Jim’s Blog

Single Speed News

Thu, 31 Jul 2008 18:25:10 +0100

So, here’s the latest on the single speed GT project; took the rear wheel to Tredz (www.tredz.co.uk) today and they very expertly fitted a nice new freewheel hub - I’m hoping this will cure the over-run problem I’ve been experiencing.

Great guys in Tredz workshop, really knew their stuff, awesome display of Park tools on the wall, let me watch how they did the job, would be happy to do it myself next time.

Interestingly, the grease inside the hubs was almost solid - if you remember, although the GT is over 10yrs old, it’s probably covered no more than 50 miles in its life and this showed as the hubs were perfect.

I’m going to service the front hubs myself having seen the state of the old grease in the rear; picked up a 15mm Park cone wrench so I can do the job properly, forgot to pick up grease, next time for sure.

In case you’re wondering, the photo at the top of this page was taken in Boston, summer 2008; it’s the staircase in the new Apple shop - I went on a pilgrimage there, very impressive.

How to single speed - Part 6

Wed, 23 Jul 2008 18:24:35 +0100

The half links turned up today and they are great; they shorten the chain by exactly one link and this has made the world of difference. The chain now has way less slack, stays with the rear sprocket for longer, perhaps by a tooth.

This has made everything look better and it seems to perform better too; I’ve not been able to make the chain slip on the sprocket today, even pedaling hard uphill out of the saddle - a very worthwhile £3.50 investment from www.charliethebikemonger.com

Also fitted some cheap, light alloy pedals today, £12 from www.tredz.co.uk and to these I fitted some Power Grips £15 http://powergrips.mrpbike.com/index.php?section=index I bought them last weekend in a little bike shop in Brecon www.bipedcycles.co.uk

Just had a quick ride round the village and my first impressions are that I kind of like them, although the little Japanese pedals are a bit narrow for my UK size 12’s - may have to get some wider ones, we shall see. If anyone can recommend some quality, wide pedals that will work with Power Grips then I would like to hear from them.

One issue I’ve been getting it that occasionally, when I’ve been pedaling fairly hard and then I stop suddenly, the chain seems to go momentarily loose and the tensioner springs up and hits the frame. I was convinced this was because the chain was too loose and had hoped that the addition of the half link would solve this, but it hasn’t.

I asked Richard at the Bike Shed Wales (www.bikeshedwales.com) and he suggested that it was the freewheel that was at fault and I tend to agree now. His theory is that when the pressure come off the pawls in the freewheel mechanism, they occasionally stick, causing the sprocket to continue turning after I stop pedaling, which slackens the chain - the tensioner no longer has anything to push against and it pops up and hits the frame.

Seems that if I throw £30 at the problem it shall be solved :-)

How to single speed - Part 5

Mon, 21 Jul 2008 20:42:10 +0100

Ok, just a few more observations on the single speed project that might help you with yours.

I now wish I’d gone for an 18T on the back and a 40T on the front - this would give me the same ratio, but with the 2 extra teeth on the rear providing more for the chain to bite into, meaning that chain slip would be much less likely.

Now, to be fair, this hasn’t happened again since refitting the original chain tensioner, but its in the back of my mind when pedaling hard out of the saddle - I may make the change when funds permit.

Actually, the shortened chain may solve it, as a little more of the chain will be in contact with the rear sprocket, that would be good, we shall see.

Went up to a great little bike shop in Brecon last weekend and bought an “old” Kalloy stem that was shorter, had more rise and was much lighter than the stock one. It also had a removable faceplate clamp thing, which meant I could also fit some Bontrager wider riser bars that I had hanging around - much better position for me now and easier out of the saddle with the wider bars.

So, just waiting on these halflinks, interested to see if they make a difference :-)

How to single speed - Part 4

Mon, 21 Jul 2008 20:26:19 +0100

So, the bike’s back together, first ride around the village, exciting.

Everything worked really well, nothing came loose, the bike felt light and lively with all that weight gone - fab!

But it soon became apparent that the 32 X 16 ratio was a little too easy for road riding, so I took a trip down to the Bike Shed Cardiff (any excuse).

I came back with a single speed specific Surly stainless steel chainring in 36T size, so the set up would now be 36 X 16. This is a single speed specific chainring, in that it has taller teeth than a derailer chainring, as it doesn’t have to allow the chain to jump from one chainring to another like a derailer does.

Lovely bit of kit, looks right, easy to fit, had to add a link to the chain, first ride with the new ratio was much better - still easy but perfect for medium speed easy town riding with a few hills.

Took the bike for are real shakedown around town, 10 miles or so on roads and tracks, really nice with only one small problem - sometimes when I stopped pedaling suddenly, the chain tensioner pops up and hits the frame.

