This is obviously a dumb question, as the engineers who build bikes wouldn’t worry about fork rake if it really didn’t matter. However, my new OCRR frame requires a 43 mm raked fork and I can pick up a nice Ouzo Aero, but it has a 40 mm rake. The company simply says that a 40 mm might produce different handling, etc. Tell me, should I wait to find a good deal on a 43 mm and stay with the manufacturer’s specs, or can I pick up a 40 mm and not know the difference?
More rake decreases trail and makes the bike handle quicker, whereas less rake increases trail and makes the bike handle slower. How much difference 3mm makes? I don’t know.
I agree
http://www.phred.org/~josh/bike/trail.html
http://www.sheldonbrown.com/gloss_tp-z.html#trail
jaretj
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You won’t be able to tell the difference. 3mm’s? Hold up your fingers 3mm apart.
You won’t be able to tell the difference. 3mm’s? Hold up your fingers 3mm apart.
i’m tryin, i’m tryin… damn things keep shaking too much…
You won’t be able to tell the difference. 3mm’s? Hold up your fingers 3mm apart.
Talking to Dan and some other frame makers it seems you’re wrong about that. 5mm isn’t much either if you do the old “hold up your fingers” thing, but apparently it affects a bike’s handling. From what I understand I think you will feel a difference, but what I don’t know is how much.
I thought my Yaqui has a 50 degree rake. Bike handles like a dream on the fast downhills.
Dave
I thought my Yaqui has a 50 degree rake. Bike handles like a dream on the fast downhills.
Dave
I have the same bike, with a 43 rake fork. Handles like a dream on fast downhills.
I have a custom Holland that was built and outfitted with a 43 rake fork in 1993. Ten years later, I took it in for a repaint and fork replacement after a crash and Bill suggested a Reynolds fork. OK by me. I rode the bike for over a year before I learned the new fork was a 40. I called him to ask about it and he just laughed. He’s been building bikes a long, long time and he said people can only tell the difference in handling if they know ahead of time that the fork is different. If they don’t know, the bike handles the same. Funny, huh?
There is a difference between the existence of an effect and whether or not, in real life, you can actually feel it. Yes, 3mm shorter rake will lengthen the trail. There is a theoretical change in handling. But – that change is overwhelmed by other factors affecting handling…
Caster, or head-tube angle (which is more imporant than trail when defining a bike’s handling characteristics);
Wheelbase;
Rider weight;
Distribution of rider weight;
Stem, bars, tires, wind, road, …
3mm of fork rake is an “Angels on heads of pins” issue when all else is held equal.
Fork rake is one aspect, you need to take into consideration your head tube angle. Your fork rake is based off that and if you change the rake it will most definetly affect how the bike handles. Changing the fork rake changes the trail. If your head tube is a 73 degree and you have 43mm of rake you have a trail of 5.9, if you change to a 40mm rake your trail changes to 6.2, thus making the bike more stable. Without knowing the head tube angle you could cause a negative effect to the handling of your bike. Keep in mind it will also affect toe overlap.
that change is overwhelmed by other factors affecting handling…
Although you forgot wheel size all your factors are correct, but we’re talking about changing the fork on one bike instead of different forks on different bikes.
While Bill told you that there will be no noticeable difference, other equally respected frame builders have told me otherwise. Like I said before, I don’t know if 3mm rake change is noticeable but according to your experience it isn’t.
Technical Q&A with Lennard Zinn - Generics? Trail, rake and more By Lennard Zinn
VeloNews technical writer This report filed December 27, 2005
Rake and trail
Dear Lennard,
I’ve been following the discussions on bike trail and fork rake with interest. However, I’ve got a question concerning the magnitude of change (in bike handling) likely to be experienced based on changes in trail due to fork replacement. It seems that most bikes (in my size at least) list a trail measure somewhere between 5.2 and 6.0 cm. How much effect in handling would be noticed by a change in fork rake of 1-5 mm? Assume all other variables (like fork length) are constant. Given that most after-market forks have between 4.3 and 5.0 mm of rake I would think the impact is relatively slight. This is particularly important for those riders who buy frames and components separately and can’t test ride the various options.
Dean
Dear Dean,
You are right; the impact is generally relatively slight for a change in rake of 1-5mm. For instance, Alpha Q forks come in 41mm and 44mm rake, and I am willing to bet that there are very few riders who could pick out which one is which in a double-blind test, switching the forks around on their bikes with no idea of which one they are riding.
That said, there are exceptions to this when it comes to the subject of front-end shimmy, which is not a steering or stability issue (although it can result in the rider falling off), but rather a resonance frequency issue. In some cases, the interchanging of a fork with few more millimeters of rake can eliminate the shimmy problem in a bike that had a tendency to shake uncontrollably when riding with no hands on the fork with less rake.
Lennard
Dear Lennard,
Your recent column regarding rake, trail, and offset was extremely educating, especially after downloading the “Frame Geometry and Bike Stability” block from your latest primer. I must say I was thinking completely opposite in regards to fork rake and trail and you have enlightened me. Thank you very much.
