Pros/cons in inflating a tyre all the way to the maximum?

monkeypants

Following on from a previous thread, I'm running Schwalbe Ultremo ZXs that have an inflation range of 85 - 145 psi. I'm presently running 115 psi, but I'm thinking of increasing that. As a sanity check, what are the pros and cons of inflating the tyre further? I understand that the rolling resistance should decrease, but is it more/less likely to puncture?

To be clear, I'm not looking to overinflate, only looking to take it to 135 - 140 psi, less than the max pressure given.

Lumen

More pressure = worse comfort, higher rolling resistance

morana

monkeypants wrote: »

Following on from a previous thread, I'm running Schwalbe Ultremo ZXs that have an inflation range of 85 - 145 psi. I'm presently running 115 psi, but I'm thinking of increasing that. As a sanity check, what are the pros and cons of inflating the tyre further? I understand that the rolling resistance should decrease, but is it more/less likely to puncture?

To be clear, I'm not looking to overinflate, only looking to take it to 135 - 140 psi, less than the max pressure given.

I would say less likely to puncture but you have to see what the rim can take also. Remember that the harder it is the more vibration you will feel .... I put 160psi into my tubs...but I am fat!

morana

Lumen wrote: »

More pressure = worse comfort, higher rolling resistance

higher.... thought it would be lower...

monkeypants

Lumen wrote: »

More pressure = worse comfort, higher rolling resistance

So there are no benefits to inflating the tyres further?

Eamonnator

Lumen wrote: »

More pressure = worse comfort, higher rolling resistance

Lower rolling resistance surely?

Beasty

monkeypants wrote: »

So there are no benefits to inflating the tyres further?

On Irish roads, probably not - you lose traction as well

kennyb3

Lumen is about to whip out one of his famous graphs. (Remember it from a previous post on this topic)

Beasty

Well according to wiki

Over inflating tires (such a bicycle tires) may not lower the overall rolling resistance as the tire may skip and hop over the road surface

Doesn't suggest it actually increases rolling resistance though, and it does refer to "over inflating" which is arguably not the case here

Anyway, waiting with baited breath ...

C3PO

I'm also running Ultremo ZXs on the race bike! I read all the technical bumph, digested it and then decided that the yellow stripe matched my bike perfectly! :rolleyes:
Schwalbe recommend 115psi for a 75kgs rider, increasing by 1% per kilo over that to a maximum of 145psi! I'm running mine at approx 125psi without any problems.
They also state that increasing pressure lowers rolling resistance!

morana

I remember doing a race on 50psi in the rear tyre and the same route, same bodies etc the following week with 130psi and there was a dramatic increase in the power required for the 50psi event. the weather, and temp were the same.

Lumen

kennyb3 wrote: »

Lumen is about to whip out one of his famous graphs. (Remember it from a previous post on this topic)

http://triathlete-europe.competitor.com/2011/05/03/facts-figures-myths-optimum-tyre-pressure/

C3PO

Lumen wrote: »

http://triathlete-europe.competitor.com/2011/05/03/facts-figures-myths-optimum-tyre-pressure/

I'm assuming that Schwalbe would suggest that their "sweet spot" is between 115-145psi!

monkeypants

You sure that's a graph? It does look like a drawing of a tyre.

"A 25c tire creates less rolling resistance than an identically constructed tire 23c wide." - How does this work?

Lumen

monkeypants wrote: »

"A 25c tire creates less rolling resistance than an identically constructed tire 23c wide." - How does this work?

C3PO

Lumen wrote: »

So why do we run 23s rather than 25s or even 28s on our race bikes?

Lumen

RPL1 wrote: »

So why do we run 23s rather than 25s or even 28s on our race bikes?

Aerodynamics, weight.

monkeypants

I can understand that graph when comparing tyres that are quite different in terms of diameter and width, but there isn't much between a 700x23 and a 700x25 and certainly not enough of a difference to offset the extra weight and inertia.

