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Myths in cycling: wider tires are slower

renehersecycles.com

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Re: Myths in cycling: wider tires are slower

#291

Post by sliken »

et-al wrote: post #161
wolverine876 wrote: post #50

Earlier quoted context omitted.

I'm missing something: How do lower pressures lead to tubeless?

Folks want to run tires at lower pressures, but this increases the risk of pinch flats for inner tubes when the rim bottoms out against the ground. Tubeless setups don't have this risk.

Yes, a bit, but you won't want to ever bottom out, with or without tubes. You can snake bite flat tubeless, you can also damage the rim.

Generally you want enough air pressure to have enough air pressure to have a 10-15% deflection in the tire and never bottom out. Thankfully suspensions help with the pinch flat since they basically time average the impacts.

Re: Myths in cycling: wider tires are slower

#292

Post by sliken »

soperj wrote: post #133
fsckboy wrote: post #109

Earlier quoted context omitted.

you should actively pull up your leg so the down leg is not working extra to lift it, and the pull up muscles are different muscles so your idle down muscles are still getting a rest. The pulling up of your leg results in easier pedaling overall, and it is relatively as if you are pulling up on the pedal. Should you actually then pull up? You should go for the most natural sustainable pedal motion for you. When I ped…

Honestly, go try biking by only pulling up. You don't pull up.

Bike more and you will, it's not particularly noticeable while normally biking. But I really notice it on sprints, but it's also noticeable even with smaller increases in effort over cruising.

It's also quite noticeable when you switch to clipless and go for a hard ride, suddenly new muscles will be sore.

Re: Myths in cycling: wider tires are slower

#293

Post by adrianN »

bernulli wrote: post #131
dredmorbius wrote: post #30

Earlier quoted context omitted.

Static friction being constant regardless of contact surface presumes a uniform surface consistency (uniform frictional coefficient). Large (an knobby) tyres are a statistical bet that there will be sufficient friction somewhere on the contact patch. When riding over nonuniform surfaces (dust, loose pebbles, twigs, mud, leaves, and embedded rock), that's a gamble the large and contoured tyre is far more likely to win…

Is the static friction what is going on with wheels? Why do race cars (dragster, F1, etc) have wide, smooth (un-knobby) tires if it's so disadvantageous (no gain, but higher weight and moment of inertia)?

It is my understanding that race cars have wide tyres to shed more heat. Tyres melting is a problem at F1 speeds.

Re: Myths in cycling: wider tires are slower

#294

Post by rorykoehler »

vladvasiliu wrote: post #279
rorykoehler wrote: post #269

Earlier quoted context omitted.

I've been road riding with people who switched to gravel bikes and they were suddenly noticeably slower. They also seemed to run out of gas earlier which means they were expending more energy to keep up.

Weren't those new bikes heavier? My own road bike is nothing particularly fancy, but it's very light. Just because those bikes may be made to take more of a beating than a road-bike, they may be heavier. I'm thinking in particular tougher wheels and front work, possibly the whole frame.

We were riding on mostly flat terrain so it wouldn't be a big differentiator.

Re: Myths in cycling: wider tires are slower

#295

Post by sliken »

darkwater wrote: post #289
sliken wrote: post #284

Earlier quoted context omitted.

Heh, rene makes a business out of being different, and has some good ideas, but they do push it to far sometimes. Sure I get it, a stoppie shows that the brakes are not a bottleneck, it's the traction. So sure, sometimes, on some bikes, with some riders, under some conditions you get perfect braking. However in the real world there's various rim surfaces (aluminum, steel, carbon fiber), with a variation of water, gri…

When I was a city rider to commute, pads alignment was a real PITA and the main reason that made me switch to disc brakes. I was always feeling braked and spending more effort than really needed because one pad was touching the rim. With disc brakes that feeling disappeared and never came back, although you still need to do some maintenance from time to time.

Heh, yes, less maintenance, but also less finicky.

Brake pads on rim brakes are a nightmare. They follow a 3-d arc as they approach the rim, which is itself a very complicated 3d surface. Ideally the front edge of the brake pad hits slightly before the rear edge, to avoid squeal... but not too much or it will engage too softly. Even minor wear changes the engagement point. Cables need maintenance, they wear, get kinked, require lubrication, and it's easy to get the tension wrong.

It's all a mess, and even when perfect, and it's dry, not too cool, not to hot, not dusty... they still get worse with every use.

On discs it's more like replace the pads when worn (no adjustments, just remove the pin, pull the old pads, push the cyclinders in, put in the new pads, and put the pin back in). Sure there's occasionally a need for replacing brake fluid and/or bleeding. But generally way less maintenance, and you get like 90% of perfect braking all the time instead of 10-90% depending on temp, wetness, ice, grit, state of tune, etc.

Re: Myths in cycling: wider tires are slower

#297

Post by sliken »

lmm wrote: post #217
jiscariot wrote: post #137

Earlier quoted context omitted.

My only complaint about the gravel trend is that at the entry (and mid) level they are often using pretty crappy disc brakes when rim brakes would have been a better choice in 90% of cases. When they are hydraulic, they are a dream to use, but with a cable you really lose the brake feel.

Cable-pull disc brakes are still a huge improvement over rim brakes in the ways that matter, especially in the wet.

