Road Cycling - Straight blade verses normal rake ??????

What is the differnce. I have a Look HSC2 that has a straight blade design that I am thinking about using. I am now using a fork with a rake?

Bill

there aren't many forks that have no rake whatsoever to them. i'm pretty sure that look only makes forks that have between 40 and 45mm rakes. basically, the noticable difference is just how they look. rake just refers to the amount that the fork ends are offset from the steerer tube, not the curve. some people say that straight bladed forks are more responsive, but i don't see how a fork with straight blades and a 40mm rake will be more responsive than a fork with curved blades and a 40mm rake. they might be a little stiffer, maybe?

go ahead and try them out for yourself and see if you notice a difference, and report back. i'd be interested to know, since the only straight fork i've ever used also happens to be 0mm rake.

They both should have similar rake, whether traditional or straight bladed.

George

Agree with the above, the rake is still present. In fact if you look at where the fork enters the steering tube, you can easily see that the whole thing is set forward on an angle.

It is more easier to see on bikes with a shallower head tube angle, like this beautiful Colnago.


If you hold a straight edge up to the picture(piece of paper) along the head tube, you will see that despite the straight bladed fork, the hub is still farther forward.

I never liked the way the back of the top of the fork looked, I always imagined it failing suddenly, but I believe I am being silly.

Wow! What were we talking about again? I've been blinded by the Easter bike.

Off topic...but thats a beautiful bike!

Back to the regular scheduled discussion.

there aren't many forks that have no rake whatsoever to them. i'm pretty sure that look only makes forks that have between 40 and 45mm rakes. basically, the noticable difference is just how they look. rake just refers to the amount that the fork ends are offset from the steerer tube, not the curve. some people say that straight bladed forks are more responsive, but i don't see how a fork with straight blades and a 40mm rake will be more responsive than a fork with curved blades and a 40mm rake. they might be a little stiffer, maybe?

go ahead and try them out for yourself and see if you notice a difference, and report back. i'd be interested to know, since the only straight fork i've ever used also happens to be 0mm rake.

I think the reason a stright blade fork is supposed to be more responsive is becuase it is supposed to be stiffer. not sure about the validity of that statement, though.

I think the reason a stright blade fork is supposed to be more responsive is becuase it is supposed to be stiffer. not sure about the validity of that statement, though.


yeah...i actually had never heard of that until yesterday when i read it in the new performance catalog. they were talking about the forte forks....i have my doubts about the statement as well...if both forks are carbon, they should be equally stiff. but i be there's a difference between curved and straight steel forks...then again it depends on the thickness of the tubing and stuff like that...so, yeah...i'm voting that there will be no difference as long as the rakes are the same.

Okay, having gone though this debate in the Mountain Bike world some 13 years ago, I would like to say this -

Curved or straight blades make no difference to the ride quality. What does make a difference is the material, it's wall thickness and the blade cross-section.

Rake as explained earlier, or more importantly, the combination of rake/head angle/trail/castor angle makes a BIG difference to handling. The rule of thumb is, the steeper the head angle, the more rake you need. Which is why Colnagos look so funky.

Best rule of thumb? Why not try these other forks and see how they feel? Unless you know what your current bikes head angle and fork rake really is, it's hard to know if the new forks will perform any differently.

Rake as explained earlier, or more importantly, the combination of rake/head angle/trail/castor angle makes a BIG difference to handling. The rule of thumb is, the steeper the head angle, the more rake you need.

I think you may have this backwards. In order to maintain X amount of trail, you must reduce the fork rake as you steepen the head angle. Trail is the distance between the point on the ground intersected by a vertical line through the hub ctr. and the point on the ground intersected by the center line of the head tube/steerer tube.

If you increase a head angle without changing the rake, you shorten the trail. If you decrease a head angle without changing the rake, you increase trail. Visualize or draw a line throught he center of the head tube. As you steepen the head tube, the point where this line intersects the pavement moves towards the rear of the bike and closer to the vertical line running through the hub ctr., decreasing the trail. To maintain trail, you must reduce fork rake to move the vertical line through the hub ctr. towards the rear of the bike also.

