View Full Version : I think it's geometry?
AARGH!
I keep making it all go away!
I'm trying to post about some observations that I made tonight that I think might help me start understanding these road bikes some, so I can start figuring out what I'm looking for when it's time to pick mine... I keep pressing something on my laptop's keyboard that makes it all disappear!
DH has caught me surfing the LBS site tonight -- he would probably say it's karma, since he keeps telling me quit looking at those road bikes!
I told him I'm studying geometry. In reality, I don't think I'm ready for the numbers yet, just the pictures.
Anyway, I saw something for the first time tonight, and maybe it's starting to make some sense: with ten pix per page of the bikes, I was able to see that indeed, frames have different shapes, and parts attach to the frames differently.
Since someone has been drooling over the Ruby Comp today, I went to the LBS site and started looking through their Specialized "catalog."
My first observations were how much more like a moutain bike my Expedition is than like a road bike. And there were some observations about mountain frames too, but I'm not interested in another one of those -- don't like single track. The occasional fire road MAYBE, as long as it doesn't go up or down hill!
I have been looking at Ruby, Sequoia, and Sirrus for half an hour or so now. Differences I've seen -- the SEquoia's top tube seems to slope more than the other two. Sequoia also has a very upwardly angled stem (the thing that the handlebar attaches to, right?) where the other two have pretty flat stems. Sequoia and Sirrus talk about their relaxed, upright riding position, but I'm not sure how they are related? Except maybe that Sirrus has the flat handlebar so you don't do drops? Hmmm, looking carefully, maybe Sequoia and Sirrus forks angle out farther toward the front than Ruby's? Wandering to other parts of the catalog, Dolce looks an awful lot like Ruby to me. So do the other models.
I think the bit more upright position that Sequoia and Sirrus are supposed to offer is probably a good thing for me, but I don't understand exactly what it is about them that makes them upright? I'd think it's related to the stem-thingie, but they don't match on the two bikes. If the big thing to make a bike more upright IS the stem, then can the Dolce and Ruby be made to be upright if I wanted them to be that way?
Not that I've got my heart set on Specialized, it was just easier to look at a few different models of one brand and see some differences...
So, did any of this make sense, or is it just a tired sewing teacher rambling uncoherently after a long day of teaching retired sewists how to use their computers to create embroidery designs to make into quilt squares?
Karen in Boise
There are 2 aspects to bike geometry that you might be confusing a bit. When framebuilders (and other geeks) talk about geometry, they are interested in things like seat tube angle, head tube angle, length of top tube, bottom bracket drop, wheelbase, trail, fork rake. These things determine how the bike will handle, how quickly it will corner, how stably it will ride, how much flex the frame will have. They are independent of the rider. You did notice that some forks stick out more than others. That is a function of head tube angle and fork rake. The other aspect of geometry you were noticing (though it's not frame geometry) is how the components position the rider in relation to the bike. But some things that catch your eye are not particularly significant to the fit and feel of the bike. The angle of the stem doesn't matter, only the final position of the handlebars. A long steerer tube and a flat stem could give you the same handlebar position as a short steerer and sloping stem. The slope of the top tube also doesn't matter, only the saddle position in relation to the bottom bracket. A sloped seat tube provides more stand-over clearances and supposedly produces a slightly stiffer frame, but it doesn't affect the important frame angles and ride quality. When you are comparing different bikes, go the the frame specifications page and look at the relative lengths of the top tubes and seat tubes (use the virtual numbers that are based on a level top tube). Otherwise it's easy for your eye to fool you as you try to compare frames with sloping tubes. Those sloping tubes do make it easier for some people to get a good fit in a bike, so they can be an important consideration. It's just that you can't make comparisons between bikes on that basis. Hope this made sense.
ladyfish
09-09-2006, 06:03 AM
frankly, all that stuff is quite confusing to me. And I'm a numbers person. You have to ride them. Go to the LBS and play! Sit on them, get them fitted, go for a ride. You will soon learn just exactly what you like and dislike. Then you can give more weight to the geometry once you have an idea of what works for you.
All my opinion of course. Once I had my bike, I could use the geometry to compare it to others to see if I think I'd like that bike too. (I've been doing this with my drooling over Bianchi bikes). I'd still need to ride it, though. But it helps me figure out which size will fit best (it's interesting that the top tube lengths are different even on bikes that are the same "size").
