Singlespeed & Fixed Gear - track frame geometry

ive heard that track frames have a steeper geometry than the standard road frame but i dont really know what that means. what makes its geometry steeper? ive noticed on a few track bikes that the top tube slants downward going from seat post to the head tube. whats that about? thanx austin

track geometry will also have a less sloping head tube and the forks will have 0 rake to them. it makes the bike very twitchy on the road, but this responsiveness is neccessary to shoot up the walls and manuever, etc. track bikes will typically have very short stays. the bottom bracket is higher as well for clearance issues.

edit: that sloping toptube you are referring to may be a pursuit bike. those will usually run a small fork with a 650c front wheel.

whats the benefit of running smaller front fork and wheel? (forgive me, im new :-) )

whats the benefit of running smaller fork and wheel? (forgive me, im new :-) )Smaller and lower frontal area for improved aerodynamics.

track geometry will also have a less sloping head tube and the forks will have 0 rake to them.


now, i haven't been into this track thing for that long (a year or so), but i've never, ever, ever seen a bike with a 0 rake fork.

a guy here in town builds track frames and forks and all of his track forks are totally straight. in 0 rake i mean they don't slope forward more than the angle of the head tube. i don't mean the fork is perpendicular to the ground or anything. his site is sort of out of date and doesn't have any pictures of his track forks, but it's worth a gander:

http://www.groundupdesigns.com/

0 is sort of a blanket statement though. very little rake...

zero rake, sloping top tube, AND 650c!! (http://pages.emerson.edu/students/justin_pyatt/media/images/vantuyl1.jpg)

edited so as not to break things.

with a zero rake fork is there more chance of pedal overlap since it seems to bring the front wheel closer to the frame? also how do people ride with pedal overlap? isnt that unsafe?

I have toe overlap on my Kogswell. Not a lot but yea, it can be tricky. You'd have to ride a bike with overlap to understand that whenvever you're turned far enough to hit your toes you can't be going very fast anyway. You just get used to tapping your feet every now and again and you learn how hard you can turn, no big deal really.

If you don't have a huge overlap, you can tip your foot down on the down stroke during a slow, tight turn too.

or you can tip it up.

my bike has quite a bit of overlap, though not as much as i've seen on other frames (*cough*KHS aero track*cough*). it also makes the steering quite twitchy. but i'll never go back to the original fork for that bike. i'm too used to being able to zip through traffic and change lanes pretty much just by shifting my hips to one side or the other. that bike is so dangerously quick.

comparing my track bike to my old road frame fixie, it takes off faster, sprints better, swerves quicker and feels "tight". On the other hand, it's not as comfy on the arms & hands for long trips, it's harder to slow down, and I do sometimes hit my toe on the front tire. It also doesn't soak up as much of the bumps in the road.

The term steeper geometry refers to the head tube angle which moves the forks into a more vertical alignment than a standard road or touring frame. The rear triangle is shorter due to the seat tube being a slightly different angle than the other type also. The combination of those factors makes for a quicker handling bike that is an advantage in a velodrome setting. It also makes for a harsher ride, but that is not of concern in the short races that take place on a velodrome.


fixedgearhead

a guy here in town builds track frames and forks and all of his track forks are totally straight. in 0 rake i mean they don't slope forward more than the angle of the head tube. i don't mean the fork is perpendicular to the ground or anything. his site is sort of out of date and doesn't have any pictures of his track forks, but it's worth a gander:

http://www.groundupdesigns.com/

0 is sort of a blanket statement though. very little rake...

youre confusing the appearance of straight blades with rake. all forks have rake, and the rake in combination with the headtube angle determine the trail (which is the important thing which determines stability). that builder uses straight blades, the rake is still there, but its at the crown vs the taper in the forks as with curved blades.

You're confused Isotope: adding rake gives a bike quicker handling by decreasing trail, and vice versa. A "zero rake" fork actually increases trail compared to a positive rake fork, making the bike more stable. Bikes meant to go very fast inside a motorycle draft (they hit speeds in excess of 130 miles an hour) generally have negative rake forks for even more stability.

Sheldon links to a great article on this of course, I recommend it.

http://www.phred.org/~josh/bike/trail.html

Does anyone know why bikes use rake? Why not slacken the ht angle and have no rake at all?

youre confusing the appearance of straight blades with rake. all forks have rake, and the rake in combination with the headtube angle determine the trail (which is the important thing which determines stability). that builder uses straight blades, the rake is still there, but its at the crown vs the taper in the forks as with curved blades.

right on.

whats the benefit of running smaller front fork and wheel? (forgive me, im new :-) )


extomesm, bikes like that are meant for races where you aren't allowed or able to draft your opponents, such as a pursuit where two people start on opposite sides of a track and the first person to get passed loses; or an hour record where you see how many laps of a track you can do alone in an hour. Basically you sacrifice some ergonomics for aerodynamics. For the same sort of reason, triathlon bikes look really weird---triathletes aren't allowed to draft each other and so they set their bikes up to fight the wind.

with a zero rake fork is there more chance of pedal overlap since it seems to bring the front wheel closer to the frame? also how do people ride with pedal overlap? isnt that unsafe?
Toe overlap doesn't matter on the track because your not going to turn your handlebar that much
edti: damn didn't know i was answering a question from 4 years ago!

holy thread necromancy!

whoa, i didnt catch that. I was hoodwinked!

extomesm is probably an ol' track pro by now

extomesm is probably an ol' track pro by now

lmao, i ddint' even notice that...holy****.
brought the thread back just to tell isotopesope he was wrong, ****ing awesome.

hahaha yeah, this thread is super old; i was still learning or mistaken i guess. me, for the lose.

