I recall hearing that those were intended for sprints, so being right over the pedals helps...

yeah. i guess you get more thigh/weight on the downstroke.

yeah i remember reading that too. and all those riders that tried it out didn't like it and went back to their old frame/geometry. what works for one guy didnt necessary works for all of them

I thought that the point of a steep seat tube was to allow for a very forward body position like TT riders use with aerobars. In order for this to be comfortable and for power transfer to work, the BB should be farther back than other bikes. This effectively increases the angle between the torso and legs.

But I could be wrong. I don't think that a steep seat tube would have anything to do with handling besides the fact that it is oftentimes built so it is parallel to the head tube which has a lot to do with handling. So most bikes with a steep seat tube just happen handle quickly.

shifting your saddle forward moves your weight forward which effects handling.

I think a steep seat tube allows a shorter wheelbase.

My Pista has a 75 and 75 head tube and seat tube, for a short wheelbase and quick handling.

My Karate Monkey has somewhere around 73 and 73, but the seat tube has a bend in it that may not shorten the wheelbase as much as it allows me to put more weight on the rear wheel and less weight on the front wheel.

Let's see then: one could say four main factors determine handling, or one could say only three factors determine the quality or nature of the handling, with other secondary, contributing factors.

But let's look at the three/four:

1. wheelbase;

2. head tube angle;

3. rake; and,

4. head tube angle and rake combined, or, trail.

Let's look at head tube angle, first.

A steeper head tube angle contributes to more immediate and linear steering response.
With a vertical, or 90 degree head tube, the steering responds directly in proportion to how much the rider turns the steering tube.

With a more inclined head tube angle, the steering responds slowly, at first, and then responds much quicker as the rider turns the steering tube, until the amount of steering seems greater than one would expect.

One can see this better if he exaggerates it, as on the chopper motorcycles with dramatically extended forks and very, very relaxed head tube angles.
When one turns the steering tube on one of these motorcycles, at first, the motorcycle hardly responds at all, seeming to have very slow handling.
However, at a certain amount of steering tube turning, the wheel begins to lay flatter on its side, and steer off at a greater angle.
The steering response increases at a greater rate than one would expect from the amount the rider has turned the steering tube; and we describe this as non-linear.

So, a steep head tube has quicker initial steering, but it remains relatively linear and does not increase out of proportion to the amount one turns the steering tube.
Conversely, a relaxed head tube has slower initial steering, which increases out of proportion to the amount the rider turns the steering tube.

Secondly, we have rake.
Rake defines the distance of the axle, either in front of, right on, or behind a line passing through the center of the head tube and extending to the ground.

But let's talk about this head tube line for a minute.

A 75 degree head tube has a 75 degree line passing through it to the ground, in front of the bike.
A 90 degree head tube would have a line straight up and down passing through the head tube, and that line would intersect the ground directly underneath the head tube.
Taking it to absurdity, a zero degree head tube would lay perfectly flat, and a line passing through a zero degree head tube would parallel the ground and never intersect the ground.

Most bicycle forks have a forward curve to them that places the axle in front of the line passing through the head tube to the ground.
A shopping cart has the axle of its front wheels behind the line passing through the head tube to the ground.
A bicycle has its axle in front of the line passing through the head tube to the ground.

Now, drop a plumbline from the axle to the ground.
On a bicycle, this plumbline intersects the ground behind the point where the head tube line intersects the ground.
Remember, bicycles have less than a 90 degree head tube angle, and this places the head tube line and the wheel out in front of the bicycle.
In fact, the head tube line intersects the ground in front of the front wheel.
The plumbline hanging from the axle and intersecting the ground, and which also signifies the point at which the tire contacts the ground, generally, this axle plumbline intersects the ground behind the head tube line.

We call the distance from where the head tube line intersects the ground, to where the axle plumbline intersects the ground, the "trail," because, the tire contact point "trails" behind the head tube line and ground intersection.

Most street bikes have a rake of about 38 to 43 millimeters, which places the axle 38 to 43 millimeters in front of the head tube line.
The greater the rake, or the further we place the axle in front of the head tube line, the less the tire contact point trails behind the head tube line and ground intersection.
The shorter the rake, the less we place the axle in front of the head tube line, and the less closer the tire contact point gets to the head tube line and ground intersection.
In other words, the shorter the rake, the greater the trail.
The greater the trail, the more the steering acts like a shopping cart wheel.

So, track bikes typically have steep head tube angles and a short rake, which means quick initial steering, but, because of the long trail associated with a short rake, track bikes also have greater stability.
So, track bikes have quickness combined with stability, which sounds good, but also doesn't make much sense.
Quickness of steering would seem to work against stability.

Hm.

Well, it does work against stability.

Track bikes do not attain the speeds that road bikes attain.
I think it fair to say track bikes live below 35 miles per hour.
At higher speeds, such as a fast racing downhill where bikes hit 50 and 60 miles per hour, a track bike would get into "high speed wobble."
High speed wobble takes me beyond my level of understanding, and so I can't say why it happens more with a bike set up for the track, but it does.
Conversely, road bikes, which, to me, have relatively dead handling, do very well at racing speeds.

