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Sizing Geometry - Something not Right

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Sizing Geometry - Something not Right

Old 06-07-11, 08:58 AM
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Sizing Geometry - Something not Right

I've taken all my measurments using the comprehensive 'Fit Calculator' at https://www.competitivecyclist.com. However my suggested measurements for a frame don't match up with the proporitions of real frames.

For example if we look at probably the two main measurements 'Effective Top tube length' and 'Seat Tube centre to Top', the Fit calculator suggests respectively 'aprox' 560mm and 600mm (and greater for a more relaxed fit).

A 600mm Seat tube (c-t) equates to a very large frame, however the 560mm Top Tube length equates to a much smaller frame. For example on the bike I own now 'Dawes Giro' I would have to buy a 53cm frame to get that top tube length. I have their largest frame (58cm) and already find the riding position aggressive and can't imagine going to a smaller frame.

What's going on? Are my body measurements freakish? (see below) or am I missing something?

Thanks to anyone who reads all this and puts in the time to make sense of what I'm saying. I appreciate it!


------------------------------- My measurements
Gender M
Inseam 89.1 cm
Trunk 66 cm
Forearm 35.5 cm
Arm 70 cm
Thigh 63 cm
Lower Leg 57.3 cm
Sternal Notch 53.2 cm
Total Body Height 185 cm
------------------------------- Fit Calculator Output for 'Competitive fit'
Seat tube range c-c 57.7
Seat tube range c-t 59.5 - 60.0
Top tube length 55.9 - 56.3
Stem Length 11.8 - 12.4
BB-Saddle Position 79.3 - 81.3
Saddle-Handlebar 55.8 - 56.4
Saddle Setback 6.8 - 7.2
------------------------------
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Old 06-07-11, 09:46 AM
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Hello there,
well, i'm not going to be much use to you because i've never used a fit calculator but i just wondered, what is your reason for doing all this research? are you buying a new bike?
If so, and you have a bike in mind, i see you just doing what i would do. i.e. sitting on one you think is about right and then going up or down a size to see how they feel and picking the one which feels best/another one which feels better. The info you have would be great if you were having a bike built bespoke but in the real world we usually compromise, and the further we are from "Mr. average" the more we compromise. Having said that, i do usually tinker with my bikes like anyone else, seatpost length of course, stem etc. which your info might prompt you to do.
Sorry i can't be more helpfull.
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Old 06-07-11, 09:49 AM
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You just fall into the short torso, long leg category. Take a look at sportive or "plush" bikes. They combine tall head tubes with slightly shorter effective top tubes. This works for less flexible riders, but the shorter reach of this setup also helps riders with short torsos.

Many of the bikes in that you should look at are discussed here: https://www.bikeforums.net/showthread...ighlight=plush
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Old 06-07-11, 11:28 AM
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Originally Posted by bus_ter
I've taken all my measurments using the comprehensive 'Fit Calculator' at https://www.competitivecyclist.com. However my suggested measurements for a frame don't match up with the proporitions of real frames.

For example if we look at probably the two main measurements 'Effective Top tube length' and 'Seat Tube centre to Top', the Fit calculator suggests respectively 'aprox' 560mm and 600mm (and greater for a more relaxed fit).

A 600mm Seat tube (c-t) equates to a very large frame, however the 560mm Top Tube length equates to a much smaller frame. For example on the bike I own now 'Dawes Giro' I would have to buy a 53cm frame to get that top tube length. I have their largest frame (58cm) and already find the riding position aggressive and can't imagine going to a smaller frame.

What's going on? Are my body measurements freakish? (see below) or am I missing something?

Thanks to anyone who reads all this and puts in the time to make sense of what I'm saying. I appreciate it!


------------------------------- My measurements
Gender M
Inseam 89.1 cm
Trunk 66 cm
Forearm 35.5 cm
Arm 70 cm
Thigh 63 cm
Lower Leg 57.3 cm
Sternal Notch 53.2 cm
Total Body Height 185 cm
------------------------------- Fit Calculator Output for 'Competitive fit'
Seat tube range c-c 57.7
Seat tube range c-t 59.5 - 60.0
Top tube length 55.9 - 56.3
Stem Length 11.8 - 12.4
BB-Saddle Position 79.3 - 81.3
Saddle-Handlebar 55.8 - 56.4
Saddle Setback 6.8 - 7.2
------------------------------
as noted, you are torso short, leg long

