During the 10 cyclocross races I did this year I often found myself riding solely in my small 34t chainring and was unable to change up and down quickly enough between corners and barriers to be able to make use of my 46t. The group set usually takes 2-3 total revolutions of the cranks to do this if it doesn't drop its own chain. To remedy this I am planing on running a 39t instead but I just wondered whether more experienced people could help me find the answer.

I am racing on a 9 speed Shimano Tiagra and was wondering whether this is more to do with the level wear of the chain rings or if it could possibly be blamed on the budget level quality of the group set. Do Ultegra group sets shift quicker or are they more about weight saving, would the best place to start be a proper service at the bike shop?

  • I doubt the fact that its Tiagra vs Ultegra or whatever has anything to do with it. Sounds like the derailleur is misadjusted, which you could either adjust at home and experiment or take it to a bike shop. – Batman Jan 20 '15 at 17:09
  • I'd expect to shift in 1/3 of a pedal rev if it's well adjusted. And I assume my front derailleur is on a par with my rear which is only Altus. – Chris H Jan 20 '15 at 20:03
  • My shimano CX70 crankset (36/46 teeth) with CX70 derailleur shifts extremly well. Almost like a rear derailleur. So I’d say it’s more a matter of components than a general problem. – Michael Jul 2 '15 at 15:50

It should not take 2-3 revolutions to shift modern chainrings. There are possibly a few things going on.

  1. Your larger chainring does not have the pins and ramps required to shift quickly.

Sometimes cross sized rings don't have all the bells and whistles.

Pins and ramps

Your big chainring should have those features. If it doesn't get a new ring. Race Face and Black Spire make 110BCD rings with pins and ramps in cross racing sizes.

  1. The derailleur needs adjusting/replacing.

The derailleur cage needs to be positioned such that it is about 2-3mm above the big chainring. The cage also needs to be curved such that it closely matches the curvature of the big ring. 46t is right at the size where a standard road derailluer has problems. It should look something like this.

showing proper 2mm clearance

If you can't get the derailleur close on both top and bottom, you can either get a cross specific front derailleur, or grind the cage of your current derailleur to match the curvature of the big chainring.

  1. Your shifting technique needs practice.

As someone who learned to shift before indexing, I have some habits that I only recently learned modern beginners often never learn. Even with indexed shifting, on the front you need to push the lever beyond the click until you hear the chain catch. This is something I was doing unconsciously since that's what friction shifting requires, a slight overshift and trim. Recently in helping a beginner learn to shift, I took a closer look at what I was doing and they weren't and realized that they let go of the lever as soon as it clicked, not as soon as the chain engaged the big ring. This makes a big difference in how fast the chain shifts.

They also needed to learn the subtleties of soft pedaling during the shift.

Modern chains and rings have gotten so good that in normal situations ( 39/52 on the road), you can often go a long time before these tricks become unconscious. Cross racing is tweaking the boundaries of what the shifting system can do for you and requires learning these old school techniques.

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Yes higher end riders will go with a larger front chain ring on parts of some courses or they would not have one.

Higher end will shift faster and it could also be an adjustment thing.

And some riders go with just a single up front (e.g. SRAM has the CX1). With a 9 speed in back it is harder to get the range with a single up front but with an 11 speed in back it makes a single more of an option. You save some weight and also get a little more ground clearance.

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Single ring up front can be a very good option but it really depends on the course. Do keep in mind that this is cyclocross RACING. I've seen (and passed!) many riders who seem hell bent on riding every inch of the course. That's not how things work in cross. Sometimes you're much faster getting off the bike and running. That said, keeping two rings up front makes the bike a LOT more versatile for everything else.

Another poster (Fred) covered most of what you should be looking at but here's a few other things to consider:

  1. Check the teeth on the chainring. Feel to see if any are hooked. The tips of the teeth should be smooth or they can catch the chain and keep it from cleanly releasing the chain. If you find any burrs carefully file them so they're smooth.
  2. Make sure the rings are mounted correctly. Rings these days are designed to operated together and for this to happen the ramps need to be properly aligned. There will be an alignment mark to indicate how the rings should align. Pretty rare for this to happen but every great now and then you see it.
  3. Make sure your cables are clean. Cross destroys cables! Shift your bike into the big ring. Now without pedaling shift down into your small ring. The chain will stay on the big ring but the cable will no longer be under tension. This will allow you to pop the housing out of the stops. Slide the housing to one end and wipe down the cable. Repeat in the other direction. Drizzle a little lube on the cable and wipe off the excess. You should do this for all of your cables and do it after every race or wet/muddy ride. If you race a full season expect to replace your cables at least once a season. I used to wrench for a cyclocross team and we'd replace cables at least twice a season here in the wet Pacific Northwest.
  4. Check the angle of the front derailleur in addition to its height. Looking down onto the derailleur the outer plate of the cage should be parallel to the chainrings. Sometimes derailleurs get knocked a little out of alignment and it's amazing how big a difference being just a little off can make!
  5. Consider a larger inner chainring. The smaller the difference in teeth between the rings the better things will shift and the less likely you are to drop a chain (this is why at Paris-Roubaix teams will often switch to a 44 or 46 tooth inner ring since the race is flat as a board). This really depends on your local conditions and fitness. If your conditions are generally pretty dry than a 34 ring is a bit on the low side. If you need a 34x27 (or lower) gear there's a good chance you'd be better off by running. OTOH if it's muddy you'll want to keep that 34.
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