Trick suspension

baz said:

The engine dosent move that much on the ISOs
How does a monoshock affect it?
I'm assuming the bottom link is attached to the gearbox plates and not the frame

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No bottom linkage. Shock is attached directly to swinging arm. More detail shown in the link referenced above by Time Warp.

Ken

Brooking 850 said:

At times like this I would suggest that Alan hasnt had any personal experience riding a well sorted street Commando and relies heavily on a Seeley framed Commando which hasnt had any race outings for sometime, so a lot of his comments are hypothetical.
Just saying!
Regards mike

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Brand loyalty is admirable, especially when it involves something as nice as a Norton Commando. However I would never attempt to race one in standard form. It is probably a bridge too far. I once looked at buying a frame, but walked away - it is too fragile.

jseng1 said:

I've experience Norton race bikes with twin shocks and with mono shock. There is no doubt that a well laid out monoshock is a better handler. It soaks up the bumps where twinshocks don't and helps you get through the corners faster. The photo below is my monoshock as I was racing it. It turned the fastest Norton times that I know of at Willow springs.

An even faster version of the bike as it was modified by Ken Canaga with 920cc motor, front end upgrade and mag wheels. With rider Rob Tuluie who was the last one to put a Norton on the podium in AMA BOTT (against a field of Ducatis).

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In Australia, most of the racing in which you can feasibly ride a Commando based bike, comes under historic racing rules. It is a pity because it stifles development. Your racing in America must be different and probably better. I am not a purist, but I like historic bikes to have some sort of authenticity. I'd prefer to ride in open road races against similar types of bike. To me the details are not so important. If someone fronted with a 961, I would still race - the year of manufacture is irrelevant.

acotrel said:

I would never attempt to race one in standard form. It is probably a bridge too far. I once looked at buying a frame, but walked away - it is too fragile.

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That is the brilliance of the Isolastic frame, simplicity by design, less was more.

acotrel said:

In Australia, most of the racing in which you can feasibly ride a Commando based bike, comes under historic racing rules. It is a pity because it stifles development. Your racing in America must be different and probably better. I am not a purist, but I like historic bikes to have some sort of authenticity. I'd prefer to ride in open road races against similar types of bike. To me the details are not so important. If someone fronted with a 961, I would still race - the year of manufacture is irrelevant.

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As you assume, Jim's monoshock Norton was not raced as a historic bike, but in the AMA Battle of the Twins class, later changed to Pro Twins, where it ran against other 4-stroke twins, including some very modern bikes. Later it would also qualify for classes run under the AHRMA (American Historic Racing Association) banner, but not considered vintage or historic. Originally, AMA introduced the BOTT classes in the early '80s, and they were very successful, so naturally AMA started dismantling them, and eventually eliminated them in the early '90s. At that time, AHRMA stepped in and set up classes to allow the same bikes to continue to compete. It was a lifesaver for those of us who had invested in race bikes for the classes. AHRMA has recently reorganized the classes, trying to keep as many bikes as possible competitive in each class.

Ken

If the shock is attached to the frame from the swing arm the steeper the the angle the more rearward force it will put in to push the engine, gearbox,swingarm and wheel to the rear of the iso mounts. i can tell the difference on a standard commando from solo to 2 up in vibration from the load with the inclined shocks trying to push the iso assembly rearward.

baz said:

The engine dosent move that much on the ISOs
How does a monoshock affect it?
I'm assuming the bottom link is attached to the gearbox plates and not the frame

Click to expand...

Kenny's original prototype 952 design uses a box section and rising rate linkage on a very nice 3-way adjustable shock. Very simple and just two small tabs welded to the frame that are invisible. The cradle is modified to accept a pair of sealed bearings (steering neck spec) retainers are visible just inside the shifter loop. The forks are Kawasaki ZRX and work great, except they limit the turning radius; difficult in a tight parking place. Triple discs are MORE than enough, (please reserve comments regarding the front fender)

Handles great, but that's just my subjective opinion, never ridden on a track by a well-trained rider that could discern nuances.

My monoshock design uses 2 standard swingarms and an upgraded rising rate linkage with better adjustment range. As with Kenny's design, it FEELS excellent, but was never on a track. (again, please disregard the front fender)

The closer the shock mount/s are to the wheel hub centerline, the less force is put into the isolastics due to the leverage ratio changing as you move the load point away from the wheel and up the swingarm towards the isolastics. This wouldn't present a problem to a frame mounted swingarm without isolastics, but a swingarm with isolastics would have more force levered into them by the swingarm as the suspension's load point is moved away from the wheel. It might not be noticeable when riding, but the mechanical configuration difference predicts some force differences to the isolatics.

lcrken said:

As you assume, Jim's monoshock Norton was not raced as a historic bike, but in the AMA Battle of the Twins class, later changed to Pro Twins, where it ran against other 4-stroke twins, including some very modern bikes. Later it would also qualify for classes run under the AHRMA (American Historic Racing Association) banner, but not considered vintage or historic. Originally, AMA introduced the BOTT classes in the early '80s, and they were very successful, so naturally AMA started dismantling them, and eventually eliminated them in the early '90s. At that time, AHRMA stepped in and set up classes to allow the same bikes to continue to compete. It was a lifesaver for those of us who had invested in race bikes for the classes. AHRMA has recently reorganized the classes, trying to keep as many bikes as possible competitive in each class.