I'm pretty much the same way, except you might be more 'extreme' on that end.
Things I've found...
Short torso, long leg usually also equates with long arms...
trying to get the long ST, short TT was a problem in the old days, not so much an issue anymore...
why?
the longer seatpost available these days menas you can downsize the frame and get the shorter TT and still get enough saddle extension.
in fact, downsizing has a favorable effect - because the torso 'weight' is in a more compact span, a smaller frame/shorter TT means you can use a longer stem and still have enough weight forward, for better handling (especially on descents...)
Caveats:
Saddle setback would be a critical dimension for longleg types like us - SO, smaller frames with steeper ST angles are best avoided. Something no more than 73 Deg. and even less, would get you the needed setback. Steeper than 73 and the setup will be tough and bike handling wil get funkier...
For example - my measurements (88 cm inseam) usually called for a 58/59 cm frame, but in modern frames I use a 56 with 73 deg ST (or less...) , 'square TT' or slightly under (usual range is 55.5 cm to 56.5 &is ok for me, and then I adjust with a 120 to 130 stem, dependin on HT height and HT angle). Arms are long enough to go plenty forward. And I have always preferred a more forward than 'upright' torso posture.
If you have to be 'upright' then try to get the shorter TT, rather than adjusting with too short a stem. Going too short ont he stem makes for really spooky handling of the front end...
in old steel I always preferred Italian Frames, since they usually had shorter TTs than English, French, Japanese or American Frames.
check out some of the 58's out there, you'll prolly find something that work real nice.
not sure how many Frame/Bike makers still spec out 57s, but that might even work for you...

BTW: I have a Marin Treviso in a 57cm (1999 Columbus NEMO steel, built for Marin by Pinarello) which is my go-to daily rider, 19.5 lbs built up, pedals and all, with 9 spd Ultegra.
Originally I bought a 59cm Treviso, built it up and rode for 100 miles, luv'd it but decided I wanted the next size down, hence the 57cm I now ride...
I still have the 59cm Treviso Frame, boxed, in the attic, in premo condition, waiting for me to get off my butt and put it up for sale... Carbon Fork, Campy chorus headset...
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Old 06-07-11, 11:58 AM
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The catch to this fit calculator is that it is not recommending a specific frame size. Rather, it helps you to understand what dimensions you are looking for and then decide which combination of frame geometry, stem length, bar height, saddle setback, and saddle height to use.

It sounds to me like you are fine on a 58. The calculator suggests you might want a shorter stem to compensate, but if you already feel a little scrunched up, then forget that.
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Old 06-07-11, 12:10 PM
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Originally Posted by cyclezen
...
the longer seatpost available these days menas you can downsize the frame and get the shorter TT and still get enough saddle extension...

This.

Focus on getting the TT right, and the rest can likely be adjusted by the amount of seatpost you have extended. ( and the amount of setback in the seat post)

Also, if you already have a bike that fits you reasonably well, take the measurements off that and star working from there.
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Old 06-07-11, 02:23 PM
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for frame comparos of size VS TT
check out the GEO specs on the bike sites
for example, Specialized Tarmac, TT tends a little 'over-square' to square (TT longer or equal to virtual ST) so a 58cm ST has a 58.2 TT
Cannondale Super-Six - slightly under square, so a 58 ST has a 57.5 TT

Orbea Orca or Onix - they do 57 cm! so even though they are 'square', their 57 cm ST comes with a 57 cm TT! a consideration!

other manus may have 57 cm with slightly under-square DIMS for TT... so you can get into the 56 cm range

and I would think that an appropriate 57cm would give a great 'fit' position as easily as a 58...

just some considerations and thinking inside a bigger 'box'...
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Old 06-07-11, 04:09 PM
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I sometimes get flack for it, but as I've said many times, the CC fit calculator does not provide enough information to get you on the right size frame because it still talks about seat tube length and ignores head tube length. Long-legged riders need a tall head tube. There's no getting around it. Try a Bianchi Infinito in both a 57 and a 59.
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Old 06-07-11, 04:12 PM
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Originally Posted by merlinextraligh
This.

Focus on getting the TT right, and the rest can likely be adjusted by the amount of seatpost you have extended. ( and the amount of setback in the seat post)

Also, if you already have a bike that fits you reasonably well, take the measurements off that and star working from there.
You cannot size by TT alone. If the rider has long legs, then the HT may short enough that the bar height will be too low even with max spacers.
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Old 06-07-11, 04:19 PM
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1. Remember these calculators are guidelines, not gospel. They probably get you in the neighborhood.
2. Yes it sounds like you have slightly longer than average legs for your height (I have the same problem but more extreme).
3. Look for traditional italian geometry bikes, I am pretty sure for example the GIOS 60cm frame has a 56cm TT.
4. You can compensate slightly by getting a size smaller frame and raising the seatpost a couple cm.
5. For perfect fit, consider custom geometry...costly but for non-stock bodies a good option.

Send me PM for detailed discussion if desired.
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Old 06-08-11, 09:51 AM
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Thanks for all the helpful replies. Really. This forum has a great community.

A little background info. I've only ever owned one road bike (my childhood was spent on MTBs), and I bought it (Dawes Giro 300) at the start of this season. It's a very low end road bike (cost me £300 online) and I sized it on the simplest of measurements (my height to frame SS size). I bought their largest frame (58cm) which has an eTT of 58.5cm. I understand it to be standard racing road bike geometry and ride it with the seat tube aprox 9cm extended. I'm really enjoying my time on the bike (doing upto 60mile rides) and want to get a better, lighter bike and start thinking about club events.

