carleton

Not sure on the rules, but the women get to use carbon frames and rear disc wheels. Not sure about the other components (front wheel, pedals, bars, etc...)

Gros:


https://www.instagram.com/p/Bh8IpoeH...=gros_mathilde

Baby Puke

I would love to know this too. They come up randomly in my FB feed, but I still do not know how to plan to watch any particular keirin race, though presumably they are all there on keirin.jp

I just can't figure out the schedule. Stupid foreigners...

carleton

I know, right? Don't they know that everyone in the internet is 'Murican?!

(FYI: We are kidding. Baby Puke lives in Japan and races Keirin.)

Baby Puke

Actually I do kinda wish their website was a bit more foreign friendly- I mean just think of all the track nerds the world over that would be all over that! And you can bet live on there too, apparently!

SyntaxMonstr

I attended a toned down version of the Keirin school for developing Asian riders and bike assembly was a significant component. We only had to do it a few times but the big dogs would be doing a full overhaul every week. It's interesting how it goes so far beyond sport into this whole lifestyle of discipline and mindfulness. And yes, JKA riders need to buy their own kit and bicycles and it's usually considered bad form to get them secondhand so you're encouraged to splash out on a new frame (the benefit being that it's custom made to your measurements).

SyntaxMonstr

There's a specific Japanese Keirin race series where the riders can use modern kit, I don't remember the name but they had a few races during the season and it was the regular S/SS class riders on Look's with disc wheels, etc.

taras0000

Fixed that for you. Lol.

Baby Puke

Indeed you did! ありがとうございます！

seau grateau

Apparently this is the 9t cog setup Bos has been using:

https://www.instagram.com/p/Bh-pPQll...mekaanikko9239

taras0000

Tha cannot be efficient. Gotta be training only. Also, it doesn't look like the rollers of the chain would seat all the way down in between the teeth of the cog, rolling on the "locknut" so to say.

carleton

Great find!

That appears to be the IG of the guy who made it.

seau grateau

Yeah, found some more on his Facebook page:

https://www.facebook.com/mekaanikko9239/

carleton

That dude is about to be reeeeealy popular.



OK, kiiiiinda popular.

I'm sure there are plenty of trackies that would pay to have one looking for that "edge". I don't think it will unlock some hidden power or whatever. But, having a 9 or 10t cog-ed wheel is an interesting training tool for functional muscle development on the track. That being said, a spin bike or home trainer would do the same thing, but at home.

I would buy one. Basically to do slow-motion standing starts to work on technique.

Baby Puke

These are for sale at at least one shop that I know of here.

southernfox

Ooof. Do they call the men's "Boy's"? ...pet peeve of mine.

Baby Puke

It's super annoying and sexist. Japan is in the 1950's in a lot of ways, unfortunately. Please don't look at their (totally pink and "girly") uniforms...

On the plus side, it's great that the women get to compete and also earn a pretty great living from being track sprinters.

tobukog

The JCF, and Keirin even more so, are stuck in the 1950s. It's bizarre to see Women's Keirin being promoted by a moribund federation -- but anything to combat declining gambling revenues I guess.

sarals 

Women are supposed to look like anime characters, right? I saw a Keirin poster for a women's event in Japan in which they did. Hmmmm....

1950's indeed.

southernfox

Yes to everything.

700wheel

I agree.
As the number of sprocket teeth decreases the chain link at the top of the cog carries more of the chain load and following links take less of the chain load. This results in deformation of chain components and increased bearing stress on the sprocket teeth; the result is more friction and decreased efficiency.
There is an interesting article on the effects of bicycle chain efficiency here:
https://www.ihpva.org/HParchive/PDF/hp50-2000.pdf
Figure 2 shows measured drive chain efficiency for 21, 15, and 11 tooth cogs. My guess is that a 9 tooth cog would yield a transmission efficiency of 91% or less.

The hub shown in post 1939 is a special design; there are several hex headed bolts holding the hub body together. To change cog size requires partial disassembly of the hub.

Flatballer

That's a really interesting article.

Surprised that the highest chain tension was the most efficient (but I don't know how high the tension was, 305N doesn't mean much to me, maybe there's a limit where it gets less efficient again, like we've all heard?).

Bigger difference in the efficiency with smaller cogs than I thought there would be too. I knew they were less efficient, but I didn't know they were THAT much more less efficient.

I'm curious if their results hold up at higher RPM and higher power, or if the loss in power isn't dependent on power and the actually efficiency would go up across the board at a more reasonable power (and RPM).

70 RPM and 175W isn't a scenario that occurs very often.

Flatballer

Ah, good point. I was just skimming quickly and didn't actually read much of it. Just looked at tables and charts.

carleton

From: https://www.instagram.com/p/BiESPd6h...aurinevriessen

Non-NJS stuff I see:
- Carbon frames from those that make steel NJS frames
- SRM
- modern Shimano Dura Ace pedals
- G-Race pedal straps (I think)
- Mavic Ellipse
- Saddles of choice
- Carbon handlebars (not sure what make/model)

Not sure if this is training or race gear, though. Interesting nonetheless.

brawlo

I think people miss the point of this whole exercise. This huge gearing is for on the bike strength training = squats on bike. Inefficiency just isn't a consideration. And then the whole inefficiency argument always gets @carleton line of "look at what others are using" in my head. The top pro guys are going faster and faster on what everyone argues are inefficient gears. Top masters guys are going faster and faster on "inefficient" gears. The efficiency argument should really die a natural death because the argument appears to be quite invalid

brawlo

That post prompted me to look into them again. And then this hub from Specialized came up. I'm not sure why it didn't come up in my searching some time ago, because it's been out a long time now. It is the hub used on their P.Fix. We don't seem to have ever had this model available in Oz. The hub is almost exactly what Bos is using now with the bolt up fixed option. No mods necessary. Specialized should consider making a re-run of these seeing how popular they are becoming for the track sprinting community

Slumworm: Game Changer : 9T Cogs & 14mm Axle Hubs