Cyclocross forks for road bike?
DemostiX
would be good to look at for a rando or touring bike. The frames I
have on hand for new forks have long chainstays.
I find these on some forks I've been shopping.
Canti brake mounts to which a top or pannier rack could be
mounted.
Eyelets for fenders.
Clearance for fenders.
So, in what way are they by design not right?
Harry Travis
Washington, DC
USA
Dark Horse
First.
Fork height. The measurement from the front axle (center) to the
crown race seat is critical. Frames are designed around a particular
dimension, and changing it alters the height of the head tube from the
ground. Directly affects head angle and trail. A good ballpark
estimate is 1" change in axle-to-crown height is 1deg of head angle. I
get that from doing the trig, and the folks at I.F. use the same #.
Cross forks tending to be more than a bit longer than road ro touring
forks, this may be an issue. The measurement is from the center of the
axle to the underside of the crown race. Use an allen wrench through
the dropouts if you don't have a naked axle. 5-6mm longer you probably
won't notice, 20 you probably will.
Find out what fork height those frames on hand were designed for,
and get the sellers to measure the forks.
Caveat Emptor, this one's for points.
Compare the two heights given in these links.
http://www.ifbikes.com/accessories2/crossforks.shtml
http://www.ifbikes.com/accessories2/roadforks.shtml
Second.
Fork rake. Without getting into a discussion of rake and trail and
handling characteristics, fork rake is a major component of bike
handling. Any frame is designed with a rake/trail combination in mind,
and the window of permissible variation is actually pretty small. The
rake on production road bikes seems to be normalizing towards 43mm,
which is a pity, but cross bikes are different. Cross bikes use
different (usually larger) rakes so that the bikes handle well in the
mud. A difference of 2-3mm you probably won't notice, but 5-10 you
probably will. Here again, find out what your frames were designed for
and what the forks are. At the end of a 1000k, you may not have a lot
of brain cells to devote to keeping the bike in a line, and that is
the handling quantity that is affected by fork rake.
Third.
I've known quite a few people who had serious chattering problems
with carbon cross forks. This may nor may not apply to the forks
you're looking at, but I wouldn't be surprised. Steel forks not nearly
so much.
Eamon
Joe Gross
> I've known quite a few people who had serious chattering problems
> with carbon cross forks. This may nor may not apply to the forks
> you're looking at, but I wouldn't be surprised. Steel forks not nearly
> so much.
I had an Airborne branded carbon cross canti fork (don't know who
actually made it) on my Airborne Carpe Diem. With any type of brake
pad I wasn't able to get it to not chatter and actually give me full
contact with the rim. There's nothing scarier than a fork chattering
during a fast deceleration.
I replaced it with an IRD Mosaic 57 Carbon fork and couldn't be
happier. It's got room for a long reach Ultegra brake and also has
fender mounts. I can't mount a rack on it, but I can shove an SKS
fender between the brake and my 28mm tires. I think it's the closest
thing to a perfect carbon randonneuring fork.
http://www.interlocracing.com/forks.html
Note: You will need to get a longer retaining bolt for your brake as
the standard one that comes with Ultegra brakes isn't long enough.
Joe
Mike Biswell
>From: Dark Horse
>Sent: Tuesday, February 12, 2008 9:11 AM
>To: randon
>Subject: [Randon] Re: Cyclocross forks for road bike?
>First. Fork height. The measurement from the front axle (center) to the
>crown race seat is critical. Frames are designed around a particular
>dimension, and changing it alters the height of the head tube from the
>ground. Directly affects head angle and trail.
Yes, and??? I think this is part of the OP's concern and possibly intent,
although the discussion gets a little more interesting if you substitute a
'road bike,' vs the OP's bikes with 'long chainstays.'
I have been hoping for this discussion to pop up for a while: Can an average
road bike be rando'ed / choppered out with a different fork, hopefully an
affordable one, thus getting the bike closer to easier tracking or whatever
the handling benefits exist for a 'less trail (aka longer wheelbase) rando
bike?'
I have a 2001 Lemond Zurich with the gross yellow Trek fork that I want to
change out. For $100 a nice Reynolds Ouzo fork could be had, improving the
bike some, and that could be a nice way to go. But could there be other
forks that stretch out the wheelbase on the front side, and by doing so,
help with the ease of tracking, and also help even if the bike front end is
a little higher than with a 'road' fork?
A higher front end = smaller head tube angle, and all fine?
I'm sure someone has played around with this. Luv to hear!
Regards!
