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From: Brent P on 11 Jul 2008 19:15 On 2008-07-11, Matthew T. Russotto <russotto(a)grace.speakeasy.net> wrote: > In article <FKKdnWUbKYHBEerVnZ2dnUVZWhednZ2d(a)comcast.com>, > Brent P <tetraethylleadREMOVETHIS(a)yahoo.com> wrote: >> >>If you were correct, that means the rear brake and rear wheel would be >>entirely useless for slowing. > They are not useless for slowing. They are useless for a > maximum-effort stop. Not at all if you want to remain stable. >>If the brake were useless it would be deleted to save weight. > I'm sure that in many racing categories if they weren't required by > the rules they'd be deleted. >>Once you've weight shifted everything >>on to the front wheel you've past the point of maximum braking because >>now the rear wheel is doing nothing. > It doesn't matter that the rear wheel is doing nothing. The braking > force on the front wheel has been increased by as much as braking > force on the rear wheel has been decreased. Either the rear wheel starts coming around on you like the rear end of a car or the motion changes into roation of the frame and rider about the front wheel. >>I don't think you're stopping as fast as you think you are. And I simply >>cannot fathom under what math a one wheel stop is better than two wheel >>stop. If it were true we could delete rear brakes on passenger cars and >>bicycles. > Passenger cars do not shift weight forward enough during maximum braking to > unweight the rear wheels, so they still need rear brakes for a maximum > effort stop. On they do become unweighted enough that the rear of the car starts coming around and/or the rear lifts up on the suspension. I'll wager that if the rear end did not have a suspension but was solidly mounted like a bicycle's wheels we'd see lift of the wheels off the ground. The suspension travel and spring displacement simply takes up the motion. >>jumping and other such things. However, I've never found an actual >>trail that was designed to be used to get from A to B that I could not >>take a road bike over. And that includes the rocky thing in Iowa that >>was called a trail to get to the top of the bluff along the miss. river. > You'd take a road bike over gravel? A touring bike, sure, but a > road bike with 25x700c tires inflated to 100+psi? I've ridden road bikes on gravel many times. One of the through the forest preserve bike trails I use because it actually goes somewhere is a fine gravel. Not that I haven't ridden on the larger stuff. I don't like it, it's not pleasant when the stones are larger but I can do it. When I was in the 4th grade or so I wanted one of what are now called mountain bikes. Back then they were dirt bikes with gears. Anyway they were more money than a regular road ten-speed so I had to settle for a road going ten-speed. I road it on the trails anyway. I learned what I had to do. Now I won't give up the on road handling and speed and I can still ride trails because I know how to navigate them. Sure I can't take a course with jumps and ramps and other nonsense but I never encounter trails that rough.
From: Brent P on 11 Jul 2008 19:33 On 2008-07-11, DanKMTB(a)gmail.com <DanKMTB(a)gmail.com> wrote: >> If you were correct, that means the rear brake and rear wheel �would be >> entirely useless for slowing. If the brake were useless it >> would be deleted to save weight. � > I don't agree. The rear brake is still useful for poor traction > situations, severe downhills, etc. If it's useful in poor traction situations its useful in all. >> Once you've weight shifted everything >> on to the front wheel you've past the point of maximum braking because >> now the rear wheel is doing nothing. > But if your weight is as far back as possible and the rear lifts, it > seems to me the front wheel has just picked up the braking force the > rear wheel would have applied. For giggles, I'll try some stops > without allowing the rear wheel to lift as well. It'll be interesting > to see, but I don't think I'll stop faster that way since I'll be > required to use less front brake in order to allow the rear wheel to > stay on the ground so that it can brake also. Assuming I cannot > balance on the front wheel to stop I'd agree, but I find in all-out > stops my bike ends up on it's front wheel. When you're lifting the rear wheel all you're doing is changing what is rotating. The bike and rider rather than the wheel. at most the distance you could possibly save is equal to the wheel base of the bicycle. Try to get more and you've flipped over. >> And I simply >> cannot fathom under what math a one wheel stop is better than two wheel >> stop. If it were true we could delete rear brakes on passenger cars and >> bicycles. > Not all riders have the balance to brake so hard with the front that > the rear wheel lifts. Passenger cars skid the front wheels before the > rear wheels lift, so there's no relevence at all. I assume you know > this. Huh? I've had the rear brakes skid first numerous times in cars. If you know how to make it happen and do it right you can swing the rear of the car around as desired. Plus cars have suspensions. The rear is lifting but the distance is taken up in suspension travel. > Who said anything about point A to point B trails? Most of my > favorite riding is done in loops throughout a section of woods. The > point is fun, not getting to point B. I like going long distances. > Here are a few examples of some of my favorite trails: > http://www.livefreeandride.com/vietnow.htm That's just doing stunts.... not my thing. > http://www.between2wheels.com/photos/nh_fort_rock/dsc00192.html I've navigated stuff like that on a road bike. Just for yards, not miles. I would get annoyed after a few hundred yards. > http://www.between2wheels.com/photos/nh_fort_rock/dsc00225.html Nothing I haven't done. Although if something I use frequently I'd build a wider bridge. > http://www.bikerag.com/images/PICTURES/nh-exeter/Dsc00775.jpg ridden trails like that more times than I can count. Never road a mat of sticks though. No reason I couldn't ride that though. > http://www.bikerag.com/images/PICTURES/nh-exeter/Dsc00785.jpg I'd dismount for that section. maybe ride over the bridge and down the other side depending.. > http://www.bikerag.com/images/PICTURES/nh-exeter/DSC00803.JPG Might do the same there. Depends on what's out of the picture. > http://www.americantrails.org/i/resourceimages/vietNEMBA.jpg dismount. > http://www.livefreeandride.com/plank.htm won't play for some reason. > http://www.livefreeandride.com/headbreaker.htm I've ridden trail like that before I just don't do jumps or go over big rocks. or ride on logs I ride around.
From: Brent P on 11 Jul 2008 20:58 Ok... I decided to think... what's a way to settle this... I started googling for motorcycle testing. I found this: http://www.motorcyclecruiser.com/streetsurvival/advanced_braking/index.html Myth #1: Use Only the Front Brake <...> So, how do you stop in the shortest distance possible? The textbook response states you should achieve full application of both brakes without skidding. As you apply more and more pressure on the front brake (up to the point of lockup), you will have more traction available to the front tire (for more braking) resulting in progressively less traction available to the rear. To keep from skidding the rear wheel, you will need to modulate the rear brake. <...> ------------------------ That's what I was able to do in my shortest run. sadly I cannot find any road tests where braking distances from different speeds were given. But there's enough advantage with motorcycle brakes and tires over a bicycle's that I would guess they would be pretty close to cars.
From: John David Galt on 12 Jul 2008 16:22 Jim Yanik wrote: > evidently,the bike's speed was -not- "acceptable" to the driver... Bingo. If a driver is capable of doing a "swoop and squat" with more than 3 feet of clearance in front of a biker, he's entitled to.
From: Brent P on 12 Jul 2008 15:57
On 2008-07-12, John David Galt <jdg(a)diogenes.sacramento.ca.us> wrote: > Jim Yanik wrote: >> evidently,the bike's speed was -not- "acceptable" to the driver... > > Bingo. If a driver is capable of doing a "swoop and squat" with more > than 3 feet of clearance in front of a biker, he's entitled to. If you hurt someone doing that galt I hope you're charged at least as severely as that doctor. |