I’ve been going to bicycle shops lately trying to sort out the challenges of carrying children on bikes. I’ve been noticing a lot of bikes have extra dedicated brake discs on the front wheels, even bikes intended for on-road use. My stupid question for today is “Why?”
The rim is already a big brake disc, right? It is exposed to flowing air so it won’t build up heat with repeated braking. Due to its larger mass it should be a lot more heat-resistant than a small disc near the hub, no?
If we already incurred the weight of having rims on the bike why would it be a good idea to add more spinning mass in the form of dedicated brake discs?
Is the answer that the latest and greatest rims are carbon fiber and somehow don’t work as well as brake discs? But if that is the answer, why does one see disc brakes on bikes with conventional aluminum rims? Are dedicated discs somehow far superior in rain or after riding through a puddle?
Who has disc brakes and can talk about the practical advantages?
Dumb question #2: The bike shops seem to be selling tubeless tires for $90 each (Amazon has Hutchinsons
I think the answer has to do with performance, especially wet performance. An alloy rim is not the optimum surface for grabbing with a brake pad. The size of the pads is very limited. The rim rides near the ground and is constantly splashed with water (and possibly grease). Disc brakes have much more even and controlled application – you’re less likely to lock the wheel and go into a skid or over the bars.
Heat build up is not really an issue on bikes in normal road use.
The high price of tubeless bike tires probably reflects low volume. If they ever become mainstream the price will come down. I see no advantage at present, at least not one that is worth the high cost.
Try riding around on a MTB w disc brakes and then a road bike and you will see the difference – the disc brakes have way more stopping power, and over the past 15 years they have been miniaturized enough that the spinning weight isn’t that big a deal vs the benefits of the stopping power. Since you’ve got the weight of the kid, which is only going up, you want that extra stopping power, even in dry. I doubt you’re doing a lot of riding around w your kid in the rain. 🙂
As far as tubeless, I wouldn’t do that. They’re a pain to change, and pinch flats are super rare, so just get normal rims and tires.
I’m trying to think of some way to weave divorce and child support payments into this comment the way you have been doing with your blog posts lately, maybe I should be working an angle like “let’s say you’re a woman getting child support payments and you can make the father buy the tires, why not get the tubeless?”
Chris: I’m glad that you brought it up, but “divorce” and “child support payments” are not related issues for the truly thoughtful plaintiff! See http://www.realworlddivorce.com/ChildSupportLitigationWithoutMarriage and the rest for how three kids with three co-parents pays 2X having three kids with one co-parent.
[I do think being a serious cyclist and child support plaintiff go together pretty well, actually. A married bike enthusiast has to negotiate weekend time off to ride. A successful plaintiff bike enthusiast can enjoy every other weekend for unencumbered riding plus, if planned correctly, enough profits from child support to fund Backroads trips, a carbon fiber tandem to ride with the latest sweetheart, etc. See also https://philip.greenspun.com/blog/2014/04/04/sun-n-fun/ for how collecting child support and an aviation hobby work well together.]
Planned obsolescence is a thing in the bike business. However, disc brakes allow you to brake later into a corners (absorb/dissipate heat faster), so they are of use in all styles of racing and will therefor trickle down to consumer products.
Tubeless tires have to be stronger (bead) and are currently sold in lower volume. So, 2 reasons for higher prices.
FWIW, heat buildup from rim brakes *can* be a problem on long, high-speed descents. Some older carbon rims have melted (!), and aluminum rims have conducted enough heat to cause tubes to fail. Tire failure at 40+ MPH is a big deal. You probably need a mix of long, steep descent, high speed, heavy weight, and excessive brake use to get it to happen, though.
More recently, the big push for discs on road bikes has been centered around better brake modulation and control, which allows people to be more aggressive while descending.
I don’t think either of those applies to anyone with a kid on the bike :-).
