I've bought a new groupset for my commuter / cyclocross pit bike / sometimes turbo bike (Its an old Ridley X-bow tat was my first cx bike). Based on recommendataions here I went with Tiagra 4700 (I needed 10sp). Because it was a full groupset it comes with a 50/34 chainset. That's great for my commuting but less good for cx. Thing is I'll only use it for cx as a spare/ pit bike when it's muddy and I can get pit crew (I commute 3-4 days a week most of the year compared to half a doznen days when I'd be using it for cx racing (and some cx training)). Is it worth spending the £60 (less whatever I get for the tiagra chainset) on a 36/46 cx50 chainset? I'd save 100g and get standard cx gearing. I question whether its worth it though - I'll have more range as is.
So why do people have little differnece between the two front rings for cx.. the only things I can think of is a) easier to shift betwen closer spaced rings if a bit mud-clogged; b) you don't need the massive range; c) a 50t chainring would be big enough to get in the way when shouldering...
Thoughts? I've never noticed needing a bigger range tha 36/46 before.. at the point I start spinning out i'm going downhill at about 50kmh which is quite fast enough for me!!
big chainring looks more pro innit? Aren't single ring setups popular for cx bikes now anyway? The make more sense than a double for that application
you'll probably get most of 60quid back for the tiagra chainset, chainsets always seem to be fairly expesnive regardless of tier on ebay.
The 34 bit was never a problem. You'll probably not need the 50 but I wouldn't have though it would get in the way, it won't be hugely bigger than a 46t.
I assume finding a 46t is tricky for an asymmetric shimano setup ? Have you looked at spacycles/zepnat/superstarcomponent/sjscycles to see if they have cheaper options.
36/46 is still nowhere near 'standard' CX gearing, it's just what's been provided on lots of bikes since 110bcd became a thing so has become normalised.
38 or 39 inner with 44 or 46 outer was the king for a long time when 130bcd was the usual unless you ran a single with guards, which was usually a 42.
The reasons for small gaps were pretty much as you say - because it made for fairly easy front shifts in thick mud that were worth 1 or 2 sprockets, the fact that CX takes place within a narrow range of speeds (running pace up to about 25mph), and also because a smaller outer ring allowed you to do the start effort on it and bang up the block rather than risk a full-power front shift halfway down the start straight.
Narrow-wides and 11/12spd pretty much makes a double obsolete for the vast majority of people.
Cheers all,
@jonba - yeah I've looked everywhere I could think of but the cheapest (and I wasnt sure it was quite right) was £85 - Genuine shimano ones seem only available at Ultegra level for £120!
As its my commuter as well as a spare cx bike (plus 10speed max) I'm not going singlering - especially in wales! I struggle in easiest gear on one of my regular hills at the moment.
If the thick mud is the reason - and I'll likely only be using it in thick mud I probably will just buy another chainset and hope @joshvegas is right about decent resale!
I'm not a racer but went from sub compact to a 34/50 with a 34t cassette when it wore out. Gear range almost identical, but significantly cheaper than a sub compact drivetrain.
I've not done many cx races, only started last season
I've a 36/46 x 11-28. I've (deliberately) never used the front shifter at all in races (to avoid droppy/snappy chain) so effectively I'm 1x10 but with two sets of ratios, one for hard or flat ground and one for clag or hilly - chosen after the practice laps. Worked fined for me. You might find that 50/34 works in the same way for you (can't imagine a "typical" course where you'd be switching between the two mid-race)
(I had never imagined a world where one might use the big ring for the starting effort! 😥 )
I found that conditions dictated what gears you needed for a course and unless the course was pan-flat and dry, a 50 ring was near redundant, plus shifting on a 44 or 46 was a lot easier. On really muddy events, I'd often just end up on small ring / big sprocket and leave it there as shifting would usually result in a jammed or shipped chain. I do remember an event in Oxford at the beginning of one season where I was gridded and we started at the far end of a football pitch so we got to gallop the full length of the pitch on our big ring to get the 'hole shot' into the woods - just before that there was a slight bank but the lead rider hit it at 20mph, launching himself into the air for a quite spectacularl OTB
I run either a 42t or a 38t single ring with 11-36 11 speed cassette on my CX bike and in those guises it's been a commuter, a CX racer and monster CX racer and a 200km plus sportive bike.
I don't see the point of a double, be it a compact or any other style for any of the above if I'm being perfectly honest.
On my good cx bike I'm running 42t and 11-32 11sp. That's great for hacking around a race course but I don't think I could make that work for all occasions
@scaredypants - I often think it's safer to do the reverse if things are getting gunked up badly; just keep it in the middle of the block and shift between the two front rings (rationale being the front mech is stronger).
Anyway- I've been given enough ammunition to back up my desire to switch the crankset so job done 😂