Monoshock Commandos

Rohan · Sep 26, 2011

Cheesy said:
Ok I have to bite, how does a monoshock provide improved suspension action? Granted it could well be better than some stuffed old commando shocks but compare it to something new and I dont see any advantage at all

GrandPaul touched on the subject of 'rising rate' suspension. This subject could fill books, but the suspension action is far more effective at damping out road bumps/shocks, and feeding the forces back into the frame without such drastic twisting moments - look how modern MX bikes can handle HUGE jumps, old twin shocks just can't do that...

HTH

grandpaul · Sep 26, 2011

The beauty of the rising rate suspension also allows the shock to compress only a couple of inches while allowing the rear wheel to travel double that amount. Plain shocks heat up and fade under heavy activity, a monoshock works less hard over the same terrain. So, not only is it more effective mechanically, it's also more durable under stress.

Hobot · Sep 26, 2011

Those MX bike landings are sure temping to mono my dirt bike Peel. The pair of Ohlins 15"'rs I've window shopped cost $1400-1800+ a pair. Mono Ohiln's top end cost nearly as much for ordinary versions and many $1000 for competition versions.

How do road racers get a mono handling advantage. Their not on dirt conditions I first studied mono applications on? I don't think simple frame tabs and the factory cradle could resist the side loads Peel is expected to take in stride quite as well as the dual shocks spread out near the swing arm ends.

This list ignores the extra beefy single sided swing arm fashion of course. It don't list mass centralized either.

1> Mono-shocks eliminate torque to the swingarm and provide more consistent handling and braking.
2>They are also easier to adjust, since there's only one shock to adjust, and there is no worry about matching two shocks.
3>Also, the linkages used to connect the shock to the swing-arm are frequently deisgned to give a rising rate of damping for the rear
4> The monoshock improves both the ride and handling if tuned well.
5> The simple reason for it being better can be understood by the following explanation- "Whenever you encounter a bump on a M/cycle with two shocks, both the shocks compress, but there is never a situation when both of them compress for the equal length. This leads to downgraded dynamics when it comes to stability. But with a single shock absorber, this problem is solved.
6> In a recent test conducted by Bike Magazine, Pulsar, Apache and Unicorn were pitted against each other on a test track. Although the unicorn was not the fastest, they said it is the most confidence inspiring and the most balanced of the lot.

Cheesy · Sep 26, 2011

Rohan said:
Cheesy said:

Ok I have to bite, how does a monoshock provide improved suspension action? Granted it could well be better than some stuffed old commando shocks but compare it to something new and I dont see any advantage at all

Click to expand...

GrandPaul touched on the subject of 'rising rate' suspension. This subject could fill books, but the suspension action is far more effective at damping out road bumps/shocks, and feeding the forces back into the frame without such drastic twisting moments - look how modern MX bikes can handle HUGE jumps, old twin shocks just can't do that...

HTH

I understand what you are saying and what Paul said after you, I just have a feeling that the trend to monoshocks is a bit more involved than rising rate linkages. For instance it is probably cheaper to make a larger monoshock than twin shocks, the machine time is essentially halved with a nominal increase in material cost. That and packaging are the only two real advantages that I can see. Sure a monoshock doesn't have the same displacement as twins but surely it must have to dissipate the same (or very close to) amount of heat for a given rear wheel movement. An interesting arrangement is the KTM/White Power shock, its offset to one side of the swing arm and it does not have a rising rate linkage.
"old twin shocks just can't do that..." is probably very true (I have never ridden a twin shock MX bike), I do wounder though how much of that is due to the old part and not the twin part

lcrken · Sep 26, 2011

This is the picture of the JPN F750 with monoshock rear that Dave Croxford rode. It's from Roy Bacon's book "Norton Twins". I was hoping someone on the list had some info on it. I have a couple friends who still worked for Norton in that period, and I'll see if either of them recalls anything about it.

Ken

Cheesy · Sep 26, 2011

Not the monoshock one but I just stumbled across this site which is quite interesting

http://www.jamiewaters.com/Frame-5-moto ... 4571796207

Carbonfibre · Sep 27, 2011

Like it or not any motorcycle which in effect has its rear wheel rubber mounted, which allows it to move independently from the front wheel, isnt going to handle as well as one with a properly designed chassis to which both wheels are rigidly mounted!

The main advantage of mono-shock rear suspension has to do with the fact that its possible to incorporate linkages, which provide a rising spring rate, and this is relatively inexpensive and easy to do.

More modern TS suspension units do work pretty well though, and will provide handling thats quite a bit better than bikes still fitted with the crude OE type rear units.

