Question About Track Geometry
 

I though track geometry meant steeper angles i.e. 74-75deg headtube and seatube angles for quicker-responding
but when I look at the NJS Panasonic track frame, only the st is 74 or 75, but the ht is 72-73deg
Does the low fork rake make up for the slack ht angle?
Is so, if I replaced my IRO Mark V with a really low fork rake, will that completely change it to track geometry?
my 50cm IRO has 74.5 st and 72 ht
Will that completely change the handling, or am I missing a point here?
http://www.tracksupermarket.com/imag...icPOS_06_l.jpg

FWIW, I was taught that 3mm of fork rake equals about 1 degree of head angle.

I was lead to believe that "Track geometry" was just something people used to sell cheap frames to eager youth, and that really what makes a bike a track bike is rear-facing horizontal dropouts. After all, some crit bikes have very steep geometry. I was talking to a regular at the restaurant I work at about the bike he rides around, and he said it's got 74-degree head and seat tube angles as well as a full compliment of gears, shifters and derailleurs.

As far as I know handling is not determined alone by head and seat angles, but rather the bike as a whole.

Can you be a little more specific? The st and ht angles do contribute a little to track handling right? I'm just trying to figure out everything that does affect the handling as a track frame before I buy a new frame.

Apparently you are missing the point. A decreased amount of rake will increase the trail and make the bike more sluggish. Rake and head tube angle effect how a bike handles, but they aren't interchangable, nor are they the only factors that determine how a bike handles. I would stick with the stock fork or something with very similar specs..it is designed to work with the geometry of that particular frame. Deviate too far from it and the bike will not handle in a way that is was intended and it is not likely to result in an improvement either.

Well, if you want to look into all the factors that contribute to handling, I would start with head tube angle, seat tube angle, chainstay length, wheelbase, fork rake, tire size, bottom bracket drop, seat tube length, top tube length, saddle height, saddle setback, handlebar reach, handlebar drop, stem length, stem height, stem angle, and head tube length. Oh, and the length of your fork will contribute some.

As far as I can tell, track frames generally have steeper head tubes and seat tubes, higher bottom brackets, and a shorter wheelbase. The specific geometry will vary from model to model, but I don't think there is an official track geometry. Even the Specialized Langster, which many people talk about as having "road geometry" has an extremely steep seat tube in the smaller sizes and a some-what steep head tube angle at the top of the size range, meeting at size 58, which has 73-degree angles. A Cannondale Caad-9 has a 73.5-degree head tube angle and a 73-degree seat tube angle in the same size. That said, these bikes will probably handle remarkably different, since almost every other aspect is likely to be very different.

All I'm saying is stop worrying so much about "true track" geometry. If you like how steeper angles ride go for it, and don't worry about the ad campaign behind it.

I thought the track's geometry was oval?

haw.

Most of this has nothing to do with a desire to effect handling, but more to do with efficiency. You might think that a shorter wheelbase is desired for quicker handling, but it is just the by product of using shorter chain stays. The shorter the chain stays, the stiffer the rear triangle, the shorter the chain, the lighter the bike, etc. The bottom bracket is high because there's no real need for the riders to put their foot down or dismount from the bike all the time (unlike you, riding on the street). The height of the bottom bracket really has no effect on the handling of the bike, and makes maybe a barely negligible difference in the ride.

If you're riding on the street, you really have no need for a super stiff rear triangle, or a high bottom bracket. If anything those features just make riding on the street more annoying and less comfortable.

OP: if you really want to know, go ask the folks in the frame building forum.

The bottom bracket is high to avoid pedal strike in the banking of a velodrome.

I think most people would disagree with this. A higher bottom bracket raises the center of gravity of the bike/rider combo and does have noticeable effects on handling. Also, in addition to being stiffer, shorter chainstays (nearly always) equals a shorter wheelbase and it's noticeably easier to turn a short bike than a long bike.

First of all, "track geometry" has changed a lot throughout the decades, to do a lot of things, including fads in bike production. More importantly, it also varies by event. A Sprint bike has the "tight track geometry" we're used to talking about here on the internet. It would probably be a pain to ride during the pursuit. A lot of performance track bikes currently being produced have more midrange geometry - parallel 73 angles, in that area.

