| Author | Message | ||
     Tbs_stunta |
Hopefully one of the anons can answer this. My understanding is that there are two main forces in braking. 1. Forces originating at the rotor as it is clamped. 2. Forces transferred to the spokes causing them to flex when the wheel is forced to rotate slower than it would with no brakes applied. How much (appox percentage) of the total forces do these two comprise? If a traditional rotor is attached to the hub, not the spokes, how significant are the forces that move down the spokes? What other significant forces are at work here? Did any of this make sense? | ||
| Swordsman |
Um... if I'm following this, wouldn't the only other force be the resistance offered by the ground itself against the force being transferred through the spokes? What is the point of this question, anyway? ~SM | ||
| Samiam |
I believe #2 should have the rolling inertia of the bike itself added to the equation. I would think that the forces would be significant enough to make other manufacturers' bikes use larger spokes in the construction of their wheels versus Buells which don't have the braking power being transferred to the ground via the spokes. Instead it is transferred directly to the outside of the wheel. Hence the smaller(lighter) spokes on a Buell. I would think other forces at work here as well would be the traction of the particular tire against the particular pavement (slick/tar surfaced/rough), the force of a bike against the pavement(gravity/centrifigul force if it's in a turn) which directly affects traction, the surface area of the tire contact patch and brake pads. As you can see, there are quite a few items involved, but you don't have to take my word for it. Sam | ||
| Marty12s |
if you're getting that into it, i'd imagine there is an amount of flex from the forks as well, or at least the head bearing. and the tire at 30 somthing psi would have more give than anything else in the equation. and don't forget the aluminum lever itself most likely has some bend in it. not to mention any padding on your hands (fat?, gloves?) ok, sorry, that came out a lot meaner than i wanted. a bad atempt at humor, please don't take offence. i'm not sure what you want to know though. | ||
| Pwnzor |
My brake rotor is attached to the rim, not the spokes. I'll assume that's what you meant. Not sure what you're trying to get to though. | ||
| Exitlandrew |
It really all comes down to two things. When the rotor is attached to the outer part of the rim you can make the center lighter, because there is less stress on the spokes. You also dont have the brake torsion that you normally get when you only have the brakes on one side of the rim. For instance, my dads springer, if you get on the front brake real hard (like just before its gonna lock up) it will pull to the right. thats the main reason most other sport bikes have dual calipers in the front. Endos prove they have way more brake than they need. You can probably get better info on the Buell site, this is just my understanding of it. I think that when the patent runs out, like the underslung exhaust, there will be alot of other manufacturers playing with it. Bimota has already come out with a concept bike with a similar design. | ||
| Tbs_stunta |
Sheesh not getting at anything, just discussing the relative merits of the ZTL vs a traditional dual disc system. Haven't you guys wanted to know specifically why your ZTLs are better, and be able to discuss it further than "Buells Roxor". So for the sake of this argument exterior variables like tire type, fork flex, lean, and all that are the same between the two systems. | ||
| M1combat |
LOL  . Do some searching . You'll find a ton of info. Geometry defines how quickly you can stop. The ZTL wasn't engineered to have "better brakes" as such. It's purpose is to work as well as a conventional brake setup AND be lighter. Unsprung mass is a VERY important thing and the ZTL reduces unsprung mass AND works as well as a conventional setup. Anony states that it offers less rotational inertia. They used to claim that it was eight pounds lighter than a competitive dual rotor setup. They never really said which one but some believe they were comparing it to an '03 or '02 RC51. The competition has lightened their setup as well, but haven't quite caught up. They won't w/o forged mag wheels IMO. | ||
| Pwnzor |
What I can say about this is as follows: When I take the front wheel off the XBR, it's very light. When I take the front wheel off the Duc 749S, it's heavy. They each stop as well as the other. Granted, I am not riding to the maximum potential of either bike. | ||
