2x7 AHH, no front derailer

[Joe Bernard]

Ok, I've got this gorgeous silvery green Hilsen frame Rocky sold me, and I'm conjuring up build options. I'm thinking of doing a semi-Quickbeam-ish thing: I have an IRD 13-32 7-speed freewheel on a Phil hub..thinking of adding my very-most-super-cool American CNCed Precision Billet rear derailer, and a Shimano XT 8-speed-era crank with the granny removed for a 42-32 double. No front derailer, shifting Quickbeam style.

 

Will I have any trouble with the chain leaping off the cranks during rear shifts?

 

Joe Bernard

Fairfield, CA.

[Allan in Portland]

Probably not, but ultimately I think depends on your chain line.

I had a 9 speed cassette with a Sugino 3 ring in front. I moved the outer ring the center position, put a chain guard on the outer position, and left off the front derailer. Riding in the middle and large end of the cassette gears was never a problem. Shifting itself was never a problem. However, if I was in the smallest 1 or 2 cogs the chain would have a tendency to pop-off the front ring and trap between the chain ring and the chain guard. It wasn't shifting that caused the problem, it was bumps/jarring that made slack that allowed the pull of the extreme chain line to derail the chain.

Good luck,
-Allan

[Cyclofiend Jim]

My initial reaction was "I'd be a little wary", but as I think about it, I'm not sure why.  There's no intrinsic reason I can come up with.  The FD might help to keep the chain on, and I do know folks who still have one in place with a single ring setup to use as a chain keeper.

There are probably two immediate things which I'd watch for: (1) the angle of the chain when on the inner ring might cause it to catch any "lifters" on the big ring (those ramps and pins used to assist shifting) if you end up in the smaller sprockets in the back, and (2) the ability of the rear derailleur to pick up chain slack when in the smaller front chainring.

You might run the gearing through Sheldon's calculator, to see if you are really gaining very much range. 

http://sheldonbrown.com/gears/

I think if you are just going to use it mostly in the larger ring, and just use the small ring as a climbing/bailout gear (only using the larger three rear sprockets, for example), it ought to work.

hope that helps,

- Jim

[Joe Bernard]

The more I think about it, the more I think it'll work ok. I'm not going to use a shorter spindle - the BB spec'd for these is already pretty short - so the two remaining rings will still be in the same position relative to the freewheel, and I already use the 32 to cover the complete range. I'm not in the habit of using big/big, which will become more prevalent with this arrangement, but I imagine the tension in that combination will have the chain on there good 'n' tight. Or maybe I'll set it up; stand back and look; feel like a doofus for trying it; and put the derailer on. ;-)

[benzzoy]

Many years ago, I tried this on a mountain bike. It didn't work well
precisely because of what Allan in Portland mentioned, that is the
normal/routine bumps and jarring can derail the chain, sometimes at
the most inopportune time. Because my mountain bike at that time had
a 11-28, the chain had to be long to wrap around that range and the
rear derailleur cage wasn't nearly strong enough to provide adequate
chain tension. That's probably why CX bikes have a chain keeper.

If you run a chain guard, it may help things (didn't try) and
certainly the flexy chain and shift ramps on modern chainrings do not
help.

Why the aversion to a front derailleur?

[Joe Bernard]

Why the aversion to a front derailleur?

 

Simplicity, clean looks, the likelihood that I'll stay in a harder gear longer instead of downshifting, the chance to stop and stretch at upshift/downshift points.

[PATRICK MOORE]

I'm inclined this way, too, at least for shorter distance vehicles:
have my trike set up currently as a 1X7 (the seven sp only because
that's what the thing came with and it's a jolly pain to remove the
freewheel: have to remove the left axle to do so. I expect I'll
eventually go to a 1X5 with 100-83-70-60-50 gears; the 100 basically
just a place holder. Or perhaps a slyly hidden granny that I can kick
into gear with my foot -- it's amusing to slow to a crawl or even a
dead stop on a hill and not fall over, and you can downshift when
backpedaling.

Of course my "main" rides are fixed, so even four usable gears seems
like loooxery, to quote the Yorkshireman.

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Albuquerque, NM
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[David Yu Greenblatt]

I concur. If you ride the bike only on smooth roads you should be fine, but if you ride on bumpy surfaces you will eventually drop the chain. I run a single chainring on my 29er MTB and on my cyclocross racing bikes, with inner and outer chainguards. Without the guards I would drop chains all the time. At the very least you should install an inner guard like the N-Gear Jump Stop to decrease the risk of inner drops, but you will still be vulnerable to outer drops.

Now, this is an extreme example, but check out how much the chains jump around in this cool video of Paris-Roubaix at around 2 minutes in:
http://youtu.be/3QSpuhIQg1A

Your chain will jump around like that if you descend on a trail and hit a bump.

