Why does advice on frame size differ so much?

[mansonpengy]

I am confused. I have just bought a medium Giant tcr1 and am wondering if its big enough for me. I am 5ft 9.5" with a 32" inseam. Although the bike is very comfortable and fast, I feel I should be more stretched out for a better areo position.

Various web-sites do calculations on-line and, when I put data such as inseam, torso length, arm length etc. they tend to say I need a 58cm or even a 60cm top tube. The Giant has a top tube of only 55.5cm with a 12.5cm stem.

Is the Giant too small and will a 13.5cm stem make it any better?

To make matters more difficult I recently ordered another frame for my touring bike with a 55.8cm top tube. Should I instead see if I can get them to swap it for a 58cm before it arrives?

Any advice would be appreciated.

 

[jitteringjr]

I am 5-9.5 with a 32 inseam too and I road rode a medium sized compact frame similar to the Giant and I was fine with that. Currently, I ride a bike with a 55cm top tube and a 110mm stem. Opinions differ on sizing because different people like to ride differently. Since I am not trying to compete on the bike, I am willing to sacrifice some aerodynamics for a more comfortable upright position. You may not want to do this.

Competitivecyclist.com offers a good write up on different sizing methods if you are not familiar with that website check the attached link then click on the "The Traditions of Road Riding and Our Three Styles of Fit" link

http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

Have you tried test riding other medium sized frames to see how they feel? Have them fit you when the bike comes in if you are really worried about it.

 

[lokstah]

Good answer and link from Jitt. Ultimately, Manson, bike fitting is tricky for more reasons than one:

1) As Jitt indicated, riding posture, determined largely by fit, isn't a standardized concept. Different folks, particularly over different decades, will favor different relationships with their rides.

2) People are shaped different, proportionally. Some folks are all leg--others have average inseams but long torsos. Arms are a factor too. I'm 6'2" with a 32" inseam, which isn't freakish, but isn't average for my height.

3) Bike manufacturers have different standards in mind when designing and sizing frames. This is a two-pronged problem. Some of the issue is related to the posture or proportionality targets the engineers have in mind as they design and spec. On another note, different manufacturers measure their frames differently when determining how to size a frame--the problem can come down to specifically what a top-tube measurement means for comany X versus company Y.

There are only 3 solutions. Firstly, you can just guess--fine if you're uber rich, or comfortable enough with a particular brand to have a strong instinct about a model. Generally not recommended. Secondly, you can familiarize yourself with all the numbers surrounding a prospective frame's geometry, and compare that information with careful measurements taken of your own body--fit calculators can help. This approach requires you know what you're looking for in terms of fit characteristics and posture, so you should either be pretty experienced, or have help from someone who is.

Finally, work with someone you trust--someone recommended by word of mouth, or whom you have a great sense about--and be fitted first hand. This person could be anyone from a particularly trusty mechanic or shop salesperson, an experienced cycling friend, a trainer, or even a professional fit specialist (they exist).

Best of luck with your purchase.

 

[dhk]

I am confused. I have just bought a medium Giant tcr1 and am wondering if its big enough for me. I am 5ft 9.5" with a 32" inseam. Although the bike is very comfortable and fast, I feel I should be more stretched out for a better areo position.

Various web-sites do calculations on-line and, when I put data such as inseam, torso length, arm length etc. they tend to say I need a 58cm or even a 60cm top tube. The Giant has a top tube of only 55.5cm with a 12.5cm stem.

Is the Giant too small and will a 13.5cm stem make it any better?

To make matters more difficult I recently ordered another frame for my touring bike with a 55.8cm top tube. Should I instead see if I can get them to swap it for a 58cm before it arrives?

Any advice would be appreciated.

I wouldn't be concerned about what the various formulas say. If your new bike is "very comfortable" now, believe you got it right. At first glance, a 58 or 60 cm top tube sounds way too big for your dimensions anyway.

I wouldn't think of a larger frame as being more aero, since you will have a smaller drop from saddle to bars when your seatpost height is set. "Conventional wisdom" has racers buying the smaller frame, so that the seatpost is up in the air relative to the bars. I'm 6', with a 34 inseam, and rode a bike with a 55.5 mm top tube for many years. I got it for crit racing. It gave me a big 10 cm drop to the handlebars which was great for short races but a bit too restrictive on long club rides and centuries.

