Magic gear

[garygkn]

I was considering a magic gear option on an MTB with vertical drop outs.
Then something started to niggle away.
If the magic gear is employed how long will it last?
Won't it go slack after a little while?

[Brucey]

yes, it will wear but then you can fit another chain. After a while you will have a nest of chains that are a bit worn. On a typical chain run 0.5% wear means that you could retension the chain if only you could move the wheel about 1/8".

You can re-use the part-worn chains on a different magic gear or on an IGH machine.

cheers

[garygkn]

Thanks Brucey.
That was bothering me.
I think I'll look for a deal on an Eno hub at least it can be retentioned.

[Brucey]

well you can always file the dropouts slightly to give you 1/16" adjustment, 1/16" slack is usually OK, and when you get to needing 1/8" total adjustment, just fit a chainring with +1T. This will make about 2% difference to the gear ratio which shouldn't be a deal breaker. No Eno hub required...?

cheers

[Des49]

I will be interested in seeing how you manage with this if you try for the magic gear as it didn't work out for me.

I gave this a go a while ago when I was using an old Specialized Stumpjumper frame with sloping dropouts and a Shimano hub gear for commuting. The frame broke and I was given a Specialized Rockhopper frame with vertical dropouts for free. After managing to find the right sprocket/chainring combination I found that even after a week or two the chain had stretched enough to give too much chain slack. This did result in the odd occasion when the chain rattled off on bumps or on big efforts up hills. I didn't think of keeping a second chainring one tooth larger as Brucey suggests.

Currently I am running a Rohloff hub on a vertical dropout MTB frame, I would love not to use a chaintensioner but again never found a perfect combination and chain stretch was too problematic. May revisit this with a 2nd chainring.

I have a friend who runs the White Eno hub on a road frame, he finds it great and doesn't seem to have had any issues. He doesn't use a rear brake that all as I assume you may have to watch brake pad alignment if you do. Depends whether your rims have a nice deep braking surface or not.

[JonMcD]

As the chain wears you could try fine tuning the chain tension with a ghost ring.

[mig]

not sure that i fancy that dropping out at speed

[Des49]

As the chain wears you could try fine tuning the chain tension with a ghost ring.

Never heard of those before!

I know one should not be dismissive without trying it, but somehow I am not tempted to try one.

[JonMcD]

As the chain wears you could try fine tuning the chain tension with a ghost ring.

Never heard of those before!

I know one should not be dismissive without trying it, but somehow I am not tempted to try one.

OT but I must say I'm more attracted to the flashing rear light that seems to be powered by an odometer type magnet on the spokes.

[garygkn]

Never seen the 'ghost ring' before. I'd be scared of losing it or some sort of unforseen accident happening? The one tooth chain ring difference could work but what would happen if started with a worn chain and a magic gear would that be just as good?

[PH]

I've never run a magic gear on a single speed but did have a go on a hub gear, there may be differences but I can't think of any. Assuming it's a freewheel rather than fixed, just how tight does the chain need to be? I got it tight enough not to fall of by using a half link (Actually using the half link originally and removing it once the chain was worn) It was still a faff and I went back to the tensioner.

[Brucey]

a half-link is a somewhat blunt instrument for adjusting chain length; it has about the same effect as 2T on either the sprocket or the chainring. If you start with a magic gear that is spot on e.g. using this calculator

http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html

then you would normally only need to remove a half-link when the chain has stretched by about 1%. This usually takes several thousand miles.

cheers

[PH]

a half-link is a somewhat blunt instrument for adjusting chain length;
cheers

Yes, but I like the idea of not having to make adjustments for several thousand miles
The question is - Is there a need for any more fine tuning, or is such a blunt instrument going to work?

[Des49]

Out of interest just ran that calculator on my MTB set up.

A 41T - 16T combination would be perfect at 46.93". With such a close result maybe this would work better than my previous attempt.

Trouble is finding a 41T chainring, plus I got a stainless steel 42 last year for it which is as yet barely worn so reluctant to play around and incur more expense. But I hate using a chain tensioner (and torque arm)!

[PH]

But I hate using a chain tensioner (and torque arm)!

Can I ask why? Could it be the type of tensioner?
I dislike the look of them, but after trying several the Alfine one with two wheels worked fine for me. After moving my Rohloff from a frame that needed a tensioner to one that didn't, I couldn't tell the difference.