Frequently Asked Questions
Using your bike as a fixed is really easy and well worth a try. If you are unsure of anything please email and we will be happy to help. Do please have a look at the pictures on the shop and gallery pages that help illustrate the information below.
For other FAQs and fixed or singlespeed websites please see the links page.
With thanks to the late, great Sheldon Brown who kindly granted permission to publish links to his site in 2007.
Do please ask first if you wish to reproduce any of this information on your website or otherwise.
Disclaimer: Dislike these things but we have to state this: The advice and opinions that follow are provided for information purposes only and this information is used at your own risk. londonfixiebike cannot be held responsible for any damage, claims or mishaps that may occur by following the information given here.
1. What is a fixed wheel bike?
2. Why ride a fixed wheel?
3. Fixed, off-road?! Are you mad?!
4. What is wrong with normal track hubs and screw on cogs?
5. What are the advantages of a bolt on ISO-Cog?
6. How does the bolt-on cog work?
1. Can I use a fixed wheel on my road/track bike?
2. What if my road frame was designed around gears?
3. My singlespeed mountain bike has track dropouts, horizontal dropouts or sliding dropouts. Can I run it 'fixed'?
4. My singlespeed mountain bike has vertical dropouts and I use a chain tensioner. Can I run it 'fixed'?
5. If not, is there any way around this?
1. Which hub/set-up is best for my singlespeed road/track bike?
2. Which hub/set-up is best for my mountain bike?
3. Tell me more about chainline.
4. So what will my chainline be if using a cog mounted on a disc hub?
5. How do I adjust my chainline then?
6. Tell me more about frame spacing.
7. Tell me more about wheel dishing.
8. Tell me about the various types of dropouts.
9. Use a Shimano hub?! On my fixie?!
1. Do I have to fit a rear brake?
2. If I mount a cog on my disc mount how do I use my rear disc brake?
3. Can I use a QR on a fixed wheel?
4. Can I use a 1/8" chain with a 3/32" cog?
5. What is a magic gear?
6. Is using a cog on a disc mount a good idea?
7. How about using a front mountain bike hub on the rear of a road bike?
8. How do I fit a solid axle and spacers?
9. How do I fit the cog to my disc hub?
10. Which bolts should I buy to secure the cog to the hub?
a) General fixed wheel questions:
1. What is a fixed wheel bike?
On a 'normal' bike a freewheel is fitted that allows the rear wheel to turn without the pedals turning. On a fixed wheel the cog is 'fixed' to the rear hub. If the wheel is turning the pedals will too (and your legs).
2. Why ride a fixed wheel?
We all know the benefits of riding a singlespeed - simplicity, minimal maintenance and weight, smoothness, a near silent transmission but mostly that wonderful feeling that comes from being freed of gears. Big hill? - push harder. Fast downhill? - spin faster. You are in control.
A fixed wheel takes it to the next level with the ultimate link between you and the bike, a wonderful feeling of connection that comes no other way. You learn to ride with real smoothness and control, the rear wheel always turning like a flywheel, driving you along. Many never go back...
3. Fixed, off-road?! Are you mad?!
Hmmm, well, are you the sort who gave singlespeeding a go and a few rides later never looked back? Geared bike relegated to the back of the shed? Niche it up a bit more - fixed off-road is a challenge at times but all the more fun and rewarding for it. Give it a go...
4. What is wrong with normal track hubs and screw on cogs?
Good question. They have been around for years and many people use them without any problems. However, search the 'fixed/singlespeed' section on any popular bike forum for "stripped" (try bikeforums.net or roadbike review forums) and you will find endless stories of how using even the best quality cogs, hubs and lockrings installed by competent mechanics resulted in problems:
Cogs or threads stripping if not done up tight enough or too tight. Seized on cogs if left mounted too long, worn threads if cogs taken on and off too much, cogs spinning uselessly on the hub as the threads finally give out. Incompatibility problems and poor fitting when combining cogs, hubs and lockrings from certain manufacturers.
Perhaps these problems have been exasperated by modern fixie trends - off road fixed riding with low gears, urban riders doing all the things we love to do - humongous skids and skip stops, equipment abusing tricks or just general hacking about.
Time trialists and riders on the velodrome once up to speed simply sit and spin (with lots of power) but they don't impart sudden extreme braking forces and unusual abuse in the way us normal folk do.