After all, unless you're doing TTs or short races, you don't want a frame that forces you into an aero position, but rather allows you to get into a good aero tuck comfortably when you want to.

 

[lokstah]

Great point from Dhk. If a bike setup is comfortable, and you feel as though it's versatile enough to accomodate both an efficient upright posture, and a tuck on demand, don't worry too much.

If you have doubts (or even curiosity), have an experienced rider, trainer, or trusted shop person have a look--maybe someone will point out an obvious area where your setup can be adjusted.

 

[53-11]

Effective top tube length for me depends on the riding position I am in. Raise the handlebars and I like less "effective" top tube. Lower the bars and I like more "effective" top tube length.


That's just me, but now that I think about your torso is going to be longer if you are more horizontal.

Which makes me wonder why the drops are in front of the brifters? (I've beat this like a dead horse on another forum)

 

[triguy98]

I am 6'2 and ride frames between 58- 60cm. I doubt those forumlas are correct. As all have mention fit is particular and varies person to person and bike to bike. If you can ride for a half hour without your back hurting, you're good. I had a too small road bike and after 15-20 minutes i would start getting REAL uncomfortable. Now with a proper fitting frame, I ride for 2hr+ with only my legs and lungs burning.

 

[biker7]

I think you are seeking some reassurance you are good and I will provide it. You are as close to average in size as an adult male comes and you are riding a medium size bike which seems correct. Preferences vary...some like small frames and some prefer slightly large frames per their body measurements. I for example fall into the latter category...I ride a slightly bigger bike than I measure. It is hard to get any consensus on what the right frame size is if you are measured say at 4 different bike shops. At the end of the day it is you that must decide what works best and this is mostly by trial and error and making mistakes to hone in on what your best frame size is for you...not necessarily specific to your dimensions. It is simple physics if you like to spread out a bit and get aero your body elongates and you will prefer a longish top bar. Typically no one bike is perfect for every type of riding. I would say if you feel a bit cramped definitely try a 1cm longer stem...you will feel a difference. Also do not discount seat set back. Get checked for seat fore/aft position. If your seat is too far forward and you plum line too far ahead of your pedal axis with your cranks horizontal that will contribute to your cramping feeling on the bike and weight falling forward. My preference is a bike I can stretch out on...not a bike I feel cramped on and yours may end up there too.
There is no right answer that anybody can provide but yourself through owning a few bikes and seeing what you like best.
HTH,
George

 

[mansonpengy]

I am 5-9.5 with a 32 inseam too and I road rode a medium sized compact frame similar to the Giant and I was fine with that. Currently, I ride a bike with a 55cm top tube and a 110mm stem. Opinions differ on sizing because different people like to ride differently. Since I am not trying to compete on the bike, I am willing to sacrifice some aerodynamics for a more comfortable upright position. You may not want to do this.

Competitivecyclist.com offers a good write up on different sizing methods if you are not familiar with that website check the attached link then click on the "The Traditions of Road Riding and Our Three Styles of Fit" link

http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

Have you tried test riding other medium sized frames to see how they feel? Have them fit you when the bike comes in if you are really worried about it.

I have been amazed by the quality and quantity of replies to my thread. I am really grateful to everyone for such excellent advice.

Jitteringjnr gave a great web-site link that has provided me with much reassurance - I never realised that there are different bicycle fit philosopies that apply to different situations.

Dhk gave me reassurance that my new bike is about the right size for going fast providing I drop the bars a bit. I want to go fast on this one and intend to fit tri-bars so I guess its not such a bad fit after all.

In response to Biker7, the first thing I did when I realised it felt a bit short was put the saddle back about 6mm. I will probably try the longer stem too.

Nevertheless, I am now getting my new frame from Ribble swapped for a 58cm top tube, instead of a 55.8cm. (They are out of stock of 57cm and for £100 inc carbon forks, the deal is too good to pass up). I will use this new frame for audaxing and club riding and dont want the bars too low.

Again, thanks to everyone who has replied so far. I would still welcome any further advice, however - I find it all both useful and fascinating.

I am really impressed by this forum and by the people that contribute to it!

Mansonpengy.

