Sorry for the long essay, there is a point to all this . . . . (!)


I like to ride big gears (I am currently on 48/14 and 48/15).

I have no argument against those who say this kind of gear ratio is far from efficient as they are basically right, but I just find lower gearing too spiny for me (I ride almost exclusively on the flat) and have always pushed gears at the taller end of the range + I love being able to really drag the bike up to some hair raising speeds, something my legs won't let me do on lower gearing, I simply haven't got the supplesse that some spinners have (I would come absolute dead last at a Rollapaluza).

So . . . all is good, I am happy with 48/14-15 been riding this gearing (give or take a tooth) for a couple of years - but as you can imagine controlling the rear wheel or skidding is not an easy task on a 90 inch gearing, the only way I can effect a skid is to lightly feather the front brake so the rear lifts and then I can lock my beautiful legs, and this can only be done at speed. Even bringing to bike to a controlled stop (without using the brakes) from a moderate speed is not an easy task at 90 G.I - (by way of reference I find it fairly easy on 46/16).

This got me thinking, it would be nice to have a large gearing to spin the bike up to horrific -check-your-life-insurance- speeds, whilst also have a low gearing to modulate your speed and to skid.

So I came up with the following idea and would like to run it passed the massive throbbing collective brain of Londonfgss.com to see if I am overlooking anything obvious that would put a spanner in the works ?

On the drive side of my bike I will put a drive side crank arm and a 48 tooth chain ring.
On the non-drive side I will put a drive side crank arm and a 42 tooth chain ring.
The rear hub will be a fixed/fixed Phil.
On the drive side of the rear hub I will put a 15 tooth freewheel.
On the non drive side I will put a 23 tooth freewheel

Being on the non drive side of the hub the 23 tooth freewheel will be reversed - it will freewheel when the cranks are driven forward and 'drive' when the cranks are turned backwards - the freewheel on the drive side will, obviously act normally, drive when driven forward and freewheel when reversed.

Conclusion: So forward pedaling gives me 48/15 (84.1 G.I.) and back pedaling gives me a 42/23 drive (48 G.I.), making it easier to modulate speed and even skid.

The only small problem I can see is that the non-drive side pedal will need to be reverse threaded and has the potential to unscrew itself, not a major problem.

But can anyone think of any other hindrances I have overlooked that will stop me from completing my evil 'EasySkid™' plan ?



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Short Version

I was thinking, it would be nice to have a large gearing to reach high speeds on the flat - whilst also have a low gearing to modulate your speed and to skid. So I thought of doing the following:

Drive side = drive side crank arm and a 48 tooth chain ring + 15 tooth freewheel.
Non-drive side = drive side crank arm and a 42 tooth chain ring + 23 tooth freewheel.

So forward pedaling gives me 48/15 (84.1 G.I.) and back pedaling gives me a 42/23 drive (48 G.I.), making it easier to modulate speed and even skid.

But can anyone think of any problems I have overlooked with this plan.


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Try it sounds like a plan.

I heard someone mention you could use a tandem crank on the left to avoid the reverse threading issues.

Do those gear ratios give you the same chainring--sprocket distance on each side? Aka will your hub be straight. I'm sure you've already thought this through and I'm too tired to work it out.

we had this discussion a few months ago, and i think the consensus was that this is not possible, but i can't remember why.

try it and see?

Sounds completely mental... Dumbstruck!

the innersha of the high gearing will still be in the system and as soon as you try to back pedal well you wont be able to. get a back brake.

or learn to spin to win!

[edit] inertia!

I remember reading something 3 or 4 months ago here, but that was someone trying to run two forward gears by placing them on each side - I was in agreement with everyone who said that it simply would not work.

This is not what I am planning here, only one forward gear, but back pedaling freewheels the drive side rear cog and 'drives' the non-drive side cog - making the bike essentially fixed but with differing ratios on forward and backward drive.

