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Slightly undersized frame(13 posts)

Slightly undersized frameCHRoadie
Dec 26, 2002 1:52 PM
I'm about to buy a bike, and I've got a couple of options. One way that I can go is to buy a frameset and have the bike built. However, in this particular model a 58 would be a good fit (when measured, my current bike would be about a 57.5 when comparing apples to apples), but I can get a good deal on a 56. The 56 can be made to fit just fine with spacers, etc. since it's just a frameset. My question is: what kind of issues might come up from getting a frame that's a hair on the small side? I've read a few disparaging comments on this site re: spacers, but functionally, will I even notice a difference?
re: Slightly undersized frameFez
Dec 26, 2002 2:34 PM
The general rule of thumb when comparing comparable framesets are smaller = lighter, stiffer, and presumably more agile. But in reality you should try to ride the 2 and see for yourself. The larger one may feel more comfortable, a plus for longer rides.

But most importantly, compare the geometries. That way you will know what dimensions fit you better and what doesn't and then you can make the best choice.

Look at chainstay length, front center length, fork rake, etc. Also look at head and seat angles. Sometimes you can compensate for different seat angles with use of straight or setback seatpost. And calculate effective reach by factoring in the different tube angles, don't just go on top tube alone.

And remember, smaller frames give you more standover, but they can also give you shorter headtubes. Although I don't have a problem with 1-2cm of spacers, you may have a safety problem if you get the smaller frame and have to go with a lot of spacers because some carbon steerers have a 3cm spacer limit.

Alternatively, you can get just a tad less standover and get a taller headtube and not have a bunch of exposed steerer tube.
Want a pure opinion unmarred by actual data?retro
Dec 26, 2002 2:39 PM
I'm too tall (6'4") for the 62cm frames that are the biggest most bikes shops stock. Still, I rode 62s for about 20 years because that's what they had, they'd give me a good deal at the end of the year, and long seatposts and stems (this was before threadless and spacers) would make it fit.
To be honest, I was pretty comfortable, rode thousands of miles and I didn't think I had any fit issues. When I bought an Atlantis, though, I followed Rivendell's sizing recommendations. They called for a 65cm, which Riv didn't make at the time, so I bought a 64.
It made a huge difference. I can't really separate the frame size, the higher handlebars and the Brooks saddle to tell how much each contributed to the bike's comfort, but I'll never buy a frame smaller than 64 again, and if I break down and buy Riv's new Redwood, it will be a 65.
Moral of the story: Before you pay for the 56, be SURE it fits. But if you decide on it, I don't think the spacers will cause any trouble if they don't bother you aesthetically.
I'm debating this with myself nowDougSloan
Dec 26, 2002 2:40 PM
My Colnago is a 54, and I have had about 8 55 cm (nominal) Bianchis. The Bianchis always felt perfect to me. I recently got an older (1998) Bianchi in a nominal 55 size, yet the tt and st measure 56 (so I call it a 56). For some reason, the position on this bike feels much more natural and comfortable. I just can't pin down why, though. Even with a 130 mm stem on the Colnago, it never felt as naturally comfortable (in positioning, not damping, stiffness, etc.).

I have bitched and griped here about people making too much out of fit issues, but maybe I was wrong. Maybe it's wrong to think that something "close" can be shimmed and adjusted to work well. Maybe you'll get by, but then maybe something else will be better. I think I'm finding this out. I'll let you know for sure after I ride a double on the 56 Bianchi.

I think you don't want to buy a frame to save money if it's not as close to perfect as you reasonably can get. I wish I could more fully explain why, but it boils down to feel, and that's hard to describe.