 

[biker7]

The only comment I would make is a 58cm top bar is a long bar for a guy of your measurements. I am 6'1" and most of it being legs and I bought a 58.6 cm top bar bike for the long steerer tube to get the bars up and it is right on the brink of acceptability in terms of being too long with a short stem. Its a balance or a tradeoff. I am uncomfortable on bikes with the bars too low and being long legged that is what I get if I don't push the limit on top bar length. Granted my seat is a bit farther back due to my femur length depending on how our seat post angles lining up...mine is 72.5 deg. Crank length matters too.
You may love a big frame for your body size. It really is a personal choice replete with tradeoffs and why it is hard for someone to tell you what size frame you should ride. I bet if there were a survey almost every cyclist...not all...would comment about some dimension of their bike they may change.
Will leave you with one more bench mark that many long time bikers use when sizing up a bike because top bar sizing is so important. Many use the rule, that with the seat in the correct fore/aft position based upon leg dimensions and crank size, take one arm bent at 90 degrees with outstretched fingers and place your elbow on the tip of the seat. If the tips of your fingers bearly reach the handle bar then your top bar is the right length. Some prefer a bit longer reach and some a bit shorter.
HTH,
George

 

[Doctor Morbius]

Why does advice on frame size differ so much?

Because it often depends on what somebody is trying to sell.

 

[lokstah]

I have been amazed by the quality and quantity of replies to my thread. I am really grateful to everyone for such excellent advice.

I am really impressed by this forum and by the people that contribute to it!

You're welcome, though we'll disappoint soon enough...

 

[darrenf]

The only comment I would make is a 58cm top bar is a long bar for a guy of your measurements. I am 6'1" and most of it being legs and I bought a 58.6 cm top bar bike for the long steerer tube to get the bars up and it is right on the brink of acceptability in terms of being too long with a short stem. Its a balance or a tradeoff. I am uncomfortable on bikes with the bars too low and being long legged that is what I get if I don't push the limit on top bar length. Granted my seat is a bit farther back due to my femur length depending on how our seat post angles lining up...mine is 72.5 deg. Crank length matters too.
You may love a big frame for your body size. It really is a personal choice replete with tradeoffs and why it is hard for someone to tell you what size frame you should ride. I bet if there were a survey almost every cyclist...not all...would comment about some dimension of their bike they may change.
Will leave you with one more bench mark that many long time bikers use when sizing up a bike because top bar sizing is so important. Many use the rule, that with the seat in the correct fore/aft position based upon leg dimensions and crank size, take one arm bent at 90 degrees with outstretched fingers and place your elbow on the tip of the seat. If the tips of your fingers bearly reach the handle bar then your top bar is the right length. Some prefer a bit longer reach and some a bit shorter.
HTH,
George

Hi Biker 7

I think I "suffer" if that's the right phrase from the same thing. I am 6ft tall (183cm) with an inseam of 90cm. I never thought this out of the ordinary until some time after buying my first ( and current) road bike a few years ago.
I was fitted by my LBS who advised a 57cm centre to top (conventional) frame with 74 degree seat tube and 55cm top tube with 120mm stem. Length wise the bike is fine. I have subsequently done various online sizing guides and found that my ideal "reach" (frame length plus stem) is 66cm to 67cm. By coincidence, I had swapped my stem to a 110mm, giving my total reach of 66cm. The problem I have had, like you though is getting the bars high enough as I have loads of seatpost showing to get the correct saddle height.
I have just about got the bars high enough to be comfortable by stacking 3cm of spacers and flipping my stem to give me another 3cm of rise. My bars (top of) are now 8cm below my saddle ( top of) height which feels about right for me but I can't help feeling the bike "looks a little odd". A minor problem maybe, considering that it now "fits" but still, I want my bike to look good too!

As a consequence, I have been looking at new frames and many are too long when I look at the larger sizes. I have found a few european frames that have a 58cm top tube on approx 60 cm centre to top seat tubes (which would give me the main thing I am aiming for of longer head tube) and a 73 degree seat angle. I figure that the more relaxed seat angle would mean that my saddle would be slightly more forward in it's clamp to give me the same position as my current bike in relation to the bottom bracket, which should mean that a 58cm top tube, coupled with a 90mm or 100m stem should give me the same overall fit, but with bars at a slightly higher level (without looking odd).

Do you have any tips on which frames to look at (basso is looking promising as they seem to have longer head tubes than average too) and do you think I should be following this route (with zero margin for error in sizing if it turns out to be too long with a 90mm stem).