In engineering terms the idea of securing a hardened steel cog and lockring onto a few fine threads on soft aluminium seems to be a less than perfect idea.
5. What are the advantages of a bolt on ISO-Cog?
- An end to stripped hubs, seized cogs, stuck lockrings and ruined threads.
- You can change a cog with one small torx or hex key - no bulky and expensive chain whips or lock ring wrenches needed.
- It gives a 100% solid mount - six M5 hardened steel bolts give the stiffest most secure interface possible. Zero slippage or movement possible, simply 100% power transfer - forwards or backwards.
- Allows precise dialling in of the chainline to match front and back, something that is much more difficult to do with a screw-on cog.
- Converts a mountain-bike to fixed in the easiest possible way. Flip the wheel round, bolt on our cog and ride. No other expense involved and reversible in a minute.
- Traditional quality. Unlike cheap stamped or laser cut cogs, londonfixie ISO-Cogs are precision machined from solid blanks of EN36 chro-moly to be perfectly round - sounds odd but not all cogs out there are as round as you might expect...
- After machining (teeth are milled on hobbing machines - the old fashioned way), our cogs are heat-treated for strength and wear resistance, in addition they are reversible without affecting chainline for even longer life. The mounting holes are drilled to very tight tolerances to ensure perfect mounting on any standard 6 bolt disc hub.
- A londonfixie ISO-Cog is guaranteed for life to the original owner. If you wear one out we will replace it absolutely free of charge. See shop for details.
6. How does the bolt-on cog work?
It's very simple. Instead of using a thread on the centre of the cog to screw onto a matching thread on the hub we use a bolt on cog - for all the advantages outlined above.
The majority of mountain-bike disc brake hubs use the ISO standard 6 bolt mounting. Instead of mounting a brake disc onto these mounting holes we manufacture a custom made series of cogs with the same drilling pattern. Thus our cogs simply bolt onto the hub in place of the disc.
As the cog is bolted (fixed) to the hub it can be driven by the chain forwards or backwards and becomes a fixed wheel.
For full details of set-up and the many advantages this system offers please have a look at the other FAQ's listed here.
b) Can I run a fixed wheel on my bike?
1. Can I use a fixed wheel on my road/track bike?
All track frames and singlespeed specific modern road bikes (Specialized Langster, Kona Paddy Wagon, Surly Steamroller, Fuji Track, Bianchi Pista etc) use track dropouts. Most (but not all) older steel road bikes have horizontal dropouts. As long as your frame allows the wheel to be moved forwards or backwards to tension the chain you can run it fixed.
See also: Tell me about the various types of dropouts.
If your bike is a modern (probably aluminium or carbon) frame designed around gears and with vertical dropouts you will not be able to run it fixed. The exception is if such a frame has an eccentric bottom bracket (very unusual) or you use an ENO eccentric rear hub with disc mount. Oh, there is of course the final chance of finding a magic gear.
See also: If not, is there any way around this?
2. What if my road frame was designed around gears?
If you have an older road frame with horizontal dropouts designed to be used with gears the rear frame spacing will probably be 126mm or 130mm. Most of these older frames will be steel which can happily be squeezed in or out a few millimetres.
If spacing is 126mm use the set up as per a road/track frame with 120mm spacing and add another 3mm of washers each side (see shop) or you could squeeze the dropouts together as you tighten the wheel nuts - steel will not complain. Chainline in this situation will be the same as a 120mm spaced frame.
If you have vertical dropouts see here too: If not, is there any way around this?
If spacing is 130mm on your steel frame, a good idea is to use a 135mm mountain bike rear hub and spring the dropouts apart slightly. This gives the advantage of being able to use a flip/flop fixed/free set up. Chainline in this situation would be around 53mm so a longer bottom bracket or a mountain-bike chainset may be necessary.
See also: How do I adjust my chainline then?
3. My mountain bike frame has track dropouts, horizontal dropouts or sliding dropouts. Can I run it as a fixed wheel?
Yes. More about dropouts here: Tell me about the various types of dropouts.
4. My mountain bike frame has vertical dropouts and I run it as a singlespeed using a chain tensioner. Can I make it into a fixed wheel?
