fixed gear questions

Francesco Devittori said:

I finished my fixed gear and have a couple of questions for the experts.

1) Chainline: how "perfect" should it be?
The best I can with my setup is still off by 1.5 mm. Looking at the
chain from the top of the cog towards the chainring I see a straight line.
Is 1.5 mm too much to be safe?

It should be OK, but you might add a spacer behind the cog (if that is the
correct direction). You can get spacers at bike shops, especially those
that deal with BMX bikes.

Quoted message said:

2) Chain tension: I really can't decide how much tension to put in. Is
there a general rule of thumb?

AS tight as it can be, without binding at any point in the stroke.
Tension will not be exactly constant; check several times after rotating
the cranks.

To my eyes it's always either too slack

Quoted message said:

or too tight. It is also a bit difficult to adjust because I have
semi-horizontal dropouts. I wish I had track-ends!

that would not eliminate the problem. Plus, with track ends, moving the
wheel puts the rear brake (if you have one) off of the braking flats on
the rim.

Quoted message said:

3) Quick release on rear wheel: is a modern Dura-Ace strong enough for
this use? I can close it quite strong but still, I don't want the wheel
to come out!

Of course it is strong enough. It holds in a multi-speed cog on a bike
with horizontal dropouts. Fixed gears do _not_ put more pressure on the
wheel than derailleur bikes.

Quoted message said:

4 (and last) Chain deraillement: the thing I fear most is throwing off
the chain. How can I check that everything is alright? (possibly not the
hard way)

Be careful on downhills. Get your chainline closer to perfect. Use
brakes; at least one.

--

David L. Johnson

__o | Some people used to claim that, if enough monkeys sat in front
_`\(,_ | of enough typewriters and typed long enough, eventually one of
(_)/ (_) | them would reproduce the collected works of Shakespeare. The
internet has proven this not to be the case.

David L. Johnson said:

Francesco Devittori said:

1) Chainline: how "perfect" should it be?
The best I can with my setup is still off by 1.5 mm. Looking at the
chain from the top of the cog towards the chainring I see a straight line.
Is 1.5 mm too much to be safe?

Quoted message said:

It should be OK, but you might add a spacer behind the cog (if that is the
correct direction). You can get spacers at bike shops, especially those
that deal with BMX bikes.

If that's not the correct direction, you can move a cartridge bottom
bracket over a little bit by loosening the right side cup and tightening
the left side. But I think 1.5 mm ought to be just fine if it passes the
test I describe below.

Quoted message said:

Quoted message said:

4 (and last) Chain deraillement: the thing I fear most is throwing off
the chain. How can I check that everything is alright? (possibly not the
hard way)

With the bike on the stand, try to derail the chain by pushing sideways
on the chain while pedaling slowly. Be careful! Don't get your fingers
caught between the chain and cogs during this operation! If you can't
derail it intentionally, it will be pretty tough to derail it on the
road. Check it after the first ride to make sure it's still tight.

--
Dave
dvt at psu dot edu

David L. Johnson said:

Francesco Devittori said:

I finished my fixed gear and have a couple of questions for the experts.

1) Chainline: how "perfect" should it be?
The best I can with my setup is still off by 1.5 mm. Looking at the
chain from the top of the cog towards the chainring I see a straight line.
Is 1.5 mm too much to be safe?

It should be OK, but you might add a spacer behind the cog (if that is the
correct direction). You can get spacers at bike shops, especially those
that deal with BMX bikes.

That's what I had to do. Worked like a charm. Note: get a chainring
bolt spanner and be sure that they are tight.

Quoted message said:

Quoted message said:

2) Chain tension: I really can't decide how much tension to put in. Is
there a general rule of thumb?

AS tight as it can be, without binding at any point in the stroke.
Tension will not be exactly constant; check several times after rotating
the cranks.

Here's what I do (your QR skewer might prevent this): I pull the wheel
back and get it straight. Then I loosen the non-drive side and tilt the
wheel towards the chainstays. Tighten that side, loosen the other and
straight the wheel. Basically, I "walk" the wheel back until the
tension is good. I've heard some people describe being able to "pluck"
the chain. Seems good to me.

Quoted message said:

Quoted message said:

4 (and last) Chain deraillement: the thing I fear most is throwing off
the chain. How can I check that everything is alright? (possibly not the
hard way)

Be careful on downhills. Get your chainline closer to perfect. Use
brakes; at least one.

I second this. Your chain will mostly likely get thrown on high cadence
descents when your resisting the pedal movement with uneven strokes.
You'll hear the chain get noisier -- that's because it's looser on the
topside. Use the chain noise as feedback.

--
Paul M. Hobson
Georgia Institute of Technology
..:change the words to numbers
if you want to reply to me:.

Francesco Devittori said:

I finished my fixed gear and have a couple of questions for the experts.

1) Chainline: how "perfect" should it be?
The best I can with my setup is still off by 1.5 mm. Looking at the
chain from the top of the cog towards the chainring I see a straight line.
Is 1.5 mm too much to be safe?

