wphamilton

The OP post became provocative as soon as it was moved to the fitting forum but it does raise a question. Let's look at it geometrically instead of from the fitter's perspective. Given two bikes with the same geometry, one 50 cm and one 54, both adjusted so that the rider's body has the exact same position and orientation on both bikes, what's different? Granted the seat tube angle and head tube angle can differ between those two sizes but for the sake of OP's question suppose that the head tube angles are the same, and that you can adjust the saddle for position.

Basically, he has the same distance and angles between pedals, saddle, and handlebar. His body's center of balance is the same, his power transfer is the same, he feels the same weight at each point of contact and the same forces so comfort is the same.

The only differences that I see are the smaller bike will have a slightly lower center of gravity, and slightly different steering inputs. Very slightly lower, since his body is in the exact same height on both bikes and the difference is the top tube is lower. The longer lever arm of the stem on the smaller bike alters the steering input. Slightly smaller turning radius with the shorter wheelbase. The smaller head tube means you can get the handlebar lower, smaller frame is slightly stiffer.

That's it, the sum total of the differences. The change in the center of gravity is too small to be very significant for most riders, and we're stipulating the same position on both bikes so the head tube length isn't a factor. So in this case it boils down to just the difference in steering input, as the only significant feature between the 50 and 54. And 0.5° difference in head tube angle.

tarwheel 

I'll offer a contrasting viewpoint. Fit might not be so important for some individuals, particularly if they don't ride very often or very far. However, if you ride a lot of miles, fit becomes more and more important. I started developing all sorts of aches and pains when I went from being an occasional cyclist to riding 7,000+ miles a year. At that point, I had a professional fitting done and got a new bike that fit me much better, and the problems went away.

However, I will concede that a bike fitting is just a starting point. It will get you in the ballpark for what size frame to use, but it takes a certain amount of trial and error for a cyclist to find the right size stem, handlebar height and other fit parameters. And, of course, many cyclists can ride bikes within a certain size range by adjusting stem lengths and saddle heights. My bikes range from 56-58 cm according to manufacturers sizing, but I've got them set up very similar by using different stems, handlebar heights, etc.

Many new cyclists don't have a clue about what size bike to get, and fall prey to the fallacy that you fit a bike by standing over the top tube. That is where a good fitting can make a difference. In my opinion, the most important dimensions are top tube lengths and head tube lengths, and I can fit a range of bikes if those two measurements are within my zone. However, if a bike has a top tube that is too long or a head tube that is too short, I will never be comfortable riding it for very long. Standover is practically useless for fitting bikes, IMHO, yet many people rely on that almost solely.

Bandera

Current fitting processes are generally aimed at providing the option of distinctly different "base fits" for popular high effort/long distance cycling activities.
It's convenient for me to think of them as the French/Randonneur, Classic/Merckx Race and Modern Race fits.



Selecting an appropriate frame size & type for each style of riding is essential. A frame sized for a French fit will not allow the low/long/aero position that current elite road racers are adapted to and a Team Shy replica will not be decaleur friendly. Horses for courses as they say. Carefully selecting the right breed (and ignoring what Captain Fast is braying about in Starbucks parking lot) for the type of riding you will actually do in the proper size is a wise investment in hardware. Putting in the seat time is what they are all for.

-Bandera

FrenchFit 

This. I've seen my adult kids adapt to different sized frames easily. However, time and distance tell the story. After a season on a bike 2cm too large my son developed neck and shoulder problems, especially after long rides. And, cheating the fit with different stems and seat adjustments doesn't address the fact that the bottom bracket stays in the same place, and your center of gravity isn't where it is supposed to be. I can ride 54cm to 58cm road bikes and 15" to 19.5 mountain bikes, but cheating a proper fit is asking for trouble -- in both performance and endurance.

Bandera

Step #2A in most classic fitting systems is setting the seat height, #2B is setting cleat position, #2C is setting cleat to pedal spindle.
An under/over sized frame, particularly with a short railed saddle like a Brooks, may not allow enough adjustment to get the proper fore/aft/KOPS the rider needs.
Cycling is a pedaling sport, compromising pedaling efficiency is not a place to start.

Weight distribution in situations that require handling precision, will never be "right" on over/undersized frames with the saddle slid fore/aft to accommodate 2C.
High speed descents, tight pacelines and cornering in the rain with a additional loads like HB/Seat bags require a delicacy of input.
Having the proper frame size keeps wheels firmly planted and following a line effortlessly, a good thing.

An undersized frame for a recreational rider puts the position towards Modern Race, an oversized one towards French Rando fit.
Neither either be as comfortable and efficient as the proper size.

For plootering about and short distances feels good is good enough, close enough is good enough.
For long term use by high effort/long distance riders it's simple enough to just get the proper frame size and have at it.

