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Shaft Drive + Telelever Suspension, Reaons?


KentB

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I'm currently riding my first BMW motorcycle and I am loving it. I am, however, wondering about two features I've never seen on other bikes.

 

Why shaft drive? What're the advantages and disadvantages of shaft drive?

 

Also, why telelever suspension? Again, what are the advantages and disadvantages of employing such a system?

 

Thanks for helping a new guy get acquainted with his BMW.

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Dennis Andress

Why shaft drive? What're the advantages and disadvantages of shaft drive?

 

Have you ever packed a can of chain lube on a long trip? It gets real messy... eek.gif

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russell_bynum
I'm currently riding my first BMW motorcycle and I am loving it. I am, however, wondering about two features I've never seen on other bikes.

 

Why shaft drive? What're the advantages and disadvantages of shaft drive?

 

Also, why telelever suspension? Again, what are the advantages and disadvantages of employing such a system?

 

Thanks for helping a new guy get acquainted with his BMW.

 

Shaft Drive: In general...it requires less day-to-day maintenance than chain drive. The downside is more weight, and the cost of a drive failure is much greater than a simple broken chain.

 

Telelever: It is an anti-dive device. It uses tricks of physics to reduce front-end dive under braking. The result is the suspension stays closer to the middle 1/3 of its travel where it works best. Downside is reduced front-end feedback. I imagine that telelever is also heaver than conventional forks, but I don't know that for a fact.

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bakerzdosen
I am, however, wondering about two features I've never seen on other bikes.

 

Why shaft drive?

You'll see shaft drives on other touring bikes (not just BMW's) for the reason that Dennis brought up.
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russell_bynum

Why shaft drive? What're the advantages and disadvantages of shaft drive?

 

Have you ever packed a can of chain lube on a long trip? It gets real messy... eek.gif

 

Bah.

 

The mini can of chain lube I carry on the Tuono is about the size of a soda can. It's got a lid on it and is no more messy than a can of hairspray or something like that. About every other fuel stop I take a couple of minutes to spray some on, and that's it. No mess at all.

 

Granted, that's more day-to-day work than a shaft drive, but it really hasn't been a big deal at all. And I can call a huge number of aftermarket companies and have a new chain and sprockets sent to me in the gear ratios that I desire vs. being limited to the BMW dealer and a small number of ratio options.

 

I dunno. I didn't really have any complaints with the shaft drive (other than my failed final drive on the RT), and I don't have a problem with chains either.

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russell_bynum
There is some interesting information to be found on motorcycle suspension here:-

Motorcycle suspension.

 

That's cool, but I'm confused by this statement: "The design of the Telelever effectively reduces fork flex under braking to near zero which in turn reduces dive under braking. "

 

Now...I understand how the telelever could provide greater rigidity of the forks and would therefore reduce flex. But what does that have to do with dive?

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ShovelStrokeEd

I actually think that both points are valid. The forks flex less because the lowers are connected to the frame via the A-arm, unlike conventional telescopics where the connection is at the the lower triple clamp. Longer lever arm for the same diameter slider plus braking forces are transmitted through the A-arm.

 

As to the anti-dive, that is a function of the shock mounting angle and A-arm geometry. If BMW had wanted, they could have made the suspension rise under braking forces and therefore load the tire even more but, the feeling is pretty weird. The old, plunger frame, Earles fork BMW bikes actually did this and they have a feel, under braking, that is strange indeed.

 

BMW has long had a tradition for both shaft drive and unconventional fork arrangements. The current crop of bikes is just following that tradition.

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........a simple broken chain. ..........

 

 

The last broken chain I saw also included a cracked engine case stranding the rider on the side of the road in a pool of oil/coolant frown.gif

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and the cost of a drive failure is much greater than a simple broken chain.
Chains wear out too, and the cost of replacement of the chain and sprockets as a part of normal maintenance isn't cheap. A final drive costs much less to operate over the life of the bike (well, most bikes... smirk.gif)
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BitScribbler
I'm currently riding my first BMW motorcycle and I am loving it. I am, however, wondering about two features I've never seen on other bikes.

 

Why shaft drive? What're the advantages and disadvantages of shaft drive?

 

Also, why telelever suspension? Again, what are the advantages and disadvantages of employing such a system?