Now, I thought I could solve this with a better tensioner, so I got hold of a Surly Singulator from Wiggle for £30 - bit pricey really. It didn’t make any difference and if anything was worse - it didn’t have nearly as much tension as the other unit, so it’s going back. Also, when really moving slowly and trying to get up a steep incline, the chain skipped on the rear cog for the first time ever, probably again due to the lower tension provided by the Surly unit.

My current theory is that the chain is too slack, even with a tensioner, so I’m hoping that when the chain halflinks arrive, this wlll solve the problem.

How to single speed - Part 3

Wed, 16 Jul 2008 20:05:27 +0100

Refitting the original bottom bracket was a bit of a nightmare, mainly because it was designed to accept the bracket I mentioned earlier - it had a section of about 3mm that had no thread. The “expert” at Halfords said it didn’t matter and that I should just screw it in tight; not true and I should have followed my instincts...

I was trying to screw a section of bottom bracket that didn’t have thread on it all the way to the end, of course it wouldn’t work, what was I thinking?

So, a trip to the boys at the Bike Shed Cardiff, £16 for a nice Shimano bottom bracket, a bit of free advice and I was off again.

With that done, I removed the rear cassette - dead easy with my new chain whip tool and the correct tool to unscrew the retaining ring, anti-clockwise. The cassette just pulls off and you’re left with a shaft where the cassette used to sit.

I’d already ordered all the bits I needed from Charlie at www.charliethebikemonger.com - I got one of his excellent “everything you need kits” which includes a rear sprocket, spacers, small chainring bolts, a chain & a chain tensioner.

First, I took 2 of the 3 chainrings off of my new chainset - I say new chainset because the one that came with the bike had all the chainrings kind of spot welded together so they were kind of all one and the same; they could not be removed individually.

I kept the 32 tooth middle chainring in the middle position, replacing the stock bolts (which are designed to go through two chainrings) with the replacement bolts from Charlie’s kit (which are shorter and perfectly suited to going through only one chainring). I’d also bought a little tool to hold the backplates of these little bolts to make sure I could do them up real tight - this was a good £5 investment and is far superior to trying to stuff a screwdriver in there somewhere instead.

A quick word on chainline - you have to ensure that there is a near perfect line between the chainring and the rear sprocket or you’re going to get problems with wear on the chain, sprocket, chainring and even the tensione I guess - but this is easy, you place the spacers on the rear hub shaft, best guess at first, tighten the lock ring and refit the wheel. Have a look down the chain, great if it’s straight, retry the spacers in a different position if its not, not too tricky and quite satifying.

Fitting the chain tensioner was easy too, the photos say it all really.

Issues: the chain was a bit slack, so I tried taking the minimum possible amount of links out - now it was too short and I couldn’t get it on at all. As there is zero adjustment with a vertical dropout frame, thats the best I could do, or so I thought. I have since discovered and have now ordered some “half links”; literally half the size of a full link, with the hope that this will shorten the chain by just the right amount - we shall wait and see.

Another little lesson learnt at the point - having got everything straight in the chainline, which involved putting 2 of the smallest spacer shims in place (these are 1mm each, so together 2mm obviously, which fitted better than using the next size up which was around 4mm) and fitting the chain, I noticed a little shimmy in the rear sprocket.

Now, this could have been the sprocket being out of shape, or the hub being out of shape, but I thought it must be something else. It was; basically I’d put the two smallest spacer shims on first and then the larger ones. The 1mm shims are quite delicate, and I think they had deformed slightly up against the “castellated” edge of the shaft. This had thrown all the subsequent spacers, sprocket etc out of true.

So, I removed the lot, and put them back in a different order, thick spacer first, up against the castellated shaft, then a 1mm shim, then another thick one and so on - have a look at the before and after photos. Not only did this cure the shimmy, the silver shims in between the black spacers looks pretty cool!

How to single speed - Part 2

Wed, 16 Jul 2008 19:48:53 +0100

So, all the easy bits are now removed, probably took a half hour.

Now, my front derailer was attached to a bracket (top right of the picture) that was attached to the bikes bottom bracket, rather than being clamped to the frame downtube which is more often the case. I hadn’t intended on removing the bottom bracket crank and bearings as I’d never done it before, didn’t have the correct tool and was worried that all kinds of bearings and stuff would fall out over my kitchen floor.

But, I couldn’t have lived with myself if I’d simply left a big ugly bracket in place that served no purpose other than to add weight to the bike and upset me, so I decided it had to go.

Popped down to my local Halfords and bought the correct tools - one for removing the crank at about £5 (that the pedals fit to) and one for removing the bottom bracket at about £6 (the bearings/crank etc inside the frame). I unscrewed the crank bolts, used the satisfying crank puller tool to pop the crank arms off the crank, then starting on the opposite side of the bike to the chainrings/derailer, I used the bottom bracket removal tool to unscrew that side of the bracket in the usual anti-clockwise direction.

WARNING - on the opposite side of the bike to this, the same side that the chainrings and derailer are on that is, the bottom bracket unscrews in a clockwise direction - no one told me this...

