Rear Wheel Dancing!

I'm trying to find a possible reason, I have placed flat handle bars on my Mk 111, also I have rear sets, the riding position is now very comfortable( 6ft and approaching my 7th decade), anyway on a Blast through the Park today, on one corner it felt as if my rear tyre was going flat( No it was alright) through the rest of the ride with wet and dry corners, No Problems. On the way home no reoccurance till put the brakes on at a red light, then rear wheel skipped and capered behind me, could the reason be that by puting the flat bars on I have put slightly too much weight onto the front wheel? Any discussion would possibly be informing.

Thanks Peter

Peter
If you are coming into the corner try a tiny bit of back brake and try no to lean to heavy on the bars that may keep the front from compressing . I found rear sets and flat bars comfy too, but it does set you forward which is good but it can make you grip bars tighter. I have had no probs 750.
Please disregard this if you think it is tosh!

Obviously check tyre wear and pressures first, and that the wheels are properly inline, but also check your Isolastics are correctly set and that your chain is not too tight!

After those go through the swinging arm bush checks, and the head steady and make sure the wheel spindles and engine/gearbox mounting bolts are tight.

It may be that moving your weight a little reveals issues that were not obvious before.

Even if you decided to change the bars back it would be good to do all these checks to make sure there is no problem with them.

Hi Peter

Take a ride & don't use the rear brake!!!
I back off the rear brake as much as possible as I find that the rearsets with flat bars or clip-ons change the angle of your foot on the lever. You might find it is coming on harder than you think. Had to take the rods of my Triton as I have heavy feet & lock the back up to easily.

Chris

What the break efficiency ratio again I forget? And it's a big twin . After all the criticism I've been getting I am making no comment other than. Who else has their rear brake disconnected ?

I know that feeling so inspect the routing and fouling and tensioning of the rear brake cable run from new rear set and make sure the axle clamp force is holding axle fixed.

hobot said:

I know that feeling so inspect the routing and fouling and tensioning of the rear brake cable run from new rear set and make sure the axle clamp force is holding axle fixed.

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No brake cable on a MkIII.

auldblue said:

What the break efficiency ratio again I forget? And it's a big twin . After all the criticism I've been getting I am making no comment other than. Who else has their rear brake disconnected ?

Click to expand...

I have a rear master cylinder to slave ratio that makes the rear brake in-effective. I find that any rear brake is too much rear brake unless the road surface is gravel or the speed is very slow. Jim

comnoz said:

auldblue said:

What the break efficiency ratio again I forget? And it's a big twin . After all the criticism I've been getting I am making no comment other than. Who else has their rear brake disconnected ?

Click to expand...

I have a rear master cylinder to slave ratio that makes the rear brake in-effective. I find that any rear brake is too much rear brake unless the road surface is gravel or the speed is very slow. Jim

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My point exactly it is used for control rather than stoping. In most cases.

Cheers for that jim.

L.A.B. said:

hobot said:

I know that feeling so inspect the routing and fouling and tensioning of the rear brake cable run from new rear set and make sure the axle clamp force is holding axle fixed.

Click to expand...

No brake cable on a MkIII.

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:lol: :lol: :lol:

The most likely cause is loose Isolastics. On the prototypes, they weren't adjustable and the spacer tube between the rear ones hd no flanges. Over a relatively short time, the tube would go slightly bell-shaped at the ends and clearance would open up, allowing sideways motion of the swing arm.

Sorry peter

Have I read this correctly " on a blast" for me means you are shifting at some speed with the intention of gaining some exhilaration due to some high speed manoeuvres ,and not toddling about in second.
And to do that your bike must be in a fair state of repair. No!

J

Sounds like something in your isolastics or or swingarm is loose, but it could be the wet and dry road conditions you were riding in confusing the issue as well.
Commenting on the rear brake use: Having a front drum brake, It's necessary to utilize the rear brake in conjunction to reduce stopping distance and relieve the stress on your right hand, which requires all 4 fingers for an aggressive scrub of speed. Luckily, the rear drum brake is very forgiving and wouldn't lock up unless I really stood on the brake pedal. I wouldn't try it leaning over in a turn, just setting up for the tip in. Then trail brake with just the front brake.- sorry, getting off topic.

Ugh L.A.B. I need warning alert on models after '73's. The rear skip condition description doesn't sound to me like he's over leaning &or over powering rear tire traction. If source not found/fixed could eventually escalate to take ya down. Imagine happening on easy turn that had sand or wet area just then. W/o cable self grabbing drum brake - Maybe just maybe the summer heat expanded brake fluid to self apply pads for an instant. There are known issues of fine tuning the master cylinder plunger length not to lock up on occasion.

