isolastics

"And once again I realize I'm just repeating stuff I've posted before, so I'll stop trying to preach to the unbelievers on the virtues of isolastics, at least for a while."

Ken I think most of us are all ears when it comes to your opinions about anything Commando related.

I read anything that Ken posts, very carefully. It is always valuable information obviously gained by doing the hard yards.

'And once again I realize I'm just repeating stuff I've posted before, so I'll stop trying to preach to the unbelievers on the virtues of isolastics, at least for a while.

Ken'

Ken I was brought up racing in the era when we didn't have tyres. If you had the slightest change of mind, you were on the deck. I still ride as though I was back then. Speed is only relative, if the tyres and handling are good, the speeds rise and you find yourself back in the same situation where if you blink you crash. I believe a lot of young guys these days simply ride around their handling problems without becoming aware of how good their bike could be. I've never ridden a standard commando with those isolastics, however I've read about the weave. If my bike did that, I'd weld the isolastics up solid. I have crashed a lot of times in my life. Nobody can afford to be launched at full speed.

Thanks for the kind words, guys. It seems to me that I sometimes end up running on a bit, and I don't want to be the old guy who goes on and on repeating the same old stories. Much as I love Commandos (and other Nortons), I've also raced more modern bikes, and nothing I could do to a normal Commando would make it work as well as some of today's bikes. That doesn't keep me from trying to improve my Nortons, and I still find riding my Mk 3 on modern 19" tires to be great fun, but I've ridden plenty of modern bikes that would run circles around it in most situations. I've surprised a lot of riders with how well the Commando works in the twisties here, and that's good for my ego sometimes, but I also know I could get through even quicker on a modern sportbike, except for the fact that my back and knees can't handle the riding position any more.

Alan, I also started racing back before the era of modern race tires, although maybe not as early as you started. I started racing in 1972 when I was 30 years old. Couldn't afford it before then (and probably not after, but I did it anyhow). I started racing on the Dunlop K81s (TT100) that came as original on my 1971 Commando Production Racer, 3.60x19 front and 4.10x19 rear. They were considered pretty good race tires back then, but were nothing like the modern rubber. As the years passed I went through the Dunlop KR73 and KR76 triangulars, then the early Michelin 18" slicks, followed by Dunlop 18" slicks, still all bias ply designs. They all worked on the PR with it's original isolastics, although the rest of the bike saw a lot of mods. Before I quit road racing, I had a lot of experience on modern radial slicks in Sound of Singles/Supermono classes, and found they were so much better that I wasn't skilled or brave enough to find their limits. I'm not sure the PR would have worked as well with them. Much as I liked the old girl, the modern slicks put a lot more load into the chassis, and I'm pretty sure the PR wouldn't have been stiff enough for that, even with all the reinforcing I'd done to frame, engine cradle, swingarm, and forks. I don't think that's so much a criticism of the isolastics as it is of the state of overall frame design in the '70s. I'm pretty sure that throwing a set of Superbike sized 17" race wheels and slicks on any period bike (Seeley, Manx, etc,) and trying to find the adhesion limits would show up the flex in those frames too. They just weren't designed for those levels of tire performance.

On the other hand, it is certainly possible to build a bike around the Commando engine and gearbox that will take the modern rubber and handle with the modern bikes. The monoshock Norton that Jim Schmidt built is an example. I bought the bike from Jim when he quit racing, and fitted Marvic mag wheels with TZ250 sized 17" slicks, a 920 cc engine, Quaife 5-speed, 40 mm Ceriani front forks, and Spondon disk brakes, and it ran with the modern twins in AMA Pro-Twins racing. It's still the last Norton to take a podium position at an AMA national road race.

Rambling again, but that's what us old guys do best.

Ken

Keep rambling, Ken. I remember how poor the grip of K81s was on the street, especially wet roads or any sand. My rear tires slid sideways on more than one occasion. Relatively weak drum breaks were a safety feature since it was impossible to lock up a wheel. Those were the days when motorcycle cops were taught to lay the bike over to avoid a crash.

I was slip sliding away on P!! dragster in 71-74 so relate to old vs new age profiles and compounds. In their early days isolastics could be competitive but soon enough no one but no one tries to use an un-tamed isolastic against solid mount vintage and few solid mount vintage are eager to take on a real sports bike with good new tires. I'm sorry if you ain't got balls enough, but I force myself to sqealing howling screaming >>> Involuntary in my helmet to make sure I've no mystery left in how a tire or tires will let go and re-grip, or I'd better not get too frisky. The sadest badest thing about solid moderns is the tires are more capable than the bikes and unpredicable things slash together to flip bike down or up regardless of grip. Only Doug McRae on on Herb Beck's almost solid triple swash plate Cdo is able to match the Seeleys and such in handling. Vibration dulls pilot proprioceptive sense of feed back and response and even visual focus and also adds resonance to tire patches, especially on edges.