Subjectively, hydraulic disc brakes feel much nicer than rim brakes to me while I’m braking. They need less adjustment, right up to the point where you need new pads. Cheap disc brakes are horrible; I had a set of BB5s on a bike (which were supposed to be middling at the time, not horrible), and they needed adjustment *every single ride*. If I went 3 or 4 rides without adjusting them, then I’d be really short on braking power.
For commuter-ish riding someplace without steep hills and constant rain (cough, Seattle, cough), they’re probably overkill.
On the tubeless front, yeah, they’re overpriced. They’re also hard to find, hopefully they’ll get more popular and cheaper soonish. I switched to Hutchinson Intensive 25s a couple years ago, and the difference was night and day. They were comfortable, not too heavy, and I could Just Ride. Without them, I was fixing a flat practically every week. It depends on your roads, though. They’re a pain to put on and take off, though, so if I ever had a flat in the field, I’d probably end up needing a ride. I doubt I could actually get a tube tucked into them without a heavy-duty set of tire levers and maybe a few extra hands.
My guess about the tires is that cyclists, especially road bike cyclists, are used to paying a lot for everything associated with their hobby (c.f. sailing and general aviation), and see their bike as something worth spending money on, whereas for 95% of people, car tires are something that they get annoyed at having to spend money on replacing every few years. But it’s probably mostly the volume.
(WAG #2: It may also be more technically challenging to make a tubeless bike tire lightweight enough for a road bike and still be durable; the fact that the car tires have more rubber in them may actually be why they are cheaper).
My guess about the disc brake thing is that as disc brakes have gone from being niche specialty items only found on top-end mountain bikes to a pretty mainstream part, it may be easier for bike manufacturers to source disc brakes these days, and they are perceived to be an upgrade over other brake types.
Also, having disc brakes removes the design constraint on your wheels that they include a flat braking surface (the rims on my mountain bike with disc brakes have a nice curved shape right up to the tire; I’m not sure if this has any practical advantage but it looks cool).
Tubeless tires came into fashion about 35 years ago for bikes out west. We put them on lots of “motocross bikes” because tube types got flats a lot when used off road. Kids loved them and so did Dads like me. Well fast forward a few years and they got worn badly and needed replacing. Well guess what, tubeless tires were impossible to remove due to age hardening of the rubber. You had to destroy the rim to get a old tubeless tire off the rim. So people quit buying them. Well fast forward some more and no one uses them any more for this reason thus crazy high prices for the few that are sold.
This was for a mountain bike, but the bike shop told me the disc brakes were mostly better when riding through puddles. I tried a few bikes in the $450 to $800 range some of which had discs and some without. There wasn’t much difference on dry pavement that I could tell and I chose to save the money and went with the rim brakes. I’m sure serious riders scoff at my $500 bike, but got no complaints. The brakes have rarely needed adjustment and even going trough some mud puddles they still have more grip than the tires do (in other words they are more than adequate). Still I sometimes wonder if getting the discs would have been better in some way.
The other advantage of disc brakes is that you are not wearing out a key structural component of your bike when you brake. If you do a lot of riding in the wet with rim brakes all the grit that gets picked up is essentially acting like sandpaper when you brake which eventually results in the walls of the rim becoming thin enough that the rim fails.
The stopping power is less of an issue as modern rim brakes work pretty well. The consistency of the braking performance in all weathers is the real selling point.
As mentioned above it should also allow greater freedom in rim design which may result in aerodynamic gains. Although realistically speaking you need to be capable of sustaining at least 20mph for a chunk of time so it’s not really a factor for most people.
As a a point of reference there’s very little difference in price between tubeless and non tubeless tyres in the mountain bike world where they’ve been in wide use for quite a number of years. However, the tyre pressure used is much lower so that may make them easier to manufacture.
Struan: Wearing out the rims? On how many bikes have you seen this? The other day I met a recreational and commuting rider on a Motobecane from the 1970s. It had some new drivetrain components but the rims were, I think, original.
Other readers: Has anyone else ever seen a rim worn through from the brake pads?
“Bike Brakes for You, but Not the Pros (Yet): The rider at home is being offered an even more advanced bike than the pro rider on TV” explains part of it.
