Why don't more motorcycles have driveshafts?

Chains wear out and require maintenance/replacement and adjustment. Chains are lighter and that is why most all sport/dirt type bikes have them. Shafties are heavier and more expensive so they are on touring style bikes. My buddy just bought a kawasaki concours 14 so his bike kinda straddles the sport/touring zone but has a shaft.
Some older shaft driven bikes have a "jacking effect" when on and off the gas that has been mostly cured on the newer models.

 

Shaft drive is a good method of putting power to the rear wheel of a motorcycle. But theres a few drawbacks when compared to chain or belt drive. i.e., They're heavier, have more seals/moving parts, more expensive, sap hp from the engine (less efficient), etc.

The biggest + with shaft drive is virtually zero maintenance.

My old BMW R100's seat would rise up about 3" whenever i grabbed a handful of throttle. I guess thats the "jacking effect" Randall mentioned. It took a while getting used to that, but overall I was happy with the shaft drive - no more adjustments for stretched chains!

 

I own a 1990 Harley bought new ,now with 90K on it and original belt still going strong.

 

And belt drives are so quiet, bliss, compared with rattling chains. Smoother acceleration, too as the belt drive has the same tension, chains stretch and change over time.

 

No really on sport bikes.
The problem with high horsepower bikes and shafts is that the pinion gear wants to "walk down" the ring gear. That means the rear of the bike wants to rise up under hard acceleration. It gets a little scary coming out of a corner and grab a fist full of throttle and the front and back of the bike lifts up. Ask any one that ever rode a old V 65 Honda.

 

BMWs and Moto Guzzis have had shaft drive since they began. BMW only recently began putting chains and belts on bikes in the 90s.

I like shaft drive bikes because the drive typically requires less maintenance than a chain/belt. They also seems to ride smoother to me.

 

Hi.

Judging by Your question, you have never owned one.

Shaft is superior to chain or belt in many regards, but for most of the manufacturers it's not worth the added hassle.

Desmodromic valvetrain, or shaft driven valve train regardless whether it's desmodromic or not, is also superior to any other means of getting those camshafts to spin. You won't see 'em in many engines either.

The bottom line is that chain is ultra cheap, 1/20th or so of the cost of the shaft. Excluding the engineering of course.

Regards
Sam

 

Yep. Shaft is much better, but chain is so much cheaper (too bad price is the issue).

Also - if I am not mistaken - the engine is usually rotated 90 degrees so the driveshaft is in line with the crankshaft. Some engines may be too wide to do this.

 

Simplicity, cost, weight. My favorite final is a chain-driven single-sided swing arm as on most Ducatis and on Triumph's Speed Triple.

 

Another reason, at least for us Harley riders, is tradition.

Also, because they spin, shafts have an impact on the handling of the bike, due to the torque generated when spinning. It might be minor, but it's there.

edg

 

I had a 1984 BMW R80 GS that I bought used w/2500 miles on it in 1986 for $2500 (a buck a mile!) that served me very well for 22 years when I finally quit riding altogether mostly due to a knee problem I developed that affected my ability to shift gears (the "4 up" of the "1 down/4 up") but also because there is so much traffic, unnecessary stop lights & signs, speed bumps, radar and photo enforced stop lights and speed limits here in the "greater" Washington, DC area that riding was becoming a bit tedious. I'd also owned a bike since 1978 and was un-maimed and still alive to tell the tale and decided to "quit a winner". But I digress ... my understanding is that chain drive is better for high performance bikes (read:crotch rockets) and shaft drive is better for smooth touring machines. My R80 GS was indeed a smooth running machine. I got so used to that bike, it was like wearing an old pair of Chucks. I had an epiphany while riding my Yamaha 650 Special II (the bike I had before the BMW). One time, the chain broke on me and fell off while I was going highway speed. The repair guy who installed the new chain told me that once in a blue moon, a broken chain will tangle up in the works and the rear wheel will seize up. I was never able to get that out of my mind after that and vowed that my next bike would have a shaft drive for sure. I did notice the "jacking effect" when I first got the BMW but after riding it for a while, I guess I got used to it and didn't notice it anymore.

 

^ truth. ^


Was off-roading with a few buddies riding an old XT 250 and it threw the chain. Instant lock-up. Needless to say, I bit the dirt really fast. Scares me to think about that happening on the street during high-speed cornering.

 

The three main drive types of a motorcycle have their pros and cons:

1) Chain:
Pros: Cheap, reliable, and efficient
Cons: Maintenance and if the chain breaks (rare), it can either punch a hole in your engine case or bind the rear wheel. But his is RARE..RARE.

2) Shaft:
Pros: Ease of maintenance, clean, reliable (unless your BMW differential catches on fire)
Cons: Shaft jacking effect, high transitional losses as the power has to make two 90 degree turns, cost (especially when things go wrong), weight, complexity.

3) Belt:
Pros: Low maintenance, clean, inexpensive, doesn't chew up sprockets, quiet, no slop (if a idler pully is used)
Cons: When it breaks...you're stuck, gearing changes not possible, fragile (avoid gravel if at all possible)

I've owned a bikes with all three types of drives. Chains aren't really that much trouble. I lube mine every so often and just ride the thing.

 

My first bike, a 1985 Nighthawk 650 was shaft driven and had what I called "elevator action" during shifting at various times and as already described. This was especially troubling and difficult while shifting on curves and corners.

My next bike was a 1998 Ninja 600, and after riding that, I am convinced that God intended for bikes to be chain driven.

When I'm an old fart, I'll maybe get a shaft driven cruiser, Goldwing style bike.

 

They answer to any question that starts with "why don't they" is almost always "money." Shaft is too expensive for most people.

There are other reasons, too, such as the fact that shaft is dangerous when pushing the envelope because of the way it moves the suspension.

Belt is the best drive system for most motorcycles, excepting racers and racer wannabes. It's light, clean, durable, and behaves the way one would expect.