Help - Fitment Gurus - I have questions

Actual measurements are what you can measure on the bike. Virtual is what you would have if the bike had a traditional level top tube geometry. On compact and semi-compact frames (which the Look is), the virtual top tube is shorter than the actual top tube, and the virtual seat tube is longer than the actual seat tube. Top tube length, virtual or actual, is measured center of head tube to center of seat tube. The virtual center-to-center seat tube is longer than the actual center-to-top measurement because the top tube is sloping.

Riders with long legs and short body should seek frames with relatively short top tubes. Also, compact frames in smaller sizes with extended head tubes might work.

Azikara said:

[font=Times New Roman]I've looked at [/font][font=Times New Roman]www.bikefitting.com[/font][font=Times New Roman] and Colorado cyclist to figure out my frame size. I also went into a store and had a Trek dealer fit me. I think I have a 83cm inseam and stand 5'9.5" I came out as a 56 on the Trek. I'm trying to buy a Look. The Look choices are either L (55) or M (53). [/font]

[font=Times New Roman]When using the above calculators with my 83cm inseam I should have a C-C size frame of 54 cm and C-T of 55.6 cm. [/font]
[font=Times New Roman]When I look at the Look geometry they have a real C-C and a virtual C-C. [/font]
[font=Times New Roman]For example, for the L frame: real C-C = 50.5cm and virtual = 55.7cm[/font]
[font=Times New Roman]Q1: Is the L frame too big for me?[/font]
[font=Times New Roman]Q2: This is puzzling, the C-T (Actual) measurement is 55cm but the C-C (virtual) is 55.7!! Can the C-T actual really be smaller than the C-C virtual?[/font]

[font=Times New Roman]Note: the Look website is for the 2008 555 frame not the 2007 which is the one I'm thinking of. Are there any differences?[/font]

[font=Times New Roman]Thanks in advance for your help:[/font]

[font=Times New Roman]Azzy[/font]

First, you need to be clearer which virtual and real measurements you're talking about. It gets a little confusing and I really can't tell if you're talking about real and virtual top tube, seat tube or both.

Just in case you don't understand, the "virtul" top tube and seat tube measurements are made as if the top tube were horizontal. The "virtual" top tube measurement is often called the "horizontal" top tube measurement.

The virtual seat tube measurement is taken to the point that the virtual or horizontal top tube would intersect it. Therefore, yes indeed if you sketch out a diagram, the "real" CT measurement of the seat tube could be less than the "virtual" CC measurement.

In my opinion, you should be looking at the top tube mesurements, not seat tube, because it is that measurement that determines the reach. That (reach), and the head tube height that comes with it are less "adjustable" than the seat tube length. Also, it should be the virtual/horizontal top tube measurement , not the real top tube measurement.

You can probably fit a top tube (virtual or horizontal) that is a cm shorter or longer than your ideal with an appropriate stem. What you really need to know is the overall reach you need, then you decide if the top tube (again, virtual or horizontal) is of a length that a 90cm to 130 cm stem would give you that reach. Most people recommend a stem length of 100 - 120, but I use a 90 and no problem. In fact, some use an 80 with no problem.

After you decide if the reach can be achieved with the top tube length, then you decide if you want to get a shorter top tube + longer stem OR a longer top tube + shorter stem. Generally, the longer tube/shorter stem combo will also come with a head tube that will alllow you to get your bars up higher *in relation to to the seat*. The shorter tube/longer stem combo will usually get you a lower head tube, and therefore your bars will tend to be lower *in relation to the seat*.

People looking for a more aggressive position will tend to get the smaller frame and put longer stem on it - more aggressive position with bars relatively lower than the seat. People looking for a more relaxed position will tend to go the other way.

By the way, this all has to do with the geometry since some frames are made to make it easier to get the handlebar/seat relationship either more even or less even, depending on the purpose of the frame.

I hope this helps. You really need to talk specifics with the bike shop and actually get a preliminary fit and ride both options.

Good luck!

