If you take a mountain bike not really meant for hardcore downhill riding, and then ride it that way, you can get it to happen.
I’ve also made it happen with a piece-of-crap minivan in the mountains of Colorado.
Having said that, yes, I agree with you that disc brakes for bicycles are a vast improvement over rim brakes, for a lot of reasons.
I inherited some money a few years ago. I put most of it in an investment account for my son, and some into a savings account, that was medium-yield, but had no penalty for withdrawal, and I’m so glad I did, because we’ve withdrawn a lot over the last year.
I also spent some on buying really good versions of things that it paid to have good versions of-- bikes, laptops, and a couple of other things that are way safer and less prone to breakdown when you just spend about 30% more.
We donated all the old ones.
Anyway, that’s how I moved up to a bike with disc brakes. I’m never going back. I got my old bike tuned up, and gave it to the just-turned-13-yr-old neighbor girl who always watched our apartment and cat any time we went out of town (which we did pay her for, but still), and it wasn’t a bad bike-- Schwinn, but top-line Schwinn. She had a kid’s 1-speed that didn’t really fit her, and the bike I gave her (cleared it with parents first!) was a 10-speed. She was so happy, it was almost as good as my getting the new one.
Looks like a Slavonic language, but not Polish and perhaps not Czech or Croat. Definitely not Hungarian, but maybe Balkan?
Popped it into Google Translate and it says it is Bosnian.
Thanks!
Reading all of this I admit I am lost.
A bigger rotor is better. More surface area means heat is spread out more (good). More mass allows for more heat capacity (good).
More holes (good).
But, more holes equals less mass (bad). But holes (good). More holes (more good).
But then less mass (good). But we decided earlier that more mass (good).
Color me confused.
Holes are a tradeoff. They reduce mass = static heat capacity some. They increase cooling = dynamic heat capacity some. Which “some” is bigger?
Depends on the details we’re not digging into. But the fact holes are a commonplace on discs for bicycles through race cars says the engineers who do the calcs we’re not bothering with conclude that at least some holes help more than they hurt.
Holes = cooler = rotors are harder = good (less wear; less warping; less need to return to previous shape; replace less often). It’s a sound trade-off for the loss of material.
Also, holes allow for expansion when the brakes do get hot (well, warm, not white-hot), so the surface stays true, and there is less pulsating. No holes = no warping = no uneven wear of both discs and pads = no pulsating AND sounder braking ability.
There’s a sweet spot some place, where you maximize the benefit of hole size, number, and placement in a rotor, without weakening the rotor to the point that the holes are a problem. There are mathematical formulae that determine these things, but I don’t know what they are.
No doubt some PhD engineer types run simulations to find this sweet spot. Optimization and simulation are large components of engineering these days.
Oh, there are people who live for this type of stuff. There are people who solve problems like this as foreplay.
Or solve these problems because they must in order to get their PhD. (Ahem.)
For fun(?) I would add another variable: I’d try to account for difficulty of manufacture, as an analogue to “cost.” For an F1 race car, I guess you could go all funky and difficult with your brake geometry if doing so allows you great performance, while keeping it simple and cheap could be acceptable (if not required) for bicycle brakes.
Lots of steps for designing a final product. First, you come up with a design that actually could work. Then you have to revise the product so that the parts can actually be made (or made cheaper). Then you have to revise it so it’s not terribly difficult to assemble the whole thing. Then you have to revise it so it’s not terribly difficult to service/maintain. There may be several iterations of this before you freeze the design and start cranking out parts.
One more variation below on the main question here, “Does a bigger brake rotor on a wheel help brake performance?”
There are situations where you need more braking performance, but you’re space-limited. One of these is on large aircraft: they’ve got to absorb a lot of energy when they land, but the rotor diameter is limited by the wheel diameter. So instead of one single rotor squeezed by a pair of friction pads, they make these brakes as a stack with many pressure discs and many friction-material discs. The pressure discs have splines on their inner diameter that engage with fixed splines on the axle, and the friction-material discs have splines on their outer diameter that engage with splines which rotate along with the wheel. When you apply the brakes, a hydraulic ram compresses this whole stack. Presto: now you’re dumping heat into maybe half a dozen discs instead of one, plenty of material to take on all that heat. If you know how a typical motorcycle clutch pack works, this is pretty much the same thing, except without the oil.
A couple of pictures. First one, you can see that the even discs are splined on their OD, and the odd discs are splined on their ID:
Here’s one with the hydraulic ram installed. Whereas your car has a caliper that only squeezes one part of the rotor, this ram has 14 pistons that squeeze the entire circumference of the brake pack:
(I can’t post media, so here’s a link)
Great pix.
For scale, that pack is ~14" thick and ~24" in diameter. The A350 has 6 of them.
I love engineering.
