RNAV

It seems proponents of going tubeless claim two things (in addition to the no-flat thing):

1. Improved (i.e. decreased) rolling resistance.
2. Improved ride quality by being able to run lower pressures.

So my question is this: if I'm running tubeless at 85psi to obtain the benefit of better ride quality, am I still achieving less rolling resistance as compared to a clincher's rolling resistance at 120psi?

I'm having difficulty understanding the relationship between rolling resistance and ride comfort at given tire pressures between tubeless and clincher.

For example:

Tubeless @ 120psi & clincher @ 120psi: which tire has the least rolling resistance? Which tire has the more comfortable ride?
Where's the "break-even point" where a tubeless @ xxx psi has the same rolling resistance as a clincher @120psi?

Are my questions making sense?

chaadster

In my experience, ride quality is better irrespective of whether or not the pressure is lower.

Specifically, I typically run my tubeless setup only 10psi lower than tubed, down to 100F/110R, a pressure drop which would not net a noticeable difference in tubed tires.

Therefore, I'd suggest that the improvement in ride quality has more to do with construction and the absence of the tube, than it does with pressure.

rpeterson

Rolling resistance increases pretty dramatically with pressure, so at 85psi vs 120psi you've probably got way more comfort and speed. However that might not be much better than clinchers at 85psi.

RNAV

I was under the impression that rolling resistance decreased as you increased pressure. In my experience, flat tires resist rolling more than fully inflated tires.

Sangetsu

This reminds me of the old argument between tubular vs clincher tires. Having used both for many years, tubulars offered lower rolling resistance, and better response. On the other hand, repairing punctures is a royal p.i.t.a. I would have to carry an extra tubular tied to the bottom of my seat, and add a tube of glue to my tool kit. I decided that it was simply more convenient to switch to clinchers, and carry an extra tube.

Increasing tire pressure lowers rolling resistance, and increases efficiency. Lowering pressure increases comfort as the softer tires can more easily absorb shocks and bumps. But lowering tire pressure increases resistance, I can tell the difference in effort when one of my tires has developed a leak, and started losing pressure. Personally, I run as high a pressure as possible. The max pressure depends on the tire, and the weight of the rider. When choosing between tubeless and regular tires, I think about weight, quality, and variety. Regular clincher tires exist in every size and type, and can be found anywhere. They are light, simple, and easy to install. If you can find tubeless tires which are comparable in weight, price, and convenience, then they are a good choice, if not, stick to normal clinchers.

Bob Dopolina 

I swear I have written this post 20 times.

Higher pressure yields lower rolling resistance, to a point, then resistance increases.

The max ratings on a tire are not about max performance, they are based on several things which include, but are not limited to, performance, comfort and safety (traction, for instance). To understand this you need to consider what manufacturers mean by these numbers.

With any tire there will be a best pressure for each of the factors considered. There will be a sweet spot for rolling resitance, there will be a sweet spot for traction, there will be a sweet spot for comfort, which is at a lower pressure but not so low as to comprimise whatever flat protection is designed into the tire.

The manufacturers look at these numbers and then set their recommended pressures at the MAXIMUM INTERSECTION of these values; If you want a more comfortable ride then go to the lower end of the recommended pressures. If you want the best performance, go to the higher end. Pretty simple.

These values will vary from tire to tire based on things like materials and construction. Using pressures outside of this range and your tire will underperform IN ALL AREAS.

StanSeven

Thanks Bob for another really informative post. You really are appreciated providing both good information on subjects like this but a great perspective from a knowledgeable industry source.

Sangetsu

Not to be argumentative, but I have never heard of nor experienced increased rolling resistance as pressure has increased. I have run 120 to 170 psi on the track, pretty much the max possible without damaging the tire or wheel. Each increase in pressure resulted in lower resistance, but never was there an increase in resistance. The only reasons I would run lower pressures is that the tires develop fine cracks, and reduced life when run at very high pressures, and when I spend $80 or more for a tire, I want to get a lot of life out of it.

Of course one can't run these kinds of pressure on the road, as you say, there is a sweet spot where ride quality, resistance, and traction are optimal. Increasing pressure will reduce comfort, and traction, but it will not reduce resistance.