-Bandera

Inpd

Ah come on. You change your saddle height depending on your shorts?

Its well known that you loose 1% of your height during the day (see Do People Actually Get Shorter Late In The Day? )
Do you change you saddle height based on the time of day? 1% of an average male is about 1.8cm (edited) which is much more than a couple of mms.

If people are that sensitive then I have a million dollar idea. A saddle that changes its height as you ride. It can use a smart phone to access the time of day, your birthday and hell even your mood, because its also well known that when your sad your posture changes!

wphamilton

4 cm frame difference, with the same geometry, less than an inch is needed to move the saddle back for the smaller frame. To have the exact same position relative to the pedal, and therefore imposing no compromise to pedaling efficiency, nor any other aspect to pedaling.

Weight distribution is absolutely unaltered when the three points of contact are congruent.

You'd have to explain how the frame size has any effect at all on keeping the wheels planted. As above, the only physical difference is in steering response.

IF, due to the smaller head tube, the rider sets it up that way. On the other hand, as OP stipulated, the rider position is the same on both bikes, that consideration is irrelevant. It will be as comfortable and efficient on one bike as on the other.

This is kind of illustrative of what provokes OP's ire, IMHO. Someone who disagrees with the fitters eventually gets a kind of condescending response: if you ride long distance or with any speed you'd understand.

FastJake

This is the key. A 15 mile ride is NOT nearly far enough to determine if your fit is wrong. It's enough to determine if it's way off but not much more than that.

Go for a 100 mile ride on both bikes (preferably not on the same day ) and report back. I bet you'll have a different view.

ThermionicScott 

I think he should do them back-to-back. Dude needs to learn some humility and take a little time to ponder how people might have more specific fitting needs than himself.

Bandera

It's a simple reality that one has to have actual experience cycling to have a "feel" (back pain, numb hands, squirrely handling, the dreaded butt issues and on and on) for the issues involved in a proper fit. That's why Seat Time trumps reading/posting on inter-web forums. There simply is no substitute, cycling is not an academic activity. Low efforts and short miles won't bring out fit issues unless something is grossly wrong, that's just how it is. To expect otherwise is unrealistic.

High levels of effort and demanding precise handling such as racing just have to be experienced to be understood as fit issues.
On a closed course shoulder to shoulder max effort sprints and apex clipping cornering reveal much about handling/weight distribution that can't be experienced anywhere else.
Keeping wheels planted is a matter of weight distribution that a proper race fit addresses.

Back to sizing.



That's not how race frames are built, there is no "with the same geometry" from 52-60cm, glance at this geometry chart:

Pinarello Dogma 65.1 Think 2 Road Bike Frameset - 2014 | Competitive Cyclist

The pic is of my old 56cm road racing bike.
When it was built the seatpost that I preferred would not be long enough for my seat height in a 52cm size.
Does that tell us anything? Yep, too small.
If a modern 350mm post was fitted the saddle would have to slide forward upsetting the balance over the rear wheel.
No thanks, I climb steep hills and descend on rough surfaces in all conditions.

A 120mm stem is fittied w/ 5.5cm of drop, there was no 150 1-A back when. Does that tell us anything? Yep, too small.
On a 52cm frame the drop would be extreme Modern Race, not the Classic Race I am adapted to for >40 years.
I not only need to see and breathe but the forward weight bias would negatively affect handing and the all important tire contact patch.

A properly fitted rider is well balanced putting the correct weight on the tire contact patches keeping the wheels planted in all conditions and levels of effort.
Try cornering at speed w/ your weight shifted fore/aft and w/ positions changed from drops to hoods to get a feel for this, it matters at pace and in the rain.

A 60cm Vitus would be a big pig for me and pose a different set of fit/handling problems that are resolved by simply riding the right frame size.

-Bandera

RR3

I don't know about you but I certainly do not lose 0.76 inches of height by the end of the day. This is the most ridiculous thing I have read. The distance from my hip socket to my pedal cleat does not change throughout the day. Now, people do tend to slouch but that has no impact on saddle height.

if you read more carefully.....if I ride the shorts with thicker padding (Assos Mille) and the ride is long (300 or more), yes, I most certainly do lower the saddle about 3 mm. Most riders have their saddle too low. Too high a saddle on a long ride and you will feel it behind the knee. I forgot to make that adjustment on a 400 recently and rectified my oversight at a control at around the halfway, that extra 3 mm lower was like magic.

wphamilton

The reality is that the people you're speaking to probably do have the actual experience and seat time. The assumption that anyone who takes issue with you must be inexperienced is what grates on people.

Now it's racing? Give it a rest.

Once again there is no difference in weight distribution of the two bikes, with the rider in the same position and same orientation over the bike. None of these generalities apply to the question OP asked.

