Why dry clutch?

[TowJam]

Disclaimer: I'm not a wrencher, plese be gentle....

 

Given the (seemingly) obvious advantages of wet clutches, why does BMW continue to use the dry clutch in the R bikes? Is there any technical reason the R series couldn't be reworked with a wet clutch?

[ShovelStrokeEd]

About 100 reasons. There is nothing wrong with a dry clutch to begin with and, given the longitudinal crankshaft in the boxer motor, it makes for the simplest design. Same design used in cars and light trucks for lo these many years.

[russell_bynum]

What Ed said.

[upflying]

The only thing wrong with dry clutches is they don't like a lot of slipping, you get smoke and hot brake odor in extreme cases.

Wet clutches take more slipping abuse. Wet clutches also tend to be easier to change and service.

Sure you should not slip a clutch excessively but some forms of low speed LEO training involves a lot of "gray area" clutch slipping.

[russell_bynum]

The only thing wrong with dry clutches is they don't like a lot of slipping, you get smoke and hot brake odor in extreme cases.

Wet clutches take more slipping abuse. Wet clutches also tend to be easier to change and service.

Sure you should not slip a clutch excessively but some forms of low speed LEO training involves a lot clutch slipping.

 

Wet clutches tend to be easier to change and service because they're generally used when when the engine is mounted transverse rather than longitudinally.

[Haynes]

A dry clutch does not contaminate engine and transmission oil. It would be great if dry clutches could be engineered for easier servicing.

[dirtrider]

Evening Haynes

 

A Harley wet clutch doesn’t contaminate the trans or engine oil as it has it’s own case with separate oil supply.

 

The Ducati dry clutch is about as easy to service as any. Takes about 10 minutes.

 

 

 

[russell_bynum]

Evening Haynes

 

A Harley wet clutch doesn’t contaminate the trans or engine oil as it has it’s own case with separate oil supply.

 

The Ducati dry clutch is about as easy to service as any. Takes about 10 minutes.

 

 

 

+1

 

The difficulty of service with BMW's dry clutch is because it's buried between the engine and transmission and requires major surgery to get to it....like with a car's clutch.

 

The upside is, assuming you aren't slipping them excessively, they last a very long time. From what I've seen, most Oilhead clutches, if treated properly, will last longer than the transmission itself.

[SageRider]

From what I've seen, most Oilhead clutches, if treated properly, will last longer than the transmission itself.

That's not saying much....

[baggerchris]

Comparison:

 

1971 HD Electra Glide with Dry Clutch

 

1997 BMW R1100RT with Dry Clutch

 

1997 HD FLSTC with Wet Clutch.

 

Never had a problem with the RT but I will say that the HD wet clutch is wonderful. Didn't particularly like the HD dry clutch.

The HD wet clutch is very easy to access and service and has taken much abuse and pretty much acts like a Timex.

The HD dry clutch would never 100 % disengage and until you worked it in the morning, would try and stick and the bike kept wanting to go forward a tiny bit even when "out". It would also take a beating however without complaint. Same service level as their wet clutch. Easy.

[russell_bynum]

From what I've seen, most Oilhead clutches, if treated properly, will last longer than the transmission itself.

That's not saying much....

 

[loboheritage]

I have one of each. Find wet to be far superior to dry. Modulates well. Never complains with burning smell. Already has oil all over it, so an oil leak on it can't kill it. Tends to last forever...Ed

[notacop]

Dry clutch, since 1923 for out loud. I changed the clutch on my 80/7 at 100K miles because I was mounting a sidecar to the bike...DUH.

My R65LS went 150 when the trans blew up. Changed the clutch then just because. I guess the CHP threw a new clutch in my RTP sometime before the 60K when I bought it. HAd 122K and I hadn't changed it, ran fine.

Works fine lasts a long time, don't flog it. If a wet/dry clutch is a concern, Yamaha, Kawalski and Honda do Automatics.

Make yourself happy, don't reinvent the wheel.

[nrp]

Probably a space issue in that it would require a longer wheelbase to accommodate the engine transmission combination (that spec probably came from BMW marketing).

[Green RT]

My R60/5 went 175,000 miles on the original dry clutch. It had life left when my son and I took the engine apart for rings and valves.

[moshe_levy]

Just took a "Ride Like A Pro" class to review for MCN - basically, the whole trick to their control is slipping the clutch and applying rear brake in slow speed maneuvering. Those of us with BMWs were smelling up the range. Very unnerving. The cops said that's one of the reasons they don't like BMWs - the cost to service the burned up clutches was enormous compared to Harley clutch service, and according to them the Harley clutches lasted forever, even under police conditions.