Azikara said:

[font=Times New Roman]I've looked at [/font][font=Times New Roman]www.bikefitting.com[/font][font=Times New Roman] and Colorado cyclist to figure out my frame size. I also went into a store and had a Trek dealer fit me. I think I have a 83cm inseam and stand 5'9.5" I came out as a 56 on the Trek. I'm trying to buy a Look. The Look choices are either L (55) or M (53). [/font]

[font=Times New Roman]When using the above calculators with my 83cm inseam I should have a C-C size frame of 54 cm and C-T of 55.6 cm. [/font]
[font=Times New Roman]When I look at the Look geometry they have a real C-C and a virtual C-C. [/font]
[font=Times New Roman]For example, for the L frame: real C-C = 50.5cm and virtual = 55.7cm[/font]
[font=Times New Roman]Q1: Is the L frame too big for me?[/font]
[font=Times New Roman]Q2: This is puzzling, the C-T (Actual) measurement is 55cm but the C-C (virtual) is 55.7!! Can the C-T actual really be smaller than the C-C virtual?[/font]
[font=Times New Roman][/font]
[font=Times New Roman]Note: the Look website is for the 2008 555 frame not the 2007 which is the one I'm thinking of. Are there any differences?[/font]
[font=Times New Roman][/font]
[font=Times New Roman]Thanks in advance for your help:[/font]
[font=Times New Roman][/font]
[font=Times New Roman]Azzy[/font]

Problem is that one maker's '56' is different from another maker's '56', in terms of top tube length and seat tube angle. Go to a shop with a fit cycle so they can determine those 2 essential dimensions.

+1 to Peter's recommendation. You would do yourself well to take a look here too.

Dave

What size frame are you riding, now?!?

How flexible are you?

Can you touch your toes with your legs straight & without bending your knees?

Can you lay your palms flat on the floor with your legs straight & without bending your knees?

How old are you?

Were you planning on racing, toddling along the bike path, or something in between?

The fit you get from a calculator is an arbitrary starting point ... and, the fit you get from a "pro" is often based on his/her biases.

If you are uncomfortable on your current frame, then you are probably better off spending some time/miles tweaking the position before throwing down a lot of money on a high-zoot/(any) new frame regardless of what you read or are told (including, now!).

FYI. As noted, "virtual" almost always refers to the top tube length ... as measured from the center of the stem to the center of the seatpost along an virtual/(imaginary) top tube.

C-T means center-to-top (of the seat tube). Look at the diagram on the framemaker's website or sales brochure to see if that means the top of the actual seat tube at the clamp (basically, the center of the bottom bracket to the top of the clamp) or of an actual top tube.

FWIW. Despite the indifferent sizing by my LBS way-back-when when they asked me what size frame I wanted and I ignorantly told them the size frame I thought I wanted (I started with a 60cm Gitane w/ 72º angles! The top tubes on the smaller frames were probably all the same ... but, I lucked out in getting a 90mm stem with that frame size whereas a smaller frame would have probably had a shorter stem), and there was no attempt to dissuade me from that size frame OR to suggest another size ... I'm 5'9".

The ACCIDENTAL FIT (after adjusting the height of the saddle -- essentially, serendipitous sizing ... kids, don't try this at home!) is actually/fortunately the same for me then-as-now even though the frames I currently have vary between 52cm (c-c) and 57cm (c-c). While the top tube lengths vary & the stem lengths vary (in part, based on the particular handlebars), the difference in the distance from the rear of the saddle (an arbitrary point for me to measure from) to the back of the "horn" on the brake lever body is within a half inch along the diagonal after establishing the relationship between the saddle and the pedal. That is, all of my bikes FIT beneath me the same despite the frames being different sizes (the larger frames do have handlebars with deeper drops) ...

There are times when I've intentionally used a shorter stem for a given top tube, but have gone back to the right-for-me length. I've tried a longer stem for a given top tube, and they were indeed too long, but not so much so that I couldn't ride with it.

IMO, at some point, if you aren't racing, the frame size of a ROAD bike that you choose is cosmetic IF you know how the bike is supposed to fit beneath you.

BTW. A frame with a 56cm top tube should NOT be too long/large for you ... measure your current frame's top tube and decide, accordingly. The stem length on your current bike should probably (?) be ~110mm if your current frame's top is 56cm long. If BOTH are true & your current frame is comfortable, then the "large" LOOK is not too big for you. If your current frame is the fore mentioned size & uncomfortable, then you need to address some fitness issues before throwing that kind of money down on a new bike.

