Gaining proficiency at speed
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From: Timberwoof on 22 Mar 2007 00:19 In article <gfq203t8vq2ibk4k067goq1pk2tteogvbi(a)4ax.com>, Blazing Laser wrote: > On Wed, 21 Mar 2007 05:11:34 -0400, Fred W <malt_hound(a)yahoo.com> > wrote: > > >> When I ride the Beemer I am a lot more careful about speed, following > >> distance, etc. because I know I'll have a harder time stopping. It's > >> not like the brakes are deficient, they were state-of-the-art in their > >> day. Brakes are just a lot better these days! > > > >Even an old beemers brakes can be brought up to modern standards. It's > >mostly a matter of selecting the right pads and making sure you have > >enough mechanical advantage in the master / slave cylinder arrangement, > > They probably could be improved, but most modern bikes of that type > (i.e. not cruisers or scooters) have twin disks up front. I guess that means I can ride a BMW R1200C: it has dual-disc brakes with four pots each and is therefore not a cruiser. }: ) > >> But the Harley I rode had brakes more like the ST1100. I think if > >> anyone has a list of bikes with their stopping distances from 60 mph > >> (or whatever), you'll find the Harley is as good as any bike it's size > >> and weight. Also I think there is an advantage in that long > >> wheelbase. > >> > > > >I don't think there is because it means the angle of transference of > >weight to the front contact patch is more acute and therefore you can't > >apply as much brake force. I suppose it matters what model Harley we're > >talking since they aren't all choppers, but many of the stock models > >have a large rake to the front end. > > That seems logical, but I really don't know how much those things > have to do with it. Steering rake doesn't have anything to do with it. The front tire's coefficient of friction and the location of the bike's center of mass determine whether the bike skids or stoppies past maximum braking. At maximum braking, given equal tires, the bikes will stop equally (given that the cruiser is also braking with the back wheel). > >What is it's size and weight? I'd bet my stock FJR1300 at just shy of > >600 lbs wet would stop a hell of a lot faster than any stock Harley. > > Well you can't bet on that because we'd both be betting on the same > side. 8^) Compared to a Harley, the FJR is a sport bike. The ST is > 50-75 lbs heavier, but I think it's about the same otherwise. Extra weight means extra traction. > >> Also a Harley might not have been going as fast as you were. > > > >45mph is not very fast for the road I was on. I was just toodling along > >enjoying the sunny day. > > > >> OTOH the > >> Ducati would have a better chance of swerving to avoid an accident. > > > >FWIW, this was on a Monster 750 with (only) a single front disk. But > >the bike weighs less that 400 lbs and that one disk gives plenty of > >braking power. I did not use the rear brake in this instance as the > >back wheel was barely in contact with the ground. > > The Harley I rode, I hardly ever used the back brake because it was > just very clumsy for me to pick up my foot off the floorboard and > bring it down on the big, clunky automotive-style pedal. But the > front brake seemed to have a very light touch, more mechanical > advantage than any bike I'd ever ridden. And with both brakes > together the bike stopped very well. It also had very wide tires, > which might have something to do with it. -- Timberwoof <me at timberwoof dot com> faq: http://www.timberwoof.com/motorcycle/faq.shtml It's easy to say a war is so important your neighbor should go fight it for you.
From: Blazing on 22 Mar 2007 04:18 On Wed, 21 Mar 2007 21:19:06 -0700, Timberwoof <timberwoof.spam(a)infernosoft.com> wrote: >> They probably could be improved, but most modern bikes of that type >> (i.e. not cruisers or scooters) have twin disks up front. > >I guess that means I can ride a BMW R1200C: it has dual-disc brakes with >four pots each and is therefore not a cruiser. }: ) Well ask anyone riding a Harley or a VTX or a Victory if the 1200C is a cruiser. The whole idea of 'BMW Cruiser' is oxymoronic. BMW and cruiser are like oil and water. Yeah, if Microsoft made a cruiser, the engine would seize up solid every now and then and you'd have to turn it off and restart it while traffic built up behind you. If BMW made a cruiser it would have dual-disk brakes with four pots each. (But point well taken.) >> >> But the Harley I rode had brakes more like the ST1100. I think if >> >> anyone has a list of bikes with their stopping distances from 60 mph >> >> (or whatever), you'll find the Harley is as good as any bike it's size >> >> and weight. Also I think there is an advantage in that long >> >> wheelbase. >> >> >> > >> >I don't think there is because it means the angle of transference of >> >weight to the front contact patch is more acute and therefore you can't >> >apply as much brake force. I suppose it matters what model Harley we're >> >talking since they aren't all choppers, but many of the stock models >> >have a large rake to the front end. >> >> That seems logical, but I really don't know how much those things >> have to do with it. > >Steering rake doesn't have anything to do with it. The front tire's >coefficient of friction and the location of the bike's center of mass >determine whether the bike skids or stoppies past maximum braking. At >maximum braking, given equal tires, the bikes will stop equally (given >that the cruiser is also braking with the back wheel). I said I didn't know. 8^) The center of mass is farther back behind the front wheel, all other things being equal? Just seems like there would be more downward force on the front wheel. That would work also towards keeping the rear wheel on the ground so it could help brake. Maybe that has nothing to do with it. You would know. >> >What is it's size and weight? I'd bet my stock FJR1300 at just shy of >> >600 lbs wet would stop a hell of a lot faster than any stock Harley. >> >> Well you can't bet on that because we'd both be betting on the same >> side. 8^) Compared to a Harley, the FJR is a sport bike. The ST is >> 50-75 lbs heavier, but I think it's about the same otherwise. > >Extra weight means extra traction. But the Harley was about 75 lbs. ligher than my ST. It felt -much- lighter because of the low center of gravity.