Good luck. I tried out several bikes, and it kept coming back to how good I felt on the one I bought. Go play at the LBS.
Triskeliongirl
09-09-2006, 09:11 AM
When I struggled to find a bike that fit after my beloved custom bike friday was stolen last year, I did what you suggest. I looked at the geometry tables of the bikes that had worked for me in the past, and of the ones I test rode and hate. In doing that, I learned that I need a bike with a 73 degree seat tube angle or less, or I can't get positioned right over the bottom bracked, I like a bike with a top tube of 48-49 cm, or I need too short a stem and end up with squirrely handling, I like bikes with trail values in the 5-5.5 range, and hate ones with values 6 and up since their handling is very sluggish. Based on this analysis, I searched the web and found a bike that matched my needs, the 2005 terry titanium isis. I bought her site unseen, the great folks at Harris Cyclery built her up to my specs and when I took delivery she was love at first site.
frankly, all that stuff is quite confusing to me. And I'm a numbers person. You have to ride them. Go to the LBS and play! Sit on them, get them fitted, go for a ride. You will soon learn just exactly what you like and dislike. Then you can give more weight to the geometry once you have an idea of what works for you..
Ladyfish -- EVERYTHING about bikes confuses me! I do plan to ride as I get more serious about a road bike for me. I decided I need to have a bit more understanding of what makes bikes different, and what makes some bikes cost $300 and some cost $3000 before I buy the next one. We kind of blindly bought low end Comfort-Beasts this spring, since we had no idea just what we were buying, they felt like a huge improvement over what we had before, and we didn't have a clue what we were getting into when it came to our new summer sport!
It didn't take long for me to decide that I want a road bike eventually. I want a little bit more idea of what I want in a bike than blue or green paint next time, you know? So, I've been looking at parts and what they might do for me all summer. The other night, a casual glance at a bunch of thumbnails showed me that there really are visible differences that go beyond the consmetic, and reading the differing descriptions about various bikes, I started to get interested in what makes bike A different from bike B different structurally -- the relaxed/aggressive thing, y'know?
Perhaps DH is rubbing off on me. I used to be much more impulse-driven...
(we were looking at lawn mowers yesterday. He asked if self-propelled is really worth doubling the price of the cheap mower -- I asked if he was going to mow the back yard. He said no, I said, then self-propelled is pretty important, if I have to mow that hill! Now he thinks we should have the old mower repaired one more time.)
Good luck. I tried out several bikes, and it kept coming back to how good I felt on the one I bought. Go play at the LBS.
Thank you for your input! It's all going to be helpful!
Karen in Boise
There are 2 aspects to bike geometry that you might be confusing a bit.
I don't mind being confused a bit, Deb! I know I can start unraveling my confusion with the help of you and the other ladies here at TE!
When framebuilders (and other geeks) talk about geometry, they are interested in things like seat tube angle, head tube angle, length of top tube, bottom bracket drop, wheelbase, trail, fork rake. These things determine how the bike will handle, how quickly it will corner, how stably it will ride, how much flex the frame will have. They are independent of the rider. You did notice that some forks stick out more than others. That is a function of head tube angle and fork rake.
From what you've written here, it sounds like I may not need to understand the structural part of this geometry stuff quite as well at this point -- like I'll feel this more than see it, yes?
Terms -- I think most of these I've heard/read, know what they mean, but "trail"???? What's that?
Handling -- cornering -- you mean I can take corners without slowing to a snail's pace and without using the entire road on some bikes? Flex? This would be how it takes bumps?
The other aspect of geometry you were noticing (though it's not frame geometry) is how the components position the rider in relation to the bike. But some things that catch your eye are not particularly significant to the fit and feel of the bike. The angle of the stem doesn't matter, only the final position of the handlebars. A long steerer tube and a flat stem could give you the same handlebar position as a short steerer and sloping stem.
So, am I understanding that perhaps a bike can be "amended" to make it work as I evolve as a rider, at least to a point? It sounds a bit like the things that would make a bike work for me as a beginner wanting a more relaxed position could be changed out so that I could have a more aggressive "stance" if I wanted it at some point? I can see where there would be limits to this, of course, but???