I'm debating this with myself nowflying
Dec 26, 2002 3:06 PM
I think you hit the nail on the head.
I did the same had a 55 C-T Colnago
Went to a 54 C-C Look & it feels so much better fit
wise I cannot believe it. In my case I know it was also the geometry change but still this is more than a little better.
I like you wish I could explain it even for my own future reference but I cannot. Instead I am just glad I have found this fit & will take note of all the measurements for future reference.
I'm debating this with myself nowCHRoadie
Dec 26, 2002 3:20 PM
One thing I've got working for me is that the owner of the LBS where I'll be buying the bike is an expert at fitting, and I have confidence in his abilities to make the frame work for me. Still, though, I don't want to spend the kind of money I'm about to drop if everything isn't perfect. Thanks for the insight!
Some forks have a limit on spacersMR_GRUMPY
Dec 26, 2002 8:32 PM
If you get a carbon fork with an aluminum stearer, you'll be OK, safetywise. Personally, I don't like the look of a bike with two inches of spacers, but that's just me. The most important dimension on a bike is the TT length. If you don't get that right, you're in trouble.
I'm debating this with myself nowFez
Dec 26, 2002 9:10 PM
I have ridden a number of 53 and 55 C-T sizes, within the same brand and model.

From my own experience, I feel the most comfortable on the larger one, even when the contact points are set up identically to that of a smaller frame. I don't know if this larger frame makes me go marginally slower up hills or when I need to accelerate, but I do feel more stable, comfortable, and less fatigued. This really makes a difference after the 3rd hour of riding.

And I really don't know why, because the dimensions and contact points are set up nearly identically.
1 cm big diff!Jowan
Dec 27, 2002 1:22 AM
As stated above, be sure to check things out. Feel is everything. I had a Bianchi 56cm frame for some time and always believed it to be just somewat small. When replaced under warranty for a nuw frame, I ordered a 57cm. This 1cm in frame size made a huge difference.

I think you can compensate somewhat with stemlength and spacers, but a difference of 2cm seems to big. Even if the smallest frame gets you a better deal, it's money down the drain if it's not a good fit.

found an internet-aricle on the importance of a goof fit, hope it can help you.


same here - the "fit triangle"?DougSloan
Dec 27, 2002 6:35 AM
The contact points basically form a triangle, from the saddle, handlebars, and pedals, right? It seems strange that the same triangle dimensions can be the same on two bikes, yet the feel is different. I don't get that. Anyone care to speculate?

Weight distribution.Len J
Dec 27, 2002 7:04 AM
I've been having the same thoughts as I compare the feel of the new bike with my old one's and I think that the difference comes down to how my weight is distributed over the bike, which affects handling and comfort.

In addition, I changed setback, drop, and chainstay length aimed at improving long ride comfort so I could be just rationalizing all these other changes.

same here - the "fit triangle"?Mel Erickson
Dec 27, 2002 7:27 AM
Weight distribution, frame material (even within the same basic material, alu, steel, etc. there are significant differences), tube construction, lugged, tigged, etc., stays, wheels, tires, saddle, post, shorts. These are just some of the variables I can think of that would affect the feel of the ride besides basic geometry. There are so many variables it's impossible to pin it down. The "size" of the frame is only one of many, and not necessarily the most important one. My first reference is top tube, then seat tube angle, both of which go into determining weight distribution. IMHO these are much more important than the measurement of the seat tube (whether it's CC or CT or C to top of seat tube or whatever).
same here - the "fit triangle"?Jowan
Dec 27, 2002 7:45 AM
Although I'm not an expert on the subject, I'd like to explain. A different frame size does have an effect, even if you would adjust for a smaller/bigger size by placing an longer/shorter stem, spacers or sett-back seatpost.

When the triangle of the frame gets bigger, the whole frame will get proportionally bigger. For one this will result in a longer wheelbase, giving more stability. Some manufacturors differ the angle of the seat/steerer tube according to size, which can give a different handling. Using a shorter/longer stem means that you alter the steering leverage to the fork, adding or reducing stability. A longer seatpost or a post wiht more sett-back, can alter your position to the bottom bracket, see triathlon bike were riders are seated almost above the bb, in stead of behind the bb. So even if the 'contact points' remain the same, the bike can give you a total different ride.

For example, you could make the steering angle much steeper (as on criterium bikes), wich in most cases will require a slightly longer top-tube. To compensate for a longer top tube use a shorter stem. The contact points stay the same, but the steering is much different.