Bike porn

less chain & shorter chainstays - lighter bike, surely?

Also silly coloured chain ring bolts with matching QR's and seat collar. Plus mismatched headset cups and Shouty chain.

porn bedwetters club

Looks great to me.

(apart from negi-stem and spacers....)

less chain & shorter chainstays - lighter bike, surely?

Yes. Also, shorter chain flexes less, as do shorter chainstays - in theory.
I would have thought Mr Marginal Gains over there would have grasped this, but I'm dying to hear the explanation as to why it isn't the case.

Where have I seen those clearances before...

less chain & shorter chainstays - lighter bike, surely?

lighter ≠ faster

Yes. Also, shorter chain flexes less, as do shorter chainstays - in theory.
I would have thought Mr Marginal Gains over there would have grasped this, but I'm dying to hear the explanation as to why it isn't the case.

Let me count the ways.

Shorter chainstays = worse chain line (i.e. it has to bend sideways more to reach the sprockets). That's a loss of efficiency.

Shorter chainstays only flex less if you don't make them stiffer to compensate, it doesn't take much material to win back the stiffness lost through a small (~5%) change in length between too short and just right.

Excessively short chainstays make climbing steep hills problematic, as the front wheel lifts off the ground. You have to change to a non-optimal position on the bike to prevent this.

Longer wheelbase means more bump attenuation for the rider even with a perfectly stiff frame. More comfort can mean more speed over long stages.

Of course, shorter stays and a shorter chain will be lighter, but in the balancing of desirable characteristics which will yield the fastest bike over a given course, 100g or so of weight difference is rarely worth bothering about, much less placing near the top of your priority list.

Some might argue that shorter chainstays = less chain + better power transfer.

I've never heard that one.

Shorter chainstays themselves make a difference according to bikeshop myth... er as tester says.

This is actually amey-shaped if it had a DH stem.

I've never heard that one.
Shorter chainstays themselves make a difference according to bikeshop myth... er as tester says.

Well, according to Tester's very detailed response above (thank you), I can determine that short chainstays (aka mad toight clearances yo) should hereby remain the preserve of the Track Bike. Upon which, my theory holds true.
It stands to reason that a shorter driveline (in almost any prop or chain-driven device) increases acceleration response - ie it's more snappy.
You only have to take it to the other extreme (ie tandem/cargo bike) to see why.

You should get the pro peloton on microdrive and compact chainsets then. :)

Well, according to Tester's very detailed response above (thank you), I can determine that short chainstays (aka mad toight clearances yo) should hereby remain the preserve of the Track Bike. Upon which, my theory holds true.
It stands to reason that a shorter driveline (in almost any prop or chain-driven device) increases acceleration response - ie it's more snappy.
You only have to take it to the other extreme (ie tandem/cargo bike) to see why.

but longer wheelbase will make the track shorter.

You should get the pro peloton on microdrive and compact chainsets then. :)

A different argument entirely*.

*Somebody more knowledgable than I may come along to explain why

but longer wheelbase will make the track shorter.

Not sure if...

But it is actually true!

By lengthening the wheelbase, the contact points subtend a greater angle on the curves of the velodrome, thus lifting the rider further from the surface, thereby shortening the path travelled by the centres of gravity and pressure. Although the wheels still roll 250m per lap, the shorter distance travelled by the main mass and drag bodies allows for a higher average speed.

There is a trade off because of the larger scrub angle of the back tyre, but it's non-trivial to calculate the optimum wheelbase for a track bike.

It stands to reason

Never, ever, use this expression if you wish to be taken seriously.

A longer chain (or drive shaft) of otherwise similar dimensions will have more backlash from elastic deformation, but there is no evidence that this is a bad thing on a bicycle within the range under discussion. This is partly because any stretch in the chain under peak load is almost fully recovered as usable energy when the load drops (very little hysteresis) and partly because 'wasted' movement at the pedal (i.e. the foot position tending to lead the wheel position during load peaks) is composed mainly of flex in the pedal spindles and cranks, so you would need to make the chain very long for it to become a major part of the total system backlash.

Sometimes you put people right on something and I think it was needlessly harsh Tester.

Then there the times when I learn something and it's interesting to see the theory, or fact, behind it.

Then there's the extremely rare and very disconcerting moments where I understand and agree with you... and now my brain hurts. >_<

All that and no one's called out the now-dismissed-by-science q-ring.

Never, ever, use this expression if you wish to be taken seriously.

I'll take that as the engineering/debating equivalent of 'Here we have' from the classifieds.

I still think a short path is quicker than a long one, except when it comes to the barrel of a firearm.
Surely in a track sprint, as little backlash as possible = a good thing.
Right?

All that and no one's called out the now-dismissed-by-science q-ring.

Science vs Froome is still using unmarked osymetrics. Tough call.

All that and no one's called out the now-dismissed-by-science q-ring.

See the timetrialling thread

Surely in a track sprint, as little backlash as possible = a good thing.
Right?

Who knows? If zero backlash were an unambiguously good thing, we wouldn't have cush drives. A quick and dirty Fermi Estimate suggests that the pedal position might lead the wheel position by about 1° of crank rotation at peak torque from chain elongation alone. If we look at the Q-Ring problem above, it's pretty clear that it's all but impossible to find any biomechanical/physiological effect with such a small variation in the effective gain ratio at different crank phases (Q-Rings obviously provide a much bigger variation), and the hysteresis problem is vanishingly small too.

By letting the pedal effectively make a run for it when the rider applies maximum force, the actual peak force on the body is slightly reduced (same argument as a cush drive reducing peak loading in an automotive drive train). Although this is a tiny effect, an argumentative person might hypothesise that protecting the muscles from extreme overload in this way could reduce the amount of micro-rupture in the muscle fibres, leaving more fibres available for work later in the race. This would be an argument for having more elastic backlash on your race bike than on your training bike :-)

Deep.
Begs the question... why are so many track bikes built with mad-tight-clearances-yo?

Design inertia.

Until Look actually measured stuff, people assumed that running the rear tyre tight in the seat tube cutaway was the most aerodynamically efficient position. After they published their findings, you saw a lot of people with other frames suddenly leaving a 10mm gap :-)

Same with clearance around the tyre at the fork crown - it used to be tight until somebody actually bothered to ask why, see my earlier post of UKSI/Trek/Look forks with big spaces for the air to pass through.

you mean sprint specific track bikes no? endurance track bikes are not that tight

So much tester approved science here