 

-MKL

[Rich06FJR1300]

it would take a major re-design for the R bikes to go with a wet clutch. Guzzi also uses a dry clutch on their twins...while honda had a CX500 with the same V-twin config with a wet clutch. The one advantage though i can see is that you wouldn't have to do a spline lube anymore with a wet clutch being the splines will be lubed by the engine's oil. Well, scratch that, there would still be splines coming from the tranny to lube but probably a lot easier to get too.

[pbbeck]

The Ducati dry clutch is about as easy to service as any. Takes about 10 minutes.

 

... and they sound great!

[Ken H.]

Just took a "Ride Like A Pro" class to review for MCN - basically, the whole trick to their control is slipping the clutch and applying rear brake in slow speed maneuvering. Those of us with BMWs were smelling up the range. Very unnerving. The cops said that's one of the reasons they don't like BMWs - the cost to service the burned up clutches was enormous compared to Harley clutch service, and according to them the Harley clutches lasted forever, even under police conditions.

Because they don’t know how to ride them then. There is no good reason slow, or any other type of maneuvers can’t be done with a dry clutch w/o ever smelling a thing.

 

Actually I think how to correctly use a clutch, any clutch is a dying art. There is almost never a good reason to ‘slip’ any clutch. Why do instructors (in any venue) teach slipping instead of feathering?

 

[Paul Mihalka]

"teach slipping instead of feathering?"

 

What is the difference? I would think "feathering" is in/out slipping.

[RockBottom]

I was wondering the same. I feather the clutch a lot. In the ERC, at least, I never smelled a thing. And when I took it a few weeks ago, there were only two students (rain drove away the other 9 enrolled) so I was riding almost constantly.

[Ken H.]

I would think "feathering" is in/out slipping.

It is. But the difference is total time. The total time, over time, that the two surfaces spend rotating at different speeds while in contact with each other; is the deciding factor on wear and life of the clutch’s surfaces.

 

With a continuous slip that total amount of time where the two surfaces are wearing against each other is much greater than if the same maneuver/exercise/ride was done with a feathering approach where the surfaces are only momentarily in contact with each other at different speeds.

 

Say I’m pulling away heavily loaded, up hill, from 0 mph to 10 mph. If I use a slip approach the clutch might be in the friction wear zone say 60% of the total time it took me to get to 10 mph and the clutch fully engaged. Where as if I do the same pull away using a feathered approach the clutch is only wearing 30% of the time it takes me to get to the 10 mph.

 

The difference is a result of forward momentum. Each feather moment builds upon the forward momentum created by the prior one.

 

[Dave_zoom_zoom]

Feathering--GOOD!

 

Slipping--BAD!

 

[moshe_levy]

Ken-

 

My RLAP instructors were two current motor officers, each of whom has been riding for over 25 years and certified by the state and MSF as instructors. These guys were doing 18 foot circles on full size machines like it was nothing - and teaching Palladino's method which has been in use by police department motor officers since the 1930s. I say this to respectfully dispute the notion that "they don't know how to ride." If they don't know how to ride, the rest of us mere mortals are in serious trouble!

 

Now, to quote from my forthcoming MCN article reviewing the course: "The secret of the complete control our instructors had over their motorcycles was what they termed “creating a tug of war” between the motor driveline and the rear brake. Bringing the engine speed to a constant – typically at least twice idle RPM or more – the students had to finesse forward in the friction zone, while simultaneously applying the rear brake gently to manage speed. The engine’s consistent higher RPM helps to create a stabilizing gyroscopic effect, while the engaged rear brake squats the chassis. The end result is a taut, controlled feeling motorcycle, even at nearly maximum lean angle at crawling speeds."

 

Feathering / slipping or whatever you want to call it is in effect, because the rpm is constant, but clutch and brakes are variable - in this method, at least.

 

We're kind of veering off topic here, but the method did produce that burning brake pad smell from dry BMW clutches, and nothing from the wet clutches on the range. There were frequent "breeeze out" and "cool down" periods for the bikes, so I'm not saying damage was done. I AM saying the motor officers teaching AND in the course all said the BMW clutches were seen as a negative by the departments due to high cost and frequency of replacement.

 

Oddly, they also complained of BMW brake pads fading early and being worn down early. This is in direct contradiction to my experiences. My last RT's pads still had meat at 55,000 miles, whereas my Harley couldn't last 20,000 on the same commuting route. The Harley pads were about 1/4 the price of BMWs, but still....

