Fixed Wheel and Single Speed Bicycle FAQ's (part 3)

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VeloSolo Fixed Wheel And Singlespeed Frequently Asked Questions - part 3:

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d) Other technical and miscellaneous questions:

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?
11. Tell me about singlespeed tensioners.
12. What is a (chain) half-link?
13. How do I know what BCD my chainring is?
14. Why do chainrings need different length bolts?
15. What is the difference in bottom bracket tapers?
16. Any advice on gear ratios and chainring/cog sizes?
17. How do I fit bars to quill stems without scratching them?
18. Tell me about the various handlebar and stem sizes.

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 (except with a big dose of ingenuity - see pic below). Most mountain-bike frames still have rim brake mounts 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 fixed wheel bikes with no problems.

Important thing is to use a decent steel one, this is no place for 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 bit 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" 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.
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 cogs are precisely machined with closer than normal tolerances for the mounting holes.  This ensures the bolts locate tightly and perfectly in the mounting holes with no 'slop'.
7. How about using a front mountain bike hub on the rear of a road bike?

The XT M756 hub as recommended for bolt-on cog conversions  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 borozon 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.  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 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 into 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 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 general rule choose 10mm or 12mm for disc brakes, 12mm for disc cogs and 15mm if planning to use extra spacers.  (The 20mm bolts are really just for dualcog use).  The longer bolts 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.

11. Tell me about singlespeed tensioners.

With vertical drop-outs, no eccentric BB or hub and no magic gear then a chain tensioner is what you need to get the chain tension on a singlespeed spot on.  It replaces the rear derailleur and pushes against the chain to take out any 'slack' and provide a smooth drivetrain.

Some tensioners are sprung like a rear mech, others are moved until they push against the chain to set the tension just right and are then locked in place.  The tensioners we sell spring downwards to tension the chain but they can be modified to be non-sprung and able to be locked in place.  We are happy to do this FOC - please ask when ordering.  See the singlespeed section of shop for more.
To fit a tensioner first make sure your front and rear chainline is matched to within a couple of mm's.  Fit the tensioner to the rear frame hanger with the metal stop where the 'B' tension screw on the mech would normally go and tighten the mounting bolt.  Pivot the tensioner round and adjust the movable jockey wheel so it is exactly in line with the chain.  The metal chain guide loop can be used but it is not really necessary - removing it allows the tensioner to be used with 1/8" chains and makes the whole set-up less fiddly for chain maintenance etc.  Note: pic shows tensioner on a horizontal drop-out frame, normally these are used only with vertical drop-outs.
12. What is a (chain) half-link?

If you need to shorten a chain the links have to be removed two at a time as they fit together in pairs of 'male' and 'female'.  This means a chain can only be shortened in 1 inch chunks at a time.  A half-link combines this pair of links into the same space as one link allowing smaller chain length adjustments for fine tuning.  This is especially useful when needing to positon the wheel exactly in the frame or struggling to find a 'magic gear'.

To sum up, the half-link allows the wheel to be moved back by just 1/4 inch at a time.  We sell various half-links in the shop in  both 1/8" and 3/32" sizes.  Choose from male to male and male to female links.

13. How do I know what BCD my chainring is?

BCD is Bolt Circle Diameter which is a measurement of the diameter of the circle that the mounting bolt holes describe.  There are many various BCD's in use but the common ones are as follows: 

  • Modern 4 bolt Shimano MTB chainsets (not XTR) = 104mm
  • Standard road double middle/outer (Shimano and others) = 130mm
  • Modern Campagnolo road double middle/outer = 135mm
  • Older Campagnolo and some track chainsets = 144mm

There are many others of course, especially in MTB chainsets from the last 20 years.  It is easiest to check your BCD by measuring from the centre of one bolt hole to the adjacent one and comparing it to a chart such as the one at Sheldon's site here: Sheldon on BCD.

14. Why do chainrings need different length bolts?

On a mountain bike triple or road double the middle and outer rings use the same bolts to secure the rings to the chainset.  If you want to remove one ring (to convert to singlespeed) you will find the bolts (actually inner 'nuts') are now too long preventing them tightening properly.  There are two solutions - either add some chainring washers to space out the bolts or use shorter bolts.

Sometimes 'single' chainring bolts will be too short when converting to SS and normal 'double' bolts will be too long.  Typically this occurs when mounting a middle chainring on the outer position of a chainset (for a neater appearance or to change chainline).  As the bolt recess on the chainring is now on the 'wrong' side single bolts are too short and double bolts are too long.  Say you have a Campag double road chainset and want to move the inner 39t ring to the outer position - the original bolts will be too long - simply add a 0.6mm spacer behind each inner part of the bolt (ie the 'nut') on the inside of the ring and you will not need a new set of bolts.  Chainring washers are available in different thicknesses  - very handy little things to have in the toolbox.
15. What is the difference in bottom bracket tapers?

