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Fork rake angle ?

13321 Views 19 Replies 9 Participants Last post by Kontact, Sep 20, 2013

TheMilkMan

Discussion Starter · Sep 12, 2013

I cracked my carbon fork and have found a fork to replace it with. My current fork has a rake angle of 45 mm. The replacement fork has a rake angle of 44 mm. Will the one mm of difference have an effect on the way the bike handles?
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laffeaux

· #2 · Sep 12, 2013

There will not be enough of a change for you to notice it. In theory the 44mm fork will be slightly more stable at speed - but again you'll likely not be able to detect it. (assuming that the axle to crown length is the same)

Scooper

· #3 · Sep 12, 2013

Nit-picking here, but fork rake is not an angle; it is a dimension representing the offset of the fork dropout center from the straight line of the steering axis (centerline of the fork's steerer tube).

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c_h_i_n_a_m_a_n

· #4 · Sep 12, 2013

Should it not be the other way round? A shorter fork rake makes the bike more responsive and so-called less stable at speed? But 1mm is negligible. I could be wrong.

Randy99CL

· #5 · Sep 12, 2013

c_h_i_n_a_m_a_n said:
Should it not be the other way round? A shorter fork rake makes the bike more responsive and so-called less stable at speed? But 1mm is negligible. I could be wrong.

You're right. And since 1mm is only 1/45 (about 2%) different I wouldn't expect to feel much change.

Mike T.

· #6 · Sep 12, 2013 (Edited)

c_h_i_n_a_m_a_n said:
Should it not be the other way round? A shorter fork rake makes the bike more responsive and so-called less stable at speed? But 1mm is negligible. I could be wrong.

Less rake = more trail = "slower" handling.
More rake = less trail = "faster" handling.

Huhh.....RBR pics thing still not uploading.

Doing it the hard way -

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Scooper

· #7 · Sep 12, 2013

Mike T. said:
Less rake = more trail = "slower" handling.
More rake = less trail = "faster" handling.

Here it is -

Huhh.....pic not uploading. I'll try again later.

laffeaux and you are correct. More rake = less trail = less stable, but 1mm difference in rake won't be at all noticeable.

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Mike T.

· #8 · Sep 12, 2013

Scooper said:
laffeaux and you are correct. More rake = less trail = less stable, but 1mm difference in rake won't be at all noticeable.

Yep, 1mm is nothing.

TheMilkMan

Discussion Starter · #9 · Sep 13, 2013

Thanks for the help guys

Kontact

· #10 · Sep 19, 2013

Less trail is more stable at low speeds. More trail is less stable at low speeds. At high speeds, the opposite becomes true.

Scooper

· #11 · Sep 19, 2013

Kontact said:
Less trail is more stable at low speeds. More trail is less stable at low speeds. At high speeds, the opposite becomes true.

Can you elaborate a bit on why "less trail is more stable at low speeds?" I'm just trying to learn.

Dave Moulton: Trail, fork rake, and a little bit of history

Dave Moulton said:
Less fork rake, increases trail, because the wheel center is moved back away from the steering axis. More fork rake means less trail because the wheel center is moved forward.

Cycling Tips: The Geometry of Bike Handling

Cycling Tips said:
TRAIL

The product of head angle and fork rake gives you what is referred to as “trail“. Trail is a figure that will reflect how fast a bike actually steers. More trail equates to slower steering, less trail will make faster steering. Increasing fork rake for a given head tube angle will decrease trail, therefore giving faster steering at the front end. More trail is good at high speeds, but at slower speeds it can make the bike feel sluggish. Trail can be thought of as the tire contact point trailing behind the steering axis.

Doesn't "sluggish" mean more stable rather than less stable?

bikerjulio

· #12 · Sep 19, 2013

Less trail is more stable at low speeds.

???

My test of low speed stability is the ability to easily ride "hands off"

I have a NN frame that could not be ridden hands off with one fork.

Substituting a fork with 3mm LESS rake, and therefore MORE trail, got me a bike I could ride hands off. To me that is more stable.

ZachUA

· #13 · Sep 19, 2013

What would be the reason that a fork would have a 'reverse' rake? (Not sure if that's the correct term)

Example:

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Mike T.

· #14 · Sep 19, 2013

ZachUA said:
What would be the reason that a fork would have a 'reverse' rake?

Visual advertising? Being different? The past 100+ years of cycling history is littered with forks of different shapes. It matters not the shape of the fork as long as the rake is within acceptable specs.

