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Re: Tire Pressure Poll [plant_based] [ In reply to ]
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That is out of date-- or rather the thinking that higher-is-better is out of date. Those types of analyses only factor static casing losses and ignore impedance losses. They are good for comparing different products, but not for determining best pressure for the anticipated road surface.

Check this out: https://blog.silca.cc/...stance-and-impedance
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Re: Tire Pressure Poll [rruff] [ In reply to ]
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rruff wrote:
DFW_Tri wrote:
The roads arenā€™t THAT different




Please tell me if I read this right... from the 2nd graph... I'm on ok-to-rough ashphalt mostly (rare to have concrete road surfaces where I live... and rarer to have nice new asphalt either - last time I saw some of that was when TdF visited Yorkshire and Derbyshire and miraculously some new surfaces appeared over Beirut-bomb-cratered roads over the Strines šŸ˜).
I'd read it as being best off around 90-100psi.
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Re: Tire Pressure Poll [exxxviii] [ In reply to ]
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I am in awe of those that do take up the battle to attempt to educate those who do not comprehend...I have neither the time nor the energy.


However, I do have data from doing my own field testing several years ago with multiple, multiple loops at various tire pressures. I was quite surprised that I was indeed faster on normal, older New England roads (asphault/chipseal) at lower pressures.

I'm a science guy (*ie evidence based) and Josh's data proved all I needed to know/confirm. Now, how to tell how bad the composite road surfaces are at various venues to appropriately lower the pressure to the 'optimal' on race day-hmmmmm. Someone please, please post THAT.



Carry on and good luck...
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Re: Tire Pressure Poll [BobAjobb] [ In reply to ]
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Potentially. And that's where your own weight and such comes in to it. But also consider this: if you decide to run 80psi you're losing max 1-2 watts regardless of the road surface AND you get a more comfortable ride. At 100 or even 90 as soon as you hit extra bad surface you're losing more than the 1-2 watts. So it's probably net even to run lower and you get increased comfort.

Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors
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Re: Tire Pressure Poll [realbdeal] [ In reply to ]
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You got me thinking on this (which I try not to do...it just seems to hurt the ballclub, lol): I did ST.G 70.3, as did you, which is why I'd like to add this little tid bit in, and as to why you got me thinking. I am no "real" triathlete, but I don't completely suck (2:50 on the bike, but lost time...which is why i'm posting).

I'm 200lbs (not fat). I run my tires up at 110psi (GP4000, 23mm, Flo 60/90 combo). I was always of the "hard is fast" mentality. And I thought the roads of St.G were nice and smoooooth, so this would be a good thing. But that was not the case (or maybe it was and I'm completely wrong). I thought the St.G course was ROUGH AF!! Not horrible, but I felt EVERY.SINGLE.CRACK. And to that point I remember thinking "fuck, my back and shoulders are tired because I have to absorb and take every bump and hold on in aero", to the point that the last stretch into town I was flying 40+mph...and all those little ridges from the expansion cracks that have been sealed were being significantly felt in my body. And then it happened: a bumpy stretch (didn't look bumpy) and my chain got thrown.

So all this talk of the bumps and the up and down and lighter PSI got me thinking: pretty sure I need to drop that PSI a bit and maybe that won't make the ride suck so bad, and maybe those bumps won't be felt (rolled over, instead of pushing the bike up as I go over) as much so my chain doesn't get thrown. Just got me thinking because I know a lot really like the St.G roads...but I thought they sucked...and maybe that is because I was running such a high PSI (in Butyls if that matters, but will be in latex from now on).
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Re: Tire Pressure Poll [BobAjobb] [ In reply to ]
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BobAjobb wrote:



Please tell me if I read this right... from the 2nd graph... I'm on ok-to-rough ashphalt mostly (rare to have concrete road surfaces where I live...I'd read it as being best off around 90-100psi.


Yes, assuming the bike-and-rider combined weight is ~same as the test (190lbs/86kg), you're on the same tires (25c GP4000S) mounted on similar internal width wheels (test wheels were Zipp 404 Firecrests, 16.5mm).

Change any one parameter (weight, tire, wheel width, surface) and the graph is going to change. Whatever the trace, t's better to error on the side of low than high, as the slope is steeper past the impedance inflection point.

"They're made of latex, not nitroglycerin"
Last edited by: gary p: Aug 28, 19 15:55
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Re: Tire Pressure Poll [JMike] [ In reply to ]
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JMike wrote:
Why is tire pressure always addressed as 'run' or 'ran'?

