155 HP 920cc Norton on Nitros - crash at Bonneville

I talked to Fred and he said that the bike went into a speed wobble, he gave it more gas and it got wild and that's all he remembers.
If you look at the top photo you can see that the top frame rails don't turn down to the swingarm pivot as they should - not stiff enough. The spindly swingarm was probably also too weak for that motor. Anything could have happened. The frame tubes broke at the welds at the steering head & the swing arm was twisted - from the crash or who knows when. That much HP causes frame flex.




Now we're talking about a new frame designed for LSR.
I'm going to offer him my triangulated monoshock (or twin shock) frame plans but with more rake & trail & longer swingarm & lower fuel tank than in the photo below.

Rohan said:

hobot said:

The man who drives the dynamometer advised me that almost any chain driven bike, from ES2 to GSXR1000, will loose 12-13bhp between crank and rear wheel.

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That doesn't strictly make any sense either ?

If a std Commando does that, and you add supercharger and double the engine power output, why would the transmission absorb any more power than it did previously....

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Adding a little observation here, with correct gearing i would guess a 3 hp electric motor would drive the rear wheel and transmission quite easly,
My Harrison lathe use's little amps to drive heavy lumps with a gear box 10 times bigger than a Norton...10-14 bhp ? when starter rollers use only 1/3 hp to start a engine, and thats driving the whole lot with compression as well :!:

Power loss in the drive train is a percentage of the driving horsepower, not a fixed amount of horsepower. A typical motorcycle final drive chain has a transmission efficiency of 96% - 99% at norrmal road speeds (up to maybe 75 mph), but can be as bad as 85% between 75 mph and 150 mph, for a typical 600 cc sport bike. At least according to a Bristol University research paper. For our 600 cc example, if it makes 120 hp at the crankshaft at 12,000 rpm, it could loose as much as 18 hp just in the drive chain at high speed. But at low speed, and low rpm, where it makes maybe 30 hp cruising along, the loss would could be as low as 1/3 hp. The culprit for the lower efficiency at higher speeds seems to be losses due to "inertial tension", whatever that is. In our old Nortons, you get to add the primary chain (or belt) drive losses, as well as the gearbox losses. The common assumption of 15% - 20% loss from the crankshaft to the road surface at high rpm and speed doesn't look that unreasonable in this light.

Ken

Ugh, drive train loss is more a sliding scale of percentage that varies non-linearly with the load and the rpms. But our engines don't spin up fast a moderns so never enter their level of parasitic drag by 'internal tension. Still Norton with few exceptions have same drive train so someday we should graph it power drag objectively. Run engine up electrically and measure the watts, then add on each element of drive train till mystery solved.

Just guessing by deep gut reaction that hit me last am, I suspect that Fred let off too long on the last shift to so load shifted too much on front, which no way on God's white salt can oscillate that much and not conflict and over whelm the rear's part in keeping aim straight ahead. I believe this is what I'm so sensitive-pensive about on fr/rr air differences when testing traction and handling limits. I know I ain't got no speed limits on THE Gravel, all is fine -as long as I can keep on increasing power and do drag racer like smooth snick up shifts- yet w/o spin out rear, just small rooster tail slippage, but soon as I let off- or hesitate on shits so front is not being about floated- front instantly becomes a rudder on the wrong end of too short a boat so all hell breaks loose at both ends w/o much traction to do anything about but hang on with Wes's well expressed summary flashing inside...

"Its like snot, maybe you'll make it, mabye you won't..."

Although the goal was not achieved, that should not cut off applause. Congratulations to all involved. Thanks to Jim for bringing it to our attention.

As for "inertial tension" yes Ken, whatever that is. I can only imagine that as power rises the friction of transmitting that power rises too but . . . . . that the rate that that friction rises is more than linear.

Up to 2008 my brother was racing at Bonneville on two different types of bikes, Naked and partial streamlined. The last run he took was a speed wobble at 190, Did the same thing to him. He would have walked away without a broken bone if it was not for the bike hitting him. Those were some really cool times on the salt watching the team set records every year they were there. He has had 5 surgeries to repair the arm. He had told me he never really liked racing the naked bike as it was very hard to handle at speeds over 150, Yet the fully faired bike would settle down at higher speeds. Still have a lot of friends on there way to the bub this next week, I may still try and make the Shoot out event and see Rocky Robinson try to set a new record of over 400 mph, He was so close last year. Hope Fred has a speedy recovery and gets back out there, Here is a picture of his bike from one of the years I was out on the salt.