Trading 43 rake for a 50 rake fork?

[GrantM]

if they did it your way, a range of the same road fork design with different offsets would have varying brake clearances

It's not really a significant point. It would be easy to manufacture carbon forks where
the brake hole to axle distance can be consistent for different rake forks even if axle to crown is not.

The best post here is Curt's... the reality is that manufacturing tolerances varies more than the amount we're talking about.
If Zank had posted the numbers earlier, and not Marks string of formulas, it would have been clear, at least to me,
what's going on.

As to the other stuff you wrote, I look at it differently. To compare two different designs,
you need to measure the same thing, the same way. People compare bike chainstay length
from model to model all the time, and don't consider BB height in the equation,
they take the numbers from the geo charts.

-g

[blasdelf]

It's not really a significant point. It would be easy to manufacture carbon forks where
the brake hole to axle distance can be consistent for different rake forks even if axle to crown is not.

but then they become dramatically different designs as far as the composites are concerned, they ain't just picking a spot to drill a hole

If Zank had posted the numbers earlier, and not Marks string of formulas, it would have been clear, at least to me,
what's going on.

if you aren't comfortable with a pile of trigonometry, maybe you don't have as full a grasp of "frame design by numbers" as you thought ATMO

smashing your thumbs with the jig out in the shed and designing linearly a la e-richie is perfectly valid

it's totally possible to end up with the same result from both approaches

As to the other stuff you wrote, I look at it differently. To compare two different designs,
you need to measure the same thing, the same way. People compare bike chainstay length
from model to model all the time, and don't consider BB height in the equation,
they take the numbers from the geo charts.

you're still not tracking

BB height is in the equation, it's part of the chainstay length, and that's on purpose

the only lines square to the ground that really matter on a road bike are the saddle setback and frame stack

[GrantM]

BB height is in the equation, it's part of the chainstay length, and that's on purpose

BB height isn't BB drop.

Unless you're assuming all bikes are designed for the same tire size.
that's why I think the center line is a better place measure
where the rear wheel is, feel free to disagree.

-g

[e-RICHIE]

When I plot for front center or rear stays, the measurement is on the ground, directly forward from a point noted by the bb center to a point below the front axle, and similarly rearward to a point below the rear axle. When I measure it with a rule (which makes me, e-RICHIE, the ruler...) I do it differently and get different results. When I plot an/or measure the fork span, it's from the crown race to the front axle line measured on the diagonal.

[blasdelf]

BB height isn't BB drop.

Unless you're assuming all bikes are designed for the same tire size.
that's why I think the center line is a better place measure
where the rear wheel is, feel free to disagree.

if you're trying to make that comparison between bikes with tires of significantly different sizes, you have much bigger problems

[blasdelf]

When I plot for front center or rear stays, the measurement is on the ground, directly forward from a point noted by the bb center to a point below the front axle, and similarly rearward to a point below the rear axle. When I measure it with a rule (which makes me, e-RICHIE, the ruler...) I do it differently and get different results.

don't you make almost all your bikes with the trademark lowest-in-the-game BB?

how often does the rear axle holder on your jig move vertically?

[Mark Kelly]

can we just confirm which is correct all my drawings have the rake perpindicular to the actual fork length so it looks like a right angle triangle

is this not right

caveat is that these are suspension forks and are set sometimes sagged

Yes, that's correct.

The two commonly published measurements are rake (parallel to steerer, 90 degrees) and Axle to Crown,
(direct distance from the center point of dropouts to center-line of the fork crown, at the race.)

-g

250px-Bicycle_fork_labeled.svg.png

As the wikipedia article makes clear, the two standard dimensions are both virtual dimensions, taken using the steerer axis as the datum line. The rake is the distance from the axle centre to this datum line, the A to C length is the distance from the rake intersection to the crown race seat.

It is evident that some people use direct A to C but none of the major fork manufacturers appears to use this, so it's safest to assume the standard method.

[e-RICHIE]

One thing - I wouldn't trust WikiPedia on everything. I have read/seen
the one on me, and that's where my opinion on this comes from atmo.

250px-Bicycle_fork_labeled.svg.png

As the wikipedia article makes clear, the two standard dimensions are both virtual dimensions, taken using the steerer axis as the datum line. The rake is the distance from the axle centre to this datum line, the A to C length is the distance from the rake intersection to the crown race seat.

It is evident that some people use direct A to C but none of the major fork manufacturers appears to use this, so it's safest to assume the standard method.

[e-RICHIE]

The front of my fixture AS WELL AS the rear part - these both move in order to set drop.
Otherwise, I might need a slide rule to figure out where the bottom of the head tube should
be. Or I could simply rely on personal experience.

don't you make almost all your bikes with the trademark lowest-in-the-game BB?

how often does the rear axle holder on your jig move vertically?

