apparent preference for 18" rear wheels against the original 19". Why is 18" favoured over the 19". Is it better choice of available tyre size options, less unsprung weight, lower gearing, marginally smaller head angle etc etc ? Thanks.
 
An 18" rear wheel size gives more tyre options, the choice of 19" rear tyres being rather limited these days.
 
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