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Straight fork blades vs radiused, which gives the softer ride, is there a difference?

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Straight fork blades vs radiused, which gives the softer ride, is there a difference?

Old 05-22-12, 01:03 PM
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calstar 
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Straight fork blades vs radiused, which gives the softer ride, is there a difference?

I've wondered about this for awhile and it just came up in the "disc brake location" thread. If one design gives a "softer/cushier/etc" ride why so, or is there even any difference?. Given the short length of fork blades and the loads they're subjected to, and if the blades have the same profile(round or oval, probably not even different then) seems like the material and wall thickness would be the most relevant factors.

thanks,

Brian

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Old 05-22-12, 02:52 PM
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I think words like softer or cushier vastly overstate any possible difference. Obviously the curved fork will be more compliant, but the existence of the straight fork, and this type of question, indicates it is a meaningless difference at the implied level of magnitude.

However, perception is very odd. Often people say one thing and mean another. There is no real suspension effect, or major compliance like fat vs skinny tires, I'm guessing. but whether there is a difference in vibration pattern, onset of vibration, damping, sound, or something humans are responsive to, that is possible. But even then I think it would be unlikely to be consistent for some of the reasons you suggest.
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Old 05-22-12, 03:28 PM
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[QUOTE=MassiveD;14257984...... indicates it is a meaningless difference at the implied level of magnitude.

However, perception is very odd. [/QUOTE]

+1 Until I see some empirical data showing me how/why the straight/radiused blades differ in ride quality I'll consider the differences to be subjective. Other opinions from you builders out there......

Brian
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Old 05-22-12, 03:54 PM
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I would love to see high speed footage of a curved steel fork going over a bump.
I would actually expect that the amount of flex in the fork would be rather surprising.
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Old 05-23-12, 08:26 AM
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Dave Kirk did some dynamic testing on straight blades vs. curved blades while he was at Serotta that resulted in objective data.

http://forums.roadbikereview.com/276129-post20.html

Richard Sachs seemed to think Colnago's Precisa straight bladed forks were more about the economics of building the rake into the fork crown rather than bending thousands of blades with identical bends.

http://richardsachs.blogspot.com/200...t-compact.html
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Old 05-23-12, 08:34 AM
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I think that straight forks are ugly, but they make it so you don't need to bend. Not that big of an advantage. I can't really tell the difference, but I know I'm insensitive to that sort of thing.

Originally Posted by AllenG View Post
I would love to see high speed footage of a curved steel fork going over a bump.
I would actually expect that the amount of flex in the fork would be rather surprising.
I should try that, but I need to find a bump where I can set up my high speed camera next to it
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Old 05-23-12, 08:53 AM
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"The "hit a bump - load path test" showed a significant difference with the curved fork having a good bit greater movement" from Dave Kirk's testing.

I'd really like to see the plotting from that test, also what forces resulted in the difference. Very interesting stuff. Seems like large manufacturers would test something as basic as this(at least on their high end bikes) rather than just stick on a fork and call it good. I'm inquiring about steel only, as I don't no squat about carbon fiber(other than that I have a WoundUp on a steel bike) and most likely will never build one.

Brian

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Old 05-23-12, 11:19 AM
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Originally Posted by calstar View Post
I'd really like to see the plotting from that test, also what forces resulted in the difference.
My guess is that the data are either buried deep in some file cabinet at Serotta or have been thrown out during a spring cleaning or a move.
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Old 05-23-12, 01:27 PM
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I've always wanted to build fixturing to put bike frame parts on one of my fatigue machines, but that's a lot of work for no payoff

The reason that a straight fork and a curved fork have approximately the same compliance is that the straight fork has a larger moment arm over more of the blade. So with a straight fork more of the blade moves as a result of a load.

Last edited by unterhausen; 05-23-12 at 01:30 PM.
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Old 05-23-12, 01:35 PM
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After nearly six years of commuting on my Steelman cross bike (with a straight fork), I just switched over to my recently finished new commuter w/ a curved blade. I can honestly say I've noticed no difference. In fact, I hadn't even thought about it until now. The frames are very different in sizing, but I switched the wheelset over, so that's not a variable. I don't dislike straight blades, so I'd ride another one in the future.
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Old 05-23-12, 01:43 PM
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Originally Posted by calstar View Post
...I'd really like to see the plotting from that test, also what forces resulted in the difference...
Originally Posted by Scooper View Post
My guess is that the data are either buried deep in some file cabinet at Serotta or have been thrown out during a spring cleaning or a move.
A reply to that request from Team Serotta came with a non-disclosure of content statement, sorry.



Originally Posted by calstar View Post
...I have a WoundUp on a steel bike...
Please share your impressions of the WoundUp fork.
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Old 05-23-12, 02:57 PM
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Seems to me that 5PSI of tire pressure difference would far outweigh the blade shape influence. Andy.
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Old 05-23-12, 04:24 PM
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Originally Posted by Werkin View Post
Please share your impressions of the WoundUp fork.
I can. I had one for a couple of years on an aluminum co-motion single I got while racing. Not the lightest available, but it was plenty stiff, rode nicely and I always had 100% confidence in its manufacture. As a bonus, the carbon weave was stunning when the sun was getting low in the sky during after work training rides. I sold that bike a few years ago. I don't miss aluminum, but I wish I'd have kept the fork and D/A 9 speed parts.
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Old 05-23-12, 09:50 PM
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I can truthfully say that there is a marked difference between the ride of these two bikes with the same tire pressure and on the same road surface. There are significant differences between the bikes other than the the fork blades (one is a road bike with Reynolds 953 OS frame and a Reynolds 531 taper gauge fork with curved rake, while the other is a track bike with Reynolds 853 Double OS frame and a chromoly almost straight blade fork with most of the rake built into the crown), so I can't say with certainty that the noticeably greater front end road shock/vibration absorption of the road bike is due to the curved taper gauge fork blades, but I believe it is.