| Anonymous |
There have been some articles on this in Fuell magazine. Basically the deal is as M1 says, it wasn't designed to stop better than a dual disc on an ideal surface, just to do that as well. It was designed (and succeeds)to reduce weight and inertia. What does that mean riding? Well, here are a few advantages: A ZTL will significantly out-stop a conventional system on a bumpy surface, because the lighter unsprung weight keeps the tire in better contact with the surface. A ZTL will have higher potential cornering speeds due to the lower unsprung weight, once again the bumpier the road, the more advantage. A ZTL system increases the acceleration rate of the vehicle because it weighs less and has less inertia to spin up. A ZTL equipped bike is less likely to have headshake over bumps because it has less mass rotating about the steering axis, which is one reason XBs need steering dampers less than bikes with dual discs. There are more advantages, but hopefully this starts you down the path. | ||
| Glitch |
You also dont have the brake torsion that you normally get when you only have the brakes on one side of the rim. What!? For instance, my dads springer, if you get on the front brake real hard (like just before its gonna lock up) it will pull to the right. There's something wrong with your dad's springer. thats the main reason most other sport bikes have dual calipers in the front. Wrong, think again. Think about it. One brake will not pull to one side. Buells have always had one brake. Explain why you think it would pull to one side. Now a car will pull to one side if only one brake works. | ||
| M1combat |
I can vouch for the handling benefit enabled by the ZTL... One particular road I ride has a section where you come down a hill around a ~240 degree right hand turn losing about 30' elevation or more. The corner is marked 15 and is pretty bumpy. I can ride right behind pretty much anyone heading towards that rurn. As soon as we lean into that turn their front gets un-stable and they start walking towards the yellow line. They get out into the outside tire track and it's less bumpy and they can hang there. Just at the bottom of the turn it moves into a sharp left and then a 100' or so of straight (well... fairly straight). If you can't hang on the inside of that carousel you can't get a drive onto the straight coming outta the left... Only the Buell can maintain good speed around that turn. Everyone else I've watched either has to shed about 10-15MPH or move to the outside. Most people don't realize that it's better to shed speed. They need to sacrifice the first turn to get a good drive out of the second. The washboard bumps make it difficult to sacrifice the turn. That's a real world benefit of the ZTL. It also works really well in very bumpy brake zones. | ||
| Court |
>>>For instance, my dads springer, if you get on the front brake real hard (like just before its gonna lock up) it will pull to the right. | ||
| Court |
CAVEAT: (lest I be called a liar) ) "Absent something seriously wrong...like a front axle made of rubber" | ||
| Anonymous |
Back to your original question, Tbs. Note, the Fuell article will help you understand the following because without pictures, it's tough. The forces are just those generated by simple leverage. Here's a basic calculation: If your bike and you weigh 600 pounds, are stopping at 1G, and the rear wheel is just off the ground, the horizontal force at the tire contact patch from braking will be 600 pounds. So, using statics, we freeze any moment that this is happening, and figure out the forces involved. Say your front tire is about 24" in diameter. Your brake pads need to generate enough force to oppose the rotational force of 600 pounds of force (lbf) acting on a 12" lever arm (tire radius, so 600 ft-lbf. The ZTL rotor has it's drive pins on about an 8" lever arm, so the force that must be generated by these pins will be 600*12/8, or 900 lbf. Split up over 6 pins, that means about 150lbf on each pin. This force is being put into the stubs directly connected to the rim, and the tire force is input into the rim via the tire bead. So no load goes through the spoke, it all goes through the rim. With a conventional disc, the load will go into the main brake pad diameter, which is probably at about 5.5 inches on radius, so this load will be 600*12/5.5, or 1300 lbf. But at the bolt circle where the disc is connected to the hub, probably at about a 2" radius, you would find the load on those bolts, or the joint they clamp, to