interesting read

Savagea

What is the combo you enjoying so much? 450SX big bore?

Related story, the year was 1972, I had a fast young MX rider working for me, he had the latest Husky 250CR. That was a big compramise in itself as the crank wheels where the same pieces as the 400. On a 400 the outter edge of the big end of the rod matched the outter edge of the crank wheel.

On the 250 there was about 6MM of excess steel there or rod was 6mm in from the edge.One day we had it aprt for some other project and I got a wild hare, took the crank apart and turned it in the lathe taking off that 6mm (of radius, 12mm of diameter).

Next a made a wood mold and cast an epoxy filler, (being a two stroke the crankcase volume plays into a primary compression ratio). He came back from that weeks race just blown away with how much quicker steering the bike was.

Now we gotta be carfull in talking about steering! What crank weight does is slow down the transition from leaned left to leaned right! You have ridden a 250 2 stroke MX bike & then a 125?? The 125 felt 30% lighter but was really more like 5 or 10%? This is crank inertia.

The next factor is where the weight is!When the bike makes this left right transition it does so via you steering the tires contact patch out from under the Center of Mass (COM) and pivots at the COM thus creating a roll center.

Where is this roll center, well maybe if you do a wheelie and have someone snap a pic just before you go over backwards, then do a stoppie and do the same, draw a verticle line from the tires contact patch, overlay the two pics where the line crosses will be where the crank is centered on the 09 Huseberg. I have not ridden one yet but the parties I have spoke to the have they have it right!

One friend said pushing the bike around it feels top heavy and clumbsy, let the clutch out and a 570 feals like a 125.

Why is Husebergs moving the center of the cark to the COM advantagois? When we do that left right transition with a conventional bike we are swinging the gyroscope of the crank side to side below the COM.

A couple years ago I was at the cycle show, I stopped at the Beull display to admire their peice and this branwasher Harley guy working for a local dealer starts telling me how the "Beull has the lowest Center of Gravity of any bike made."

I ask him, "Which is heavier, muffler or crank, transmisson, cases etc.?"He said "Engine & trans is heavier, the muffler is mostly empty!" So I ask "Wonder why a bright engineer with a Road Racing background like Eric Beull raised the engine up and put a truck muffler under it when he could have lowered the engine and hung the muffler out the back like everyone else does?"


He just went back to admiring his tattoo, Fact is the excellent handling Beull has the highest COM production bike made.

Another side story; Ever noticce that guys that get a BMW twin usually stay on them forever (13 years for me), similar with MotoGuzzi, Honda Goldwing, all of these bikes have a North South crankshaft orientation.

Pros & cons;

Pros; the gyro effect is stabilizing front to rear rather that side to side.

Cons; if you are not steady on the throttle the bike twitches side to side and the overall drive train is heavy showing little advantage as drive chains have improved