Mike
Tim McNamara
Ride height- the distance from the fork crown to the dropout. On a
'cross fork the fork legs are (generally) much longer to allow for
mud clearance, which raises the headset and alters the steering
geometry. Road bikes are (generally) built for forks with shorter
legs. But you might find a combination of a particular fork and a
particular frame that's workable.
Mike Biswell
>From: Tim McNamara
>Sent: Tuesday, February 12, 2008 2:50 PM
>To: randon
>Subject: [Randon] Re: Cyclocross forks for road bike?
>Ride height- the distance from the fork crown to the dropout. On a
>'cross fork the fork legs are (generally) much longer to allow for
>mud clearance, which raises the headset and alters the steering
>geometry.
Thereby decreasing the trail, and effectively slacking the seat tube and
steerer column angles: rando-izing the bike for better tracking??? I'm
asking. And the pitfalls?
Not asking for anyone to vouch for any particular setup, just talking about
low-cost (relatively!) rando bike ideas....
And also the OP was asking too about the bells and whistles (fender room,
lights, et cetera), so apologies for somewhat subverting the thread the
performance related concerns.
Regards!
Mike
Tim McNamara
>> From: Tim McNamara
>> Ride height- the distance from the fork crown to the dropout. On a
>> 'cross fork the fork legs are (generally) much longer to allow for
>> mud clearance, which raises the headset and alters the steering
>> geometry.
>
> Thereby decreasing the trail, and effectively slacking the seat
> tube and
> steerer column angles: rando-izing the bike for better tracking??? I'm
> asking. And the pitfalls?
>
> Not asking for anyone to vouch for any particular setup, just
> talking about
> low-cost (relatively!) rando bike ideas....
>
> And also the OP was asking too about the bells and whistles (fender
> room,
> lights, et cetera), so apologies for somewhat subverting the thread
> the
> performance related concerns.
Good questions and no guarantees I have good answers.
First, raising the ridge height of a frame will slack the head tube.
Slacking the head angle and changing the fork offset can be done but
must be done carefully. A 'cross fork can raise the front end of the
bike 2-5 cm, depending on the ride height of the original fork and
the ride height of the 'cross fork. Are there some particular
combinations that might work? Sure, but it's a case by case basis.
If you look at the old classic rando bikes, they tended to have
neutral to steep head angles (73-74 degrees) and large fork offset (50
+ mm) resulting in low trail (30-50 mm). These bikes will still
steer fairly quickly and nimbly. As the head tubes gets slacker the
steering gets slower but not necessarily more stable. Just swapping
in a cross fork is likely to just raise the ride height and slacken
the head tube and that may not help the steering, but the specifics
of the frame, fork and wheels have to be taken into account. If the
changes are relatively small, the effects on handling may be very minor.
It might be cheaper to just have cantilever pivots brakes onto an
existing frame and touch up the paint.
pamela blalock
a new Cyclocross frame to use for commuting. 3 weeks later I found myself on
the hood of a car. My lovely new frame was fine - as it's very gracious
carbon fork with carbon steerer sacrificed itself for the frame. Driver's
insurance is covering all. I order the replacement fork and discovered it is
half what I paid for frame, fork and headset.
So if you are worried about screwing up the geometry, for not a lot of
money, you can get a nice cyclocross frame to go with your cyclocross fork
:-)
And for those who will ask, no broken bones.
pamela blalock pgb at blayleys.com
care-free in watertown, ma http://www.blayleys.com
Dark Horse
>> I have been hoping for this discussion to pop up for a while: Can an average
> road bike be rando'ed / choppered out with a different fork, hopefully an
> affordable one, thus getting the bike closer to easier tracking or whatever
> the handling benefits exist for a 'less trail (aka longer wheelbase) rando
> bike?'
considerations of personal preference.
The rule of thumb that I was taught is that stability at speed is
directly related to the amount of trail. More trail gives stability at
higher speeds, and vice versa. It's easiest to think of this stability
as a "window" of sorts, with the trail # determining where in the
speed range it falls. Touring bikes tend to have lower head angles and
more rake, resulting in a more stable machine at touring speeds (8-15
mph). The tradeoff here is that at higher speeds, the bike feels less
stable. Net result is a bike that requires little constant attention
to hold a line at those lower speeds.
For a racing/ road sport bike, the situation is reversed. The higher
trail # moves the "window" up the speed range, so that a racebike has
a tendency to wander at lower speeds, but is much more stable at
higher (15/18 mph +).
Randonnee bikes are somewhere between the two, with a front pannier/
bar bag thrown in. I'm not very familiar with the geometry changes
entailed by a front-end load, for that you should ask Jan.
