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Colnago sizing/geometry (paging C-40 and others)(16 posts)

Colnago sizing/geometry (paging C-40 and others)03Vortex
Oct 6, 2003 11:06 AM
I currently ride a 55 Vortex that has a 73 STA and 55.5TT. With Colnago being unique in their sizing and geometry, would a 55 Colnago with a 74 STA and 54.3TT be the same fit? The standover on the LS is 79.2 but do not know the standover on the Colnago. The Colnago has a slacker Head tube angle.

Thoughts/insight welcome
re: Colnago sizing/geometry (paging C-40 and others)03Vortex
Oct 6, 2003 11:11 AM
Forgot to cycling inseam is 32 in. or 81.28cm
re: Colnago sizing/geometry (paging C-40 and others)CurtSD
Oct 6, 2003 11:18 AM
I would think the 57 would be about right. It has a 55.6 TT with a 73 STA. I have an Ovalmaster in this size - let me know if you'd like any measurements from it.

Oct 7, 2003 4:23 AM
There is no significant difference in the way that Colango and Litespeed measure there frames. Colnago lists both the center to top size and c-c size clearly on their geometry charts.

To answer the question, Colango's steeper seat tube angle makes the 54.3cm TT length of the 55cm size frame, effectively the same as the 55.5cm TT length on the Vortex. You add 1.2cm per degree to to compensate for the difference in seat tube angle.

The height of the saddle above the top tube should be checked on the Vortex, before deciding on the Colnago size. You should strive for 17cm above the top tube, measured near the nose of the saddle. Measuring the saddle height from the center of the BB to the top of the saddle, along the seat tube will also help determine the appropriate frame size. This measurement is often more accurate that an inseam measurement, which many folks don't take properly. My saddle height is approx. 71cm and my frame size is 17cm less.

The posted 81cm inseam is too short for a 55cm frame. I have an 83cm inseam and ride a 54cm, with the saddle about 17cm above the top tube.

The standover height of a 55cm C-40 is approx. 79.5 and the standover height of a 54cm is approx. 78.5. Of greater importance is the head tube length. With a campy headset, the total length on a 54cm frame is 150mm, and 10mm more for the 55cm frame.
Oct 7, 2003 4:41 AM
Thank you but I would like clarification on your thoughts. The saddle on my LS is 17cm above the top tube with a saddle height of just about 72cm. Is your repsonse "NO" to mean that I shouldn't be considering a Colnago in 55? Would I still be able to maintain 17cm above TT on the Colnago given the 74 degree STA (or would I be looking at something less)?
Oct 7, 2003 4:45 AM
C-40. I apologize because I think you were replying "NO" to the post that I should be considering a 57. If that is the case, I agree that is not my size in a Colnago
Oct 7, 2003 5:00 AM
The STA does not have a significant impact on the appropriate frame size, but does lengthen the TT significantly (once the saddle is in the same position relative to the BB). If you have a 72cm saddle height, then a 55cm would most likely be the correct size. I would also say that either your inseam is quite a bit more than 81cm, or you may be placing your saddle too high. Different pedal & shoe combinations also affect saddle height. I use speedplay pedal with Sidi shoes. This combo results in about the lowest possible saddle height. LOOK pedals with shoes that require cleat adapters could raise saddle height by more than 1cm.

Be sure that you can drop your heel well below horizontal with your leg locked out at the bottom of the stroke. This insures that you will have some bend in your knee at the bottom of the stroke during normal pedaling. I frequently see riders who have their saddles too high, forcing them to pedal with the heel up and the toes down at the bottom of the stroke. Although it may be possible to pedal effectively in this position, it's the exception. Generally it results in a reduced cadence and power output. I often see these folks plugging along at a much-to-low cadence, which is very inefficient.
Please clarify.djg
Oct 7, 2003 5:45 AM
I asked you this once before and you didn't respond. I think it's nice that you so often take the time to walk folks through the junior high trig they've forgotten (or perhaps in some cases never learned) or, as in this case, simply provide the numbers for them. And I think you often provide sensible fit advice. But why on earth do you repeatedly cling to such a specific distance between the saddle and the top tube? I can see no obvious reason why this matters. It's not that there's no such thing as a bike that's too tall, independent of its length (at some point there's not enough room to get the saddle set up properly; and at some--probably different--point, a bike becomes so large that one cannot reliably mount and dismount the bike). And it's not that there's no such thing as a bike that's too short. It's just that this particular precise figure that you offer seems curious to me, and for some folks probably quite an inconvenience.
saddle height range...C-40
Oct 7, 2003 6:55 AM
There is a limited range of saddle height that is optimum. If the saddle is at 15cm above the top tube, then it is likely that the rider will have the absolute miniumum safe standover clearance of approx. 2cm. Saddle to bar height difference will be around 6-8cm. Many touring cyclists favor a frame fit like this.

