Cassette position

desweller

S'pose this should go in here, in the absence of a Nostalgia forum.

I was looking at my rear triangle the other day and thought, 'Would there be any advantage to mounting the cassette on the outside of the frame?'

Has this ever been tried? Any opinions? I thought it might confer a slight aero improvement as the chain and seat stays could be brought closer to the wheel.

MajorPayne

Don't really understand what you mean, but from reading and my basic understanding of bikes.

If you mounted your cassette on the outside of the frame, that would mean you'd have to widen the main crankshaft no? Would your legs not have to be wider apart too?

I'm interested in what your thinking, but I don't fully understand. I had thought you first meant turning your cassette 180 so the larger cog is facing the frame and the smaller cog nearest the wheel hub. But on second reading I'm sure you mean actually on the outside of the frame.

Also what about the chain? if your leaving your crankshaft alone and moving the cassette then wont that be a pretty left to right flex for the chain?

I'd like to hear more to be honest, I'm all up for crazy ideas and not much brushed up on my technical lingo to be honest.

Kind regards,
MajorPayne

andrewjoseph

I thought it might confer a slight aero improvement as the chain and seat stays could be brought closer to the wheel.

But then you'd have an unsupported cassette who's axle will bend as soon as you pedal, the rear deraileur would likewise have to move outboard. As stated by the other poster, the chainline would be extreme in the smaller cogs.

There is a reason bikes are the shape they are.

tatanab

andrewjoseph wrote:

But then you'd have an unsupported cassette who's axle will bend as soon as you pedal, the rear deraileur would likewise have to move outboard.

It could work - look at the motorcycle world with single sided swinging arms with an outboard sprocket. The rear mech would have to be inboard mounted, and I assume the poster's idea is a very narrow rear triangle so that chainline is not affected.

Other than practicalities, I do agree that bikes have evolved they way they are for a reason.

desweller

Yes, I mean cassette on the outside of the frame. I did wonder how you'd get round the chainline problem! And the bearing required to support the cantilevered cassette mounting assembly would have to be fairly hefty.

The reason I thought of it was, I was lusting over the Cervelo P4 page on ProBikeKit and wondered what else could be done to reduce cross sectional area. As you say, my thought was that you could run a much narrower rear triangle.

The chainline would be too aggressive on a conventionally geared bike, but how about a hub-geared or bottom bracket geared bike? Could that confer an aero advantage?

I mean, they do things like fairing the brake callipers into the forks and chainstays so they are hunting every little bit of drag!

mz__jo

Better to go for a single-sided rear end. It would work on a track bike or a fixie. For a road bike the chainstay would have to be derailleur side which might negate some of the potential advantages. Ask Graeme Obree he would make it work (and the UCI would ban it).

Of course all this is old hat. If you want decent aerodynamics try a recumbent. Also refused by the UCI. In fact look at everything banned by the UCI and you would end up with a pretty good, if a bit radical, bike.

desweller

mz__jo wrote:

Of course all this is old hat. If you want decent aerodynamics try a recumbent. Also refused by the UCI. In fact look at everything banned by the UCI and you would end up with a pretty good, if a bit radical, bike.

You forgot to add, 'Bah humbug'!

stickman

What are the rules on hub gears on time trial bikes, because the derailleur mech and chain circuit it creates looks about as welcome as a dog turd stuck to the bike in terms of aerodynamics.
Are single/fixed with a giant chainring banned?

It's worth having a think on how the tour de france started - as a fixed wheel race where derailleurs were not allowed for a number of years.

desweller

stickman wrote:

What are the rules on hub gears on time trial bikes, because the derailleur mech and chain circuit it creates looks about as welcome as a dog junk stuck to the bike in terms of aerodynamics.

I'd imagine that, along with recumbents etc., they've been banned? Hub gear assemblies are usually pretty heavy, but that's probably because the development drive to lighten them isn't present as they're not being raced. I don't know how they compare in terms of mechanical efficiency.

stickman

They're lighter nowadays, with the option of aluminium shells but the thing with weight these days is keeping rider's bikes above the minimum limit. Don't know about the efficiency situation though.