I've experienced what its like on a totally neutral handling motorcycle that has innate sideways and twist skew wise suspension in its frame plus a traction control power pulse hook up 3rd power unit suspension, and 4th an innate energy storing device that can hold it as long as needed as a set pressure to increasing to insane pressures and able to release in dribble or all at once like a sling shot, all the while only feeling the rear tire patch molecular bondings and the wind eddies without working up a sweat beyond breath control to keep the lights on. Swing arm flex and feed back is one of the biggest factors to conquer and only a rear link can control that level of forces in isolastics, so as much as top and front links are famous for helping, only 3 examples reported so far, McRae, hobot and a few weeks byJoe Piska, who texted me he's starting to take corners like stuffing it in a shoe box and blasting out. Prior Joes favorite was his paired down and pumped up Honda 500 cafe bike in upper NY state Mt's.

Adding cushions in rear softens the engine vibes too amazingly enough.
Adding air in tires softens engine sense also. If iso's set too close I think the tip or skew of engine lets the space close in an angle so metal metal contacts.
I got a pebble stuck once between skid plate and front iso for horrific vibes like I'd blown my engine and headers off just going 40-50's on THE Gravel.
My opinion now is bike should have a type of over lapping hinge in the middle but very firm towards the axles.

If Peel had no over rev event I'd already have track day and stunt lot video to demo why I have such low poor respect for even $250+ a pop pure non DOT balloon race tires, especially near edges. Only their speed rating has any appeal to me any more. One more weld job to make Zplate swing arm swash plates.

Chris, when I was a kid most Australian race bikes used T1 compound Dunlop Triangulars (KR73?) and methanol fuel. A bit later we had 398 and 498 compounds which were marginally better (good ?). In the late 60s Ron Toombs brought the Henderson Matchless to meetings wearing Goodyear tyres which had a block pattern, and none of us knew how he had obtained them. We did not have 'gumball' tyres until the mid 70s, and when those arrived the angles of lean of classic bikes changed dramatically and racing became much safer. When I was racing my short stroke Triumph 500, I only ever had the T1 compound tyres which I used to run at very low pressure to get some heat into them. The bike itself had an extreme top end motor, and a close 4 speed box, and when fitted with 4 inch megaphones was a real bastard. THe only way it was ever competitive on our local circuit was to drop the tyre pressures and gearing as low a s possible and soften the suspension. The two into one exhaust was essential. Then it had a major advantage on the very twisty part of the circuit. The races were all bump start, so you could blitz them off the start. If you failed to do that, it was all over . My bike was always about 12 years older than most of the others in Allpowers C Grade, and I still managed to rough them up a bit. It was a learning process which I wouldn't recommend to anyone. I walked away from every crash except one.

I love hearing the stories of racers from what were probably the golden years of racers.
I never raced on a track, though; there wern't any open to us, just lots of rural roads. I was a rebellious hooligan (juvenile delinquent) in my wayward youth and was asked by my father to leave home at graduation from high school. I rode Triumphs on the windy hilly narrow roads of rural New England, often at speeds that blurred my vision and vibrated the speedometer enough to make it impossible to know how fast I was going, but certainly over the ton and (once) faster than a police car; a Plymouth Fury. I also rode with friends who wore patches. I cleaned up my act as I saw little future in that direction and friends were either dying or getting locked up. Things would probably be different if kids had a better outlet for their exuberance.
My gradfather was a chemical engineer at Uniroyal, that used to make automotive tires. I have a copy of his patent for a method of vulcanizing rubber. The amount of chemical engineering that has gone into modern tires is phenomenal. I have modern tires on my '79 Bonneville (my ol' reliable former daily rider) that grip well and have never put me into a slide on pavement and only controllable slides on dirt roads. I put Metzler Lasertec tires on my Laverda RGS. I had to grab a bunch of front brake once and did my first "stoppie" without any squeeling or sliding. This kind of grip is nothing short of miraculous for those of us that learned to ride on K81s, or even Avon Speedmaster ribbed tires and drum brakes.
I knew somebody who raced a Ferrari in one of the Cannon Ball Runs. He asked me to copilot one year, but by then the police had effectively put a stop to them. The word went out nationwide when the Cannonball started and the police had descriptions of each car and even knew the names of the drivers.

hobot said:

I'm sorry if you ain't got balls enough, but I force myself to sqealing howling screaming >>> Involuntary in my helmet to make sure I've no mystery left in how a tire or tires will let go and re-grip, or I'd better not get too frisky

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Smile when you say that, pardner!

Seriously, I've had well over 20 broken bones from finding the limits of my tires on race tracks, and have no interest in doing the same on the street. There are no ambulances and paramedics standing by at the local canyon twisties to whisk us away to the nearest intensive care unit.

When your rear tire "let go and re-grip" on a race track, the result is usually a nasty high side crash. Must be different in your world, eh?

Ken

I have low-sided but fortunately never high-sided. Do K-81s have enough grip to high-side or does that only happen with sticky tires? On the street, it is usually hitting a curb or car that sends a rider airborne.

christulin said:

I have low-sided but fortunately never high-sided. Do K-81s have enough grip to high-side or does that only happen with sticky tires? On the street, it is usually hitting a curb or car that sends a rider airborne.

