Singlespeed & Fixed Gear - Frame Upgrade... Geometry?

So, I've been riding a fixed gear ever since I got to the city three years ago. My converted Centurion Sport DLX has made me very happy. But now its time for an upgrade! I would like to get a new frame that has tighter geometry but is still primarily for urban riding. Its a bike for commuting, working, and leisure, with that nimble track feel.

I have spent some time comparing geometries of frames I have been interested in (Angus, Bareknuckle) and started wondering what really makes the difference. Like... how much does 3* in the H/T angle change things? The Bareknuckle is clearly "tighter" than the Angus, but it is really noticeable? What should I be looking for in a forgiving track geometry?

I feel like my biggest problem is lack of experience and the opportunity for it. Not only have I only ridden one "track" bike (Giant Bowery), but I don't know of anywhere where I can try out an Angus or Bareknuckle! Thanks for the input...

This is the same situation I'm going through. I will lurk your thread to await a reply.

This may not help and I may be stating the obvious but there's more to a good bike than geometry. Don't strike one off the list because of it. You may be surprised at what you like.

I have had about 6 bikes and the the one (a Mike Appel frame) before my current one, I had the chance to create what I thought would be the ideal geometry for me.

Move on to the bike I now ride, a 3Rensho NJS track frame that was built for some keirin racer named K. Yoneda, which is painted on the top tube. It's a little big and I have no idea what the geometry is but I'm loving it.

Like... how much does 3* in the H/T angle change things?

I am no expert, but I have 2 bikes with different Geos. a Fuji Track with 73.5* H/T angle. And a road conversion with a more relaxed H/T angle. I can say after riding both I personally love the track way more. I included a couple pics so that you can compare the 2 bikes and see how the geo is different. What it really boils down to is preference.

I ride a Bianchi Pista and love the handling.

I describe it as nimble.

It seems to thread its own way through road debris.

The Pista has a 75 degree head tube, which corresponds to very quick steering.

Conversely, it has a very short rake of 28mm, the shortest I have encountered, which corresponds to stability.

The two seemingly contradictory qualities, a steep head tube and a short rake, work together very well in the Pista.

Mercian builds their Super Vigorelli with a relatively steep 74 degree head tube and a relatively short rake of 33mm (second in shortness only to the Pista's 28mm).

If in kzac's situation, I would ride as many different bikes, having different head tube angles and rakes, as possible, and find out what I like.

The Pista has a 75 degree head tube, which corresponds to very quick steering.

Conversely, it has a very short rake of 28mm, the shortest I have encountered, which corresponds to stability.

The two seemingly contradictory qualities, a steep head tube and a short rake, work together very well in the Pista.

Could you please elaborate on what stability means in this case? I know what "quick steering" or "twitchiness" feels like, but I don't know what the difference would be between stable and unstable. Does more rake = more stable or does less rake = more stable? thanks.

Could you please elaborate on what stability means in this case? I know what "quick steering" or "twitchiness" feels like, but I don't know what the difference would be between stable and unstable. Does more rake = more stable or does less rake = more stable? thanks.

Wheelbase, rake and head tube angle all work together to define the handling of a two-wheeled vehicle, whether a motorcycle or a bicycle.

Let's start with a head tube angle of 90 degrees, straight up and down.

This head tube angle provides immediate, linear steering; neither stable nor unstable.

As one tilts the head tube, so that the front wheel moves forward, the wheel's contact point moves backwards in relation to a line drawn through the head tube to the ground, so that the wheel trails behind the steering axis.
Taking this to an extreme, imagine the exaggerated forks of "chopper" motorcycles, in which the builder has tilted the head tube and moved the wheel forward so as to allow a longer fork for personal aesthetic reasons.
A line drawn through the head tube extends far ahead of the point on the ground where the wheel makes contact with the pavement.
This makes for non-linear steering, in which the bike initially has slow steering, but also steering which quickly increases out of proportion to the amount one turns the handlebars; slow at first and then progressively faster.
In this configuration, the wheel's contact point trails too far behind the intersection of the steering axis with the ground.

In a bicycle having too much trail, one might bend the forks forward, so as to move the wheel's contact point closer to the intersection of the steering axis with the ground.
This would increase the initial sensitivity of the steering, and, correspondingly, decrease the end sensitivity of the steering.
In other words, this would balance the initial steering sensitivity with the ending steering sensitivity, or bring the two more into proportion with each other.

Bicycles typically have steering angles between 73 and 75 degrees; and rakes between 28 and 40 millimeters.