Too much trail results in a bike that doesn't want to steer(understeer). Too little trail results in a bike that is prone to oversteer. Traditionally, road racing bikes have ~2.25-2.4" of trail.

This is why bikes with >73deg will have shorter fork rakes(eg a stock 2001 Bianchi Pista that has ~75deg head angle and 28mm fork rake). Touring bikes, which traditionally have shallow head angles, also have longer fork rake(>45mm).

Bianchi Geometry chart:

http://www.bianchiusa.com/pista.html

Colnagos are very much an anomally in the racing bike market, having rather shallow head angles compared to other race frames. In addition, Colnago takes a one size fits all approach to fork sizing, using a 43mm fork rake on bikes with head angles ranging from 71deg. to 74deg. Of course, this keeps manufacturing costs down, but doesn't optimize handling.

A formula for calculating trail can be found by searching at www.bikelist.org Just search the archives for Trail.

You're right, I wasnt thinking properly. You'd think after researching the stuff for so long I could remember the simple stuff, but noooooo.

Steeper head angles do indeed need less rake to maintain trail and castor, and yes, I often wonder why people actually like Colnagos. When I was 17 I thought the Master was the most awesome road bike I've ever seen, then I picked one up, rode one, spent the next 15 years getting more into bikes and finaly saw them for what they were....

Overpriced technicolour anomalies =] ( sorry Colnago owners ).

i think when thylacine was talking about "trail" he might've meant "tracking distance, or difference." or the difference between where the front and rear tires are in a turn. like on a car, if you turn a corner too quickly, your rear wheels will run over the curb. which is something completely different, but still related to fork rake/head tube angle....there was a discussion about this yesterday in another thread..."will i notice a difference???" or maybe thylacine WAS refering to trail as you see it...

Colnago's handle pretty well in the mid range sizes. I have a 58cm with a 72.5 head angle and an 43mm fork. it's a little quick, but that's ok. I have considered putting a 50cm fork on this bike, which would probably give it "neutral" handling, meaning it would be inclined to respond to deliberate rider input, rather than oversteer or dive into corners. Haven't been able to pull the trigger on that modification though.

The extreme large and small size Colnagos are where, at least on paper, it would appear one would run into handling peccadillos.

The PDF file I posted above is one Colnago no longer posts at trialtir. In their new charts, they leave out the head angles, for what are obvious reasons to me.

Who knows WHAT I was talking about? I talk crap mostly anyway =]

Don D - if you ever want me to TIG up a nice steel fork for your Colnago, with the proper 51mm rake, just let me know. It'll handle like a dream.

All forks have rake : when they first made Ti forks they couldnot bend the material so used straight fork legs , this became a fashion in other materials .
The same happened with carbon - seems to be a fashion thing now , some like one some t´other .

it is thought that straight forks are more responsive because without the curve, there is less material. The curve also is thougth to allow the fork to flex, like a bow (as in a bow and arrow). Look at all the rage with the curved seattubes. this assumes the same type and thickness of material.

And yes, Colnogos are the biggest supporters of straight forks, one year (I think '96) the rage was to use a rockshock fork in the Paris-Rouboux. Riders on the Mapei team wanted to change out their forks, but the Colnogo factory was insistant that they ran the stock forks (steel and straight). They not only won the race, I think they finished with 3 in the top 5.

All forks have rake : when they first made Ti forks they couldnot bend the material so used straight fork legs , this became a fashion in other materials .
The same happened with carbon - seems to be a fashion thing now , some like one some t´other .


not all forks have a rake. i have a set of kinesis 650c aluminum forks that are straight bladed, and have no rake and no dropout offset to them whatsoever. i can spin my handlebars all the way around on that bike. i don't think they're made anymore though. which makes me sad...

Who knows WHAT I was talking about? I talk crap mostly anyway =]

Don D - if you ever want me to TIG up a nice steel fork for your Colnago, with the proper 51mm rake, just let me know. It'll handle like a dream.

What do you have in mind for a design? materials?