When I lived in Seattle I had a bike with disc brakes, because they’re supposed to be better in wet weather.
Depending on the geometry and design of the fork and tire and brakes, it can be significantly easier to remove and replace a front wheel that has disk brakes. If you remove your wheel a lot in order to lock up your bike, this can add up.
I’ve never owned a bike with disk brakes, but I’ve ridden a couple of them, and braking with disk brakes is much nicer than with rim brakes. Obviously this is a subjective aesthetic thing, but it is as real as it gets.
jseliger: Thanks for that. People talk about rim brakes fading. I wonder if that is actually the (small) pads heating up rather than the (huge) rims. Are the pads for bicycle disc brakes much larger and better able to dissipate the heat than the pads on a standard rim brake?
I guess I am also wondering if people are just tired of pulling hard enough on standard brakes. Is there a huge amount of mechanical advantage gained when using discs? So they feel more powerful even though they aren’t (given a rider willing to squeeze the levers hard and the fact that the tires will skid before the brakes run out of force).
In my experience, yes, disc brakes stop the bike notably faster in wet weather than rim brakes do. And hydraulic disc brakes are another notable step up.
Another consideration is how often they need maintenance. Rim brakes wear down and the cables stretch, requiring regular adjustment, especially when the brake cables are new. Regular disc brakes need less frequent adjustments, but when they wear down it often takes only a short time before braking power degrades substantially, so you don’t get much of a warning. Hydraulic disc brakes are expensive but can wait a long time between adjustments.
I recently paid a lot of money to replace my commute bike’s regular disc brakes with hydraulic ones, because I didn’t want to take the unnecessary risk of slower braking, especially once every 3 months when the brake pads wore out. I’m very happy with my newfound ability to stop on a dime in traffic.
I’ve never seen a rim worn through from the brake pads, but I have had maladjusted brake pads that wore through the tire itself (where it meets the rim) rapidly, causing the tube to explode while riding.
Bike nerds have a gullible streak surpassed only by audiophiles (and I say this as a bike nerd). Almost none of the vogue tech makes a bit of difference to one’s riding.
One of the more elegant things about bicycles is their extreme simplicity. Cable-operated brakes and a cable-operated transmission. It takes a perverse personality to want to replace that with hydraulics and wireless electronic control.
It’s true that rims will get hot, quickly, under braking on a descent. Touch yours after going down a moderate hill and you can burn your fingers. However, conservation of energy being what it is, you can only get out what you put in so it takes a pretty fit rider for heat buildup to become a problem in practice. The feeble performance of road bicycle brakes (compared, say, to motorcycles) is generally limited by the tires and the short wheelbase, not the brakes.
Mountain bikes are another kettle of fish. Keeping the braking surface out of the muck and away from the rocks has its advantages.
Rain.
philg: “I wonder if that is actually the (small) pads heating up rather than the (huge) rims. ”
The huge rims can get burn-your-fingers hot. It wouldn’t be that hard for you to experience that first hand. Rims overheating isn’t a normal problem. One issue is keeping very high heat away from the tire and tube. The compound used for rim brake pads might be more prone to fading than the pads in disk brakes.
Indeed, rim brakes are a form of disc brake.
philg: “Wearing out the rims? On how many bikes have you seen this? The other day I met a recreational and commuting rider on a Motobecane from the 1970s.”
Wearing out rims is more of an issue for high-mileage riders in wet and gritty conditions who use their brakes “frequently”. It’s not a normal problem.
On carbon rims you’ll see wear and fade (particularly when wet). Of course, you got those carbon rims for weight so a heavy disc brake does you no good. Also, to see wear you have to ride a lot more than a normal human. Like car commuter distances. Most people who have them like the fact that they modulate better than rim brakes.
As for the tires, First, volumes are much lower so less economy of scale, that’s the primary driver. Secondarily, they’re fairly complicated beasts. Your average car tire weighs more than most modern road bikes and attaches to an equally heavy rim all to maintain a psi of maybe a third of a bicycle tire. Getting a lightweight rim and bead combo that wouldn’t just blow off at a 100 psi was kind of a pain.