Rohan · Sep 27, 2011

Carbonfibre said:
Like it or not any motorcycle which in effect has its rear wheel rubber mounted, which allows it to move independently from the front wheel, isnt going to handle as well as one with a properly designed chassis to which both wheels are rigidly mounted!

This is only true if all other things are equal.

However, in the case of Commando vs featherbed, all things are not equal.
And since in their day a Commando went round the IoM circuit faster than a featherbed ever did, obviously other things come into play. Engines, and riders, included...

Manx featherbed frames had the interesting property that the steering appeared to be strongly tied to a level of frame flexibility (like racing bicycles ?, where too stiff a frame killed the performance)) - manx race bikes didn't have steering heads with gussets added ( like the road bikes) - and adding the gussets altered the steering qualities, not for the better.
So even with isolastics, a Commando may still be keeping its wheels in line better than a featherbed. ?

Interesting research material there - 40 years ago would have been an interesting subject ?
Ducati probably are researching much the same thing with their current MotoGP bike - too much frame stiffness is adversely affecting front end performance, where chatter under braking is proving insurmountable ?? Ask Rossi - and Stoner.

Cheers.

Cheesy · Sep 27, 2011

Heres some more random stuff, no monoshock bike though

http://translate.google.co.nz/translate ... md%3Dimvns

Rohan · Sep 27, 2011

lcrken said:
This is the picture of the JPN F750 with monoshock rear that Dave Croxford rode. It's from Roy Bacon's book "Norton Twins". I was hoping someone on the list had some info on it. I have a couple friends who still worked for Norton in that period, and I'll see if either of them recalls anything about it.

Ken

Thanks for the pic Ken, good memory for these things.

Thats an awfully thin looking upper swingarm triangle frame tubes setup.
One wonders if a bit more strength there would have assisted suspension performance.?

The geometry is not visible, but you'd also wonder where the upper anchor point was - if not far enough up the spine frame, you'd imagine the geometry was more a lash-up than a full monoshock setup. Wonder what they did for the monoshock - shock quality is rather important here...

Cheesy · Sep 27, 2011

Rohan said:
lcrken said:

This is the picture of the JPN F750 with monoshock rear that Dave Croxford rode. It's from Roy Bacon's book "Norton Twins". I was hoping someone on the list had some info on it. I have a couple friends who still worked for Norton in that period, and I'll see if either of them recalls anything about it.

Ken

Click to expand...

Thanks for the pic Ken, good memory for these things.

Thats an awfully thin looking upper swingarm triangle frame tubes setup.
One wonders if a bit more strength there would have assisted suspension performance.?

The geometry is not visible, but you'd also wonder where the upper anchor point was - if not far enough up the spine frame, you'd imagine the geometry was more a lash-up than a full monoshock setup. Wonder what they did for the monoshock - shock quality is rather important here...

It looks like it is right below the inlet manifold behind the cylinders

Carbonfibre · Sep 27, 2011

Rohan said:
Carbonfibre said:

Like it or not any motorcycle which in effect has its rear wheel rubber mounted, which allows it to move independently from the front wheel, isnt going to handle as well as one with a properly designed chassis to which both wheels are rigidly mounted!

Click to expand...

This is only true if all other things are equal.

However, in the case of Commando vs featherbed, all things are not equal.
And since in their day a Commando went round the IoM circuit faster than a featherbed ever did, obviously other things come into play. Engines, and riders, included...

Manx featherbed frames had the interesting property that the steering appeared to be strongly tied to a level of frame flexibility (like racing bicycles ?, where too stiff a frame killed the performance)) - manx race bikes didn't have steering heads with gussets added ( like the road bikes) - and adding the gussets altered the steering qualities, not for the better.
So even with isolastics, a Commando may still be keeping its wheels in line better than a featherbed. ?

The main reason for rubber mounting the Commando motor was to reduce vibration, and allow the continued use of a power unit whose basic design dated back to the 1940s.

Its not really sensible to compare the Commando race frames, most of which I would imagine had engine and gear boxes bolted up solidly, rather than rubber mounted, to road going machines which in standard form would be not be a lot of use for racing.

Handling problems related to early Jap machines were mostly to do with frames which flexed.............the Commando has much more flex built in as standard, so it seems strange that in 2011 that this flex doesnt seem to be affecting Norton handling at all?

Interesting research material there - 40 years ago would have been an interesting subject ?
Ducati probably are researching much the same thing with their current MotoGP bike - too much frame stiffness is adversely affecting front end performance, where chatter under braking is proving insurmountable ?? Ask Rossi - and Stoner.

