What is jackshaft?

[Bowtied]

i talked to xschop a while back about one of his chain drive kit's and he said that with the skinny tire the xs11's came with it led to alot of "jackshaft". What the hell is jackshaft? He said that with his kit and a wider rear tire it would greatly decrease the feeling give it better performance in the handling department. Etc etc. But anyways, i'm bored and was just curious what he mean by "jackshaft".

[fredintoon]

Hi Bowtied,
what xschop said and what you understood of that, I dunno.
But a jackshaft is a second shaft mounted just behind the final drive sprocket. One end is chain driven from the final drive sprocket and it's other end has a sprocket which chain drives the rear wheel sprocket. It's purpose is to move the drive chain outward far enough to clear a really wide rear tire.

[Jerry]

Not sure if this is the same, but shaft-driven bikes have a reputation for a handling anomaly known as jacking. This happens because a shaft-drive bike has to turn the power 90 degrees through a ring-and-pinion gear set. When you get on the power, such as coming out of a curve, a shaft-driven bike tries to 'climb' the ring gear, causing the back of the bike to want to rise. On a chain drive, the pull at the top of the rear sprocket tends to pull the wheel up, causing the back of the bike to drop. Therefore, handling characteristics of a shaft vs chain are very real.

In both cases, suspension can be set up to minimize the effect through spring rates and other suspension tweaks. Some people feel the chain drive, which is usually several pounds lighter than a shaft, is more easily controlled in to-the-balls driving situations. Others feel the shaft drive puts more HP to the ground in this situation since it forces the tire into the pavement instead of pulling it away from the pavement. Me, I've never tested equal bikes in that kind of riding, so have no first-hand basis for an opinion. Chain drives can also give you a choice of gear ratios, shafties don't.

So, I think xschop is talking about shaft jacking, not jackshafting. Shaft jacking is real and often commented on in shaft drive bike reviews, but as with most quirks, once you get some experience you tend to forget its there. He is also correct in that the shaft limits the size of the tire that can be fitted to an XS11; with a chain conversion a wider rear tire, with more of a contact patch, can be fitted.

A quick definition of 'jackshaft' can be found on answers.com:
*A short shaft that transmits motion from a motor to a machine, especially in an automobile.*

Another, more generic definition:
*Jack shaft (Mach.), the first intermediate shaft which receives power, through belts or gearing, from a prime mover, and transmits it, by the same means, to other intermediate shafts or to a line shaft.*

In any case, a jackshaft generally receives the power from your prime energy source and transfers it into the rest of the machine.

[Crazcnuk]

Most of these effects are more imagined than real. There is some power loss due to all the direction changes.

Early shaft drives had a few bugs to work out, but in reality, the worm gear can try and 'climb' all it wants, it goes no where.

The beauty of chain, for racing, is you can easily change sprockets for every track.

I have driven both, and personally I wouldn't buy another chain drive bike as my main ride.

Shafts are smoother, quieter, cleaner, require minimal maintenance, and don't eat your pant leg, or passengers shoes.

The big fat tires only help to a point. Most nowadays are beyond that point and actually hurt performance.

Just like all those go-karts you see with the really tall rims and no sidewall. Drifting was invented because when people got ridiculous with thier tire/rim ratios, they couldn't hook up any more.

People used to lower thier cars for handling, then twits slammed them right to the ground. Same with choppers.

People will go beyond ridiculous with anything, when they have no understanding of how cars/bikes really stay on the road.

[xschop]

shaft torque reaction

Jerry pretty much summed it up.... Every XS11 I've owned has a scary quirk to it when you are cornering left, a tight left at a quick speed and if you are in a lower gear at the time and throttle it, the bike will get squirrely in the rear from the "Jack-shafting".....Other than this situation the shaft from the XS11 is just fine....And can handle some serious torture. Watching Trbig bust wheelies with a 1179 kit and 750 FD will eliminate all doubt.

[TopCatGr58]

Very little to add.

I clearly remember getting my XS11 back to the states from Japan where I was stationed in '83, I had not had a chance to ride it there due to the registration requirements. I had the NEW stock shocks set for the most dampening, and STILL had the "bucking bronco horse" effect in the lower gears in stop and go traffic, made me feel at times like I was driving a car with the rear hopped up on air shocks!! But I got used to it, and just rode it mostly for transportation, not much "FUN" riding for 9 years. Then the tranny died, parked for 9 years, then finally put it back together in 2000.

The OEM shocks were all rusted so I picked up a cheap pair of those Monza shocks from JCW, PNM, MikesXS,etc., but was immediately aware that it DIDN'T have the bronco bucking affect that it used to!!

And as for the need for a really fat tire, I put on a 140/90-16 wanting to get as much as I could squeeze into the swingarm....rubbed the raised white letters off , but otherwise worked just fine, but is still no where near as wide as those 200mm ones some folks desire! I have ridden this rebuilt machine for "FUN" now, running the twisties in northern Ga, Tenn, North Carolina, and near the edge of the bike/frame's performance scraping mufflers and footpegs, and the skinny tires
DUNLOP EliteII's have held just fine. I, too, like the looks of the larger tires, but don't really think that for performance/handling that they are really needed for OUR BIKES with their level of frame/suspension technology! YMMV!

T.C.

[Axel]

suspension

I recently softened up my rear suspension and I noticed a difference . A decrease in shaft effect as well as smoother ride . I am currently running 20 lbs at setting "4" . I may go down a setting next as an experiment .