# Balloon tyres for commuting



## Armchair Spaceman (Jun 21, 2003)

Anyone out there using big fat tyres like scwalbe super motos or big apples? Do they measure up to the hype about low rolling resistance in real life, compared to a smaller diameter tyre? I've tried a few slicks and semi-slicks like Ritchey Tom Slicks, Geax City Runners in recet times and now running 26x1.4 Maxxis Xeniths. All fine although the Xeniths don't last very long at all.


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## wim (Feb 28, 2005)

People love to tell the old "bigger tires have less rolling resistance" story because it never fails to surprise the listener. Trouble is, the rest of the story is never told. A bigger tire has less rolling resistance than a smaller one only _if both are run at the exact same pressure_. But no one does, and for good reason: a 700 x 32 @ 120 psi will feel like solid concrete, and a 700 x 23 @ 80 psi will pinch flat.

/w


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## ispoke (Feb 28, 2005)

*I disagree*



wim said:


> People love to tell the old "bigger tires have less rolling resistance" story because it never fails to surprise the listener. Trouble is, the rest of the story is never told. A bigger tire has less rolling resistance than a smaller one only _if both are run at the exact same pressure_. But no one does, and for good reason: a 700 x 32 @ 120 psi will feel like solid concrete, and a 700 x 23 @ 80 psi will pinch flat. /w


Of course no one uses such different tires at the same pressure. I doubt people assume otherwise.

A 700x35 at 80 psi rolls a lot smoother than a 700x25 at 100 psi, and it's very likely that this translates to less "rolling resistance". Sorry my numbers are different but it's just what I've used. What it's really about is the fact that a larger tire needs less pressure to support an equal weight (you). The less pressure in the tire, the better the casing deflects to soak up irregularities in the road. Whereas a skinny tire needs high pressure and consequently is more rigid - thus giving up some of the pneumatic suspension that tires were conceived for.

Is there any real world scientific evidence (not lab/drum test) that a hard skinny tire is faster? I doubt it. The most persuasive hypothesis on this topic is that hard skinny tires *feel* faster because they transmit a higher frequency of road vibration to the rider through her hands. But that doesn't mean those tires are really faster...


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## pdh777 (Oct 7, 2005)

Less patch on the ground - skinnier tire = less rolling resistance. 

Harder surface - skinnier tire = less rolling resistance

End of story


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## wim (Feb 28, 2005)

> _Of course no one uses such different tires at the same pressure_


Of course, but the misleading statement that "larger tires have less rolling resistance" rests on the false assumption that people do..

At equal pressures, the casing tension of the larger tire is higher and flexes less than the casing tension of the smaller one. Therefore, it rolls easier. This has nothing to do with contact patches or drum tests or feel—it's just plain physics. To calculate circumferential casing tension in a thin-walled, flexible closed tubular container (like a tire), you use this so-called boiler formula:

t = P x D / 2 x S

t = axial casing tension
P = pressure
D = inside diameter
S = casing thickness

Even doing the math just once, you'll see that casing tension increases substantially as inside diameter increases. That's why an exploding car tire at 30 psi will rip your head off, whereas an exploding bicycle tire at 120 psi will just make a startling noise.

As an aside: with increasing pressure, circumferential tension t increases much faster than longitudional tension a. That's why bratwurst always splits the long way when overpressured. 

/w


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## ispoke (Feb 28, 2005)

*groan!*



wim said:


> ...Even doing the math just once, you'll see that casing tension increases substantially as inside diameter increases.../w


I was afraid it would come to this. Look, I'm a mechanical engineer and I took physics. In fact I used to review pressure vessel calculations and am familiar with the hot dog formula. But that equation is only intended for a homogeneous material (such as metal) with a high modulus of elasticity. It has nothing to do with a pliable tire casing made of woven fabrics, braided wire and a blend of rubbers. So put down your textbook and combine that intelligence with common sense observation.

If you've ever pressed your thumb into a 35mm tire at 80 psi then a 25mm tire at 100 psi, you know the wider tire has more give. Rolling resistance has a lot more to do with pneumatic suspension and of course the suppleness of the tire casing. The casing is key, and I think that wide tires get a bad rap because most are overbuilt and clunky and indeed are slow. But if you splurge on high quality fatties such as those made by Panaracer (Grand Bois, Riv Roly etc.), you'd feel differently. The Schwalbe Marathon "Supreme" also looks promising.


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## ispoke (Feb 28, 2005)

*life's easier when you oversimplify*



pdh777 said:


> Less patch on the ground - skinnier tire = less rolling resistance. Harder surface - skinnier tire = less rolling resistance
> End of story


Perhaps on champagne pavement (as rollerbladers describe new asphalt) your simplistic analogy and the laboratory drum tests would suffice. In fact on really smooth asphalt we might ride fastest on rubber coated solid wood or metal wheels. So your point is well taken.

But in real world conditions, especially on older pavement, that approach falls short. Why not consider a limiting case: If you've ever pedaled over a rumble strip on the shoulder of the road on 25mm tires at 100+ psi, you might already realize the benefits of the pneumatic suspension on a fatter tire and you'd know intuitively that the fattie would roll over the rumbles faster. Sure it's an extreme example, but it helps illuminate the nuances that are too frequently overlooked.

I'm signing off of this topic. I'm sure it's been debated ad nauseum and those in each camp are unlikely to change their opinions. I couldn't help but write in (twice) this morning because I'm an advocate for balancing theoretical approaches with real world observation and reasoning. Feel free to take another shot and have the last word.


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## Armchair Spaceman (Jun 21, 2003)

*Well Then...*

This theoretical tub-thumping is all very well, but I started the thread to know if anyone is ACTUALLY USING BALLOON TYRES FOR THEIR COMMUTE and if the experience lives up to the hype. A 30mm tyre is not a 'balloon' tyre - a 50 to 60 mm tyre is. I'm riding 40's and am thinking about going to 60s just for fun - I was wondering whether I'd work a lot harder or roll easier and/have more fun on my 30km each way, mostly flat, mixed surface commute.
Anyone out there actually using them and want to share their experiences?


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## buck-50 (Sep 20, 2005)

Armchair Spaceman said:


> This theoretical tub-thumping is all very well, but I started the thread to know if anyone is ACTUALLY USING BALLOON TYRES FOR THEIR COMMUTE and if the experience lives up to the hype. A 30mm tyre is not a 'balloon' tyre - a 50 to 60 mm tyre is. I'm riding 40's and am thinking about going to 60s just for fun - I was wondering whether I'd work a lot harder or roll easier and/have more fun on my 30km each way, mostly flat, mixed surface commute.
> Anyone out there actually using them and want to share their experiences?


I tried it a couple times- I found a set of hutchinson 2.2" slicks on Nashbar and threw them on my mountain bike/test platform.

They rode OK- not as fast as my road bike, but faster than knobbies or semi-slicks. 

Definitely had a Cadillac ride- they're big, round, and as slick as a motorcycle racing tire. 

Here's the only issues I had- 

1- they're 26", so yer pretty much stuck with a mountain bike frame. 
2- The ones I used were totally slick, so wet wooden bridges were deathtraps. 

However, they were definitely comfortable and faster than normal MTB tires.


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