Should Moto Guzzi consider a belt in place of the CARC shaft?

[willowstreetguzziguy]

There seems to be a fair amount of dislike on here for the CARC shaft drive on the larger bikes. I myself find no fault with it on my 1200 Sport but I know it does add a decent amount of weight. With Harley having success, I think, with their belt drive, is it maybe time for Moto Guzzi to possibly think about replacing the CARC on the larger bikes with a belt? How would you feel about that change?

[twowings]

I'll take an enclosed shaft in an oil bath over a belt exposed to UV rays, dirt, grease, gasoline, and vandals most every time...just my two centavos...

[Chuck in Indiana]

It would take a clean slate redesign. Doesn't make sense to me. .

[fotoguzzi]

the layout of the Guzzi v twin doesn't lend itself to that kind of drive, it's perfect for a driveshaft out the back of the tranny, you'd have to turn the power 90* to adapt a belt.

the Buell I had with belt was superior to chains and rivaled the DS set up.

[beetle]

No.

[Daniel Kalal]

...be a fair amount of dislike on here for the CARC shaft drive...

I don't follow your premise.  Most of what I've seen on this forum is that the CARC is quite rugged and has the tremendous advantage of making it possible to remove a rear wheel in one minute.  You've really seen a fair amount of dislike on wildguzzi.com?  Count me in the "like" camp.

The only real criticism (and it counts for a great deal) would seem to be from the coin-counters that rule Guzzi (they're probably not Guzzi employees, but that matters not one bit).

[ITSec]

No dislike of CARC here - in fact, an active dislike of (in increasing order of unpleasantness):

• Shaft drive with dual-sided swingarm
• Chain drive
• Belt drive

To my mind, any bike over 750cc should preferably come with a low-maintenance drive, single-swingarm shaft being the most desirable.

The possible discontinuation of CARC significantly lowers the likelihood of me purchasing a new Moto Guzzi in future; in fact, in many designs I'd prefer a chain to a dual-sided swingarm shaft, and definitely to a belt. This comes with some experience; I've sold motorcycles with belts as well as those with chains and shafts and have extensive ride time on them all.

[pete roper]

Well at least at the moment its immaterial as the CARC or indeed any sort of reactive rear drive has been discontinued. The idea that the unit is particularly heavy is also a red herring. It certainly weighs no more than the unsprung weight tied up in a late model Tonti or Spineframe swingarm and final drive but has the advantage of both having reaction control so it can work properly and a rising rate suspension system.

As others have pointed out the longitudinal crank in the current motor requires the drive to be turned through 90* to make the back wheel go round. This can either be done at the rear wheel or at the gearbox. While doing it at the gearbox will allow less unsprung weight you will still get the mechanical losses of the 90* change of direction and then will add further losses from the belt or chain rear drive.

I really like the CARC design. Sure it's built down to a price a bit but generally it is grotesquely over engineered and strong as an ox! I've had very very few problems with them over the years and the two commonest failures are the big crownwheel support bearing chopping out due to water intrusion and a few cases of the pinion nut loosening for want of Loctite!

I have no real problem with modern chains, they are robust and very long lived if you maintain them properly and that is hardly a chore. I have no experience of belts but they seem to work in the applications they are used in. At the end of the day though a decent reactive system like the CARC is, IMHO, the best compromise for cleanliness, ease of maintainence and performance for a machine like a Guzzi.

So, you ask, why didn't they continue with the system? Well the Cali's are stupid heavy and have a swingarm about a kilometre long so torque reaction isn't much of an issue and it's a cruiser so it's not expected to handle. With the V9's? The people who these are aimed at don't know or care how stuff works as long as it *Looks* right to them. The bike could handle like a feral shopping trolley with a wonky wheel but they wouldn't care as long as it looked 'Cool' and had a USB port to charge their phone.

Pete

[sib]

...With the V9's? The people who these are aimed at don't know or care how stuff works as long as it *Looks* right to them. The bike could handle like a feral shopping trolley with a wonky wheel but they wouldn't care as long as it looked 'Cool' and had a USB port to charge their phone.