The slope of the top tube also doesn't matter, only the saddle position in relation to the bottom bracket.
this relates to the knee over pedal spindle thing, yes? and how does it affect comfort? At times, I find myself scooching back a bit, and leaning a bit more forward, which seems to give me more pedaling power -- now my current bike has me very upright, since it's a "comfort bike" so I can't say my forward lean is necessarily very far: there's no drops to get into, and the bars are shaped to sit me almost totally upright.
A sloped seat tube provides more stand-over clearances and supposedly produces a slightly stiffer frame, but it doesn't affect the important frame angles and ride quality. When you are comparing different bikes, go the the frame specifications page and look at the relative lengths of the top tubes and seat tubes (use the virtual numbers that are based on a level top tube).
How can it make more stiffness? I understand the clearance issue -- oy do I understand clearance! (learned that young, and boy, you don't forget, do you?) Comparing numbers --- oh, boy, that's going to be a challenge!
Otherwise it's easy for your eye to fool you as you try to compare frames with sloping tubes. Those sloping tubes do make it easier for some people to get a good fit in a bike, so they can be an important consideration. It's just that you can't make comparisons between bikes on that basis. Hope this made sense.
Yup, Deb, it makes lots of sense -- at least as far as what I've learned at this point! I'm going to keep studying, and will also keep asking questions. I sure do appreciate the time you take with us newbies!
When I get there (the bike shop) I'm REALLY going to appreciate all the help you (and others) have been!
Karen in Boise
Terms -- I think most of these I've heard/read, know what they mean, but "trail"???? What's that?
Handling -- cornering -- you mean I can take corners without slowing to a snail's pace and without using the entire road on some bikes? Flex? This would be how it takes bumps?
See http://www.phred.org/~josh/bike/trail.html for an explanation of trail. You will feel a difference in steering for bikes with different trail. The longer the trail, the more the bike likes to go straight all by itself. The shorter the more manueverable. Too short and most of us would have trouble handling the bike, find it "twitchy", or just have to concentrate too much while riding. The shorter trail bikes do let you take corners faster at higher speeds.
As far as flex, a longer wheelbase has more flex than a shorter wheelbase for the same frame material. More flex, less of a jarring ride on rough roads. But too much flex (especially in the chainstays) and some of your power goes into bending the frame instead of propellling the bike forward. But with new frame materials, builders are making bikes with a stiff drivetrain and a more comfortable ride. So frame geometry alone won't tell you much here without a test ride. You want to test ride by hammering up a hill in an almost-too-big gear to compare frame flex and power transfer.
So, am I understanding that perhaps a bike can be "amended" to make it work as I evolve as a rider, at least to a point? It sounds a bit like the things that would make a bike work for me as a beginner wanting a more relaxed position could be changed out so that I could have a more aggressive "stance" if I wanted it at some point? I can see where there would be limits to this, of course, but???
Exactly. You'll hear some riders here talk about "flipping the stem" to go from an upward slanting stem to a flat stem that positions the handlebars lower. Or you can replace the stem with one of a different angle and length. But if the bike is designed with a high head tube relative to the saddle position (which some bikes with slanted top tubes are) then you will be limited. Your handlebar position (at least when you start riding more aggressively) needs to allow for significant weight distribution to the front wheel when you are descending in the drops and climbing out of the saddle. And to give you more aerodynamics when you want it, like on a windy day.
DebW: "The slope of the top tube also doesn't matter, only the saddle position in relation to the bottom bracket." this relates to the knee over pedal spindle thing, yes? and how does it affect comfort? At times, I find myself scooching back a bit, and leaning a bit more forward, which seems to give me more pedaling power.
Yes, it's putting your body in balance over the pedals. As Lisa.S.H. recently observed when changing her stem length, which let her move the saddle to a better position and get weight off her arms. There doesn't seem to be any real science confirming "knee over pedal spindle" but it's a good starting place if there is saddle adjustability around that point. No one position is going to be perfect for every second of every ride, so you always need some "scooch room" anyway. Seat tube angle is more about proper body positioning over the pedals than about a particular geometry being better, though the type of riding could make steeper or shallower seat tube angles better (e.g. touring vs. time trialing).
DebW: "A sloped seat tube provides more stand-over clearances and supposedly produces a slightly stiffer frame." How can it make more stiffness? I understand the clearance issue -- oy do I understand clearance! (learned that young, and boy, you don't forget, do you?)
