banerjek

First of all, you make time going up hills, not down. Secondly, at 46x11 (presuming a 26/36/46 MTB triple) spins out at 40mph. 52x11 spins out at 44mph.

Going down, speed becomes more about aero and handling as the grade increases. Are you seriously trying to suggest that going down a 15% grade (half what the OP was talking about) that spinning out is your limiting factor? Please indicate which roads with such inclines where you've encountered this issue.

What is macho about recommending gears that correspond to climbing that he actually asked about? The macho idiocy we get around here is people pretending you can use regular road gearing on crazy steep hills and that spinning out is such a big problem. As if so many people can pedal 40mph without a push and don't have trouble running out of low gears on long steep climbs.

If you're in hilly terrain, close gear ratios aren't important -- you tend to use the bottom gears going up and the top gears going down. When you go in the flats, you mount a tighter cassette. It's not rocket science.

Curiously, the people I see in real life on rides that are hilly for real use gears that make sense and some of these people are plenty strong.

Jiggle

2x11 Road bikes aren't made for mountain goats who live on the Angliru.

CliffordK

One of the differences between road bikes and MTBs is weight.
Obviously there are some high end MTBs out there... and low end road bikes...

But, I would much rather do a 20% hill climb on a 20 lb bike than on a 40 lb bike.

gsa103

Fargo Hill is .11mi. For something that steep just walk. The thing with road biking is that there's usually an alternate route around something that steep.

Heathpack 

You rock @banerjek.

People ride under different paradigms. Such classic BF BS to ignore this concept and just answer a question from your own narrow perspective. Just answer the question the OP asked. Don't assume he doesn't know what kind of hills he has. Don't tell him he shouldn't use a road bike for steep grades. Just answer what he asked and if you don't know, don't answer.

I do some gnarly climbs. When we do one of these climbs, frequently the first question the experienced guy will ask me is "you have a 32 cog?" When I say yes, the answer is "good". The right gearing is not a sign of weakness. It's a sign of intelligence. Just because you cannot imagine or don't frequently experience the type of terrain where this gearing is useful does not mean it does not exist. Road biking is not all about the fast flat group ride. Many people actually ride road bikes up very big hills.

znomit

Anything over 15% the limiting factor is how stupid you aren't (or brave you are). I get freaked out around 70kph on 15% descents. Probably wouldn't do well at 100+ on a 30% slope.
Bicycle Speed (Velocity) And Power Calculator

rpenmanparker 

No, the macho part is the idea that every hill has to be climbed just because it is there. Obviously if you happen to live in an area that was all 30% grades on excellent paved roads, your bike would be a road bike equipped somewhat differently. It wouldn't be general purpose. But OP didn't say that was how all his riding was going to be. He just said his riding included that. It is sensible to assume it will also feature some more "normal" apsects as well. Sure it is only my narrow perspective, but if I had a choice how my bike was going to be equipped, it would be for the majority of my riding, not the minority. Maybe it is just because I am a chemist, but I have never believed in the 5% solution. (Pun alert) I prepare for the main thing, not the rare thing. If I were going to jettison part of a ride as unsuitable for my bike, it would be the minor portion of the ride, not the major portion. So personally in hilly terrain these days, I would have a 50-34 front and 12-32 rear. Anything that couldn't get me up, well, I just wouldn't ride up that.

banerjek

Agreed.

I live in an area where I get to deal with this exact issue -- we have a wide variety of roads of pretty much any grade you like.

In practice, I find that for shorter hills, the maximum I actually enjoy climbing is a tick over 15%. For extended climbs that value is closer to 8%. I personally think roads much above 15% are idiotic because they're dangerous in ordinary wet conditions, unusable for wheeled vehicles when there is any kind of ice, and very slow even under the best circumstances. Just because you can go on these doesn't make it worthwhile.

Descending, my favorite value is around 8% for any length over about 100 yards. You pick up loads of speed and there's some outside chance that the roads are straight and smooth enough to not waste loads of energy on braking.

The stupid steep hills typically have tight switchbacks or garbage surfaces that severely limit top end and handling of road bikes gets severely compromised so the only muscles you strain are operating your brakes.

