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Fork rake 40-43-45???

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#21 ·
giosblue said:
Well! I tried the 40mm rake, 80 mile Sunday club run.
And as near as damn it. no difference.
Certainly not worth bothering about.
Click to expand...
Glad it worked out for you.

Just curious. Aside from your noticing no difference in handling, how did the Reynolds fork compare to the Easton in ride quality.
 
Discussion starter · #22 ·
Much to my surprise the Reynolds was more responsive. The Reynolds is a Pro Peloton, stiffer than the Easton, A nice ride, but not a long distance touring fork.
 
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#23 ·
PJ352 said:
I'm not familiar with all TT forks, but the diagram you posted shows a straight bladed fork. That given, their method of measurement wouldn't skew the results, but with a curved bladed version, it would.
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Why does it matter if the blade is curved or straight? If you're just talking about measuring the distance from the dropout to the crown race, the fork could have ANY shape (it could even be S-shaped) but the measurement should not change.

Asad
 
#24 ·
asad137 said:
Why does it matter if the blade is curved or straight? If you're just talking about measuring the distance from the dropout to the crown race, the fork could have ANY shape (it could even be S-shaped) but the measurement should not change.

Asad
Click to expand...
Here's a clarification. With a straight bladed fork, IF the rake is built into the crown/ steerer interface, using the particular method of measuring that CurbDestroyer posted shouldn't skew the results.

I've never measured an S-shaped fork, but as long as the rake occurs below the crown, IMO/E the method of measuring I initially posted should be used.

I think that's the fundamental difference. I believe rake has to be taken out of the equation, while others using a simple point A to point B measurement, do not. But if you refer back to the OP's third post, my method worked.
 
#25 ·
PJ352 said:
Here's a clarification. With a straight bladed fork, IF the rake is built into the crown/ steerer interface, using the particular method of measuring that CurbDestroyer posted shouldn't skew the results.

I've never measured an S-shaped fork, but as long as the rake occurs below the crown, IMO/E the method of measuring I initially posted should be used.

I think that's the fundamental difference. I believe rake has to be taken out of the equation, while others using a simple point A to point B measurement, do not. But if you refer back to the OP's third post, my method worked.
Click to expand...

The rake ALWAYS happens below the crown, it's impossible for it to happen anywhere else... if you are only measuring the distance between two points, then how they are connected by the fork does not matter. straight fork, curved fork, pinarello onda fork, any shape you like, it doesn't matter.

I always thought axle to crown was exactly axle to crown, not along a line parallel to the steerer tube, but I might be wrong. it doesn't really matter anyway, because if you have either one of those measurements and the rake, then you can calculate the one you don't have.

I do think that some manufacturers might use a slightly different point on the crown when measuring the distance though, so it might be worth checking that.
 
#28 ·
wim said:
More rake = faster steering.
Less rake = slower steering.
Click to expand...
must be translation because more fork offset gives slower steering IE centre line of steering column to front wheel axle centre, the longer the measurement the slower the steering.Same as altering head angle a steeper angle gives quicker turn in but less stability
 
#29 ·
MrPerkles said:
must be translation
Click to expand...
Not sure what you mean by "translation," but if you're talking about rake (also called offset) on a bicycle, less rake or offset increases trail, which slows steering while more rake or offset decreases trail, which quickens steering. It's easy to get confused because one of the lines defining rake and one of the lines defining trail cross each other, reversing what one might feel intuitively.
 
#31 ·
foz said:
The rake ALWAYS happens below the crown, it's impossible for it to happen anywhere else... if you are only measuring the distance between two points, then how they are connected by the fork does not matter. straight fork, curved fork, pinarello onda fork, any shape you like, it doesn't matter.

I always thought axle to crown was exactly axle to crown, not along a line parallel to the steerer tube, but I might be wrong. it doesn't really matter anyway, because if you have either one of those measurements and the rake, then you can calculate the one you don't have.

I do think that some manufacturers might use a slightly different point on the crown when measuring the distance though, so it might be worth checking that.
Click to expand...
I agree with everything you've offered. My comment regarding where the rake occurred was in relation to the two methods of measuring. If rake is just below the interface (as is the case with straight bladed forks), the results won't be skewed when measuring axle to crown. A curved (and I'm presuming S-bend) will IMO need to be measured the way I originally posted, taking rake out of the equation.