Depends. Many make pretty ugly compromises. Poor pads, not much leverage, and even being single sided which often drags and requires the disc to bend for good braking.

So cable-pull disc vs rim brakes is less clear, more susceptible to case by case differences.

However hydraulic discs are always (AFAIK), double sided, and almost always better than even the highest end rim brakes.

Not to mention who wants to destroy their nice rims by dragging brakes on them, leading to relatively short lives as the rim walls get ever thinner, right up till they start cracking. I'd rather replace a disc than a rim after 5-10k miles.

Re: Myths in cycling: wider tires are slower

#298

Post by usrusr »

matsemann wrote: post #271
vecinu wrote: post #208

Earlier quoted context omitted.

The only caveat is carbon wheels. I hate rim brakes on carbon wheels,they legitimately suck and disc is way better for that application. I actually just sold my carbon wheels and downgraded back to aluminium until I buy a disc bike for the long term.

Rim breaking on deep dish tempo wheels sounds horrifying.

They are certainly not the kind of wheels you'd want to use on steep roads with unpredictable weather (e.g. because the trip was planned months in advance and the bike), anybody into that kind of toy usually keeps a set of low section wheels for those occasions (or bike/bikes, if the looks just don't match). Disc brake doesn't change that by the way, because crosswinds can be brutal in the mountains.

Re: Myths in cycling: wider tires are slower

#299

Post by stinos »

Swizec wrote: post #201
auxym wrote: post #175

Earlier quoted context omitted.

In many ways, modern gravel bikes are a comeback of the "sport touring" road bikes that were popular from roughly the mid 70s to the mid 90s, then became mostly absent from market. Compared with "racing" bikes, they had wider tires, a more relaxed geometry, and various conveniences such as mounting points for fenders and racks. Thus, they were a much better option for the majority of riders who did not participate in…

In my neck of Europe those bikes reached peak popularity in the 90's and early 00's. We called them "city mountain bikes". Their distinguishing feature was that a "mountain bike" comes with gears (normal bikes don't), which was very popular. The city edition came with fenders, luggage racks, a nice bell, stand, etc. Big fat tyres, comfy geometry. The tires usually had a slick strip in the middle and grooves on the si…

These aren't the types of bikes meant by the one you're replying to, I think: these are basically mountain bikes with modifications for day to day road use. The other are gravel bikes (which is what I assume means the ones used in cyclocross i.e. a sturdier version of a road bike) modified for day to day road use. But yes these citybikes were very popular in Europe.

Re: Myths in cycling: wider tires are slower

#300

Post by sliken »

kazinator wrote: post #39

Narrower tires, necessarily inflated to a high pressure, are actually inefficient on a bumpy surface. A tire's job is to absorb surface defects in the road, and that is not only for comfort, but rolling efficiency. The extreme example of this occurs off-road. Off-road vehicles benefit from wider tires that are inflated to a lower pressure. If you have an off-road vehicle, it behooves you to take some of the air out o…

Heh, well thin tires are lighter, accelerate better, and have less rolling friction.

Alas, that's only true on perfect roads. Even normal road texture on asphalt and cement is enough to lose a fair amount of energy causing vibrations (which is after all a cyclic acceleration) in the bike and rider.

I've ridden 125 psi racing tires on a racing bike and noticed that I was noticeably faster (on the speedo) when riding a painted line than on the asphalt. When riding a gentle slope along a river it was quite apparent as I switched back and forth. It was also much quieter. I also trained with my racing team occasionally with my mtb with slicks and clipless pedals, no such difference at 60psi and 1.8" tires.

So it turns out that wider tires allow lower pressures, which are better at absorbing vibrations and allowing most of the energy to return. A compressed tire causes some heat, which some of which is released into the environment, but some also goes back into forward motion as the tire expands again.

So the ideal inflation changes with the roughness of the surface.

A relatively recent development is improvements in material science that allows for wider rims with a smaller weight penalty and lighter tires. Lower pressures also help lower the weight of the tires/rims (less force) and wider tires generally give more protection to the rims, allowing the rims to be lighter. Tubeless also has been a big help, less weight, less internal friction, and more compatible with the wider tires which have higher volumes and lower pressures.

So 10 years ago 50% wider tires/rims had a significant weight penalty, not so much today. So in every biking segment from weight sensitive racing bikes to various flavors of mountain bikes are going wider. A decade ago 1.95-2.1" mtb tires were the most common. Today it's 2.35-2.6", which is a bit deceiving. Tire width for the same performance decreases with diameter. 10 years ago 26" was the most common, today the large majority of decent mountain bikes (say over $1000 for a hard tail or $1500 for a dual suspension) are 27.5" or 29".

So the air in a 27.5" x 2.6" tire is significantly more than the old 26" x 1.95".

Also, humans frankly stink as an engine, and are VERY susceptible to vibration, rpm, temperature, comfort, etc. So unlike a car where comfort isn't directly related to performance, on a bike a happier rider = riding faster and longer. So being 10% more comfortable can lead to real performance gains, and high pressure tires can be very uncomfortable, even to the point of numbness.

So now even road bikes that claim to be the world's most efficient bikes, fastest for a given rider input, are having ever wider tires. People are realizing even at the highest levels of racing a few more mm and a few less PSI can lead to faster race times.

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