From: Timberwoof on 22 Mar 2007 03:52
In article <3ee403l6gnq1m20tt7utmg63rgvv669spi(a)4ax.com>, Blazing Laser wrote: > On Wed, 21 Mar 2007 21:19:06 -0700, Timberwoof > <timberwoof.spam(a)infernosoft.com> wrote: > > >> They probably could be improved, but most modern bikes of that type > >> (i.e. not cruisers or scooters) have twin disks up front. > > > >I guess that means I can ride a BMW R1200C: it has dual-disc brakes with > >four pots each and is therefore not a cruiser. }: ) > > Well ask anyone riding a Harley or a VTX or a Victory if the 1200C is > a cruiser. The whole idea of 'BMW Cruiser' is oxymoronic. BMW and > cruiser are like oil and water. > > Yeah, if Microsoft made a cruiser, the engine would seize up solid > every now and then and you'd have to turn it off and restart it while > traffic built up behind you. If BMW made a cruiser it would have > dual-disk brakes with four pots each. > > (But point well taken.) :-) Well, the R1200C looks like a cruiser to me, and you can even get a transparent alternator belt cover for it. It's a cruiser... > >> >> But the Harley I rode had brakes more like the ST1100. I think if > >> >> anyone has a list of bikes with their stopping distances from 60 mph > >> >> (or whatever), you'll find the Harley is as good as any bike it's size > >> >> and weight. Also I think there is an advantage in that long > >> >> wheelbase. > >> >> > >> > > >> >I don't think there is because it means the angle of transference of > >> >weight to the front contact patch is more acute and therefore you can't > >> >apply as much brake force. I suppose it matters what model Harley we're > >> >talking since they aren't all choppers, but many of the stock models > >> >have a large rake to the front end. > >> > >> That seems logical, but I really don't know how much those things > >> have to do with it. > > > >Steering rake doesn't have anything to do with it. The front tire's > >coefficient of friction and the location of the bike's center of mass > >determine whether the bike skids or stoppies past maximum braking. At > >maximum braking, given equal tires, the bikes will stop equally (given > >that the cruiser is also braking with the back wheel). > > I said I didn't know. 8^) The center of mass is farther back behind > the front wheel, all other things being equal? Just seems like there > would be more downward force on the front wheel. That would work also > towards keeping the rear wheel on the ground so it could help brake. > Maybe that has nothing to do with it. You would know. I was drawing different force diagrams to see if I could make it as simple as possible. I came upon this one (and I'm going to have to revise the drawings on my web site): On a side view of the motorcycle, draw a rectangle with one corner at the bike's center of mass and the rest of the box forward of that point. The height of the rectangle is proportional to the weight of the bike; the width of it is proportional to how hard it can stop (weight times Mu). The diagonal gives the combined force vector of weight and max deceleration. If this diagonal intersects the pavement ahead of the front wheel contact patch, it will stoppie. If it's behind, it won't. Simple as that. > >> >What is it's size and weight? I'd bet my stock FJR1300 at just shy of > >> >600 lbs wet would stop a hell of a lot faster than any stock Harley. > >> > >> Well you can't bet on that because we'd both be betting on the same > >> side. 8^) Compared to a Harley, the FJR is a sport bike. The ST is > >> 50-75 lbs heavier, but I think it's about the same otherwise. > > > >Extra weight means extra traction. > > But the Harley was about 75 lbs. ligher than my ST. It felt -much- > lighter because of the low center of gravity. Oh. I should have said "less weight means less for the reduced traction to do." ;-) Friction is a funny thing: with more weight on it, the sideways force it can cause increases ... pretty much by how much you increased the weight. That's why it's a coefficient. *Theoretically* a fully loaded bike would stop as fast as one with me riding it on an empty tank. But then all kinds of other things enter into it, like how well the brakes work ... they have their own friction and force to factor in, not to mention their behavior when hot. And then comes how well the weight squeezes the rubber into pavement irregularities... -- Timberwoof <me at timberwoof dot com> faq: http://www.timberwoof.com/motorcycle/faq.shtml It's easy to say a war is so important your neighbor should go fight it for you. |