[Closed] Road bike sizing???

I'm 5'9" and a bit and tend to ride 54 road bikes although sometimes I find I prefer their 56's. While it is of course down to personal preferences I wouldn't have thought a 54 is unreasonable if it feels comfortable.

Same measurements as you and I'm on a 54cm Trek Domane

Most brands 54cm is five six to five ten in height but that's only a start. Depends a lot on your build, also depends on the type of bike you're looking at, endurance geometry is shorter and more upright so can feel smaller than a similarly sized racier model. Also depends on how companies measure their bikes, top tube length a better way to size bikes than random measurement of seat tube.

If it helps, when I was shopping for my road bike I made a spreadsheet of the vital measurements of all the bikes I was considering.

I have a 54 Genesis CDA which I find comfortable and used that as a basis to go from, knowing I wanted something with a racier position, but ultimately similar standover etc.

Ended up on a Medium Genesis Zero (coincidence that the bike was the same brand).  I did originally want a Giant, but they didn't have the model I wanted in my size, I tried the next size up desperately wanting it to fit, the chart said it wouldn't be comfortable, it was right.

I did sit on the bike I eventually bought to be sure, but if I couldn't I'd have been pretty confident that the fit would have been good.

5’9” with a 31” inside leg here. Always gone for mediums/54cm frames. Last toad bike I bought I got a bike fit done and turns out I’m a 52cm/small framed chap. Went with it and is working out fine.

I’m 5’9 / 32” inside leg and on a 54cm Cannondale Caad12 disc. I think my Boardman Team Carbon I had before that was either a 53cm or 54cm model. The Caad9 before that was a 54cm too. I guess all of those are fairly racy geometry bikes.

I don’t think I’d be comfortable if I sized up - I wouldn’t really want a bigger standover height or anymore of a stretch to the bars. A taller headtube wouldn’t go amiss but I’ve left the bike with all the spacers under the stem as it came and I find that comfortable.

5'8" here and i'm on a 54/medium on every roadbike i have had. 56 is fine but definitely not smaller!

I'm an odd shape so about the same height as you but long back and short legs, always gone 54cm but needed longer stem and would prefer shorter seat tube. Gone custom now and all is happy. Don't be afraid to play around with a few different stem lengths to fine tune a fit.

Thanks for all the replies, I’m looking for an endurance style frame. I’m not looking to race and don’t have the flexibility to get right over the bars. Just wanting a bike more suited to faster rides. I spoke with ribble online and they recommended a small frame but if it didn’t fit they would exchange no problem. Canyon and rose websites push me towards the small frames, giant and genesis suggest medium.

5'10" and 31.5" inseam. Ride with maybe 9 or 10cm of saddle to bar drop.

I ride a 54 CAAD8 (100mm stem, 10mm of spacers, no top cap) and a 52 CAAD12 (110mm stem, 10mm spacers, 15mm top cap). Both have the same 40mm bars, 172.5mm cranks, and similar geometry numbers (bar the CAAD8 being little longer little taller).

The CAAD12 handles a lot better than the 8, not night and day but far more confidence inspiring and hence it is easier to ride faster.

You could try this as a guide.

https://www.competitivecyclist.com/Store/catalog/fitCalculatorBike.jsp#measures

No advice will be definitive though, you need to figure out what you like. Using the link puts me on a 53-54cm bike but most of them are just a bit too long in the reach for me so I tend to go down a bit. I'm 5'7" with 32" inseam (cycling, via the book rammed in crotch method) I switch between wanting a 50 and 53c Croix de fer but ride an old specialized road bike in iirc 56. Go figure.

5'10 and I fall dead on the boundary of most size charts for either 54/Med or 56/L.

If you've already got a comfortable position measure up the relative positions of the Seat/Bar/Cranks/axles.

My road bike is a 56, but with an 80mm stem and 440mm bars (probably not as intended by the designers), it might be the MTBerist in me but it seemed to make sense and the bike is comfortable this way.