So, having mistakingly tightened this up to almost breaking point, I realised the error of my ways following a quick look on the internet. I tried to undo it - no luck; the tool didn’t insert as far as on the other side for some reason; as a result it kept popping out and it was getting knackered - very frustrating.

Another trip to the net and I discovered the solution - put a crank arm bolt through the tool (I needed to use a large washer as it would just go right through otherwise) and screw it into the crank - this holds the tool in place and from then on it was plain sailing. I was relieved to see the bottom bracket was all one piece - I’d half expected millions of tiny ball bearings to fall out as I removed it.

I was able to remove the pesky bracket and all was good in the world....

...until I went to refit the bottom bracket.

How to single speed - Part 1

Wed, 16 Jul 2008 19:00:08 +0100

Ok, first my “get out” clause - I’m totally new to single speed bikes and fairly new to bike mechanicals in general, so I’m not for one moment claiming to be an expert. However, I did this conversion in under a week, acquiring all the tools I needed from the internet and local bike shops and doing the work in my kitchen; I made mistakes, broke some stuff and learned loads - I hope this serves as a very basic “how to” guide and provides useful information to anyone considering doing a similar project. Photos of the bike are all on the photos page of my blog.

By the way, I’m not totally up on the correct names for everything I’m talking about here, but believe this adds a certain charm right? :-)

So, let’s start at the very beginning...

My donor bike was a GT 21 speed “Outpost Trail” (7 speed Shimano cassette at the back, 3 chainrings at the front) “triple triangle” design bike. Just before starting out with the conversion, I stumbled upon an excellent online resource, namely Charlie of www.charliethebikemonger.com (where else). I watched his “how to” video and began to strip the GT; I ended up buying most of the parts needed at Charlie’s site.

I removed the rear derailer, front derailer and associated cables, reflectors, bell, stand etc etc - don’t worry about cutting cables etc

Now, I needed to remove the brake levers, as the gear change levers formed part of them - I could have left them on but I would have been carrying the weight of the gear change levers for no reason, so I decided they had to go to get the clean look I was after. I picked up a pair of brake levers for my GT’s cantilever system from my local bike shop (LBS) Sunset MTB in Cardiff for just £5.00. NB my bike is over 10yrs old and uses cantilever brakes, these are similar in looks to V brakes, but the brake arms themselves are shorter than the more modern V brakes and have a wire strop above them that attaches to a little bracket on the headset under the handlebars.

So, off with the handlebar grips; I kind of rolled them off like a very tough condom as I wanted to put them back on again (unlike a condom) - you can get a bit of GT85 spray between them and the bars to help them come off (oil based so also not for use on condoms) if need be - then simply loosen the single allen bolt and slide the grips off.

You can see most of the parts I removed on the photos page.

Why single speed?

Wed, 16 Jul 2008 17:58:27 +0100

Pretty much every bike I’ve ever owned has been geared and I’ve always considered this to be the sensible status quo; after all, why would anyone want to struggle when all you need to do when meeting a hill is simply select a “granny gear” and off you go.

Now, I do a fair bit of mountain biking at weekends with steep 500m plus single track climb outs and, for the moment at least, I intend to stick with gears - I enjoy the leisurely, technical nature of the climbs in the saddle and really don’t want to rush, the scenery is so lovely (the ride back down is another thing all together...)

I think it was at my local bike shop that I first set eyes upon a single speed mount and I loved it; the simplicity, the lightness, the pure look of a single sprocket providing the backdrop to a frame uncluttered by derailers, cables and other paraphernalia.

But surely the people who own these bikes are young fit specimens, able to forgo gears, making up for their absence by pure grunt right?

Well, yes and no. It all comes down to what you want to do on the bike and, taking into account your level of fitness, choosing the correct gear ratio.

Chatting to those who know, I discovered a whole new single speed language; indeed, something fresh for me to get obsessed about. Spacers, shims, single speed specific chainwheels & sprockets, gear ratios, shortened chainwheel bolts and exotic sounding purveyors of all things SS.

It all interested me so I started to do some research and to my surprise there were plenty of SS bikes available off the shelf, many of which come from well known manufacturers - Kona, Specialized, Felt along with some more exotic names, Pearson, Genesis, Lemond & Bianchi.

I was very close to buying a Specialized “Globe Centrum” singlespeed, a kind of a hybrid creation erring on the side of mountain bike, with an easy pedalling 2 to 1 ratio (every full rotation of the pedals/crank results in two revolutions of the rear wheel) which sounded ideal for me - I’m not a strong pedaller.

It was around this time that I remembered the existence of an as new GT mountain bike belonging to my father, which was sitting in his garage gathering dust - he was in the states so an email for permission to experiment on it was sent and the go ahead was granted.

The following pages chart my progress on the project over the period of about a week that it took to complete.