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Scooper

· #15 · Sep 19, 2013 (Edited)

2

ZachUA said:
What would be the reason that a fork would have a 'reverse' rake? (Not sure if that's the correct term)

It's a style thing like the Pinarello wavy fork.

The fork doesn't really have negative rake, it jut looks that way.

"Stayer" bikes do actually have negative rake (lots of trail) for extra stability at high speeds.

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ZachUA

· #16 · Sep 19, 2013

Mike T. said:
Visual advertising? Being different? The past 100+ years of cycling history is littered with forks of different shapes. It matters not the shape of the fork as long as the rake is within acceptable specs.

Man, that 2nd fork is different looking and kinda neat. seems like there'd be a ton of stress at the bend.

Scooper said:
It's a style thing like the Pinarella wavy fork.

The fork doesn't really have negative rake, it jut looks that way.

"Stayer" bikes do actually have negative rake (lots of trail) for extra stability at high speeds.

Thank you for the overlay of lines!

So if I bought that frame and swapped the fork for a straight one, that would result in slower handling, right?

laffeaux

· #17 · Sep 19, 2013

ZachUA said:
So if I bought that frame and swapped the fork for a straight one, that would result in slower handling, right?

The shape of the fork does not define the rake. Most "straight" forks have an offset at the crown - the fork legs are not an extension of the steerer tube, they come off at an angle. Forks with straight legs come in various offsets.

A fork with less offset will make the bike handle slower (as the bike is more "self-centering") regardless of the shape of the fork legs.

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Mike T.

· #18 · Sep 19, 2013

ZachUA said:
Man, that 2nd fork is different looking and kinda neat. seems like there'd be a ton of stress at the bend.

That's a Bates Diadrant fork from the ex UK framebuilder EG Bates. Back years ago, in UK racing, advertising on bikes or clothing was not allowed so frame makers came up with many creative ways to make their frames noticeable. Fork shape was one of them.

Many frame makers still do this. You really think there's a real benefit to those weird forks on Pinarello bikes?

So if I bought that frame and swapped the fork for a straight one, that would result in slower handling, right?

Only if the fork had less rake (which equals more trail which equals slower handling) than the original. Someone else posted - straight blade forks ALWAYS have rake built into their attachment to the fork crown.

Scooper

· #19 · Sep 19, 2013

laffeaux said:
The shape of the fork does not define the rake. Most "straight" forks have an offset at the crown - the fork legs are not an extension of the steerer tube, they come off at an angle. Forks with straight legs come in various offsets.

Right!

Here are two forks, one (on the left) with curved blades to provide the rake in the curve, and one where the rake is cast into the crown and the blades are straight (on the right).

The crown on the right with the built-in 7° offset will generally produce a rake of between 40mm and 45mm for a 700c wheel (there's enough play in the crown socket to give that 5mm range at the dropout before brazing the blades to the crown).

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Kontact

· #20 · Sep 20, 2013

Scooper said:
Can you elaborate a bit on why "less trail is more stable at low speeds?" I'm just trying to learn.

Dave Moulton: Trail, fork rake, and a little bit of history

Cycling Tips: The Geometry of Bike Handling

Doesn't "sluggish" mean more stable rather than less stable?

I don't think it is a stretch to say that bikes appear to handle differently at different speeds, and that some bike makers seem to use rake angles that are above, below and at "neutral trail". Agreed?

There really isn't a good vocabulary set for talking about this stuff, but at higher speeds bikes are steered (and therefore balanced) by leaning, and that leaning is created by counter steering to upset the current lean angle and establish a new angle.

At low speeds the bike is actually steered directly - you turn the front wheel where you want the bike to go.

Low trail forks are easier to accurately steer at low speeds. I imagine that issues of wheel flop and caster effect are the direct reasons for this. Merckx tended to design his bikes with low trail specifically because low speed stability is really important on cobbles in the spring classics, for instance. At high speed, low trail feels vague, giving the rider less input where the wheel is pointed.

High trail forks resist being taken out of their current plane at speed, making counter steering more deliberate and causing the bike to change lean angle in a slower, more controlled manner. This is very comforting when you're going 50 mph downhill. This is favored by most big brands because fast unstable is scarier than slow unstable. But at low speeds the front wheel is less guide-able and makes hands off riding very difficult - try riding a high trail bike hands off at 10 mph and you'll tend to agree.

Neutral trail bikes don't feel particularly extra-stable at any speed, but they don't change character. A lot of the American build crowd, like Spectrum, prefer this.

Keep in mind that until very recently, no one could even accurately model bicycle steering and stability, so we are using an inaccurate shorthand to even talk about it.

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