At angles closer to 73 degrees, which have slower initial steering and quicker ending steering response, designers tend to use rake lengths closer to 40 millimeters in order to move the wheel's contact point forward, closer to the intersection of the head tube angle and the ground, so as to decrease trail and thus increase initial steering and decrease ending steering response; again, bringing initial and ending steering sensitivity more into proportion with each other.

In the extreme case of the Bianchi Pista, the designers gave the head tube the steepest angle conventionally used, so as to quicken overall steering; and, at the same time, they gave the Pista the shortest rake presently in production, 28 millimeters, in order to move the wheel contact point further back from the intersection of the steering tube angle and the ground, and thus give the Pista a normal amount of trail.
The combination makes for very quick and yet stable (meaning non-divergent and predictable) handling at track and normal street fixed gear speeds.
These handling qualities would not work for a geared road or racing bike that sees speeds of 40 and 50 miles an hour, as it would result in handling qualities described as "speed wobble."

It all has to do with the speed range and intended purpose of the bike.

I spend all my time below 20 miles per hour and on the street, and so the Pista's combination of nimbleness and stability in that speed range and setting works perfectly for me.

In comparison, the Mercian Super Vigorelli, with one degree less of head tube angle and five more millimeters of rake, has handling similar to the Pista's but intended for a higher speed range, such as one might see on the track.

In my most recent post, I should have included the example of a shopping cart's castering wheels.

A shopping cart's wheels have a head tube angle of 90 degrees.

If the wheels had zero trail, they would not trail behind the steering tube angle and they would not align with the direction of travel.

In contrast, imagine shopping cart wheels with an absurd amount of trail, such as 12 inches, or more.

If one would just imagine a shopping cart having castering front wheels, with a 90 degree head tube but with varying amounts of trail, or negative rake, he will quickly start intuiting the effect of trail on handling.

Now, take that same trail, or whatever amount of trail, and move it forward and backwards, or lengthen and shorten the wheelbase, or the distance between the front and rear wheels.

Fun, eh? :)

75 / 75 angles

in answer to your question, 3 degrees is a lot. what two track frames are you comparing that have a three degree difference in angle?

angle measurements are quantitative, words like "nimble" and "stable" are qualitative. the relationship between the two is complicated.

check out http://www.dcfixed.com. a lot of us ride anguses, and we have a few bareknuckle riders on the board. much better to feel the difference than to talk about it.

YO Ken man that really helps clear things up! It is weird to think of a front wheel trailing the axis of steering. Especially when all forks are angled forward instead of backwards (like the shopping cart). But then I realized its the wheels contact point on the road that is trailing the steering axis everything clicked. Thanks for taking the time to type all of that. It was very insightful!

in answer to your question, 3 degrees is a lot. what two track frames are you comparing that have a three degree difference in angle?

I was comparing the Angus 53cm (72*) and the Bareknuckle 52cm (75*).

I'll post on dcfixed to see if I can try any out, that would be epic!

I'm willing to bet most people here couldn't tell apart two bikes with completely different geometry unless they were told which is which.

I'm willing to bet that most people here have no idea what they are talking about when they talk about geometry (Ken Cox obviously excluded).

I'm willing to bet you will be happy with whatever geometry you end up getting.

Pista geometry is somewhat problematic, because it makes it hard to replace that craptastic fork it comes with. I know that I probably won't know the difference, but I like the way mine handles and don't want to mess it up.

The angus is meant to go offroad and so it's set up to be more stable than a road bike; the idea is for it to track straight through ruts, roots, rocks, drops and so on. On the road it will tend to feel like a bomber not a fighter (not that you can't still go fast, turn hard and kick ass in traffic on it). Yoshi is wrong; it will feel obviously different from a true track frame.

Cox brings up a good point: geometry is about a lot more than ht angle. Trail and rake (heck also wheelbase and a few other factors too) contribute significantly to handling. want to know more? Read Dave Moulton biatch!

http://davesbikeblog.blogspot.com/2007/04/head-angles-and-steering.html
http://davesbikeblog.blogspot.com/2006/06/squirrelly_30.html

The angus is meant to go offroad...

Yeah?

Another example of a fairly interesting geometry is the soma rush: 75* headtube, 38 mm rake ~= 51mm trail!! i think the "stability" loss is made up for with a fairly long wheelbase of 982mm (for size 59 frame and their matching fork).

the rob roy is the cross bike. The angus is for the street.

the rob roy is the cross bike. The angus is for the street.

DURR my bad. OK just ignore my earlier post.