Suspension in the Twisties

[RONST1300]

I have heard a lot about the performance of the ST in the twisties. And then I was reading an old discussion about the shaft drive, and he says only the chain does not decompress the suspension. I thought Twisted Throttle said, all bikes decompress in acceleration. So which is it? Does the ST decompress in acceleration or not? My thought is that it is, however there is still some power loss with the shaft.
Ron

"In addition, to repair the belt, even if done roadside, requires you carry an entire belt with you...for a chain all you need is a spare $5 link. I also know that for superbike racing they like the chain drive because when you're using chain (or belt) and you keep the throttle on, it decompresses the suspension, which is important to do through turns because it gives the suspension some available travel to soak up bumps and keep the tires on the road. Shaft drive doesn't offer that benefit. Shaft drive proponents will tout that as a benefit that it DOESN'T spring the bike, the chain/belt folks see that as a downside...they have different needs for their vehicles. I suspect most shaft drivers aren't bombing through corners in a manner that completely squashes out the suspension travel."

 

[dduelin]

LOL, he obviously never rode an shaft driven bike like my BMW R100 which has a large amount of shaft jacking (the suspension decompresses or extends during acceleration and compresses or collapses under deceleration). All shaft bikes as well as chain and belt drive bikes will do this. In shafties I think it comes from the pinion gear trying to "climb" up the ring gear under acceleration. Manufacturers have design features to reduce or eliminate it. BMW for instance has their Paralever swing arm, Kawasaki and Moto Guzzi use a similar design. These designs feed jacking forces into the frame and away from the swing arm. Honda and other manufacturers can reduce it through careful choice of swing arm length and geometry of swing arm pivot and transmission output shaft location. The ST1300 has very little shaft jacking but it is still there. Try this: from a stop accelerate briskly to maybe 45 mph in first then immediately apply brakes and come to a stop with the rear brake applied. When stopped release the front brake, then the rear brake. You should feel the rear of the bike settle some small amount when you release the rear brake. That was the amount it rose under acceleration.

 

[Gear driven]

Ok, I'm new here, but this is one topic I can speak on with a good deal of knowledge. Jacking is real, and what dduelin said is very accurate. The information you read and quoted left out some details about the different driveline configurations. Chain drive is not selected on sport bikes because of it jacking the suspension under duress. It is selected for two primary reasons. One being it is the most efficient form of power delivery of the three, and second it is the lightest. The performance characteristics of a chain drive system are sorted out during the design stage when chain torque angle and countershaft position relative to the swingarm pivot are all juggled to get the desired results. This includes the diameter of the rear sprocket relative to alignment with the countershaft. Bikes with smaller rear sprockets (like my RC51, and Ducatis) inherently can't run as much chain torque angle as one with a larger diameter rear sprocket because of how the alignment interacts with the countershaft. This is a very critical element in getting drive off a corner under WOT and high lean angles. In a perfect world, no jacking would occur at all.

Now that being said the ST with it's shaft drive has very little jacking compared to many I have ridden, although if you are sloppy with the on/off throttle at higher RPM leaned over in a corner, your going to notice it. No system, be it shaft, chain, or belt, benefit from sloppy control. The suspension likes the world to be in a steady state and the sloppier the control inputs, the harder the suspension has to work at controlling that instead of doing what it should be doing, which is tracking with the road.

In a nutshell, each system has it's advantages and disadvantages. A well designed chain drive system is very good at what it does, as is a shaft system, and the Honda one is a good one.

 

[sherob]

The C14 has even less if none from shaft drive due to its design... as mentioned above by Dave.

 

[NorCalBusa]

Easy demo- put your front tire against a wall, throttle up a bit (or not), in first let the clutch out a bit LESS while watching the rear end. You'll see how much it moves and what direction.

 

[Raj_Zin]

When stopped release the front brake, then the rear brake. You should feel the rear of the bike settle some small amount when you release the rear brake. That was the amount it rose under acceleration.

I get this effect on the ST even when coming to a hard stop from a steady or slowly decreasing speed...

-STeve

 

[RONST1300]

Thanks guys. There is a lot I am still learning about my ST. And I still love my ST and it's handling.
Ron

 

[Igofar]

Easy demo- put your front tire against a wall, throttle up a bit (or not), in first let the clutch out a bit LESS while watching the rear end. You'll see how much it moves and what direction.

Sounds like somebody's been doing burnouts

 

[T_C]

When stopped release the front brake, then the rear brake. You should feel the rear of the bike settle some small amount when you release the rear brake. That was the amount it rose under acceleration.

So if I am cruising along at a stead speed and I apply brakes, come to a stop, release front, then rear. The settling of the rear is it's how much it raised from acceleration?

 

[dduelin]

Yes, pretty much. If you chop the throttle from a steady speed then apply brakes the engine braking effect will compress the rear suspension so when you come to a stop the rear suspension is already lost the extension/decompression that come from the brisk acceleration.

 

[T_C]

the engine braking effect will compress the rear suspension

So if I'm cruising along in neutral or just grab the clutch and brake I won't compress suspension?

 

[dduelin]

That's correct. The suspension will be at it's static sag setting under weight of bike and rider.