First bike, need help with basics

Discussion in 'General Questions' started by aflaclover123, Jul 27, 2016.

  1. aflaclover123

    aflaclover123 New Member

    So I'm building my first bike and I need to know the basics of how to start the motor, braking, and oil mixture. Also any routines or things I should do when I start the bike. Finally how to properly break the bike in.

    P.S.: I heard someone say you have to have the clutch in to brake. Is this true and if so, what do you do if you have to stop quickly if a car pulls out.

  2. Frankenstein

    Frankenstein Active Member

    All this info can be found in the 2stroke and general questions sections of the website, mostly in the pinned posts.

    As far as braking quickly, squeeze the clutch and the brakes at the same time, and steer away from the obstacle, like a car
  3. aflaclover123

    aflaclover123 New Member

  4. crassius

    crassius Well-Known Member

    my GF has three brakes on her bike - I told her if a bus is coming at you hit all three and to hell with the engine
  5. Frankenstein

    Frankenstein Active Member

    I've seen a special double brake cable, so it's one line, split to 2 lines, and those go to front and back brakes, it's linear so they don't make up for wear on the brakes, unlike the lever type double lever. I could see somebody effectively hooking up 2 double lines to a double brake lever, and in turn actuate 4 brakes at once, say 2 rim brakes and 2 disks... Talk about stopping power, throw in a coaster brake and a tractor-trailer couldn't push the bike out of the way if it wanted.
  6. FurryOnTheInside

    FurryOnTheInside Active Member

    Unfortunately the dual pull lever already divides the effort from the lever by two. Connecting it up to four brakes would divide your effort by four, and also gives you the drag of all four cables on the one lever.
  7. Frankenstein

    Frankenstein Active Member

  8. burrus

    burrus New Member

    This is the dual lever I installed on mine. I am 6'4" 245lbs. and I drive my bike like I stole it. This lever will stop my bike almost to the point of a skid. I have linear pull brakes on front and rear and the longer pads installed on them. Initially, while I was building, I thought about a disc in the front, but I just don't need em'. Brakes work perfectly. The dual lever is part of the throttle/kill switch assembly all- in -one. Made well. Very happy with it. brake.jpg brake 2.jpg
  9. Frankenstein

    Frankenstein Active Member

    I'd think it's a miracle that we humans could stop 250 pounds of anything traveling downhill at 40mph with one hand just by squeezing a tiny lever.

    Divide by 4 or divide by 13 if you will, almost seems like if the lever can be pressed as much as it physically can and you're still moving then there's room for more friction.
  10. Frankenstein

    Frankenstein Active Member

    Hmm now is the force being divided evenly between the brakes, or is it doubling the force being put on the lever?

    These might be just cables but let's look at hydraulic brakes seen in most automobiles. If at the point where the brake pedal meets the hydraulic line we have a 1 square inch of contact with the fluid, and we are to put 25lbs of force onto the square inch, and at the other end the fluid reservoir opens to 4 Sq inches of contact with the fluid, then while the braking surface moves 1 quarter the distance than the pedal did, it's actually applying 25inch/pounds on 4 Sq inches, in effect applying a total of 100 pounds of force to the braking surface. Now whether that's being applied in a square inch of brake Pad, or spread across 20 square inches is irrelevant, it's still 100 pounds of force on the surface. If you divide that forces across 4 wheels it's still 100 pounds of force on each brake surface, as long as the lever or pedal moves 4 times the distance it did to achieve 100lbs on 1 wheel.

    So if a brake cable is a reverse hydraulic line, where it's pulling not pressing, and the cables are linear devices not being used to fill in gaps like a fluid does, then is the force being actually divided up or are we just making the same force cause more points of contact who in themselves are being multiplied by a lever that is part of the brake system?

    Long question short, why do we use 2 brakes if what you're saying is that 1 brake should be equally effective, since we are apparently dividing the force up if we use 2 brakes.
  11. Frankenstein

    Frankenstein Active Member

    Here's a simple picture, in the top drawing, you can clearly see that pulling on a lever will pull the cable 1 inch at the end of the cable housing, which in turn will pull 1 inch at the brake mechanism, bringing the end of 2 levers 1 inch closer together, now the brake pads are roughly 3/4th of the way down to the fulcrum, the point that's mounted to the frame and pivots on. So each brake Pad moves a quarter of half an inch closer together, pressing on the wheel and slowing you down. Whatever.

