Why Road Bike Sizing Charts Don't Work (Bike Fitter Explains)

Summary

In this conversation, expert bike fitter Neil Stambry discusses the inadequacies of road bike sizing charts and emphasizes the importance of individual differences in bike fitting. He explains how factors like flexibility, body proportions, and personal comfort can significantly affect the choice of bike size and model. The discussion highlights the necessity of professional bike fitting to ensure optimal comfort and performance for cyclists.

Bike Fit Fundamentals: https://roadcyclingacademy.com/bike-fit-fundamentals/

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Takeaways

Road bike sizing charts often fail to account for individual differences.
Flexibility and body proportions play a crucial role in bike fitting.
Two cyclists of the same height may require different bike sizes.
A good quality bike fit is essential for comfort and performance.
Bike models can vary significantly in geometry, affecting fit.
Self-assessment of body proportions may not be sufficient for accurate fitting.
Professional bike fitters can help identify the right geometry for cyclists.
Understanding one's own physiology is key to finding the right bike.
BikeFit Fundamentals offers a structured approach to bike fitting.
Comfort on a bike is vital for long-distance rides.

 

Chapters

00:00 Introduction to Road Bike Sizing Charts
03:06 The Limitations of Sizing Charts
05:46 Understanding Individual Differences in Bike Fitting
08:52 The Importance of Professional Bike Fitting

 

Transcript: 

 

Cam Nicholls (00:00.046)
Welcome back to the RCA podcast where today I am joined by expert bike fitter, Neil Stambry, and we're gonna be talking about why road bike sizing charts don't work. Just be aware this chat is also intended for YouTube. So please excuse any visual references. Let's get into it. All right, so Neil, recently I wanted you to write an article for the RCA website on a blog about road bike sizing charts. And you're like, hang on a sec.

They don't work, so I'm writing an article. like, oh, we should make a video about this then.

We should yeah deceptively simple question with a really annoying long-winded answer, so let's dive into it What is a road bike sizing chart so look some of the manufacturers you look on their website And you'll see a chart. It's got a list of like

like you.

Cam Nicholls (00:50.904)
Bites of sizes, small, medium, large.

Here how large this is how tall you are. This is the frame you need then you're okay She's all right better go and get that medium or whatever that is Why don't they work some of them have are really quite detailed some of them have like

Obviously can work because they're there and you know.

They can sort of work. They can sort of work. I'll explain. They're very hit and miss. There's plenty of, there's enough people out there that fall, even though they fall into one of the correct ranges for the correct height, they should go for a different size bike. We'll try and nut out a little bit about why that is. Some of them are a bit more detailed. They have multiple data points. A lot of them just have your height and this is the one you should have, which is obviously insane. But if you've got really long legs or short legs or something, it can totally change the frame geometry that you'd look for.

Well, it's like an anecdote as well before you go. I rode a 56 for maybe five years. Did you? Yeah. Yeah. Because I'm right on the border of a 56 and a 54 and I do have short legs. Yes. And then I went to a 54 and my life changed.

Neill Stanbury (01:47.822)
Yeah, you're unusually low seat height for a 56 centimeter frame. It'd be you're right in the realms of a 54. Yeah, so yeah, you're great example. Yeah, just just here. So Yeah, why don't they work? Let's use let's use two hypothetical twin brothers, right? They both got exactly the same height

They both got exactly the same leg length, same arm length, right? So they're falling within some of these, let's say they fall in the range for a 54 centimeter race geometry frame. One of them has got hips which don't flex up beyond 120 degrees because he inherited a different set of genetics from his mum versus his dad, which means that his hip joints are particularly immobile. In addition, he's been sitting at a desk eating Twinkies for 20 years and he's 15 kilos overweight. He's got a bit extra around the middle and he's all hunched over because he's an

and the other guy is a supple yoga teacher who flexes around a lot and he's 15 kilos lighter and he's got amazing hip mobility. So these two guys have the same skeletons, right? But vastly different flexibility levels and vastly different, in particular, hip mobility levels. And hip mobility, as your knee is coming up to the top of the stroke, is one of the primary determinants of how much drop you will tolerate to the front end. So if your hips can come right up, you've got amazing mobility in your hip joints, it's likely that you're gonna ride in a more

deeply flexed position preferentially compared to a more upright position relative to your identical twin brother who sits at a desk and eats Twinkies. So what this will mean is that the guy who's really flexible who's got amazing hip mobility his drop to the bar might be 50 to 80 millimeters more sort of severe than the guy who sits more upright because he's got the extra weight and his hips are not so flash. So you might choose a bike with a 30 or 40 millimeter lower stack in the front end which immediately moves you from

something like Specialized Roubaix which is one of the one of the least aggressive geometry endurance frames on the market. It's a really short tall bike. We often sort of recommend these to older guys who sit quite upright, people who don't have a lot of capacity for reach and drop in the front end and they're a fantastic bike for that. You might go for the you might you know the the guy who's the accountant he might go for one of those but the guy who's the yoga teacher who's really hyper flexible he might need 50 80 millimeters more drop you know a normal sort of

