Road Bike, Cycling Forums banner

1 - 15 of 15 Posts

·
No pain, no pain.
Joined
·
168 Posts
Discussion Starter #1
I'm trying to find a road bike for my wife to try for at least a few months. Can't afford to buy retail (I never pay more than about 40% of retail) so I feel dumb going in to a bike shop for a fitting. (I buy stuff from the LBS regularly, just nothing expensive). Plus, I wouldn't trust them to fit anybody anyway - when I actually was looking for a frame from them, the owner told me my size less than 20 seconds after I walked into the shop. Not very confidence inspiring.

At any rate, she's 5'4" and pretty average proportions. She rides a medium frame mountain bike with a 22.5" top tube, which is fine, but she's probably on the extreme short end of people who would fit that frame. I was under the impression that she would probably fit about a 50-52cm top tube, but other opinions seem to vary on this site. I don't think 650c wheels are a good option for compatibility reasons, plus I don't think she's short enough to need them. For those of you who are 5'4", what size frames do you ride? I'm only interested in the top tube length, as I have yet to figure out what the point of using the seat tube length as the "size" of the bike is. The fit is entirely based on the top tube length (and influenced by the geometry).
 

·
Registered
Joined
·
32 Posts
I am 5' 2" and I went into my LBS for a bike fitting. I needed a 44" frame. I was right on the border for an x-small bike, or a small. I went with the small frame. My guess is that your wife would also need a small. I was at the beginning height for that size, and was at the top height for an x-small.
 

·
No pain, no pain.
Joined
·
168 Posts
Discussion Starter #3
cyclegirl said:
I am 5' 2" and I went into my LBS for a bike fitting. I needed a 44" frame.
What is the top tube length on your frame? (Measured center to center). Also, since "small" is kind of a non-specific term, what brand of small frame are you riding?
 

·
Registered
Joined
·
32 Posts
I bought a Giant OCR1. I got the specs out and tthe seattube/Toptube length (cm) a x-small is 42/52, a small is 44/53.5, and a medium is 50-55.5. I hope this is what you are looking for.
 

·
Registered
Joined
·
10,160 Posts
not just TT length...

You don't seem to understand frame sizing. Not surprising since there are at least three common definitions of "frame size". To avoid this confusion, measure the head tube length, including the headset, but not the spacers. This will give you an accurate idea of the handlebar height that is possible. If you have the bike in hand, also measure the standover height, since the HT might be fine, but you want 2-6cm of standover clearance.

Without an accurate cycling inseam measurement, it's impossible to predict frame size. Some folks have long legs and others have long torsos for their height.

TT length by itself does NOT always tell you the frame's reach. In the small sizes, some frames may have a 74 degree STA and others may be as steep as 75 degrees. A small frame with a 74 STA and 53cm TT will fit about the same as one with a 52cm TT and 75 STA, so just looking at the TT length may lead you astray.

Read up on how to measure cycling inseam at www.coloradocyclist.com/bikefit. Be sure to use saddle like crotch pressure when taking the measurement.
 

·
No pain, no pain.
Joined
·
168 Posts
Discussion Starter #6
C-40 said:
You don't seem to understand frame sizing. Not surprising since there are at least three common definitions of "frame size".
It's not that I don't understand frame sizing (although I know you're much more of an expert than I am), it's just that I think that the top tube measurement is usually the best indicator of whether a bike will fit. I do know that seat tube angle is important, but I think it's more important because of how it affects the relationship of the seat to the BB, than how it affects top tube length. For example, the seat tube angle on my 56cm CAAD4 frame is too steep - the length is dead on, but even with a ton of seatpost setback, I still wish my bottom bracket were farther forward relative to my saddle. I think it's because my body is top heavy, which means my center of gravity is more forward than a lot of people, putting more weight on my arms than I like. Having my BB farther forward would give the weight of my legs more leverage relative the weight of my torso. Does that make sense?

For a 52-53cm seat tube, you have to have at least 2 degrees of change to make a 1cm difference in the effective top tube length. (Each degree corresponds to just about half a centimeter in a frame that size).

For this bike, I'm pretty sure the handlebars are going to be relatively high. I don't think she'll like a lower position so much, so I'm not worried about head tube length. Plus, in frames this small, the head tube is usually more than short enough - especially if it has an integrated headset.

