Dry vs. Wet Clutch

[Professor]

Since most motorcycles have wet clutches and can spend significant time in the friction zone (for slow speed maneuvers, etc.), why does BMW (and Moto Guzzi) use dry clutches? What are the pros and cons of each?

[Cruzin]

My personal opinion is that the dry clutch shifts much smoother and is more dependable. I have a friend who owns a 2006 Ducati Multistrata. His wet clutch siezes after two days of being parked.
Just the comments of an amateur motorcycle "mechanic".
I was wondering why you pose the question? I was leary about buying my first BMW for that very reason. I didn't want to be changing the clutch plate after 100,000 kms. The salesman asked me if I had ever changed the clutch on a car with 100,000 kms. My answer was no. My fears were quenched.

Cruizin

[Andy VH]

Probably the biggest arguement in favor of a dry clutch is the simplicity of the clutch setup and actuation (especially a cable operated one). Also significant is that a dry clutch means the engine oil and tranny oil are seperate volumes of the best oil/lubricant to use for the intended operation.

And since the clutch is not bathed in engine oil (as it is on many bikes) the clutch wear does not contaminate the engine or tranny oil. This can mean longer intervals between oil changes.

If by your riding style you tend to "ride" the clutch, well then you can wear out the clutch quickly. But the occasional slow speed manuever of u-turns and parking lot manuevers don't do much damage as relates to clutches.

[wsteinborn]

In stop-and-go traffic on the way home from work, I really wish I had a wet clutch again.

[jingdog]

wet clutch: easier to change if need be
more robust
not subject to being ruined by oil leaks
contaminates the engine oil if abused

dry clutch hard to change
not as robust
subject to damage from oil leaks
doesnt pollute engine oil

advantage: wet clutch

[screwtop]

I like my clutches like my martinis.....Dry. With the exception of my 82 Yamaha Maxim, every bike I've ever owned has had a dry clutch, and I've never had to replace one. I agree that the wet clutches are definitely smoother, but with hydraulic actuation on the newer dry clutches (and the ability to get bigger slave cylinders on some models), I think the dry clutch can be pretty smooth as well. When I had my Ducati, I got one of the ventilated clutch covers and it sounded really cool. Just my $.02

[Professor]

Thanks for the information. I appreciate it.

[Motor31]

wet clutch: easier to change if need be
more robust
not subject to being ruined by oil leaks
contaminates the engine oil if abused

dry clutch hard to change
not as robust
subject to damage from oil leaks
doesnt pollute engine oil

advantage: wet clutch



+10 on that.

I was in an inservice training session. Two of the Kaws had smoked their clutch. Since that put us down a bike for training we had to get one fixed. There were no mechanic services available. I changed the clutch plates out while the rest of the guys went for lunch. The job was over in less than 45 minutes and was done with the basic tool kit from the bikes. Did we do the bike any favors with the contaminated oil, nope but we finished training instead of having to do it over again. If they had been beemers it would have been a no go all the way around. I'm a fan of the wet clutch system and apparently BMW is seeing the same thing with the change in the latest designs.

[rinty]

...contaminates the engine oil if abused.....Jingdog

Isn't the reverse a concern as well? i.e. possible damage to the clutch by contaminated engine oil.

I like having them separated. But the wet clutches seem to work well, and I would not decline to buy a bike just because of wet clutch concerns.

Rinty

[saab93driver]

wet clutch: easier to change if need be
more robust
not subject to being ruined by oil leaks
contaminates the engine oil if abused

dry clutch hard to change
not as robust
subject to damage from oil leaks
doesnt pollute engine oil

advantage: wet clutch

The dry clutch is hard to change on a BMW and MG due to the drivetrain layout and what you have to do to get to it, not simply because it is a dry clutch. I had a friend who had a custom Harley big twin with a dry clutch conversion and belt drive primary, he could change out that dry clutch in under an hour because it was accessible.

As far robustness I wore out clutch friction discs on my Honda CB 450 by 30K miles , I've never had to replace a dry clutch in any of my BMW's nor any of the past 5 cars I have owned which have all been dry clutches.

OTOH, a wet clutch does make the drivetrain design more compact, lighter, and probably cheaper to produce but if they were so great you'd think manual shift cars would have swithed a long time ago.

[osbornk]

OTOH, a wet clutch does make the drivetrain design more compact, lighter, and probably cheaper to produce but if they were so great you'd think manual shift cars would have swithed a long time ago.

Dry clutches are still used because they are simple and work best when the engine and transmission are separate. 90+% of the vehicles on the road have wet clutches. The clutches in an automatic transmission and a wet clutch motorcycle are almost identical.

I've had several motorcycles (about a dozen) and about half had wet clutches and about half had dry clutches. I've had both cable and hydraulic operation on both and I've never had a problem and I don't see much difference in the way they perform

[twins4life]

Having had both on a number of bikes, I prefer the BMW dry clutch over the Japanese wet design. I never liked the idea of the clutch wear material in the engine oil.