To WM3 or not WM2 be?

Chris,

It depends what size tyre you're fitting. See

http://www.avon-tyres.co.uk/motorcycle/roadrider

Currently I've 100/90 19 Roadriders front and rear using 2.5" width rims (WM4 I think) which is what Avon recommend. They cause no problems what so ever. However when the front is changed next I'll experiment with a 90/90 19, as just about every production bike I can think of uses a narrow front tyre in relation to the rear.

I can state categorically what causes problems on standard Commando's is errors incurred through production techniques and incorrect dimensions of critical parts.

This results in the rear wheel offset to the drive side and away from the frame centre line to between 0.2" -0.3". In addition the swing-arm spindle axis is not square to the steering head axis in the plan and end views, which gives the symptoms of worn swing-arm bushes as the suspension moves, due to the rear wheel centre line moving left and right in relation to the frame centre line.

Once the Commando frame and rolling chassis are as they should be the bikes handling is transformed to the extent that when leaned hard over through bumpy corners the bike is stable and goes where you want. A much safer and faster motorcycle.

Regards,

Simon.

I know that we have been here before and I have studied the previous postings, but thought I would ask again before spending time and money.

Does anybody know of any adverse effects from using a 19" WM3 rear rim with an AM26 Roadrider? Some sources suggest that this tyre should be used with a WM3 rear anyway.

Previously anna jeannette Dixon wrote:

Hello your rear swing arm will only let you fit a Wm3 rim And I do not rate Roadriders any way Dunlops are the best on the rear take it from me or not the choice is yours anna j

Anna,

I have, fitted, a 2.5" (WM4) rim on my Mk3 Commando with a 100/90 19 Roadrider and there is approx. 0.5" clearance between tyre and swing-arm at the narrowest point. Roadriders are excellent tyres,

Regards,

Simon.

Simon, before buying a 90/90 X 19Roadrider, check out the 3.25 X 19 version. Almost identical spec, [ a millimeter here and there ] but £13.00 cheaper on Pneus Online website.

I currently have Roadriders - 90/90-19 on a WM2 on the front and 100/90-19 on a WM3 on the rear. The tyres sit well and look 'right'. I really like them. They're grippy and predictable and completely ignore white lines and even Belgian rain grooves which used to have part-worn TT100s tying themselves in knots.

Prior to this I had Super Venoms on 18" rims - 100/90 on a WM3 and 110/90 on a 2.5 ('WM4').

If I were to have wheels built again, I might go up a size on width as that is what Avon now seem to recommend but the Akronts I'm using were built by Hagons back in about 1985 and at that time they were the recommended sizes for 3.60 and 4.10 TT100s.

I suspect that there may be slightly faster wear if a tyre is used on a narrower rim and perhaps the change of section when banking over might be noticeable on the track but for normal use, and having done it when changing from the original chrome WM2s, I'd say that there is little real difference unless going to extremes - and certainly less than when replacing worn tyres with new.

Agree with the comments regarding Roadriders. Considerable better than TT100s or particularly the dastardly K70.

They're grippy and predictable and completely ignore white lines and even Belgian rain grooves which used to have part-worn TT100s tying themselves in knots.

+1 I bought mine with TT100's on, after one week of trying very unsuccessfully to steer clear of white lines I changed to Roadrunners and have stuck with Avons ever since and its now running Roadriders and they are even better than the Venoms they replaced.

Previously Chris Grimmett wrote:

It looks as if WM3 is fine then if even a WM4 can be used. What does the assembled Brains Trust know about the changes in handling, if any, that occur when a tyre of a given size is used with different rim sizes?

I did also make the transition to a 90/90 front at the same time and agree with Simon that things were greatly improved over the wider tyre profile (in my case a 4.10).

With a wider rim the tyre contact patch increases. The tyre effectively is flatter. Obviously provides more grip but is slower to turn into corners - and is prone to white lining. On a properly aligned bike the only changes in handling would be slower steering and maybe whitelining a bit more but only when the rear is well worn

The reason I'll be putting a 90/90 19 on the front is because cornering forces are split approximately 40% front to 60% rear on a bike accelerating through a corner, the force on the front tyre is less than the rear so does not require as great a contact patch as the rear. A 'paired' narrower tyre on the front provides enough grip. The tyre is lighter, reducing inertia, so steering requires less force and is quicker.

It always seemed that the correct size of rim for the old 3.50 tyre, or 4.10 as it was called a bit later, was a WM2. But I recall from racing that people used WM3 rims for the more recent classic racing tyres of that section, I assume because it imparts a bit more stability on the base of the tyre.

