Surpin

A first biomechaist told me a Scott Addict 20 Disc 2020 in size 54 would fit me great, but then a second one I consulted, because the first is on vacation right now and I needed a consultation, once he heard I was going to buy the bike, confidently told me that it would actually be huge for me!
Now I am somewhat confused. I am thinking of waiting for the first biomechanist to come back at work and ask for a reevaluation.
But what would you think on the matter?

I am tall 169.7 cm with 83.2 cm inseam length.
The bike geometries are in the MD column here: [https]://ibb.co/HxtbhGZ
(remove the brackets around https! I still can't post links as a new user unluckly)

Thank you very much

Inusuit

If I've done the metric to English measurements correctly, you are about 5'6" tall and a 32 3/4" inseam? If those are correct, you may have fit issues regardless of frame size to accommodate what seems to be long legs and a short torso. Have you ridden the Scott or another bike in size 54.

I'm 5'7" with a 30 inch inseam and comfortably ride a couple of 54 bikes but have changed stems to reduce reach on both of them. I would probably have been better fit with a 52, but in the pandemic shortage, I bought what was available and have been happy with the choice.

I am 78 and a recreational/fitness rider.

brianmcg123

Wouldn’t hurt to just wait. But it’s in the ballpark. I definitely wouldn’t say it’s “huge”. A lot depends on how you want it to fit and your riding style.

chaadster

Unless the OP’s fittings included power measurements, *all* of it depends on how they want the bike to fit and riding style.

The short of it is, simply, that there is not one correct answer. There are many ways to fit, and it’s largely dictated by fashion and dogma, such as beliefs about how much saddle setback is appropriate, what sizes of stems look right, and what differences between so-called “race” and “endurance” fits might (or even should) be.

And of course, they don’t know your body or what you’re capable of, so they have to make guesses based on your feedback and their experience, which is a dynamic situation leaving a lot of room for error. I know may folks who have been to a pro fitter more than once. It’s not an exact science, and it’s definitely not formulaic, regardless of how many lasers, gonimeters, or “points of adjustment” are used.

In the end, I don’t think it matters a great deal until the rider knows what they want. The irony is, by the time the rider knows, they’ve probably got the experience to not need a pro fitter! Not always, of course, and for
those cyclist who need and/or want a pro fitment— for whatever reasons— it’s a matter of “paying your money and taking your chances.” It’s not that the “huge” bike will be unrideable, it’s a question of whether the OP prefers huge, small, or just right.

DaveSSS 

I get this for the geometry: https://www.scott-sports.com/us/en/p...icle=286425054

Stack is 572.4 and reach is 390.9. That's way too big. I'm 168cm with an 83cm cycling inseam and 72-73cm saddle height. I'd pick the 47 or 49cm size. I see that this is an endurance bike, but that usually calls for a 20mm taller stack with no increase in reach. The 52 has too much reach, unless a 90-100mm stem is used.

Most bikes have a headset top cover that adds 10-20mm to the stack. My bikes are setup for a racing fit, so my saddle to bar drop is 10cm. That's what I get with a 505mm stack, plus the 10mm headset top cover and one 10mm spacer, with a -7 degree stem.

PeteHski

I would ask them both to explain their reasoning in detail and see if one makes more sense to you than the other.

Bah Humbug

Amazingly, that means it's taller and only a hair shorter than my 56 S1. That's huge for a 54.

rsbob 

Two biomechanics walk into a bar. The first one hits his head so hard he falls to the ground. The second one has a fit laughing.

I’ll be here all weak.

cxwrench

I've worked with some really talented and experienced bike fitters. Some at shops I worked at, some through working for teams, and one working for Trek. I will say this: You could have 5 different people with lots of experience and great reputations do fittings for you and you'd end up with 5 distinctly different set ups. That being said, that 54 sounds too big.

DaveSSS 

If you put your dimensions into the Scott size finder it says a 52, with a 93mm stem, which should produce the intended relaxed fit.