In other words, designers can tailor the geometry of the bike, meaning, wheelbase length, head tube angle and rake (which together determine trail), for a given speed range.

My Bianchi Pista has the steepest head tube (75 degrees) and the shortest rake (28mm) of any bike known to me.
It handles very well at the street speeds where I live, below 20 miles per hour.
In fact, at 20 miles per hour and below, I can't imagine it getting any better than a Bianchi Pista.

In comparison, a Mercian Super Vigorelli, a real track bike, has a head tube angle of 74 degrees and a rake of 33mm; which means, the Mercian folks designed this bike for more competitive, higher track speeds than the typical Bianchi Pista rider will ever see.

If a person wants to ride a fixed gear with a big chain ring and a small cog on the street, and go very fast, he might want a frameset with a more relaxed head tube angle and a longer rake than one would find on a Bianchi Pista.

I've ridden my Bianchi with a big chain ring and a small cog, at 82 gear inches, and I can do it and the bike can do it, but the bike doesn't feel good doing it.

I like zipping around town, with lots of acceleration and deceleration, shortcuts and precise handling at slow speeds, and the Bianchi Pista works great for me at my present low, low gearing of 59 gear inches.
I never go very fast, as much as I go quickly. :)

So, in what speed range does a rider want his bike to excel?

Slower?
Then the rider wants a steeper head tube, shorter rake, and shorter wheelbase.

Faster?
Then the rider wants a more relaxed head tube, a longer rake, and a relatively longer wheelbase.

Or something in between...

The only important thing you need to know about track frame geometry is that you can describe it as "agressive," "tight" and "responsive" and wax lyrical the virtues of such geometry on the street.

so steep head and short rake is stable at low speeds and squirrely at high speeds?

and slack head and long rake are slow to steer at low speeds and come into their sweet spot at higher speeds?

Ken Cox: Post of the year? I think so.

My new signature.

Hahaha, thanks!

i just jizzed

Certainly track bikes normally have a steeper head angle, typically 74 or 75 degrees. The seat angle can be shallow as on short indoor tracks the pros tend to sit back, I believe to get weight over the back wheel.
The sloping top tube would be on a "low pro" previously used for pursuits.

Ah, you're right, I hadn't considered that. Would it make a noticable difference? We're barely talking inches.

And Ken Cox.. great post! Very, very informative. Thanks!

Great post Coxy. That bit about how response curves change at different ht angles was new to me.

Yes if you shift the bars forward to match it will be quite noticeable.

As usual ken cox's post is the rambling of an ignorant loudmouth. He's read some and thought a lot but most of what he says is either a misinterpretation or flat out wrong. At least this time he's not endangering anyones health with his ****ty advice and ridiculous assertions.

haha, why aren't you a mod yet?

Ahh, I can but dream of one day being "cool enough" to rouse the angry dutret.

Seriously, what exactly about Ken's post was off?

Typically, dutret calls me names and doesn't tell us with what that I've written he disagrees, nor why.

I should collect all of dutret's insults and post them in a thread on that subject.

I've decided to have a sense of humor about dutret, like my own personal gremlin on this forum.

I can really stir him up if anyone would like to see it.

Kinda amusing.

By the way, has anyone here ever heard the phrase "projectile vomiting?"

I see examples of it every now and then in my line of work.

Funny I should think of it now.

Hm.

Oh, I remember.

Did dutret say something about me?

not sure whether I read this here or in Japanese on Mixi, but someone said that the keirin frames with ultra steep seat tubes were the product of a fad spawned by a successful racer who had a frame made super steep......and then everyone else who copied him for a while.

-His choice of four main factors which effect handling was laughable.
wheelbase should be towards the bottom for a road bike.
rake has little effect outside of trail and weight distribution yet is listed by itself.
Weight distribution is incredibly important in handling but isn't mentioned.

-His dissection of headtube angle shows a complete lack of understanding of how a bike steers. We don't turn the bars to lean we lean to turn the bars.

-His discussion of trail while not wrong is overcomplicated by his continual reference to the position of the axle and a plumbline rather then the simpler point where the tire meets the pavement. He uses the generic shopping cart analogy but doesn't explain what it means. I'm not completely sure if he even knows. While this is not in itself incorrect it shows how he doesn't really understand the concept very well and risks confusing others.

-His discussion of speed on and off the track is laughably uninformed. The fastest bikes on the track(other then stayers bikes) have the steepest angles.

This is part of a general trend with ken cox's posting. He knows a little about bikes and thinks about things a lot. He then makes these incredibly long winded posts that are accepted as insightful due to their length and the complexity of his reasoning.

As far as his assertion that I always blast him without explaining why I usually take the time to point out all of his mistakes and assumptions since his posts are usually about fit and health and the errors are dangerous. Last night I noticed that the blowhard was up to his usual games and it was being accepted as fact but didn't feel the need to point out all of his specific errors because they weren't endangering anyone as normal.

Random thought: Has anyone ever made something like the equivalent of the Serotta Fit Bike (adjustable top tube, angles, stem length, etc) but actually rideable? That would be an awesome way to experiment with geometry on the go as opposed to on a stationary platform with no wheels or anything.