No. You cannot use a singlespeed style chain tensioner with a fixed gear bicycle. See question below for further options.
5. If not, is there any way around this?
Yes, if you have vertical dropouts that do not slide then you may also have a frame with an eccentric bottom bracket (as fitted to the latest Santa Cruz Chameleon for example). If not you may be able to find a magic gear. Lastly there is the option of using an ENO eccentric hub with disc mount. Sheldon Brown has more on these various options.
c) Set-up questions:
1. Which hub/set-up is best for my singlespeed road/track bike?
First ensure you can run a fixed wheel with your frame - see above.
Yes? OK - frame spacing, this determines the best choice in hub. The most common spacing on track and SS specific frames is 120 mm. This is the modern standard that virtually all track frames and single speed road bikes are made to.
By far the best choice for a hub to utilise a bolt on cog is a mountain bike front disc hub, specifically a Shimano M756 disc hub or similar. Why this hub? See question below: Use a Shimano hub?! On my fixie?!
In short the hollow QR axle can be replaced with a solid axle and two 10mm spacers added to fit the hub perfectly into the standard rear track/singlespeed road frame width of 120 mm.
Normal chainline on a track/singlespeed road bike is approximately 42mm. A cog mounted on a disc hub as above will give a chainline of approximately 41 mm. It is a simple matter to add spacers or washers between cog and hub to dial in the chainline perfectly to exactly match your front chainset. For instance adding a 1mm spacer makes your chainline 42mm, adding a 2mm spacer will make it 43mm.
If you are not concerned about using a track chainset or keeping the 42mm chainline then a superb alternative set-up all round is to use the same M756 hub but place a 5mm spacer on the drive-side and a 15mm spacer on the non-drive side. Not only will this give you a non-dished wheel it will give a chainline of approx 46mm. This matches perfectly the outer ring position on a standard road chainset (46mm). Thus a world of second-hand or new road chainsets and bottom brackets from Campagnolo, Shimano etc becomes usable.
Some older track/Keirin frames use 110mm rear spacing. In this case just use a 5mm spacer each side. Chainline will be approx 41mm. For more on spacing the hub see also: Tell me more about frame spacing and Tell me more about wheel dishing.
2. Which hub/set-up is best for my mountain bike ?
First be sure you can run a fixed wheel on your frame. See above questions.
Yes? Great - the route to fixed is easy. The rear spacing on virtually all mountain bikes is 135 mm. The best set up is a normal rear cassette hub with 6 bolt disc mount - you probably have one of these on your mountain bike right now.
By mounting a drilled cog on the disc mount and a normal singlespeed cog and spacers on the freehub side you have a flip/flop fixed/free wheel. As simple as that, no alterations are necessary and the wheel can be used with gears again simply by removing the singlespeed cog and mounting a cassette.
Using a cassette wheel with a single cog and spacers allows the chainline on the freehub side to be adjusted to match the fixed side perfectly. Thus when flip/flopping the wheel your chainline stays spot on. A cog mounted on the disc side will in most cases give a near perfect chainline with the outer front ring.
Or use a standard mountain-bike singlespeed (ie screw on freewheel) 6 bolt disc hub.
3. Tell me more about chainline.
On a singlespeed or fixed wheel bike you want the chain to run in as straight a line as possible. Ideally the two measurements; from the centre of the frame (at the seat tube) to the front chainring and again from the centre of the rear dropouts to the rear cog should be within 1 or 2 millimetres of each other.
This measurement is your chainline front and back. Standard chainline measurements are as follows:
- Track and singlespeed road = 42mm
- Road double inner ring /outer ring = 41mm/46mm
- Singlespeed mountain bike = 54mm
- Mountain bike triple; middle ring/outer ring = 48-50mm/52-54mm
These are standard measurements but in practise chainline often (nearly always) varies from these numbers and is rarely spot on front and back. Always measure your own chainline to be sure. See Sheldon here for how to and more on chainline.
4. So what will my chainline be if using a cog mounted on a disc hub?
Chainline will be as follows:
- M756 disc hub converted to fit on rear of road bike with 10mm spacer each side (slightly dished wheel) = approx 41mm
- As above but with 5mm spacer drive side, 15mm spacer non-drive side (non-dished wheel) = approx 46mm
- Bolt on cog to rear disc hub on a 26"/29er mountain bike = approx 53mm
5. How do I adjust my chainline then?
Compare the measurements in questions 3 and 4 above - simply add 1mm or 2mm spacers between hub mount and cog to create a perfectly matched chainline with the chosen chainset.