There is no doubt in my mind that the new Avon AM26 tyre is a good one: it feels good on a 1950 plunger ES2, on a MK3 Commando and I have a new pair on the Commander. But they are probably a bit softer. My Commando rears lasted: Avon GP 9,000 miles; TT100 7,800 miles, Avon AM21 8,600 miles; and just replaced AM26 4,700 miles. In that time I have also discarded a TT100 and Avon GP early because of age and not wear.

On the Commando front wheel the Avon GP and AM20 in 90/90x19 looked right. But the new 90/90x19 AM26 is a much smaller tyre section. I quickly took mine off and fitted it to the ES2 where it is fine. I put a 100/90x19 AM26 on the Commando front which has virtally the same rolling radius as the old GPs and AM20s.

I agree that smaller section 19 tyres will give a quicker handling Commando but I'm an old cruising boy now. With the 100/90x19 WM2 front I have a 110/90x18 WM3 rear, that again has the nearly same rolling radius. It handles perfectly, and I have pushed it scratching at Jurby holding off a Manx until the noise of scraping underneath got too much. The comments in earlier threads about 18 inch rears not working are nonsense. I fitted the WM3 18 rear many years ago when Jem wrote about it in Roadholder and decided it was a good idea.

Norm

Previously norman_lorton wrote:

With the 100/90x19 WM2 front I have a 110/90x18 WM3 rear, that again has the nearly same rolling radius. It handles perfectly, and I have pushed it scratching at Jurby holding off a Manx until the noise of scraping underneath got too much.

Norm

Norman,

I'm genuinely interested to what you have done to your bike for it to handle perfectly. Especially regarding rear wheel centre line to frame centre line and getting the swing-arm to steering head axes perpendicular. The Commando's I've corrected so far have all been way out,

Regards,

Simon.

Previously norman_lorton wrote:

On the Commando front wheel the Avon GP and AM20 in 90/90x19 looked right. But the new 90/90x19 AM26 is a much smaller tyre section. I quickly took mine off and fitted it to the ES2 where it is fine. I put a 100/90x19 AM26 on the Commando front which has virtally the same rolling radius as the old GPs and AM20s.

The comments in earlier threads about 18 inch rears not working are nonsense. I fitted the WM3 18 rear many years ago when Jem wrote about it in Roadholder and decided it was a good idea.

Norm

Disagree re tyre widths. The new AM26 90/90 x 19 has a width of 99mm, where as the AM20 90/90 x 19 width is 95mm. Diameter of each tyre is the same.

Regarding 110/90 x 18 (which I'd have thought would only be necessary if you'd been spinning the back wheel in corners) is'nt the tyre rubbing the chain guard, or very close, with the rear wheel spindle parallel to the swing-arm spindle.P.S Interested in a Norton group track day next year?

I can state categorically what causes problems on standard Commando's is errors incurred through production techniques and incorrect dimensions of critical parts.This results in the rear wheel offset to the drive side and away from the frame centre line to between 0.2" -0.3".

Simon, I'm aware of yr frame aligning success and read the Phantom Oiler files years ago but I am confused by yr comments which i hear repeated every now and again talking to other owners. I've done a little work on my 750 and others by making sure all offsets (so at least the drive train is pointing in the right direction) are the same, that is front mount, main cradle and head steady which are all designed with 1/8 to 3/16 offset to the left deliberately (you seem to be stating these are manufacturing errors? The error that I see is the 1/16 variance). On 750 and 850 the rear wheel is offset to the right in a symmetrical swingarm to centre in the frame and forks with front wheel. I know little of MK3 which I have heard has an offset swing arm so the wheel is centred in the arm but since it uses the same p/n head steady as others (for service purposes) it must have the same offsets in front mount and cradle, no?

If I've misunderstood you I am really confused since the engineered offset is common knowledge.

Previously anna jeannette Dixon wrote:

Hello your rear swing arm will only let you fit a Wm3 rim And I do not rate Roadriders any way Dunlops are the best on the rear take it from me or not the choice is yours anna j

Anna,

I have, fitted, a 2.5" (WM4) rim on my Mk3 Commando with a 100/90 19 Roadrider and there is approx. 0.5" clearance between tyre and swing-arm at the narrowest point. Roadriders are excellent tyres,

Regards,

Simon.

Keith,

I've never seen the original Commando drawings, so I do not know what offsets where incorporated in the design.

What I have found on the Commando frames I've corrected so far is that the rear wheel is between 0.2" - 0.3" biased to the drive side. I know this because I can accurately (+ or - 0.002") position the frame so that the frame centre line is horizontal in relation to a horizontal datum. I use an engineering grade granite surface table.

With the rear wheel assembled to the frame I can then determine (to within + or - 0.005") the difference between the frame centre line and the rear wheel centre line.

