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Fork upgrade--is rake an issue?(33 posts)

Fork upgrade--is rake an issue?patagrande
Dec 4, 2001 11:56 AM
I am looking to upgrade my steel fork to a carbon fiber one. How important an issue is rake? The fork on my bike now has a rake of 45 degrees.

Does one model of fork come in several different rakes?

Thanks,
Chris
re: Fork upgrade--is rake an issue?brider
Dec 4, 2001 12:09 PM
45 degrees? Yeah, right. You don't know what you're talking about, do you? Do you mean 45mm? As to the question of "is fork rake important," the answer is: Only if you care how the bike handles. Rake is one of the determining factors of trail, which is the real determiner of how the bike handles. Best advice is to duplicate the rake you have in the new fork. You might not end up with the fork you're initially wanting, but don't get stuck on brands. There's nothing intrinsically superior to CF forks over steel.
I gotta say, brider, that when a guy comes asking a question,bill
Dec 4, 2001 12:36 PM
I think that the very act implies that, no, he is not at all sure of what he's talking about. THAT'S WHY HE'S ASKING THE QUESTION. DUH.
I also think that he's trusting us not to abuse him for it. I cringe a little when that trust is broken, particularly with a guy who's being thoughtful enough to consider rake in making a fork purchase.
I agree with your answer except that, while there may be nothing intrinsically better about CF over steel in that the cheapest, least-designed CF is not going to make your bike ride and handle better than the best steel fork (or so I've heard; I don't really know anything about the best steel forks, which are rare, which is part of the point), it is no secret that the better builders for the better bikes are spec'ing CF forks (with the exception of a few, like Waterford), so that the design money is going to CF forks. I daresay it's a lot easier (maybe not cheaper, but easier) to get a good CF fork than it is to get a good steel one.
Most if not all fork manu's make them in different rakes, between maybe 40 mm and 50 mm for road bikes, although not in 1 mm increments, generally. Get the rake you used to have.
Dittomorrison
Dec 4, 2001 12:46 PM
Okay, you called me on that one...brider
Dec 4, 2001 2:13 PM
Seems I'm getting spanked on a couple different forums for this sort of thing. 'Net etiquette duly noted. [he walks away repeating to himself "I am not a troll. I am not a troll. Iam not..."]
Actually...SamDC
Dec 4, 2001 2:27 PM
A CF fork will probably be lighter, have better damping than a steel fork.
Well ...tarwheel
Dec 4, 2001 7:33 PM
A carbon fork generally will be lighter than a steel fork, but will not necessarily damp vibrations any better. A lot of frame builders will tell you that there is nothing more comfortable than a well made and tuned steel fork. The main advantage of carbon over steel is the weight. However, there are some very stiff carbon forks out there -- just ask some of the guys with Colnagos. BTW, to get the full advantage of carbon, you need to get a carbon steerer tube. With a steel steerer tube, the carbon fork is not much lighter than a total steel fork. You have to be careful with full carbon forks, however, because you can't add many spacers at the top. So you have to be comfortable with low handlebars, unless you have an extended head tube or use a positive rise stem.
PS ...tarwheel
Dec 4, 2001 7:39 PM
I recently talked to another biker on a metric century who was riding a steel Merckx w/ the stock chrome steel fork. He told me he had installed a carbon fork to the frame, but had to remove it because it messed up the handling so much and it wasn't as comfortable. Apparently the carbon fork had a different rake than the original. The lesson here is to be very careful to match the geometry/rake of the original fork or you might end with something worse than you started with.
re: Fork upgrade--is rake an issue?Bobo
Dec 4, 2001 1:07 PM
AME Alpha Q comes in a variety of rakes. Look HSCs (all models) are available with 45 degree rake as well.
re: Fork upgrade--is rake an issue?mr_spin
Dec 4, 2001 1:17 PM
Unfortunately, there aren't a whole lot of opportunities to try out different fork rakes. Forks certainly aren't like saddles. So unless you are fairly wealthy and can buy a whole bunch of forks (and install them), you are best off sticking with the rake you have.