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Or a 'tank slapper'.

Seen the effects of a few of those on various riders.
And bikes, repaired a few of them. Not nice.

One of them didn't have his fork clamp bolts done up tight.
Never leave home without your forks fully assembled... !

lcrken said:

When your rear tire "let go and re-grip" on a race track, the result is usually a nasty high side crash. Must be different in your world, eh?

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To be fair, Commandos on dirt roads are rather prone to sliding about, especially on K81 tires.
Not quite as pronounced if on the old Avon Roadrunners.

Ah yes, I had a tank slapper once, induced by panic maneuvering to avoid hitting a deer on a Vincent. I was terrified. The old lore was to keep tire pressures low to avoid them, since motorcycle wheels normally oscillate a little.

please stop the horrific flash backs fellas. Commandos are kind of weird on Gravel when taken with a bit of spirit, they seem to me to skip front and rear tires out line in opposite directions about 1/3 tire width and pivot above tire patches while other bikes seem to skip about as much but pivot on tire patches more like tarmac handling. Commandos are still dang handy off road if not in some extremes nor race like risking. A big part of my wonder in Ms Peel linkage is I found her more handy that purpose built trial and MX bikes I've tried in same rough back woods course. Were talking ravines so sharp even my 2" front lifted Cdo hi centered, ugh before launching off committed to out race gravity to retain some direction control on forks and faster yet to bottom to have speed enough to blast up taller far side and peel off at diagonal angle of slope kind of skewed side ways like a flat tracker just to keep straight-ish line out of there. Nothing climbs loose slopes like my Combats but Trixie is no match to zoom up like Peel could. Part of the magic I love about isolastics is their innate traction control. To 'safely' test your isolastics handling behavior upset limits weirdness do some short rides on low aired tires.

Sorry that I'm so negative about isolastics , they are probably OK on a road bike. However I must be a bit superstitious and paranoid. I hate the thought of things waiting to grab me by the throat. There is enough to contend with without that. What happens when you get 'the weave' at high speed - can you grab a bigger handful of throttle and ride through it, or does it get worse ?

acotrel said:

What happens when you get 'the weave' at high speed - can you grab a bigger handful of throttle and ride through it, or does it get worse ?

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You can ride through it sometimes and sometimes not. I depends on wind direction, road conditions, fuel level in the tank and at least a dozen more variables of which any combination of said variables may help either or hinder this effect.

I feel that if the Norton Commando has a dark art, it is this.

What bikes are these ?
Were the iso's set up to spec ?

The 850 got slightly altered steering geometry - so some of us haven't experienced this ?

Alan in a number of ways an un-tamed isolastic Commando is one of the most dangerous bikes ever as feels just fine then oscillations set in that tend to increase if power let off releasing what little thrust tension was taking out some the slap slack or giving more throttle to keep iso and frame tensioned so higher freq with lessor amplitude oscillations, *if road and radius allow you time space to widen up the turn because if you put more inward turn pressure while using butt and knees and bars to stifle the weaving it can't build up enough whip lash to sudden tank slap you silly. To me if feels like a fish flopping off the deck back into the drink. I though I was going to die horribly the first time Hinge Hit going 85 in a sweeper on top a dike, YIKES> Sometime it still catches me out by unexpected combos of road ruffles to wind gusts flashing fear spikes up from groin. Sometimes going so easy lazy no though of handling issue suddenly bobbing about unsettingly. With devices that both allow the frame and iso rubbers to compress taking up tire confilcts and also not allow any rebound beyond just back to null centered, a tamed isolastic is so so good I'm out to prove it or go down in flames. Like you before your 850 Seeley supriser, similar with me never expecting a iso Cdo to hook up more power faster and sharper harsher than any thing else yet not take any athletics and so claim and smooth its exhilarating refreshing not wringing you out, hehe like other motorized bicycles. I can only say I don't believe anyone knows what they are missing out on if really into testing traction and lean and throttle till their eyeballs popping out screaming UNCLE!

I like my un-tamed Trixie but she is so freaking scary so easy I don't dare do anything but parking lot circles or mild off road roostering on her - it.

I put new Konis on the back of my 850 when I got it - the Girlings were shagged, and they'd only a done a few thou miles.
You checked your rear shocks ?

Hobot, I'm screaming uncle!
I don't know what Ms. Peel and Trikie are, for starters. I can usually decipher your posts, but please clarify "untamed" isolastics, since Vivian's (I just gave that name to my Commando) isolastics are my current focus of attention.
I have always considered the Kawasaki Mach 3 the benchmark for dangerous motorcycles because of the combination of an engine that would suddenly spew out gobs of horsepower and a chasis made out of Twizzlers (and usually ridden by dumb kids). I thought Commandos were known for outstanding handling.
I can imagine what "the weave" is but I don't think I want to experience it.