Calling all CX bike sizing experts!

RonanCFD

I'm looking at getting a Focus Mares CX bike but I'm struggling a bit with sizing.

Both my road bikes have 570 effective top tube, and I'm running 120mm stems on both. I just assumed that I would go for similar top tube length on the CX, but this puts me onto the largest available Mares (60, XL). The retailer (in Germany) has recommended a 56 (M) based on my height of 183cm - two sizes down from what I expected!

Do people usually go shorter on CX bikes than their road bike size?

I should add that this is going to be more of a do-it-all bike rather than being CX raced a lot, and it will probably spend most of its time on the road with slicks. Its not really an option to use a LBS for help with sizing as this particular bike would literally be 2.5 times the price.

Here's geometry for my (very comfy) winter bike (note they got 1 & 2 muddled on the diagram):



And here's the Focus Mares geometry:


Thanks all!

Lumen

What is your saddle height from BB centre to saddle top measured along the seat tube?

RonanCFD

760mm

Lumen

IMO the XL will feel way too big. The head tube is steeper and the seat tube is shallower than your Equilibrium, so I think you get more effective reach for a given top tube length.

Although the head tube on the Mares looks short, the fork is longer so it'll feel quite tall in a given size. The stack on your Equilibrium is half way between those on the size M and L Mareseses. For pure CX use I'd probably pick the M and size it up with a longer/risier stem but if you're using it on the road a lot the L might be more comfy.

Stack aside, CX bikes tend to feel bigger due to the higher BB, larger tyres and longer wheelbase.

RonanCFD

That all makes a lot of sense. It will see a lot of road use so sounds like the L is the way to go.

Thanks very much for the advice!

My only other concern is the cantis - are they as bad as half the internet thinks they are? By the looks of it, the ones it comes with (Avid Shorty 4) are not the greatest but I'm happy to change them if need be (say to Avid Shorty Ultimates). There is a disk model at a fairly good price but the deal is not so amazing, and the colour scheme might result in me getting a bit of grief in my intended place of use!

dave2pvd

I agree with L.

We're actually around the same height and use same top tube: I'm 6'1" and go for 565mm on the road. For CX, I bring the bars back 1cm and up 1cm. Looks like the L will get you there.

If you do end up using it for CX, the last thing you need is to have too much weight on the front wheel. So that's an argument against going too small - a long stem will put you too far over the front axle.

Re cantis: don't read into the hype. Go on Shelton Brown's website and use his setup guide. It's detailed, but if you have that geometry right and good pads installed, you end up with very effective brakes. Of course then your pads wear and you have to recheck and adjust, which is a pain.

RonanCFD

Thanks, Dave, L it is then. And thanks for the reassurance on the cantis - I'll have a good look at what Shelton has to say about them

Weepsie

I've a Focus Mares CX Comp in that size. Welcome to try it out for size assuming the geometry is still the same or size. I'm shorter, and use 54 road bikes, but this is just my runaround/commuter. Might end up having to move it on when I eventually get fitted.

RonanCFD

Thanks, Weepsie - any idea what year it is? I'm amazed at how much Focus change their geometry charts each year!

smcclaw

I'm 183cm and have a 2015 medium mares (disc) which you're welcome to try.

Weepsie

RonanCFD wrote: »

Thanks, Weepsie - any idea what year it is? I'm amazed at how much Focus change their geometry charts each year!

Its a 2010, so quite possibly changed in that time

RonanCFD

Thanks both of you, are either of you on the North side?

Weepsie

IFSC mon-fri (though I'd need notice as I sometimes get a lift into work). Navan Road area otherwise and pass through Glasnevin and Dub 15 a lot.

RonanCFD

Weepsie, I did a bit of googling and found the chart for Mares 2010 models:



So it looks like your size L is what Focus are calling an M now!

<edit> actually the numbers are looking quite different, top tube & head tube don't align with the 2015 geom</edit>

RonanCFD

Weepsie wrote: »

IFSC mon-fri (though I'd need notice as I sometimes get a lift into work). Navan Road area otherwise and pass through Glasnevin and Dub 15 a lot.

Thanks, I'm in Portmarnock but occasionally in D15. I'm feeling pretty confident about the size now though, so its probably not worth putting you to lots of trouble.