I'm no expert on the properties of forks, but there are also straight bladed forks to consider. I throw that in just to mess things up. Technically, they still have rake, but I don't know how that works.
re: straight-bladed forks -- the consensus (convinced me) isbill
Dec 4, 2001 1:54 PM
that the shape of the blade is cosmetic. Rake is defined by the distance between parallel lines, one running down the headtube axis and the other through the axle. How that distance is achieved is thought not to matter one little bit.
re: straight-bladed forks -- the consensus (convinced me) isbrider
Dec 4, 2001 2:06 PM
Actually, I've seen it shown (but have no personal experience with) that a straight bladed fork will put most of the stress and deflection into the crown (or very near the blade/crown junction), while a curved blade fork tends to distribute this over the length of the blade. I would imagine that straight CF forks can be tuned to distribute the deflection along its length. However you are correct in that the steering characteristics are independent of the shape of the blade.
Reality Checkgrzy
Dec 4, 2001 4:04 PM
The shape of the blades will have a significant effect as to how the fork flexes - one must consider for and aft deflection as well as vertical. Obvious problem is measuring the differences and then assuming that humans with "calibrated bodies" can actually tell the difference. A skilled racer - sure. Joe Biker - maybe not.

Rake mearly allows one to put the axle at the same point in space. Knowing this gives you a better chance of getting a good fork vs. bad - - for your bike and riding style.

the safest thing to do is to match your current rake spec, unless you have a very good reason to change it.
now wait just a doggone minute. this issue was beat up prettybill
Dec 4, 2001 4:36 PM
good some time ago, and the near enough to be universal opinion of the technical types was that shape as such had NOTHING to do with where and how the fork flexed. Although some forks are meant to flex a little and some are meant to flex a little more or a little less, here or there, the mainest, coolest thing about carbon fiber in particular was that the lay of the fibers, etc., (i.e., the design of the material) determined how a part flexed, not the shape in the abstract. I recall the technical types going on about how conventionally curved forks, steel or alu or whatever, DO NOT, as we all intuitively thought, flex at the curve. They may flex overall, but that would not be specifically at the curve.
Ahhhh.....grzy
Dec 4, 2001 6:33 PM
Ahhh, I was one of those technical types that hammered the discussion. If you go back and check the archives you'll see my handle all over the discussion.

To say that only the number and direction of fibers and not the cross sectional design does not matter is naive. What we were discussing is where the loads were applied and the maximum moment.The problem is that it's not a black and white world - two composite objects using the exact same number of fibers can have very different properties if the section is changed - same as with steel. This is typically quantified as the cross sectional moment of inertia (Ixx, Iyy, & I zz). The real challenge is in understanding how each variable works and what effect it has on the system. Ultimately a fork is like a stubby fishing rod - maybe this will help.

You may in fact remember people agreeeing that a particular variable had no effect on a certain parameter, but it's the context that matters. An example would be: the cross section and material of a fork has no bearing on the static moment applied at the fork crown - as long as the structure isn't failing.

You can never seprate the design of a structural object and it's material unless it's so over built that any analysis is irrelevant. Engineers love to remind architects about this.

What you remember from the discussion has some basis of truth, but the way in which you repeated it is not true.
now wait just a doggone minute. this issue was beat up prettytr
Dec 4, 2001 7:26 PM
From a dynamics point of view (vibration, etc, not rigid body)it depends on the natural frequencies and mode shapes (deflection shapes) of the fork, which depend on the shape and material properties. And yes, you can tune the fork with a change in material properties (with the angle of the layers). The shapes that describe the vibrations of the forks will be different for the curved versus the straight fork. In general, the distribution of load will be better and more gradual for a curved fork. The Romans and others used a lot of curved arches and surfaces for this reason.
re: Fork upgrade--is rake an issue?josh_putnam
Dec 4, 2001 8:21 PM
>Unfortunately, there aren't a whole lot of opportunities to try out different fork rakes. Forks certainly
>aren't like saddles. So unless you are fairly wealthy and can buy a whole bunch of forks (and install
>them), you are best off sticking with the rake you have.

Warning: the following suggestion can be quite dangerous if applied carelessly. Do it at your own risk.