 

-MKL

[Boxtop]

Just took a "Ride Like A Pro" class to review for MCN - basically, the whole trick to their control is slipping the clutch and applying rear brake in slow speed maneuvering. Those of us with BMWs were smelling up the range. Very unnerving. The cops said that's one of the reasons they don't like BMWs - the cost to service the burned up clutches was enormous compared to Harley clutch service, and according to them the Harley clutches lasted forever, even under police conditions.

Because they don’t know how to ride them then. There is no good reason slow, or any other type of maneuvers can’t be done with a dry clutch w/o ever smelling a thing.

 

Actually I think how to correctly use a clutch, any clutch is a dying art. There is almost never a good reason to ‘slip’ any clutch. Why do instructors (in any venue) teach slipping instead of feathering?

 

There are situations where avoiding a burning clutch smell on my RT is beyond my capabilities:

 

A long, steep upgrade at a constant 4 mph, like in a parade

 

A cobbled creek bed where idle speed is way too fast, and you're constantly having to lift the front wheel over 6" cobbles

 

In these situations, it's always interesting to see which will give out first, the clutch or my left arm. So far, it's been the arm.

[Ken H.]

I say this to respectfully dispute the notion that "they don't know how to ride." If they don't know how to ride, the rest of us mere mortals are in serious trouble!

Okay, admittedly “Don’t know how to ride” might have been a bit harsh. But I still maintain there is a better way to do slow speed stuff with a dry clutch than keeping it partially engaged slipping.

[ShovelStrokeEd]

I'm with Ken on this. The technique used by the instructors in this case is really not appropriate for a dry clutch. Any dry clutch. That, I'm pretty sure, is what Ken meant by "they don't know how to ride".

 

Let's compare the two bikes for a bit.

 

Harley - wet clutch, huge flywheel mass (often mistaken for lots of low end torque), asymmetric firing order gives different torque application characteristic to drive train, wide bars and lots of steering lock with a really low c. of g. The whole package lends itself to easy slow speed maneuvers with that constant engine speed (relatively high) constant clutch slippage, and modulating speed with the rear brake.

 

BMW - dry clutch, very low flywheel mass relative to bike mass, symmetric firing order, narrow bars, limited steering lock and higher c. of g. A much better technique here is to keep the clutch at the inside (relative to lever travel) of the friction zone and build momentum by lightly applying bits of power till the bike will accept a fully engaged clutch. One wants to keep the RPM's just off idle for this. Now, this does require a good running bike. I have had my 1100S with me at 240 lbs and a 200 lb buddy on the rear seat and I was still able to pull away, on level ground, at no more than 1400 or so RPM using the above technique. Clutch fully engaged by about 10 feet of movement. It's all about throttle control balanced against momentum and feeding in the clutch in small steps.

 

I still use this same technique on both my bikes in normal riding. Seldom take off at anything above idle, just catch that friction zone and keep feeding throttle in balance with the clutch engagement. I have some difficulty describing this as I more or less feed in clutch at a constant rate and balance against that by feeding throttle to match. Seldom does the rear wheel make a full turn before the clutch is fully engaged and I'm on the throttle and accelerating. Drag race starts are, of course, very, very different. There, I'm at 6000 RPM or so and feed in clutch just enough to keep the front wheel hovering a bit off the ground.

[Little_Brit]

According to Wikipedia "as of 2008 over 75% of cars manufactured in Europe use manual gearboxes" with single plate dry clutches.

 

These have to suffer far more abuse than any bike is likely to give them, endless queues, constant stopping and starting with plenty of up hill starts to boot.

 

Throw in trailers/caravans plus all the families wordly goods and yet these inadequate devices typically last well past 100,000 miles.

 

They may well smell when abused but they still continue to function and provide a simple, compact solution for an inline angine and gearbox configuration as found in the boxer twins.

 

I have taken three different oil head/heaxhead BMWs on five long European tours - two up with maximum luggage over some of the most demanding roads one could wish to meet from city rush hour to Alpine pass and never had more than the merest wiff of lightly toasted clutch!!

 

If it ain't broke don't fix it...

 

Derek

 

 

[cali_beemer]

After having many BMW's I have grown to accept the feel of the clutch. The positive is that it feels good, the downside is the clutches dont hold up very well IMO. I have toasted a few of the BMW clutches. In order to get them to last, one must be gentle, very gentle.... When I switched to the ST 1300 the clutch was much nicer and you would really launch the bike of the line without worry of destruction or death to the clutch. My only gripe with the ST was the clutch had very little feedback on where it was in the friction zone. Now my Vstrom has a wet clutch and it has the best of both worlds, its very smooth, can launch off the line without destroying it and it has pleny of feedback. I have never understood BMW's love for dry clutches. They degrade performance, require a ton of work for replacement, and to top it off many of the models are prone to leaking oil all over it.