Frame size numbers or letters just don't mean much these days. All you need is stack and reach, plus the seat tube angle to be certain that there's no seatpost setback problem. I've seen models with a steep STA and only 15mm of setback on a proprietary seatpost.

I build-up all of my bikes so test rides aren't possible, but I do know what geometry I need.

datlas 

Bike fit is like religion. There may be a few basic premises, but they go in all different directions and you can never “prove” who is “right” or “wrong,” and you may have to decide on what feels best to you.

rsbob 

What has worked best for me is going out and riding the two bikes and seeing which one feels better. Have them both adjusted as best as possible at the shop and then ride. The right one will be obvious. If you are buying online…. I have read nothing but horror stories about getting bikes which don’t fit.

OK, I lied. There were two people who exactly knew what their the right dimensions would be for the bike and it worked out. But just two out of a brazillion.

Sy Reene

Did the fitters have nothing to go by other than your height and inseam? ie. Arm length, tibia length, neck length, head height or whatnot?

Iride01 

Were both talking about whether that particular bike model and size was to big for you or might one of them just be talking about that size in general and not considering the geometry of the specific bike?

If you like being stretched out you might like the M54 size.

Also, bike fitters don't always fit you for the utmost in comfort. Some go more for putting you in a position to maximize your power for the distance and effort you put in to your rides.

There isn't one bike size that is correct for every person with your body dimensions. Usually you can fit a range of sizes pretty well, IMO. So until your fitter knows your personal desires for a bike, I don't find it odd for two different fitters to have different opinions just like we do. I've fit well on bikes from a 64 cm to a 56 cm. So I'd never say one size was the only size for you.


Were the biomechanist trained in bike fit? Not every biomechanist is a bike fitter from the brief introduction of the term I just read after googling the term.

wheelreason

Try some low rep high weight resistance training...

Kontact 

This makes zero sense to me. If someone of average height is supposed to be riding the XXS or XS frame size, what are short people supposed to be riding? Sometimes a taller person needs a small bike to deal with reach issues, but on average the medium sizes are for medium people.

There is also this bizarre trend of people riding road bikes with the handlebars located almost straight below their shoulders. Which is maybe what you do when you've decided to ride a 47 but are much too tall.

@Surpin, the correct sizes for you are the 540 or the 520. As they have only 1 cm of difference in reach, the important difference is the that front end of the 540 is 2 cm higher. High is good if you aren't flexible. But the reach issue is a choice between a 100mm stem and a 90.

veganbikes

Did you actually do a fit with either of these people? If not go and do a fit with one of them and maybe try the one who is suggesting a 54 and try that geometry on their fit bike and see what they say.

One good way to figure out a potential victor is if one is doing a static fit and one is doing a dynamic fit. The dynamic fit is the way to go. I have done both and the static fit was terrible especially at seatpost height it was way off luckily I had the good sense to lower it but maybe eventually a bit more than I needed but after the dynamic fit, he suggested insoles and spindle adaptors to make things longer and they made a HUUUUUGE difference and I felt really comfortable afterwards like it was a new bike vs the first one I felt awkward and uncomfortable.

rsbob 

Two very fit biomechanics walk into another bar. As they are both on the ground holding their heads, one says to the other, ‘This is the second bar we have walked into in this thread, and as biomechanics it shouldn’t be a reach to better judge bar heights because this has set (us) back on our butts. Now lets go get a drink.

Rim shot

DaveSSS 

At 168cm, I'm always the shortest man in the room. Average male height is 175cm. Back in the 90's I rode 54 or 55cm frames that were sized to my long legs, but always a little long on reach. My Colnago C-40 frames were slammed with no spacers, but I did use a -6 stem rather than a -17. If you read the details of my post more carefully, I clearly posted my 10cm saddle to bar drop, as a racing fit. If a rider wants only 4cm, that's best done with more stack height, more spacers or more upward stem angle, but NOT more reach. The smaller sizes I mentioned would produce a fit with more saddle to bar drop.