 

Thanks for helping a new guy get acquainted with his BMW.

 

Of course you realise that your bike, like all the new K series, doesn't have telelever? It has duolever, originally invented by Norman Hossack many moons ago. See here for more info on Norman and his design.

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Why shaft drive?

 

I'm surprised nobody mentioned the crankshaft orientation. The historical reason for BMW's preference for shaft drive has everything to do with crankshafts.

 

For ages, BMW has made boxer engines. When the cylinders stick out the sides like that, the crankshaft will be oriented longitudinally. A longitudinal crankshaft is ideal for connecting to a drive shaft, which is also longitudinal. Moto Guzzi V-engines are the same way, with cylinders that stick out the side, turning a longitudinal crankshaft. So Moto Guzzi uses shaft drive for the same reason as BMW with its boxer engines.

 

On the other hand, for V-engines where the cylinders are fore and aft, as well as sport-bike style transverse engines, the crankshaft is longitudinal. That's oriented the right way to turn a sprocket for chain or belt drive. As an example, the new F800 BMW bike has a transverse cylinder configuration which is ideal for its belt drive.

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There is some interesting information to be found on motorcycle suspension here:-

Motorcycle suspension.

 

That's cool, but I'm confused by this statement: "The design of the Telelever effectively reduces fork flex under braking to near zero which in turn reduces dive under braking. "

 

Now...I understand how the telelever could provide greater rigidity of the forks and would therefore reduce flex. But what does that have to do with dive?

 

Russell, anti-dive (anti-squat) as well as anti-lift has a been a term used in the auto industry for many years now.. In fact all modern automobiles have both anti-dive & if a front wheel drive anti-lift designed into the front end geometry.. The anti-dive is as you would think, from braking moments & the anti-lift is to control front end lift on acceleration.. In most (but not all) cases the anti-dive is a function of front end suspension control arm bushing angles & or bushing rates & caster angle..

 

An easy way to visualize the anti-dive moment event is to picture pushing a car with a stick.. Imagine the stick is attached to the vehicle being pushed at it’s rear bumper center (about 2-1/2 feet off the ground).. The stick is then attached to the pushing vehicle at the same 2-1/2 feet off the ground.. (the stick is parallel to the ground)..

When the pushing vehicle pushes the pushed vehicle, all the pushing force is transmitted through that stick in a straight forward direction (no upward of downward force transmitted, only forward).. So now let’s lower the stick’s attaching point on the pushing vehicle 1 foot (same height on front pushed vehicle).. Now a portion of the forward pushing force it also pushing the rear bumper of the pushed vehicle upward as well as forward.. The higher the force needed to push the front vehicle the more the lifting force on the rear of the pushed vehicle (the stick attaching points are not level any more so the lower point tries to go under the higher point therefore lifting the rear of the vehicle)..

 

Basically that is how (geometric) anti-dive functions.. If the instant center of the front end braking forces are lower than the fixed center of the rear bushings on the front control arm it will want to lift the front end of the bike on braking.. The secret here is to figure out how much weight is transferred to the front of the bike on brake application (that’s what makes it dive to begin with) then counter act that force with the correct amount of lift from the braking force in the form of front end lift.. That is done through control arm attitude (angle) ,, bushing rate,, front fork caster (rake & trail) brake load direction,, shock valving, etc..

 

There are many types of brake activated anti-dive, from front brake caliper reaction shock valving control to electrical shock valving control activated from the brake light switch, to passive or linkage systems used on Springer front ends or other applications.. .Most are inferior to the BMW system in that they can only slow the dive rate of the front end by restricting the fork oil flow in the compression direction (basically you still get dive but it happens over a longer time frame so the forward weight transfer is pushing against the fork valving through most of the braking event.. One of the problems with most of the fork control type anti-dive’s is you loose a lot of fork shock control during braking (especially hard braking on a bumpy surface).. On the other hand BMW geometry type anti-dive still allows full shock control on heavy braking.. Does that make the BMW system that much better? Not necessarily so.. In some cases (especially on bumpy road heavy braking the BMW system is probably better).. On the other hand it restricts front end dive enough to stop a lot of weight forward bias on hard stops so the front tire isn’t loaded as much as the hydraulic designs (BMW probably needs more rear brake apply than the hydraulic types as the weight transfer is lower)..