I sounds more complicated that it actually is in reality, it's a fairly straightforward, if not conventional, setup !!

yeah i get what you're saying, and i can't think of why it wouldn't work, even though it sounds batshit mental. as i said above, try it and see!

hmmm... my brain tells me it could work if your two ratios required exactly the same distance from BB spindle to hub.
Not easy!

I actually thought about this, but I have a couple of other fairly simple ideas to fix the pedal against unscrewing.

People ride differing chain ring/cog set ups all the time, they just adjust the chain length to fit.

if he's using freewheels could he use a chain tensioner to skirt this issue?

I also thought of this (in fact it is still a small concern/confusion for me).

What do you make of this question:

Two bike one geared at 48/15 - one geared at 42/23.

Take both up to 25 mph - which would be easier to stop.

P.S this is not a rhetorical question, I am genuinely curious, my instinct says the one with the (massively) lower gearing would be easier to stop (or at least modulate) due to the much bigger leverage at the hub ?

don't dismiss rich's second point! it's the same one I made...
(you are trying to find 2 magic ratios which will work with the same chainstay length)

I mean, when I flip my wheel over to use a different sprocket, I slide the axle forward in the dropouts.

There's an article on 63xc.com about choosing "magic gears" and you'd have to do something like that to make sure both your ratios will be compatible. But, as I said, I'm sure you've already done this so I'll shut up.

http://www.63xc.com/toddp/halflink.htm

but you can't do this for both combinations at the same time. So you'll have to find two magic-gear ratios that will allow you to run the wheel in the same positon, or one chain will be slack.

damn good point. This could get ugly though... ;-)

magic gear calculator: linky

on both sides? nuh-uh.

Why would I need two specific ratios, my brain tells me that any two ratios would work.

Imagine the set up in your head with two very differing ratios, and imagine this to be correct and working - now mentally grow one of the chain rings by a substantial amount.

My imagination also forces me to also lengthen the chain to accommodate the larger chain ring.

I'm pretty sure it wouldn't work. Not quite sure why but I have a bad feeling about it. At the very least, the LHS tensioner would have to be upside down, no?

I suspect that the larger freewheel will unscrew itself, jam itself against the rear chainstay and chuck you over the handlebars.

Imagine having a loose chain.

If i remember correctly, the distance your axle moves in the dropouts when you (say) add 1 tooth to your chainring is not the same as the length of 1 link of the chain.

At the very least it would involve using halflinks, although at £2.50 each these would be the cheapest part of the whole project.

This is because you are using the same chain length for both ratios, my set up would have the chain length tuned specifically for each ratio.

With a freewheel the tensioner only prevents the chain from jumping off, doesn't actually take the strain of the drivetrain (which is on the 'top' of a conventional chainline).
So a single tensioner on the right hand side, used with the leftie drivetrain set at correct tension would be okay.. right?

Yeah I think you are right, unless I choose my ratios carefully I might have one chain a little slacker that the other.

But I will work the maths out and, if needed use a half link, to keep the chains fairly taught.

Sir, I refer you to my previous point, and provenrad's comment.

Essentially what we're saying is that tuning chain length is not as easy as it sounds if you want to avoid having a slack chain (and you do want to avoid this).

By the way, this does sound like a fun idea and should be fairly cheap to try out, even if it doesn't work. I'm not trying to sound negative, hope my comments don't come across that way!

What'll you use to keep the reverse freewheel on the hub?

If I use front brake in a skid I normally (always) fall off.

You will have 2 different chain lengths, which, all things being equal, will mean one side will wear / stretch faster than the other. So if you do manage to get the rear wheel straight in the dropouts after a couple of months I would imagine you will struggle to. Perhaps the effects of this won't be noticeable.

I can't get my head around why having different ratio forwards to backwards won't work, seems possible but perhaps not practical. I do wonder if it's possible that the pawls in your freehubs could lock to oppose each other and not allow the cranks to be moved in either direction. I'm not too sure. {edit - this is bollocks}

Try it! Tell us what happens!

Once the wheel is locked the gear ratio is irrelevant. Have you tried leaning further forwards?

+1

No real need for tensioners.