Does a long chain get dirtier than a short chain?

A diamond frame rider named Joel posted the following message on Peter White’s Google Bicycle Lifestyle forum:
>> I have always been curious about the long chain on most recumbants.
>> To this decidedly-not-an-engineer that seems a possible source of
>> maintenance issues.
>> Are any recumbant designers experimenting with the drive shafts that >> have been popping up on bikes of late? Is this even an issue?
(Photo: Timo Sairi’s shaft drive prototype recumbent — with smile. www.pyora.fi)
The following was my reply on the forum:
First of all, please understand that, like diamond frame (DF) bikes, recumbent models vary in quality and have a wide variety of designs. Some of the manufacturers’ engineers have addressed the problems mentioned, and some have not.
First of all: ‘bent designs
There are two basic ‘bent designs: long wheelbase and short wheelbase. I only work with short wheelbase ‘bents since a) they are the best adapted to the widest range of uses and b) the manufacturers I choose to work with only make short wheelbase models and c) I like them better.
Chain wear:
My belief is that chain metal experiences wear when it moves and hinges to pass over cogs, and no additional wear as it moves through the air. ‘Bents use identical gearing systems to uprights, with identical cogs and pulleys except that many ‘bents also use one or two guide wheels — called idlers — to maintain chainline and tension. It seems that, overall, long chains wear slightly slower than short chains since any given link is passing over a cog fewer times over a 100 meters of travel distance.
Accumulation of chain dirt:
It seems to me that dirt is introduced onto a chain from the bike’s own tires, from other nearby vehicles and from the wind. It is logical to believe there is a saturation point for dirt on any given link on any given chain; once a chain link is covered with dirt, no more dirt will accumulate.
Naturally, a 2 meter chain saturated with dirt will be hold more weight in dirt over it’s length than a 1 meter chain saturated with dirt. However, I would anticipate that each dirt-saturated chain link is saturated with the same amount of dirt.
Chain care:
It’s the same on ‘bents and DFs. A 2 meter chain will have more dirt over its length than the one meter chain; so a two-rag cleaning job on a ‘bent will be (roughly) a one-rag job on a DF.
Protecting the chain from dirt and your pant legs from the dirty chain:
The most common way to protect the chain from dirt, as on DFs, is with fenders. Everyone knows about those.
Specific to ‘bents, the next most common chain protection is the chain tube, best implemented by HP Velotechnik (HPV). HPV’s chain tube is intended to protect the rider’s legs from chain dirt, to slow down the accumulation of dirt on the chain, and to help prevent chain dirt from getting on the clothes of fellow passengers when you take the bike on a train (or ferry, etc.). This photo from the HPV website shows the chaintubes.
Dutch manufacturer Flevobike, with their Green Machine ‘bent, follows the Dutch tradition of attempting to design a low- or no-maintenance bike. They fully enclose the chain. It’s an intriguing solution since they seem to be using the chain-protecting case as a structural element. But it’s also about 50% more costly than a similarly specced HPV. The metal chain cover appears almost certainly to be structural, efficiently serving a dual-role.
If the bike is not an HPV, I prefer to fit it with fenders, at minimum. With the HPVs, the chain tubes come standard.
Alternatives to Chains:
Shaft drive:
Timo Sairi (www.pyora.fi), a Finnish architect has designed a shaft-drive ‘bent, not yet in production. One can see it here. We do not think the rider is Mr. Sairi.
More info. http://www.recumbent-gallery.eu/finnish-recumbent-with-shaft-drive/
Gates carbon:
While the most promising cost-effective solution would be Gates Carbon Belt Drives, there are numerous design challenges involved in having a long belt drive. At Interbike 09, Gates belts were shown as tandem timing chains, so we are hopeful to see them on a bent some day.
Imagination Drive:
An entirely maintenance-free and weightless solution that is available everywhere for free.

All best,
Robert

————
Robert Matson
copyright 2009 Robert Matson