Reynolds has made a point of emphasizing the road shock absorption qualities of it's curved taper gauge fork blades. Marketing hype? Maybe, but intuitively and from my own experience I believe it's true. Dave Kirk's test results at Serotta reinforce my beliefs.

Originally Posted by Reynolds 531 Catalog
Reynolds Taper Gauge Fork Blades

Reynolds 531 oval/round taper gauge fork blades are made from a tube single-butted 18/21 g, with a long gradual change of gauge, for lightness and to ensure that when the tube is tapered the fork has the necessary resilience at the rake while maintaining its strength at the crown.
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Old 05-23-12, 10:34 PM
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This brings up an old memory. In the day it was claimed that Columbus tubing was stiffer then Reynolds. Now we know better but then I was not convinced by the claims. In time i relized that most columbus frames were far "tighter" in geometry and their stays and blades were straight gauge BEFORE tapering. Reynolds frames were often more relaxed and had TAPER gauge stays and blades. So dah! How does this relate to today? Just that personal testomony has no place compared to actual measurements and science. Andy.
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Old 05-23-12, 10:45 PM
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Originally Posted by Andrew R Stewart View Post
....... personal testomony has no place compared to actual measurements and science. Andy.
+1 Certainly one's personal view may be proven to be correct(hey, you got a 50/50 chance) by science, but sciene has no bias(in a perfect world). That being said, I plan on building a fork pretty soon and it will be radiused(continental) and taper gauge. Taper seems like a no brainer(there's that personal view factor), and I like the look of radiused over straight.

Brian

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Old 05-23-12, 10:48 PM
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Originally Posted by Scooper View Post
I can truthfully say that there is a marked difference between the ride of these two bikes with the same tire pressure and on the same road surface.
In this case, a simplified model of a fork as a pair of cantilever beams with end loads is good enough to see that the Reynolds fork is not going to be as stiff as the other fork
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Old 05-23-12, 10:54 PM
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Originally Posted by Andrew R Stewart View Post
This brings up an old memory. In the day it was claimed that Columbus tubing was stiffer then Reynolds. Now we know better but then I was not convinced by the claims. In time i relized that most columbus frames were far "tighter" in geometry and their stays and blades were straight gauge BEFORE tapering. Reynolds frames were often more relaxed and had TAPER gauge stays and blades. So dah! How does this relate to today? Just that personal testomony has no place compared to actual measurements and science. Andy.
Yep; I didn't mean to imply that my belief was any more than a belief based on my own experience. Valid tests with repeatable results would be expensive and a lot of work with little or no payoff like unterhausen says.
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Old 05-23-12, 11:58 PM
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Older forks for less smooth , even unpaved roads used a tighter radius ,
closer to the tip.

trying to keep blade wall thickness the same, while OD is tapering down ,
is where tip flexibility also improved.
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Old 05-24-12, 08:26 AM
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Originally Posted by fietsbob View Post
Older forks for less smooth , even unpaved roads used a tighter radius ,
closer to the tip.

trying to keep blade wall thickness the same, while OD is tapering down ,
is where tip flexibility also improved.
That's not what the tubing manufacturers say. The fork tip resilience is better when both the blade wall thickness (gauge) and tube diameter are tapered.



Nova, for example, sells taper gauge blades that are 28mm x 20mm oval (0.9mm wall thickness) at the crown, tapered to 12.5mm round (0.6mm wall thickness) at the tip.

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Old 05-24-12, 09:11 AM
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lower priced stuff lets the wall thickness go up as the straight tube is tapered..

Im thinking the bikes in the 40's , just post WW2 when the roads were more un improved or, like the cobbles of the North-of-France ,
that they run to Roubaix over.

take your favorite blade , and make the tooling to make the bend you wish.

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Old 05-24-12, 10:38 AM
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Originally Posted by fietsbob View Post
lower priced stuff lets the wall thickness go up as the straight tube is tapered..

Im thinking the bikes in the 40's , just post WW2 when the roads were more un improved or, like the cobbles of the North-of-France ,
that they run to Roubaix over.

take your favorite blade , and make the tooling to make the bend you wish.
OK; that makes sense.
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Old 05-24-12, 11:36 AM
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Originally Posted by Scooper View Post
...Nova, for example, sells taper gauge blades that are 28mm x 20mm oval (0.9mm wall thickness) at the crown, tapered to 12.5mm round (0.6mm wall thickness) at the tip...
That's the same OD spec as my straight disc brake fork. Is this fork tube specification common?

P.S - I found an answer for that question, Continental Oval spec 28mm x 20mm on the large dimension, taper length is common also, wall thickness varies. Most likely for a disc brake application wall thickness increases on the small end. Wall thickness on the taper is not always related to price.

Last edited by Werkin; 05-24-12 at 12:43 PM. Reason: question answered
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