Lumen

monkeypants wrote: »

I can understand that graph when comparing tyres that are quite different in terms of diameter and width, but there isn't much between a 700x23 and a 700x25 and certainly not enough of a difference to offset the extra weight and inertia.

You're comparing one small thing against other small things and drawing a big conclusion. :pac:

dave2pvd

I run 25s on my training wheels. Michelin Lithions. Super comfy - really helps cushion road vibration nicely. Inflation pressures are a lot less than the Pro Race 3s I use for racing - perhaps 12-15psi front and rear. On chip and seal, these tyres feel faster than 23mm race tyres.

On criterium circuits with high speed corners, I run 100 and 105 front and rear on the PR3s. RRs, ~105/110, which is right where the Michelin chart on the package recommends. I am ~72Kg.

I don't understand why my lighter teammates are inflating to 130psi....perhaps they believe rolling resistance is less?

niceonetom

All this stuff can be very counter-intuitive. Sure you wouldn't know what to be doing... I'm certainly sceptical of graphs with no values on their axes (Lumen knows better too) and they're provided by triathletes too. Hrmm.

This PDF is a bit bewildering and somewhat nullified by the fact that the testing was carried out on rollers rather than a surface that mimics the irregularities of an actual road but at the end there is a little exploration of the effects of different pressures:

Crr does appear to go down as tire pressure increases. Empiricism says so. It's science. You can't argue with science.

dave2pvd

I agree re the roller vs road issue. He admits it:

"Crr values are typical for very smooth surfaces - Crr on typical road surfaces may be 50 to 100 % higher"

So all he's really measuring is friction about the contact patch. Sidewall deformation energy loss, any stickyness between road surface & roller and frictional losses within the tyre/tube interface.

As others have indicated, with a textured (a rather kind description) surface, energy is wasted by vertical motion as the tyre/wheel/bike bumps up and down over transitions. If your tyre can absorb some of this by deflecting, less energy is wasted. Experienced cyclocross racers know this - a tubular able to run at lower pressures is far more efficient on a rough surface than a clincher that can only run at a relatively higher pressures.

C3PO

Can't imagine any of this is going to stop me getting dropped the next time I race!

dave2pvd

To your question,

"Pros/cons in inflating a tyre all the way to the maximum?"

the more obvious are:

Pro: you potentially reduce Crr

Con: your energy loss to 'textured' surfaces will increase.


Edit: didn't the Tour of Ireland a couple of years back have some of the pro teams riding on 25mm tyres during one of the stages out Wesht?

Beasty

Lumen wrote: »

Surely that's why you run narrower tyres at higher pressures than wider ones. Increasing the pressure effectively reduces the "deflection amount" and "active area of sidewall". I presume those diagrams are assuming the same pressure in each tyre

Mycroft H

dave2pvd wrote: »

I run 25s on my training wheels. Michelin Lithions. Super comfy - really helps cushion road vibration nicely. Inflation pressures are a lot less than the Pro Race 3s I use for racing - perhaps 12-15psi front and rear. On chip and seal, these tyres feel faster than 23mm race tyres.

On criterium circuits with high speed corners, I run 100 and 105 front and rear on the PR3s. RRs, ~105/110, which is right where the Michelin chart on the package recommends. I am ~72Kg.

I don't understand why my lighter teammates are inflating to 130psi....perhaps they believe rolling resistance is less?

That scale go any higher for us lard asses? I roll on 32mm paselas at 95psi. Fairly comfortable and quite a quick tyre for the size.

dave2pvd

Beasty wrote: »

Surely that's why you run narrower tyres at higher pressures than wider ones. Increasing the pressure effectively reduces the "deflection amount" and "active area of sidewall". I presume those diagrams are assuming the same pressure in each tyre

Which is why the diagram needs a pinch of salt.