Pete

That's rather uncharitable, Pete.  Personally, I don't want or need a reactive rear end on my V7II Stone, because I don't care to push the bike to the point where the advantages of having one would compensate for the extra weight and complexity it comes with.  You ride your way, I'll ride my way, and we'll make our own evaluations.

[Bulldog9]

CARC forever...... The CARC system should be further developed not dropped. Its why I own a Guzzi.....

[RayB]

I'll take an enclosed shaft in an oil bath over a belt exposed to UV rays, dirt, grease, gasoline, and vandals most every time...just my two centavos...

That would be great :1:

[sib]

As long as we're telling Moto Guzzi how to design their products, I would like to have a shaft drive with a genuine constant velocity joint instead of a U-joint.  The latter, as I recently learned, does not have a constant output velocity when the input velocity is constant.  Instead, the output rotation rate has an superimposed sine component whose amplitude depends on the angle between the input and output shafts.  This apparently is the primary reason why such drives need cush rubbers, to absorb the rotation rate variations.

[Tom]

The work/production to get it to work may offset the advantages to run a belt.  Replacing a belt is no picnic either.

[ITSec]

As long as we're telling Moto Guzzi how to design their products, I would like to have a shaft drive with a genuine constant velocity joint instead of a U-joint.  The latter, as I recently learned, does not have a constant output velocity when the input velocity is constant.  Instead, the output rotation rate has an superimposed sine component whose amplitude depends on the angle between the input and output shafts.  This apparently is the primary reason why such drives need cush rubbers, to absorb the rotation rate variations.

So the CARC either doesn't produce such harmonics, or is missing the cush rubbers? And why do chain and belt drive bikes so often have cush rubbers? There's something in your explanation I'm just not understanding.

[WitchCityGuzzi]

I really like the CARC on our Stelvio and Griso. I'm not interested in a rubber band powering my motorcyle. I find it unlikely, the belt would work that well offroad either. Seems like it's life span in the muck would be pretty short.

[Triple Jim]

As long as we're telling Moto Guzzi how to design their products, I would like to have a shaft drive with a genuine constant velocity joint instead of a U-joint.  The latter, as I recently learned, does not have a constant output velocity when the input velocity is constant.  Instead, the output rotation rate has an superimposed sine component whose amplitude depends on the angle between the input and output shafts.  This apparently is the primary reason why such drives need cush rubbers, to absorb the rotation rate variations.

That's true for a single U-joint.  That's why vehicles use two joints, either together like Guzzi, or separated with a shaft between them, like older rear wheel drive cars.  The intermediate shaft does have a non-constant rotational speed when the U-joint is not at 180 degrees, but when the joints are oriented properly, the output shaft does indeed turn with constant speed, because the second joint's non-uniformity cancels that of the first joint.  It all does have to be designed carefully for that to work.

Wikipedia's article "Constant-velocity joint" explains it, and has some nice animations to demonstrate it.

[pete roper]

So the CARC either doesn't produce such harmonics, or is missing the cush rubbers? And why do chain and belt drive bikes so often have cush rubbers? There's something in your explanation I'm just not understanding.

Not quite.

By using paired Hookes couplings the varying output from each one cancels the other out pretty much meaning the forces imposed are greatly diminished. The further apart they are the more effective this is. It's the reason why the newer driveshafts have a coupling at each end and last so much better than the earlier UJ's used on loops and earlier Tontis.

And Doug, I hate to tell you but your Stelvio and Griso both have 'Rubber' drives. :D the shaft is a two part assembly with some sort of bonded, synthetic, high hysteresis rubber in between the two to act as a Cush drive. It seems to work well as I've only heard of UJ failures, never a failure of the Cush.