Everyone here says they are ā€œrunningā€ this or that for anything. Canā€™t stand that.
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Re: Tire Pressure Poll [SBRmd] [ In reply to ]
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SBRmd wrote:
JMike wrote:
Why is tire pressure always addressed as 'run' or 'ran'?


Everyone here says they are ā€œrunningā€ this or that for anything. Canā€™t stand that.
Cyclists go super slow when they run Marathons!
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Re: Tire Pressure Poll [SBRmd] [ In reply to ]
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SBRmd wrote:
JMike wrote:
Why is tire pressure always addressed as 'run' or 'ran'?

Everyone here says they are ā€œrunningā€ this or that for anything. Canā€™t stand that.

Donā€™t know you but I like your thinking
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Re: Tire Pressure Poll [realbdeal] [ In reply to ]
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realbdeal wrote:

We're so used to feeling the vibrations of the road and thinking that's fast because that's how its always been. Instead we need to start telling ourselves that smooth is fast. My approach to this has been to slowly work my pressure down to the point where the right PSI feels "normal".
Ultimately, for most of us right now, it comes down to being willing to trust the science more than we trust our bodies. That's super hard.

I was thinking about this statement and it hold water for me. 'Feeling normal' or even 'comfortable but slow' may be the goal because smooth is fast.
That is something I believe.

Smooth is fast. Yessssir. I like the way you think, Ben.

(*I found the link to what I posted on BT back in 2016)
https://beginnertriathlete.com/...id=542235&page=1


edited to add:
my 70.3 PR (bike and OA) was from IMAC in 2018-and I 'ran'/used 80/80 on race day-front 23/back-25; Zipp 808/conti 4000's both: with light rain and cool temps that day. Weight distribution 45/55% by scales x 2.


It got me to Worlds, so I'm not complaining or questioning the logic too much
Last edited by: dtoce: Aug 28, 19 17:23
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Re: Tire Pressure Poll [plant_based] [ In reply to ]
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plant_based wrote:
https://www.bicyclerollingresistance.com/...grand-prix-5000-2018

Rolling resistance is lower on GP4000IIs and GP5000 at 120psi

resistance is lower, with every tire, every width, at the highest pressure tested. the prevailing thinking is that the testing equipment does not incorporate elements in actual road riding - the way the rider and his weight react on the tire, the way the road reacts to the tire - so doesn't generate an accurate picture of what pressure is best. what it lacks in accuracy it makes up for in precision, that is, it can identify very small changes in energy required to turn the drum at speed (or however the thing works).

Dan Empfield
aka Slowman
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Re: Tire Pressure Poll [realbdeal] [ In reply to ]
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Interesting - they seem to be in the lower pressure camp. I posted this in another thread but maybe I should have posted it here:

Some of the information out there on tire pressures seems to be conflicting.

Here is Roval's recommendation (I run a Roval CLX 64 front wheel)


Here is HED's recommendation (I run a Jet Disc Plus on the rear)


My 23c GP5000 tire measure 26mm at 85 psi on my front wheel. Roval does not say if it's chart is for measured or labeled tire widths, but it would recommend >107psi if labeled, 89 if measured. HED's chart is for labeled width so they recommend 72 psi. Quite a huge difference! What is one to do? They cannot both be right.

On the rear, I've been running a 23C GPTT which actually measures 27.75mm on my HED Jet Disc Plus! I'm re-thinking that tire right now, given the 25mm brake track on that wheel, but the aerocoach testing puts it ahead of the GP5000 on their wheel - need to get the width of that wheel. At least in the back it's shrouded.



From Silca's website, I cannot find a chart with enough data to really select a pressure given tire width and rider weight, but there is this, which seems to suggest even higher pressures than roval, but we do not know rider weight:


Here's a chart from Flo (They apparently got it from TomA) which I'm pretty certain refers to measured width and recommends about the same as roval, ~90.


My inclination is to go with the Flo(TomA)/Roval recommendations since they agree, and Tom does a solid job in this testing.

Is there a better source that I am missing?

-------------
Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
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Re: Tire Pressure Poll [rruff] [ In reply to ]
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Ingles, por favor.
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Re: Tire Pressure Poll [Trirunner] [ In reply to ]
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Ditto and ditto.

I used to run 120, basically the max.
That was like 15+ years ago.
Then was at 115 for a while.
Then was running 105 for a few years.
Now Iā€™m typically at 95.

