FrankCerny

I recently took apart a 1974 Bridgestone Kabuki Skyway (at least I think that's the year) and I came across a Shimano Freewheel which I had not seen the likes of before. My knowledge of freewheels is amateur at best, so I was hoping someone else would have seen this before. My main question surrounding it, is why do the two largest cogs have such large gaps between teeth? The largest cog is 18T, but the third largest cog has 22T. This is contrary to all I thought I knew about freewheels and gearing and am hoping someone can enlighten me on why a freewheel would be designed as such and what effects it has on riding.

Note: The title is slightly misleading since it's uncommon only in my eyes, since I have never seen it!


The freewheel in question

canklecat

That wasn't unusual on 5-speed consumer grade and touring bikes then. Combining larger cogs with only 5, 6 or 7 cogs will require at least one or two awkward steps between cogs.

This previous thread on the Bridgestone Kabuki Skyway includes a magazine review, including specs for a 5-speed 14-32 freewheel, with reasonable steps for the three smallest cogs, and pretty big jumps for the largest two cogs.

My 1976 Motobecane came with a 5-speed freewheel of around 14-30, if I'm recalling correctly. After about a year of riding that I was in much better shape and found the gearing steps annoying. I switched to something like a 13-26, not a racing setup or ideal for loaded touring, but perfectly okay for my rides.

My heavy comfort hybrid/errand bike (35 lbs with rear rack) originally came with a 7-speed 13-32 MegaRange freewheel. The sixth cog was 24T, so the jump to the 32T big cog was huge and really awkward in the middle of a climb with a loaded bike, especially my first year back on the bike when I wasn't in good shape. I hated that freewheel so much I replaced it with a cheap but good SunRace 14-28, with more sensible steps, and the 28T big cog was plenty combined with the 28T smallest chainring, even when I was lugging 50 lbs of stuff uphill.

JacobLee 

Wow, a skip-tooth freewheel. I’ve never seen one either! Somebody will come along and enlighten us all.

oneclick 

Weight-saving and shifting. A larger sprocket can have some teeth missing and still have enough to engage the chain and carry the load, and the chain can be pulled sideways onto and off the sprocket more readily.

You have an especially odd skip-tooth sprocket with the odd-toothed one.

verktyg 

That's a Shimano Wide Ratio 5 Speed 14-34T freewheel with Alternate Teeth (Skip Tooth) on the two largest sprockets. They were made in 14-17-22-28-34T with or without the skip tooth feature on the two largest sprockets.

They started appearing on some Japanese bikes in 1974: the ultimate in Alpine Gearing.

From the Shimano section of the 1974 JBM (Japanese Bicycle Manufacturer's) catalog showing their freewheel offering.



I think that they were also made in a version with only the 34T tooth sprocket with the skip tooth design. That's the one that I think that I may have. I mounted it on my road bike along with with a Shimano Crane GT rear derailleur whenever I went touring.

Here's a "Twist Tooth" Uniglide 14-34T FW without the skip teeth.

Here's a warning that I posted in velobase.com in 2009:

"These were well made freewheels but required a special remover that didn't fit over most standard QR rear axle nuts. Removal usually required removing the axle from the left side first. If you got one these on a Phil Wood or similar sealed bearing hub, the only way to remove it was to disassemble the freewheel and hold the body in a vise while turning the wheel."

The original style FW remover that didn't fit over most axle nuts.

verktyg

pastorbobnlnh 

FWIIW, this is the first time I remember seeing the 4th sprocket with both skip and normal teeth on the same sprocket. Maybe I was just not paying attention in the past, but I doubt it. When I remove and clean sprockets, I would have certainly noticed those three spots where the teeth or normal.

oneclick 

Any "odd-numbered" skip-tooth sprocket will have to have at least one pair of normally-spaced teeth; the sprocket in the picture must be a 27A, although there is only a 27 (no A, normal spacing) listed in the chart above. As 27 is divisible by three, there are three such pairs.

JohnDThompson 

The "skip tooth" large sprockets were to facilitate shifting onto those sprockets. Later "Uniglide" and still later "Hyperglide" tooth profiles were found to work better and can be done to improve shifting on all the sprockets. As @verktyg notes above, these early freewheels require the TL-FW20 freewheel tool for removal from the hub, but it appears the OP managed to find one.

Pompiere

I had a Kabuki with a freewheel like that as a teen in the 1970s. I don't recall if any more than the largest cog with skip teeth.

T-Mar

They go back farther than that. Shimano's AT (Aternate Tooth) freewheels are in the 1972 catalogue and shown in 1971, Japanese market, advertisements. It wouldn't surprise me if they even pre-date 1971.