Also, you referred in previous posts to "average" proportions. Do you have any sources of such info you could refer me too. I have come to the conclusion that I am longer legged than average for my height (some might say gangly!) but I would be interested to find out more about this.

Many thanks in advance

 

[biker7]

Hi Darren,
Yes you and I are built the same only you in the more extreme with even longer legs relative to your overall height. It isn't atypical BTW for tallish guys to have a lot of height in their legs....torso length being more comparable to the rest of the population. I understand why they put you on a smaller frame with its shorter top bar but handle bar height as you mention is then the tradeoff. For kicks measure yourself using the on-line calculator referenced in the other thread. It puts me on a 60-61cm bike using the Eddy and a little bigger bike with a French fit. I chose a 61cm c-t-t bike which I mentioned is definitely on the high side for my measurements. Honestly I wouldn't sweat the so called social acceptance of what is aesthetically pleasing as there is huge variability out there and many ball busting compact frame bikes showing a lot of post with big guys riding them and they don't look good either to my eye but some love 'em. When you have a slight disproportion to your measurements again depending on your riding bias...you (we) will end up with a slightly different looking bike if you want it to fit because you are filling an inside straight so to speak. In our case we want a tall bike with shortish top bar and since frames are designed upon statistical norm's to fit a broad population for anatomy (car's are designed based upon a 5th-95th precentile spread for example) you and I will need a shorter stem if we don't want to tie our shoes while on the drop bars. In my case its a big bike with a short stem but not a lot of spacers or much rise to the stem. There is nothing wrong with your set up on a smaller bike with a longer reach and higher rise stem in my view. As to which frames...it has been speculated that Italian frames have proportionately shorter top tubes. I think it is manufacturer and model specific as designs and trends are morphing all the time. It is normal to always want something else particularly the more you learn. On my new bike honestly I am having the most difficulty adjusting to 175mm cranks coming from a 170mm crank bike. To me it is a BIG difference and haven't completely embraced the longer cranks yet. I may over time...I hope so. It just ain't easy but many out there...the real big guys in particular, have much greater challenges in getting a bike to fit.
90% guys (bell curve) like you and me don't have big problems. I enjoyed your post Darren and being a thoughtful guy you will come to the best conclusion for yourself.
Safe riding brother,
George

 

[darrenf]

Hi George.

Thanks for your reply.

I did the competitive cyclist fit calculator and it came out with a 61 to 62 centre to top frame size on the "Eddy fit". By the description on the website, this is the type of fit that most accurately decribes what I am after. It did however, say my ideal frame length is 55.5 to 56cm and I haven't seen any frames (even italian) that fit these measurements!

The italian frames do seem to have shorter top tubes than most others which I can conclude after spending quite lengthy periods scouring various manufacturers websites

I currently ride a Gios and reckon I could go up to a 60cm, possibly 61 centre to top, and by using a short stem, create the same set up as my current steed.

Question is, can I justify the cost of a new frame to myself (let alone the wife) when I have managed to tweak my current bike to actually fit anyway?
Like you say, it is normal to want something else the more you learn. I have learnt that my current frame is perhaps a bit small height wise (don't blame my LBS particularly as length wise it fits the bill), and I now want to get a taller frame which I feel will be a better fit. Do I really need a new frame? The sizing issue has been tweaked so my current frame fits, BUT it would be nice to have a better fit AND those nice new spangly, shiny italian frames (gios, de rosa, casati etc) in the window of my LBS are just begging me to come on in and buy them every time I drive past

Ho hum, decisions decisions. I do have at least a half decent excuse that my current bikes a bit small to go out and splash some cash

Note to self: I really should stop pondering about such trivialities and get out and ride instead

Cheers for now

Darren

 

[biker7]

Hi Darren,
I think if you are into it...which many that follow this list are...it is very common to second guess whatever frame decision you make. Why? Because every single frame is trade off dimensionally relative to your body proportions. As mentioned, we are in the same boat...only I opted for a big frame with short stem. Is it better?...not sure...maybe worse. In the pecking order of priority, most rate the top bar length more important than the seat tube size. Ideally you want both top bar and seat tube to match your particular body size but unless you are proportioned in accordance with the statistical norm, this will likely never happen short of having a frame made which I personally think for a recreational cyclist is overboard. I would say dance with what's you got and enjoy it. You likely will have many more bikes before your done. Yes those fancy Italian frames do beckon don't they?
Cheers,
George