It's not wrong. Just misleading.

superlav

Lennard Zinn seems to agree that fat tyres roll faster than an equivalent narrow one

Beasty

superlav wrote: »

Lennard Zinn seems to agree that fat tyres roll faster than an equivalent narrow one

... at the same pressure.

doozerie

For what it's worth Josh Poertner, head engineer for Zipp, also takes the view that higher pressure = greater rolling resistance (click on "Rolling Resistance" and "View Josh's response":

The Corsa Evo CS will be perfect for that wheel, and I would recommend 100-125 psi (6.9-8.6 bar) depending on your weight. You will want to run 0.2-0.5bar more in the rear than the front to account for weight bias. I personally weigh 155lbs (70kg) and run my tires at 105 psi front (7.2 bar) and 110 psi (7.6 bar) in the rear. When I was racing and lighter I ran them at 100/105, but now that I'm heavier it is safer to run a few extra psi and I may go even higher on bad roads, which has worse rolling resistance, but better protects the wheels from damage in the event of hitting a pothole or something else which could damage a rim or tire. The better option is to run a wider tire at lower pressure on rough roads, but that is just not always feasible, so I would rather have higher rolling resistance and protect the wheels than lower rolling resistance and increased risk of damage to the wheel.

Higher pressure is definitely slower on anything other than perfect surfaces. Think of it in terms of a bunch of 1mm tall bumps in the road. If you have a lower tire pressure, the casing of the tire will deflect over each bump (we'll assume the casing deflects the entire 1mm) converting a small amount of energy into heat as the casing deflects, but the amount of energy necessary to compress the air is almost non-existent. Now at a higher pressure, we will assume that the tire deflects half as much. Now the bike and rider are lifted by 0.5mm and the casing deflects by .5mm, the energy necessary to deflect the casing by .5mm is less than it takes to deflect it by 1mm, but is nothing compared to the amount of energy necessary to lift the bike and rider by 0.5mm, so the end result is that the total energy requirement for the high tire pressure condition is much greater.

The other thing that happens is that on smoother roads, high tire pressures keep the casing from deforming over and into small cracks and crevices and over pebbles, which means that some of the deflection is transferred into the tire tread, which is not as elastic as the casing. Excessive tire wear comes about as the tire rubber begins to fail in shear as it is deformed by the road surface, and this generates heat as well as breaks down the cross-linking within the tread material.... overall, you are using more energy to go slower and you're wearing your tires out faster. The problem is that high tire pressures feel fast as your body perceives all the high frequency vibrations from the road surface as being faster than a smooth ride.

Lennard Zinn had a great analogy when he said that 100kph in a Jeep will scare the crap out of you but 200kph in an S class Mercedes feels effortless...the same is true of bike tire pressures, but it's just hard to convince ourselves of that. As athletes we tend to buy into the 'if some is good, more must be better' philosophy, but this is rarely true. Of course the tire manufacturers have given up on this and continue to try and make higher pressure tires as that's what the consumers demand, as I think that they've decided that it is easier to just give people what they think they want than to try to educate and argue with them :-)

cdaly_

monkeypants wrote: »

You sure that's a graph? It does look like a drawing of a tyre.

niceonetom wrote: »

All this stuff can be very counter-intuitive. Sure you wouldn't know what to be doing... I'm certainly sceptical of graphs with no values on their axes (Lumen knows better too) and they're provided by triathletes too. Hrmm.

niceonetom wrote: »

It's science. You can't argue with science.

Of course you can. Arguing is what science is all about...





PS. I have nothing useful to contribute to this discussion...

Lumen

From a practical and subjective perspective, a nice 28mm tyre is fast and pleasant to use for non-competitive use, but they are hard to find since most tyres over 25mm are aimed at commuting, touring and hybrids. My 28mm Ultremo R1s were probably the nicest tyre I've used on Irish roads.

Anything over 28mm feels heavy and slow regardless of pressure, and if you're going to pump a 35mm tyre to 80+psi it will feel both heavy and harsh. I am currently running 35mm Schwalbe Kojaks (the lightest tyre in that size) at about 70-80psi, and they're really not any more comfortable than 28mm tyres at 90psi.

ednwireland

meh i run my panaracer crosstown and michelin pilot sport at 85 (both 32)