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I am 5’10.5” exactly, with a 31.5” inside leg.
IIRC, my road bike, which feels great to ride, is 55 cm, while my previous road bike, which didn’t, was 57 cm.
I have been told to size down for CX. How come? Do you think a 56 cm frame would be too big? (Trying it out before buying is not an option in this case.)
Size down advice is for racing, and even then I wouldn't say it was explicit as that - you just want to avoid a top tube in the baws when you're throwing it around on a Sunday. So a not-on-the-bigside bike is important. If it's not for racing then I'd be trying 56s definitely.
I think the sizing down thing is because you move about much more on the bike when you're off road. Personally as I only use my cx bike for reasonably tame bridleways I'm on the same size frame (57 @ 6ft1).
You want a 54. Same size as you and a top tube of 55 is what you need. You can adjust reach with stem, it not stand over.
Brand will magnify this. A CAADX in 56 will feel huge. A Boardman in medium will be fine, as will a medium TCX
I'm exactly the same size and just bought a Ridley and it's a size 52. Their size chart recommended it and it's fits well.
It's all about stack and reach.
Look at the frame geometry stack/reach and perhaps standover specs from ~54cm to ~57cm, decide how upright you want to be and how much you care for your crown jewels.
I could be wrong, but I wouldn't expect the stack and reach needs to be much different between a sportive road bike and a CX/adventure.
My 58cm Cube Attain GTC Pro Disc has 588mm reach and 610mm stack, if I downsized the 56cm would have 385mm reach and 591mm stack, which could potentially risk upsetting my weakened middle aged lower back. https://www.cube.eu/uk/products/road-race/attain/cube-attain-gtc-pro-disc-greynflashred-2016/
The Cube Nuroad Pro has very similar stats, 389/609 vs 386/588 for the 58/56cm frames. The smaller frame has a lower front end than the Attains, not a likely choice for me. https://www.cube.eu/uk/2018/bikes/road/road-cyclocross/nuroad/cube-nuroad-pro-blackngrey-2018/
Similar rider stats here, ~178cm with ~83cm cycling inseam, long torso and short legs for height.
I’m exactly the same size and just bought a Ridley and it’s a size 52. Their size chart recommended it and it’s fits well.
Interesting. I am the same height as OP and have an X-Trail, but in size Medium which Ridley claim is around a 56cm. I was a bit worried about it being too big, but it's absolutely perfect and I can spend all day chucking it around without a problem. A small would have been too short for me and would have given me a very upright posture which I don't really like. Geometry-wise, it's quite similar to my 56cm road bike, but with a much lower top-tube (more MTB than road), so my gentleman's vegetables remain safe and secure.
Size-down - extra standover if you have to put a foot-down on the downward slope. Also, if your racing or riding technical stuff, particularly being able to get your weight over the back wheel for extra grip - my CX bike set-up has a slightly shorter stem and bigger saddle set-back - means you can drive through with your quads whilst seated on the really muddy stuff - can be the difference between riding and running.
I'm 5'11" with a 32" inside leg, I ride a 56cm Allez on the road and race a 55cm KTM Canic CXA.
I wouldn't bother sizing down too much, it's a bit like the smaller MTB's are more chuckable myth
Daft idea, I know, but how about you try before you buy?
Daft idea, I know, but how about you try before you buy?
I did, but it's hard to get a feeling for the fit of a bike in a relatively short test ride. I'd need hours and hours on the thing before I'd be 100% confident that it fits.
Also, for many people, it's not practical to buy from an LBS (or even a not-so-LBS) as these bikes are still not as widely stocked compared to road or MTB. The huge LBS near me which prides itself on being one of the biggest in the country has a pathetically small range of CX/gravel bikes considering the size of the shop.
My "CX" (read: mixed terrain, not racing) bike is based on the exact same frameset as my road bike. I have something like 15mm extra of spacers under the stem on the former, but other than that they're basically the same (same length/angle stem, similar bars, same seat position—though a slightly more forward seat position for off-road wouldn't be a bad thing in principle). Works for me: gives a slightly more upright position and a bit more stack for getting out of the saddle, without being cramped when seated. YMMV.
though a slightly more forward seat position for off-road wouldn’t be a bad thing in principle
Says the person that's very obviously never ridden a very muddy CX race - puts more of your weigh over the bars and you'll probably wash-out on the first corner. Get out the saddle and your back wheel will fishtail as it struggles for grip.
Says the person that’s very obviously never ridden a very muddy CX race
What, the person who explicitly said "not racing" (and "YMMV") in his post? Well deduced, Sherlock 😉
It's hard to know what "CX" means when someone asks about it. It might mean racing, but much of the time people use it to mean other things. If it means racing in this case then what works for me isn't terribly relevant, hence I qualified my reply.
5'10" here and a similar inside leg to you OP; 56cm on the Road and a 56cm "CX" bike too, although I'm sure it's considered more "Gravel" by current standards, I've done a couple of CX races and didn't die to bits.
More important than the Seat tube length is the reach and relative bar height IMO, again both my Road and CX bike frames have similar top tube/reach lengths, but I use a 10mm shorter stem on the CX bike and the bars are ~10mm higher than the road bike.
Both use 44cm compact drops seat heights are similar and saddle position relative to BB is set up about the same, same crank length (Although the Road bike is using SPD SL where the CX has SPDs), basically their respective positions are very similar but the bike that goes off road allows me a slightly more upright position at the front...
The advice to Size down for CX is probably based on shortening the reach relative to your road bike a little to allow you to sit up more off road, but of course that assumes you wouldn't just change the stem from stock if you bought an 'L' rather than a 'M' sized bike...
personally I'd size it similarly to your road bike but be prepared to change the contact points to suit.
As ever YMMV...