Hub gear experts - advice please!

neilob · Post by **neilob** » 3 Jul 2008, 1:40pm

Some advice on hub gears would be gratefully received! I've lusted after a Rohloff but decided it's too much dosh as well as the new bike to fit it to! I just want to update my Thorn Nomad for reliable winter commuting; it's too good to ditch and I have another bike for touring and weekend rides anyway.

But I'm attracted by the hassle-free experience that a hub gear promises to offer. So I've looked at the SRAM iMotion 9. It seems to give a good range (300+%), albeit in biggish steps, and it's reasonably cheap at £160. But is it really reliable? Does it have the same baggage as Rohloff - like you need a new frame? Or lots of additional fittings? What's the verdict among you gurus?
Neil

KimBowers · Post by **KimBowers** » 3 Jul 2008, 2:04pm

I've no experience of the iMotion 9 (mine is a Rolhoff :-)

)
But have you seen this site : http://hubstripping.wordpress.com/i-motion-9-sram/ ?
There are hub comparisons and some user comments.

workhard · Post by **workhard** » 3 Jul 2008, 2:28pm

Have you seen this thread

Maintenance free? Perhaps not after all, though I've never maintained mine.... :shock:

neilob · Post by **neilob** » 3 Jul 2008, 2:50pm

Yes, looked at that thanks. I kind-of understand the question of reliability and the wisdom of the occassional oil or grease change. But what it doesn't tell me is whether I can fit a SRAM iMotion 9 wheel to my Thorn without tensioners, torque thingys, concentric bottom brackets and new cable routers. My frame has vertical drop-outs so how do I keep the chain tight? If I have to add something that looks like a rear changer on a diet it seems pointless.

CJ · Post by CJ » 3 Jul 2008, 3:11pm

neilob wrote:My frame has vertical drop-outs so how do I keep the chain tight? If I have to add something that looks like a rear changer on a diet it seems pointless.

It is the only way to do it. And I'd agree. So don't do it.

If you must do it, do it with a Sram 7-speed. Much more reliable in my experience. It will come with anti-turn washers to fit the dropouts.

But on that bike I'd rather weatherise and trouser-protect the derailleur system by getting (somehow) one of those hump-backed chainguards you see on German and Dutch trekking bikes.

neilob · Post by **neilob** » 3 Jul 2008, 3:30pm

Thanks Chris....I guessed that might be the answer.

7_lives_left · Post by **7_lives_left** » 3 Jul 2008, 7:08pm

My bike has hub gears and vertical drop outs. I would dearly love to fit a chain case to it but the ugly shimano chain tensioner fitted to it that prevents you from doing that. However I spotted a chain tensioning device on St John Stree Cycles web site (link to part here). It is describe as

POWERPLAY CHT100 Single Speed Chain Tensioner for making horizontal dropout bikes singlepeed

I take it that that is a typo and they actually mean vertical dropouts, you wouldn't need a device if you had horizontal drop outs surely.

I can't tell you if it works or not because I haven't stumped any cash for one yet, I want to find a chain case first, but it looks like it might just work with a chain case. If any one has tried one or has an opinion on it I would like to know. If I do buy one I will report back.

pigman · Post by **pigman** » 4 Jul 2008, 8:53am

CJ wrote:
neilob wrote:My frame has vertical drop-outs so how do I keep the chain tight? If I have to add something that looks like a rear changer on a diet it seems pointless.

It is the only way to do it. And I'd agree. So don't do it.

CJ's generally right, but you might just get lucky with a magic gear, ie. some single speed combination that just fits your frame. If you've got lots of sprockets and chainwheels it might be worth experimenting. I managed 42x20 as a single speed on an MTB frame with vertical dropouts and it work fine ... good luck.

MartinC · Post by **MartinC** » 7 Jul 2008, 10:23am

Yes, you might find a combination of Chainwheel and Sprocket that gives you the right chain length. Using a half link in the chain should make this possible but you'd have to scour the net to find them - Sheldon Brown's shop used to sell them I think.

I agree that a chain tensioner isn't elegant and must add some friction to the transmission but I've often thought about fitting one to my hub gear bike - it avoids moving the wheel as the chain wears and upsetting the brake block alignment.

I've seen some that extreme MTB'ers use to avoid unshipping the chain that fit very closely to the chainrings. Again you'd have to scour the net.