Also, I've learned the importance of the right saddle. In my experience, different saddles can make the fit of the bike feel completely different, even if it seems that they're positioned exactly the same way.

Personally, I'm not concerned about standover height. As long as there's clearance when I'm on the saddle, that's all I care about. My wife, on the other hand, probably would want some standover height, although she doesn't have a problem with the standover height of her mountain bike, which is 30.5" at its lowest point. I'll have her measure her inseam officially today...

I guess what I'm looking for is more specific recommendations regarding specific brands - i.e. who measures C to C and who measures "effective TT" etc. I realize that there's no way to guesstimate a frame size with 100% accuracy, but I am hoping to get close enough to be able to "tweak" the fit if necessary with stem/seatpost/saddle changes.
 

·
Registered
Joined
·
10,160 Posts
some corrections....

You're wrong about the effect of STA on the reach of a frame, even in this small size. For example, with a 50cm c-c frame the difference in the reach is 50 x (cos74-cos75) = .84cm. The rough rule of thumb of 1cm per degree is valid for a pretty large range of sizes. In the smallest sizes it's quite common to see a smaller frame that has about the same reach as the next size larger, just because of a difference in the STA.

The STA really does NOT affect the relationship of the saddle to the BB as much as you seem to think. If you would like your saddle further back on you 56cm C'dale, then try a post like the FSA K-force. It's got 1.5cm more setback than most traditional posts. Your choice of saddle may also be part of the problem. Some have short rails that don't allow the saddle to go very far back. Try a Fizik Arione or Gobi.

You're not worried about the head tube being too short? That's one of the most common complaints posted on this board. With limitations on spacers, many riders are forced to use a 96 or 100 degree stem to get the bars up to height. When I look at a sloping TT geometry chart, I look at four things, the head tube length, the TT length, the BB drop and the STA. These tell you all you need to know about fit. Of course I also check out the head tube angle, front-center, fork offset and trail to evaluate the handling characteristics.

As for you worries about who measures a frame in what manner, all brands measure the TT length the same way, horizontally. Some will call this a "virtual" or "effective" length, but it's really just horizontal. A few will also list the diagonal measurement of a sloping TT in their geometry chart, but I have no clue why.

I think you're going about this search backwards. You should find an available bike that you can afford and then figure out which size is needed. Most every brand covers about the same basic size range. A few won't have the very smallest size, but you don't need a frame than small for your wife.
 

·
No pain, no pain.
Joined
·
168 Posts
Discussion Starter #8
C-40 said:
You're wrong about the effect of STA on the reach of a frame
Dang it, you're right. Ever since high school, it's always been the simple math that gets me. Stupid error.
What is the range of STAs on "normal" bikes? Do most of them fit within the 74-75 degree range?

As for head tube length, no, I'm not overly concerned about it being too short. They don't make forks with carbon steerers in my price range, and spacers aren't limited with metal steerers. (I've got 1.25" of spacers on my 5+" suspension "freeride" mountain bike). Unless you count the fashion police, that is. (Although I think a ton of spacers is WAY better looking than a stem that angles UP). ;^) I'll probably end up going with an older used frame (due to budget constraints), and they tend to have longer head tubes anyway. Of course, a used bike probably won't have extra steerer to experiment with spacers. Dang. I wish I could just go buy a NEW bike!

On my bike, I have an Easton CT2 seatpost, which has quite a bit of setback, plus my saddle is a Koobi Xenon, which has about 8cm of usable rails. I have it set as far back as possible, and I don't think it's bad, but there are times when I wish I had less pressure on my hands due to shoulder fatigue. (I've tried adjusting stem height, length, etc with mixed results. Overall I'm happy. Heck, I did 370 miles in 3 days, and it didn't bother me too much, so I guess it's okay).

The STA really does NOT affect the relationship of the saddle to the BB as much as you seem to think.
Doesn't it affect the horizontal relationship to the BB just as much as it affects the reach of the TT?

If this bike were for me, I would consider the fork offset and trail, but I don't think she would notice the difference or really care one way or the other. I personally would prefer a fork that's more stable at speed than my C'dale Slice. It's stable at slower speeds, but twitchy at high speed, which seems backwards to me. Then again, I don't race crits (or anything else for that matter), so I should probably be on something like a Synapse... I'm sure she would prefer something that's stable all the time.
 

·
Registered
Joined
·
10,160 Posts
answer...

