Sizing question

[John Moore]

I'm looking to buy a road bike on eBay, to replace the Carrera Valour I've had for some time. Because I'm buying via eBay, I can't use the services of a local bike shop to get fitted correctly (and I don't know of one locally whose expertise I would trust), so I've been looking at the various calculators on the Internet to determine what size I need. Most come up with 56cm for me, a few with 58cm, one or two with 57cm. I am male. My height is 5'10.5" (179cm), and my inseam (crotch to floor) is 33".

I believe my proportions are fairly normal, so would I be safe to go for a 56cm frame and hope to make any required adjustments via saddle height? Or would I be better going for a 58cm? I.e., which is better to err on the side of, small or large? Or should I be able to get away with either?

The Carrera Valour is 'medium' size, which the booklet I got with it said was 'equivalent to conventional frame size' of 56cm (although I'm not sure what they're measuring). I've always felt it was a little too small for me, though, and use a stem extender with it. But when I sat on a 56cm Cannondale Synapse in a shop the other day, it felt just right. Don't know what, if anything, this reveals.

 

[festival]

The length of the top tube is more important than the seat tube length.
Buying mail order without checking the details is always risky.
The Valour has a semi compact frame design I believe and a medium would be about 52 cm and effectively about 56 but as I say its really only half the story as the top tube length will vary from model to model.
From what you say, your current bike could be a little small for you.

 

[John Moore]

When a single figure is mentioned for a frame size, I am right in thinking it's the seat tube that's being referred to, am I not? So a 56cm frame is a frame with a 56cm seat tube? I want to compare some measurements across bikes, to see if I can work out what I need - e.g., why the Cannondale felt good to me, where my Carrera does not, although nominally the same size. I imagine a key dimension is the horizontal top tube length, which is presumably a virtual measurement (i.e., the top tube itself is sloped and will usually be shorter than this figure).

 

[John Moore]

Just measured the Carrera, and effective top tube length is 56cm. Given that the seat tube is much shorter than this, I'm presuming that the 56 figure ('equivalent to conventional frame size') in fact refers to the effective top tube length, not seat tube.

 

[Canrider]

Just measured the Carrera, and effective top tube length is 56cm. Given that the seat tube is much shorter than this, I'm presuming that the 56 figure ('equivalent to conventional frame size') in fact refers to the effective top tube length, not seat tube.

It could, or, the 56cm refers to the seat tube length if the frame was a conventional diamond frame, rather than a modern 'compact' frame. This is to at least try and keep consistency between the sizing of different manufacturers, even if in practice there are a lot of confusing and confounding factors at play.
Here's a resource with diagrams showing the difference between the two:
http://www.velofitter.com/blog/2011/11/22/road-bike-sizing-why-its-confusing.html


FWIW, you're nearly the same size as me (6', 33-34" inseam), and I'd be shopping for a 58cm frame myself.

 

[goody]

If the Cannondale felt right then look up the geometry chart and check the horizontal top tube length compare that to whatever bike you are looking to buy. I'm 5'10" and my top tube is 55.5cm with a longish 130mm stem. But then I'm old and reaching to far makes my back ache. For me 58 would be too big, I could use it with a shorter stem i.e 100 mm stem would give me the same effective top tube length but if it was the same model the head tube would be taller and not as much seatpost showing maybe transmitting more shocks to the saddle.

 

[John Moore]

Thanks to all for the input. There are so many permutations and variables, it's hard to get a clear picture! But to some degree it is now moot. The eBay auction I was interesting in came to an end today and I ended up putting in a successful bid for a Forme Longcliffe 2.0 in size 56, with a little confidence gained from determining that its dimensions were very close to the Cannondale I tried a few days ago. I have already collected the bike, it looks really nice and I'm looking forward to taking it for a spin once I've replaced a punctured inner tube (mentioned in the listing). The dimensions are definitely different from my Carrera, and I'm actually wondering whether the Carrera might in fact have been a mis-labelled small size. Some playing around to be done, I'm sure.