If you DON'T currently have a ROAD bike, then consider starting with a complete bike that costs half what that frame costs ... and, get a LOOK frame in a couple of years when you absolutely know the right size for YOU.

alfeng said:

What size frame are you riding, now?!?

How flexible are you?

Can you touch your toes with your legs straight & without bending your knees?

Can you lay your palms flat on the floor with your legs straight & without bending your knees?

How old are you?

Were you planning on racing, toddling along the bike path, or something in between?

The fit you get from a calculator is an arbitrary starting point ... and, the fit you get from a "pro" is often based on his/her biases.

If you are uncomfortable on your current frame, then you are probably better off spending some time/miles tweaking the position before throwing down a lot of money on a high-zoot/(any) new frame regardless of what you read or are told (including, now!).

FYI. As noted, "virtual" almost always refers to the top tube length ... as measured from the center of the stem to the center of the seatpost along an virtual/(imaginary) top tube.

C-T means center-to-top (of the seat tube). Look at the diagram on the framemaker's website or sales brochure to see if that means the top of the actual seat tube at the clamp (basically, the center of the bottom bracket to the top of the clamp) or of an actual top tube.

FWIW. Despite the indifferent sizing by my LBS way-back-when when they asked me what size frame I wanted and I ignorantly told them the size frame I thought I wanted (I started with a 60cm Gitane w/ 72º angles! The top tubes on the smaller frames were probably all the same ... but, I lucked out in getting a 90mm stem with that frame size whereas a smaller frame would have probably had a shorter stem), and there was no attempt to dissuade me from that size frame OR to suggest another size ... I'm 5'9".

The ACCIDENTAL FIT (after adjusting the height of the saddle -- essentially, serendipitous sizing ... kids, don't try this at home!) is actually/fortunately the same for me then-as-now even though the frames I currently have vary between 52cm (c-c) and 57cm (c-c). While the top tube lengths vary & the stem lengths vary (in part, based on the particular handlebars), the difference in the distance from the rear of the saddle (an arbitrary point for me to measure from) to the back of the "horn" on the brake lever body is within a half inch along the diagonal after establishing the relationship between the saddle and the pedal. That is, all of my bikes FIT beneath me the same despite the frames being different sizes (the larger frames do have handlebars with deeper drops) ...

There are times when I've intentionally used a shorter stem for a given top tube, but have gone back to the right-for-me length. I've tried a longer stem for a given top tube, and they were indeed too long, but not so much so that I couldn't ride with it.

IMO, at some point, if you aren't racing, the frame size of a ROAD bike that you choose is cosmetic IF you know how the bike is supposed to fit beneath you.

BTW. A frame with a 56cm top tube should NOT be too long/large for you ... measure your current frame's top tube and decide, accordingly. The stem length on your current bike should probably (?) be ~110mm if your current frame's top is 56cm long. If BOTH are true & your current frame is comfortable, then the "large" LOOK is not too big for you. If your current frame is the fore mentioned size & uncomfortable, then you need to address some fitness issues before throwing that kind of money down on a new bike.

If you DON'T currently have a ROAD bike, then consider starting with a complete bike that costs half what that frame costs ... and, get a LOOK frame in a couple of years when you absolutely know the right size for YOU.

The last years model road bikes you can find on sale for $2000 are so much better than the ones that Pro's rode a decade or so ago it's not even funny... Why people think they "need" a $5000 piece of road jewelry to go fast is beyond me, although there's nothing wrong with owning a bike as expensive that you could buy half of Burkina Faso.... you just don't need something that good to go fast.

Alfeng's user name reminds me of a fast guy who used to love to drill holes in his bike. I wonder if his handlebars used to whistle at 30mph?

To the OP - I think you are stressing too much about the sizing, because, which ever one you pick, you will adjust it to fit you. We can't really advise you here, because we don't know how flexible you are or how stretched out you like to ride. All you can do is understand the things that matter and the things that don't.

Like everyone has said: ignore the seat tube length - it's irrelevant. You will be able to stand over the bar of both the L and the M and you will adjust the saddle up or down to get the right height, so forget it and move on.