There are other ways - use a longer/shorter bottom bracket (BB) spindle or spacers on the BB cups. Use a different chainset or mount the chain ring in a different position.
6. Tell me more about frame spacing.
Frame spacing is simply the distance between the inner face of the rear dropouts. Common measurements are as follows:
- Track, singlespeed road frames and some old 5 speed frames = 120mm
- Some older track/Keirin frames = 110mm
- 6 and 7 speed road frames = 126mm
- Modern 8/9/10 speed road frames = 130mm
- Mountain-bike 26" and 29er frames = 135mm
As always see Sheldon for more on frame spacing.
7. Tell me more about wheel dishing.
If you space a M756 disc front hub (100mm spacing) with 10mm of spacers each side to fit on the rear of a road frame then the chainline will be approx 41mm. The wheel will be slightly dished due to the disc mount.
If you want a non-dished wheel simply add a 5mm spacer to the drive side and 15mm (10mm + 5mm) on the other side. Chainline will be approx 46mm.
A road double chainset with just one ring in the outer position works brilliantly here as the normal chainline for this is 46mm. This also gives you access to endless options of chainsets and plenty of superb value second-hand Campag lovelyness on ebay.
8. Tell me about the various types of dropouts.
There are three main types of rear dropout with many minor variations: Horizontal dropouts, vertical dropouts and track ends.
Most older road bikes and much older mountain bikes have horizontal dropouts, most newer road and nearly all modern mountain bikes use vertical dropouts.
Singlespeed specific bikes (road and mountain) mainly use track ends but you will also find sliding or adaptable dropouts on many singlespeed mountain bikes of recent years. Illustrations of various dropouts can be seen on Sheldon's site here.
9. Use a Shimano hub?! On my fixie?!
Hey, we love Campagnolo etc as much as the next man, and use it wherever we can. However, you have to hand it to the big "S", if you want a good quality strong hub, that is affordable, easily serviceable anywhere in the world, will roll and roll for years and converts to fit a bolt on cog to a road bike in minutes then XT is perfect.
The M756 XT hub has double seals, excellent bearings with polished races and is high flange to build into a good stiff wheel. Most importantly it takes a 10mm axle, thus, the hollow QR axle can be replaced with a solid axle to take track nuts.
This allows a 10mm spacer to be added each side to take the hub width from the standard front wheel width of 100mm to the standard rear track/singlespeed frame width of 120mm.
You could always buy one of our lovely polished hubs with XT logos hardly visible. Or check out our londonfixie decals - cunningly sized to cover up the logos on a M756 hub...
Check the pics in the shop and gallery to see how 'factory' the converted hub looks.
d) Other technical questions:
1. Do I have to fit a rear brake?
In most countries two brakes are legally required. If riding a fixed wheel this counts as your rear brake (using the resistance in your legs to stop the pedals and wheel turning).
Some prefer to have a separate rear brake too. Many run without a front brake altogether, the choice is yours.
2. If I bolt a cog to my disc mount how do I use my rear disc brake?
You cannot do both. Most mountain-bike frames still have rim brake mounts ("V", cantilever or caliper brake) so you can of course still run a rim brake in fixed or freewheel mode.
If your frame is disc only then in fixed mode the fixed wheel acts as your "brake" anyway. See question above.
3. Tell me more about using a QR on a fixed wheel.
Some say yay, some say nay. Many people use QR's on off-road fixies with no problems.
Important thing is to use a decent steel one, this is no place for flimsy lightweight Ti skewers. Stick to a reliable Shimano skewer cranked up good and tight.
4. Can I use a 1/8" chain with a 3/32" cog?
Yes. A 1/8" chain (wider) can be used on a 3/32" (narrower) cog but it will have a lot of 'slop', best to match like for like. You cannot use a 3/32" chain on a 1/8" cog. Remember also that many 3/32" singlespeed and fixed cogs are too wide for certain 9 speed narrow chains. 10 speed chains are a definite no no. Note: our 3/32" ISO-Cogs are for use with traditional 7 or 8 speed chains not narrow 9 or 10 speed chains.
