Road Cycling - Frame geometry questions????

how does frame geometry influence ride characteristics(climbing, sprinting, aero, comfort, etc)?

ie.

top tube length
chainstay length
wheelbase
bottom bracket height
compact(Giant) vs traditional (C'dale)

TCR1 vs R2000


thanks

a longer top tube will allow you to use a slightly shorter stem, which will quicken up the handling a bit since you'll be closer to the steering axis.

short chainstays help in power delivery.

a short wheelbase makes a slightly twitchier, faster-handling ride.

a higher bottom bracket does the same, sort of, since your center of gravity is higher.

i refuse to believe that compact geometry offers any benefits for the consumer aside from a slightly lower price.. people will say the frames are a little stiffer, but you're stuck using a longer seatpost when will flex a lot more than a traditional geometry frame will when doing hard, seated efforts.

short chainstays help in power delivery.

Please tell me how this is so.

shorter chainstays = less flex. Think of a chopstick. hold it at the end. press on the other end. See how much it flexes. Hold it in the middle. See how much less it flexes at the end.
Shorter chain equals less flex, giving better energy efficiency = more 'pull' to the sprockets at the back.

In the old days, when all tubing was the same diameter, builders could only make frames stiffer by making them shorter.

Now, tubes are available in a wide variety of diameters, so you can chose any length, with sufficient stiffness for the task. If you want a long but stiff chainstay, thats what you use. Of course it may weight a bit more, but so what.

Large manufacturers use a variety of geometries for the same bike, in different sizes. From the largest to the smallest size, there is a wide variation in proportional length, centre of gravity, stiffness and steering geometry, and not always to the riders advantage.

how does frame geometry influence ride characteristics(climbing, sprinting, aero, comfort, etc)?

Nice thread. Apart from the valuable theoretical input on offer here, I would encourage you to engage in some serious test riding. I can tell you from my own experience that riding a bike that doesn't fit you (sizewise) in the long run negatively affects your performance. This means that whatever your preferences are regarding handling/responsiveness, your anatomy 'asks' for a certain seat and (virtual) top tube length.

shorter chainstays = less flex. Think of a chopstick. hold it at the end. press on the other end. See how much it flexes. Hold it in the middle. See how much less it flexes at the end.
Shorter chain equals less flex, giving better energy efficiency = more 'pull' to the sprockets at the back.

That would be nice if the chainstay was a chopstick, but it's not. Most of the load there goes through the DRIVE SIDE, but it's in COMPRESSION. Shorter chainstays do not = more power.
About 4% of a riders energy is absorbed by the frame. About 1.06% through the drive side chainstay. Lets assume you're correct and compare a 410 chainstay over a 425, which is roughly 4% longer than the 425. A small leap of faith says you're loosing 0.04% by going with longer stays.

Can you spell 'ludicrous'?

Geometry and frame loading are very complex issues. There are so many myths going around that its no even funny. Ones like "Compact frames are stiffer", "Long chainstays don't climb", and "High bottom brackets are more unstable". All of these statements are incorrect, but the prevailling attitudes and the marketing clout of the larger companies have us hoodwinked into believeing their myths.

does anybody know of bikes that are at the really far extremes of the spectrum for each of these properites? I know that rivendell advertises its low bottom bracket, but who has high BBs?

Also, are there any bikes out there with proportionally short chainstays vs. longer ones?

are the TCR and the R2000 really the two ends of the spectrum?

I just went to the two sites and got he geometry...they are actually pretty similar. In my size (57-58cm TT) the seat angles are identical, the chainstays are 8mm different (TCR=40cm, R2000=40.8). The wheelbases are nearly identical (less then half a centimeter diff) and the cannondale's BB drop is 6.7 vs the 7.01 of the TCR.

REally, those two bikes are not especially different.

Thats the deal with off the shelf bikes. You can blame the product managers for that.

More importantly, what are the head angles and fork rakes? What about top tube length?

the giant was like 74 degree HT, and the R2000 is a 73.5. The trail, the true measure of the turning quickness, was about the same on both.

That would be nice if the chainstay was a chopstick, but it's not. Most of the load there goes through the DRIVE SIDE, but it's in COMPRESSION. Shorter chainstays do not = more power.
About 4% of a riders energy is absorbed by the frame. About 1.06% through the drive side chainstay. Lets assume you're correct and compare a 410 chainstay over a 425, which is roughly 4% longer than the 425. A small leap of faith says you're loosing 0.04% by going with longer stays.

Can you spell 'ludicrous'?

Geometry and frame loading are very complex issues. There are so many myths going around that its no even funny. Ones like "Compact frames are stiffer", "Long chainstays don't climb", and "High bottom brackets are more unstable". All of these statements are incorrect, but the prevailling attitudes and the marketing clout of the larger companies have us hoodwinked into believeing their myths.

Read the posting again. You're missing something there. You're dealing with a question from someone with only a basic knowledge of bikes, the reason why he posted the question in the first place. Therefore, my response was intended to be basic. No one asked for percentages, etc. In other words, K.I.S.S.

Ludicrous? I think not. Remember, no one likes a smart .......

Read the posting again. You're missing something there. You're dealing with a question from someone with only a basic knowledge of bikes, the reason why he posted the question in the first place. Therefore, my response was intended to be basic. No one asked for percentages, etc. In other words, K.I.S.S.

Ludicrous? I think not. Remember, no one likes a smart .......

Okay, hows this then -

Short chainstays arent better from a power point-of-view.

Why perpetuate a myth? Why am I a smart-arse for pointing out the fact that even chainstays that are 10mm longer would result in no percieveable difference? Do you think a newbie can tell if a bike has the right rake? If the seat angle is 73 or 72???

If you're so interested in KISS, my advise would almost be to ignore geometry if you're a relative newbie. Get basically the right size in terms of TT/ST length, and get the best value bike for the money. That means either a better frame and you can upgrade the components as they wear, or vise-versa. Find a good bike shop, get good value, be happy with your purchase.

Thats my KISS smart arse advise for the day :)

phatman asks: "does anybody know of bikes that are at the really far extremes of the spectrum for each of these properites? I know that rivendell advertises its low bottom bracket, but who has high BBs?"

I've been riding a track bike for the past couple of months and it definitely has a much higher BB and short stays. It also has steeper geometery than my previous 80's road bike and my c'dale roadie.

I'd say there's a very different feel to the more extreme track bike that is even apparent to my friends (hybrid c'dale & 80's trek road). There's no doubt that the handling is extremely precise (some might say twitchy). Also I am more pitched forward on the track bike which makes it easier to accelerate, stop, and climb. The negatives are big downhills find me in constant fear of endos and we'll see how 60+ mile rides feel when it gets a bit warmer.

anyways those are just my opinions. I'd like to hear from someone with a cruiser bike for a little more compare/contrast

jeff

See the article linked in my sig line- "How to fit a bicycle" by Peter White. It discusses how frame geometry affects comfort and power output.

I believe that if you go to

http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

and use the fit calculator then read what it all means, frame geometry will become much clearer as far as fit.
For general-purpose road bicycles, the frame geometry will not be too dissimilar; the greatest variations will probably come from the difference between compact and traditional frames.

Even then, fit and handling are so personal that you literally have to ride different bikes, even with similar geometries, to feel the differences.

When I bought my last bike, I rode several competitive brands in the same price range: Giant, Cannondale, Specialized, Trek, LeMond, etc. Since most had comparable frames and components, I went strictly by feel or fit.

What feels good to me, however, may not feel good to someone else. That's why it's best to ride different bikes for at least a little more than a parking lot jaunt.