The virtual top tube length is more important, but there will be no more than 15mm or so difference in length between the L and the M, so you will simply put on a longer or shorter stem to compensate and get the same reach to the bars, so again, don't stress too much about it. Personally though, I think that if you end up with a stem less than 100mm on the larger bike, it's a sign that you should have gone to the smaller size. A 90 mm or 80 mm stem can be perfectly fine, but it will sharpen up the handling and may make the bike twitchier than you might like.

The other issue is head tube length. To get your desired bar height, the smaller bike will require you to have more spacers under the stem than the larger one. You can't put more than 30 or 40 mm max of spacers on, so if that's not enough you may have to flip the stem up. If you have long legs this can be an issue. However, at 5'9" and 83cm inseam it's not like you have exceptionally long legs for your height so this doesn't seem to me like the M would be a problem for you.

Personally I always think "when in doubt, go for the smaller size". It's always easier to make a small bike a little larger than the other way around.

swampy1970 said:

...

Alfeng's user name reminds me of a fast guy who used to love to drill holes in his bike. I wonder if his handlebars used to whistle at 30mph?

Oh, those were the days (for everyone) ...

BTW. I gave my last, hand-drilled (aka "drillium"😉 53t Campagnolo chainring away decades ago ...

scirocco said:

...
The other issue is head tube length. To get your desired bar height, the smaller bike will require you to have more spacers under the stem than the larger one. You can't put more than 30 or 40 mm max of spacers on, so if that's not enough you may have to flip the stem up. If you have long legs this can be an issue. ...

Personally I always think "when in doubt, go for the smaller size". It's always easier to make a small bike a little larger than the other way around.

I agree with everything Scirocco wrote, but the last statement is definitely up to debate. I used to feel the same way, and it definitely is a common opinion. The main one being the statement he made before that - about the head tube. Because of the limitations of threadless headset/steer tubes these days, in some ways it might be easier to make the larger frame work better, assuming the top tube length allows you to get the reach you want with a minimum of a 90 mm stem.

Thanks everyone for the thoughtful responses. I eventually bought the L size frame. I can comfortably stand over it and that is not an issue. Also, my inseam turned out to be about 84.5cm vs the 83cm I originally thought. For the stem, it looks to me to be about 130mm which is quite long. But when I am on the drops the handle bar is directly in line with the front hub. I'm assuming this is correct.

The bike looks great. Now I just have to get out there and ride.

Azikara said:

Thanks everyone for the thoughtful responses. I eventually bought the L size frame. I can comfortably stand over it and that is not an issue. Also, my inseam turned out to be about 84.5cm vs the 83cm I originally thought. For the stem, it looks to me to be about 130mm which is quite long. But when I am on the drops the handle bar is directly in line with the front hub. I'm assuming this is correct.

The bike looks great. Now I just have to get out there and ride.

130mm IS really long ... in reality & cosmetically/proportionally.

How did you come up with that length? 1cm doesn't sound like a lot, but it can be ... you do want to be able to extend your arms out when you are holding onto the hoods of the brake levers with your elbows slightly bent.

Without seeing you on the bike, I'd recommend that (after you log several hours in the saddle) you consider swapping that 130mm stem for a 120mm (which I presume the shop will let you do in the first week-or-two).

BTW. What width bars did they install. I can envision that if they installed narrower bars (40cm, c-c @ the brake lever mounting) that the 130mm stem might seem right ... but, you may want 42cm (or, wider!?!) bars.

alfeng said:

130mm IS really long ... in reality & cosmetically/proportionally.

I was thinking along the same lines. The guideline is to block out the front axle in the hands-on-hoods position, which is about a centimeter shorter from where you are. If you were built like a gorilla or riding a super-short frame I'd say the 13 was appropriate, but you miss on both counts.

Don't be too proud to swap down to a 12, or even an 11. But I'm betting a the 12.

Azikara said:

For the stem, it looks to me to be about 130mm which is quite long...

Yes, 130mm is pretty long. Is that 130mm flipped up or flipped down? I'm amazed you can even get comfortable with it on the L size frame. Are you sure that the shop didn't just slide the saddle way forward to compensate for the long stem? (Which is the wrong thing to do.)

I'm also guessing that you must have the bars fairly high relative to the saddle. Longer-term you may want to get them down a bit lower. Not only is it more aero, but helps to get your weight more onto your legs rather than your butt, which can help if you get any numbness down there. But lowering the bars will increase the reach required, so a shorter stem will help there.