I'd endorse CJ's comments aboutthe Sachs 7 - I've been running one for 8 years and it's still faultless.

CJ · Post by CJ » 7 Jul 2008, 1:40pm

pigman wrote:CJ's generally right, but you might just get lucky with a magic gear, ie. some single speed combination that just fits your frame. If you've got lots of sprockets and chainwheels it might be worth experimenting. I managed 42x20 as a single speed on an MTB frame with vertical dropouts and it work fine ... good luck.

I don't believe in magic!

It'll only work fine with a brand new chain and will take less than one link (i.e. ½in) of wear before the chain is slack enough to jump off. Which is fine if you don't mind putting a new chain on every few hundred miles.

Alternatively keep a one-tooth different chainwheel or sprocket (equivalent to ¼in chain length adjustment or moving the wheel to and fro by 1/8in). But to get full life out of a chain you'll also need a jogged link, and they're hard to find.

To my mind that much expense and/or fiddle runs counter to the whole idea of hub gears or single-speed.

DaveP · Post by **DaveP** » 7 Jul 2008, 2:03pm

CJ wrote:Alternatively keep a one-tooth different chainwheel or sprocket (equivalent to ¼in chain length adjustment or moving the wheel to and fro by 1/8in). But to get full life out of a chain you'll also need a jogged link, and they're hard to find.

1 tooth equivalent to 1/4 in chain adjustment - Thats a valuable and hard to find piece of information. I think I could work out why, but I couldnt prove it to my own satisfaction. Thanks

If "jogged link" means a half link then Hubjub have some, in 1/8 or 3/32.

neilob · Post by **neilob** » 7 Jul 2008, 2:55pm

Thanks for all the thoughtful replies. I decided to bin the idea because the hassle seems to outweigh the benefits on an existing frame built for derailleur gears. That doesn't mean I've abandoned the concept but will wait to see state-of-the-art when it comes to buy a new frame. By which time Rohloff will be selling at £37.50 each......
N

thirdcrank · Post by **thirdcrank** » 7 Jul 2008, 2:59pm

I've been running a Sachs Spectro 7 about 8 years. (This is the predecessor of the SRAM and although this was the old model when I bought it, I was attrracted by the slightly closer ratios with some resulting slightly smaller steps.) I've had no reliability problem at all, but it can be a faff if I puncture.

I had the frame custom built, although the builder (Chris Marshall) is really a deraileur man. I realised horizontal dropouts would be necessary but I had the shorter camapg ones fitted. They do work, but the amount of adjustment available is not really satisfactory and longer slots would have been much better. I see somebody earlier mentions having vertical dorpouts - I should have thought they would be a nightmare. It's hard for me to envisage how they would work without some pulley system to take up slack.

7_lives_left · Post by **7_lives_left** » 7 Jul 2008, 10:33pm

thirdcrank wrote:I see somebody earlier mentions having vertical dorpouts - I should have thought they would be a nightmare. It's hard for me to envisage how they would work without some pulley system to take up slack.

Yes, if you have vertical dropouts you have to have a chain tensioner unless you get lucky like pigman or MartinC (some people make their own luck I guess). Don't dismiss vertical dropout out of hand though. So long as the frame has been manufactured right, it is a no brainer to get the wheel aligned and it is impossible for the wheel to shift out of alignment with vertical dropouts.

My previous bike was an Orbit Orion (still have it, just needs some serious maintenance) . This has a SRAM 7 hub in a aluminium frame with horizontal drop outs. I had persistent problems with the back wheel shifting in the frame. I let the outermost nut on the drive side chew up the outer surface of the drop out. Once this had happened, the wheel was prone to slipping, each time removing more material from the face of the dropout. I am now very suspicious of aluminium frames with horizontal dropouts.

On the chain tensioner, it only need to take up a tiny amount of slack, about zero to two teeth worth. That's why I was so disappointed with the Shimano chain tensioner. It can take up a slack of about 16 teeth, which is fine if you want run a double chainset, but it ends up putting the chain about 10cm nearer the tarmac where it collects all the dirt from the road. I have a single chainset and am more concerned with getting the chain covered in a chain case instead.

I ordered the alternative chain tensioner from SJS Cycles, I hope it works. Still haven't found a chain case yet though. I might have to get creative with some fiberglass if I can't find one off the shelf.