forks: steel vs. carbon, straight vs. curved
 

Hi. I'm building a Gunnar Roadie and trying to decide between a Waterford steel fork (which appears to be offered as a straight blade only), and the BRC Profile and Reynolds Ouzo Pro, which are similar in geometry with a slight curve.

Aesthetically, I prefer the Waterford (retro-grouch in training!), but my questions are more about performance, so here goes:

1. Is it rake or trail that determines how stable the handling on a bicycle is? Or a combination of both?
2. Will a straight fork be more "squirrely" than a curved fork? I don't want to be thinking about/correcting my path as I ride down the road, but I don't want a Cadillac, either. (In motorcycle terms, I'm looking for a Ducati ST2, and not a 916....)
3. Will a straight fork ride as smoothly as a curved fork (steel or carbon)? It just doesn't look like it offers much in the way of compliance.
4. Will the Waterford be as laterally stiff as a carbon fork?

Thanks!
David

1. Rake and headtube angle (and wheel radius) determine trail and trail is the controlling factor in how a bike handles. For a given headtube angle and wheel size, more rake = less trail.

2. A straight fork can be more rigid, less rigid or the same as a curved fork. The rigidity is dependent on crown and blade thickness, not whether the blades are curved.

3. Same answer as #2. Remember, straight forks are raked too but the rake is set by the angle of the blade/crown interface, not by the blade curve.

4. Depends on the carbon fork.

1. Handling is determined by head tube angle and trail. Note that rake actually means head tube angle to some (although from vertical, not horizontal - i.e. a 73 deg head tube angle on a bicycle is a rake of 17 deg) and fork offset to others. In the motorcycle world, rake typically means HTAFV and in the bicycle world, it typically means fork offset. If you keep HTA and tire radius the same, increasing the offset decreases the trail and decreasing the offset increases the trail so I suppose you could also say that HTA and offset determine the handling.
2. No. A straight fork with the same offset as a curved fork will handle exactly the same.
3. Some people say no. I haven't noticed a difference.

Mmmmm, a straight steel fork? Is that truly retro? :)

Well, just because I'm old doesn't mean I'm stuck in my ways....

Thanks for all the replies. I found this via Google, if anyone is interested:

www.tonyfoale.com/ Articles/RakeEx/RakeEx.htm

David

Main diffs are that the Carbon fork will be a bit lighter, and more likely to snap (rather than bend) in a crash, and the carbon fork will probably do a little better job of dampening road buzz. Note that the latter characteristic is not about shock absorption, which is a physically different thing.

I actually love the look of steel forks, specifically curved ones. You should be able to get Waterford to get you a curved-blade steel fork. They certainly make enough of them, but they don't offer them as a typical option on the "modern-welded-steel" Gunnar line. But I think you'd be able to get a curved one if you want to - just ask a few times.
Curved steel blades should be able to be tuned to flex a bit in the vertical plane, better than straight-blade. But tests have always been inconclusive; straight-blade works just as well or the same from everything that I've seen. So go with what look you like on the curve question.

Hillrider's post is correct.

Are you sure about that?

Carbon forks, in comparison to steel, are more likely to snap rather than bend in a crash. That's pretty clear, both from reports and from the nature and design of the material. I don't know if that actually makes steel any safer, though. A crash hard enough to snap a carbon fork or badly bend a steel fork is probably pretty dangerous regardless of whether the fork bends or snaps.

other good reads
http://www.phred.org/~josh/bike/trail.html
http://www.kreuzotter.de/english/elenk.htm
http://www.slowtwitch.com/mainheadin...geometry2.html
http://www.dclxvi.org/chunk/tech/trail/
http://www.sheldonbrown.com/rinard/

Carbon provides no warning before it breaks.

What a wonderful feature in a load bearing component.

I agree, I think your first post came across the opposite of what you meant.

Isn't there a slight variable in the "length" of the fork? Specifically, the stright line distance from where the fork seats in the head set & the axle center line. A difference in this length will slightly raise or lower the head tube & therefore change the rake. Correct? Or, have I have too many cups of coffe today? Bob

True. But road forks don't vary much in length. A few quick calculations show that it takes a fork about 15mm longer to slacken the head angle by 1 degree. Fork length is a much bigger issue for MTBs where they can vary by over 50mm, especially rigid forks.

You will not be disappointed by the Roadie, regardless of which fork you choose.

The only objective reason to go with carbon is to save a non-trivial amount of weight. (And that is a legitimate consideration.)

The "road buzz" argument is mostly bogus IMO. Gunnars are amazing bikes. My wife rides a Sport with a steel fork and it's a truly fantastic ride. Way smoother and way less "road buzz" than on her old Trek 1200c with a carbon fork. Granted, we're talking about a significant jump in price point and quality, but it does show that carbon is not =inherently= smoother and will not, by itself, make a great ride.

If you buy the whole exploding carbon fork theory, you might want to stick with steel.