Phil,
I spent 4 years in the bike industry out of college making high performance bike wheels that Tour de France riders used (Spinergy) and never saw rims wear though, or even heard about it. I also raced for a long time and now ride w a guy on the board of Specialized, and disc brakes are better because they just have a lot more stopping power for less effort, so in cases where it makes sense to, they are adding disc brakes. I ride around town with my girls (4 and 6 yo) in one of those little trailers on my town bike, which has cantilever rim brakes and often wish I had more stopping power.
re divorce above, your plan sounds good, except I’m the breadwinner. I spend all my marriage points on a Saturday morning bike ride, which leaves no time for flying, so I’ve let my currency lapse for now (I have ~300 hrs in pipers and cessnas). Good thing my wife is not into flying lest she idolize Patty Wagstaff!
Cycling technology is frequently a solution in search of a problem. The fact is that 25 year old technology (18 speed, indexed shifts on consumer bikes) is vastly adequate for nonathletic bike users. But if a 500km/year bike stored indoors stays usable essentially forever, how can you sell people new bikes all the time? By inventing must-have features. And thus hardcore racing features (rear suspension, disk brakes for mountain bikes, >7 speed rears, aero bars and carbon components for road bikes) invade the consumer space, resulting in glamorous, but ultimately less practical bikes than before.
Not all features are bad. Cartridge bearing bottom brackets and quite possibly the newer “outboard bearing” type solve a real need, for example.
Rims do wear out, if you do downhill racing in muddy conditions with rim brakes. But again, cosmetics and fashion rule. Disk brakes are cool, and perfect, unblemished rims look pretty.
Other readers: Has anyone else ever seen a rim worn through from the brake pads?
I have. The bike is mine, the rim saw plenty offroad use (possibly more than road use wear due to extra grit).
I’ve personally worn out several front rims from riding in the hills in the Oregon rain. The rim gets thin and eventually the air pressure in the tire pushes the rim apart (e.g. the bead gets pushed out, making the braking surface concave). Keep riding and the entire side will eventually come off in a nice big loop, which I’ve also seen.
If you ride in the wet, you’ll notice a lot of black grit on the rim. That’s not the brake pad, it’s the aluminum from the rim. You can prove this to yourself by using a colored brake pad (e.g. Kool Stop salmon) or switching to a ceramic rim (no black grit on rainy days).
I agree with Philip; the only reason for disc brakes on road bikes is the cool factor. Ultimately, your stopping power is limited by your contact patch with the ground, and when it’s the size of a thumb print, more does not necessarily mean better. Anyone who has went over the handlebars on their bike can attest that there is such a thing as too much stopping power.
A disc brake does allow you to ride with a bent rim and it keeps the braking surface farther from a wet road/trail. While they don’t need adjustment as often as a rim brake, when they do, it’s a pain. I can attest to that, bleeding my Hayes hydraulic mountain bike brakes with DOT 3 brake fluid is harder than tightening a cable.
I think discs took over the mountain market as a perception thing, just like front shocks. Sure, if you’re doing the 1% of rides, they help, but completely not necessary for the five mile Sunday ride on the bike path.
The bike industry sees the road disc as a revenue source. Suddenly, everyone’s $5000 road bike is now obsolete, just like the old ones with the brake cables coming out of the tops of the hoods.
often end up with an uneven rim after hitting sidewalks too hard. So now I’ve bought a bike with disc brakes, because they won’t be affected as much.
Mr. Neumann is correct. Rim brakes aren’t as effetive in ice/snow/mud/rain as disc brakes. I’ve got hydralic disc brakes on my Christiania bike and they’re awesome. The need to be. Sometimes the total load is in excess of 400 pounds.
http://www.christianiabikes.com/en/addition/hydrauliske-bremser-pa-forhjul/
What about hydraulic rim brakes? I’ve been using the same ones since 2000 and they provide plenty of stopping power that seems unaffected by water an mud on my MTB.