You asked: "Doesn't it affect the horizontal relationship to the BB just as much as it affects the reach of the TT?"

For given seatpost, the STA actually affects the relationship of the seatpost (not the saddle) to the BB even more than the reach. Using the same formula as before, but substituting the saddle rail height inplace of c-c frame size, you get a larger number. What this tells you is how much more or less seatpost offset is need to place the saddle where you want it. The STA usually affects the saddle position only if you allow it to.

As an example, I have two frames, one with a 72.5 STA and another with a 74.5 STA, using a saddle rail height of 68cm (for me), you get 68 x (cos72.5-cos74.5) = 2.3cm. I have a straight-up Thomson post on the bike with the 72.5 STA and a FSA K-force SB, with 2.5cm more setback on the other bike. This positions both saddles well centered on the rails and in the same position relative to the BB. Fortunately, the TT length of the frame with the 72.5 STA is also 1.5cm longer, which almost makes up for the 1.7cm difference in reach.

The Easton EC-70 post has about as much setback as you'll find. I couldn't get any info on the CT2. Moving the saddle further back might help your shoulders, but it will also change your pedaling action, the bike's weight balance and handling. You can over do it.

http://www.eastonbike.com/PRODUCTS/POSTS/post_ec70_'06.html
 

·
Registered
Joined
·
432 Posts
I can understand the feeling that the seat is too far forward relative to the cranks, but there is another way of adjusting that. Changing the upper body angle up a degree or so. This would require having your bar higher and further to the rear. It would give the same affect. As far as pedaling efficiency, seat height relative to the crank is the determining dimension, any rotation of the seat around the radius due to seat tube angle or seatpost setback make no difference in pedaling efficiency. In order to get that balanced feel, though, you must be able to lean forward just enough such that your pedaling counters the weight on your hands. Sounds to me like you would benefit from a shorter reach to the bars.

Bike fit is body-specific and there are shops that have people that understand that well and benefit their customers with that knowledge.

It's a common problem to find a bike small enough for a smaller woman. In the bike industry the geometry of most production bikes has too long a top tube relative to the standover because they aim toward racing geometry (which sells bikes). The newer models that some manufacturers are coming out with more upright stance makes the most sense for adults who are recreational and fitness riders. These adults are not going to benefit from the aero tuck that racers get into on their bikes.

Certain brands of bikes make so-called WS (women-specific) geometry bikes. Look into smaller bikes like those may better-fit your wife.

There is a problem in asking for top tube length since most bikes are measured by vertical measurement. One thing you can do is go to web sites and check out the geometry tables many manfacturers put up. Alternatively, find a good bikeshop that will adjust fit and, "shop," for a bike for your wife. Observe the way the fitter goes about their job and use that knoweledge to good effect yourself in trying to find a cheaper solution that suits you.
 

·
Banned
Joined
·
476 Posts
rethink 650c

a lot of women who are small prefer bikes with 650c wheels
they do feel easier to handle and have some accelleration charactertics that are good
for lighter riders

plus - I think the geometry on a 650c wheeled bike can more easily be 'normalized' when you are dealing with 50c down frames [like with 29 or less standovers]

Terry and Motobecane both build small womens bikes with 650c wheels
and larger womens bikes with 700c wheels

5'4" is small and if she has very short legs - a 650c bike may fit better
 

·
IndyFab girl
Joined
·
71 Posts
I'm 5'4" with a 30" inseam on a custom IF frame. Here are the measurements:

Seat tube length (c-c): 48cm
Top tube length (c-c): 50.5cm
Head tube length: 70mm
Head tube angle: 72.0
Seat tube angle: 74.5
Wheelbase: 96.1cm
Standover height: 74.1cm
Trail: 56.9mm
Chainstay length: 410mm
Fork rake: 50mm

I have a 100mm stem parallel to the ground (no rise), 1.5 inches of spacers, with approx. 3" drop from saddle to handlebar.

Cranks are 170mm (am considering switching to 165mm or 160mm to eliminate toe overlap, but it's not a big deal), wheels are 700c.

Hope this information overload helps.
 

·
No pain, no pain.
Joined
·
168 Posts
Discussion Starter #13
jp_nyc said:
I'm 5'4" with a 30" inseam on a custom IF frame. Here are the measurements:
Thanks! This is exactly the kind of answer I was looking for. Anyone else have specs like that?
 
1 - 15 of 15 Posts
Top