I just purchased a new bike that has a 73.5-degree head tube and has a Reynolds Ouzo Pro fork with 43.5mm of rake. It is quick steering or has what I feel is a fidgety front end. I have been thinking about how to make it a little more predictable in terms of steering, especially at high speeds. For reference I am using an 11cm over sized Deda Newton stem with a Deda Newton bar and a Chris King 1-1/8-inch threadless headset.
My question is if I installed a similar fork with a 40mm rake (or other small decrease in rake), as opposed to the current 43.5mm rake, would I be able to tell the difference or is the difference negligible? How much of a difference in rake would I need to go before I would notice a difference. I ask because I have limited funds to purchase different forks to experiment with.
John
Dear John,
As you can see from my previous answer, a change of a few millimeters in rake is not enough usually to elicit notice from the rider, but I have found that this is often not the case on a bike with which the rider has difficulty. In this case, small differences in rake, as well as a change in stiffness or alignment of the fork brought on by a change in model or brand of fork, could make a profound difference in your feeling of handling confidence on this bike.
A 73.5-degree head angle with a 43.5mm rake is steeper than I generally use with a fork like that (I usually couple a 44mm fork rake with a 72-degree head angle to get more fork trail and hence more stability), it is not out of the ordinary at all; there are plenty of bikes out there with fork trail similar to yours with which their riders are quite happy. I suspect that stiffness and alignment issues in the frame and fork may also be playing a role in your bike’s fidgetiness, and a fork change may be just what the doctor ordered.
Indeed, changing to a fork with 40mm of rake will increase the trail, slow down the steering, and increase the stability of this bike. I suspect that it is just enough on the edge of your sense of comfort, that this change will be to your liking. I would say that it is worth the investment to give it a try.
Lennard
Dear Lennard,
I enjoyed your column on rake, trail, and offset, and it all makes perfect sense to me now. The question I now have is, do (or should) time trial bikes have a little more trail than road bikes, since the additional trail might help the time trialist ride a straighter line? According to Trek, their 54cm road bike has a 4.5cm offset and a 5.6cm trail, whereas the corresponding time trial bike has a 4.0cm offset and a 6.0cm trail. Coincidence?
Assuming it’s not already set up like this, how much would a time trialist benefit, say, over a 40k time trial, by simply switching their 4.5cm offset fork for one with a 4.0cm offset, thereby increasing trail 0.5cm?
Tom
Dear Tom,
The answer is yes, they often do.
I certainly build my time trial bikes with less rake and more trail for exactly that reason.
In fact, I made a fork with negative rake on which John Stenner (a great rider and friend who tragically died in a bike/car accident more than a decade ago) won the U.S. time trial national championship in the early 1990s. This was before the UCI had mandated that the front and rear wheels had to be of the same size, so Stenner wanted a smaller (26-inch) front wheel for reduced aerodynamic drag, yet he did not want the front end of the bike to drop (and its head angle to steepen and hence trail and stability to decrease) as they would have by simply switching to a 26-inch fork and wheel. He also wanted a lot more stability so he could just concentrate on powering the bike. The solution I came up with was a unicrown fork with negative rake made out of teardrop-shaped steel strut tubing made to separate the wings of biplanes.
As you can see from the formula and discussion in the previous column or in Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists, decreasing the wheel radius would have decreased the fork trail and hence the bike’s stability. Couple that with a steeper head angle by dropping the front end due to the smaller wheel radius and shorter fork, and you lose a lot more trail and stability. However, by making the fork a long unicrown bend with this aerodynamic tubing which could not be bent sharply, made the fork longer, and turning it around backwards so that the rake was negative lifted the front end yet more. John ultimately decided that he wanted to be a bit lower and wanted to drop the bottom bracket height a bit as well, both to get down out of the wind more. So, we ended up with 0.5 degrees less head angle, 70mm (!) less rake, and around 22mm less wheel radius, all resulting in a net large increase in fork trail.
We worked on the countersteering skills that it takes to put a super-stable bike into a lean and to rapidly turn it (also covered in the primer.). Once he mastered the necessary countersteering, he realized that this bike was also giving him a big advantage at the turnaround. The 70mm reduction in rake reduced his wheelbase, and hence his turning radius, by almost 70mm as well. After winning Nationals, he excitedly described how he was able to just stomp the pedals and not be concerned at all with steering; the bike just went straight without him, and he zipped around the turnaround so fast that he could hear the spectators exclaiming about it! It’s a shame he is no longer around to invent things with.
Lennard
Dear Lennard,
I’ve recently upgraded bicycles from a 2000 Klein Quantum to a 2003 K2 Mod 5.0 frame, but it’s much less stable than my Klein. In fact, the difference is so dramatic that it saps all of my confidence on the road!
While on my other bicycle, I can ride and steer with no hands in comfort. On this bicycle, riding with just one hand on the bars takes much concentration. It feels like I’m riding on a sheet of ice all the time.
The bike takes a conscious effort to ride in a straight line. It’s quick to steer and eager to wobble.
Help! I fear I’ll not be able to race on this bike this year as one can’t race without confidence in their ride.
Rob
Dear Rob,
It sounds like a combination of insufficient fork trail combined with front-end shimmy. I suspect that there is also an alignment problem in the frame or fork. I would try a fork with less rake in hopes of eliminating all three problems in one fell swoop. Good luck!
Lennard