Monoshock and PR at Daytona 1990

The monoshock layout and the dampening rates were taken from the Ducati TT2

jseng1 said:

The monoshock layout and the dampening rates were taken from the Ducati TT2

Click to expand...

And they work extremely well. I didn't mean to imply that we had a serious chatter problem. Rob was an extremely competitive rider, and was pushing the bike to its limits before the chatter started to show up. Modern radial slicks stick so well that front end chatter is just one of the performance factors that you have to juggle in trying to optimize the handling. It's all tradeoffs. Too much weight distribution one way and you get chatter, another way and you get prone to high sides. An adjustment that improves handling in one area often degrades it in another. We were lucky in a way. We didn't have all the adjustments available that modern race bikes have, so our options for change were limited to pretty simple choices. You can get completely lost in all the adjustments a modern bike gives you. High speed damping, low speed damping, pre-load, front and rear ride heights, spring rate choices, adjustable steering heads for trail, adjustable swing arm heights. You need to be much more of a suspension techie to set up bikes properly now.

Ken

Thanks for the Ducati reference though over my head to use. I found I like to feel the rear end squat on tight turns, especially if enough squat to about totally relieve front tire aim traction effect. If I can go in hot enough the front lifts out of effective traction though still in contact- so hitting grit don't bother it and rear is loaded enough it don't just skip right out from under. If rear does slip I don't like it to change lean angle, just widen turn some or turn bike a bit on its CoG, till it stops slipping [one-few inches] and aimed a bit more into the turn to finish.

The more 'interesting' upsetting to me phenomena is when power cut while leaned and weight shifts back on front. Front may not hold and if loaded so it does then rear gets iffy again. I tend to avoid this by not letting off leaned.

Don't know yet how the rebound valving, geometry, height of rear shock effects this. Most seem to like rear end higher i seem to like it lower, hm.
Did JIm's mono shock height remain same as Norton at rest?
Did it allow more travel range? Did shock have dampening adjustment?

lcrken said:

jseng1 said:

The monoshock layout and the dampening rates were taken from the Ducati TT2

Click to expand...

And they work extremely well. I didn't mean to imply that we had a serious chatter problem. Rob was an extremely competitive rider, and was pushing the bike to its limits before the chatter started to show up. Modern radial slicks stick so well that front end chatter is just one of the performance factors that you have to juggle in trying to optimize the handling. It's all tradeoffs. Too much weight distribution one way and you get chatter, another way and you get prone to high sides. An adjustment that improves handling in one area often degrades it in another. We were lucky in a way. We didn't have all the adjustments available that modern race bikes have, so our options for change were limited to pretty simple choices. You can get completely lost in all the adjustments a modern bike gives you. High speed damping, low speed damping, pre-load, front and rear ride heights, spring rate choices, adjustable steering heads for trail, adjustable swing arm heights. You need to be much more of a suspension techie to set up bikes properly now.

Ken

Click to expand...

Modern suspension is something that has the potential to improve the performance of any older bike enormously, but many people dont seem to be completely aware of the fact that adding modern parts to an earlier machine can in some circumstances mean other problems show up. These are often related to lack of chassis rigidity, which can be very difficult to deal with, and in some extreme cases may mean bikes may not be suitable for use in serious competition.

In terms of TS suspension the best in the world currently seems to be the Maxton T260-C units, which are used on serious classic racers such as MV and Paton. For anyone contemplating fitting modern suspension parts, its worth remembering that most of the TS units commonly available currently are based on designs which are at least 30 years out of date, and are obviously not going to work as well as modern TS suspension units.

Carbonfibre said:

In terms of TS suspension the best in the world currently seems to be the Maxton T260-C units, which are used on serious classic racers such as MV and Paton. For anyone contemplating fitting modern suspension parts, its worth remembering that most of the TS units commonly available currently are based on designs which are at least 30 years out of date, and are obviously not going to work as well as modern TS suspension units.

Click to expand...

I'd say the kits made by Cosentino Engineering to be superior to anything Maxton is doing. The kits are comprised of the latest (2010) Showa shim-stack technology cartridges, and feature adjustable compression, rebound and preload, with 6 different spring rates available.

They drop right in to any standard Commando fork system with no modifications. Kits are also available for Triumph T140-on, and Ceriani forks, all with the same features.

Before I sold the bike to Ken it was set up with wire wheels and tube tires. The forks were modified with slippery synthetic bushings top and bottom. This was the mid 1980s. At that time none of the fork dampening units were that sophisticated. They were just beginning to use compression dampening. So I built my own wafer disc type front dampening units using Marzochi rear shock components, recalibrated them and fit them into the forks. The front end was dropped and the upper fork bushings were raised to increase the overlap distance and reduce friction. No one ever passed me in the turns. And I surprised a lot of riders by cruzing around them at absurd lean angles - my entire leg up to me knee and boot and toes dragging on the pavement. The bike was so stable you could just push it until the tires began to slide and hold it there at any speed. I could take the big fast turn (8) at willow springs wide open somewhere around 140 mph or whatever that bike could do, feeling the tires skitter and drift a little while I was laying forward on the tank keeping the front end planted. In first gear I could get broad slides coming out of the last slow turn at Laguna Seca. I remember the flagmen freaking out each lap because they thought I was going to lose it. I used a close ratio 4 speed and that was a big disadvantage compared to a 5 speed and it cost me a lot of ground waiting for the cam to hit (the 850 was pumped up for max top end). In those days the option was a wimpy 5 speed quaife and I had already burst a gear case and worn my gears at an angle from so much gear shaft flex. I just didn't have the $ for everything. By then the watercooled Ducatis were coming out and there was no catching them.