It's OK for a bushingless chain Within 1mm is ideal, and vital for a
chain with bushings.

Quoted message said:

2) Chain tension: I really can't decide how much tension to put in. Is
there a general rule of thumb? To my eyes it's always either too slack
or too tight. It is also a bit difficult to adjust because I have
semi-horizontal dropouts. I wish I had track-ends!

There should be no *visible* slack, but when you spin the cranks with
the wheel off the ground it shouldn't bind (i.e. stop at the same point
each time).

Quoted message said:

3) Quick release on rear wheel: is a modern Dura-Ace strong enough for
this use? I can close it quite strong but still, I don't want the wheel
to come out!

Yes. There's no difference in chain tension between a fixie and a
derailleur. Chain tension is only determined by crank length, chainring
size and how hard you push.

Quoted message said:

4 (and last) Chain deraillement: the thing I fear most is throwing off
the chain. How can I check that everything is alright? (possibly not the
hard way)

Try to pull the chain off while rotating the cranks. WATCH YOUR
FINGERS! My sister has a friend called "Stumpy" Carr because she didn't
watch her fingers when doing this...

Zog The Undeniable said:

Francesco Devittori said:

4 (and last) Chain deraillement: the thing I fear most is throwing off
the chain. How can I check that everything is alright? (possibly not
the hard way)

Try to pull the chain off while rotating the cranks. WATCH YOUR
FINGERS! My sister has a friend called "Stumpy" Carr because she didn't
watch her fingers when doing this...

I'm gonna go out on a limb here and suggest that you try this "manual
derailment" with some sort of tool. Better to ruin that and your
chainring than a finger.

\\paul
--
Paul M. Hobson
Georgia Institute of Technology
..:change the words to numbers
if you want to reply to me:.

"Francesco Devittori" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I finished my fixed gear and have a couple of questions for the
experts.

1) Chainline: how "perfect" should it be?
The best I can with my setup is still off by 1.5 mm. Looking at the
chain from the top of the cog towards the chainring I see a straight
line.
Is 1.5 mm too much to be safe?

This depends which way the offset is. A chain ring to the left of the
sprocket is far worse than to the right. Next question, why? BB
deflection to the left (right pedal down) is greater than to the right
due to chain tension (it assists left deflection and resists right
deflection). The possibility of derailment is greater with the chainring
offset to the left. Slightly to the right (1mm) is probably optimal.

Phil H

Francesco Devittori said:

I finished my fixed gear and have a couple of questions for the experts.

1) Chainline: how "perfect" should it be?
The best I can with my setup is still off by 1.5 mm. Looking at the
chain from the top of the cog towards the chainring I see a straight line.
Is 1.5 mm too much to be safe?

You want it to be as straight as you can manage. Bad chainline leads to
thrown chains, which are more serious with a fixed gear than a freewheel
bike. I'd say 1.5mm is a little too much; a judiciously placed 1mm spacer
will cut that to 0.5mm -- much nicer.

Quoted message said:

2) Chain tension: I really can't decide how much tension to put in. Is
there a general rule of thumb? To my eyes it's always either too slack
or too tight. It is also a bit difficult to adjust because I have
semi-horizontal dropouts. I wish I had track-ends!

You want it to be as tight as you can get it without binding. Once again,
loose chains lead to thrown chains, yada, yada...

Quoted message said:

3) Quick release on rear wheel: is a modern Dura-Ace strong enough for
this use? I can close it quite strong but still, I don't want the wheel
to come out!

If you really don't want it to come out, use a solid axle and nuts.
There's a reason track bikes use 'em.

Quoted message said:

4 (and last) Chain deraillement: the thing I fear most is throwing off
the chain. How can I check that everything is alright? (possibly not the
hard way)

Check your chainline -- use a straightedge (e.g. meter stick) laid against
the chainring and extending back to the cog. If the outer edge of the
straightedge lies right against the outer edge of the cog without overlap
or gap, then you're good.

Make sure your chain is tight enough. See above.

--

John ([email hidden])

Quoted message said:

2) Chain tension: I really can't decide how much tension to put in. Is
there a general rule of thumb? To my eyes it's always either too slack or
too tight. It is also a bit difficult to adjust because I have
semi-horizontal dropouts. I wish I had track-ends!

Find the slack spot in the chain during the crank/cog rotation, and tighten
it at that spot. That will be your point of derailment, if any. If it
binds a small bit, it's okay.

--
Phil, Squid-in-Training

Phil said:

Quoted message said:

2) Chain tension: I really can't decide how much tension to put in. Is
there a general rule of thumb? To my eyes it's always either too slack or
too tight. It is also a bit difficult to adjust because I have
semi-horizontal dropouts. I wish I had track-ends!

Find the slack spot in the chain during the crank/cog rotation, and tighten
it at that spot. That will be your point of derailment, if any. If it
binds a small bit, it's okay.

Thanks to everybody for the suggestions, my ideas are now more clear.
If you don't see messages from me in the next months it means I wasn't
able to follow them strictly :-)

Francesco

P.S. to Paul Hobson: smart idea to use a tool to perform the "manual
derailement"!