[upflying]

 

Now, to quote from my forthcoming MCN article reviewing the course: "The secret of the complete control our instructors had over their motorcycles was what they termed “creating a tug of war” between the motor driveline and the rear brake. Bringing the engine speed to a constant – typically at least twice idle RPM or more – the students had to finesse forward in the friction zone, while simultaneously applying the rear brake gently to manage speed. The engine’s consistent higher RPM helps to create a stabilizing gyroscopic effect, while the engaged rear brake squats the chassis. The end result is a taut, controlled feeling motorcycle, even at nearly maximum lean angle at crawling speeds."

 

Feathering / slipping or whatever you want to call it is in effect, because the rpm is constant, but clutch and brakes are variable - in this method, at least.

 

 

-MKL

I am one of those who now uses the "tug of war" between the clutch and rear brake to clean my patterns successfully. But there is another school of thought. When I went through the CHP course in '89, the instructors did not want to see your brake light activate. You were instructed to have the speed set prior to pattern entry and use the throttle and partial clutch engagement to perform the maneuvers.

It appears these instructors are performing the patterns with the clutch fully engaged. I think "motorman587" also teaches this method of enforcement training. Maybe he will check in.

 

[Peter Parts]

Great discussion. Here're some of my 2-cents, off-center thoughts.

 

1. Experience with a wet clutch is harmful to driving properly with a dry clutch. Check out anybody who complains about short life on a BMW clutch and you'll find that's who they are.

 

2. The BMW clutches can last like forever if used properly. I've never said this before on any forum before but, "...and after 44 years, I should know, eh".

 

3. The business of finesse in driving, feathering a dry clutch, and fine engine control is immensely helped by having a throttle counter-force spring.

 

4. Moshe's quote about gyroscopic force applies only to the cross-bike engines at low road speeds, not boxers.

 

5. An essential riddle for low speed control is the human factors safety issue that you have to stall in first gear at idle. Which means first gear must be too high for proper driving at low speeds without feathering the clutch.

 

6. Sure nice to have hydraulic activation in my BMW clutch - not sure if it is easy to go hydraulic with wet clutches... or if you need to.

 

Guess I really can't say if a durable, positive feel, dry clutch (which has to also be a large-diameter flywheel) in a bike works better than a slippable clutch floating in the engine oil (makes you laugh, eh). Some reasons to favor each.

 

Ben

[SuperG]

Great discussion.

....

1. Experience with a wet clutch is harmful to driving properly with a dry clutch. Check out anybody who complains about short life on a BMW clutch and you'll find that's who they are....

Ben

 

So true...similar to when some one transitions from a Honda stick shift car to a diesel stick shift pickup.

It usually followed by a clutch job on the pickup.

Slipping a clutch on a diesel is no-no, too much torque at low RPM.

 

I ride my Rt like a diesel pickup. Take off with low rpm (don't worry it wont stall), fully engage the clutch then accelerate, also shift without slipping the clutch much. Works so far.

 

[cali_beemer]

 

I ride my Rt like a diesel pickup. Take off with low rpm (don't worry it wont stall), fully engage the clutch then accelerate, also shift without slipping the clutch much. Works so far.

 

Thats the way you need to use the clutch on the BMW dry clutch. But, the beemer isnt a diesel and you dont have to do this with a wet clutch design. I dont see the benefit to the BMW dry clutch, but i see alot of positive reasons for a wet clutch. Theoretically, a dry clutch is a reliable, long lasting design when treated properly but BMW has been able to remove the reliable aspect out if it with leaky O-rings. One of the best things BMW has done lately is going to a wet clutch on the new K-bikes.

[ShovelStrokeEd]

I can't believe how many people fail to understand that a wet, multiplate clutch just won't work with the layout of the boxer engine or, for that matter, the flying brick K bikes. The new K bikes have a crankshaft laid out across the chassis and thus, the wet clutch makes perfect sense in that design as does the dry clutch in the boxer/brick configuration.

[Tony_K]

They sucked you back in Ed! Too funny!!!!

