So RR 31 is out -- great, must buy it. Good article. Whatever G's take on trail, he's built me three excellently handling bikes.
On Thu, Dec 30, 2010 at 9:50 PM, Bill Gibson <bill.bgib...@gmail.com> wrote: > 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. >> 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. > -- Patrick Moore Albuquerque, NM For professional resumes, contact Patrick Moore, ACRW at resumespecialt...@gmail.com -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. 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