I know that traditionally, raked fork blades are said to be more comfortable/compliant than straight blades on a regular classic steel rim brake road bike.
But how much of a difference do you actually feel? I’ve only ever had raked blades on all my bikes but if I’m going to build a simple rim brake bike as my first frame I’d like to build a matching fork as well and I like the look of straight blades, but I also like comfort of course.
I know that when I stand up and push into the fork, they all flex a bit but I suppose straight blades would also flex because they’re at an angle compared to the ground. (Especially with a relatively slack HTA of 72.5°)
I’ve done a ton of work on this. There’s virtually no difference in the way straight or curved blades flex (assuming wall thickness, diameter etc is the same). Forks generally flex at the crown, not midway down a blade. The flex is predominantly back and forward, not up and down (think wheelbase growth).
Obviously, two forks that are made of different blade profiles will flex in different ways and by different amounts but the curve of the blade isn’t the thing making the difference.
Thanks Steven, it’s what I expected because I could only find explanations that didn’t make much sense to me, but good to hear your experience confirms this.
Many posts on other forums also state higher stresses in the fork crown on straight bladed forks with what sounds to me like nonsensical explanations. My limited experience with stress calculations says there’s no difference there since the points where forces act are the same. Of course I only have experience with simple static stress calculations so there can always be things I’m missing.
The points where the forces act are the same but the curved blades are physically a bit longer (because the shortest distance between two points is a straight line), and the shape is obviously different.
There should be a little bit less bending at the crown, because the blades make a smaller angle with the steerer there than straight ones would, at the expense of a bit more flex at the bend.
So I don’t know what the end result is (would be interested to see an FEA if anyone has done one). Maybe it’s only a tiny difference.
Moving some of the strain to the curve and away from the crown might be a good thing for durability for the same reason we butt tubes.
I suspect what Jan is seing here is the additional flex from a blade that is designed to flex. It’s not because it’s curved, it’s because it’s significantly thinner at the dropout end.
raked blades are longer, and the longer your spring is the softer. The angle that the tube is at relative to the force vector is also different. with a 7 degree crown and straight blades and +/- 72 degree HT angle the blade is basically parallel to the vector.
This is the stiffest possible geometry for a cantilevered beam.
The empirical tests confirm this as well. If anybody has a hypothesis about why a straight blade would be better than or equal to a raked blade I’m interested to hear it. Until then I think we should just agree that raked blades are more compliant (every thing else being equal). @Hananas build whatever you like! Even better build a straight one and a raked one and ride them back to back. @Chris.D My experience is that over 40mm the tire really mutes the differences.
Hahn Rossman
Good idea! Excellent fork building practice as well.
Although I just got some 30mm Vittoria corsa pros which really smooth out the chatter on rough roads wow so I’m not sure how well I’ll feel any differences.
The SLX fork in its original state with just chrome and no paint was 860g
Fun fact both of these bikes are Ampello bikes handbuilt in Torhout just a short train ride away from where I live and both were put up on the kerb to be taken for free which I find absolutely insane. The blue SLX bike has been completely stripped and repainted though, it looked a lot worse than this when I got it.
Back in the day people were less conservative with the wall thickness. Reynolds 531 is slightly lower strength than modern CrMo but they drew it thinner!
Clearly it’s stood the test of time in the real world (even if it might not pass unrepresentative ISO testing).
I don’t recall ever seeing a 531 fork that was thinner than 1.0 mm. Even 753 was the same thickness, just stronger. They chickened out on making the 753 blade lighter, a missed opportunity IMO. They did make the 753 steerer lighter though, by simply leaving the butt off (plain gauge), brilliant!
Steel blades lighter than Col. SL have always been rare. Tange made a Prestige blade in 0.8 briefly, I used a few but I don’t think any OEMs picked it so it was dropped. Excel made some thin ones too, I wanna say 0.7 maybe, but those had next to no market share and were gone in a few years.
I’d be happy to be wrong, please clue me in if there are lighter steel blades that you can buy today.