 

[John Moore]

Just been out for a brief spin on the Forme, and it certainly seems to be the right size for me, as it feels natural without any adjustments other than saddle height. Maybe the 58cm would work as well, but I feel confident the 56cm can be adjusted to fit me perfectly.

Very puzzled about the Carrera Valour, though. It's clearly much smaller than the Forme, even though it's labelled a medium, 'equivalent to conventional frame size' of 56cm. It explains why I've hitherto struggled with a 56cm bike - because it isn't really what it claims to be. I know that Halfords doesn't have the greatest of reputations, but surely even they couldn't put a Medium sticker on a Small bike, could they?

 

[Venod]

Bike size is very personal if feels OK it probably is OK as you have found out with the Carrera V the Forme, I am 5' 10" and ride a 54cm I could ride a 56cm but I find the slightly shorter top tube suites me better, stem lengths & seat position can be adjusted to fit, hope you enjoy the new ride, as mentioned before I find top tube length to be the most important measurement.

 

[John Moore]

Yes, I feel I'm in the right area straight off. There may be tweaks with saddle height and position, maybe even a stem spacer (probably not), but I'll not be needing to go far from the base position, which is something I never felt with the Carrera. Excited about the bike now! Maybe a whole new lease of life for my cycling. Only thing now is that when I get overtaken by people at speed, I can't blame it on my bike any more.

 

[festival]

The Carrera road bike range usually has well thought out frame designs despite being a halfords brand.
I am sure it was a genuine medium but what does that really mean?
The important thing is you have found the right bike and gained some knowledge along the way.
Giant e.g. size their bikes xs through to xl, so as not to confuse the issue, all the dimensions and measurements are listed to guide the customer but like all good brands they strongly recommend expert fitting where possible.
Plus the suns out, so enjoy.

 

[John Moore]

Unfortunately it seems the Forme is not quite right, as currently set up, having done a couple of rides on it. If I adjust the saddle height to optimum position for power, it puts the saddle a fair bit above the handlebars, which means that when I ride, even with my hands on the hoods, the craned neck position gives me real neck problems. The thing is, it looks to me as if this phenomenon seems to be intrinsic to compact frame geometry - I looked at the measurements of the 58 as against the 56 and it seems pretty certain that I would be still riding with the saddle quite a bit higher than the bars. I'm in my 50s, with a problematic neck from working at a computer for 20 years, so it may be that what would work perfectly well for 95% of the population just wouldn't work for me.

I had a similar problem with the Carrera Valour initially, but managed to get the handlebar height up to nearly level with the saddle by using a Satori stem raiser and flipping the stem. This of course made steering rather twitchier (whenever I turn my head to look behind me I find myself lurching out into the middle of the road, for one thing), so I'm a little reluctant to go down that path with the Forme. Besides which, the stem is not flippable (or certainly not intended for flipping), and only has a 7 degree angle which is already in the right direction (upwards). The spacers are also all below the stem as it is, so there's no inbuilt way to get a bit more height.

At the moment I'm inclined to go for an adjustable stem such as this one - http://www.amazon.co.uk/Ritchey-Adjustable-Stem-Black-28-6/dp/B00165EC7K/ref=pd_sxp_grid_pt_2_0. I'll try to find someone locally (Norwich) who really knows what they're doing to do a proper bike fitting for me, though, as maybe some small adjustments will help.

Apart from that, the bike is a true delight, though! It's only about 1.1kg lighter than the Carrera but I seem to be capable of much more rapid acceleration on it. I wonder why that might be? Stiffer wheels? I'm also enjoying the carbon forks on rougher road surfaces.

 

[John Moore]

LATER: Closer examination revealed that the stem was actually angled down, not up as I mentioned. I nipped down to my helpful local bike shop and bought a second-hand 100mm stem (the Forme one is 110mm), with a rather greater angle, and I've swapped this over now, bringing the bars a little higher (and effectively a little closer to the saddle, which may help reduce the problem if over-stretching is part of it). Going for a ride tomorrow and will see if it's better.