Tires went from Michelin ProRace to those Bongtager Rwhateverā€™s that were rated as fast (but very brittle), then GP4ks and now the IIā€™s.
I have 5kā€™s waiting to mount up once the current dancing shoes wear out.
All in 23ā€™s.

So, other than that first response, none of my answers technically match the poll.

I replied 100, because Iā€™m certainly not at ā€œ90 or lessā€.

I still have somewhat traditional narrow R rim, but a HED Jet C2 (and the road/training equivalent) up F.


float , hammer , and jog

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Re: Tire Pressure Poll [DFW_Tri] [ In reply to ]
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DFW_Tri wrote:
Ingles, por favor.

The ideal tire pressure will vary a lot depending on the road surface... among other things.

https://blog.silca.cc/...stance-and-impedance
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Re: Tire Pressure Poll [RowToTri] [ In reply to ]
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RowToTri wrote:
Is there a better source that I am missing?


You aren't considering road quality. The Silca study is best for that. And besides rider+bike weight, the tire design (not size) also influences ideal pressure.

And the chart you are referencing from Flo via Tom... I think originated from Michelin. At least it looks like one of theirs.
Last edited by: rruff: Aug 28, 19 21:04
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Re: Tire Pressure Poll [Slowman] [ In reply to ]
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"i think josh and tom a. and some of the other guys posting here have made an impact on you all. "

That I can agree with. I know they did for me, indeed.
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Re: Tire Pressure Poll [gary p] [ In reply to ]
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Thanks.
(I'd not spotted the rim width or all up weight was for the graph).

Interestingly, I'm heavier, on slightly narrower rims and now with 23mm GP5000s (rims narow and limited clearance on my bikes). I usually go about 100psi rear and 90 front. A few psi lower when wet.
So on the 'low' but 'safe' side if trying to extrapolate.

I'd bebattered to death on a long ride where folks are talking of 120+psi.
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Re: Tire Pressure Poll [smccauley49] [ In reply to ]
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smccauley49 wrote:
130 lbs
TT bike: 700 x 25 @ 80psi
Road bike: 700 x 28 @ 70 psi
Gravel: 700 x 32 @ 60 psi

Ouch, at your weight you would probably have a much better ride on gravel at around 35 to 40 psi. Ive got 20 pounds on you and that is what i ride. 60 psi is for when those rides when the tires don't go off pavement.
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Re: Tire Pressure Poll [RowToTri] [ In reply to ]
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Thanks for organizing these here. But, these charts are giving me a headache. Just when I was convinced lower is better, several of these suggest a much higher PSI than say the HED model (I typically run slightly higher than the HED model but much lower than the other ones)
Last edited by: DFW_Tri: Aug 29, 19 5:31
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Re: Tire Pressure Poll [plant_based] [ In reply to ]
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plant_based wrote:
But, I read that rolling resistance was lower on these at 120psi.

It is...on a glassy smooth testing roller or perfect surface velodrome. Even what you would consider a very good road surface is significantly rougher than that though.
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Re: Tire Pressure Poll [Bioteknik] [ In reply to ]
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Interesting, I'll give it a shot and see how it feels.

Thanks for the suggestion!
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Re: Tire Pressure Poll [smccauley49] [ In reply to ]
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smccauley49 wrote:
Interesting, I'll give it a shot and see how it feels.

Thanks for the suggestion!

Of course, I forgot to mention that tubeless or not makes a difference, as you don't want to pinch flat, but ride as low as you can without. Funny that in fall/winter/spring the gravel roads here are in better condition usually since there's enough rain to keep the braking bumps down, in summer those roads get considerably rougher.
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Re: Tire Pressure Poll [rruff] [ In reply to ]
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rruff wrote:
RowToTri wrote:
Is there a better source that I am missing?


You aren't considering road quality. The Silca study is best for that. And besides rider+bike weight, the tire design (not size) also influences ideal pressure.

And the chart you are referencing from Flo via Tom... I think originated from Michelin. At least it looks like one of theirs.

I am considering road quality, and bike weight. I've seen no data that would allow me to adjust pressure based on tire design (what like open the vs molded?) The silca road surface study does not include multiple rider weights and multiple tire widths so you kinda have to start at where you should be on smooth asphalt from other sources and use their road surface data to influence how much lower you might need to go from there.

-------------
Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
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Re: Tire Pressure Poll [Bioteknik] [ In reply to ]
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Yeah I run with tubes still so I'll probably start at 50 and drop down from there to see how it feels.

I'm familiar with that phenomenon all too well since I live on a gravel road. It's the worst when they resurface or grade it and bring all the loose stones up to the top!
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