Ken

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In Australia when we create a race class, the first thing the guys involved do is think about what they DO NOT want to race in that class. I would be extremely happy to race my Seeley 850 in an open class of air-cooled four-stroke twin-cylinder motorcycles of up to 1000cc engine capacity - no other rules ! - Forget fuel, tyres, suspension, year of manufacture - it is all bullshit !
Sadly for me, it is too late - what could have been is never going to happen.
About seven years ago, there was a guy in a superbike race at Winton, riding an air-cooled 1000cc Ducati who was going very well. His bike would probably cream my Seeley 850 , but I would love to have a go at him. They are there, but not often.

In the 1960s Ken Blake raced the 730cc Jesser Triumph in Australia. It always ran a mix of nitromethane, toluene and methanol in A grade races in which most bikes were methanol-fuelled Manxes. Nobody complained, even when the Triumph spread it's guts all over the ground and crashed four other riders. It was always extremely good racing. These days most guys seem to want the easy win and try to get it by fiddling with rules. The result is that many good race bikes stand idle.
I can even think of two entire race classes which have become defunct - 'Sounds of singles and Harley 883 Sportsters' - those bikes are still sitting around and you can buy them cheap. - All excluded by the rules.
I have seen historic races with four bikes on the start-line when the circuit is licenced for thirty.

when I fitted a horizontal monoshock above gearbox to a custom framed Mk3, I added a horizontal tie bar ( with heavy duty rodends) below shock, between engine plates and frame, to stop Iso compression front/rear direction. Luckily, a Buell Ohlins shock has very similar leverage ratios and lots of adjustment...

jan nelder said:

when I fitted a horizontal monoshock above gearbox to a custom framed Mk3, I added a horizontal tie bar ( with heavy duty rodends) below shock, between engine plates and frame, to stop Iso compression front/rear direction. Luckily, a Buell Ohlins shock has very similar leverage ratios and lots of adjustment...

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Very interesting... pictures...?

lcrken said:

As you assume, Jim's monoshock Norton was not raced as a historic bike, but in the AMA Battle of the Twins class, later changed to Pro Twins, where it ran against other 4-stroke twins, including some very modern bikes. Later it would also qualify for classes run under the AHRMA (American Historic Racing Association) banner, but not considered vintage or historic. Originally, AMA introduced the BOTT classes in the early '80s, and they were very successful, so naturally AMA started dismantling them, and eventually eliminated them in the early '90s. At that time, AHRMA stepped in and set up classes to allow the same bikes to continue to compete. It was a lifesaver for those of us who had invested in race bikes for the classes. AHRMA has recently reorganized the classes, trying to keep as many bikes as possible competitive in each class.

Ken

Click to expand...

My fondest memory of AMA BOTT racing action was, in the mid/late eighties, at Loudon, NH (Laconia Rally).
The airheads, Spirtsters all duking it out, quite competetive.
Meanwhile, a few Kawasaki EX500 Ninja’s were running rings around them.
At some point, there was a change to call the class “American Twins”.

n

Fast Eddie said:

Very interesting... pictures...?

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not signed up for pics on this forum, and difficult to see with bike assembled.

concours said:

My fondest memory of AMA BOTT racing action was, in the mid/late eighties, at Loudon, NH (Laconia Rally).
The airheads, Spirtsters all duking it out, quite competetive.
Meanwhile, a few Kawasaki EX500 Ninja’s were running rings around them.
At some point, there was a change to call the class “American Twins”.

Click to expand...

A decent race class probably should not be that specific. It does not achieve much. In Australia, we had a one-make class for 883 Sportsters - it did not last very long, All it needs to be is a BOTT for aircooled four-strokes up to 1000cc. With air-cooled motors, heat build-up creates a development wall which inhibits the use of more valves per cylinder. So the playing field becomes more level.

As far as the Kawasaki Ninjas are concerned - there are plenty of bikes which are faster than most air-cooled four-stroke twins. I once watched a guy on an RS125 Honda ride around a whole field of guys on 600cc sports bikes. It proves nothing. When you race, the guys you have to beat are those who are riding the same TYPE of bike, and I am not talking about brand, age or nationality. In my own case, I ride in historic races against all types of bikes. The only one that interests me, is a guy who rides an SD900 Ducati bevel , in another period. I can move the eligibility of my bike up one period to get into the same races as him - all too difficult !

In Australia, there was only ever one air-cooled four-stroke twin cylinder race bike which had four valves per cylinder. It was Bob Brown's 851 Ducati Pantah which Kevin Magee rode at Bathrurst. It was probably on methanol. All factory four-valve Ducatis have been water-cooled. It then becomes a different game. I don't believe that Norton twins have reached the end of their potential development. They still do not resemble Patons.