Want to know what differences in rake and trail feel like? Find a cheap, used fork the right length for your bike. Borrow the fork alignment gage and bender from your local bike shop. (A case of good beer may help with that part.) Bend the forks to match your existing rake, install them, and ride them for a test ride. Stick them back in the alignment gage, and bend back a centimeter of rake, increasing trail. Install again and ride again. You will definitely feel a difference. Stick them back in the gage, bend forward 2cm, so you have 1cm more rake than your original forks, and ride them once more.

Now take them off and cut the legs off the forks so nobody will mistakenly use the forks you've bent all over the place.

An alternative, if you have a tinkering nutcase in your neighborhood, get him to build you a test fork with long, horizontal dropouts so you can move the wheel forwards and back to find just the right spot. If you aren't looking for a light, durable fork that will actually be used long-term, he can just replace the dropouts on an existing fork with a pair of rear track dropouts.

Once again, if you don't keep this fork under your control, destroy it so nobody will hurt themselves treating it like an ordinary fork.

For an illustration of how to measure and calculate rake and trail, see
http://www.phred.org/~josh/bike/trail.html

If you're interested in building your own test fork, or want to find your local tinkering nutcase, you might want to look at the framebuilders mailing list, http://www.phred.org/mailman/listinfo/framebuilders
Take yer chances!!!Rusty McNasty
Dec 4, 2001 2:12 PM
You obviously don't know $h!t about what you are saying, so go ahead-let natural selection make it's choice!!
Take yer chances!!!Bernie
Dec 4, 2001 5:13 PM
A carbon fork with a rake certainly can have some dampning qualities that you will not find in a straight bladed steel fork. I have an older Colnago Dream that came with a straight bladed steel fork. I changed that by putting on an alpha Q fork with the 44 rake. Now it much better suits my type of riding. I don't get the crap kicked out of me. As for the amount of rake, I'm going to quote Kyu Lee (founder of alpha Q fork) "Rake either 44 or 42, 42 for big bike"
Natural Selection?djg
Dec 5, 2001 9:28 AM
What, pray tell, is the differential fitness associated with:

a) Asking innocent questions?
b) Knowing a great deal of bicycle terminology?
c) Being a prick?
Maybe....grzy
Dec 5, 2001 10:03 AM
Maybe he's only got enough blood for one head (i.e. the little one).
Another upgrade considerationNessism
Dec 5, 2001 6:16 AM
Some carbon forks are longer in overall length than a typical steel fork. This longer length will have the effect of decreasing the head tube angle - which will slow down steering. How much depends on the height difference between the origional fork and the replacement.

For a better explination of what all this means check the following link. Good luck.

http://www.sheldonbrown.com/rinard/forklengths.htm
Some helpKrill
Dec 5, 2001 8:00 AM
If you post what make and model bike you have, I will tell you what CF forks and specs will work best for you.
Some helppatagrande
Dec 5, 2001 5:39 PM
I've got a 2001 Jamis Quest which I have had for a bit more than a month now. The handling is great--I use it as a commuter and trainer, putting 100+ miles a week on it--but I would like to drop a bit of weight and get a smoother feel up front.

I plead ignorance on all the snooty gear stuff as I am by nature a mountain biker, and until just a few month a go I was riding an old Panasonic from the late eighties which I put a lot of miles on. I'd still be riding it but parts were beginning to need replacements, and it didn't seem worth the money. So I bought the Jamis at a year end sale after looking at a few bikes in the $1,000 range. This one was the best deal, fit me well, and I am enjoying the difference compared to my old beater.

If you can suggest a decent fork, I'd be greatful.
Some helpKrill
Dec 5, 2001 10:28 PM
You don't mention the size of your bike, but it should have either a 72 or 72.5 degree head tube angle. Assuming your are using 23 or 25mm profile tires, you'll want to have a fork with at least 45 to 48mm of rake. Since most carbon forks are not available with more than 45mm of rake, that is what you are probably going to have to settle for. Any less rake than that and the bike is going to feel lethargic at lower speeds. Jamis uses a standard axle to crown race dimension of 367mm so this is ballpark for most aftermarket CF forks.

Quality CF forks with 45mm of rake - if you order one be sure to specify 45mm of rake:

Reynolds Ouzo Pro
Wound Up
AME, these may not be available for some time.
Some Time models though I think all the 1-1/8" steerer models are 40 or 43mm rake.