Francesco Devittori said:

P.S. to Paul Hobson: smart idea to use a tool to perform the "manual
derailement"!

Also to check tension. Every single time. --D-y

Francesco Devittori said:

I finished my fixed gear and have a couple of questions for the experts.

1) Chainline: how "perfect" should it be?
The best I can with my setup is still off by 1.5 mm. Looking at the
chain from the top of the cog towards the chainring I see a straight line.
Is 1.5 mm too much to be safe?

Nope, sounds fine

Quoted message said:

2) Chain tension: I really can't decide how much tension to put in. Is
there a general rule of thumb? To my eyes it's always either too slack
or too tight. It is also a bit difficult to adjust because I have
semi-horizontal dropouts. I wish I had track-ends!

As you spin the wheel you will notice the chain goes tight/loose a bit.
The tightest part should still have a deflection of about 5mm.

Quoted message said:

3) Quick release on rear wheel: is a modern Dura-Ace strong enough for
this use? I can close it quite strong but still, I don't want the wheel
to come out!

It doesn't come out when you ride a multi geared bike, it won't come
out with a fixed gear-forces from you are the same.

Quoted message said:

4 (and last) Chain deraillement: the thing I fear most is throwing off
the chain. How can I check that everything is alright? (possibly not the
hard way)

Chain tension is the thing that can have the chain come off, check
that.

Quoted message said:

TIA,
Francesco

John Thompson said:

If you really don't want it to come out, use a solid axle and nuts.
There's a reason track bikes use 'em.

The reason is the absence of a protruding QR lever that could flip open
or impale somebody in a crash. Allen key skewers are perfectly
acceptable too.

Zog The Undeniable said:

John Thompson said:

If you really don't want it to come out, use a solid axle and nuts.
There's a reason track bikes use 'em.

The reason is the absence of a protruding QR lever that could flip open
or impale somebody in a crash. Allen key skewers are perfectly
acceptable too.

Actually, as I understand it the ban was originally of wing-nuts, for that
reason, and QR levers suffered from guilt by association. I doubt that
anyone has even anecdotal evidence of an errant QR lever actually
stabbing someone. Wing-nuts probably scraped up a lot of folks in crashes.

OTOH I don't recommend the usual allen-key skewers. The ones I had, at
least, screwed the skewer rod into a nut on the other side of the wheel,
and if you try to get it tight enough to hold a rear wheel onto horizontal
dropouts, you risk shearing off the rod. The nut-end of one such skewer
shot across my workshop one day for just that reason.

Are there any allen-key skewers where the key actually functions as the
lever in a regular QR skewer?

--

David L. Johnson

__o | It is a scientifically proven fact that a mid life crisis can
_`\(,_ | only be cured by something racy and Italian. Bianchis and
(_)/ (_) | Colnagos are a lot cheaper than Maserattis and Ferraris. --
Glenn Davies

David L. Johnson said:

Are there any allen-key skewers where the key actually functions as the
lever in a regular QR skewer?

I've seen QR skewers that use a torx key in place of the lever. I
can't tell from the picture, but I think these are another variation:
http://tinyurl.com/bxrsv

-Vee

Or, find the tight spot and get it as tight as possible without binding
at that spot, and hope it doesn't go too slack everywhere else. If it
does, get a more circular chainring than the one your using. I've seen
rings so out of round before that if you tightened the chain for the
slack spots, it'd be impossible to pedal at the tight spot.

Scott said:

Or, find the tight spot and get it as tight as possible without
binding at that spot, and hope it doesn't go too slack everywhere
else.

Hope? We don't operate on hope here. Imagine the uproar if someone said,
"let's hope our disc brake wheel doesn't eject!"

If you find the slack spot and make it tight there, the chain generally
can't come off. If one were to use your method, rough pavement and chain
tension from pedaling could cause derailment.

Quoted message said:

If it does, get a more circular chainring than the one your
using. I've seen rings so out of round before that if you tightened
the chain for the slack spots, it'd be impossible to pedal at the
tight spot.

Obviously, at that point, you'd try to find another solution.

--
Phil, Squid-in-Training

Phil,

I'm sure you read the entire message before responding, so why'd you
respond to the first paragraph out of context??? I did NOT suggest
riding with a 'too slack' chain. What I DID was suggest that you not
ride with a 'too tight' chain.

Scott said:

Phil,

I'm sure you read the entire message before responding, so why'd you
respond to the first paragraph out of context??? I did NOT suggest
riding with a 'too slack' chain. What I DID was suggest that you not
ride with a 'too tight' chain.

Ooh... my brain is not working as well as it should be... my apologies... I
didn't comprehend your post correctly.
--
Phil, Squid-in-Training

David L. Johnson said:

Are there any allen-key skewers where the key actually functions as the
lever in a regular QR skewer?

I think I've seen some as a kind of anti-theft device, but it may have
been years ago.

My track bike has Goldtec hubs, which bolt into place using an
internally-threaded axle and allen bolts. Easier than carrying round a
15mm spanner.