Cheers.

grandpaul · Sep 27, 2011

Cheesy said:
Sure a monoshock doesn't have the same displacement as twins but surely it must have to dissipate the same (or very close to) amount of heat for a given rear wheel movement.

Nobody remembers the name of the cave man that invented the simple lever, but he didn't sweat as much lifting that first boulder as the six other guys that tried to lift it.

Bernhard · Sep 27, 2011

lcrken said:
There's been a lot of discussion on this forum about grandpauls adventures with building his monoshock Commando, everything from accolades to pretty much calling it a death trap. I just wondered if people are aware that Norton built and raced their own monoshock John Player and Gulf sponsored F750 racer back in 1974? There's a picture of it in Roy Bacon's book, with Dave Croxford on it, and a brief mention of it in Mick Wollett's book. Mick says that the bike was originally designed for the Cosworth Challenge, but was fitted with a Commando engine because the Cosworth wasn't ready in time. As far as I know, all the other F750 bikes, including the down-sized Commando style, the monocoque, and the space frame used isolastics. I'm curious if the monoshock also used them. Does anyone on the list know more about this bike?

Ken

Perhaps this was the frame that ‘crasher Coxford ‘ broke and the Norton mechanics turned into a lampshade for him with the inscription ‘3 weeks to make it, 3 seconds to break it’

:cry:

Seeley920 · Sep 27, 2011

Bernhard said:
lcrken said:

There's been a lot of discussion on this forum about grandpauls adventures with building his monoshock Commando, everything from accolades to pretty much calling it a death trap. I just wondered if people are aware that Norton built and raced their own monoshock John Player and Gulf sponsored F750 racer back in 1974? There's a picture of it in Roy Bacon's book, with Dave Croxford on it, and a brief mention of it in Mick Wollett's book. Mick says that the bike was originally designed for the Cosworth Challenge, but was fitted with a Commando engine because the Cosworth wasn't ready in time. As far as I know, all the other F750 bikes, including the down-sized Commando style, the monocoque, and the space frame used isolastics. I'm curious if the monoshock also used them. Does anyone on the list know more about this bike?

Ken

Click to expand...

Perhaps this was the frame that ‘crasher Coxford ‘ broke and the Norton mechanics turned into a lampshade for him with the inscription ‘3 weeks to make it, 3 seconds to break it’ :cry:

No, that was a monocoque chassis!!

Cheesy · Sep 27, 2011

grandpaul said:
Cheesy said:

Sure a monoshock doesn't have the same displacement as twins but surely it must have to dissipate the same (or very close to) amount of heat for a given rear wheel movement.

Click to expand...

Nobody remembers the name of the cave man that invented the simple lever, but he didn't sweat as much lifting that first boulder as the six other guys that tried to lift it.

In that case its the rocks name that we want

The shock (damper part of it) is essentially dissipating energy by transforming kinetic energy to heat energy, the leverage ratios do not effect this, they do however dictate the physical nature of the damper (ie size and valving etc).

lcrken · Sep 27, 2011

Thanks for the pic, Cheesy. It does show more detail than the one I have. I'm still really curious if it used isolastics, like the other F750 bikes.

I've sent an email to my friend, Mick Ofield, who worked for Norton in that time frame, and was around the race shop a lot, asking if he has any info to share. I'll post anything interesting that I find out. I'll see if I can reach Brian Slark and ask him about it. I think he was still at the factory during that time frame.

Ken

Carbonfibre · Sep 27, 2011

Why use rubber mounts on a race frame? Seems to me anything that means the wheels are not rigidly attached to the chassis, while being perfectly ok to reduce vibration on a road going machine, is not likely to be acceptable for racing?

Cheesy · Sep 27, 2011

lcrken said:
Thanks for the pic, Cheesy. It does show more detail than the one I have. I'm still really curious if it used isolastics, like the other F750 bikes.

I've sent an email to my friend, Mick Ofield, who worked for Norton in that time frame, and was around the race shop a lot, asking if he has any info to share. I'll post anything interesting that I find out. I'll see if I can reach Brian Slark and ask him about it. I think he was still at the factory during that time frame.

Ken

I stole it from the link I posted above with the translated French forum, has anyone read the Peter Williams book? sounds like that could have most of the answers to these questions, also on the home page of the first link I posted is a picture of the Cosworth bike in bits

Cheesy · Sep 27, 2011

Carbonfibre said:
Why use rubber mounts on a race frame? Seems to me anything that means the wheels are not rigidly attached to the chassis, while being perfectly ok to reduce vibration on a road going machine, is not likely to be acceptable for racing?

It obviously was acceptable for racing otherwise they would have hard mounted them don't you think?

Monoshock Commandos

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