This is done after I have corrected the frame and cradle so that the swing-arm axis is perpendicular to the steering head axis and the swing arm has been calibrated. The wheel spindle slots are corrected so that the rear wheel spindle is parallel to the swing-arm spindle in the end view. The calibrations ensure the rear wheel spindle is parallel to the swing-arm spindle in the plan view.

Please ask away if any of the above is not clear.

P.S The Commando frames I've worked on so far have been between 1971 and 1975. The method I use can be applied to any frame. In fact the first frame I corrected (apart from my own) was a butchered Featherbed.

Agree with the comments regarding Roadriders. Considerable better than TT100s or particularly the dastardly K70.

Quite apart from the matter that Roadriders are far more predictable and grippy in terms of acceleration, braking and cornering and that Commandos are quite tall heavy motorcycles when compared with those for which the K70 was originally intended, the 19" K70s are 'P' rated which indicates 93MPH.

Suggesting the fitment of anything lower than 'V' rated tyres to a Commando intended for road use can't really be regarded as a good idea and should be accompanied by a disclaimer.

Previously anna jeannette Dixon wrote:

Hello that maybe what you have done but there not much room in the swing arm in my manuals is says a Commando rear wheel is 400x19...... K70s at lest they last a long time , were has your modern Avon's will not last has long and we do not do fast riding any more.......

Anna,

I've posted previously - there's 0.5" between the tyre edge and swing-arm each side.

What's wrong with fast riding?

Previously K Glassborow wrote:

....I've done a little work on my 750 and others by making sure all offsets (so at least the drive train is pointing in the right direction) are the same, that is front mount, main cradle and head steady which are all designed with 1/8 to 3/16 offset to the left deliberately (you seem to be stating these are manufacturing errors? The error that I see is the 1/16 variance)....

......If I've misunderstood you I am really confused since the engineered offset is common knowledge.

Keith,

After searching online I couldn't find any drawings relating to Commando frame mounting bracket offset, so I'm very interested to know from which source you obtained the offset dimension(s), as you state two - 1/8" and 3/16" - which one is correct and what datum do you use? or how do you know either are correct?

The fact is the extent of variation between frames dictates the need to treat each chassis assembly as a one off. Hence whatever offset there is, is somewhat irrelevant. As mentioned before, I determine the frame centre line and with this parallel to a horizontal plane (granite surface table) I can then very accurately determine swing-arm spindle axis in relation to steering head axis and rear wheel centre line in relation to frame centre line - which shows the rear wheel offset from the frame centre line of between 0.2" to 0.3",

Regards,

Simon.

Simon, Thats the problem. No-one knows anything, not even Norman White who I asked yesterday down at AN's open day. Bob Rowley one of the original factory testers was there and Norman suggested he or Joe S would know. Unfortunately both were in demand and I didnt get to talk to them. I think an email to Joe Seiffert would clear it up since he must have mount and cradle drawings. All I can repeat is what I've measured and what the old and current Commando fora have discussed/stated..that depending on whose parts are measured the cradle, mount and headsteady offset is 1/8" to 3/16". I have recorded my bike and the front mount measurements have the RH tube end 0.55" from sideplate and the LH 0.31". This had been 0.61" and 0.31" so 0.155" to 0.120" from centreline. I removed appx. 06" from the RH (adding a 06" washer to the LH) to match the cradle which had slightly less offset and the bike always weaved over 75mph. The whole plot had been pointing left for years. With empty crankcases and unmodified mounts the front mount had to be pushed to the right to slide in place. The mod did the trick and it now tracks straighter. I can't say its in the league of what you do or the 'Phantom' Norton but it solved a nasty characteristic. In addition Central Wheel had build the rear wheel to centre in the swingarm. It had to be moved 1/8" to the right to align with the front. Of course my frame probably is not straight in many areas, the tabs are probably not in accurately correct positions but these changes helped a lot. I did this back in Dec 2006 and filed the swingarm forks/dropouts also. Have a look at a std headsteady or front mount if you have spares (750 or 850) and see what measurements you get. ATB.

Keith,

Thanks for the reply. I'm thinking the offset dimensions are another part of Norton folklore. They must be on the original drawings, but the manufacturing tolerances where so far out that there is no definitive answer, measuring off a frame just adds to the confusion.

I'm hoping Joe Seifert can contribute to this thread..

Unfortunately the accumulative manufacturing errors in several critical areas are the reason for the excessive mis-alignment on a Commando chassis. It's not just the bracket offsets. I'm glad you've made progress in improving your bikes handling,

Regards,

Simon.

I think the original question has been answered quite adequately and I am locking this conversation.

A discussion on Commando offsets! continues elsewhere.

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