This is where the personal taste comes in. different people can have
very different handling preferences. I, for instance, have biased the
front-end geometries on two of my bikes towards a high trail # (73deg
HA, 40mm rake). I strongly prefer a bike that descends with enthusiasm
and confidence, and willingly pay the price of some low-speed
stability. I do not run a front-end load on either, and do not intend
to. Other riders have different priorities and weight their steering
geometry differently.
Trail and wheelbase have no necessary relation to each other. Trail
is purely a quantity of the front end of the bike. I would think that
a bike with a relaxed HA and a touring rake would handle a bit oddly
with short stays, but I can't say that I've ridden one like that. That
would be the result of putting a longer fork with more rake onto a
road or road sport bike. Touring and Rando bikes have long stays for
reasons of overall stability, and race bikes have short stays for
quick handling and minimal turning circle. I do think that the
combination would be...odd.
As with many other things, there are only two meaningful questions.
Does it work?
Do you like it?
> I have a 2001 Lemond Zurich with the gross yellow Trek fork that I want to
> change out. For $100 a nice Reynolds Ouzo fork could be had, improving the
> bike some, and that could be a nice way to go. But could there be other
> forks that stretch out the wheelbase on the front side, and by doing so,
> help with the ease of tracking, and also help even if the bike front end is
> a little higher than with a 'road' fork?
questionable in the extreme. Remember that almost all available forks
fall between 40 and 50mm of rake, and 43 is becoming the OEM default.
I don't recall the trig at the moment, but I seem to recall that a
50mm longer fork lengthens the wheelbase less than a cm. Your maximum
available increase is ~15mm, all of in the front.
Quickie trig puts the wheelbase change from a 2cm taller fork at
5.8mm, + 7mm of rake increase for a total increase of 12.8mm.
This is a useful little utility, for front-end geometry, and other
things as well.
http://www.kreuzotter.de/english/espeed.htm
Tim McNamara
On Feb 12, 2008, at 7:14 PM, pamela blalock wrote:
> Well here's a slightly different perspective. Right before
> Christmas, I got
> a new Cyclocross frame to use for commuting. 3 weeks later I found
> myself on
> the hood of a car. My lovely new frame was fine - as it's very
> gracious
> carbon fork with carbon steerer sacrificed itself for the frame.
> Driver's
> insurance is covering all. I order the replacement fork and
> discovered it is
> half what I paid for frame, fork and headset.
Umm, while it seems like a good thing that only the fork needs to be
replaced, this scenario IMHO reveals multiple problems with bike
design. In terms of the rider's immediate safety, the fork is far
more important than the frame. A broken frame (non-carbon fiber)
will almost never dump you into the street or cause to to
instantaneously lose control of the bike. A broken fork always
will. The frame has redundancy for each tube, the fork has none for
the most critical and most highly stressed tube, the steerer. The
fork bears more impact stress than the rest of the frame.
The fork should be strong enough IMHO that it will preferentially
survive a collision. If the fork fails the rider has no control over
the bike and a catastrophic crash is far more likely. Unfortunately
many people- including frame builders- treat the fork as the crumple
zone to protect the frame, seeing the frame as more important. IMHO
it's the other way around- the fork is far more important than the
frame in terms of the rider's safety. If the fork breaks in an
accident and the frame is undamaged, this is a serious failure of
design.
Pamela, your accident also shows the problems with carbon fiber
forks. Carbon fiber has very poor fracture toughness and and is IMHO
the worst material available from which to make a fork. The worst of
all worlds IMHO is a carbon fiber fork with a carbon fiber steerer.
I don't mean to harsh your mellow but your report sounds very loud
warning bells. Your fork should have survived the crash without
breaking, and that it broke is a severe problems IMHO.
> So if you are worried about screwing up the geometry, for not a lot of
> money, you can get a nice cyclocross frame to go with your
> cyclocross fork
That too can be a very good choice. I rode a lot of brevets on a
'cross frame and fork. Modern 'cross bikes have much more road-like
geometry than used to be the case, in large part because of clipless
pedals of all things. They can be excellent bikes on the road.
> And for those who will ask, no broken bones.
I'm very glad to hear you were not seriously injured. Yowza! In a
collision with a car, a cyclist is at a serious disadvantage (carbon
fiber forks aside).
pamela blalock
Tim McNamara responded to my story of fork sacrificing itself for frame...
<<<
Umm, while it seems like a good thing that only the fork needs to be
replaced, this scenario IMHO reveals multiple problems with bike
design. In terms of the rider's immediate safety, the fork is far
more important than the frame.
>>>
Without going into all the gory details, I will say that I am all too well
familiar with what happens when a fork fails. As you state, it's not pretty.