Ken installed better breaks, magnesium wheels and tubeless radial tires and put in a 920 motor. The bike was faster and he and Rob made a great show of it. I'm grateful that he took it a step further and earned a BOTT place on the podium.

The photo below shows an earlier version than Ken's. Note the bluish color of the overcooked front tire. Kens version is the photo at bottom. With Kens encouragement I have made the frame plans available for only $10 at my website (jsmotorsport.com) . I would sure like to see some of these frames completed and running on the street or track.

Jim Schmidt

Holmeslice said:

Carbonfibre said:

In terms of TS suspension the best in the world currently seems to be the Maxton T260-C units, which are used on serious classic racers such as MV and Paton. For anyone contemplating fitting modern suspension parts, its worth remembering that most of the TS units commonly available currently are based on designs which are at least 30 years out of date, and are obviously not going to work as well as modern TS suspension units.

Click to expand...

I'd say the kits made by Cosentino Engineering to be superior to anything Maxton is doing. The kits are comprised of the latest (2010) Showa shim-stack technology cartridges, and feature adjustable compression, rebound and preload, with 6 different spring rates available.

They drop right in to any standard Commando fork system with no modifications. Kits are also available for Triumph T140-on, and Ceriani forks, all with the same features.

Click to expand...

Cartridge fork kits wont work very well on the back of the bike which is where the T260-C shocks are fitted! Maxton also do custom cartridge fork upgrades, which are purpose designed for each specific application, and like the T260-C rear units are used on very serious race bikes.

Much less costly one size fits all cartridge fork conversions are certainly going to be an improvement on old 1960's internals, but are not comparable to custom made set ups, often used on classic race bikes.

Thanks for describing the excellent handling at extremes of lean and power Jim. No room to lean more mostly d/t leg meat in the way! That is how secure Ms Peel was so I don't know if she's just up to your 2 decade old standards or able to exceed them. I know Combat 750 was not enough power to catch your 140 flings.

Was there any sense of bike tending to fall on down or want to rise back up in these topped out leaned turns?

Did you have a damper? Part of rules or just made nicer?

'"those were the days, my friend, we thought they'd never end." '

I recently attended a meeting of our local council about the future of our town. The council people had a popular saying 'in the future, we will be doing jobs which we cannot imagine'.
Perhaps that is our problem - LACK OF IMAGINATION ?
In my opinion any commando-based bike is an excellent machine, and will always be successful when racing against the same TYPE of machine:

i.e. AIR-COOLED FOUR-STROKE TWINS OF SIMILAR CAPACITY.

I am now 75 years of age and my deepest regret is that I could not race my Seeley 850 back in the 70s against air-cooled Ducatis, Guzzis and BMWs.

These days a simple answer would be only air-cooled motors in a Battle Of The Twins class. Then the days might really 'never end'.

Why have people got problems with their Seeleys vibrating ? I run an 850 motor which has standard pistons. However I have threaded a steel plug into the hole in the other side of the flywheel so the balance factor is now 72%. The bike rocks backwards and forwards while idling, but at 7000 RPM it is dead smooth. If you think about it, do you believe that big hole was there when that crank was used in the Atlas ?
I have never ridden a Commando with isolastics, so I cannot comment on the handling. Should a rider who has never ridden a Seeley comment on it's handling ? All I know is that my Seeley is much better than any other bike I have ever raced. Not that I have ridden a lot of different bikes in road races. It is extremely direct and fast steering. It has Ceriani forks and Koni shocks and the suspension never gets out of control. It's an old formula, but tried and true.

My earlier photos aren't showing up so heres a pic of an earlier version of the monoshock with spoke wheels as I raced it before I sold it to Ken.



I addressed the vibration problem with lightweight pistons. These are the 1st I made (from Wiseco blanks) back in the late 1980s. It was an 850 but the pistons weighed the same as 750 pistons. They were shorter so I had to cut the cylinder to lower the head because I was using stock rods back then.

The light-weight pistons and long rods probably partially solve two problems. Piston inertia has a major effect in slowing acceleration of the motor's internals. Reducing it is probably a much better way to go than lightening flywheels. And the longer rods lengthen rock-over time - better for developing horsepower with little loss of torque.
The trellis frame looks good, it should be very rigid, however there looks to be a lot of un-necessary weight. In all of these things often what you lose on the hurdie gurdie, you pick up on the merry-go-round. I think it is difficult to beat the Mk2 Seeley frame. I followed my Mk3 Seeley rolling chassis around for about two years before buying it in the 70s, when many people did not know what it was. The MK3 is good, however I think the Mk2 is better. The other aspect is provenance - Gus Kuhn raced Seeley Commandos extensively and successfully, back in the era. So a replica has some kind of history associated with it.

The monoshock Norton frame was not designed to compete against Seeleys. It was designed to compete against the monoshock Ducatis that were just coming out at the time and blowing everything else into the weeds. The monoshock Nort was designed for a 6" wide rear tire and it was also raced with radials. The Seeley wasn't designed to handle that kind of sticktion. I could lean it over 53 degrees (past 45) and drag my leg from the knee to ankle until the tires began to slide and just hold it there through the turn with no chattering or wobbling. No one passed me in the turns. But the competition was outpowering me with 90hp monoshock Ducs, 100+ HP Motoguzzis in custom monoshock frames (Dr John) and "Lucifers Hammer" (XR1000cc HD) in a redesigned frame. These were the fastest twins on the circuit at the time (mid & late 80s). You have to be on a track at a National championship race (BOTT) with riders like Marco Lucchinelli and Gene Church on these bikes to know what I'm talking about.