amazinmets73

I am currently building a cyclocross bike that I intend to use for commuting, off road adventure riding, and racing. Obviously, that's quite a load for one bike, and I'd like advice on what gearing combination will best suit those needs. If possible I want to use only one chainset, so I purchased a mountain bike RD in order to use a cassette with a wide range of gears.

My thinking is that a 53-39 or 52-39 is paired with a 11-34 cassette is optimal. For road riding it will give me large gears for flats, and small enough gearing to spin up most climbs, and I can live with the large jumps between gears; for off road gravel grinding-touring I'll probably be using the lighter gears on the top chainring; for cross racing I'll drop to the 39t gear and race using only ring.

krobinson103

If you want options what about a triple? I've tried getting 53-39-30 and 48-36-26 and find both are very good when it comes to versatility. Otherwise a compact 50-34 and 11-34 gives you a good low range and a decent high range. Its really hard to build a single bike that will do it all so you have to compromise somehwhere usually. I eventually settled on the 48. I don't race so speed isn't important but I do tour so lower gearing is more useful than high gears that only get used on the downhill.

amazinmets73

Isn't 50-34 undesirable for cross racing? 50 being too high and 34 too low?

CharlyAlfaRomeo

I'd go with compact in front paired with a wide range cassette. The difference between 50/11 and 53/11 is negligible below 65 KPH or so.

I'd maybe even go with 46-34 considering you want to ride off road and race. Honestly 52 and 53 tooth chainrings are unnecessary with an 11 tooth cog unless you need to hit 80 KPH regularly.

amazinmets73

Oh, I should have mentioned. I'll be running 9 speed

CharlyAlfaRomeo

I'm not sure why that would matter.

krobinson103

It won't other than changing the spacing. An 11-34 9 has some pretty big gaps. Good for a tourer, not so good for a racer. At any rate if 50-34 isn't good for cross 53-39 would be worse. You'd get even less low and a high thats only useful downhill on a good road.

amazinmets73

What would you think of a 48-36? My main concern with that option would be its performance on the road

krobinson103

I'm running a triple 48-36-26. On the road with 48-11 you get a good top speed of around 50kmh at 85rpm - not that I can hold that sort of effort on the flat anyway and not kill my knees. A lot of dedicated cx bikes even come out as standard with 46 so 48 is a pretty good compromise. Honestly unless you plan on road racing then 50 is overkill. In any event you wouldn't race against road bikes on a cx bike anyway. Different sort of machine.

TGT1

Just went from 34/46 11-32 to 34/48 12-32

Don't know about racing, but it's about the perfect road + gravel grinding setup.

today's loop included;

34.6 miles total
5 mi fire road (dirt)
2188 ft gain
max grade one mile average 7.3% (estimated max grade for multiple short (<100 yd) sections on the fire road 15- 25%)
39.83 mph max speed
111 rpm max cadence
12.7mph average speed.
+
The average cadence was 60, but cyclemeter doesn't have a cutoff rpm so decelerating and coasting figure into the average. Going off the graph the median was about 75-80 rpm.

Why a 50t big ring and an 11t small cog are industry standard for a compact is a bit bewildering.

The 36/46 11-32 standard also has some annoying gaps right in the middle of normal road cruising speeds and isn't really low enough for grinding up fire roads, although in a CX race you'd probably dismount and run up anything that a 36 wouldn't handle.

The 48 - 12 only gives up 5 gear inches over the 46-11. Both get you north of 30 mph @ 90 rpm.

gamby

My cross beater currently has a standard 50/34 compact and a 9-speed 12-32. I have a 46T ring coming in the mail, just to get the gaps a little closer. I like the 34-32 dump gear, which I can spin up just about anything (on or off-road) and I don't see myself taking this bike to speeds where the 46T won't be enough gear. I have another dedicated road bike for that (with a 50/34 and a 10spd 11-28).

Kopsis

How fast do you ride? You won't use a 53-11 at anything less than 30 MPH. A 46-11 will carry you all the way to 33 MPH at 100 RPM. For descending hills, you might want more top end, but the idea that you need a big gear for flats is flawed unless your ability is well above average (in which case you'd have no need to go all the way down to 39-34 for climbs). The conventional 36t/46t or 38t/46t cross crankset has proven to be extremely versatile for most riders (hence it's popularity). I'd start there. You can easily swap it out for a 50t if you find the 46t limiting, but I doubt you will.

bikebreak

Are you married to a double?
52 42 30 is great for all around, I used that with a 12-25, great spacing

if it has to be a double I would try 48/34 with 11-28

amazinmets73

I bought a 48/34 crank... Question: for road riding, would it be preferable to switch to a 50t chainring, or use a 48t with a 12-21 or 12-23 cassette?

DirtRoadRunner

I wouldn't think so - I rarely spin out the 50/11 on my road bike, and occasionally spin-out the 46/11 on my gravel bike. It just depends on how fast you want to descend downhill - if you want some pedaling left above ~33 mph, then go with a 50t.

TGT1

if you have anything steep enough or a big enough tailwind to use a 50-12 the 34-21 or 23 either aren't going to get you up the other side or be enough to buck the headwind.

