Bill in VA

I have a question for the framebuilders.

What is the reason that there has been a great increase in the use of straight-legged forks versus the more traditional curved blades? This is not a question related to trail.

By this, I am asking if there an engineering (1” or 1 1/8” steerer, disk/caliper/canti/v-brake, etc.) rationale, or are there material choice (steel, Ti, alloy, carbon) justifications (or both), or is for ease of mass production by major brands (no bending of blades) that is driving this change. Or is it more of a stylistic / popularity move?

Thanks.

unterhausen

Engineering in framebuilding is extremely rare, outside of testing. My understanding is Colnago introduced straight blades a couple of decades ago because it was cheaper. We have just gotten used to the looks.

Cynikal 

I would guess that it's just easier to build and requires one less tool. The trade off is less control over rake.

Andrew R Stewart 

Straight or curved blade shaping has nothing to do with how much or little rake/trail there is. The exact same amount of both can be made with either type of blade. The suggestion that a straight blade restricts the rake options is a, sadly too frequent, miss conception. Andy

Cynikal 

Interesting. From what I have read is that you want a tight fit between the crown and the blades, which would limit the amount of adjustment. Can you expand on this?

unterhausen

there is considerable slop in those 7 degree fork crowns. I made a straight blade road fork with 55mm rake, for example. OTOH, every bike made in the last decade has 45mm rake.

Cynikal 

I have done the same but the fork I built was around 390-395 A-C but I had a really tight fit with mine which I preferred because I was using silver Anyway, that's good info, I'll switch to brass for the next one I have get personal with.

unterhausen

I don't think there is anything wrong with using silver

Andrew R Stewart 

As mentioned when using an off the shelf crown with a set blade angle there's some room for blade fit. Then there's the blacksmithy added amount. Then there's the self made crown method. Then there's the segmented fork. Then there's the unicrown fork. And oh, did I mention the drop out fit into the blade end can change the rake too?

I note the lack of exclusion in the OP's question or the initial replies. If one wants a specific type of construction then say so right off the bat and don't assume we can read your mind. Andy

Cynikal 

Fair enough. I guess I assumed a few things and limited it to my experience. I've only built a fork with a crown with a 7 degree angle, straight blades and socket dropouts. Now I understand what you meant.

Bill in VA

Actually, I did not exclude or include anything as I was seeking info on why there has been the shift to the straight blades on many current bikes and wanted to get a non-judgemental explanation which I did receive. My question deliberately avoided the trail aspect as the distance from the steerer centerline to the axle (rake) is the same whether it takes a longer curved blade or a shorter straight blade and that the trail/rake calculations is a frame/fork fitting and geometry design issue. This is part of my education as I am considering a steel frameset that I want to have select modern features, but with a traditional appearance and clearance for a second wheelset with up 700x38mm tires.

Personally I do not like the appearance of straight blades (granted, that is my taste), but was curious if maybe it was for discs brakes (similar to the rise of through axles), and wanted to see if there was a technical design justifications from a frame builders viewpoint. I prefer the look of a curved blade, and wanted to continue to use cantilevers brakes and a more traditional frame (although a slightly sloping TT is fine), but I like to ride a bike with a French fit so the bike has the bars and seat close to level.

guy153

I think you just buy a cast crown with a bit of an angle built into. Then the blades go straight in.

See: https://ceeway.com/NEWPARTSPAGES/Cast...k%20Crowns.htm. A few of those have a 7 degree rake built into the crown and say they are for straight baldes.

Andrew R Stewart 

I should apologize for taking out my frustrations on this forum. These days I'm getting home rather burned out from the bike shop. As many of you know some of us (like in NYS) have been going full bore and still falling behind in the service while we also are disappointing so many customers with the inability to supply them with their needs. It is getting harder to answer the same few questions over and over (Are you open? Do you have a XXX bike in 20" and blue? Why can't you just ramp up your staff so my bike can be fixed sooner?) I should have been more specific to who I was referring to in my rant, or just have been less rantful

As mentioned disk brakes have changed how forks are designed. It's far easier to weld/braze on a disk caliper mount onto a straight blade then a curved one. I do find it interesting that, unlike rear drop outs, there's no commonly available front drop outs with a caliper mount already included. Andy

unterhausen

Some people have asserted that a straight blade withstands disc braking forces better than a curved blade. I'm not sure I believe that, I think it's just as easy to put a backwards bend into a straight blade as it is to unrake a curved blade.

Straight blades predated widespread use of disc brakes, so that's not why companies are using them. I know there are a lot of people that like the looks of straight blade better

Andrew R Stewart 

Eric makes a good point about the historic use of straight blades. I think every high wheeler I've seen (and ridden) have had straight blades. Also the comment about the bendability of a straight VS curved blade is what I feel is correct. But count me on the curved blade looks better side of the road.

Off to the war now. Andy

Cynikal 

Thanks. That's what I have done in the past.

Cynikal 

Thanks. That is helpful.

Cynikal 

Thanks for this. These are rough times, rougher for some more than others. For some of us bike stuff is a welcomed distraction others, not so much. Try to take care of yourself where you can.

wsteve464

Maybe because 90 % of the disc brake bikes sold use a carbon fork so not much market for a steel one. OTH there is a much larger market for steel frames to use disc brakes, just a thought.

fietsbob

One thing I grasp, A disc caliper exerts a force un bending a bent blade tip a little ( amount Varies) when on the back of the left blade.
so you stiffen the blade, harsher the ride .. ISO mounts with a spine spreading out the force only seen with a straight base..
Never seen or ridden a Tout Terrain bike with a fatter left than right.. fork blade for disc brake adaptation..

only own a stubby straight fork, 20" wheel Bike Friday disc.. bike, myself .. One other bike Tange MTB fork Curved is drum braked.. the rest rim.

Offset by triple hole twin plate fork so parallel offset to steerer, and a bit of rake 40-622 wheels went on the tour/cargo-bike..
some design winging it on that one.. mean to measure the trail someday

fietsbob

SJS Cycles did say no discs on their raked forks, just straight ones.. haven't looked at it changing , since..

squirtdad

Kirk frameworks builds customs with curved forks and disc brakes (in steel to be specific) so I am guessing there is no specific need for straight forks for discs