When I go for a hilly ride and have a choice of terrain, I like a mixture of shorter but very steep sections interspersed with flatter areas that allow recovery going up with long but moderately steep (6-8%) sections going down. This kind of terrain can be enjoyed with setups that are appropriate for general road riding.

LateSleeper

Several skeptical replies to the OP's query seem based on the assumption that there's always a better (less steep) road. Well, maybe, but it's probably some noisy superhighway that no one would want to ride. Maybe the OP's goal is to take the quieter scenic route. So what if it's hard? I imagine the rest of the loop makes it well worth the suffering. There are many wonderful mountain loop rides where I live, and a steep segment or two is just the price of entry for a great day of riding.

This seems like a job for a triple crank, and probably not one of those silly "racing" triples made by Shimano or Campagnolo. The key question is how small an inner ring the spider will accommodate. Touring triples can have inner rings approaching what's typical on a mountain bike. That, and a wide-range rear derailleur will get the job done. You can add these as after-market upgrades, but it's more costly. Suitable cranksets are made by Specialties TA and Sugino. You could also fit a mountain bike crank, but be careful about the chain line. When considering feasibility and cost, be sure to check bottom bracket compatibility.

I understand makers like FSA still make triple cranks for the European market, but here in the US nearly every new road bike comes with a 50/34 compact double. The trouble with these is the 110 BCD spacing prevents using anything smaller than an 33 tooth inner ring. When replacing the crankset on my 'cross bike, I found good options from Sugino (OX801D, OX601D), White Industries (VBC), Specialties TA, IRD, Middleburn, Velo Orange, and Rene Herse.

Nobody in this thread has mentioned the obvious fact that once you go up, you must also come down. I'm fairly certain that a climb featuring 30% peak grade also features bad pavement and hairpin switchbacks. Given that, you probably shouldn't consider any bike that doesn't have disk brakes. But the latest full-hydraulic offerings from Shimano and SRAM might limit your ability to match shifters with the derailleurs you'll need for your unusual gearing. I'd stick with cable-actuated disk brakes to keep your options open. I think the TRP Spyre, with its two-sided actuation, is an excellent choice. The TRP HyRd is even nicer, but at higher cost and higher weight.

Shimagnolo

I was looking forward to road disc brakes...until I became aware of the fact mfgrs were putting too much emphasis on "small and light", and not enough thought to heat-shedding ability, especially on long descents at road bike speeds.

Example: Road Bike Disc Brakes Are Coming, But Will They Work?

The energy a brake must dissipate is proportional to the *square* of velocity.
i.e. brakes stopping a road bike from 50mph are generating *four* times heat of brakes stopping a mtn bike from 25mph.

banerjek

It's actually worse than this.

At the lower speeds, you simply don't have as much need to slow down so there is less braking to begin with. In addition, any given spot on the wheel takes a longer time to come around before it is in contact with the brake pads so there is more time for the rims to dissipate heat. It's one thing if you're only going down a couple hundred feet. But if you have a really long descent, you simply can't ride your brakes. The heat can be enough to melt the bead on your tires, glaze your pads rendering them near useless, and other bad things. If you touch your rims after even a short amount of heavy braking, the problem is obvious -- they'll be hot enough to burn you.

I only apply brakes for a couple seconds at a time on extended descents. If I had to ride them regularly, I'd switch to discs.
This affects my routing. Cars hate 10mph switchbacks and crappy surfaces. So if you like solitude, those are the roads you want.

CliffordK

I'm sure that could lead to a long discussion.

Coming straight down a 30% grade, one's limitations on braking may well be traction and balance, and not the grippiness of the brakes.

Perhaps also planning ahead. I normally don't ride my brakes, but if I was going down Fargo street, I'd plan on modulating my speed long before I got to the bottom T interchange, and that may be actually the worst thing for the disc brakes to handle.

Personally I've always found normal caliper brakes were sufficient to stop me when used with aluminum rims.

I would consider disc brakes for use with carbon rims if I make the jump to CF.

happyscientist

Climbing on a road bike is much different than climbing on a mountain bike. The road is more about steady cardio and pushing through. Trails require bursts of power (which is hard for me). If you can race a mtb, you can get up the hills on the road. I am a 42 year old woman with a few extra pounds, and I can easily get up hills with double digit grades with a compact double and 11-28t. The hardest climb around here averages 17% for over a mile with some stretches that are steep enough to make my front wheel pop off the ground, but I can still make it. Sometimes, though, it makes sense to take a slightly longer route and avoid the steepest hills.