Based on that, you can't go wrong with either a Reynolds or a Wound Up. Which ever one appeals to you is the one you should get. On your frame with its slack head tube angle, it is important you do not go less than 45mm of rake if you wish to maintain decent handling.

You didn't ask, but a cheap way to soften up the front end of your bike is to just run lower air pressure. Though the tires may be rated for 120psi that does not mean you can not run less. Less tire pressure will not slow you down if you keep it in reason. Try riding at 100 psi and notice how much more comfortable the ride is.
2mm will make no differenceSpokeman
Dec 5, 2001 12:37 PM
You will not be able to tell a bit of difference between a 45mm and a 43 mm fork.

Both of my road bikes were originally spec'd with 45 mm and I swapped to 43mm, no difference in handling whatsoever. If I would have to say there is a difference I would say the bike is now even more stable.

This point has been covered many times on this forum and all the other forums.

I mention 43mm because that's the most common rake in aftermarket forks.

just my $0.02

SM
It will make a differenceKrill
Dec 5, 2001 10:46 PM
and it did in your example. By switching from a 45mm rake fork to a 43mm rake fork you increased your bikes trail and as you say, this would increase stability. 2mm can make more of difference when you are at the edges of good trail numbers.
It will make a differenceSpokeman
Dec 6, 2001 8:22 AM
What I said was that if I HAD to say anything, it is more stable. IOW, the difference was positive and not negative. I really don't think there is a bit of difference.

Thank you for knowing more about how my own bikes rides than I do.

SM
Misunderstanding?Krill
Dec 6, 2001 9:43 AM
You said: "What I said was that if I HAD to say anything, it is more stable. IOW, the difference was positive and not negative. I really don't think there is a bit of difference."

I said: "(It will make a difference) and it did in your example. By switching from a 45mm rake fork to a 43mm rake fork you increased your bikes trail and as you say, this would increase stability. 2mm can make more of difference when you are at the edges of good trail numbers."

So in other words, you say that by going to a 43mm rake fork from a 45, if you had to say anything you would say it was more stable, in my reply I said that the resulting change in trail would support your feelings. So your feelings and the numbers agree -- that is good so why are you mad?

My original point was that bicycle handling is the result of group of design elements, not just one, and one should pay attention to the details. The closer you get to the edge of acceptable handling, the greater the impact of minor changes. If your bike had 55mm of trail with a 45mm rake fork and by changing to a 43mm rake it changed to 57mm of trail, that is a small change and may well go unnoticed by an insensitive rider (that is not a bad thing so don't get upset), but as you move closer the edges of acceptable trail numbers, that same 2mm change can make a noticable difference. In this case, the persons bike already had a 72 degree head tube angle, going to a 43mm rake fork would have resulted in a trail number of 64mm. Not a bad number if you are riding a mountain bike, but a tank on a road bike. So, in his case, rake becomes very important to maintain good handling. I was not trying to offend you.
I was told there would be no math!Spokeman
Dec 6, 2001 10:03 AM
If I got testy, I apologize.

Once again, what I really want to convey in my messages and what comes out are two different things. I knew I should have not skipped that creative writing class in high school. :)

I'm coming from the point of view that in my experience, and the experience of others, that 2mm diff of rake will not cause a change that you can notice in the handling/stability of the bike.

That said, you bring up a good point that when those numbers are at the extreme, the 2mm can make a difference.

Ride on!
SM
Contradictiongrzy
Dec 6, 2001 11:41 AM
Sorry, but you've totally undermined any point you may have tried to make. At least that's how it reads from here. Which is it: absolutely no change, but I'll say there is one if pressed OR there is a slight change. You can't have it both ways and not expect to get called for it. Pick one.

Fact of the matter is the 43mm is not the same as 45mm and one would reasonably expect a small chage - although many may not be able to detect it - some may. In my book 2mm is noticable. It's a matter of degrees.

In my book 2mm is noticable.
gloves are off now!Spokeman
Dec 6, 2001 1:30 PM
Okay,

I think that only nitpicking dweebs would worry about 2 STUPID MM.

Is that clear enough?

SM
Why didn't just you say so?grzy
Dec 6, 2001 5:21 PM
Hey, you wanna look like an ass, that's your business.