I'm thinking instead of welding the tubing together into a fixed geometry, you could just thread the ends of each tube and have it screw together into threaded lugs. You would have a set of threaded lugs with slight angle variations which would allow you to play with seat and head tube angles. Then you just screw the whole frame together and tighten it down with washers (like on a threaded headset). This would let you fine tune tube lengths and angles, and the construction might be rigid enough to be rideable (gently) so you could try the geometry out. Seems like the perfect tool for custom frame designers.

I want a bike made of right angles.

You're right, but it's still true that the headtube angle introduces nonlinearity to the steering response. It also allows you to lean while steering, something that is hard to do with a vertical HT. Just using the word "nonlinear" helped make things clear.

Perhaps, but it's not wrong, and I had no trouble understanding it.

Agreed, it was a little confusing to introduce this analogy. The explanation would be fine without it.

I think he is referring to steering stability at speed but I'm confused as well. Clearly even he was a little confused by his own reasoning. Care to 'splain it?

=====

Dutret inferred a priority which I did not imply.

=====

Actually, I devoted over seven paragraphs to the subject of rake and head tube angle, how these combine to create trail, and how trail effects handling.

Beginning:

Ending:

I then gave documented examples of known and published head tube angles and amounts of rake for two track-type bikes, one sold for the street and the other for the track.

A person genuinely interested in the conversation could, if he wanted to, have given documented examples of other bikes with different head tube angles and amounts of rake, and shared his subjective experience with these bikes.

=====

I used the generic shopping cart analogy because everyone here has experienced the castering of a shopping cart's front wheels.
For some reason, because I used the shopping cart as a method of simplifying an explanation, and because I didn't spend several paragraphs explaining intuitively-understandable castering shopping cart wheels to bicycle enthusiasts, dutret thinks I don't understand the concept.

Hm.

I wonder why dutret, then, doesn't explain it to us in terms simple enough for even me to understand.
Perhaps he will.
I would love reading about castering shopping cart wheels.

It remains, though, that I didn't spend seven more paragraphs explaining castering shopping cart wheels because I didn't think anyone had that great an interest in castering shopping cart wheels; and, besides, the mention of them had already served its purpose because everyone intuitively, if not verbally, understands why shopping cart wheels caster (they trail behind the head tube line by quite a lot, eh?).
I wonder if trail has anything to do with it.

=====

I respond to dutret because I assume people expect me to do so.

If I had true compassion for dutret, I would ignore him, wouldn't I?

My apologies to dutret for noticing him.

In the meantime, perhaps dutret would give us the real skinny on bicycle handling, and how weight distribution, wheelbase, head tube angle, rake and trail all interact.
And I don't mean "this good," and "that bad."
I mean a real explanation so we can all understand it as well as dutret does.

no nonlinearity is part of the problem. It sounds good but it does not describe reality.
Lineraity of response is the type of meaningless verbosity that kencox excels at.

1. The non-linearity he speaks of is meaningless.
2. Even it was he's talking about the bikes response to turning the handle bars. That's just not how bike handling works unless your riding under 10mph.
3. A steeper HT if you somehow managed to hold all else equal would result in a LESS responsive bike not a more responsive one since the bike would respond less to shifts in the riders weight and leaning.

It's not wrong but it completely misses the point. The only time he even comes close to explaining trail is with his passing mention of the shopping cart analogy. It makes me highly suspect that he understands trail himself.

He's trying to use the little bit of knowledge he has about bikes and his own reason to make broad unsupported generalizations. It's classic KC babble.

If anything the pista is a better high speed competition track bike then the mercian for many reasons. In general track bikes meant to be used at higher speeds have steeper hts because they also have to respond faster. The exception of course being stayers bikes which just go straight.

Road bikes on the other hand are not relaxed for high speed descent which is a tiny fraction of what they do. They are relaxed because they are ridden farther at lower speeds and don't have to respond as quickly as frequently.

dutret, you said in point 3 that a steeper headtube, if it were possible to hold all else equal, would result in a less responsive bike.
then you said the steep angle track bikes are steep because they have to respond faster.
do they respond faster because all else is not held equal...so a combination of the steep HT and the shorter rake fork, plus shorter wheelbase distributing the riders weight differently make both of those statements true?

Yes it is impossible to hold all else equal. If you increase HT angle you bring the wheel in closer. To keep trail the same you decrease rake now it's in even closer still. Lengthen the TT and you change the relation of your hands to the wheel.

In practice though within the small range between 71 and 75 degrees where most bikes are I don't think the actual effect of HT angle on steering is that great. The effect of HT angle on trail and rider position ends up being much more important.

Come on, dutret.

Instead of telling us how we have it wrong, explain it to us.

Give us your version.

By the way, a second-grader understands counter-steering.

We don't go left by leaning left, because you can't lean left (for every action...) without the bike leaning right.

And so, to go left, we steer right.

Did I really need to explain that?

In any event, I await dutret's discussion of track frame geometry.

How does the head tube angle effect rake?

I thought head tube angle and rake together determine trail.

I look forward to dutret explaining it for me.