At 17cm the standover clearance will be an ample 4cm and the saddle to bar height difference will be in the 8-9cm range with no steering tube spacers and an 80-84 degree stem. This makes a nice looking setup. If you can't tolerate and 8-9cm drop, additional stem angle (preferred) or spacers can reduce this distance.

With the saddle 19cm above the top tube, the standover clearance will be an unnecessarily large 6cm and the bar to saddle height difference will increase to 10-11cm, which is more than most people can tolerate. With the saddle this high, most folks would need at least 2cm of steering tube spacers and some would also need a high rise stem to reduce the saddle to bar height difference. Larger riders are more likely to tolerate this large drop.
Well sure there's a limited range.djg
Oct 7, 2003 8:14 AM
Maybe just a few centimeters for smaller riders and more for really tall folks. I'd say it's not trivial to substitute a precise figure for a larger range in this context, as we might be talking one or even two sizes of bikes/frames being at issue, depending on the mfg/model.

The preferred saddle-to-bar drop is a function of a number of variables, including rider flexibility, rider preference, and rider arm length. Also, one imagines that the sheer size of the rider makes a difference. The actual saddle-to-bar drop has nothing to do with the distance between the saddle and the top tube, except as this is somehow a proxy for overall saddle hight at one end and head tube length on the other (although even head tube length is something of a fudge-able constraint). Heck, up to about a cm it's probably a function of saddle design.

I'd question whether 2cm standover is the "absolute minimum safe standover clearance." It seems just fine to me (although maybe you're happy enough with "just fine" given that this meets your minimum, if only barely and absolutely). The fact is, the sorts of accidents people can avoid with, say, 4cm of standover but not 1 cm are pretty tough to imagine. Let's see, you fall forward--so there's some forward momentum--but not so far forward that you hit the stem and/or bars--so there's really not much--and you drop right down toward your top tube, while holding your bike upright and while getting at least one leg straight down to support yourself without your knee bending or your slipping substantially on a cleat--(how much is "substantially" for kneee bend, or leg splay or cleat slip or ...? Well, that is governed by the 4cm/1cm difference). Seriously unlikely. Even Lance's freak pitch forward in the tour this year didn't quite make it.

I imagine that your 17 cm is fine for most folks, but I really think this is a case of false precision, which is rarely a good thing. That is, I also imagine that 15 or 16 or 18 will be fine for many folks. It wouldn't matter, but for the fact that often an easy way to get a good fit (a comfortable fit) on a bike that somebody likes is to size up or down one or 2 cm from what lots of folks might think ideal. Buying an extra 2cm with extra spacers or stems is not always a better solution.
missed the point....C-40
Oct 7, 2003 10:05 AM
The answer that I provided was for the specific requestor riding a 55cm frame. Not a small person or a large one. It was also for a C-40 which I own and therefore have the exact frame dimensions.

Your statment that saddle height above top tube does not relate to the drop to the bars is quite in error. The length of the head tube extension above the top tube on stock frames rarely varies more than 1cm. Therefore, there is a direct correlation between saddle height and the height difference between the saddle and the bars. If a requestor has some more specific criteria, like maintaining a specific bar to saddle height difference, then my advice is always to measure the head tube length of the frame (with the headset).

If a specific saddle height is provided to me, I can tell you within 1cm or less the saddle to bar height difference that will be produced by any bike on the market that lists the head tube length.

My goal when building a bike is produce a setup that requires few or no head tube spacers with a moderate stem angle of 80-84 degrees. If the rider can't tolerate at least a 7-8cm drop from the saddle to the bars, then spacers and/or a high rise stem are unavoidable, without a custom frame.

Where did I say anything about avoiding injury in an accident? The 2cm minimum clearance is a generally accepted value that assures that you can mount and dismount without the discomfort of hitting the top tube, since the 2cm clearance is to "hard contact", not just a touch. If you want to buy a frame that's larger be my guest. Like all advice, you can take it or leave it.
Don't think so.djg
Oct 7, 2003 12:55 PM
I suppose the essential point about safety has to do with what sort of safety we are trying to achieve. I don't know how widely accepted it is that it's not safe to ride with less than 2cm standover, but it seems to me that I've heard what seem to me several red herrings tossed about regarding standover and safety--and that they've almost all been keyed to either "1 inch" or "2.5 cm"--and I'm sorry if I attributed the wrong one to you. So, I'll say it here: I don't think that a 1.5 cm standover (yes folks, to hard contact) is dangerous when it comes to mounting and dismounting a bike. I think that numerous little kids in every neighborhood in the land manage the feat of mounting and dismounting bikes with such limited standover--and less--everyday. They tilt the bike a bit and get on. They tilt the bike a bit and get off. It's fine.