Secondly, it sounds like you're unclear on what goes into steering your bike. Don Walker has an article called "the truth about track geometry." bunch of links here: http://nooneline.wordpress.com/2009/...e-angle-trail/ ... basically speaking, a low rake fork and a steep head tube angle balance each other out in order to achieve a decent trail measurement. trail is how far the contact patch of the wheel lags behind the steering axis (an imaginary line drawn from the headtube to the ground). If you lower a headtube angle from 75 to 72, it pushes the steering axis further forward, and in order to maintain a sensible trail measurement of around 60mm, you have to ADD fork rake. for steep headtube angles, you need a lowrake fork so that the bike will be stable.

Adding a low-rake fork to your IRO would result in a very high trail measurement, which will mean very slow handling. I know this from experience. I rode with a bianchi pista concept fork on my IRO for a bit, just cause I had it lying around. It did the opposite of changing the bike to track geometry.

and yes, I think everybody can agree that everything on a bike, most importantly the rider, affects a bike's handling.

I don't know if I would say it is noticeable. I notice that I am slightly higher up, but I don't notice that having any effect on how the bike handles. True if you're on a tall bike it makes a significant difference, but... In any event would you want or need a higher center of gravity for casual riding?

I already mentioned that the shorter chainstays are primarily for efficiency, not to make the bike more maneuverable - the gain in maneuverability is simply incidental to the primary goal of more efficiency. I'm not disagreeing that a shorter wheelbase results in better maneuverability. Though unless you're using your bike competitively, there's not much need for really tight rear triangle.

Lets work this backwards: What are you really trying to accomplish?

agree.

for me i wanted a combination of being able to ride with no hands easily, good response so maybe just a little twitchy but not to a point where it affects ability to ride in straight line, and overall comfort when riding. to accomplish this, i really had to test ride a few bikes at the lbl, memorize how each ride was, and then look at each bikes geometry. what i found for me was that the bikes that were more twitchy or quick responding were the ones that had less wheel base and chainstay length. i thought rake and head tube angle would have a lot to do with it but at the end of the day, the important thing is trail and most bikes have a similar amount. 55-62mm trail, which i feel is enough to handle well and/or ride ina straight line depnding how all the other factors affect it.

so to summarize, i rode bikes with various ht angles and rakes equaling different trail sizes and at the end of the day, i noticed that wheel base and chainstay length affected the ride more. the longer it was, the easier it was to ride in a straight line, the shorter it was, the more responsive it was. this may be true for you or it might not be because the bike may have a diferent reaction to your body type. the best thing to do is to try a few different bikes and get your own opinion.

oh just to add, i also noticed that the better the steel quality, the smoother the ride. by that i mean shock absorbtion. not sure what those panasonic frames are made out of but i rode some italian frames made of columbus zona and those felt so much better than just cheapy 4130 cromo...

just to add, i am 6'4

Steep head angle is for slow speed turning in match sprints (before the 250m burst). If you're racing the miss-and-out, points race, Madison, pursuit, kilo, etc, then a slacker head angle is better. Back in the day, when you road "track" you rode it all include match sprint, so the universal, do-all track bike had a 75* HA, ala the Paramount.

I ride a very traditional track geometry bike on the street, with a 75 degree head tube and a 75 degree seat tube.

However, before I discuss this any further, I suggest the reader visit Anvil Bikes' home page and click on "trail calculator."

http://www.anvilbikes.com/

This will download an .xls file that will allow the user to play with all the factors that determine trail, and this will give the user as complete an understanding of trail as one would want.

Continuing then, a steep head tube gives the rider "quick" steering, and a complementary short rake restores stability to that "quick" steering.

With my 75 degree head tube angle, 28.5 mm of rake/offset, and 25mm tires, I enjoy 60.5 mm of trail, which puts me right about in the middle of the industry standard range for trail (50 - 70 mm).

Returning to "track geometry," the steep seat tube puts the rider far forward on the bike and "opens" his thigh/hip joint for pedaling power, thus making possible a level-back aerodynamic riding position.

This level-back aerodynamic riding position, with so much weight on the arms, hands and front wheel does not lend itself to daily riding.

A person can accommodate him/herself to this riding position, but a more upright "on the horns" roadie-type of position really works better for long-term on the street, mixing with traffic and dealing with road irregularities.

However, a more upright "on the horns" position, in combination with a steep seat tube angle, makes the "cockpit" too short (or the center of weight too far forward), and so, in my case, I ride with a setback seat post.

Alternatively, many riders can "get by" just by sliding their saddle further back on a conventional seat post.