[russell_bynum]

 

 

 

Now looka, I say looka here...I can't believe how many people fail to understand that a wet, multiplate clutch just won't work with the layout of the boxer engine or, for that matter, the flying brick K bikes. The new K bikes have a crankshaft laid out across the chassis and thus, the wet clutch makes perfect sense in that design as does the dry clutch in the boxer/brick configuration.

 

You folks is about as sharp as a sack of wet mice.

 

Fixed it for ya.

 

 

[flars]

"..a wet, multiplate clutch just won't work with the layout of the boxer engine ..."

With the popularity of the Ducati, HD and Suzuki Vs, BMW has decided that the 2013 R1400RT will still be a boxer, but the engine will be turned 90 degrees, so the cylinders will point fore and aft. This will allow the use of a multiplate wet clutch, but will reduce efficiency due to having to turn the power 90 degrees. Main seals will no longer be a problem since any oil escaping will just drip onto the ground, a la 1960s era Triumphs.

[ShovelStrokeEd]

Yeah, I know, sigh.

In my defense, I posted at 2:05 AM and I always get grumpy right after I catheter myself. Can't wait till the operation.

[carolinarider]

Dang, you mean I rode a Honda Valkyrie (boxer motor) for 6 years without realizing it had a wet clutch!!??

[crmdgn]

My sincere thanks to everyone for their carefully thought out ideas on clutch work on a BMW boxer.

 

Coming from an HD Roadglide, I had a lot of trouble leaving from a stop, especially on a hill. The HD would just idle off, with nary a conscious thought. My RT I stalled a lot early on.

 

Without reading the erudite thoughts on this forum, I intuited(?)that letting the clutch out as quickly as possible with concurrent throttle increase seemed to be most efficient.

 

Whatever I was doing, I neither slip the clutch nor stall, well one time a cute FSU student caught my eye, but that is another story, lol.

 

Good info here for sure.

 

paul

[OlGeezer]

From what I've seen, most Oilhead clutches, if treated properly, will last longer than the transmission itself.

That's not saying much....

 

What do you mean? Mine (both clutch and transmission) are still going strong at nearly 149k miles.

[TowJam]

... 6.Sure nice to have hydraulic activation in my BMW clutch - not sure if it is easy to go hydraulic with wet clutches... or if you need to.

+1 for hydraulic activation.

 

With the exception of the beemers, all of my other bikes have had wet clutches and a number of those were hydraulic. I especially like the fact that they are self-adjusting and as a result, tend to retain the same feel even as the miles accumulate.

[TowJam]

The Ducati dry clutch is about as easy to service as any. Takes about 10 minutes.

 

... and they sound great!

My first BMW was an '04 K1200RS - with a dry clutch. I absolutely hated that rattle.

[John Bentall]

"..a wet, multiplate clutch just won't work with the layout of the boxer engine ..."

BMW has decided that the 2013 R1400RT will still be a boxer, but the engine will be turned 90 degrees, so the cylinders will point fore and aft.

 

To keep the rear cylinder cool enough your R1400RT will have to be water-cooled!

[SageRider]

From what I've seen, most Oilhead clutches, if treated properly, will last longer than the transmission itself.

That's not saying much....

 

What do you mean? Mine (both clutch and transmission) are still going strong at nearly 149k miles.

There are always exceptions. Glad you've won the Oilhead tranny lottery...

[russell_bynum]

The Ducati dry clutch is about as easy to service as any. Takes about 10 minutes.

 

... and they sound great!

My first BMW was an '04 K1200RS - with a dry clutch. I absolutely hated that rattle.

 

??

[TowJam]

The Ducati dry clutch is about as easy to service as any. Takes about 10 minutes.

 

... and they sound great!

My first BMW was an '04 K1200RS - with a dry clutch. I absolutely hated that rattle.

 

I'm referring the characteristic rattle of the flying bricks' dry clutch. VERY pronounced when idling in neutral.

[russell_bynum]

The Ducati dry clutch is about as easy to service as any. Takes about 10 minutes.

 

... and they sound great!

My first BMW was an '04 K1200RS - with a dry clutch. I absolutely hated that rattle.

 

I'm referring the characteristic rattle of the flying bricks' dry clutch. VERY pronounced when idling in neutral.

 

Clutch in or clutch out?

[TowJam]

Clutch in or clutch out?

If I remember correctly (BIG if since it's been about 5 years), it was with clutch out. That and the brick's tendency to belch smoke at startup made for tease fodder from my Harley-riding buddies.

[jmseattle]

I have the 04 GT and have gotten used to the typical box of rocks sound with the clutch out. Not as pronounced as the Ducati but it's definitely noticeable