Bob Dopolina 

Agreed. Track is a different animal. You don't need to deal with deflection due to surface irregularities which is where the increased rolling resistance comes from.

What I posted applies to road riding only (since we are in the road forum). Increased rolling resistance does happen with pressures that are too high as the tires lose their ability to deflect efficiently and you lose energy lifting the bike up and over tiny pebbles and rougher road surfaces instead of having the casing deform around those minute obstacles.

WestPablo

+1

Ding! Ding! Ding!

We have a winner here!

'Tis true...

Rolling resistance 'decreases' with an increase in tire pressure!

UnfilteredDregs

No.

WestPablo

+1

There's an optimal point where increased tire pressure no longer contributes to lowering the rolling resistance. Pressure added beyond that point makes the tire more sensitive to road irregularities, causing it to behave less efficiently and actually increases rolling resistance.

WestPablo

Yes, I insist!

UnfilteredDregs

gah!

UnfilteredDregs

It's all about contact patch and efficient deformation over surface irregularities. Dial pressure accordingly...


(...What Bob & Pablo said...)

gc3

If you really don't want to be convinced, why not be more upfront in how you start the thread. Maybe something like "I think tubeless is bullsh*t and you can't change my mind, but please try anyhow?"

RIRview

Make that 21.

djb

not to mention too high pressures will beat you up, therefore you'll be more tired. Also cornering will be better also on bumpy roads as at a lower pressure, the tire will do its "suspension" thing better, allowing you to corner faster and smoother.

what the sweet spot for pressure as mentioned, depends on different factors, rider weight, bike weight, tire width, road conditions, the tires themselves (some tires are more supple than others and so will feel different at the same pressure than a different tire)

WestPablo

I'm actually agreeing with Bob!

What are you talking about?

As you increase the pressure within a road bike tire, the patch area becomes more rounded and its radius decreases. As the patch area becomes more rounded, the tire loses more rolling resistance. As the radius of the rounded area becomes smaller, the rolling resistance further decreases. However, once you've reach a certain optimal point, increased pressure ceases to decrease rolling resistance. Instead, the tire begins to interact with road irregularities much more and begins to bounce and resist more efficient forward motion.

Rolling Resistance | Schwalbe North America

UnfilteredDregs

Yes.

chaadster

first, as I said upthread, you don't need to run dramatically lower PSI to obtain benefit of better ride quality. To your question specifically: at any given appropriate riding pressure, assuming all else the same (e.g. tread, compound, width, load), tubeless will always have lower rolling resistance.

I don't think I understand the mechanics well enough to clearly explain why, but it has to due with elastic hysteresis of the tube, and the tube/tire internal friction.

tubeless and tubeless
This answer gets complicated because Crr (rolling resistance) will always be lower for tubeless *all else being equal*, so in order to get the Crr to match, you have to make things unequal, like PSI, but then we need to know more like load (i.e rider weight) to figure that out for real-word relevance.

I suppose that, assuming a 160lb rider on the road with a 40/60 weight bias, that the question could be interpreted as, "what is the lowest PSI he can run tubeless before Crr really goes up?"

My suspicion is that other factors, like impact risk, and ride quality elements, like tires feeling soft when out of the saddle, will stop you from hitting that Crr breakpoint, and before it can be a factor. So, I'm sure there's a theoretical answer (or two), but for real-world, there are so many variables and contingencies that it's probably best to gather info on specific tires for a given rim, rather than speaking in theory.

To that end, perhaps Scwalbe, who make the One in both clincher and tubeless, can offer some insight if they publish any data.

Myself, I'm content to know that in most every scenario, tubeless offers every performance advantage over clincher, and it looks likely that tubeless options will continue to improve in the near future. It's also clear to me that there will always be more important performance factors than margins between high performance tires, so I worry more about putting out more watts and losing pounds than reducing Crr of already hi-performance tires. Every advantage is an advantage, though!

RNAV

Chaadster, thanks for the response. That's the level of understanding I was hoping to obtain!

UnfilteredDregs

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