Technical Progress

I fancy building a mountain bike again: it’s a while since I had one and I think I would like one again. I plan to use it for training in the winter as it’s more fun than using the turbo trainer (and I get too cold in full-Lycra outdoors). I also hope to go on some of the rougher-surface sky rides this summer: Cerys was able to do them on her hybrid bike but they were a little much for road tyres. To help with this endeavour I have been reminiscing about last time and looking at what’s changed in the market since then.

My recall of what I built last time is surprisingly definite, given it was 12 years ago, whether it is accurate is another thing: if Ed’s reading this perhaps he will tell me if I got things right:

  • Specialized S-Works M5 frame
  • Marzocchi Bomber air/oil forks – 100mm travel
  • Hope hydraulic brakes with 4-pot brake callipers and 6-bolt steel rotors
  • Race face low riser handlebars
  • 26″ Mavic Disc-specific rims
  • Panaracer Fire XC Pro 2.1″ tyres
  • Shimano Deore quick-release hubs for 6-bolt discs
  • 3×9 Shimano Deore XT drivetrain
  • Specialized road saddle

My thinking has, naturally, been around what I would do differently now. Things have moved on a little since then:

  • Frames and forks are now almost all disc-only. Makes things prettier and fractionally lighter but isn’t really important.
  • Hubs and forks now generally use a through-axle system rather than quick release. Makes the front-end stiffer and helps align discs with callipers more reliably, probably noticeable improvement to handling.
  • Some frames and rear-hubs also use a through-axle system rather than quick release. Makes the rear-end stiffer and helps align discs with callipers more reliably, probably no noticeable improvement to handling.
  • Wheels and tyres are now more readily available in other sizes, 29″ is particularly popular. Larger tyres generally reduce rolling resistance and improve ride quality but make the steering less responsive. The latter two are probably noticeable without data.
  • Tubeless wheel and tyre systems have been made viable by tyre sealant products and improvements to tyre bead design. Self-healing tyres is a big improvement over changing and patching tubes.
  • Center-lock disc brake rotor mounting system has been introduced. This is a theoretical improvement over 6-bolt disc mounting that reduces the chance of a failure mode I never heard ever happened and helps align discs more consistently.
  • Post-mount disc calliper mounting has become ubiquitous, again reducing the chance of an already-rare failure mode occurring.
  • Disc brake rotor cooling has improved significantly, improving safety.
  • 10- and 11-speed drivetrains have been introduced. Largely pointless.
  • Double-chainring systems are now commonly available. Largely pointless.
  • Single-chainring systems are now commonly available. This seems like a good idea to me as (from memory) I generally only used the middle ring when off-road. Having only a single chainring means you can get rid of the front shifter, its cable, and the front mech. It also means that you can use a chainring with deeper-cut cogs which the chain is less likely to jump from. The latest generation of chainrings have alternate wide- and narrow-cogs to match the alternating pattern of the chain, reducing chain noise.
  • Roller-bearing clutch derailleurs have been invented. These reduce slack-chain-related problems to the point of near-elimination.

From all the above technologies there is nothing so compelling that I would throw out a working component in order to get it. However some of them are worthwhile if you are replacing a worn component.

If you need to replace a rear mech, definitely consider exploiting the new clutch-derailleur system if you can. If this means you need a new rear shifter because the actuation ratio has changed it is probably still worthwhile. You should have no problem using a 10- or 11-speed cassette/rear mech with one-less-speed front system provided the chain is for the higher-speed system.

If you need to replace a 6-bolt-disc hub, it is worth considering the centre-lock disc mounting system. It’s designed to eliminate the very rare case when most or all of the 6 bolts shear under braking and there is consequently no connection between the braked disc and the rotating wheel. You can’t be immune from this even if you always use a torque wrench to tighten your bolts because the rotor expands as it gets hot under braking and thereby weakens the bolts. It’s probably more likely to happen on older bolts as repeated expansion-contraction cycles of the rotor lead to metal-fatigue in the bolts. You were probably happier with 6-bolt before you read this paragraph.

If you are replacing a quick-release hub, it’s may be worthwhile to get a through-axle hub and then use a quick-release converter axle to allow you to fit it to your existing frame/fork. If you then later replace the frame/fork you can then pick either a QR or through-axle replacement and you won’t need to re-replace the relevant hub. I would say this is a good idea on the front wheel as (a) the benefits of the through-axle are greatest at the front, (b) there are only two standards of front through-axle and it’s easy to know which you might later want on a given wheel (110×20 for downhill, 100×15 for everyone else), (c) most through-axle frames can also use QR hubs with an adapter (usually supplied with the frame) and (d) you’re more likely to replace the fork than the frame anyway.

If you need to replace a rim, get a designed-for-tubeless rim. Various manufacturers call this different things; I have seen at least UST, TRS, TCS, 2Bliss ready, tubeless ready and probably many more. If you see a diagram of a cross-section cut through the rim it’s easy to spot the designed-for-tubeless ones because they have two ridges in the bed which sit behind each bead of the tyre. You can use tubed tyres with tubes on these rims, so you aren’t committing to using tubeless tyres by buying tubeless rim.

Although it is possible I personally would not want to ride a normal clincher rim converted to run tubeless tyres; the bead-retaining ridges are important for rider safety in the event of sudden deflation when using tubeless tyres (they also reduce the occurrence of sudden deflation).

You don’t typically need to spend any money to try a single-chainring system. Just set your front mech over the middle ring, set the limit screws so it can’t move, and disconnect the shifter cable. Then if you like it after a few rides you can remove and discard the front mech, front shifter and the other chainring(s). Later, when you need to replace the remaining ring you can take the opportunity to fine-tune the tooth count and switch to the alternating-tooth-width design.

I’ll tell you what I’ve picked for my new build (and of course why) shortly. It was going to be in this post, but it’s already rather long (and I’ve not yet finished making all my selections).

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