SkinGriz

So the Suburban frame I’ve been pondering on for years has a BB shell width of 64ish mm. And I’d like room for bigger tires (26x2.125 max is fine).

Where did 68mm come from? Which Chicago Schwinns have this BB shell if any?

Is it a safe assumption that Varsities are also ~64mm?

Thank you.

Iride01 

Your Suburban has a 1 piece Ashtabula crank doesn't it? If so, the BB shell would have to have an adapter put in it to run something like a BSA threaded BB.

My Suburban, Varsity and other cheap Chicago Schwinn's were all that same 1 piece crank. The more expensive Chicago Schwinn's had the 3 piece square tapers in a BSA threaded BB shell. Maybe some of the later were cartridge BB's but still probably BSA.

I considered the bb shell adapter for my Varsity. But the expense even 15 years ago was more than the bike was worth. So I sold it and found a real nice Raleigh Comp GS from the same time period and later a virtually unused Paramount frame from the original owner. They were nice riding bikes. And much lighter than the boat anchors the Varsity and lesser models where. Though I still might say my Varsity was the best riding bike. But it could wear me out on just a 20 mile ride. My new Tarmac makes 20 miles seem like nothing.

SkinGriz

I don’t mind Ashtabula cranks.

I just didn’t know they weren’t all the same width.

Iride01 

I don't know that they are all the same width shell. But the big thing for them is the BB shell is a bigger diameter than BSA's 1.37 inches. And I don't know if there is any other BB type for any other crank that will work in their shells.

I guess I misunderstood what you are wanting to know. Why does the width of the shell matter to you if you aren't changing the crank? Or do you need another 1 piece crank?

Andrew R Stewart 

The bare Ashtabula type shell on my computer tower measures at 65.3mm wide. I have to admit I have don't remember ever having to do this measurement (on a 1 pc. crank/BB) in my nearly 50 years of turning wrenches.

As builders of frames using more current parts and specs have found out the chainstay shape, as they pass by the tire and rings, is of far greater concern then a very few shell width mms are. So even with 73mm wide shells many wider tires still need stay indenting and bends (and sometimes replacement of the stay section is this area with a plate or strip treatment) to provide adequate clearances.

I, for one, wouldn't put too much cost and effort into a frame that used a part spec that was so limiting as 1 pc. cranks are. Yes, one can use a 3 pc. BB adaptor (installed a number of these early on in the MtB craze) but in my mind that's just one more kludge and to be avoided if possible. Andy

FBinNY 

I suspect that the OP is conflating BB shell width with chainstay tire clearance.

While there's a loose correlation, it's very loose, because chainstays are typically bent or crimped to establish the desired tire and sprocket clearances.

FWIW 68mm is the overall width of a British standard shell. I believe (from long old memory) that US standard unthreaded BB shells are 2-1/2" wide. Please don't hold me to this because it's not something I ever worried about memorizing since they were all the same.

SurferRosa

Every Schwinn I've owned with a 3-piece crank had a 68mm bb shell: Paramount, Circuit, Letour, etc...

well biked

All of the built-in-Chicago models that had an English threaded bottom bracket shell. Paramount, Superior, Super Sport, Le Tour (built in Chicago for a year or two), probably more that I've forgotten to mention.

well biked

Keep in mind, the Chicago plant closed in 1983, and for all practical purposes, a little earlier than that. Was there a Schwinn Circuit produced 1983 or earlier? I'm genuinely curious. Also the Letours were at first imports (probably Panasonic built), and then from '83 to the early '90's were built in the factory that replaced the Chicago plant,the newer Schwinn factory was located in Greenville, Mississippi. I think there was only one model year LeTours were built in Chicago, and that was year model 1980. Pay no attention to "Chicago Schwinn" headbadges as far as place of manufacture, Schwinn's corporate headquarters remained in Chicago at least through the '92 bankruptcy, but the actual bikes were made all over the place during most of the '80's and into the early '90's.

Sorry, don't mean to be argumentative, I just really like Schwinn history and all the little details.

dmark 

A 68 Super Sport now stripped and on workstand measures 68mm BB width.

SkinGriz

Looking to build another cheap junky klunkerish bike.

The cranks in the beach cruiser I was messing with were bent. They weren’t even forged, just bent and threaded.

So I took the cranks out of a Suburban, cleaned and swapped everything to include bearing cups. The real Schwinn cranks are better quality and I don’t think they’d tweak unless I really abused them.

But the whole assembly is thinner and the chain line doesn’t match. The Suburban had a double. If I reassembled it as a double the outer ring would line up, but it’s a 52 (I think) and I was trying to stay maybe between 55 and 65 gear inches.

Was hoping to stay one piece (yes, I know it’s technically inferior).

I just didn’t know that there were different widths of one piece cranks.

That’s where the question comes from.

Bill Kapaun

https://www.sheldonbrown.com/opc.html