90 rpm on a 48-12 is over 30mph.

ThermionicScott 

I personally wouldn't. 48/13 is plenty for me up to 35 MPH or so.

SpeedyStein

I was running 50/34 with 11-34 on my Novara Zealo, and found the high too high, the low too low, and the 16t gap between chainrings would always make me spin out when shifting down to the small ring. This was my first "modern" road bike - before this I either had MTB (which mostly have 10t gaps between front rings - and a triple that could work the whole cassette from the middle ring) or "vintage" road - 52/42 or 52/40. I had to think about front shifting way more with the compact crank because of the huge 16t jump.

I normally carry 10-20lbs on a rear rack - clothes, lunch, and a book or two, and just couldn't push the 50t on the bottom half of the cassette. I am not a fan of crosschaining, so I would shift to the small ring frequently - making me either spin out immediately or cross chain small-small.

I thought about going to a 13-30 or thereabouts cassette, but that wouldn't make the front shifting any better. Instead, I installed a 46/36 crank, and I am soooo much happier with that than I was with the compact, because it eliminated the awkward front shifting gap. I can (loaded) push the 46t on the bottom half of the cassette without any issues, and 36-34 is plenty low enough to get me up any hill I am going to ride up. The transition to the small ring in front is much smoother too.

I think off-road is really where the 46-36 shines though, since I can work through the cassette and the chainrings without really changing my cadence - a very useful touch when trying to balance grip and torque while climbing a hill with loose dirt/gravel on skinny tires. Essentially, the gearing increments feel more like the MTBs that I am used to.

That said, for unloaded road riding, the 50/34 crank was fine, and I think a 48/34 would be good for all around riding with a wide-ish range cassette. I would probably go with a 12-30 or 12-32.

fietsbob

Get the 50-34t crankset, 50:12 should be high enough..
when you want to race Cyclocross simply change the Chainrings .. they bolt on .
and swap the chain and cassette , to suit the race..
IDK what your Course layouts are to say what sizes you need .. common when bought in CX bikes

from The factory, specs, builds are 46-36 or so , but 42t single rings are used too..

Sunday night , put the commuter stuff back on (hopefully you did not crash & bend up or break things)

Gus90

+1 on the 46/36 vs the 50/34, my first cross bike was a 2013 TCX Advanced SL frame that I got used and slapped on some used parts including the compact gearing, I always spun out shifting between the front rings. I've since gotten a new TCX with the 46/36 set up and it's way better for multipurpose riding. I don't miss the 50 at all and changing between front rings is drastically improved. No more spin outs. My average speed, top speed, etc has pretty much stayed the same as before.

SlowJoeCrow

36T inner rings are awesome, they don't spin out as quickly as a 34T but still climb much easier than a 39T standard ring. Also if a standard 36-46 CX crank is too low at the top end you can run a 36-52 mid-compact road crank or DIY with a 48 or 50 big ring. Personally I run a 36-46 with an 11-28 cassette on the road and when I'm in shape that gets me up anything I'd want to climb, although I do prefer a 12-27 cassette for actual cyclocross use since the gearing is more smoothly spaced and anything steep is a run up.

DinoShepherd

If you are considering going 1x, may as well go all in.

I ran a 44 in front with a 11-36 in back and it was pretty awesome for all around. The only challenge was running out of top end on very fast group rides. But it was plenty of gearing for our local cross races.

Jiggle

Thanks for telling us your weight, approximate FTP, and prospective terrain this gearing will be used for. This information really helps us all make informed suggestions.

Barrettscv 

II also agree with the triple.

Triple divetrains are the most versatile. I use 50, 39 & 26 chainrings with a 12-27 ten speed cassette with a tighter 12, 13, 14, 15, 16, 17, 19, 21, 24, 27 cogset. The middle chainring does it all on flatter routes unless I'm enjoying a tailwind or I'm in a paceline. The large chainring is perfect for fast conditions, above 22 mph. The granny gear helps with steeper climbs, but is very rarely used.

The 50 & 34 compact double inevitably require the use of both chainrings in the 15 to 20 mph speed range. I'd rather just shift across the cassette while riding on flat routes and then use the big or small chainrings when the riding becomes very fast or when the route is very steep.

A 39 chainring with an 12-27 cassette has a faster speed range than a 34 chainring with any 11-2X cassette. The 34 chainring 11 cog combination provides 23.2 mph while the 39 chainring 12 cog provides 24.4 mph at the same cadence and tire diameter. Also, a triple with a 12-27 provides both a wider range and tighter cog spacing than a Compact with any available 10 speed road cassette if a 26t small chainring is installed.

The popular Compact and 11-28 cassette combination is inferior to the 52, 39 & 30 triple with a 12-27 cassette. The triple provides both tighter cog spacing with a very usefull 12,13,14,15,16,17,19 block that can be used from 15 to 33 mph. Please click on the link below, it will take you to a graph comparing popular double and triple divetrains.








I also use triples on my vintage bikes. I'll use 48, 36 and 26 chainings with a 13-24 freewheel.