Lockable rear tire is kind of fun = risky to learn about its benefits beyond actually needing to slow down somewhat. Weak rear brake is way safer more useful for sane thoughtless hard usage.

Hi All, and thanks stuff to check today.
Yes I may have been over cooking it a bit, also with my rear sets I need to actually take my foot of the peg to apply the brake, which could mean over pressure, tho I have been very aware of this fact.
Again thanks it will give me something to do instead of the lawns!
Peter

I'm trying to find a possible reason, I have placed flat handle bars on my Mk 111, also I have rear sets, the riding position is now very comfortable( 6ft and approaching my 7th decade), anyway on a Blast through the Park today, on one corner it felt as if my rear tyre was going flat( No it was alright) through the rest of the ride with wet and dry corners, No Problems. On the way home no reoccurance till put the brakes on at a red light, then rear wheel skipped and capered behind me, could the reason be that by puting the flat bars on I have put slightly too much weight onto the front wheel? Any discussion would possibly be informing.

Thanks Peter

Click to expand...

I want to keep picking your report apart Peter as it directly applies to me on my un-tamed Combat and may save you too. I on purpose work up every bike and every tire into skip outs in good conditions so I know what to avoid. Tire traction loss gives a very fast sharp short jerk-step outward either front or back with next instant catch back and carry on - educated. It always surprises me with a scare as feels like on rails right up to the let go and the fear spike kind of pisses me off as there is no warning, so more reason I force self to find out purpose. So sounds more like you got a taste of THE Hinge onset - likely with a bit of wind gust &/or road lump just then too. Its possible to foul and lift rear for this skip out sense but you'd of felt the scraping and usually only if rear loaded down with cargo I found. Skipping out by creeping up on it is not same thing as way over doing it on purpose to start a real drift or slide when ya have pure ballistic momentum control it till the saving hook up again. I never on purpose slide drift an un-tamed Cdo on pavement no thank you very much.

The rear hop with rear brake could well be as you say just less mass on rear while also applying front brake which lifts rear out of traction even more so. Rear can hop with hi speed down shifts too which is fun as can be until ya can stand the wear that causes. Sometimes I stab the rear just prior to hard front brake to really slow down as tends to squat whole bike and fork so less severe fork collapse hollowing the front.

All and all though I encourage your continuing fun finding the little quirts that limit the desirable thrills on un-tamed Commandos.

There used to be a theory that the rear brake only does about 25% of braking, and that its of most use for "settling" the motorcycle entering a turn. My final project when finishing at College was titled "Motorcycle Suspension", in it I tried to determine the main forces on a motorcycle so that the suspension could be designed. One of those forces, in fact the major force in normal use, is generated by braking. The tests that were completed, pretty much confirmed that at best the rear brake contributes only about 25% to overall braking effectiveness. During the tests I developed a fair proficiency at hard braking, to the extent that I was able to do "stoppies" pretty much at will, the other thing that became apparent was how skittish the motorcycle became when the rear wheel was at, or just past the point of losing grip. This was fairly easy to deal with in a straight line, but fairly exciting when in even the slightest of turns.
The outcome of all this is a fairly firmly held belief that the front brake is (or should be!!) smooth and very powerful and predictable, whilst the rear brake needs to be smooth in operation and much less powerful, and treated with some respect.
Probably a case for getting the rear brake set up better and desensitised!
cheers
wakeup

Wake up

Thanks for that, any more info on the subject?

J

Weight shift on hard braking means at some point only traction left to brake is on front as rear lifted out of effect or even in air. If ya really want to learn about rear brake don't think of it as a slowing feature but a steering aid and on a stupid trail braking lost front, as a hi side save feature = which only takes one instant of the hard rear stomp down panic to get bike back up "in line" so front brake back in action, *in line tires bolt upright * in case ya missed that VITAL detail for life saving braking. if you are rear braking while leaning then you will learn the hard way about rear brake not functioning to slow from any significant speed. Yet if ya do play with rear brake in leaned turns you see why the supermotards and flat trackers use it but for sure ain't got nothing to do with going slower. In slick loose conditions where one tire can't take the loads w/o locking then both brakes at once work rather better. One neat trick that was a surprise for me to lean that ya might like to perfect on your own is hitting rear to lock it under 40 mph which will tend to swing out and skew bike but just steer into it so bike travels in sort of crossed up skewed angle but the CoG through pilot seat travels a straight diagonal off to edge of road till stopped. Strange wonderful sensation to be facing one way but not going that direction.

Wake up and Hobot,

Thanks, I thought I had just tapped the rear brake at the entrance to the corner. Also I have my shocks on the firmest setting, something else to look at.
Peter