Go to a couple bike shops and see what they have in stock. If everyone is riding a certain gearing, that tells you what the typical rider needs in your area.

Bunyanderman

How long is the 30% grade? Usually having a max gradient us pretty meaningless.

hamster

The physics of it is pretty straightforward.

Braking turns your kinetic energy into heat. All else equal, when stopping from the same initial speed, a 80-100 g road disk is going to heat up to a 5-6x higher temperature than a 400-500 g rim. (Specific heat capacities of aluminum and carbon composites are almost equal. Steel is at about 70% of aluminum or epoxy, meaning that it gets hotter gram for gram.)

Disks are much smaller than rims (roughly a quarter of the diameter) and they don't present much of an aerodynamic drag. Which is good as long as you're not trying to brake, but makes it harder to shed all that heat.

An average sized guy (180 lbs bike+rider) stopping from 40 mph to zero using a 80 g front disk would heat a steel disk by ~330 degrees Celsius. (Braking from 40 mph to 15 mph alone would contribute 280 degrees.) Touching your rims after heavy braking as @banerjek suggested is bad enough. Touching a disk is an extremely bad idea that involves the possibility of third degree burns. It's not hard to see that alloy disks are no go in road bikes (aluminum melts at 600 C, and we don't want our disks melting after a couple of episodes of hard braking in short succession). Steel can work, but we need pads that handle temps far higher than rim brake pads ever get.

It's ultimately a lose-lose proposition. 160 mm ultralight rotors like the one described in the linked article (65 g) are pretty on paper but easily overheat and fail (as the author of the article learned in a painful way). A system like the one used on CX or downhill bikes, with 180 mm, 130+ g cross-drilled rotors, would do a decent job, but it would not sell, because, between extra weight and drag, you might as well simply switch to an alloy rim in front.

rpenmanparker 

Just a few of corrections to your rationale. While aluminum and carbon have similar heat capacities (I am taking your word for it.) their conductivities are vastly different. The aluminum rim will spread the head out over its entire mass quite effectively, while the carbon rim will concentrate it at the brake track. So temperatures will be much higher on the carbon rim where it matters, near the contact points with the tire. And conductivity will affect your other conclusions as well.

My second complaint is regarding language. When you say "heat up to a 5-6x higher temperature", I think you mean a "cause a 5-6x higher temperature increase". Unless you are talking in Kelvin degrees, you can't compare actual temperatures as multiples of each other. Only changes in temperature or differences in temperature.

Finally you are neglecting all forms of heat dissipation such as radiation and conduction such as heat transfer to the air, which as long as the bike is moving, is considerable.

Carry on.

Shimagnolo

Agreed, but that didn't stop Shimano from doing something stupid like the "ice-Tech" rotor: DSC_0054.jpg Photo by ds2199 | Photobucket

banerjek

This is what braking on long steep roads ultimately boils down to.

I don't think there is any inherent problem with light weight disc systems. In fact, they might well have advantages over heavier systems with equal diameter rotors because they should be able to dissipate heat faster.

In the article, it sounds like the author was simply riding his brakes at a fairly decent clip. You just can't do that for the simple reason that you're constantly adding heat at a rate that will lead to failure if sustained. I also see cars riding their brakes down mountain roads. I think they're completely insane.

In my mind, the wins for discs are superior wet performance and you don't chew your rims up if you frequently ride in slop. But the technique used should basically be about the same except there should be less need to intentionally heat/clear wet or grime covered braking surfaces.

indyfabz

I once spent 7 weeks touring in Andalucia, Spain. Some nasty, nasty climbing. You are right about donkey paths. Some of the roads seemed like they simply widened a donkey path and put blacktop over it. Another sometimes ordeal was getting into the center of town. Many old towns were built on steep hillsides, probably so they could throw hot oil down on the invading Moors. Had to walk a couple of times even with my MTB gearing. The funniest hill experience was seeing two kids on a moped trying to get up a hill towards Andujar. One of them had to get off and push the thing while the other worked the throttle.

hamster

You are correct about heat conductivity. However, in a moderately deep carbon tubular rim, the area under brake pads and contact points with the tire account for something like half of the mass anyway.