5. What is a magic gear?
This is a clever combination of front chainring, rear cog and chainstay length (effectively distance between the two rings) that allows the perfect length of chain to give correct chain tension on a frame with vertical drop outs. Sheldon has more on magic gears here.
6. Is using a cog on a disc mount a good idea?
Well, consider an eight inch travel full-suspension off-road bike, piloted down the side of a mountain by a pro downhill rider. The front (and/or back) disc brake happily take the strain of hauling this 40lb+ bike (and rider) to a stop with a six pot hydraulic calliper straining on an eight inch disc.
Now there are some strong fixed wheel riders out there but in comparison a 'fixer' twirling the pedals on a cog mounted in the same way or using as much braking/skidding force as desired is producing much less stress on that same mount.
Our ISO-cogs are precisely machined to very close tolerances. The bolts locate tightly and perfectly in the mounting holes to ensure the cog is absolutely central.
7. How about using a front mountain bike hub on the rear of a road bike?
The M756 hub as suggested has the same 10mm axle as any rear hub and large strong flanges, the hub body is also far more substantial than a typical skinny road hub.
Distance between flanges on the M756 is 55mm - that's wider than those on a normal MTB rear cassette disc hub and equal to or wider than most typical rear road cassette hubs.
Bearings in a M756 front hub are 3/16" but Shimano fit 20 of them running on high quality polished races. For many years Campagnolo used 7/32" bearings (1/32" bigger than 3/16") on the drive side of rear hubs.
As with the question above, XT front hubs are happy clattering down a mountain on a rigid or suspended mountain-bike. On the rear of a fixed wheel road bike they work superbly, this is backed up by practical experience in use.
8. How do I fit a solid axle and spacers to my Shimano hub?
You will need a pair of the correct size cone spanners with very thin jaws - Shimano use very narrow flats on their cones. Even professional Park spanners may be too tight. First remove the rubber seals (on M756 hubs). Remove the outer locknut from one side of the axle, unscrew this followed by the cone. Withdraw the axle carefully and remove the other locknut and cone noting any thin washers fitted.
Onto your new solid axle loosely screw on the first cone followed by the original thin washers if fitted, appropriate londonfixie spacer(s) and lock nut and insert axle into hub. Re-grease bearings if necessary.
Repeat on other side and adjust position of cones to give correct axle protrusion each side for your set-up. Adjust bearings correctly and tighten locknuts as normal. Finally slide/squeeze rubber seals over axle and spacers until they pop ino place.
9. How do I fit the cog to my disc hub?
Position cog over disc mount, adding any spacers between if required. It's a good idea to add a smear of grease between cog and mount face. Loosely screw in the six bolts (using locktite, thread prep or grease as appropriate).
Make sure torx or hex key is fully inserted in bolt head to avoid slippage and tighten down bolts loosely in the following clock face pattern: 10, 4, 8, 2, 6, 12. Repeat a couple of times increasing the torque as you go round until the bolts are fully tightened. Reverse process to change or remove cog.
10. Which bolts should I buy to secure the cog to the hub?
Originally, disc hubs always used hex (allen) key bolts with socket heads. Torx button head bolts are now sometimes fitted. These are neat looking but do be careful to always ensure you use a good quality Torx tool and it does not slip.
Standard Torx bolts can be difficult to remove if the head becomes ruined. We specify our bolts with a large deep head for excellent tool location and easy removal.
As for material, we mainly stock and recommend high-tensile steel bolts. Having said that, we all love shiny things so we also stock Torx head bolts in high-spec A4 Stainless Steel.
Remember though that compared to high-tensile steel, stainless is weaker (even the superior A4 grade) and can be prone to seizing (galling) in aluminium and stretching. If using stainless steel in aluminium hubs always use a thread prep or lube.
All our steel hex bolts are the very highest grade 12.9 high-tensile steel for ultimate strength.
As a rule choose 12mm for the greater thickness of 1/8" cogs.
The longer bolts (12mm or 15mm threading) allow for more spacing washers but make sure the bolts you choose will not be too long for your hub and butt up against the spoke flange. Washers can also be placed under the bolt head to prevent this.
Thanks for looking, once again do please email if you have any questions not answered here.
© londonfixiebike 2007.