I refuse to tempt fate any further. My point was that when bought
independently, a fork may be a substantial fraction of the cost of a
frame/fork bought together or even complete bike. If one has concerns about
mismatching frames and forks, it may be relatively cost effective to buy the
set :-)
Mike Biswell
From: pamela blalock
Sent: Wednesday, February 13, 2008 6:40 PM
Subject: [Randon] Re: Cyclocross forks for road bike?
>Without going into all the gory details, I will say that I am all too well
>familiar with what happens when a fork fails. As you state, it's not
>pretty.
Glad to hear you are okay. If the driver's insurance is covering, not clear
to understand how is it "fork failure," and not evil car?
>I refuse to tempt fate any further. My point was that when bought
>independently, a fork may be a substantial fraction of the cost of a
>frame/fork bought together or even complete bike. If one has concerns about
>mismatching frames and forks, it may be relatively cost effective to buy
>the set :-)
This is more a rando hot-rod discussion, cost concerned - oh yeah always,
but also trying to isolate, and put to use the performance ideals espoused
within the notion of a 'rando bike,' and whether rando bike performance
could be improved thru "mismatching."
Thanks Pamela, Tim, Eamon. Cool replies. OP Harry too.
Regards!
Mike
pamela blalock
<>Without going into all the gory details, I will say that I am all too well
<>familiar with what happens when a fork fails. As you state, it's not
<>pretty.
And Mike asked...
<Glad to hear you are okay. If the driver's insurance is covering, not clear
<to understand how is it "fork failure," and not evil car?
Two completely separate incidents. Years ago, I was on a bike that had a
defective fork failure.
Four weeks ago I was on a bike that was hit by a car, resulting in a broken
fork.
Pamela
DemostiX
roadbikes. I mentioned the long chainstays for anyone who had a theory
about interaction between front end and rear end designs.
I do understand the trig and the calculations. But, I'm looking for
likelihoods of success here. When Cogswell makes forks which will vary
in the trail they produce from 30 to 50 mm, and changing tire size can
produce changes of +-2 mm, I'm looking for close or likely as an
answer for suitabiliity.
I just measured lengths of forks mounted on 3 road bikes.. Not
bothering to remove the wheels,quick and dirty, ignoring the offset
and just going to estimated middle of the quick release.
So, is typical length of a cyclocross fork 395mm with rake 48mm, as
with the IF model posted earlier?
The IF "touring fork" is 391mm, and rake varies from 45-52. The road
fords are 375mm
Note that with a 28 or 32 mm (nominal) tire in the cross fork we're
beginning to get vanishingly small differences. Unless the stiffiness
and damping built into a cross fork is different.
So, it is looking to me that a robust cyclocross fork will do nicely
if correctly specified according to intension to load the fork and
steering with a light front rack. I appreciate repondents' careful
specification, but unless the paragraph just above holds, there are a
number of $130 surplus cyclocross forks out there that would suitably
update a road bike to a randoneusse or light tourer. These rando forks
seem a better bet and fit than any of the carbon road forks, subject
as they are to weight shaving for sales.Touring" forks are special
order and therefor expensive.
But, please, tell me if I'm wrong so the final words in this thread
are better than my speculations.
Harry Travis
DC USA
Jim Bronson
A lot of builders post there that everyone has heard of, such as
Richard Sachs, Curt Goodrich, etc.
Not saying this is a bad place to ask the question, just saying that
Framebuilders is an excellent place to post geometry questions.
--
I ride my bike, to ride my bike.
Tim McNamara
On Feb 16, 2008, at 9:34 PM, DemostiX wrote:
<snip>
> I just measured lengths of forks mounted on 3 road bikes.. Not
> bothering to remove the wheels,quick and dirty, ignoring the offset
> and just going to estimated middle of the quick release.
>
> So, is typical length of a cyclocross fork 395mm with rake 48mm, as
> with the IF model posted earlier?
> The IF "touring fork" is 391mm, and rake varies from 45-52. The road
> fords are 375mm
>
> Note that with a 28 or 32 mm (nominal) tire in the cross fork we're
> beginning to get vanishingly small differences. Unless the stiffiness
> and damping built into a cross fork is different.
>
> So, it is looking to me that a robust cyclocross fork will do nicely
> if correctly specified according to intension to load the fork and
> steering with a light front rack.
<snip>
Hey, give it a try and see. I think that raising the ride height of
the frame by 2 cm is going to make your bike handle like
wheelbarrows, but give it a try and see. It's not going to explode
or anything like that.
FWIW, I see no correlation between cantilever forks and
randonneuring. Most of the randonneurs I know ride road bikes with
sidepulls.