[Mark Kelly]

One thing - I wouldn't trust WikiPedia on everything. I have read/seen
the one on me, and that's where my opinion on this comes from atmo.

Richie

I used the wikipedia illustration so I referenced it.

As stated previously in this thread, the "standard model" is also supported by Sheldon Brown's site, all the major CAD programs and the manufacturers of modern forks such as ENVE, whom I asked directly, so in this case (and only in this case) wikipedia can be trusted.

Re your wiki article, yeah, that must be an experience, one that's unlikely to happen to most of us. You know you can edit the bits you don't agree with, or get someone you trust to do so?

[e-RICHIE]

Richie

I used the wikipedia illustration so I referenced it.

As stated previously in this thread, the "standard model" is also supported by Sheldon Brown's site, all the major CAD programs and the manufacturers of modern forks such as ENVE, whom I asked directly, so in this case (and only in this case) wikipedia can be trusted.

Re your wiki article, yeah, that must be an experience, one that's unlikely to happen to most of us. You know you can edit the bits you don't agree with, or get someone you trust to do so?

I like Assange too much to fuck with his head. When his order comes to the top of
the pile I'll probably spell his name wrong on the top tube, just to get even atmo.

[Mark Kelly]

Will you deliver to the embassy in London? If so, who pays for the security checks?

BTW I hope he's fit, cycling in Ecuador sounds like a game for the very stout of heart.

[e-RICHIE]

Will you deliver to the embassy in London? If so, who pays for the security checks?

BTW I hope he's fit, cycling in Ecuador sounds like a game for the very stout of heart.

I lay odds that by the time he sees his frame he'll be a Republican atmo.

[GrantM]

It is evident that some people use direct A to C but none of the major fork manufacturers appears to use this,
so it's safest to assume the standard method.

Bikecad specifically says there is no universal "standard" method.
Not sure what the point of trying to say that the direct Axle to Crown method isn't used,
I think from this discussion, most fork makers use it.


-g

[ron l edmiston]

I lay odds that by the time he sees his frame he'll be a Republican atmo.

-- "BOFFO.."

ronnie with a smile

[Mark Kelly]

Bikecad specifically says there is no universal "standard" method.
Not sure what the point of trying to say that the direct Axle to Crown method isn't used,
I think from this discussion, most fork makers use it.

-g

As you discovered, if forks were actually measured as you suggest, each rake would
result in a change to the head angle of the frame, but i don't believe that's how the
forks are really measured.

It might help to visualize the fork not as a curve, but and "L" with two dimensions,
vertical and horizontal offsets. Length being the vertical, rake being the horizontal.

The axle to crown measurement given by the fork makers is actually
measured parallel with the steerer tube, so it's a constant dimension that
does not change with the variation for different fork rakes, and all the various
rake options in a given model have the same distance from ground to headset.
Only thing that changes is the horizontal offset.

-g

I know it's not universal, I said it appears to be the standard. As did you.

I have never said that direct measurement isn't used, in fact example 2 in my first post uses it. I know most people just gloss over anything with an equation in it but I assure you it's there.

I said most fork manufacturers, not most fork makers. As stated previously, the OP seemed to me to be comparing off the shelf options. If he were going to take it to an Fbuilder who still builds steel forks, the problem wouldn't arise, or at least would be taken care of by said Fbuilder.

BTW thanks for the counterexample, if I could edit my previous statement that I couldn't find a fork manufacturer using the direct measurement I would, but I can't. Which manufacturer is that? The forks look like Apha Qs a bit.

[GrantM]

I know it's not universal, I said it appears to be the standard. As did you.

I was wrong!!!!!!!

-g

[e-RICHIE]

I would like to invite everyone to Ballers 4.0 next May where, rather than talk about bicycles and minutia, we beat
the ever living shit out of each other during the day, and then consume alcohol when we are done. There's red meat,
lots of cursing, even more lying, and we talk about every asshat we don't like because -

What happens at The Acorn Inn stays at The Acorn Inn atmo.

[Curt Goodrich]

I would like to invite everyone to Ballers 4.0 next May where, rather than talk about bicycles and minutia, we beat
the ever living shit out of each other during the day, and then consume alcohol when we are done. There's red meat,
lots of cursing, even more lying, and we talk about every asshat we don't like because -

If there's a BikeCAD blackout, I'm there.

[e-RICHIE]

If there's a BikeCAD blackout, I'm there.

Ballers - The Outward Bound School of Framebuilding atmo.

No loading dock.
No name tags.
No $200 black drapes.