Technical FAQ: Tips for cyclocross rookies

Lennard Zinn /
Riders during November's Koppenbergcross event in Belgium. Photo: Tim De Waele | TDWsport.com

Questions from a ’cross newbie

Dear Lennard,
I had my first taste of ’cross in 2017 on a touring bike and now I’m hooked, so I purchased a Giant TCX SLR1 to do double duty as my commuter and race bike. The Australian race season in my city starts in April 2018, and I have some tech questions so I can prepare my bike. Perhaps you know some people who are riding the northern ’cross season and can pitch in with their current setups this season?

I’m looking to purchase a set of race wheels so that I can still commute during the week (on the stock Giant rims and road tires) and swap out to lighter race wheels (tubeless CX) for skills training and race day. I don’t want a lot of hassle and adjustment when I swap out.

My bike has the 12mm thru-axles, the front is 100mm) and the rear is 142mm, plus flat mount hydro brakes and an 11-speed SRAM Rival 1X.

1. Is the 12mm thru-axle a standard that includes disc/hub/cassette spacing so I can do a hot swap without caliper or derailleur adjustment?

2. Is it safe to shim a rotor mount on one wheelset to get spacing compatibility between both sets? If so, would you recommend 6-bolt or center-lock for the race wheelset?

3. Is it possible to adjust the hub position and hence caliper/cassette position on the hub axle?

4. Would there be much derailleur adjustment if I went from an 11-36 (commute) cassette to an 11-32 (race) cassette, or would you recommend keeping the same cassette type?

5. If I have a race wheelset and cassette, would you recommend a race chain to go with it? I tend to use KMC with quick links, so swapping is easy.

6. I was also going to get a spare hanger and my LBS said to get it installed and pre-bent before putting it in the toolbox. Any other hot tips for a CX newbie?

Thanks heaps. Also, your book is great! 
— Murray

Dear Murray,
I’m glad to hear you’re hooked on cyclocross and that you get to start your season right after ours ends. My answers are numbered to match yours.

1. Yes, you should be able to swap straight across with your thru-axle wheels, and the derailleur and brakes should line up the same as on the other wheelset. That said, the positions of the rotors may differ slightly. See No. 2.

2. Yes, you can shim the rotors to get both sets of wheels to plop into your bike with no brake rub. I have done this with both 6-bolt rotors and with center-lock ones, although it is easier with 6-bolt rotors. For 6-bolt rotors, you can use shims like these, although you can use separate disc-caliper-mounting shim washers at each hole, or you can even cut your own shims out of a beer can. You can mount 6-bolt rotors (and a shim or two if you wish) onto a center-lock hub with an adapter like this.

I find that if you just have a little bit of brake rub, you can avoid the shimming process completely and just true the rotors to line up the same in the brake. In that case, it is irrelevant whether you have 6-bolt or center-lock rotors. You need a tool like this, ideally with a dial gauge on and a truing fork or two to very precisely get it straight in exactly the plane you want to not have brake rub.

3. No, you cannot adjust the position of the hub on the axle.

4. The best performance will be if you have the same cassette on both wheels. That’s because the chain will have to be considerably longer for the 11-36 than for the 11-32, and you will probably also have to crank down further on the b-screw with the 11-36 as well to avoid chain noise from the upper jockey wheel pinching the chain against the cog. If you then slap an 11-32 on there, there will be more chain slack than need be, and the upper jockey wheel will probably be constrained to stay further away from the cassette than is ideal, so shifting will be more sluggish. The potential for a jumped chain will increase with all of that extra chain slack having to be taken up by the jockey wheels.

5. Yes, if you are not using the same size cassette on both wheels. See No. 4 above. If you had two different chains, you could improve the shifting and chain retention by running a shorter chain with the 11-32. I still anticipate that you’d want to also loosen the b-screw a bit as well, even though you don’t want to do any adjustments.

6. I suppose that’s a good idea, although I have rarely seen the need to bend a new derailleur hanger into proper alignment. Certainly having the extra derailleur hanger is a must. It’s not a terrible idea to have an extra rear derailleur as well.

Here are some other tips for you:
— Mark your seatpost height at the top of the seat binder and check to make sure it does not slide down with repeated jumping on and off of it.

— Tighten your saddle well so it doesn’t slide back or tip back with repeated jumping on and off of it. Mark the rails so you can tell if it has slid back. Unless you’re a really lightweight rider, avoid carbon saddle rails.

— If you have Crank Bros. or Time pedals, set your cleats on the narrower release angle to aid in getting out earlier as you come flying up to a barrier.

— Put steel shoe shields under your cleats so you don’t crack your carbon shoe soles where the rear spring digs into it right behind the cleat. This is especially important with Crank Bros., Look, or Time pedals.

— Consider tubulars rather than tubeless tires for your race wheels. You will be able to run lower pressures without fear of burping air on corners.

Have fun!
— Lennard