The concept of deleting cog teeth to faciltate shifts goes back to early days of derailleurs. Charles Boizot filed a 1909 patent for his Tri-Direct derailleur that included cogs with several consecutive missing teeth and a ramp to facilitate shifts. It's interesting that Shimano would adopt and develop both concepts, to give us what ould eventually become Hyperglide, 80 years later. It is also worth noting that this patent is the first known, docmented use of the term "derailleur".

verktyg 

I'd seen some vague suggestions and references online that they went back earlier than 1974 did but not find any documentation.

I assembled bikes at the first shop that I worked at during part of 1973. We sold Gitanes, Nishikis, Takaras and Azukis. I seem to remember seeing a few cheap Azukis or Takaras with those huge Shimano 14-34T freewheels but without the skip teeth. They added a pound to the weight of those 34+ Lb. bikes.

By 1974 a few more Japanese bikes came with those FWs and that's where I first saw the Alternate Tooth styles. I bought one for loaded touring in 1975. I'm certain that only the 34T sprocket was skip tooth. I may still have it somewhere but I think that it was on my rough stuff off road trekker that got stolen in Japan Town in 1982.

verktyg :50;

FrankCerny

I appreciate everyone's' help with this! Especially the images! I never really think about the chain having issue shifting, as it just works so well these days. Extremely interesting the way they tried to make the shift easier by removing the teeth. Not exactly sure if I will put it on my touring bike, but at least I know it wasn't a manufacturing defect. If I ever climb a mountain though, I know what FW to use

As a note, I was able to find the "old style Shimano remover" needed on eBay (Kengine makes them I think?). It definitely was more of a pain to take off than I was expecting.

TPL

That specific tooth profile on that Shimano FREEWHEEL is NOT 'skip tooth' ....it is what Shimano called ALTERNATE TOOTH

'Skip tooth' is a mongrel, bastard term ....chainrings with every other tooth present and matching cogs found on very old bicycles, often equipped with coaster-brake hubs that have every other tooth present are actually 1 INCH PITCH

COASTER BRAKE hubs are too often bastard termed as 'kickback' hubs

REAR WHEELS are too often bastard termed as 'back wheels'

FREEWHEELS are too often bastard termed as 'cassettes' ....or 'flywheels'

WHEELS are too often bastard termed as 'rims'

700c sized wheels are too often bastard termed as '29er'

650b sized wheels are too often bastard termed as '27.5 inch'

PatTheSlat 

Oh good, you seem like a reasonable fellow, maybe you can help me then.

I picked up an old English Racer ten speed with one of these Shimano Skiptooth freewheels. I need to replace the back wheel because I want to convert to 29er rims instead of the original 27" but I can't figure out how to remove the cassette flywheel. I've only ever worked on single speed bikes with those old kickback hubs so I'm just not used to this stuff... I do have a 27.5 inch mtb but never had to work on that thankfully.

base2 

Man, everytime I think I may have something to add to the discussion, y'all beat me to it! The only one I ever saw in person was about a week ago on a vintage 1974/5 Shimano disc braked pile-o'-lugged Japanese gas-pipe.

I pulled the caliper, the rear wheel, reassembled the hub so it at least turned by hand & set the whole mess aside for a volunteer to put on eBay.

Good show, BF!

pastorbobnlnh 

...and--- just to make certain that the corrector is corrected---

SPROCKETS are too often "mongrelized" and "bastard termed as" ---- (wait for it) "cogs" (see above quote)!
Sheesh!

Mount Washington Cog Railroad cog system. Looks nothing like a sprocket for a bicycle cassette, freewheel, or "flywheel."

Yet, we interchange "sprocket" and "cog" all the time and we on C&V are intelligent enough to know the person posting--- means the same thing.

oneclick 

Um, yes it does. The shape of the sprocket/cog is best determined with reference to the mating part; the rack on which that sprocket/cog rides has cylindrical sections on which the sprocket/cog rides, much the same a bicycle chain, and thus the form of the teeth is similar; obviously different from the spur-gear teeth beside it.

However, perhaps all should be reminded that in English dictionaries, and by extension definitions of words, are descriptive not prescriptive.

ThermionicScott 

I find value in the terms "29er" and "27.5". They are specific to a use case with relatively large (~3") tires. Your typical 700C road bike won't fit 29er tires, ditto for many 650B gravel/touring/rando bikes and 27.5" tires. Until recently, it was often a useful way to distinguish rims, since the MTBs labelled "29er" or "27.5" had already adopted discs.

No amount of anger will make the bicycle tire system simpler, so the best option is to embrace the quirks and diversity.