I'm not sure I believe the marketing hype for compact frames. The frame itself becomes stiffer if the seat tube is shorter, but then you sit on a longer seat post which has no cross-bracing. It should be stiffer for out-of-saddle sprints, I'm not convinced it's helpful for in-saddle riding. So I don't think you should go looking for a compact frame, but there's nothing wrong with one either unless that gives you a ridiculously long seat post. Just check the height difference between your saddle position and the top of the head tube so you don't limit your handlebar positions. You want a range of between level and at least 2 inches, maybe as much as 4 inches, handlebars below saddle.
See http://www.phred.org/~josh/bike/trail.html for an explanation of trail.
This was so cool! It was a very good thing that there were pictures, or I would have come back with still more questions, but I get it! I haven't gone out to play with it on my bike yet and see where mine is in relation to nothing in my frame of reference, but I want to, even though I can also look it up.
As far as flex, a longer wheelbase has more flex than a shorter wheelbase for the same frame material. More flex, less of a jarring ride on rough roads. But too much flex (especially in the chainstays) and some of your power goes into bending the frame instead of propellling the bike forward. But with new frame materials, builders are making bikes with a stiff drivetrain and a more comfortable ride. So frame geometry alone won't tell you much here without a test ride.
Makes sense -- I get some experience with that when I notice the shocks on my bike "smooshing."
You want to test ride by hammering up a hill in an almost-too-big gear to compare frame flex and power transfer.
I had to laugh here: At least on my current bike, there's no such thing as a gear that's not too big for a hill -- hammer up a hill? If I ever get on a bike and manage to "hammer" up a hill....
"So, am I understanding that perhaps a bike can be "amended" to make it work as I evolve as a rider, at least to a point?"
Exactly. You'll hear some riders here talk about "flipping the stem" to go from an upward slanting stem to a flat stem that positions the handlebars lower. Or you can replace the stem with one of a different angle and length. But if the bike is designed with a high head tube relative to the saddle position (which some bikes with slanted top tubes are) then you will be limited.
This is very exciting! It seems to mean that while I already feel limited on my current bike after just a few months, a well-fitted road bike would give me much more "grow room," yes?
I'm not sure I believe the marketing hype for compact frames. The frame itself becomes stiffer if the seat tube is shorter, but then you sit on a longer seat post which has no cross-bracing. It should be stiffer for out-of-saddle sprints, I'm not convinced it's helpful for in-saddle riding. So I don't think you should go looking for a compact frame, but there's nothing wrong with one either unless that gives you a ridiculously long seat post. Just check the height difference between your saddle position and the top of the head tube so you don't limit your handlebar positions. You want a range of between level and at least 2 inches, maybe as much as 4 inches, handlebars below saddle.
I think I've heard the term "compact frame" but I'm not sure I understand this -- There seem to be "generic" frames (man-bikes, as we've been calling them), WSD frames, and are these "compact" frames something else? Are they specifically related to the sloping top tube? Do I understand that this "compact" thing, sloping top tube thing, and the WSD thing mostly affect how my upper body reaches the handlebars?
Now -- that handlebars/saddle thing -- is this the flat top part of the bar, the drops, or the hoods?
This is fun! So far, I don't have a clue what the numbers mean, but it's fun to look at the different models, compare numbers and see if I can spot the differences in the pictures! I don't think I'll worry about the numbers, but it's interesting to compare the bikes and start seeing what's different about them. One of these days, I might start poking around looking at materials...
Thanks again for your time Deb!
This is very exciting! It seems to mean that while I already feel limited on my current bike after just a few months, a well-fitted road bike would give me much more "grow room," yes?
yes.
I think I've heard the term "compact frame" but I'm not sure I understand this -- There seem to be "generic" frames (man-bikes, as we've been calling them), WSD frames, and are these "compact" frames something else? Are they specifically related to the sloping top tube? Do I understand that this "compact" thing, sloping top tube thing, and the WSD thing mostly affect how my upper body reaches the handlebars?
Compact frame just means that the top tube isn't level. Frames designed for either men or women may be built with either horizontal or sloped top tubes, but for small women it's easier to design a frame with a sloping tube. Traditional frames all had horizontal top tubes, so this is kind a new thing, or maybe a marketing gimmick. Having a sloping top tube may or may not affect how your upper body reaches the handlebars.
Now -- that handlebars/saddle thing -- is this the flat top part of the bar, the drops, or the hoods?
The top of the bars.
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