I also agree that some manufacturers list fork length in their specs, while others use the axle to crown measurement, so as you say, it's good to reference those specs (or contact the manufacturer) along with taking measurements.
 
#32 ·
MrPerkles said:
im not confused it must be different terminology we use,I have built frames all my life and more rake how I define it = centre line of steering column to front axle distance = slower steering on anything I have built ,ridden and raced
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I define bicycle rake or offset exactly like you do, so one of us is confused about what it does. Let's just leave it at that. :)
 
#33 ·
MrPerkles said:
must be translation because more fork offset gives slower steering IE centre line of steering column to front wheel axle centre, the longer the measurement the slower the steering.Same as altering head angle a steeper angle gives quicker turn in but less stability
Click to expand...
That statement is incorrect. All else being equal, the greater the fork offset, the quicker the steering.

But that aside, IMO the confusion stems from your using motorcycle terminology and applying it to bikes.

Source:
http://en.wikipedia.org/wiki/Trail_(bicycles)

In motorcycles, the steering axis angle is called rake. In the bike world, we call it head tube angle. Motorcycle forks have offset, bikes have rake. Suffice to say, what you're calling rake, we call trail.
 
#34 · (Edited)
PJ352 said:
That statement is incorrect. All else being equal, the greater the fork offset, the quicker the steering.

But that aside, IMO the confusion stems from your using motorcycle terminology and applying it to bikes.

Source:
http://en.wikipedia.org/wiki/Trail_(bicycles)

In motorcycles, the steering axis angle is called rake. In the bike world, we call it head tube angle. Motorcycle forks have offset, bikes have rake. Suffice to say, what you're calling rake, we call trail.
Click to expand...
im not using motorcycle terminolgy ive commercially designed and built frames for over 25 years :) A track bike has in the main steep seat and head angles and a short wheel base ,they turn in quickly dont they or have I got that incorrect ? I would like to be proven wrong I enjoy learning something new very day
Actually in the old days rake at least in the UK was also describing the amount of curve on the forks
 
#35 ·
MrPerkles said:
im not using motorcycle terminolgy ive commercially designed and built frames for over 25 years :) A track bike has in the main steep seat and head angles and a short wheel base ,they turn in quickly dont they or have I got that incorrect ? I would like to be proven wrong I enjoy learning something new very day
Actually in the old days rake at least in the UK was also describing the amount of curve on the forks
Click to expand...
You'll have to argue that first point with Wikipedia. It says you are.

I'm not disputing your abilities as a frame builder, but the statement you made previously is not correct. Whether they be track bikes, road bikes, hybrids or cyclocross, the principles are the same.
For reference:
View attachment 214565
Rake (as you now offer) is the amount of offset from the head tube angle. If you reference your previous post (specifically the statement I bolded), then use the pic as reference, you're describing rake - and saying more rake slows steering is incorrect.

Assuming the same head tube angle (or in m/cycle terms, steering axis angle) more rake = less trail = quicker steering. Conversely, less rake = more trail = slower steering.
 
#36 ·
PJ352 said:
You'll have to argue that first point with Wikipedia. It says you are.

I'm not disputing your abilities as a frame builder, but the statement you made previously is not correct. Whether they be track bikes, road bikes, hybrids or cyclocross, the principles are the same.
For reference:
View attachment 214565
Rake (as you now offer) is the amount of offset from the head tube angle. If you reference your previous post (specifically the statement I bolded), then use the pic as reference, you're describing rake - and saying more rake slows steering is incorrect.

Assuming the same head tube angle (or in m/cycle terms, steering axis angle) more rake = less trail = quicker steering. Conversely, less rake = more trail = slower steering.
Click to expand...
Actually PJ i just re read your posts and you explain it perfectly and I agree how you define rake.If you change nothing on a frame and keep the same BB height and alter rake it affects wheel base yes ? A longer wheel base frame steers slower hence why touring bikes have long wheel bases and shallow head angles with longer rake forks.Am I making any sense now or have I gone mad :) This is from real life experience not Wikipedia,the current carbon frames tend to be short and I find quite twitchy to ride,I just refinished my brothers old steel race frame and it looks like a tandem compared to current geometry
 