Pete

[twowings]

As far as I'm concerned, my 2008 Norge IS the pinnacle of form AND function...stick on all the bells and whistles you desire, my motorcycling 'needs' are already met! :thumbs:

[oldbike54]

As far as I'm concerned, my 2008 Norge IS the pinnacle of form AND function...stick on all the bells and whistles you desire, my motorcycling 'needs' are already met! :thumbs:

 I felt the same way about my 1970 TR6R Triumph back in 1971 

 Dusty

[sbaker]

Carc heavy ???? Every time I think I would increase my gas mileage if I didn't have a Carc that weighted so much, I step on the scale... Case closed.

[Daniel Kalal]

...The latter, as I recently learned, does not have a constant output velocity...

With two u-joints in series (as used with all the big blocks: CARC, Spine, Tonti and Loop), if the input shaft is exactly parallel to the output shaft the result will be perfectly constant rotation at the wheel.  The CARC is best at doing this--you need a 4-bar linkage system (which means a floating rear drive) to work best, else your best bet as a designer is to try to be close to parallel within the normal shock stroke.

[twowings]

To paraphrase Lee Iacocca, "If you can find a better bike, buy it!"

[sib]

With two u-joints in series (as used with all the big blocks: CARC, Spine, Tonti and Loop), if the input shaft is exactly parallel to the output shaft the result will be perfectly constant rotation at the wheel....

But, that's also true of the 1 U-joint system.  The difference is that with 2 U-joints, it is possible for the input and output shafts to be DISPLACED but still parallel.  Now, we need an expert to tell us whether, with a 2 U-joint system, it is possible for the input and output shafts to turn at constant velocity when they are NOT parallel.

[pete roper]

(Groan.)

[Daniel Kalal]

But, that's also true of the 1 U-joint system

No; it's not.

possible for the input and output shafts to turn at constant velocity when they are NOT parallel

No; it's not.

This is pretty basic.  The calculation of u-joint characteristics is a topic for a freshman engineering class.  You'll find the Wikipedia entry for "Universal Joint" gives the needed equations.

[Nic in Western NYS]

Guzzi did real well with CARC.  Substantial, lasts 150k+ miles, solid engineering.  Few failures.  What's the problem with it other than weight?  And shaving ounces isn't what Guzzi's been about. 

[leafman60]

I've owned and ridden both H-D's and BMW's with belt drives and I like them better than any other drive system. They are simple, light weight, efficient, reliable, permissive of ratio changes and low maintenance.

However, I do not expect it on a longitudinal crank bike like the Guzzi. Since the power output of from the engine is longitudinal to the bike, adapting to a belt drive would still require a 90-degree change of direction in the power train that would bleed off some of the inherent efficiency of the belt drive.

Maybe a special-designed transmission with a side output would work.

As far as the belt itself, though, they are great.

[Triple Jim]

No; it's not.

Actually it is.  The double Cardan joint, like in most Guzzi rear drives, is a CV joint.  In any double Cardan joint system, when the input and output shafts are parallel, or if their angles are the same, the input and output shafts runs with smooth rotation (CV).  The double Cardan joint in many Guzzis is a CV joint.

Again, the Wikipedia article "constant-velocity joint" explains it well.

[Daniel Kalal]

...are parallel, or if their angles are the same...

Exactly.  If the angles are the same then they are parallel and the output is constant*.  That's the special case where  two u-joints in series behave as a CV joint.  Real CV joints are more clever than that.

* and if not parallel, then the output is not constant, which was my earlier comment.

[Triple Jim]

Exactly.  If the angles are the same then they are parallel and the output is constant*.  That's the special case where  two u-joints in series behave as a CV joint.  Real CV joints are more clever than that.

* and if not parallel, then the output is not constant, which was my earlier comment.

There's one more special case, and that's when the two angles are the same, but not opposite as when the shafts are parallel.  For example, each shaft is angled 10 degrees, for a total of a 20 degree angle.  The joint is CV in that case too.  It's the case in a double Cardan joint, as I said above, and is why Guzzi uses a double Cardan joint in its swing arms.