David G, Madison WI

[Joe Bernard]

I hear ya about the bumpity-bump. I don't plan on any major mountain biking, but it IS a country bike, and China Camp IS part of a loop I ride. Riding one of the calmer trails there is a possibility, which tells me I'm gonna wish I had mounted that derailer. Thanks for the feedback, folks.

[Jeremy Till]

Are you using the stock rings on the crankset?  If you decide to go the derailerless route I'd make sure you were using singlespeed specific rings (which you should be able to get in both 32t and 42t) or old rings from the era before there were ramps and pins and "profiled" teeth.  Having uniformly tall teeth and none of the little shift aids might just be enough to prevent the chain unshipping for your type of riding. 

[charlie]

Finally something making a little sense......I can't see any chain
coming off a chain ring assuming there is tension from the rear
deraileur....I've been scratching my head wondering what the heck all
the chatter is about. There have been quite a few 1x5's 1x7's 1x9 set
ups made over the years and I've never heard of chains derailing due
to chain angle.......if this were true you would derail all the time
(front derailer or not) every time you hopped a root or hit a
chuckhole.....if your rear tension spring is weak get a new one. Off
my soapbox now......its early and my coffee was decaf........

[Steve Palincsar]

On Sun, 2011-10-09 at 09:53 -0700, charlie wrote:
> Finally something making a little sense......I can't see any chain
> coming off a chain ring assuming there is tension from the rear
> deraileur....I've been scratching my head wondering what the heck all
> the chatter is about. There have been quite a few 1x5's 1x7's 1x9 set
> ups made over the years and I've never heard of chains derailing due
> to chain angle.......

And yet, 1x7s and 1x9s are known to throw the chain. Some bikes do it
so often owners have claimed their bikes are possessed by evil spirits.
Here, for example http://www.foldsoc.co.uk/mchaink.html is an article
about a chain keeper devised to prevent AM-7 and AM-8 Alex Moulton
bicycles from thowing chains. Trust me, if it didn't happen nobody
would bother with devising such things!

[Garth]

Well heck, if you need to use a device to keep the chain on .... why not just use a derailler ?   If a shifter and a cable is just too much to deal with .... Better off with a single speed.  . . lol.

[Thomas Lynn Skean]

This sounds like a good experiment. I'm virtually always on my middle chainring anyway. I think soon I'll just remove my derailer (it's a braze-on style that's bolted to a clamp) and see what happens. I've never noticed the chain hitting the front detailer's cage during rear shifts. But it might be happening sometimes.

I too have an IRD FW/Phil-hub combination in back (LX RR derailer), Sugino XD2 24-36-46 up front (IRD alpina-d derailer). I'm using a 7-spd 13-28 freewheel, not the 13-32, though. So my experience may differ from yours. Of course, where and how one rides I'm sure has a big effect.

I'll post any results.

Yours,
Thomas Lynn Skean

[Jim Thill - Hiawatha Cyclery]

I've done fder-free doubles many times. One chainring that I use always, and one bailout ring. Never had issues with dropping the chain, but I suppose if you were doing cyclocross or other rough riding, it may be an issue. Usually I run a triple with the outer ring replaced by a Salsa Crossing Guard.

[PATRICK MOORE]

I wonder if your chances of a stable chain depend partly on the
ring/cog combination -- ie, if you spend most of your time with a
straight chain, perhaps the chain will jump less? My front
derailleur-less setups have always had the chain on the cruising gears
more or less centered and I've not dumped the chain except once when
the shift lever slipped very suddenly.

On Mon, Oct 10, 2011 at 9:01 AM, Jim Thill - Hiawatha Cyclery
<thil...@gmail.com> wrote:
> I've done fder-free doubles many times. One chainring that I use always, and one bailout ring. Never had issues with dropping the chain, but I suppose if you were doing cyclocross or other rough riding, it may be an issue. Usually I run a triple with the outer ring replaced by a Salsa Crossing Guard.
>

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[Steve Palincsar]

On Mon, 2011-10-10 at 09:05 -0600, PATRICK MOORE wrote:
> if you spend most of your time with a
> straight chain, perhaps the chain will jump less?

Probably not, since mostly from what I've read this happens on bumpy
roads. IOW, it's not the angle that sets this off, it's the fact that
the chain is jumping up and down. From what I've read. I have no
personal experience.

[CycloFiend]

Yeah, it's more to do with slack in the system while negotiating bumpy
terrain. Doesn't necessarily have to be off pavement - sharp ripples can
just throw a wave into the chain that the derailleur can't tension out.

- J

--
Jim Edgar
Cyclo...@earthlink.net

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