Maybe pictures will help?

Note that the track frame has 75° head tube and seat tube angles, whereas the road frame has a more relaxed 72° head tube and seat tube angle. The track frame has shorter chainstays (440 mm vs 460 mm for the road frame), and less fork rake (20 mm vs 35 mm for the road frame) resulting in a shorter wheelbase for the track bike.

The steeper head tube and seat tube angles, shorter chainstays, and reduced fork rake of the track bike make the handling quicker and steering a little less stable than the road bike.

These Nervex frame designs are from the late 1950s, but today's traditional geometry frame designs haven't changed much.

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/TrackvsRoadFrameGeometry.jpg

so, what is the 'standard' point that distinguishes track frame geometry.... 75 deg. 74 deg? how steep do they go.. 80?

I'm curious as to what my headtube/seattube angle is, but I don't have a protractor and am too lazy to pull out the makeshift geometry contraptions right now...oh well

so, what is the 'standard' point that distinguishes track frame geometry.... 75 deg. 74 deg? how steep do they go.. 80?

I'm curious as to what my headtube/seattube angle is, but I don't have a protractor and am too lazy to pull out the makeshift geometry contraptions right now...oh well

i seriously doubt anything is as steep as 80, the downtube would cause interference.
how steep the geometry is depends on what type of track event the the frame is built for. also, it seem that not many frames built recently are steep like the bike of the 80's.

there was a good thread, or atleast a good reply that kind of explained this. pretty sure it 11.4 that posted the reply.

I have toe overlap on my Kogswell. Not a lot but yea, it can be tricky. You'd have to ride a bike with overlap to understand that whenvever you're turned far enough to hit your toes you can't be going very fast anyway. You just get used to tapping your feet every now and again and you learn how hard you can turn, no big deal really.

familyman: you're using an old Kogswell fork - the latest version has about 20mm more offset (bend) which lowers the trail and improves handling and has the nice side benefit of reducing and sometime eliminating toe overlap - lots of owners of older models are changing to the new fork - think about it - Matthew

i seriously doubt anything is as steep as 80, the downtube would cause interference.
how steep the geometry is depends on what type of track event the the frame is built for. also, it seem that not many frames built recently are steep like the bike of the 80's.

there was a good thread, or atleast a good reply that kind of explained this. pretty sure it 11.4 that posted the reply.

http://www.fixedgeargallery.com/2005/dec/AaronPratt-2.jpg

http://velospace.org/files/3rensho_014.jpg

i've seen a handful of keirin frames with supersteep seattubes - i think shants mentioned that the st on his makino was 78 or 79 degrees. but those are anomalies. i don't know why such a near-vert st would be beneficial to somebody - i can't really figure out the body type that that would be good for. but i suppose it exists.

a lot of newer track frames these days aren't being built like the track bikes of old (angles near 75/75), which makes perfect sense. there's a lot more that goes into designing a bike than the steepness of the angles.

the oldness of this thread ammuses me.

i'm impressed (or disappointed) by my memory of knowing exactly where to find those two pictures.

I think combined with asians being generally shorter with maybe shorter thighs than others, and to position themselves over the cranks for maximum power output when in the saddle.

well, they're anomalies, so i don't think relying on the stereotype of short asians really explains a handful of oddly-built bikes in the market.

i recall reading something (i have no idea who wrote it) about one successful rider prefering a very steep seat tube, and his style was mimiced.

personally, i need to be further back in order to spin, and too much weight on the front makes me feel unstable.

but hey, they ride six laps.

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.

well, they're anomalies, so i don't think relying on the stereotype of short asians really explains a handful of oddly-built bikes in the market.

i recall reading something (i have no idea who wrote it) about one successful rider prefering a very steep seat tube, and his style was mimiced.

personally, i need to be further back in order to spin, and too much weight on the front makes me feel unstable.

but hey, they ride six laps.

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.

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.

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.

My new signature.

Hahaha, thanks!

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

i just jizzed

ive heard that track frames have a steeper geometry than the standard road frame but i dont really know what that means. what makes its geometry steeper? ive noticed on a few track bikes that the top tube slants downward going from seat post to the head tube. whats that about? thanx austin

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.

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

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.

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!

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.

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?

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.


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?

　
http://velospace.org/files/3rensho_014.jpg

i've seen a handful of keirin frames with supersteep seattubes - i think shants mentioned that the st on his makino was 78 or 79 degrees. but those are anomalies. i don't know why such a near-vert st would be beneficial to somebody - i can't really figure out the body type that that would be good for. but i suppose it exists.




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.