A good friend of mine has a Suzuki Hayabusa, and he offered to let me drive this weekend. We live in an area of Connecticut that has lot’s of country, winding roads where cornering can be quite fun. I am not an expert motorcycle rider - I had a crotch rocket whilst in Grad School in Arizona…but I have not owned one since.
Anyway, my friend was telling me that his 2004 Hayabusa is a veritable gyroscope on the pavement, nearly impossible to dump it around corners…essentially you can get as close to the pavement on a good turn as possible, and not dump the bike.
When I took the bike out for a spin I was very impressed at the handling…granted I did not push the bike, as I was not as confident in my abilities as the owner was…but I could tell it was a very fun bike at speed.
So does anyone know the engineering behind such wonderful bikes? How do they get the bikes to be so stable, so gyroscop-ish…? And are they really that safe at speed?
All motorcycles (and bicycles) have a gyroscopic effect because of the wheels; they spin and their angular momentum resists changes in direction. Plus, the class of bikes you asked about have very low centers of gravity, what with the rider being hunkered down and everything. I’d say both these things add up to a bike that has a greater tendancy to stay vertical at speed.
If all of the parts that contribute to the gyroscopic effect (wheel rims, any gears spinning in-plane, etc.) are made of dense material like tungsten or nickel-steel, and all the other parts are either reduced in weight or moved as low as possible, then you can maximize this effect. If you can manage to get the CG below the axles, then the bike will “hang” between two gyroscopes, and gravity will team up with the gyroscopic effect to pull you towards the vertical (rather than away from it).
High gyroscopic forces enable the quick flicking from upright to deeply heeled over in a turn. A slight coutersteer force on the handlebars harnesses the powerful gyro to slam the bike over on its side.
But once leaned over, gyro forces aren’t going to keep you from falling all the way in, nor from sliding out. The former depends entirely on turn radius vs speed to drive enough centrifugal (I know) force to offset gravity. And the latter is entirely a function of tire traction being sufficient to offset said centrifugal forces.
I believe the critical difference in handling between crotch rockets now and the 1980s versions the OP & I used to have is that the tire cross section is much more circular and the tread extends well up onto the sidewalls.
As the bike leans over, the tire contact patch migrates up towards the sidewalls. On 1980s street tires, that would only go so far and then suddenly the tire contact patch would become much more slick and you’d wipe out. Handling was fine & predictable up to a certain point, say 30 degrees of lean, and then suddenly deteriorated sharply.
Modern street tires are more bulbous and have the tread well up the sidewall, such that the bike can be leaned well past 45 degrees with no real change in the contact patch’s size, shape or tread.
All that and more power and less weight makes for a real ride.