Did you know the pdf author was Milhouse Vanhouten? Cali is a mythical place, you know...I have it, but I bought the pdfs from Rivendell...I hesitate to violate copyright , but I will quote, assuming you are a loyal customer..."Experiments With Rake & Trail" Fork rake is how much the front wheel is offset from the steering axis—a straight line through the center of the head tube. The aspect of the bike’s steering geometry that’s affected by fork rake is called trail. Don’t confuse it with a trail you ride on. Road bikes typically have between 2-inches (50.6mm) and 2 1/2-inches (63.5mm) of trail, and bike journalists who’ve written about trail have said 2 1/4-inches (57/58mm) of trail makes a bike not too quick, not too slow, just right. Trail theory says that more trail makes a bike easier to control at high speeds and over rough ground. Mountain bikes typically have between 2 3/4-inches (69.8mm) and three inches 76.2mm) of trail. Less trail, according to theory, makes a bike easier to control at slow speeds, but harder to control when you’re going fast, hitting bumps, or both. Trail is affected by: (1) the wheel radius; (2) the head tube angle; and (3) the fork rake (offset).There are three ways to increase trail: • Bigger front wheel. • Shallower head tube angle. • Less fork rake. Most folks who start thinking about trail temporarily get confused at least three times, and think more rake makes more trail. Nupe. To calculate trail using arithmetic: Trail = Wheel radius/Tan. of head tube angle minus fork offset/Sin. of head tube angle. If that’s Greek to you, we should be in the same club. I have it programmed on my computer here, so I just plug in the numbers and there you go…
How Trail Affects Our Frame Designs When I design a Rivendell, I find the typical tire the rider will ride, and then the biggest. For all-purpose road riding, I shoot for 60-61mm of trail with the most common tire. That’s more than what “experts have said” results in neutral handling, but they are not the boss of me. Nor should they be of you! Then I see what the trail is with the largest tire. Normally a customer will say, “I’ll ride a 700x28 most of the time, but there are some fire roads here, and I’ll ride 700x35s when I go there.” Well, that works out just fine, because the bigger tire will increase the trail, making the bike better for the fire road (so goes trail theory). Most frame designers have a trail figure they’re comfortable with, depending on the bike’s intended purpose. But some copy other manufacturer’s geometries—not a bad thing to do, and I hope we haven’t reached the point where somebody out there considers Xmm of trail to be intellectual property. Finally, some builders just know from experience what works, and don’t think about trail. That’s fine, too! In Italy in the ‘80s it was common for the top makers to put 45mm of rake on each fork, regardless of the frame’s head tube angle. The big bikes, which almost always had steeper head tubes, didn’t have much trail, but the little bikes (with slacker head tubes) had more than plenty. I wouldn’t say that’s all that fine; in fact it seems odd to me. But these same Italian frames were ridden to many prestigious victories, which will impress those in the “results speak for themselves” camp. I’m in the “trail doesn’t win races” camp. When you first learn about trail, you may find yourself getting obsessed. It happened to me and I’ve seen it happen to others. Trail is interesting, but it is not the sole ‘splainer of bike handling, something nobody knows better than Waterford’s Marc Muller (more on him later). The Educational-Type Fun Begins FOR ABOUT SEVEN YEARS I’VE WANTED to experiment with trail by getting some forks with adjustable rakes, so we did. We also got non-adjustable forks with no rake, and with 65mm (whopping lot) of rake. You can do that when you have your own bike company and a publication to get out, but it takes more than snapping your fingers. The bikes are 59cm Romuluses. The Romulus is a road bike with what I think is a perfect geometry for allaround road riding. Pertinent to this story, it has a 73- degree head tube with 42.5mm of rake, which, with the stock Ruffy-Tuffy tire (343mm radius), results in 60mm of trail. It is as familiar to me as it gets. We equipped three bikes with different forks—adjustable rake, 0mm rake, and 65mm rake; and of course we have a normal one, too (42.5mm rake), so really, four. I rode it up and down Mount Diablo and the local streets and roads. I rode it loaded and unloaded, on smooth and rough ground, holding onto the bars like you’re supposed to, and no hands; over speed bumps (with hands and no hands), with a heavy basket, and at different speeds. The Problem With This Test It combines objective numbers and subjective feelings, and what I feel may not be what you’d feel, because maybe we’re used to different bikes, or one of us is more sensitive than the other. Also keep in mind that describing bicycle handling with normal language isn’t always satisfactory. What I call “quick” might not feel so quick to somebody who’s used to a 1987 64cm Ciocc (rhymes with “poach”) Italian racing bike, for instance. Then this: I headed into this test knowing it would make a Reader story, and I found myself looking harder for things that I might not notice normally. I went out hoping to find hugely noticeable differences, and any nuance of the bike that suggested that got pounced on promptly and may be overplayed. I’m not saying I couldn’t tell a difference, I’m just saying there’s a natural tendency to overstate the differences for the sake of a good story, even when I’m aware of that phenomenon. But After All That, Here’s What I Think I could get used to any bike here. Off the bat I’d say I’d have a harder time getting used to a bike with too much trail than I would to a bike with too little, but bikes are fun to ride no matter what, so I’d get over it. Also, I suspect the differences in the extreme versions tend to get neutralized when you’re on the bike manhandling it. I think this because the biggest difference came out in no-hands riding—the low-trail bikes were easy to ride at slow speed, where the tons-o’-trail bikes were hard; and at high speeds it was just the opposite. But at slow or high speed, as long as I had my hands on the bars, it didn’t seem difficult either way. As a bike designer, I find that quite comforting, but I still work hard to thread the needle. (Go to the next page now.)... There's lot's more and pictures that explain a lot, so if Grant & co. give permission, or if we can do this in secret with nobody seeing... or buy Part No. 24-127, RR 26-35! On Thu, Dec 30, 2010 at 9:21 PM, doug peterson <dougpn...@cox.net> wrote: > Does anyone have this as a PDF? Specifically looking Grant's article > on the eternal trail question. The Atlantis & I have been out messing > with loading again....the things you start mulling about during > winter... > > dougP > > -- > You received this message because you are subscribed to the Google Groups > "RBW Owners Bunch" group. > To post to this group, send email to rbw-owners-bu...@googlegroups.com. > To unsubscribe from this group, send email to > rbw-owners-bunch+unsubscr...@googlegroups.com<rbw-owners-bunch%2bunsubscr...@googlegroups.com> > . > For more options, visit this group at > http://groups.google.com/group/rbw-owners-bunch?hl=en. > > -- Bill Gibson Tempe, Arizona, USA -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To post to this group, send email to rbw-owners-bu...@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
