# Fork rake 40-43-45???



## giosblue (Aug 2, 2009)

I'm planning to change the fork on my Litespeed Icon.
At the moment I have two options, either a Columbus Minimal with a 45mm offset, or an Ouzo Pro with a 40mm offset. Currently the bike has an Easton EC90SL with a 43mm offset.

The head tube angle on the Icon 73 degrees and most manufactures seem to spec a 43mm with a 73 head tube..

Has anyone on the forum had any any personal experience with different offsets.
I fancy the Reynolds, is 3mm less offset to big a jump from 43mm?


Any input would be much appreciated.


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## PJ352 (Dec 5, 2007)

giosblue said:


> I'm planning to change the fork on my Litespeed Icon.
> At the moment I have two options, either a Columbus Minimal with a 45mm offset, or an Ouzo Pro with a 40mm offset. Currently the bike has an Easton EC90SL with a 43mm offset.
> 
> The head tube angle on the Icon 73 degrees and most manufactures seem to spec a 43mm with a 73 head tube..
> ...


Assuming the forks you're comparing all have the same axle to crown race measurement (about 370mm's), the 40mm rake will slow steering slightly compared to the 43. The 45 will have the opposite effect, making steering slightly quicker. Your trail now is about 58mm's. Going to a 40mm rake will change that to about 61mm's and the 45, 56mm's. 

I've gone from a 47mm rake to a 43mm and couldn't tell the difference, but others have noticed changes to steering response with smaller differences in rake, so YMMV.

FWIW, if you like the way your bike now handles, I'd stay with the 43.


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## dcl10 (Jul 2, 2010)

The Easton EC90SL has a very short A-C meansurment at 365mm. The Ouzo is 371mm I believe. That would slacken up your head tube by about .6 degrees and would give you a trail of about 65, which is pretty slow. 62mm is generally considered to be the upper limit for a race style bike. Columbus generally uses an A-C of between 371-373, so you should get around 60mm which is not too bad as a good number of bikes are setup stock that way. One trick you can use is to run a 25mm tire in the rear, and a 23mm in the front. Raising the back of the bike by 2mm, will change the HT angle by almost .5 degrees, so you will basically be back at 56mm of trail.


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## giosblue (Aug 2, 2009)

The reason I thinking of changing is because the Easton is a bit on the stiff side for my ageing hands.

This A to C length is a funny one, my measurements don't seem to match up.
The Easton measures 375mm, the Reynolds non integrated is 380mm, and another Reynolds Ouzo Pro with integrated H/S measures 385mm..

Most forks seem to be in the 370 area from what I can tell.


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## PJ352 (Dec 5, 2007)

giosblue said:


> The reason I thinking of changing is because the Easton is a bit on the stiff side for my ageing hands.
> 
> This A to C length is a funny one, my measurements don't seem to match up.
> The Easton measures 375mm, the Reynolds non integrated is 375mm, and another Reynolds Ouzo Pro with integrated H/S measures 380mm..
> ...


You might not be measuring correctly, or your method is inaccurate. Measure from the axle to where the crown race is installed, following a straight line. 

Here's an example (green for axle to crown):
View attachment 213521


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## giosblue (Aug 2, 2009)

Thanks, it looks like I've been measuring it the wrong way.
Measuring it the correct way, A-C is about 5mm less, which would bring them into line with what I see published.
Easton = 370 Reynold non integrated 375, Reynold integrated 380mm.

I have a chance to try the Reynolds non integrated 40mm so I may do that. If I could find one I would fit a Reynolds with a 43mm offset, but these are hard to come by in the non integrated version.
I don't race so the more stable 40mm just might suit me.

So the 40mm Reynolds with a A-C of 375mm and an head tube angle of 73 deg would still be considered acceptable for my type of riding?


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## PJ352 (Dec 5, 2007)

Using your figures for both the Easton and Reynolds, your current trail of about 58 will increase to about 64. 

It's a matter of preference, but if you like the way your bike handles now (with the Easton), I'd suggest staying with s 43mm rake. A trail of 64 will slow steering a little.