If you are used to mountain bike bottom brackets then you may be surprised that there are two different bottom bracket tapers on road and track bikes.  Shimano and most other common Japanese component manufacturers use the JIS taper (remember J = Japan).  Campagnolo and Miche (both Italian) use the ISO (remember I = Italian) taper.  However, some Japanese track chainset manufacturers also use ISO confusing the whole issue.
Both tapers have the same angle but the length of the taper differs meaning that the two are not strictly interchangable.  Compared to ISO on ISO and JIS on JIS, an ISO chainset will mount a few mm's less onto a JIS BB, a JIS chainset will go on a few mm's more onto an ISO BB.  Many cyclists interchange the two without issue but for best performace stick to the right pairing.  Have a look at Sheldon too for more on ISO vs JIS.
16. Any advice on gear ratios and chainring/cog sizes?

Firstly, for singlespeeding off-road the traditional starting point has always been a 2:1 ratio, ie 32 chainring and 16t cog or similar.  It does not matter how you achieve this, 32/16, 36/18, 44/22 all give the same gear.  The more teeth the less wear and some believe larger rings/cogs give a smoother drivetrain.  However, smaller chainrings give better clearance off-road.  If you live in a hilly area you may need to use a slightly lower (easier) gear, ie 32/18 or similar - especially in UK winter mud.  For road use with a mountain bike a higher ratio such as 36/16 would be a minimum if you do not want to be 'spinning out' too easily.
For fixed wheel or singlespeed road/track bikes on tarmac higher gears from 2.5:1 up to around 3:1 ratio are in order.  It is easier to think in terms of gear inches to compare gears.  Gear inches are calculated by dividing the front chainring by the rear cog and multiplying by the wheel diameter (roughly 27" for a 700c road wheel).  Thus a road bike with 45/18 ratios would have a 68" gear (45 divided by 18 = 2.5 x 27" = 68" approx). The normal recommended range of gear inches on road is around 65" to 80" depending of course on how hilly your area is.  Something around 70" is a great starting point for typical use in a flattish UK city.  You don't want to go too low and be spinning like a lunatic downhill or too high and busting your knees going up hill.
Here are a few more examples of other road ratios/gear inches; 45/19 = 64", 44/18 = 66", 45/18 = 68, 48/18 = 72", 48/17 = 76", 45/15 = 81", 48/15 = 86".  Sheldon has an excellent gear calculator on his website.

17. How do I fit bars to quill stems without scratching them?

For our dedicated page on this please check our blog bar fitting article.
18. Tell me about the various handlebar and stem sizes.

As with many bike components it is definitely not a case of one size fits all.  Road bike, mountain bike, BMX - all have more than one bar and stem size together with a variety of fork steerer sizes making for a lot of combinations.  The majority of mountain bikes now use the common 1 1/8" size with a clamp on ('A-Head') stem and non-threaded steerer.  The smaller 1" and quill (expander wedge type for threaded steerer) stems have largely become obsolete and only to be found on many a 'retro' build.  The common handlebar diameter for mountain bikes is 25.4mm with the oversize 31.8mm becoming ever more popular.
Older steel road frames typically used for fixed wheel and singlespeed conversions have a threaded steerer and require a 1" quill stem.  More modern road bikes and most off the peg fixed wheel bikes now use a 1 1/8" clamp on ('A-Head') stem with non-threaded steerer.
Again within these two common sizes there are also variations in the handlebar clamp diameter.  Modern stems are simpler with most using a 26.0mm or 31.8mm clamp.  Older 1" quill stems generally use a 25.4mm clamp or 26.0mm on more modern models.  However, Cinelli make the most popular older stems and bars and they have their own standard of 26.4mm.  All these are nominal sizes though - the bar is a fraction smaller than the stem to fit into the clamp.  Measuring a variety of Cinelli 26.4mm bars in our workshop they vary from 26.20mm to 26.35mm.  Similarly Cinelli 26.4 stems vary too especially when they have been 'opened' and 'closed' many times.

So, can you mix the handlebar sizes?  Firstly, the ideal fitting is one perfectly matched to the other - A Cinelli '26.4mm' (nominal) bar in a '26.4mm' stem etc.  But with the aid of shims or otherwise bars and stems can be mixed to a degree.  A 25.4mm bar can be fitted to a 26.0mm stem using a Nitto shim for example.  You can 'make' shims from aluminium cans but the real thing is better.  A 26.0mm bar is quite often usable with the thinnest 'coke-can' shim in a Cinelli 26.4mm stem.
We make our own Squeeze bar in three sizes of 25.4, 26.0 and 26.4mm.  If in doubt, measure your own stem opening and email for advice.  In general, the most important thing when fitting bars to a 'split' (single bolt) clamp, eg Cinelli 1A or XA stem, is to remove the clamp bolt and very gently open up the clamp a fraction with a soft-edged tool while at the same time sliding the bar in.  Failure to do this will inevitably lead to horrble scratches on your lovely new bar!  See the blog bar fitting article for more.  Finally, only fitting that the last word on this FAQ should go to good old Sheldon who as always has all the handlebar and stem fitting info on his website.

If you have found this guide useful please do remember to rate our guide at the base of this page - thank you!
Thanks for looking, once again do please email if you have any questions not answered here.

VeloSolo 2011

Please visit the VeloSolo ebay shop for over 150 fixed and singlespeed products 

Please see Part 1 for: General Fixed FAQ's & Can I run a fixed wheel on my bike?

Please see Part 2 for: Set-up questions

Please see Part 3 for: Other technical and miscellaneous questions

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