be 600/12/2, or 3600 lbf. So basically you are trying to balance the 600 ft-lbf generated by the tire. The disc hub therefore is being twisted about it's center with a torque of 600 ft-lbf. And so is the wheel about it's center, because the tire friction and brake pad frictional forces are connected by going down to the hub and back out again. So the loads on the disc hub and the wheel spokes can be calculated based on knowing at on any point on their diameters, there needs to be force capable of creating the torsional load of 600 ft-lbf. So on a wheel with three spokes, if they connect to the hub at three inches from the centerline, then each spoke would be experiencing a shear force of (600*3/12) 2400lbs divided by 3, or 800 lbs shear force at that point on each spoke. On a ZTL spoke, that shear force does not exist at all. The only force is that spoke's portion of the vertical gravitational force of 600 lbs (since you are doing a stoppie), and of course the conventional wheel has to carry this as well as the shear force. That's why the ZTL wheel can be so light. Hmmm, hope this makes sense. | ||
| M1combat |
Anony... I'm assuming that there's not a specific engineering reason to have one spoke (or "set" in our case) for each mounting boss for the caliper... Would it be possible to go to three "sets" of spokes that were a bit beefier? Would it be possible to go to three "sets" of spokes like we have and three singles? I'm assuming that the forces generated while cornering make the three sets idea a bit of a stretch due to having 1/3 of the wheel not supported laterally. I think having three sets and three singles would look quite sweet though. Don't get me wrong , I like the way it currently looks . | ||
| Blake |
I like diagrams...  Conventional Wheel/Brake Loads & Reactions (Free Body Diagram)  Buell ZTL Wheel/Brake Loads and Reactions (FBD) An explanation and more of the same kind of discussion, a lot more, more than you probably can stand, can be found here. | ||
| Blake |
More here And be sure to check the faq section of the Buell website. They have some great tech articles there. | ||
| Buellfirebolt31 |
my dads sporty always pulls to the right because it has one brake.....NOT!!!!!!!!!!!!!!  | ||
| Anonymous |
M1, Any combination is possible; the spokes do not need to be at the disc mounts, although there is some weight savings by doing it this way. In fact, I think Jens even has wire wheels with rims that accept ZTL. However the design selected was the one that gave the least weight for the most strength per FEA analysis of a wide range of possibilities. | ||
| Anonymous |
BTW, a springer front end per andrew does have some weaknesses compared to a standard fork regarding a single disc, and ZTL alone would not address these. | ||
| Pwnzor |
No vehicle with two wheels in front of each other can possibly pull to the side. The bike only touches the ground in two places, and it's rear wheel drive.  | ||
| Tbs_stunta |
On a slight aside, how does the longevity, pad and rotor wear, compare to a dual system that is comparable in performance? How does heat dispersal compare? | ||
| M1combat |
WRT pad and rotor wear I would imagine that it's all down to material and surface area. When it comes to heat dispersal... Some racers have indicated that the ZTL can fade at a race pace w/o additional cooling techniques. The ZTL2 seems to solve that issue entirely. | ||
| Blake |
From a theoretical viewpoint, assuming all else is equal, a dual disk setup provides more pad area (8-pot versus 6) and more disk surface area, so it should provide commensurately improved wear and heat dissipation, assuming all else is equal. One variable? Airflow over the ZTL may be better for cooling of the disk or it may be less optimum compared to conventional dual disks, I dunno. | ||
| Glitch |
My rotor needs to be replaced now after 46thousand miles. Not sure how many of those miles were made under braking though.  | ||
| Aeroe |
I don't see why the springer, or buell for that matter, can't pull to the right. Maybe the right word isn't pull but turn. Think about it from a riders point of view: The road touches the tire on the center line. The brake caliper is a few inches to the right. The force from the road pushes the tire one direction and the caliper opposes that force with another force in the opposite direction. Put a pencil flat on your desk and put your fingers on opposite sides. Move your fingers in opposing directions and see what happens...same concept. | ||
| Glitch |
