I would not do it. I have had curved fork blades straighten from the
leverage generated by disc braking. I have even had it happen on blades
that were 1.6mm thick at the dropout end. Bigger diameter straight blade
forks seem to hold up just fine.
I’m curious, how are 21st-century steel forks made any better in that regard than 1970s forks?
The braking forces at the top of the blades, crown and steerer should be similar between rim brakes and discs, right? The limiting factor being tire traction with the ground and I don’t think that’s changed much since the ‘70s.
The difference with discs is the localized application of force down where the diameter is smaller. But modern forks are still made that way, no improvement that I can see.
The main difference between cheap fork blades and expensive ones is the expensive ones are made thinner/lighter down at the bottom by butting before tapering, for light weight and for shock attenuation. Since this old cheap bike is likely to have cheap unbutted blades (which thicken up considerably at the bottom due to the way they are tapered), I would think this fork is more likely to work with discs than a modern fork made with quality blades.
I quibbled with that and said "I would think this fork is more likely to work with discs than a modern fork made with quality blades."
That was bad judgment on my part to post that, because it sounds like I'm endorsing discs on old raked blades. I'm not. I've seen disc brakes unrake the blade, even once on a heavy tandem blade. What I meant to say is the fact that fork is old is not a good reason to not put discs on it. But there are other good reasons not to.
I'm sorry I screwed up with that previous email, didn't think before sending.
> When Reynolds lists the EB475 fork blade as "rake 15x45mm" does that
> mean the dropout end of the blade is 15mm in diameter and the blade is
> pre-raked to 45mm, or does it mean something else? I can't find drawings
> of the Reynolds blades.
I've got a drawing and the 15 is still a mistery ;)
Tip is 14, and i wouldn't be happy with a diskbrake mount on these blades.
They might not break but the one with the caliper will flex enough in
respect to the other blade that the skewer will unwind
Hi Alex and Mark,
Indeed blades can unrake themselves with the forces of disk brakes. I had it happen to me. A fork came back with a significant amount of rake undone on the disk side. I have been wondering if I am the only one to experience this and my thought is that I couldn’t be.
So far, I fixed this problem by using the “dagger” or the long disk brake mount designed by Wes Willits and sold by Paragon. I bend the piece to match the bent rake of the fork blade and it distributes the forces over a larger area and seems to solve the problem. It is a PITA to do and I am kind of anti disk brake on rigids until we get a fork blades that are engineered for this purpose. Add in the extra weight, setup issues and such and I don’t know what problem we are solving. Although Alex, Alfine is very cool and the brakes are awesome.
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The frontbrake puts the downtube under compression, a shitty 70's brake
will be much softer on the downtube than a much more effective disk.
Apart from the fact that the average American has gained a few pounds in
40 years ;)
As you said, you're "designing around the components" - traditional
fork materials seem very much a square peg to the round hole of your
I've put tabs on MTB and BMX forks. I wouldn't touch this job with a
jimg at yojimg dot net
The FB2 blades that he used are still 12.5mm at the tips.
I think I'll use a sloping crown (like the LC22), trim the legs from the bottom (a good idea from that thread), and use the thickest blades that I can find. I'm just surprised that I can't find beefier legs, since most production forks use them (for instance a Soma fork that I have lying around is 15mm at the dropouts). The tops of unicrown blades with a 28x20 profile (Nova and Henry James) seem like maybe they could be cut down and used with a crown.
I haven't heard of the Rawlands forks (which are raked and disk forks) having problems and believe that they are using blades that are 14mm or 16mm at the tips, but I can measure a friend's fork to be sure.
Someone else suggested using a segmented fork, but I'm not a big fan of the design or convinced that they are as strong as a good crown. I could also just build a unicrown fork, and may do that in the end.
> Someone else suggested using a segmented fork, but I'm not a big fan of the design or convinced that they are as strong as a good crown. I could also just build a unicrown fork, and may do that in the end.
I'm thinking that a segmented fork is actually quite ideal for a disk
application. It lets you conveniently put material where it is needed
by selecting tubing wall thicknesses, something that you don't really
get to choose when using a cast crown. Similarly, you can tune the
blade wall thickness and diameter too, more so than you can with
pre-made blades. This all makes sense to me, considering the location
and the magnitude of the loads that a disc caliper puts on a fork
Using structural elements that have evolved over time to work with rim
brakes, and trying to make them work with disks, just seems all wrong
to me (I'll qualify that by saying that I've got about 10 minutes
total, ever, of riding a bike with disk brakes and I've never built
with them so I'm clearly no expert).
I can understand not liking the aesthetics of segmented forks. I like
the functional look myself. They look like they're all business, and I
prefer the aesthetic to a unicrown.
They seem to be quite well proven in the MTB world so it would seem
that the design is pretty well refined and understood.
It seems to me the tricky thing would be the mitering and making sure
that both side of the fork were symmetrical, but you have a mill so
that wouldn't be a problem.
Anyway, that's my two cents.
Couldn't you achieve the same results with a twin or triple plate fork
On May 16, 2011, at 7:10 PM, Alistair Spence <alspe...@gmail.com>
It would have to be heavier though. A plate crown isn't using the
material as efficiently (a lot of material near the neutral bending
axis that isn't really contributing much to the fore/aft stiffness of