I'm not. That was my second paragraph: heat transfer to the air is proportional to aerodynamic drag. You can't minimize one and maximize the other. Radiation does not matter all that much. Ballpark calculation: 2 mm thick 80 g steel rotor has surface area of ~0.01 m2 (two sides). At 600 K (330 C), it loses heat via radiation at the rate of 5.67e-8 * 600^4 * 0.01 = 74 watt. At specific heat of 490 J/kg*K, that's cooling down at the rate of ~2 degrees Celsius/Kelvin per second.

rpenmanparker 

Okay, so the heat transfer by conduction is reduced proportionally to the reduction in drag, but that doesn't mean it isn't still significant just as the drag might still be significant. Actually I don't know. I'm just wondering. Folks often talk about how many watts are being saved with aero rims but seldom mention what the actual total propulsion energy loss is at the rim that is subject to improvement.

As for the radiation, it doesn't sound like much, but every little bit helps. And, of course, the greater the surface area, the greater the effect. So it would be quite more substantial in deep rims than in rotors. Naturally the cooler parts of the rim would radiate heat less rapidly, but still...

CliffordK

I'm not sure how representative of a sample that would be. Perhaps a bit.

But, traditionally "racing bikes" have had something like 53/42 on the front and 13/21 on the back, while casual bikes had big pie plates on the back. As more gearing has been added as well as more emphasis on spinning, the sizes of the cassettes have changed somewhat (on both ends), with many around 11/25 or so for the tighter gearing, and 11/30 for the not so tight gearing (it is hard to get much smaller than 25 for an 11 spd). And, of course, few high end bikes with triples, but they're common on the low end bikes for weaker cyclists.

Anyway, the gearing you see may be more representative of the class of cyclists buying the bikes than the local conditions. Perhaps a good bike store mechanic will know what people tend to ask for, but that may still be biased depending on the clientele.

------

A few months ago I was off to do a Craigslist purchase of a Fuji Ace 24. So, I was dragging my trailer behind the Colnago. And, of course the destination was in the hills. The first hill took me over 30th Ave which is a good hill, enough to take the wind out of one. Then a little downhill, followed by a turn onto Agate Street. Unfortunately I got the directions off by 10 blocks or so... So I pulled my empty trailer up about a 15% slope for 10 blocks... My lowest gearing was 41/19. WHEW!!!! I got to the top and discovered something was wrong. I had a nice coast back down. Anyway, so talked to the people I bought the bike from, and they said that they always walk their MTBs up the hill.

I did stop to put the cell phone away mid - hill and get both hands on the bars, then restarted with side-swoop move.

Perhaps the MTBs that they walked were a bad comparison. I got up the hill because I stand, I pull up, and I use cleats.

banerjek

This.

Cyclists of every age, weight, physical ability, and interest are out there. Most shops are geared towards a specific segment. If you don't happen to be in that segment, you'll get the wrong thing. If you look at bikes at a bunch of shops with the idea of getting a more complete picture, you'll see a lot of wider cassettes with a really low end because most people who buy bikes aren't in very good shape.

If you really don't know what kind of gearing you need, odds are you'll be happy with a wide cassette that goes pretty low (and a lot of that gets sold). You can get something tighter when you figure out your precise needs.

happyscientist

You do have to pay attention to what type of shop you go into. If the poster goes into a shop that sells nothing but $10k racing bikes, that is the wrong shop. There is one around here like that. Most of their bikes don't have compacts unless you specifically request one, even though we have steep hills, because the shop sells almost exclusively to people who race. The typical bike shop with bikes priced for the typical rider sells bikes with compact doubles and 11-25t, 11-28t, or 12-32t cassettes. You should be able to go into a shop, tell them what kind of riding you do and what your fitness level is, and have them work with you to find the right gears.

gsa103

Radiative transfer is going to be negligible, unless the disc is glowing. Radiative transfer is minimal compared to conduction in still air, let alone highly turbulent conditions.

Heat transfer rate is proportional to the temperature rise. So a disc reaching a higher temperature will radiate heat faster than rim at a lower temperature. That's before you account for air flow and size differences.

I know multiple riders who blown tires descending, so let's not pretend that Al rims are completely flawless for descending.

Besides the topic was about going up, not a disc brake flame war.