This may seem like an irrational quibble, but the fact is that if folks can manage safely with 2cm standover rather than 4--and I'm quite sure that most folks can--then they can SAFELY look at a larger range of bike sizes than you suggested. And that might be a useful piece of information for somebody who wants to shop a range of bikes--new and used--without looking to custom frames, but who has, for example, relatively short legs. Or to someone who wants to know whether he or she can make some particular frame work without a strange or dangerous kludge of some sort. So, having read all of your posts here, I still think that your 17 cm number is a case of false precision. It may be part of a reasonable range. It may be just exactly the part of a reasonable range, where, given your size and your aesthetic preferences re spacers/stem extension etc. things end up looking just the way you like. But it is not--to less than a centimeter's variation--where everyone needs to be to be safe and comfortable on a road bike.

So perhaps all the rest doesn't matter, but:

On the one hand, I suppose I was wrong (or misleading) to say that there is "no" relationship between saddle rise and saddle to bar drop. On the other hand, I still think it's less tight than you suggest. Heck, people with exactly the same leg length might prefer to vary their saddle height--and hence, for a given size frame--the saddle to top tube margin--by a cm given different pedaling styles.

Moreover, head tube lengths do vary across brands by more than one centimeter even when we fix the "size" of the frame. Head tube "extensions" might mean one of several things, but if we are talking about the simple vertical measure from the horizontal projection of the top of the top tube to the top of the head tube, then we might observe that these too may vary by more than a cm--and less rarely than they used to. Head tube rise is also somewhat variable as we change the angle, although this shouldn't make much of a difference given the usal range.

Even if that were not true, the drop to the bars would vary with stem rise (a function of stem length and stem angle, as you know) and height of spacer stack (as you know), headset stack height (as etc.), and head angle. Even if we accept a constraint of not more than 2 cm of spacers and some sort of "normal" constraint on stem choice, it's very easy to get this front end to move up or down well over a centimeter, without moving the saddle or the top tube.

All of these factors serve to loosen the relationship between saddle to top tube drop at one end and saddle to bar drop at the other. Easily more than 1cm. Easily more than 2.

If you want no head tube spacers--or no more than 1 cm worth--that's fine. But lots of pros use a couple cm and on most forks that's fine too. If you want a certain particular stem angle (or a certain range) that's fine too. Heck, I might want just the same things looking at my bike, but I would differentiate between "what fits" on the one hand and "what fits, given the fact that it's impor
bunch of drivel...C-40
Oct 7, 2003 2:54 PM
Barely scanned this lengthy spewing of misinformation. You obviously have a relatively poor understanding of geometry and never bothered to read dozens of geometry charts from every major brand like I have.

My credentials are 20+ years of cycling and a mechanical engineering degree. If you ever think of something factual to write which proves my advice to be incorrect and includes some specific dimensions from an example STOCK frame, feel free to write it up. Otherwiswe, you're all blow.
Back at ya, big feller.djg
Oct 7, 2003 4:00 PM
Despite a fair bit of undergraduate and graduate mathematics at what most folks regard as good institutions, I must confess that I never did much all that much geometry. Still, I did enough to know (a) this nonsense and (b) that a degree in mechanical engineering has nothing to do with it.

This has become much longer and more acrimonious than could possibly be useful to anybody, so let's just agree to think each other dense and be done with it.

My last bit of advice to the original poster is: beware overly precise internet fit diagnostics. If you're not certain of your fit requirements already, find yourself a good shop (or a good coach), where someone bother both to take measurements and actually look at you on the bike. See where they start you (and if it seems like a big change ask why) and go from there.
Oct 7, 2003 7:24 AM
If you go this route, remember that you'll need to use 1 cm more setback on your saddle. BTW, I checked the standover of my 57 ovalmaster, and it's a bit over 81 cm with 23 tires.
Colnago SizingB2
Oct 6, 2003 12:34 PM
I don't get it. What's so different about the way Colnago measures and/or list their frame sizes? I always thought center of BB to top of top tube was very common.

Looks to me that the two frames you are comparing would be darn near identical. I think that the standover on the Colnago is 79.2cm as well. My guess is that the slacker head tube angle won't effect fit, but may create some differences in handling.

Good Luck,