One might notice a trend in recent "track" bikes to a more roadie-type geometry (the 2009 Bianchi Pista now has a 73 degree head tube angle in place of the former 75 degree head tube angle).

I think manufacturers have done this in recognition of the Fixed Gear fad on the streets.

Designers can still create a head tube angle and rake that gives them a trail of around 60 mm, with only a few compromises.

I ride one fixed gear bike that has a 72 degree head tube angle and a much longer rake; I ride a second fixed gear bike that has a 75 degree angle head tube and a very short rake; and both bikes have a trail of 60 mm.

The two bikes, despite their common amount of trail, handle quite differently, and each type of handling has its virtues.

For example, the slack head tube and long rake bike deals with road irregularities much better than does the steep head tube and short rake bike.

And, comparatively, the steep head tube and short rake bike handles very nimbly, with delightfully stable agility.

Both bikes have the same trail.

However, the two bikes have differing degrees of "flop."

I'll let the reader figure out "flop" for himself, but, one could go to the following site for a program that shows "flop" IF you know your true tire diameter (rim plus tire height).

http://kogswell.com/geo.php

I don't race on the track, but I really like the feel of a track bike on the streets, especially the stiff, fast, sprint feeling (or maybe that's just riding fixed). So I'm looking for a frame with the geometry used on the track because right now, I feel like my IRO is slow to steer and is sluggish for fishtailing skids. I rode on my friend's Volume cutter with 74 st and ht, which felt a lot more responsive and easier to ride and skid.
I feel like having that track sprint feeling that I love is way more important than having the "comfortable" road choice. Because in reality, my rides are usually no longer that 10 miles at a time, and I have yet to feel uncomfortable at all on my IRO. I think the whole point of riding fixed is finding that amazing quick, sprint, muscle feeling every time I ride.

And thank you Ken Cox for the very informative post.

Like I said, putting a low-rake fork on your IRO is not going to accomplish that. Another frame will. However, don't forget to consider that one of the reasons you have yet to feel uncomfortable on your RO may be its road-oriented geometry. In the summer I would ride my TK2 about nine miles to the track, race, and then ride back. My body would feel pretty beat up afterwards, which I attribute to the rough riding of a steep-angled short-wheelbase bike. It was good for sprinting, though, but I hate riding that bike anywhere else.

14 miles on my peloton is brutal if i'm not in a bib. i don't think i could do more than that in jeans. even in bibs my junk is falling asleep around mile 9. maybe i have to adjust saddle angle and bar height.

i don't start feeling any numbness on my road bike until mile 25-30-ish, and this is with a saddle i hate.

I just feel on my sprint geo super track tarck bike, i get worn out from the aggressive geo. on the road bike i'll get tired from the pedaling.

Based on your reasoning for why you want track geometry, I would encourage you to hold off on a new frame until you have a better understanding of how a bike's measurements interact with how you are positioned on the bike to determine it's ride characteristics. Sprinting has more to do with handlebar and cockpit setup than geometry, and has nothing to do with seat tube angle since you should be sprinting off your saddle in a serious sprint. And you want stability in a sprint, not twitchyness as that would be disastrous. Get some bullhorns or track drops that suit you, get your stem length dialed in, then sprint your ass off. If you can't feel what is wrong with your ergonomics on the bike, then you don't know enough to make a sensible decision on a new frame's measurements

Oh and as an aside, the volume cutter is a trick bike and all things considered is much less of a track style frame than the IRO is. That's kind of my point about riding more until you understand what you want. If you were stoked on how the cutter handled, track geometry wasn't what did it

http://davesbikeblog.blogspot.com/20...le-bit-of.html

http://davesbikeblog.squarespace.com...-steering.html

http://davesbikeblog.squarespace.com...ebar-drop.html


A few quick reads to get you up to speed on rake, trail, head angles, etc.

Be careful swapping out forks with different rake angles. You can possibly make the bike more unstable and cause it to shimmy. A high speed shimmy can cause a very nasty crash.

I'm just curious, but can you tell me how it's not more track geometry? Because its 74, 74 with a 30 rake? Does it have a longer wheelbase? I understand that the trial should be about the same as that of my IRO ( with a 72 ht and 43 rake), because trail is the same with
steep ht +low rake = slack ht + high rake
and that a higher rake is actually more stable that low rake

and thanks bbattle, I read through those articles and they really helped me with the angle and rake thing :)