Bike porn

hm, the last two seatpost clusters posted are actually pretty ugly and I'm beginning to change my mind.

1957 Ellis Briggs - making me want to nip down the road and enquire about getting something similar built!

I've stripped a thread on a sprocket before. I'm still not sure if it was as a result of over, or under-tightening it.

A bolt on does ultimately seem like a better solution over the long term for day to day riding....

...but I guess if you're on a track and only ever applying forward pressure it doesn't matter and cogs would be faster to change.

An ideal band clamp has no bending stiffness, the aim is to create uniform circumferential tension and therefore uniform radial compression

Just because lots of people, even famous ones, make the same mistake, it doesn't suddenly change the laws of physics to suit. There's lots of terrible engineering in bicycles, from new NAHBS-wank form-over-function stuff to ancient conventions which never get changed because they kind of work and there is a huge inertia opposing reform (j-bend spokes, screw-on sprockets)

Are we talking about preventing a seatpost to slide down the tube when we put the weigh of our ass on the saddle? Isn't the required "clamping force" to be applied to provide enought friction totally peanuts? The only time I ever had a post sliding it was when I wanted to finish a built, did not have the correct size post and shimmed one stupidely as I could not wait to ride the bike...

I prefered your point about risking more dirt / water infiltration and increasing the possibility of seizing...

I had once a crack in a seatstay after a crash. It was a traditional frame where the stays are brazed to each side of the seat lug, with a nice wrap detail. The crack was where the stay connects to the lug. I always imagined that if the stays were connected to the rear of the seat lug (like on some of the examples posted previously and that engineers here don't like) the shock would have been transmitted equally to the whole circumference of the stay rather than just a portion of it, and maybe it would not have cracked (intuitive thinking, not scientific of course). I always somehow assumed that this was why Tom Ritchey was using that design on MTBs, for a better resistance against shocks when you jump for instance... The fact that the force is applied to the seattube precisely where the seatpost increases de facto its @ pinching resistance would be a plus surely?

And when you say "NAHBS-wank form-over-function" and "famous names making mistakes", would you really put Ritchey and Roberts in that category?

More fastback seat stay awesomeness.

56cm Samson by sashae, on Flickr

Many thanks sir!

Loic

Are we talking about preventing a seatpost to slide down the tube when we put the weigh of our ass on the saddle? Isn't the required "clamping force" to be applied to provide enought friction totally peanuts?

Absolutely. The change in seat-post design has more to do with limiting the "clamping force" more than much else--- to not deform really thin alu or carbon seatposts. The other major factor, I think, in the adoption of these "collars" is their low cost as they--- like threadless stems--- allow for a significant rationalization of manufacture and montage.

One can perhaps argue with the round seatpost design-- round tube inserted into close fitting round tube (milled to fit)--- but it works relatively well and provides a good range of custom rider fit.

Screw on sprockets? They work fine. The multi-bolt versions are a PIA. The reason sprockets are screwed on is that the interface allows one with a minimum of precision to make pretty good sprokets that work well.

A friend for example designed a bottom bracket where the bearings are not pressed into anything. They literally float. Remove one bolt and one can remove without a single tool the axle and bearings. The bottom bracket is so balanced that it can turn by blowing at it. Sounds impossible but it works--- and was used in all the big tours by many elite cyclists including some of the strongest professional sprinters of the day. The bottom bracket was built around the Record low profile cranks. Its secret? Incredible precision-- even the ti axle was specially milled and treated.
He also designed a hub where the cassette carrier is just mated onto a hollow axle with ti end bolts. This lets one replace the carrier with a single piece milled multi-gear train--- he did them out of Ti and Alloy. It works well and was too ridden to victory in a number of major races.

Every single part--- even the freehub--- can be taken apart, cleaned and put back together without using a single tool!

Are these designs which on the face of things seem so simple appropriate to mass production? No. They are too demanding of precision.

What is wrong with a screw on sprocket by the way?

Engineers don't transmit torque through screw threads, it's just wrong. It only works at all on bicycles because the the thread in question is huge. A spline sized to transmit the same torque could easily be less than half the diameter. In fact, it is; look at the input thread and the output spline of a Surly Fixxer. As it turns out, the thread is not in too much danger as long as the transmission ratio is quite large, say >2:1 for lightweight hill climbers or >3:1 for burly track sprinters, and it equally turns out that efficient ½" pitch roller chain drives at bicycle loads and speeds don't demand smaller sprockets than can be accommodated over a 1.370" pilot bore. But it's still wrong.

I always imagined that if the stays were connected to the rear of the seat lug (like on some of the examples posted previously and that engineers here don't like)

Having the stays abutting the seat lug is good, using them as part of the seat post clamping mechanism is bad.

And when you say "famous names making mistakes", would you really put Ritchey and Roberts in that category?

Yes. Engineering pays no respect to fame, or previous good work. Every engineering choice is assessed on its own merits.

So this is the answer, too bad it costs too much and uses proprietary cogs

We're just waiting for harmonisation of a splined sprocket which can accommodate 13T for track racing. For most people, ISO 6-bolt is fine, but racers wouldn't like having to use 64/16 for pursuit gearing, even though it might actually be a good idea. Shimano HG is the wrong shape for reversing loads (sorry Halo FixG), but CentreLock is sized appropriately, uses standard road bike servicing tools and AFAIK is free to use.

We're just waiting for harmonisation of a splined sprocket which can accommodate 13T for track racing. For most people, ISO 6-bolt is fine, but racers wouldn't like having to use 64/16 for pursuit gearing, even though it might actually be a good idea. Shimano HG is the wrong shape for reversing loads (sorry Halo FixG), but CentreLock is sized appropriately, uses standard road bike servicing tools and AFAIK is free to use.

Surely then a more svelte version of the Splined Drivers that FGFS hubs use is then the answer?

We're just waiting for harmonisation of a splined sprocket which can accommodate 13T for track racing.

don't these guys do 13T for their hubs? At least they sell a 13T version...

http://www.victoire-cycles.com/cogs/7075-t6/splined-cogs.html

Engineers don't transmit torque through screw threads,

Of course they do.. Look at bicycles!

Yes. Engineering pays no respect to fame, or previous good work. Every engineering choice is assessed on its own merits.

And there are loads of approaches.. Bicycles clearly belong to the "worse is better" school just as much of the Internet standards that we are using to communicate with one another in this forum (HTML over HTTP over TCP/IP versus BER/ASN.1 and OSI). HTML is really a good example as it was born as a very poor kludge (worse is worse) to try to copy something with good engineering (HyTime) but without the difficult engineering and development--- CERN licensed EBT's Dynabook but its pay per document revision model proved prohibitively expensive. HTTP was developed as a protocol one could write with a shell script--- following a number of other "finger protocols" such as Gopher.
And today how many billions of people are using it?

don't these guys do 13T for their hubs? At least they sell a 13T version.

I'm sure they do, as do White Industries. Splined sprockets will only take over, though, when the interface is harmonised among manufacturers.

I'm sure they do, as do White Industries. Splined sprockets will only take over, though, when the interface is harmonised among manufacturers.

You mean like ISIS bottom brackets :-)

Fair point, the successful design will have to be both harmonised and good

Back to porn....

Fastback seat stays and CX (as mentioned by veLLo). Yup.

I don't know any jargon :(

Cross chained

needs more bags

Tru

Could someone (ed) please ID the toptube bag?

When Ed sees that last bike...

Give it some mudguards and I'd ride it
function bikes>>>>>>>>>>>>>>>>>