From what I can tell I find it mostly comfortable. However as it's my only road bike it's like sitting on only one chair, after a while you're going to get used to it. Doesn't mean there aren't much better fits out there. At the moment I have one criticism in the comfort that I need to address in the new bike. After longer rides (30 miles+) the back of my neck starts to hurt. I find myself not using the drops and sitting up straight to relieve the discomfort. Doing this defeats the object of having a dropped aero position. Apart from the neck strain I enjoy the dropped bar aero position (my back seems fine with it).

I understand now I need a more sportive or 'plush' geometry (thanks). I keep trying to envision in my head how different frame dimensions will affect my riding position. I can see there are two main ways to get less stress in the back of my neck. Either the TT can be shorter which will move my arms closer to me, or the HT can be higher which will raise my arms. Both ways should sit me up more, but which is best for neck strain while keeping an aero position?

A few people have suggested I can get a shorter TT by having a smaller frame and extending the Seat Tube. The problem with this is the relative height of the head to the seat and I think it will make my neck problem worse.

Trying out frames first isn't ideal for me because 1) I'm looking to get the best value for money, so will probably buy online from somewhere like Planet-X or Ribble (UK budget online brands) and 2) I don't think a short ride would help me decide if it's comfortable or not, as I'm entirely used to my own bike I'm sure all others will initially feel less comfortable. I've included my current bike dimensions at the bottom of this post for information. What sort of changes to these dimensions should I be looking for? My current choice for a new bike is one of the Ribble Sportive bikes (they do 3-4 different sportive frames and I'm not sure which would be best.)

Thanks for any further help and advice!


My current Frame (58cm)


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Old 06-08-11, 02:18 PM
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Originally Posted by bus_ter
...At the moment I have one criticism in the comfort that I need to address in the new bike. After longer rides (30 miles+) the back of my neck starts to hurt. I find myself not using the drops and sitting up straight to relieve the discomfort. Doing this defeats the object of having a dropped aero position. Apart from the neck strain I enjoy the dropped bar aero position (my back seems fine with it).
I understand now I need a more sportive or 'plush' geometry (thanks). I keep trying to envision in my head how different frame dimensions will affect my riding position. I can see there are two main ways to get less stress in the back of my neck. Either the TT can be shorter which will move my arms closer to me, or the HT can be higher which will raise my arms. Both ways should sit me up more, but which is best for neck strain while keeping an aero position?

A few people have suggested I can get a shorter TT by having a smaller frame and extending the Seat Tube. The problem with this is the relative height of the head to the seat and I think it will make my neck problem worse.
...
the neck issue is a common problem.
and is best addressed with multiple facets to a solution.
a. bike design and your 'setup'
b. riding posture improvements

Posture - and I'm saying this not knowing how your 'posture compares'...
If you tend to ride with elbows locked and/or splayed outwards, and you ride with your shoulders hunched up near the ears; your posture is a big cause of the problem.
see these folks, all locked elbows and one gent with some serious neck issues coming on...
https://gallery.venturacountystar.com/Images/27388.jpg
We all do it. When we get tired. The key is to be aware and work towards a better, more flexible, comfortable position.
Bend and Roll elbows downward, relax the shoulders down away from ears.
try this: sit up in chair, hunch shoulders up to ears, now bend the head/neck backwards - note how far you can go, in this position.
now - relax shoulders down, bend head/neck backwards again - note how much further you can comfortably go. This works in the riding position as well.
Now look at at Cancellera here, under stress after already 100 miles into Paris-Roubaix:
https://pvbike.com/merchant/723/image...raRoubaix2.jpg
He's 6' 1", more avg proportions, rides a 56cm with a short HT, has well bent elbows , shoulders down and comfortable, and in a very good aero position for the road.
No, we're not Cancelleras, but we can all learn from the good examples of good riders.

Posture is #1

Bike/Frame - my suggestions
Find bikes which has the closest possible TT to the 56 - 56.5 cm. Find a bike with no more than 73 Deg ST angle. in a 57 or 58 cm frame size, this should be easy.
Then within that selection look at Bikes which have longer HT lengths - for race bike specs most HTs in 58cm would be 180mm to 200mm, there are plenty of great performance machines with the taller HTs 210 mm to 230mm.
Bikes like the Spec Roubaix series, the Giant OCR (or latest designation). Almost every manufacturer has a bike within those specs.
Don;t worry about Wheelbase, chainstay length, center-front, rake, BB drop. If the bike is a decent road design, all those will fall properly into place.
DO concern yourself with chainstay if you plan to tour with a rack and panniers.
The stem you get on a stock 57cm or 58cm bike will likely be quite suitable for you, if the TT length comes close.
Have someone, with some strong and noted experience, help setup your position on the bike with you - from the proper saddle position, forward.
Work on a good riding posture (a lifelong process of attention - I'm workin on yr 43 out of 62 go-rounds...)
hope this helps

Last edited by cyclezen; 06-08-11 at 02:22 PM.
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