Discs probably are superior, however, witness the Tour-de-France type events – those riders seem to be able to cope using cable operated caliper rim brakes. As to road tubeless – MUCH MUCH safer! No tube to explode in the event of a puncture with potentially catastrophic results; also, similarly, the tire will not roll off the rim in the event of a puncture. “Snake bite” punctures not possible with tubeless. Tire pressure can be run much lower offering greater comfort (especially relevant now with deteriorating road surface quality in the era of dwindling infrastructure resources). And surprising to most cyclists: noticeably lower rolling resistance with reduced tire pressure on less than perfectly smooth road surfaces. My son lives in West Hollywood and regularly goes up and down the hills (try Mount Olympus Drive) and the speeds one can attain in seconds is stupefying. A blowout in these circumstances (thorn, shard of glass, nail, staple, etc, etc,) is potential death. My wife and I ride up and down the Niagara Escarpment regularly and although nothing like coming down off Muholland Drive, we easily reach white knuckle speeds very quickly. I have put tubeless tires on five of our bikes at great expense but with great peace of mind.
The meme about the bike industry being a source of solutions in search of problems is certainly in play here.
The best argument for hydraulic disk brakes is better modulation. This is probably more important in mountain biking where the amount of braking applied varies more significantly from moment to moment due to the more dynamic/unpredictable nature of the surface you are riding over. E.g. a short section of straight dirt may present a braking opportunity prior to a hard corner over looser ground. On the road, by comparison, braking can generally be done more smoothly and anticipated more easily in advance due to much better sight lines. As a result, the modulation offered by rim brakes seems acceptable. Or viewed alternatively, the increased modulation offered by hydraulic brakes does not currently offset the weight penalty. This theory accounts for the fact that road pros universally ride mechanical rim brakes; MTB pros universally ride hydraulic disk brakes (including in dry conditions). This includes cross-country events where bike weight is very important.
As for the argument about disk brakes being better in the wet, there is something to that as well. On the other hand, for the minority of road cyclists that actually do ride in the rain, the biggest problem is cornering traction, regardless of brake type.
Rims do wear out due to even properly adjusted brakes. Last month, after about 15,000 miles my commuter bike’s rear rim had finally gotten so thin that the air pressure in the tire crimped out a four inch section. It felt as if the wheel had a really bad wobble. I just disconnected the brake, and finished the ride on the front brake which is really no bother so long as one is aware.
In all reality, disc brakes are much better in the rain. Just the slightest bit of rain increases my stopping distance by three fold. Something to consider when dealing with cars next to or in front of you. My next commuter bike will have disc brakes. Perhaps it doesn’t matter for the riders in The Tour, but for this commuter it is a must.
I don’t think anyone mentioned another important aspect of hydraulic disc brakes is the reduction of fatigue. While mountain biking in the past I would often have to stop and shake the cramp and fatigue out of my hands, and would often see others doing the same on long downhill sections. This really is not a problem anymore thanks to the leverage provided by the brake levers. I should also mention that designs vary in the modulation they provide, and they are not all the same by any means. However, they really are the way of the future.
Disc brakes work well if the bike is all muddy and wet, and left that way. You pretty much never need to adjust them. They won’t slip out of whack and tear a groove in your tire. They give even consistent braking instead of pulsed jerks even if the wheel is out of true.
In other words, disc brakes are better for the non-serious biker.
That’s why they’ve become popular with J. Random Biker like me. I don’t care why racers don’t use them, but I’d imagine many of the above considerations don’t apply, and it seems like disc brakes must weigh a bit more.
Also if you’re going to be carrying a kid on the back of the bike, you don’t want a “road bike” or a “hybrid”, you want something with big fat tires to spread the extra weight over a wider contact patch and a greater volume of air and powerful brakes. That kind of bike is called a “mountain bike”. You really want the extra stopping power and lateral traction and ability to absorb bumps, especially for the rare emergency maneuver.
(We learned this the hard way, with a “hybrid” that kind of sucked with a kid loaded onto the back.)