RR3

Cervelo and others keep the same seat tube angle irrespective of frame size. Large frames do not steer or handle well.

Climbing in the saddle with many frames will pull the front wheel off the pavement.

Zinn explains it.

Technical FAQ with Lennard Zinn: Why tall bikes often handle poorly - VeloNews.com

Technical FAQ: Designing frames and components for big riders - VeloNews.com

wphamilton

A 6'6" guy on a huge frame, which is proportionally shorter front-to-back than vertically.

We can come up with extremes for exceptions to anything, but I'm starting to repeat myself with that last post so I'll give the Fitting forum a break and I'm out.

gutterbrother

The OP in his initial post is referring to a thread which I started (https://www.bikeforums.net/road-cycli...correctly.html) where I did a $100+ fit and I didn't really notice much of a difference. I think the OP makes two good points:

a) Can't saddle height and stem length compensate for a not perfect fit?
b) Since we change during the day and over the year why does finding the perfect fit even matter?

If we could keep the discussion on those and similar issues it would be productive and useful. I think WPHamilton raises some great points and I'm not heard anyone refute them convincingly.

RR3

I am only 6'3'' depending upon the time of day.

The front wheel will come unglued during a seated climb.

I used this as an example since it is irrefutable and backed it up with a few links.

We can go to the other end of the spectrum and talk about short riders.

The more subtle aspects of handling that Bandera mentioned are real and I agree with him. Rider functionality (core strength and flexibility) has a large impact on how a frame will ride dynamically. I understood what he said to mean imprecise fitting and adjustment might be more apparent shoulder to shoulder in a sprint on bumpy roads or on a long ride than when typing on the internet or on short casual rides.

Broken clocks repeat themselves....twice per day. I do not have a single bike that I can move the saddle back another inch and even if the saddle rails allowed, how can you not realize that the rider's center of gravity would change moving a saddle back. I move the saddle back and my weight shifts towards the rear. More weight on the rear? Wheelies when climbing steep roads and washed out steering when diving into bumpy crit corners or just cornering on country roads.

New School Geometry » Steve Hogg's Bike Fitting Website

RR3

That poster's response was disrespectful and I gave it back. Tough.

Did you read the Velo News links and others that I posted. If you had, it would have improved your knowledge

Do you really believe any cyclist has a 1% change in height or whether that has any impact on saddle height. Pure rubbish.

Bike companies thrust saddle height and stem length (stack and reach) on us because carbon fiber molds are so expensive. Makes it easy for them and it works for the average rider. Short or tall? Tough luck.

gutterbrother

Back on topic. I think he/she has raised some good points so lets try to address them rather than attack the OP.

Bandera

The OP has 200 miles in. We have been having a conversation since Post #15 .
It's not all about you, grated on or not, and is "people" the same as the Royal "We"?

As noted to the OP in Post #15 "the system was designed for competitive riders and will produce a Classic road race fit, if you go through the process."
Race fit has been in our conversation all along.
When discussing the impact of proper frame size and fit on the handling of road bikes racing on a closed course is where the limits of adhesion are best discovered, not in traffic.
Experiencing those limits is the only way to know them and discuss them meaningfully, there is no virtual substitute for actual experience.

I was responding to you, if you had read my response that there is indeed a difference in weight distribution between 4cm difference in frame sizes and an impact on handling.
Both 52 & 60cm framesets do not fit me, and most certainly will not handle properly in the high speed, high stress precise environment of competition, as one is wont to engage in.
It is simply not possible to achieve "with the rider in the same position and same orientation over the bike" in the real world with a 4cm difference in frame size, that's how it is. (See previous geometry link.)

Mfgs don't make road racing frames available in 1cm increments to increase expense and inventory, it's to properly fit a wide range of rider sizes who will be exploring the previously mentioned limits with brio and enthusiasm on real road courses where a deficit in handling does not result in a typo in a website post.

The DL-1 came in men's or ladies because that was all that was required to plooter about the village.
Going to tea w/ the parson and going into a blind decreasing radius corner at pace are not the same thing, unless one was cycling to tea w/ Beryl Burton......


-Bandera

bikemig 

Heck and you don't even have to pay for them!

bikemig 

You mean like this?

Inpd

Damn there goes my retirement plans ...

jyl

The idea that riders get shorter or taller during the day makes not the slightest difference to bike fit. If you read the OP's link, you'll see that the daily height change comes from the discs in the spinal column. Since no part of the spinal column is between the saddle and the pedals, this daily height change is irrelevant to the correct saddle height.

CbadRider

I cleaned up some of the bickering. Here's a link to the forum guidelines in case anyone needs a refresher.

Chare

Hi I am about 6ft and I am looking to do up a racer... Would this frame suit me?

L'eroica Vintage Raleigh Reynolds 531c Frame & Forks | eBay