The manufacturer recommends the 52cm, taking into account the stated leg length and an average arm length. The minimum stack with the headset top cover would be at least 565mm, so it should produce a saddle to bar drop around 6cm, which isn't extreme. Spacers could easily reduce that to 4cm. The bike comes with a short 93mm stem, but the reach is a bit long at 387mm. If you don't know your preferred saddle to bar drop, that also makes it difficult to buy the right size.

Before buying a frame or bike, it's important to understand what stack and reach you need. If you know that, you'll get the right fit. One thing I don't like about Scott frames is the steep seat tube angle and small seatpost setback.

Kontact 

At 163cm, I am often the shortest guy, but there are other males my height and a ton of women who are shorter. Especially if you aren't typical white or black males. Most most Asian and Latino men average less than 176cm. If you look at the basic charts offered by many cycling brands, they usually suggest something more or less like 48 for 5'2", 50 for 5'4", 52 for 5'6, 54 for 5'8", 56 for the most common US male height of 5'10, 58 for 6' and 60 for 6'2". These are basic recommendations that apply to men and women, but lacking other information are useful guides to why manufacturers produce the size range they do.


In your specific case, you reflect exactly what I said in my commentary - you have a different fit need because you have long legs and short torso - so it should be no surprise that your needs include the shorter top tube of an otherwise small frame. Especially if you want the bars low for racing. But you aren't the average shape, so using your fit needs to guess about other people doesn't work that well.

In the OP's case, maybe the first guy selected 54 because the added stack is important for his body, like a lack of back flexibility. Dunno. But the bike isn't otherwise too long and standover height doesn't matter. I would have guessed 52. But 47**********?


As far as Scott not offering enough setback - setback isn't negotiable. If you can't get your saddle in position with a post swap, then the bike is never going to fit you.

merlinextraligh

My first question is what are you riding now? Second how does the fit of that feel for you? If it’s working for you I’d look to replicate that, or not deviate very far. If it isn’t, then what don’t you like about your current fit and work from there

DaveSSS 

You're so far behind the times that you don't realize that frame size numbers are meaningless. Stack and reach are what you need to predict the fit. I'm fairly certain that this bike has a proprietary seat post, so it can't be changed.

​​​​​I buy the stack height and reach that gives me the 10cm saddle to bar drop I want with a 110mm stem and always get it right the first time.

Kontact 

Dude, I was doing fits in one of the preeminent bike shops in North America in 2022. What were you doing?

Using height as a starting guide to fit remains a current practice, as you can see from this page on Specialized's website:
https://specialized.com.my/pages/bike-size-chart
You know how "behind the times" those guys are.

Stack and reach have limited usefulness because most people don't know that you can't compare reach unless stack is identical, and how to convert it. If the stack is 10mm taller, you have to add 3mm to compare the reach.

The real question is why someone your height needs such a teeny-tiny reach to ride a bike, or why you can't find a low enough stack in something normal.

And many manufacturers with proprietary seat posts offer both a zero and a 25mm setback version. But you must know that because you are really "with it". Or are you? The OP's bike comes with a round 27.2 seatpost. So WTF are you talking about?

Surpin

Thank you all for you incredible feedback. I could talk again to the first biomechanist. By the way, I suppose they are also a bike fitter as the technical visit I did with them was on a remote-controlled stationary bike which could modify its ride set up (saddle, handlebar position and so on..), in order to find the best posture for me.
I asked for explaination on why the Scott Addict 20 Disc 2020 would fit me in size 54 and they reassured me saying that with a stem of 100mm and spacers of 15mm I would achieve the ideal position obtained on the said stationary bike, so, his conclusion is that the bike would be appropriate for me in that size.

Is this reasonable? Can I feel safe and purchase the bike?

Surpin

Also, as it was asked, I am an absolute beginner, so this would be my first bike and I have no prior experience on what I would like or feel better as a ride posture, nor previous bikes to take as means of comparison.