Commando handling

I had a situation on my touring bike some time ago. Depending on my seated position I could induce a wobble by moving back on the seat.  I adjusted the loading in the panniers and seat pack to bring the heavier items forward.  Can you take front and rear wheel weights in the load configuration you had and then without the load?  Bathroom scales and equal depth block to level the machine. May give you some indication of what is going on?
 

cheers

Jon

Check the head steady bolts to the head have not loosened, did on mine and it felt vague until retightened, only slightly loose so even looser would make things interesting.

The only time that mine has done that under braking was with Craven panniers on. I had the support struts to the footrests but the two sides were not connected below the number plate, as the original Cravens seem to have been. I don't think it's a weight thing but have the impression that the cases were flapping a little at the rear. I got them fairly well forward, but with the Roadster exhausts, they were sitting quite high.

As John says though - head steady security is critical.

With the standard head steady and TT100 tyres my Commando weaved and wobbled everywhere. Now with a Taylor head steady and Avon Road Riders it is as good as any modern bike. I suspect that an Andover head steady will be just as good and probably more durable.

Since this is something new, what have you changed?

The only time I ever managed to make a Commando unrideable was when I loaded a lot of weight on the rack. Moving it onto the tank, although a bit uncomfortable, resolved the problem. Ever since I've been very wary about heavy loads high and out the back.

But if it's something that's happened overnight with the same load setup I'd be looking at : tyre pressures, rear tyre badly worn in centre, rear shocks, wheel bearings, steering bearings, swinging arm bearings, or something broken.

Not having a brace  behind the the numberplate  may allow some flexing  / swinging motion  to the panniers . I have experienced   tank slappers  in the past  with old worn out bikes, but never with a featherbed even fully loaded . Perhaps you should have taken the SS  !!. After your years of sprinting you must be good  at controlling  a  bike with only the rear on the tarmac. 

... on my Commando but did note that once the back tyre had flattened out in the centre it had a slight tendency to weave. Not dramatic though.

I would always advise carrying as much stuff as possible in a tank bag; moving the weight distribution to the rear is a bad idea on any normal bike.

However, I note that the problem is said to be tank-slapping while braking.

This sounds like a truly frightening phenomenon but it is hard to see how it can be due to rearward weight bias, since by definition there is weight transfer to the front when it occurs.

Also, since the issue didn't occur on the way out it seems unlikely to be due to weight distribution issues, unless you have stocked up with an improbable quantity of vino.

As others have noted, it must be that something has broken/worn/got out of adjustment.

" the swinging arm is OK the bushes having been being replaced not that long ago"

Check the spindle cotter pins are tight. I my case I got a slight wobble pulling away.

With regards to Peters reference to the DT head steady. The original link is still fitted and working well, no signs of any play.

Regards,

Dave

Considering all was well before hand, and most mechanical items have been checked. Is the tyre square and concentric on the rim, has it moved, is it damaged.

RGM disc, is it the floating type, if so does it function correctly, is there wear on the fasteners. Might be worth checking the brake closer if it only happens when braking. 

.. that I had the same issue of "rebated" pads with a Lockheed caliper but I just removed the excess material with a hacksaw.

Exactly the same issue was apparent on the genuine PR disc brake that came with the Fastback I owned in the '70s. It can have no relevance at all to your problem. There is absolutely nothing to worry about, apart from relieving the overhanging material from each pad before it can prevent them gripping the disc properly.

Of all the issues mentioned so far, play in the wheel bearings seems the most likely culprit to me.

It seems odd that this device never caught on..

Ken, I would think the instability was caused by all the weight on the back, especially if a particular load can start to 'waggle' at the same frequency as the fork oscillations. I never had full blown 'tank slappers' or anything near that, but the front end would start a weak oscillation when there was a load on the rear carrier and could be triggered at 70mph if I moved my feet to the rear footrests for a leg stretch. Slack isolastics would encourage the effect. For a few years I ran with a hydraulic damper and that that would stop it.

Can you not just go out on the bike now, with no load on the back, and see if the misbehaviour has gone away?

The big bendy may be fly by wire sensitive to all sorts of minor issues or combinations thereof.

But I think its a little off that nobody has pointed a finger at the road surface. 

A little oil or sand just allowed the Commando to do its thing.

Rider set well back ( Interstate style), well loaded with kit, going downhill, 12kg of fuel sloshing around.

Had exactly the same happen just once, full tank slapper same circumstances had to stand it up or it was terminal.

My view was lack of grip from a 1/2 worn front tyre.

No repeat of this full tank slapper after fitting a new tyre.

Over many years with an Interstate I formed an opinion that they lack grip on the front end and are more easily unsettled than other bikes. Thats in a straight line not cornering.

Front end shake tyre or steering head bearings( full of water) most likely.

Weaving most likely isos or headsteady

Front tyres wear very slowly sort of confiirming my lack of grip comment.

Best tyre on my Commando was the Avon GP front and rear. TT100s were used because they gave better mileage. Then for a long time Avon Am18 front Am20 rear felt good until the front was half worn. Avon Roadriders more recently seem a good choice.

Interestingly Commandos will also wag their tails in mid air, bars static tail oscillating hugely. Not got a clue why but it makes Hondas back off.

Commandos take a little getting used to, allowance has to be make for the bendy bits. Bit like some Meriden Triumphs  not shutting off mid corner  just keeping some power on seems to help.

Then occasionally they throw in a scary one off.

Finally wonder if "wagging and weaving " should be better documented to help those newer members who experience one or both.

Hi Ken, I have a friend who had a similar problem when loaded up. It turned out the shockers he was gifted were 5 mm longer than standard. Once he put the right length shockers on the issue was solved.

Hi Ken, I agree with Normans comments above.

I recall my first Commando, an 850 Mk 1. I fitted a craven carrier and a small craven top box. I put a heavyish tool kit and some oil in the top box and found when riding solo I had a disconcerting waggle on the bars.

I replaced the items in the top box with some light waterproof gear and the waggle pretty much disappeared. Commandos do not like weight behind the rear axle.

Over the years I have done a lot of distance touring on the Mk3 Interstate I now own. I have a craven rear carrier/comet pannier set up. In order to keep the luggage low and as far forward as possible I have adopted Interpol rear exhaust mounting plates as the swivel allows the silencers a lower run and have reverted to the earlier rear seat without the hinge as this allows the the rear carrier to move forward approx 1.5 inches. Nevertheless, two up and with a full tank of petrol and a tank bag and trying to keep weight towards the front and luggage at the rear to a minimum, I  still suffer the occasional waggle on the bars. This is also after having carefully ensured tyres, isolastics, suspension etc. were all correct beforehand. I have not yet tried a steering damper and will do shortly.

As to riding solo and laden at the rear - I try and avoid it. I had to ride the laden machine solo down the concrete ramp coming off the motorail in Düsseldorf about three years ago. At about 15 mph the machine developed a vicious tank slapper that nearly had me off. It was a real ‘change of underwear’ moment.

Not sure whether the comments will have specifically helped you but it does show you are not alone in your experience.

Exactly like Alan,850MK3 and CRAVEN Comet plus luggage carrier, in duo, BUT WITH A STEERING DAMPER and IKON shocks and never had any worries.

A different bike, A BSA A7 but the same problem. Never a handling problems for years until I had a load of heavy tins in the top box and hit a road bump at speed whilst cornering. This produced its first and only tank slapper (despite having a steering damper) putting the bike in a ditch and me in hospital. The top box has since been consigned to a shelf in the shed.