This is an enjoyable marketing video from 1982. About 6 minutes in they start telling you all the gauges and things (0.8/0.5/0.8 for 531 “Professional”, which is about the same as most 631 these days).
There’s also this (which I saved from another forum):
which shows 531 blades going to 1.0/0.5mm (and there are also some SL blades listed there, which look like they’re 0.9 the whole way).
Modern 631/853 blades are 1.0/0.6 unless you get the disk specific ones. I have used the curved 1.0/0.6 631 ones on a few builds and they are super-sweet.
So if those blades are 1.0/0.5 and your SLX ones are 0.9, would that be about 155g? It sounds plausible.
So the 531 blades are just butted to a much thinner gauge on the bottom, then the weight difference makes sense!
So I guess they should be a bit more flexy and forgiving as well, it’ll be interesting to try that fork, I haven’t ridden it yet.
All I know is the frame is quite the noodle despite being slightly heavier than my SLX frame.
Interesting, I suppose manufacturers were afraid of critical fork failures? Or perhaps issues with bending the rake in a thinner blade?
Interesting to see from guy153 that there were 1.0/0.5 butted 531 blades though! I’d really like to find a set of those to build my fork with. I bet they ride really nice and smooth, haven’t been able to ride this bike/fork yet because I’m missing a compatible front brake.
Alternatively, since I’ve read that you’ve experimented with really light forks, have you ever tried chainstays for fork blades?
I’d be really interested to see Columbus ZON114OV425 chainstays as fork blades. 30/16 oval tapered to 12.5 round, butted 0.8/0.6mm. My only concern is lateral stiffness…
Yes. Are the steerers the same length though? That could account for a big difference. Some of those tubesets seem to have 0.5mm stays as well. You can’t get any from Reynolds less than 0.6 nowadays (even though the alloys are stronger).
If you watch the recent GCN infomercial for the “Colnago Steelnovo” they mention they couldn’t even make a steel fork at all that would pass their safety tests. So you get a carbon one.
The tubing on that is “custom drawn” by Columbus, but so it can be thicker than regular Spirit! They mention the frame (without fork) weighs 1.85kg. A good 200g over what I would expect for a custom Spirit frame (and more than the Reynolds 531c frames in 1982). It’s not the weight per se that matters so much but the ride quality won’t be the same.
Safety third of course etc. but there is some question whether the testing they do in their rigs is representative of real world failures anyway. Just don’t attach a disk caliper with a stick welder or ride it down the stairs too often and you should be fine
The steerer is about 10mm longer on the lighter fork, so is the axle to crown length (to accommodate fenders), and it has that dynamo mount on it as well! And eyelets on the dropouts but those are probably insignificant.
I wonder if the steerer is butted though… I’ll check by seeing if I can drop the wedge of a stem all the way through, or if I can insert a stem from the bottom.
Yeah I saw the steelnovo video… although I suspect their extensive use of 3D printed parts might add some weight, especially the head tube. It’s designed to look fancy and fit in with the modern carbon bikes anyway.
Still, it’s indeed heavier than I would’ve expected for a spirit tubed bike. I expect my first frame should be a touch lighter with just zona tubing.
Yes should be. Mine normally come in at about 1.7kg (excluding the fork) using Reynolds 631 which is similar gauges to Zona.
There isn’t really that much difference between Zona and Spirit. Some product differentiation going on there. Any Columbus or Reynolds tube is a quality product, and 525 is available in basically the same gauges as 853 (except for the special “Pro-Team” variant).
Interesting! 853 is just more durable then?
Although the wall thickness differences in Columbus aren’t that big either, but I don’t particularly care about saving a few grams in the frame since it’s just a fraction of the total system weight.
I’m just excited about learning how to tune the ride feel and geometry to my exact preferences!
For that I’m glad my SLX frame is a good starting point. I expect the spirals in the tubes don’t really do all that much in reality and I can just use the butting and diameters as a reference?
I’d love a pair of those butted 1.0/0.5 fork blades though for extra comfort in the front end but I can’t find them anywhere.
