Monoshock Commandos

Cheesy said:

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

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I'm guessing they wanted to achieve some racing milestones with the isolastics, so they could tout the iso system's racing achievements/heritage in thier promotional literature...

"Win on Sunday, Sell on Monday"

grandpaul said:

Cheesy said:

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

Click to expand...

I'm guessing they wanted to achieve some racing milestones with the isolastics, so they could tout the iso system's racing achievements/heritage in thier promotional literature...

"Win on Sunday, Sell on Monday"

Click to expand...

That is probably true, but they did have some reasonable success so even if they were a compromise they still worked to a degree, I bet it worked for JPS as well! The top ISO in the monocoque definitely looks interesting with the large lateral separation compared to any other top ISO

just out of curiousity, has anyone tried replacing the rubber bits in the isolastic units with solid steel bits, to see what a Commando feels like solidly mounted ?

Would the frame take it ?
Where would need strengthening to permanently do this ?

I don't think the frame will stand up to the vibes as-is.

Even hard rubber donuts have been tried and they transmit a lot of vibes.

I can't help feeling that that monoshock structure looks somewhat flimsy for the loads imposed on it, but maybe someone did the calculations and thats all that was needed.
Monoshock mounted horizontally must have been challenging for the oilflow pathways inside...

What was the result of the monoshock testing ?
It wasn't pursued then ?
Obviously haven't read PW's book.

Cheers.

Rohan said:

I can't help feeling that that monoshock structure looks somewhat flimsy for the loads imposed on it, but maybe someone did the calculations and thats all that was needed.
Monoshock mounted horizontally must have been challenging for the oilflow pathways inside...

What was the result of the monoshock testing ?
It wasn't pursued then ?
Obviously haven't read PW's book.

Cheers.

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I think I might have to buy that book... If it was a gas charged shock with some sort of floating piston the orientation shouldnt matter too much. It looks like its relatively high so it may be around a 3:1 leverage ratio, not massively larger than the twin shock set up and by no means as big as most modern mono shock setups. I wounder how much influence on the chassis design the nice straight megaphones had

I've read Peter's book, and it is a great read. Unfortunately, he only mentions the monoshock briefly, with no real details. He calls it a "pretender Challenge", because it was supposed to be a development vehicle for the coming Cosworth designed Norton Challenger. They had to use a Commando engine and transmission because the Cosworth engine wasn't avaiable in time. He's not to favorable about it, saying it was too flexible to steer well and ride hard. From his description, it sounds like the swingarm and upper shock mount were both attached to the engine/gearbox cradle.

He does have only good things to say about the monocoque 1973 John Player F750 bike, which had a very successful career. He really liked riding the bike, and won the 1973 Isle of Man F750 race on it. That certainly demonstrates that an isiolastic system can work very well as a race bike. On the other hand, he didn't have a lot of praise for the Commado Production Racer, even though he did very well on it. His complaint seems mostly to be that it wasn't really a proper race bike, just a modified production bike.

I recommend the book to any serious Norton fan.

Ken

This is the only picture of the monoshock F750 in Peter's book. He is on the monoshock, and Dave Croxford is on the space frame bike (which Peter also didn't think much of).



Ken

Can we assume the mono shock and mono coup retained isolastics as no mention of special frame to take the cracking fatigue like say a Sealey. I see a way to fit mono to Peel under center of frame but don't know leverage factors to pick a mono shock spring or length of action. Wonder if a mono could give 6" rear travel, now that would have real appeal besides a few lb less mass that lives under center of bike instead of behind pilots butt. I see a way to brace swing arm spindle to the inner primary case and cradle. Inner case on Peel may end up as braced as the Z plates. Peels swing arm anti-sway bars would take the twist loads off a mono shock, so who knows what yo'all may drive me too next.

I've 3 points of reference now on flex vs rigid advantage, the Indian leaf spring girder hard tail, the Manx ungussetted stem chassis and Ms Peel. But the springing must be tamed out of the flexing, same as suspension. Regardless in case anyone cares but me, to me putting much side loads on a cycle is rather limiting dangerous way around, so I tend to lean over more so most all the turning loads work through normal suspension axis. Interestingly the more one leans the more the forks expand and the more the forks expand the more secure the lean to put loads in line with suspension action. Personally I think the flexy swing arms and forks in moderns shoots them in their own feet so to speak.

Btw does the Vincent counts as a mono shock geometry and advantage, even though two shocks were used?

Mono=1

Sorry.

hobot said:

Can we assume the mono shock and mono coup retained isolastics as no mention of special frame to take the cracking fatigue like say a Sealey.

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The monocoque bikes definitely had isolastics. The 1974 monoshock was an experiment, and I'm still trying to find out if it had isolastics. Peter says that it was "similar to the 1971 one but with a monoshock, a bell-crank swing-arm, with the Commando engine fitted as part of the frame to simulate the Cosworth engine." That's kind of confusing, because the 1971 bike was very similar to a standard Commado frame, but smaller, and had isolastics. But, the final Cosworth-engined Challenge was completely different, with the engine as a stressed part of the frame, and with twin shocks.

I've got a reply from Mick Ofield, and he doesn't have any info on the monoshock. I still have to try Brian Slark.

Ken

Oh cool, I was hoping the monocoque had isolastics and still great bragging rights on the handling. I'm both fascinated and dependent on flexing just enough w/o any rebound on release to un-wrap-snap back to its resting unloaded state. If chassis/suspension tends to rebound beyond its resting Neutral state if makes going around fast too serious dangerous racer effort/risk I'm allergic too. Not fun.
We have quite a few examples that prove mono shock + isolastics works as good as regular C'do, just don't know it can exceed its handling w/o some other isolastic taming devices.