Heavy flywheel equals more torque? (2014)

There is one very tight hair-pin bend on Winton Raceway. With the close box, it is probably second gear. I brake a third of the way into the corner and then get straight back onto the gas. The bike tightens it's line and always comes out of the corner on the low line. While it is doing that, the rear wheel is always losing traction and accelerating very rapidly. It is almost impossible for anyone to get around that corner faster than that, and it is the tightest one on the circuit. With a light crank, it might be easier to get the gearing right, but the result would be the same. If you lose revs in the corner, you are stuffed regardless.

High times you had acotrel tightening up hair pin with rear slippage, even if not drifting/sliding, its like having power steer assist easing the pilot effort. At times like that I feel theres more than traction helping hold turning lean forces. There's so so many things going on turning its hard to say which is dominate at one point or another. Jerk on a gyro hard can give strong resistance to shove off of then stops as ya relieve the load or jerk gyro the other way to get opposite reaction. BTW its been determined its not wheel gyros as main forces keeping the bike upright, its the slight fork oscillation, such as might do rolling .5 mph wiggling fork some to balance before foot down stop or stage stunter. But I don't think the wheel gryos combined are as strong as the fw at hi rpm.

We've learned here it takes ~5% less power delay to spin up or down a lighter Norton crank than factory. That the energy smoothing-taming of heavier crank on extra spunky cycles helps a lot of pilots get the most out of it. We don't yet know how much energy stored in says 6000 25lb crank/fw yet. We also don't have a sense on the gyroscopic forces generated at say 20-25 lb crank/fw of Norton dia. I know when jumping 40' ft long arc's over 4 lane hwy, I could flip forks lock/lock w/o any change in orientation. If tapped brake nose dived, if blpped throttle front rose. I did not try to lean sideways while in 2-3 sec flight (only 3-4 ft over road profile). Here's weird gyro effects as food for thought even if don't apply to our cranks.

Steve, when I ride my bike, I never do anything suddenly and I certainly never jerk it. If I have a moment, I simply ride through it as smoothly as possible. The problem is that I never just ride around a race circuit, I always push the bike as hard as possible. So I end up on the limit of tyre adhesion both when it is raining and in the dry. I was brought up racing in an era when if you blinked, you crashed. I still ride the same way. If you go slow, the risk of crashing is probably even slightly higher, because many bikes usually handle better when they are being ridden quickly.

lcrken said:

You do realize, don't you, that many Commandos with stock "heavy" cranks have been very successfully road raced with stock "wide ratio" 4-speed gearboxes, particularly back in the '70s and '80s? They might not suit your riding style, but they clearly worked well for others. Back when I was still racing Commandos, my friend Fred Eiker won a lot of road races on his 850 Commando with stock gearbox and un-lightened crank, including the 1986 La Carrera II Mexican road race. He won on high speed tracks like Willow Springs as well as tight, twisty ones like Sears Point. Fred averaged 111.19 mph for the 125 mile race on Mexican roads from San Felipe to Ensenada. And that was before we had all the currently available good stuff, like Maney cases and cylinders, billet cranks, TTI gearboxes, etc, and running on period tires. I was lucky, my PR came with a Quaife 5-speed, and it was an advantage over a stock 4-speed, but not as much as you believe. I also raced a MK3 with 920 engine and stock 4-speed for a while, and it never blew up anything. It just had to be ridden a little differently. Would it have been better with a 5-speed? Probably, but it was certainly adequate without it.

Ken

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I happened to have entered that race Fred Eiker won. That race is almost all straight. A couple twisty bits thrown in, and hardly any farm trucks on the road. Just rode my street Commando down, raced, got my tee shirt, and rode back home. I actually ran out of fuel due to confusion at the start where I couldn't get at the fuel my brother had for me. It was a ways from the hotel to the start. I talked a spectator into taking the fuel tank off of his ATC and dumping it into my tank. I only averaged 65, according to what they told me. At least I wasn't stopped by the side of the road,like the CR750 Honda and Rensport Guzzi. Later that summer, I rode over to Riverside Raceway, and Fred won the Heavyweight BOTT race there. As I recall, that also won him the AFM Heavyweight BOTT championship. The starter waved the white flag twice. Fred crashed in front of where we were spectating after the second white. It was determined that he had already won prior to crashing, which would not have happened without the flagging mishap. Both races were full of Ducatis and Moto Guzzis. Fred outrode them at Riverside. He had to have outrun them in Mexico. The straights were so so long. Four bikes averaged over 100 mph. Two of them were Commandos. One was a Cycle Magazine project Sportster built by Joe Minton and ridden by Nick Ienatsch, a potent pair. I don't remember the other. Could have been the Ducati F1 Laguna Seca. Except for mine, all of the Nortons finished in less time than all of the bevel drive Ducatis.

As to flywheel weight, I had about 30% of the flywheel weight removed from my daily driver Ford Cortina. Most of it at the outside edge where it has more effect. The idle speed had to be increased. It is much easier to stall from a dead stop. It is a BIG deal in freeing the engine up to rev out and accelerate more quickly. I think it really helped for autocrossing. On the street, not so much.

Ken
I remember Fred asking me for advice about gearing for the Mexican road race. I told him to run one or two less teeth on his rear sprocket than he ran at Willow and I think he went with two. He told me it was way overgeared but I think that kept the revs down and prevented it from blowing up. If he averaged 111 the he must have been topping out well over that.

When I built the Seeley 850, I did not believe the motor could be successfully raced due to the heavy crank. With the standard wide box, the bike was hopeless, but with the close box it was excellent.