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## giosblue (Aug 2, 2009)

I found an on-line calculator, but it doesn't take into consideration the fork length.
Also it shows two types of trail, one is mechanical.

Is the trail we are measuring "mechanical?


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## PJ352 (Dec 5, 2007)

giosblue said:


> I found an on-line calculator, but it doesn't take into consideration the fork length.
> Also it shows two types of trail, one is mechanical.
> 
> Is the trail we are measuring "mechanical?


The amount A-C distance varies from 'X' dicates how much (or _if_) it will change HT angle and in turn trail, so that's separate from calculating trail itself. You'd compensate by plugging in the new HTA value. Higher than 370 will slacken HTA, lower will steepen it. 

Mechanical trail is the vertical component of geometric trail, which is what we're calculating. Here's more info:
http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry


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## CurbDestroyer (Mar 6, 2008)

PJ352 said:


> You might not be measuring correctly, or your method is inaccurate. Measure from the axle to where the crown race is installed, following a straight line.
> 
> Here's an example (green for axle to crown):
> View attachment 213521


I thought axle to crown was axle to crown. The green line in that picture is not going from the axle to the fork crown. It should be like this.


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## PJ352 (Dec 5, 2007)

CurbDestroyer said:


> I thought axle to crown was axle to crown. The green line in that picture is not going from the axle to the fork crown. It should be like this.


Your 'B' measurement is incorrect (and I believe was how the OP was initially measuring). The correct way of measuring is from axle to crown, but_ following the centerline of the steerer_(red line). In the diagram below, you hold a straight edge at the green line and another at at the red line. Where they intersect is your correct axle to crown measurement. The green line represents the fork rake.
View attachment 213720


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## CurbDestroyer (Mar 6, 2008)

PJ352 said:


> Your 'B' measurement is incorrect (and I believe was how the OP was initially measuring). The correct way of measuring is from axle to crown, but_ following the centerline of the steerer_(red line). In the diagram below, you hold a straight edge at the green line and another at at the red line. Where they intersect is your correct axle to crown measurement. The green line represents the fork rake.
> View attachment 213720


I've never seen it measured that way. Everytime I see it, it's done the way BikeCAD defines it. 

https://www.bikeforest.com/CAD/axle_to_crown.php


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## PJ352 (Dec 5, 2007)

CurbDestroyer said:


> I've never seen it measured that way. Everytime I see it, it's done the way BikeCAD defines it.


Actually, BikeCAD defines it as I've stated. Once you get to your link, click on "*this diagram*". Once there, it states:
_Fork length is measured from the fork crown to the center of the front hub, *but along a line that is parallel to the steerer tube* as shown._

Except for the link containing the statement above, both diagrams you've posted are incorrect - or at the very least, misleading.


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## CurbDestroyer (Mar 6, 2008)

PJ352 said:


> Actually, BikeCAD defines it as I've stated. Once you get to your link, click on "*this diagram*". Once there, it states:
> _Fork length is measured from the fork crown to the center of the front hub, *but along a line that is parallel to the steerer tube* as shown._
> 
> Except for the link containing the statement above, both diagrams you've posted are incorrect - or at the very least, misleading.


Bike CAD had to definitions. Fork Length Axle to crown, and Fork Length the way you define it. 

Fork length (axle to crown) is measured along the direct line from the fork crown to the center of the front hub.









Fork length is measured from the fork crown to the center of the front hub, but along a line that is parallel to the steerer tube as shown.


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## PJ352 (Dec 5, 2007)

Your last diagram is correct. The first is incorrect - or (again) misleading. Fork length and fork length (axle to crown) are for all intents and purposes, the same. There is only one measurement of its kind. Check manufacturers specs if you doubt this. 

Re: the second diagram... forget the line that says fork length and measure the center (dotted line) to where the red line intersects (at the axle). Stay parallel with the steerer tube and you'll get an accurate axle to crown (or fork length) measurement.