My Gravel bike position (also a 56 IIRC) was set up mainly by measuring the road bike and transposing it, only significant differences are a layback post and a 10mm shorter stem, same width bars, same crank length, I did end up nudging the seat forwards so along with the shorter stem the ETT (if you like) is a smidge less but I take the bike offroad a lot more.

I've ridden 54s with stock stems (rentals) and the position is comfortable enough, but I think I just like having a slightly longer front end/wheelbase with a stumpier stem.

Just remember frame sizing is a guide only, the important bit is can you make the adjustments you need to actually achieve a position that suits you? Of course if you're already happy on a size 54 CDF why not look out for another Genesis Equilibrium/volant/zeal/Day02 in 54? the sizing should be pretty similar to what you know... Right?

A 54 is your size but geometry can make subtle changes in fit. Look at the head and seat tube angles. A half a degree in the head tube or seat tube is about a cm difference in top tube. You can make that up with saddle position on the rails or fit a longer stem if you need to. But different brands will, for the same "size", have different intial fit. I'm taller 179 cm but can happily ride a 54 Cannondale CAAD8. Cannondale come up a little larger.

You will need an effective top tube of about 53-55cm, but check those angles. Typically a classic 73 degree parallel is your starting point. Subtract a cm for 72.5 degree head angle, and a 73.5-74 degree seat angle.

The net effect of these changes - for exactly the same position relative to contact points (pedals, saddle and bars) is to move your centre of gravity relative to the wheelbase. That puts more or less weight over the front wheel. Your CDF is slack and has a shorter than typical stem, less weight over the front wheel, so will not handle as nicely as something with a shorter TT and longer stem. But my first port of call is always saddle position over the BB, not stem length.

If in doubt, size down, you can always fit to a size too small with a suitable longer stem, and the bike will handle much better. The caveat is whether the bars can be raised high enough due to length of headtube. Pros ride a size down for a lower front end when the stem is slammed. You don't have to!

TBH you're better off ignoring stated sizes because they are all variable between brands and even between different models.

Just concentrate on stack and reach, figures for which will almost always be available. Higher stack equals a more upright position. Longer reach is presumably pretty self-explanatory.

Geometry Geeks is a useful website - you can use the compare function to see how two or more different bikes will compare against each other for the key measurements.

Just remember to factor in your stem length and any spacers you run when you're trying to calculate the position you're currently running.

Stack, reach and perhaps seat tube length to make sure you have plenty of exposed post.

You would possibly fit a 56cm Cube Attain, 385mm reach and 591mm stack iirc. Size smaller than mine, I'm ~178cm and ~82.5cm inseam, could have done 56cm frame and had a bit more post showing plus slightly more aero position.

5'9" and 56cm frame here.

I ride 56cm frames and have been bike fitted to them, but all the basic guides suggest a shorter frame, no idea why the descrepency...

TBH you’re better off ignoring stated sizes because they are all variable between brands and even between different models.

Just concentrate on stack and reach, figures for which will almost always be available. Higher stack equals a more upright position. Longer reach is presumably pretty self-explanatory.

Stack, reach and perhaps seat tube length to make sure you have plenty of exposed post.

These are the replies you should be concentrating on tbh and I agree one hundred percent. From knowing my reach and stack height and looking at current upgrades for myself, I know I’m a 54cm in some brands and a 52 in others. Reach is the main factor really, seat tube measurement in a road bike means sod all. Especially when you think that some are sloped, some compact, some more traditional,etc.

I ride 56cm frames and have been bike fitted to them

By whom? Do you like lighter steering? How does it handle downhill on the drops?

Reach is the main factor really, seat tube measurement in a road bike means sod all

It didn't used to. Until Mike Boroughs came up with the TCR frame and the adjustability that meant only three sizes were necessary. In fact, the pros moaned and they made intermediate sizes as well, but the principle (and means of frame measurement) remain fixed.

Just to throw a curve ball in, I’m 5’8 and ride a 48cm road frame at the moment, slightly longer stem, low stack height (I was also fitted by a bike fitter for comparison). Next frame I get will likely be 50 or 52 depending on the brand.