 

Twisty

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BMW has long had a tradition for both shaft drive and unconventional fork arrangements. The current crop of bikes is just following that tradition.

One of the "unconventional" fork arrangements BMW was first to bring to market, was the (wait for it!...) telescopic front fork that nearly every other bike uses now. They introduced this in the mid-1930s.

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russell_bynum

I should have been more clear.

 

I understand how the Telelever is an anti-dive device. I understand how it would make the forks more rigid.

 

What I don't understand is this....his statement seemed to suggest that reducing flex reduced dive. "The design of the Telelever effectively reduces fork flex under braking to near zero which in turn reduces dive under braking"

 

I don't believe those two benefits are related.

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ShovelStrokeEd

And rightly so, Russell, fork flex will actually produce more of an anti-dive effect as it will increase side loading on the slider bearings and thus increase friction/stiction in the forks.

 

As Twisty pointed out, increasing compression damping is really a piss poor way to handle antidive. You do so at the expense of wheel bounce control, which is perhaps most important under heavy braking. This form of antidive was all the rage in the late 70's or so. My Yamaha Turbo had it and I think that was an 81 or 82. BTW, it sucked but mostly because of bad brakes to begin with and then a flexible front end like you wouldn't believe.

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russell_bynum
And rightly so, Russell, fork flex will actually produce more of an anti-dive effect as it will increase side loading on the slider bearings and thus increase friction/stiction in the forks.

 

As Twisty pointed out, increasing compression damping is really a piss poor way to handle antidive. You do so at the expense of wheel bounce control, which is perhaps most important under heavy braking. This form of antidive was all the rage in the late 70's or so. My Yamaha Turbo had it and I think that was an 81 or 82. BTW, it sucked but mostly because of bad brakes to begin with and then a flexible front end like you wouldn't believe.

 

Right.

 

Trying to control dive with compression damping is particularly problematic if you don't have a fairly sophisticated valve stack up front. The old damping rod forks, for example were horrid. They had way too much high speed compression damping, and not enough low speed compression damping....resulting in a fork that collapsed under braking, but still managed to rattle your fillings over sharp bumps.

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Of course you realise that your bike, like all the new K series, doesn't have telelever? It has duolever, originally invented by Norman Hossack many moons ago. See here for more info on Norman and his design.

 

Doh! I didn't realize that telelever and duolever were different. (I've got alot to learn.) Even after looking at sketches of them on the internet I'm not sure I understand the difference. It looks like Telelever has telescopic forks, and Duolever doesn't.

 

Thanks for the great link on how Duolever works. That helped alot. Can anyone show me a good link to explain how Telelever works and how it's different from Duolever?

 

BTW, here's a link I found that explained the Paralever rear suspension to me in case anyone else is interested:

Paralever Rear Suspension Explained

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Thanks for all the explanations so far, guys. You're providing me with a first class education on motorcycle engineering.

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Kent, in a nutshell the duolever has a pretty constant geometry even in compression & extension.. Because the system uses 2 control arms (a long & a short) the trail, & therefore the wheelbase remains pretty well constant.. The center of the tire contact patch also stays fairly constant in relation to the steering axis.. On the other hand the telelever (due to a fixed upper mounting somewhat similar to a conventional upper triple tree) only accomplishes about ½ the above.. The telelever would fall about half way between the duolever system & a conventional sliding spring-in-fork design.. On the telelever design the handle bars are right on the fork tops & on the duolever design there is usually some sort of tie link (drag link) from a remote steering head & bars to the front suspension uprights.. You can’t install bars directly on the duolever system as the entire unit moves up & down as the suspension reacts to bumps..

 

The duolever design also allows much better tuning due to being able to use the control arm bushing rates as tuning aids (bushing deflections can enhance the geometry gain under braking or bumps).. The duolever also allows a MUCH less flexible frame attachment so frame flex at the steering head is about totally eliminated..

 

If you were to equate the telelever & duolever to automobile systems the telelever would equate more closely to a Macpherson strut design & the doulever would equate to the more exotic separate upper/lower control arm with coil over’s.. Macpherson struts work great on low weight everyday vehicles but you wouldn’t use that system in a racing chassis..

 

Twisty

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