    Second illustration shows that the same 1 inch movement is producing the same 1 inch pull on each of the 2 cables, it just has to by its very own nature. Which means both brakes are now moving 1/8th of an inch (1 quarter of half an inch) closer together, on each wheel.

    If both brakes did exactly the same as the single brake did, as far as linear motion and level of "squeeze" on the wheel goes, then how could they be half the force as the single brake?

    Friction is the stopping force, which is relative to the applied force, which is relative to the leverage of our hand lever, if the leverage in the brake lever never changed, then our relative forces never changed either. So by default our friction is doubled simply by doubling the surface for what the friction is acting on, much like a hydraulic brake can take the single 25 pounds on an inch and multiply it onto 2 or 4 inches and double or quadruple the force being used as friction.

    Now that doesn't mean it's free kinetic energy, it just means that we are using wires as fluids, just not in the conventional manner, which means twice as much force needs to be somewhere if the linear pull remains the same. Where does the force come from? It comes from the second cable. And therefor the second joint on the brake lever that accepts the cable, so while I could hook a double cable to a double brake lever twice, the problem is the force acting in reverse, being a linear device, could break the brake lever, so if the lever can't stand up to the force, which you may need to pull more to get the same inch from get that force, then it will fail.

    Now all you do is put a slightly bigger lever on the handle, and you won't have to pull so hard, just pull across a larger distance, and the lever will multiply the force to the cable stops, then that same inch receives more force which is then attributed to the relative friction of the system. Again, a bigger hand lever just makes it easier to brake, and also easier to break the brake lever.

    Tldr? Bigger lever gives same stopping power on twice the number of brakes, at one point it becomes impractical, but that's why we have power steering and brakes in our cars, the foot pedal does a tiny bit of work while a machine multiplies it 10 times over using the engine as the source of power, if you ever had your master cylinder go you'd know how hard it is to stop the car, or if you drove a vehicle before power anything you'd also know it was a chore to actually drive.

    Attached Files:

  12. Frankenstein

    Frankenstein Active Member

    Still tldr? Net force, is determined by time, Mass, and distance, if you can pull the longer lever just as fast as the short lever, then you've multiplied the net force being applied to the brakes, simply by doing twice as much work, so to speak, in the same time.
  13. Frankenstein

    Frankenstein Active Member

    Still still tldr? If you ride motorized bikes have a strong grip or long fingers. That's it.
  14. FurryOnTheInside

    FurryOnTheInside Active Member

    One hand on one lever is the same effort no matter how many brakes it is connected to. It is not going to increase or decrease the amount of effort if you connect to two or four brakes, but it does increase the drag (cable friction) if you connect to two or four.
    Of course double length levers would be great if only fingers could move that far.. It is impractical as Frankenstein says. But also leverage at the _top_ of the cable increases load carried by the cable which tends to stretch, like a u brake has lots of leverage at the lever and suffers from more cable stretch compared to a v brake which suffers more drag (cable friction).

    I really dislike the drag on my double cabled rear bmx u brake.. They did it like that to halve the cable stretch, but of course they doubled the drag. But the frame's lugs are set up for that and would be awkward to change it. I can imagine four cables, no matter how well greased, would be a horrible amount of drag..
    I like that there is no friction (2x0=0 4x0=0) on a hydraulic line..
    But connecting the lever to four brakes wouldn't be increasing the effort, each brake would take a quarter of the effort and the combined effect of the four would still always be the effort of one hand. 1 / 4= 0.25 , .25+.25+.25+.25= 1 , 1 always equals 1

    I have some reservations about using extra long v brake pads in the wet, personally. I can see it increases friction in dry weather, but it decreases pressure. Pressure pushes the water away, which is why disc brakes (cable or hydraulic) work so well in the wet.
    Four and six piston disc brakes are a bit different in that the pads contact in series.. I leave that to the experts though lol. :")

    But two hands on two levers to two independent brakes seems like a good idea to me. Two hands effort is always going to be twice the effort of one hand.
    Last edited: Jul 28, 2016
  15. Frankenstein

    Frankenstein Active Member

    Not completely correct, but you do have good points, cable drag is a, well, drag. The unfortunate truth of a double cable is the cable housing is basically permanent, no removing some unless your going to mod parts of the cable routing system on the bike.

