Chain case compatible?

[jaffaman]

Noobie question.

I'm building a bike and want to use a Shimano XT trekking crankset. FC-T781 is "chain case compatible" and FC-T780 is essentially the same but is not chain case compatible. Being a 3x10 commuter there is no way I'm putting an actual chain case on the bike if that is the large chain cover for the front crank and back to the rear.

So, the question is does it matter which I get and can anyone explain what the actual difference is between chain case compatible and not compatible Shimano cranks?

Thanks.

[master6]

I dont know about it being a "noobie" question. I was intrigued, and wondered whether "chain case" was another term for "chain guard", which was a "girls" thing in my youth.
A google search of "chain case compatible" produced a wealth of information, although I did not dig far enough to determine the difference between the two chain sets you mentioned.
I found one chain case that appeared to completely encase the chain, and it reminded me of my kart racing days some years ago. We raced on a dirt track, and chains were chewed up like half a pound of sausages in front of a large dog. One of my mates built a fully enclosed chain guard, complete with a screw in plug at the top, and ran his chain in a constant shallow bath of engine oil. His chain lasted more than a season, while the rest of us were hard pushed to get two race days out of a chain and two cogs.

Back on subject; Google awaits to fill your head with information, some useful.

[find_bruce]

As I understand it chain case refers to a version of what master6's mate used -

Gear case
A chainguard that totally encloses the chain, usually found only on roadsters. Gear cases (also known as "chain cases") are extremely practical for utility bicycles. They keep the chain clean in all weather, and permit cycling in ordinary street clothes without risk of soiling. Unfortunately, a satisfactory chain case to work with derailer gears has not been developed, so they are only found on one-speed bikes or those with internal-gear hubs.

If you look at the service instructions for the FC-T781, via the [/url]Shimano tech docs site[/url] you will see the difference is in the spacers in the bottom bracket.

What makes no sense is what is the relevance of a chain case to a crankset designed to run 3 chainrings, which, as far as I can find, don't work with a chainguard.

[il padrone]

Chaincases do not run with a 3 X 9 drivetrain. The closest thing that may be used is a chainguard, but these do not demand specific cranks. Maybe the crank-set, with just one chainring fitted, is better suited to a chaincase, but on a superficial close look it is not immediately obvious how. Some modern cranks are too bulky around the crank arms to fit in a chaincase.

[jaffaman]

Thanks for the replies. It was the bit find_bruce mentioned that had me stumped too - how does a chain case make sense on a triple crankset?

I think I'll just take it that it doesn't much matter and either will do for me - there is a minor spacing difference which won't hurt one way or another.

Thanks again!

[il padrone]

It was the bit find_bruce mentioned that had me stumped too - how does a chain case make sense on a triple crankset?

This is about as close as you could get.

[jaffaman]

Thanks for the pic. That actually almost looks like something you could live with. Most of the ones I saw looked heavy and quite cumbersome.