It's not like your pencil at all. The wheel and brake rotor are one unit. Putting the brake on slows the entire wheel, not half of it. | ||
| Anonymous |
Aeroe, it can only pull if the forces deflect something in the front end. If you do a complete free body diagram of the system you will see how it works. Blake has done the free body diagram, I am sure! Any top notch engineer always wonders why something new works. Pretty amazing when Jeremy told you the system is comparable to the best MotoGP stuff, isn't it? BTW, Blake, remember the velocity, it is indeed one of the key points. Particularly the velocity against free ambient air stream at the point of maximum delta t. And think about the percentage of disc exposed to cool air. Ah, what the heck, here's some more spilled beans. The advantage in plain old mechanical leverage helps too, as fade is when you don't get the same grip with constant pressure (usually the maximum you can generate). But when a given pressure has more mechanical leverage, that helps against the effects of fade. And (last bean), there is less hose deflection and caliper deflection being wasted. So, Badwebers, more than you can get from any other source! And all because Blake rocks! He's slow, true, but he rocks anyhow! | ||
| Glitch |
A slow rock  | ||
| Blake |
Gee thanks Anony.  I really enjoy this kind of stuff. Pretty amazing when Jeremy told you the system is comparable to the best MotoGP stuff, isn't it? My jaw hung agape for a split second for sure. Not one of the three professional racers nor Don Canet had anything negative to say about the ZTL-2. It was all positive. Probably the best compliment for a motorcycle front brake system is for a racer when asked about it to say, "hmmm, I didn't even notice, it must be good." That was Cicotto's answer and he was scaring the heck out of me the way he was late breaking into turn one at TWS. Steve Crevier said much the same. For sure, FBD's are my friend. Beans rock! Especially these kind. Thank you for sharing and the kind words. Very interesting stuff for sure. Who said I am slow?! I'm plenty darn fast! At least in my mind. Wait, you are talking motorcycles, right? Maybe I am slow after all. Aeroe, Until the 3-D FBD can be sketched... See the red force vector arrows in the free body diagrams I posted above? Those represent the braking frictional load applied to the disk and its equal and opposite reaction load at the axle which is applied to the axle by the right side lower fork leg. The caliper passes that reaction load through its bracket into the fork leg then down to the axle then into the wheel. That entire loading is confined entirely within that wheel/fork/disk assembly. The size (length) of each arrow represents the magnitude of the load with the direction of course indicating the line of action of the load. For a wheel with a single disk on one side, like the Buell ZTL or any wheel with a single disk brake, the red force vectors are indeed off-center; they are in plane with the disk not the center plane of the wheel. But they oppose and cancel each other, the sum of them is zero force with only the resulting torque about the axle. The resulting torque acting only about the axle has no component which would tend to turn the front end or steer the bike. It is definitely a confusing relationship to grasp. The one factor that might lead to perturbations in steering under braking would be if the forks and/or axles were flimsy and deformed significantly under braking loads such that the front end geometry was rendered asymetric (one side not like the other). Due to its carrying the braking load reaction from caliper to axle, the lower fork leg holding the caliper will experience different internal loading than the opposite lower fork leg; thus if the forks are not robust enough to resist significant flexure, one can see where some affect upon steering might manifest. I hope that made some sense. If not, we'll get a sketch up soon. Maybe later. You may have to be patient on account of I'm kinda slow. "Slow Rock"? ... Yo, Adrian! | ||
| Jlnance |
Thus if the forks are not robust enough to resist significant flexure Ah, you've answered the question I was about to ask. I've been told that the addition of a fork brace to the Blast eleminates a tendency for it to pull under hard braking. Which is consistent with what you say. | ||
| Aeroe |
Ya, I think I got it. I just need to go outside and look at my bike. Damn FBD's, I'm tired of FBD's. | ||
| Blake |
Jim, I'd be very surprised if the fork lowers of Blast's conventional forks are not up to the task of resisting the braking load in good form. |
