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PostPosted: Wed Jan 23, 2013 7:35 am 
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WMW wrote:
I keep my ears open and look at every test I'm aware of (lots of tests by Tour) and survey several bicycling forums... and I've never heard of a psi of 75-80 being optimal for road riding. 90-120 yes...


Now you are just misquoting me, I never said optimal for road riding, I said lowest rolling resistance in a straight line, or at least the most energy efficent regarding watts used by rider, on real roads, not some fantasy race track or flat rollers.

And you mention 90-120psi, which is it? 90 or 120 is a huge difference...

Also, i quess many of us are talking about different things. When we talk wide rim tech I think we should assume 23mm tires as that's what they're designed for. And we should talk about mid-weight riders 65-70kg. So let's not talk about 95kg riders on 21mm tubs. That's not a wide rim discussion.

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Posted: Wed Jan 23, 2013 7:35 am 


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PostPosted: Wed Jan 23, 2013 8:19 am 
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If 75-80 psi is the optimum for rolling resistance, when would it be optimal to use a higher pressure?

90-120... because it depends on the road, the circumstances, and the rider weight.

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PostPosted: Wed Jan 23, 2013 8:32 am 
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Really low pressures are a bit wobbly in hard cornering. I would not do crit riding below 95f/100r psi on 23's, I'm 68kg...

Body weight ofcourse makes a huge difference to optimal pressure, but can't we for the sake of argument limit the discussion to reasonably fit riders.

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PostPosted: Wed Jan 23, 2013 4:17 pm 
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You may not like the *feel* of 75-80 psi tires in corners, but I'm pretty sure traction will be better at low pressure.

Our discussion (you and I) is about specific tests you claim were performed that show 75-80 psi to be optimal for rolling resistance. I have no idea what their protocol might have been. I've never heard of that being optimal for any rider of reasonable size.

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PostPosted: Wed Jan 23, 2013 4:53 pm 
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Sure it's good for traction, but poor for handling.

It all really boiles down to sound logic. If your tires struggle to deform, that will eat up energy. Completely wasted energy. At 120psi any tire will have a difficult time deforming as it's pretty much rock hard. It's the same reason tires with a supple carcass have much lower rolling resistance, as it takes less energy to deform than a stiffer carcass.

It's not magic nor rocket science, it's sound logic.

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PostPosted: Wed Jan 23, 2013 6:01 pm 
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There is a big error in your logic. The resistance of the tire itself comes from hysteresis in flexing the casing, tread, and tube. *That* is why supple tires tend to have less resistance. Higher pressures reduce the degree of flex, and always result in less resistance on smooth surfaces. On rough surfaces though, we need to consider the effect of vibration losses (which are mostly dissipated in the riders body) along with energy losses due to bouncing the bike up and down. Not to mention comfort.

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PostPosted: Wed Jan 23, 2013 7:57 pm 
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All right, I'm not going any further into this discussion as I'm fairly convinced your idea of a real world road is alot closer to a hard wood floor than mine...

To each his own, if 120psi works for you then all is well.

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PostPosted: Wed Jan 23, 2013 8:35 pm 
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I ride around 85psi on a 23mm tyre on a narrow front rim, and 25mm on a wider back rim. Any more "feels" faster but is definitely bouncier and less comfy. Any less is a bit squirrely and sluggish. That's on an alloy bike and I'm around 70kg.

I used to ride at 100psi+ on 23mm narrow rims, and the lower pressure is NOT slower and handles better.


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PostPosted: Wed Jan 23, 2013 9:35 pm 
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OB2000 wrote:
the lower pressure is NOT slower.


How do you know?

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PostPosted: Wed Jan 23, 2013 9:41 pm 
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DMF wrote:
All right, I'm not going any further into this discussion as I'm fairly convinced your idea of a real world road is alot closer to a hard wood floor than mine...To each his own, if 120psi works for you then all is well.


I never said 120psi worked for me, and it doesn't matter what my idea of a road is... or yours. We are discussing the veracity of your statement that 75-80 psi has the lowest resistance... backed by numerous tests (you claim).

Has anyone else seen these tests?

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PostPosted: Wed Jan 23, 2013 10:12 pm 
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As I said, I won't argue this any further (it seems a complete waste of time and a typical never ending Internet argument.). Never mind my opinion. Carry on...

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PostPosted: Wed Jan 23, 2013 10:25 pm 
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DMF wrote:
Sure it's good for traction, but poor for handling.

Extreme case is cross. I've mis-judged the pressure in my rear tire (tubular) a few times at races and have gone out with it too low. While I had GREAT straight-line traction, every time I went around a turn the casing flexed so much I started sliding. Scary stuff I tell ya!

...but there's not much like riding a 32-34c tubular at racing cross pressures! Mmmmm like riding on a pair of clouds

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PostPosted: Wed Jan 23, 2013 10:48 pm 
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WMW wrote:
How do you know?


Good point, what I really meant was that as a result of non-scientific observation on a sample size of one, I would conclude that there is no discernable drop in average or instantaneous speed taking into account riding conditions, fitness variations and perceived effort.


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PostPosted: Wed Jan 23, 2013 11:01 pm 
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Anecdotally, I may have been a hair faster on my A23/Pro3 wheels than on my Open Pro/GP4000s wheels, but its minor if it isn't just perception.

AFA I can tell my A23s ride like... ...well... wheels. There doesn't seem to be anything magical about em.

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PostPosted: Thu Jan 24, 2013 12:02 am 
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Hi,

WMW wrote:
DMF wrote:
All right, I'm not going any further into this discussion as I'm fairly convinced your idea of a real world road is alot closer to a hard wood floor than mine...To each his own, if 120psi works for you then all is well.


I never said 120psi worked for me, and it doesn't matter what my idea of a road is... or yours. We are discussing the veracity of your statement that 75-80 psi has the lowest resistance... backed by numerous tests (you claim).

Has anyone else seen these tests?


The entire discussion is a little absurd.
Rolling resistance as a measured figure in a lab test is going to give you a series of figures from which a relative picking order can be established if the test is carried out correctly.

This relative order is going to keep its relation no matter what the tyre pressure or load (load being a rider's weight and a bike's weight plus the modulation of the road surface as seen by the tyre) it is submitted to for as long as you stay within a certain margin.

Extremely low or high loading or extremely high or low tyre pressure are likely to throw the picking order of lowest rolling resistance around a bit but it won't be very extreme. The worst tyre in the lab test won't become the best performer under extreme conditions and vice versa. A few exceptions notwithstanding but those are often not designed for general road use or badly designed for it at best.

IOW you just can't throw around figures of this or that pressure number is better than this or that one unless you can also define all the other parameters. Unless you do so the entire argument is bound to become a moot point. It is devoid of meaning.

Now, if you mean by wide profile wheels a widened rim bed then that also means the volume of air is being increased so it then becomes reasonable to also lower the tyre pressure of that clincher or tubeless tyre since for the same volume of air introduced to pressure inside the tyre is spread over a larger envelope.
Reasonable also means not to lower it so much that pinch flats become within shooting distance. (pertinent to clinchers)
By widening the rim bed you automatically also widen the contact patch which in turn can reduce rolling resistance.
But that also means that the thread of the tyre is a much larger part of that contact patch. That thread is inherently the least flexible part of the tyre and having that do the all the work of absorbing the load is going to throw that rolling resistance out of the window.

This really is nothing new but like everything else in engineering there's also another side to the coin.

Bottomline: high TPI count, i.e. supple tyres would always win if it weren't for puncture resistance throwing spanners in the works.

Ciao, ;)

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Posted: Thu Jan 24, 2013 12:02 am 


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