Cyclocross is the dominant form of racing for my cycling club. So to give me the option of occasionally joining them I have picked up a CX bike that I will mainly use as a winter bike that has come with rival 1x. My club also ride the Roubaix sportive so I will probably also use it for that as it will save my road bike a beating and allow wider tyres for the killer cobbles.
As a low cadence big gear TT’er the gearing it came with is somewhat different 42chainring and a 11-40 cassette. I have a 1x 50t sram chainring I can put on though the cranks it came with are 172.5 rather than the 170’s I usually ride on the road or the 165 on the TT bike.
I am trying to decide my best options crank and gearing wise:
• Keep current cranks (what’s 2.5mm between freinds) and stick on sram 50t chainring for road (with longer chain). Plus no extra cost, minus crank length difference, no powermeter option - but winter miles, group rides maybe less important.
• Fit a pair of rotor 3d24 170 cranks I have spare the are 110 so presume the sram rings should fit. Plus crank length matches road bike, no extra cost, minus 2x crank so chain line not as good, no powermeter.
• buy a sram cx1 crank in 170. Plus chainline, chainring compatibility, minus extra cost (can sell rival cranks though), no power.
• buy a shimano 170 crank. Plus I presume I can use my Dura Ace 9000 4iiii left crank arm off my road bike with a GRX crank set? Plus if grx 1x chainline, minus extra cost, not compatible with the Sram 1x road rings I have (though have 4 bolt 1x TT rings from my Rotor P2M cranks on TT bike).
I plan on picking up a spare set of wheels & sticking on a 11-32 cassette (or 11-28).
Any advice on if it is best to stick with 1x cranks for optimum chain lines, and if it is best to keep with a crank length I am use to greatly appreciated.
SRAM makes 1x cranks in both 110 and 130 BCD across their group sets. I believe they make a 42 tooth ring in both sizes so you need to check what you have in terms of the crank. SRAM only makes the 50t ring in 130 so it may not fit on your cranks or you may have a 130 bcd 42 tooth that won’t fit on your spare cranks.
In terms of gearing I wouldn’t go any bigger than 42 x 1-40 for CX unless you only plan on doing dry flat courses. Mud really slows you down and unless you are supremely strong having something close to a 1:1 gear is useful. Even for the road I wouldn’t size the front up much if you are going to use a 11-36 or 11-32 cassette. You will be far better off running 2x if you really want a 50x11 gear plus a reasonable gear spacing on a road of CX bike. I know this setup works for some TTers but it requires always riding at race speed.
One thing to keep in mind is that the SRAM road cranks aren’t 1x or 2x specific. They are all the same cranks with either the same spider or a direct mount ring. Their chainrings are the only things 1x specific. They are machined from a thicker metal so the chainring is inboard a few mm from where it’s bolted to the spider. Putting a SRAM 1x chainring on anybody’s 2x crank will get you the chainline you are looking for. You can toss a SRAM ring on that Rotor you already have if you want the same crank length. You may not notice a 2.5 mm crank length difference, especially when on an entirely new bike.
Thanks for the info, I didn’t realise the srsm CX cranks were based on a 2x. I should have said I plan to switch between the 42t for CX and 50t for road / maybe some fireroad riding. I guess I could go 46t and try to cover all bases in one hit.
Depending on what wheels you have another option may be to switch the freehub to an XD driver so you can use a 9 or 10 tooth cog. That way you could still run a smaller chain ring for road.
I run a 40 tooth 1x setup with an 11-42 cassette on one of my wheelsets for CX and gravel, and 10-42 on another wheelset. I used to spin out the 11x40 combo on fast descents and paved sections, but havent had that issue running 10x40.
It does limit your gear options a little though. 3T has a 9 tooth cog in a 9-32 11 speed cassette. Most of the sram options will be 10-42 or 10-50.
Depending on what wheels you have another option may be to switch the freehub to an XD driver so you can use a 9 or 10 tooth cog. That way you could still run a smaller chain ring for road.
I run a 40 tooth 1x setup with an 11-42 cassette on one of my wheelsets for CX and gravel, and 10-42 on another wheelset. I used to spin out the 11x40 combo on fast descents and paved sections, but havent had that issue running 10x40.
It does limit your gear options a little though. 3T has a 9 tooth cog in a 9-32 11 speed cassette. Most of the sram options will be 10-42 or 10-50.
^ that’s what I was going to say.
Only thing is the 3T cassette is expensive. But its an easy swap if you can fit the XD driver. Maybe get a new rear wheel with it.
If its mainly a winter bike good to keep it simple. The 1x works well in the winter, I would always rather have gearing on the lower side, there’s no need to be going fast when its cold. Just put bigger tyres on and run them at 30psi to slow you down.
People win world cups on a 40, it’s also good enough for winter training. I use a 38 and it’s ok but I spin out a little on the road. For gravel I’ll run a 40 with a big cluster. I just use old octo link cranks