Neill Stanbury (04:06.416)
drop number from the highest point of the seat to the center of the bar, you might be looking at a 54 centimeter bike. A normal number, about 100 millimeters, which is about what my drop is, right? But the really inflexible guy might need 50, and the really flexible guy might need 130. Huge differences in the stack. So obviously the flexible guy, he's never gonna be able to get the bar low enough if he buys a Roubaix to be comfortable. And conversely, the guy's very, very stiff. He's not gonna be able to get the bar high enough if he buys a tarmac, or specialised.

So this is a great hypothetical example, just one of the many things of what can make these charts not work very well. They're just looking at...

You're referencing two separate bikes, just playing devil's advocate here, you're referencing two separate bikes here, not referencing the same bike.

Yeah, so you could you could go for like the what I mean is that the the recommendations for the sizing could be so far off that not only are you looking at changing the size of the frame but the actual the entire model of the frame Yep, yep, so you know

Yeah, okay, so it's almost deceiving. So somebody's like, oh well I'm actually a medium here but you actually know you should be a medium in a different bike altogether.

Neill Stanbury (05:17.046)
Yeah, so you might have something that's like long and low, know, let's use your tarmac as an example And then you've got your rubay, which is short and tall So you might be the flexible guy might be on a 52 centimeter tarmac with a hundred and thirty millimeter stem because he can get out and down to that low front end and then not only is the the short, know, the inflexible guy with a bit of a gut not only is he on a rubay, completely different bike model that's really upright and comfortable in the front end and very tall but he's probably on a 54

With a shorter stem so not only are they different sizes with different componentry, but also completely different frame models Yeah, so yeah, I've seen situations where people have rocked up and they've they've looked at her I had a great example to use a great example. I had a young fella came down from northern Queensland last year I think it was And he bought a Madone, know 20 20 odd thousand dollar bike really expensive bike and he he walked in the door He had the shortest legs I've ever seen on anyone who was a bit he was about my height, but his seat height was

When we were done his seat height was 50 maybe 60 millimeters lower than mine because his legs were so short We couldn't get the seat low enough because the Medone has a certain amount of seat post travel before the goes into the frame and it blocks out We were 20 millimeters too high even with the seat as high as it could as low as it could possibly go There was no chance of him riding it and it was a 54 because he fell right into that range of the 54 with his height and I said mate you're much better suited with a 52 because we just can't get the seat low enough first of all, but even a

or a 49 would have been fine for that guy even though he's my height. you know limb length and all that sort of stuff and flexibility levels and arm length and torso length there's just so many things that come into it which mean that sizing charts can be very hit and miss. What's the solution?

Yeah, what's solution? That's what I was gonna ask.

Neill Stanbury (07:04.622)
Solution is a good quality bike fit. Yeah, you've got to set your position up on your current bike such that you're comfortable and then extrapolate from the geometry of that. Forget about what you should be on because you're a certain height. Look at what you actually need in terms of the geometry and your bike fitter can help you out with that.

Can you self assess before deciding whether a bike sizing chart is gonna work? So for example, if you know all your limb, you know, your torso and your lower is standard and your flexibility is good, are you more likely to be served by these charts?

Possibly, possibly. But there's so many things you can't know about yourself. True. Yeah, like relative mobility levels in your hips compared to other people and all this sort of stuff. Yeah, it's very hit and miss.

Yeah, see I didn't know I had a hip impingement and I've been riding for 12 years before I came to see you.

Yeah, I mean not to harp on too much, but that is why my profession exists. It's one of the reasons my profession exists is to not only solve biomechanical problems and aches and pains and make you more comfortable, but also to get you precise correct geometry for your next bike.

Cam Nicholls (08:08.34)
Yeah, and I am way more comfortable on that bike over there, which is the BMC Road Machine versus the one directly behind you because I'm more upright.

Yeah, yeah, I think I think when we looked at the geometry for the team machine are it was I think you had 10 millimeters or so more dropped than you than you had the time I'd fitted you before which was on an SLR one I think and then that one I think we found out that the bar center was about 15 or 20 millimeters higher and that's you know You were right on your edge with the SLR one that was a little bit too low and that's very nice. Yeah for long rides

Exactly. Yeah. All right. Well, if somebody is watching this and they're like, well, I wouldn't mind some support with actually understanding my physiology and what bike might work for me. You put something together called BikeFit Fundamentals.

Yeah, it'll be a good first step to get yourself in the ballpark with your fit so that you can then extrapolate from your current geometry of your current frame to a potential new purchase and make sure you get all the componentry right. Seven part course, mate, the link's in the description. We highly recommend it. It's been a really good thing. Thanks for time. No worries at all.