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## brians647 (Mar 2, 2007)

Cool discussion about axle to crown. That clears up a lot of misconceptions that I had too.
Sheldon has a good calculator on his site as well. He also tested out fork stiffness (years back).

Based on my _limited_ experience, I don't think a fork change is going to really save your hands. If a carbon or steel blade starts flexing enough to be felt, I'd think that you have a structural issue - not a beneficial cushion. I'd mess with tire size, tire pressure, gel cushion under the handlebar tape, and a change in the handlebar tape itself.

Buying new stuff is fun. Having it not live up to expectations and hope is frustrating.


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## PJ352 (Dec 5, 2007)

brians647 said:


> Cool discussion about axle to crown. That clears up a lot of misconceptions that I had too.
> Sheldon has a good calculator on his site as well. He also tested out fork stiffness (years back).
> 
> Based on my _limited_ experience, I don't think a fork change is going to really save your hands. If a carbon or steel blade starts flexing enough to be felt, I'd think that you have a structural issue - not a beneficial cushion. I'd mess with tire size, tire pressure, gel cushion under the handlebar tape, and a change in the handlebar tape itself.
> ...


I think your points are valid, but I'd temper one by saying that IME there _are_ forks that are _slightly_ more 'forgiving' (I guess you could say 'somewhat flexy') with the result being a smoother ride, without exhibiting negative attibutes, but YMMV.

Agree on the possible remedies, and would add good quality gloves to the list. They're all cheaper than a new fork, so may be worth trying first.


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## CurbDestroyer (Mar 6, 2008)

This is from the True Temper Tech Dept. True Temper measures Axle to Crown from the Axle to Crown. This also comforms a lot of other places I've asked. 



> "Attached is a spec sheet for the critical to function dimensions for our forks. As you can see we measure axle to crown distance from the center of the axle to the intersection point of the top of the crown and the axis of the steer tube. Hope this helps."


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## PJ352 (Dec 5, 2007)

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. 

I used your method to measure my Easton fork that's spec'd at 370mm's. It measured 367. My method got me to 370mm's.


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## giosblue (Aug 2, 2009)

Well! I tried the 40mm rake, 80 mile Sunday club run.
And as near as damn it. no difference. 
Certainly not worth bothering about.


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## PJ352 (Dec 5, 2007)

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.


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.


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## giosblue (Aug 2, 2009)

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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## asad137 (Jul 29, 2009)

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.


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


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## PJ352 (Dec 5, 2007)

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


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.


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## foz (Sep 30, 2004)

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.



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.


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## MrPerkles (Sep 4, 2010)

more fork rake gives slower steering so im not sure how you guys are measuring or translating the measurements mentioned above.


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## wim (Feb 28, 2005)

*No.*



MrPerkles said:


> more fork rake gives slower steering


More rake = faster steering. 
Less rake = slower steering.


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## MrPerkles (Sep 4, 2010)

wim said:


> More rake = faster steering.
> Less rake = slower steering.


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


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## wim (Feb 28, 2005)

MrPerkles said:


> must be translation


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.


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## MrPerkles (Sep 4, 2010)

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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## PJ352 (Dec 5, 2007)

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.


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.


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## wim (Feb 28, 2005)

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


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.


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## PJ352 (Dec 5, 2007)

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


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*.


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## MrPerkles (Sep 4, 2010)

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.
> 
> ...


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


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## PJ352 (Dec 5, 2007)

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*


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.


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## MrPerkles (Sep 4, 2010)

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:
> ...


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


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## PJ352 (Dec 5, 2007)

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


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.


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## MrPerkles (Sep 4, 2010)

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.
> 
> ...


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:


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## PJ352 (Dec 5, 2007)

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:


I'll answer that by referring you to post #35.

I agree on the 2-3mm rake change. Generally not discernable to most riders.


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## giosblue (Aug 2, 2009)

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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## MrPerkles (Sep 4, 2010)

giosblue said:


> 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.
> ...


i agree 100% now i need a doctor


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