    However that's why we who-mons got good at making things more efficient, I wouldn't even grease a cable, I'd lube it with silicone coating that they make as a spray, crazy how well it works. As an added bonus, get Teflon powder and stick it in there too, with a few light drops of fishing real oil, it will be so slippery you'll think you had your hands directly on the brakes and not on 3 feet of wire.

    OK part 2 is tolerances, by getting very true wheels and disks, you can afford to remove the slop in the system, so while you might have a total gap of 1.5 mm from brake to braking surface, you can cut that down to .75mm total distance. If you can make that relative distance smaller, then the distance the hand lever must travel is also smaller, so change the leverage to multiply hand effort to an even greater extant since you now only have to move half as much, so a normal sized hand lever will only need to pull half an inch of cable with the same hand size and strength, to get the same effect as a large hand with an impractically large lever.

    Get what I'm saying hopefully?
  16. burrus

    burrus New Member

    Jeez guys....
    All I know is that my brakes stop me. Quickly, efficiently, minimal effort. All I could ask for.
  17. FurryOnTheInside

    FurryOnTheInside Active Member

    Hehe it's a fun hypothetical carousel. Let's go around again! :p Wheee! Wheee! :D

    Actually I don't think I can explain without pictures but the point about the bmx having a double cable was just that it has twice the drag, no matter how well lubed it's twice what it would have with a single cable. Actually the bike has a gyro and the upper cable length is indeed permanent but the lower 2/3rds is not.. But it's only on there because u brakes have a lot of stretch in the cable, and u brakes are only needed for clearance.. I guess it is getting off topic..
    Oh yeah..

    I think you are saying combine a u brake lever (high leverage, short cable pull) with a v brake or cable disc that is perfectly adjusted. I'm going to disagree again and say a v brake needs the clearance to allow some imperfection in the rim and the cable disc doesn't need more power. IMO :) but I suppose I should try one and see.

    I think a cable actuated disc on the rear is great because it is robust (won't leak if it is creased) and easy to attach a standard brake light, and a hydraulic disc on the front (with a "hole in the head" to prevent creasing) is best because it is drag and stretch free. Even though you have to separate the hose then put it through, reconnect and bleed it which is a total pain if you like switching your forks often.

    Personally IMO and all that. :)

    Wheee! :p
  18. Frankenstein

    Frankenstein Active Member

    Right, but a good brake system isn't dependant on you squeezing the bars like it's going out of style. The better the adjustment then the better the stopping power, being based totally on relative friction of the device used, this friction cannot be amplified however by squeezing harder after a certain point. If a disk brake is being firmly squeezed and can't be compressed any further, then the brake is doing everything it can to slow the object down. Any further squeezing is lost in the cable by the means of stretch. Hydraulics won't stretch, instead they either stop getting tighter at the hand lever or simply burst.

    A good example is it would be nearly impossible to stop the bike going 30mph down a hill and you and the bike weigh 250lbs total by using your one hand to squeeze the wheel, even with gloves, stopping it with 2 hands is also probably a bad idea. The effort, if it was even possible to put that much effort out, would be huge, to stop something like that in a timely manner, yet the wanted effect is produced from a single lever about 4 inches long, being squeezed with only a fraction of the work that's would be needed if grabbing the bicycle wheel with your bare hands, and the braking surface, at least on my disk brakes, is only about 4 square inches total, meanwhile a hand is easily 4-5 times that.

    If you want to run 4 brakes, it's not needed to apply 4 times the effort as a single brake, but is required that the tolerances be 4 times as strict, so the 4 brakes can receive as much braking power as 2 or 1 brake with lots of slop in the system that loses some of the hands effort on the way. This is why Hydraulics are so effective as power transfer or "modulation" as riders like to describe it, they are almost 0 friction in the lines from the hand to the brake, but we all know that if the brakes are cheap or in bad condition it wouldn't matter if you pressed the lever untill it bent into the handlebars, the bike wouldn't stop because the brakes were no longer providing friction and may even be acting as a hydroplane for oil, water, grease, or other contaminants.

    Exactly was bb7 brakes with twice as large pads as the bb5 brakes by the same company simply have better stopping power, all the conditions are exactly the same, but twice the friction surface so twice the relative friction across the same effort on the hand, so technically you'd have to squeeze half as hard, as long as there's no cable stretch, to get the same stopping force at the brakes.

    Give me a large enough lever, and I'll move the world.