#37 ·
MrPerkles said:
Actually PJ i just re read your posts and you explain it perfectly and I agree how you define rake.If you change nothing on a frame and keep the same BB height and alter rake it affects wheel base yes ? A longer wheel base frame steers slower hence why touring bikes have long wheel bases and shallow head angles with longer rake forks.Am I making any sense now or have I gone mad :) This is from real life experience not Wikipedia,the current carbon frames tend to be short and I find quite twitchy to ride,I just refinished my brothers old steel race frame and it looks like a tandem compared to current geometry
Click to expand...
You aren't going mad, but you are making me work here. :)

Yes, if there are no other geo changes, changing rake alters wheelbase (slightly). I generally agree with your example of a touring bikes geo, but am of the mind that specific facets of a bikes geo affect steering/ handling and ride.

As an example, (at the rear) longer chainstays (obviously) lengthen wheelbase, but also tend to smooth the ride a little, while (at the front) a slack HTA and slightly more rake will serve to lengthen wheelbase contributing to more predictable steering. But the primary factor in determining what dictates twitchy or slow steering is trail (determined by HTA/ fork length and rake), so to keep steering in the predictable range, frame designers have to use care in making that 'longer rake' too long, because trail then diminishes, making for quicker steering.

My experiences are 'real world' as well. I just used the source of reference to better describe (through text and pics) what I was trying to convey.

As far as the current crop of CF bikes is concerned, IMO/E frame material is irrelevant. The bikes geo dictates rider fit, handling, and to some extent, ride.
 
#38 ·
PJ352 said:
You aren't going mad, but you are making me work here. :)

Yes, if there are no other geo changes, changing rake alters wheelbase (slightly). I generally agree with your example of a touring bikes geo, but am of the mind that specific facets of a bikes geo affect steering/ handling and ride.

As an example, (at the rear) longer chainstays (obviously) lengthen wheelbase, but also tend to smooth the ride a little, while (at the front) a slack HTA and slightly more rake will serve to lengthen wheelbase contributing to more predictable steering. But the primary factor in determining what dictates twitchy or slow steering is trail (determined by HTA/ fork length and rake), so to keep steering in the predictable range, frame designers have to use care in making that 'longer rake' too long, because trail then diminishes, making for quicker steering.

My experiences are 'real world' as well. I just used the source of reference to better describe (through text and pics) what I was trying to convey.

As far as the current crop of CF bikes is concerned, IMO/E frame material is irrelevant. The bikes geo dictates rider fit, handling, and to some extent, ride.
Click to expand...
I havent mentioned material differences lets leave that to one side.
Most builders use set angles for a range of frame sizes,changing your jig every build isnt commercially viable for long runs.If I wanted a faster steering frame the first thing I would look at altering is head angle,if it didnt bring the wheel to close to the down tube which can be a problem on much smaller frames
We are starting to agree,if the OP put a fork with more rake on his frame are you saying it will steer quicker ? surely not :)
Lots of factors to establish steering in or out the saddle can feel very different ,long chainstays would be stable in long corners.I must be bored today sorry to be a PIA,in the real world most people cant tell the difference between 2 or 3 mm of rake difference anyhow :thumbsup:
 
#39 ·
MrPerkles said:
I havent mentioned material differences lets leave that to one side.
Most builders use set angles for a range of frame sizes,changing your jig every build isnt commercially viable for long runs.If I wanted a faster steering frame the first thing I would look at altering is head angle,if it didnt bring the wheel to close to the down tube which can be a problem on much smaller frames
We are starting to agree,if the OP put a fork with more rake on his frame are you saying it will steer quicker ? surely not :)
Lots of factors to establish steering in or out the saddle can feel very different ,long chainstays would be stable in long corners.I must be bored today sorry to be a PIA,in the real world most people cant tell the difference between 2 or 3 mm of rake difference anyhow :thumbsup:
Click to expand...
I'll answer that by referring you to post #35.

I agree on the 2-3mm rake change. Generally not discernable to most riders.
 
Discussion starter · #40 · (Edited)
More rake = less trail. Less trail = quicker steering.

Less rake ie 40mm from 43mm in my case = less rake.
Less rake = more trail = slower steering.

Not that it matters much in practice.
 
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