Seattle Forrest

As long as you don't go down to the point where it gets squishy, supple tires can better deform to the road surface with lower pressure.

ThermionicScott 

Someone asks if you have ever tried to cut something with a dull knife, and your response is to search Google?

rower2cyclist

Can't help your 12-yo brain if that was your take ha!

ThermionicScott 

Hey, at least my 12-year old brain had no trouble with hedonist's analogy!

rubiksoval

Lower pressure allows the tire to deform and "stick" to the road more.

Higher pressure causes the tire to not deform and lose contact with the ground when there are irregularities in the pavement. So any little rough spot can cause your tire to skip/slide and you can go down.

That sweet spot between maintaining maximum grip while not deforming to the point of raising the rolling resistance is what most shoot for.

Psimet2001 

I had no idea you were 5'2".

Agreed on pressure. OP you should start at like 90 or 95 and drop from there over a few rides. You'll know when you're too low.

Psimet2001 

I started the wheel company 11 years ago officially. About 6 years ago the existing bike shop that I was "renting space" from to establish some of the more discerning distributor accounts had the owner get to the point where he wanted to retire and he sold the shop to me and I moved in.

He rides daily still and occasionally he will stop in and say hey and we will talk. In between ordering the odd 20 year old Campy part to fix his worn out stuff we will get to talking a little about tech changes. I guess I intuitively knew a lot had changed in those years but I never really put it all together.

Anyway one time he was like telling a story and I suggested, "Oh you should probably lower your pressure a bit. Most of us that have been riding forever tend to be running a little high on pressure."
"Really? what do you recommend for me?"
"95-ish. Just below 100 as a start."
His eyes got big and he was like "WTF?! I ride 120! We used to just go as high as we could. The higher and the narrower the better."
"Yeah, well the fatter and lower is apparently better now."
"Is everyone going a lot faster now?"
"Nope."
"Surprise."

Same guy that used to say, "I love selling spoke wrenches. I make money when I sell the wrench and I make money when they have to come back later because they messed up their wheel."

mackgoo

They've bought into the Kool Aide.

eduskator

6'1'' and 185lbs (84kg) here and I am running 85PSI in my 25mms tubeless tires (mounted on 17mm internal width rims). I was running 100psi on my previous tubed setup. I could probably go even lower, but I am comfortable at that pressure.

They tend to lose 5-10PSI after 50-60kms and my butt is happy with that during long rides!

MoAlpha

Data point: 141 lbs; 25 mm; 70 F, 75 R. Much higher and the bike feels unstable descending fast on rough pavement, of which there is a lot where I live. Haven’t gone lower.

Maelochs

But they are traveling the same distance in the same time in far greater comfort .......

That's hilarious .... after the sting fades .....

Seattle Forrest

Analogies are grand, but you have to make sure they don't lead you down the garden path to the wrong answer. The human brain is like a computer, that's awesome, I just ordered more memory for my brain because now that I'm over 40 I can't remember what I had for breakfast.

I think everybody got the analogy about the dull knife, but it sounds off, so I can't blame anyone for checking to see if it's really analogous. And it turns out it's not, kind of like how there are a lot of ways the brain isn't like a computer.

Seattle Forrest

Now I'm getting ads for knives.

guadzilla

So after a few months of drinking the kool aid and riding at 80.85, i pumped my tires back up to 95/100 for the past couple of rides - and it has felt faster (given the wind and wattage). Was it a controlled test? No. But that loop is my main training route and I have a pretty good idea of what kind of speeds I do at different wattages and under various wind conditions, and this does feel faster. Admittedly, this is on very good quality tarmac, though.

Branko D

It depends a lot on the road. I'm 72kg and ride on 23F / 25R GP5000s (which are a hair smaller than their older tires, or as they say - more true to size), latex inner tubes and a set of LB wheels with 17,9mm internal width. For reasonably nice to good roads, I go with about 100 to 110 psi, both front and rear, 110 actually seems optimal for going faster on good roads, and research seems to suggest so. At 110 psi, I do have to be a bit more careful cornering on uneven / broken up roads, though, because the bike bounces up and down on them a bit, but, conversely, the handling is great on smooth roads. If I go over a series of big speed bumps near my house at full speed at 110 psi, my bidons fly out, though. Going a bit lower, 100 psi is a nice compromise if I'm going to go over mixed quality roads and still goes fast and handles nicely - perhaps it's a bit less ideal if I have to climb something really steep when I stand on the pedals, where the rear tire doesn't feel all that solid because a lot of weight gets shifted on the rear.

For bad to broken up roads, less. I have a collection of local backroad training climbs some ten minutes of riding away from where I live, and here I tend to use less pressure still, around 90 psi typically. I've ridden with as little as 80 psi on the worst of them where the roads are a collection of patches and potholes and it really takes the bite out of them, but below some 95 psi the tires have a bit of give when you put your weight on them - it can be a bit disconcerting while cornering, and standing on the pedals the rear feels mushy and somehow draggy. Not ideal for going fast on a nice road.

When you consider that in the old days they rode 23s on narrower rims (which reduce overall tire width and air volume, needing more pressure to compensate, since a larger volume tire is a stiffer spring at the same pressure), maybe the 120 psi pressure they used then wasn't actually far off from ideal when the roads are good.

njkayaker

The pressure to use depends on the load (how heavy you and the bikes are) and the wide the tires are.

People used to use just 120 because that was the number printed on the tire (as the maximum) and shops were abme to tell everybody one thing. It was just easy.

Many people were also using narrower tires. But, they’d use less with wider tires.

znomit

As long as it feels faster that's all thats important.

guadzilla

I know you are being flippant, but in the interest of clarifying my earlier post: I do understand the distinction between something "feeling" faster and actually being faster (and that often, wheels that feel faster are actually not so). In this case, I dont mean "feel" as in "sensations". I meant that based on my expectations of speed given power and wind (which, I readily admit, is not at all scientifically valid or precise).

genejockey 

Ah, but the REAL question is, Is everyone going a lot SLOWER now?

genejockey 

I actually AM faster since lowering the pressure in my tires. I keep scoring PRs on Strava segments I've ridden dozens to >100 times. OTOH, I lost 25 lbd and am riding a whole lot more, so as a card-carrying Scientist*, I can't really say the lower pressures made me faster.

*(Well, it USED TO say "Scientist" on my cards, till I got promoted)

Drew Eckhardt 

With a power meter you can use RChung 's virtual elevation method to determine CdA and Crr.

downtube42

Aren't you a little bit envious of people who know things with such certainty? Education is such a killjoy sometimes.

genejockey 

No, because they don't actually KNOW the things they think they know. They just BELIEVE them.

Bah Humbug

Charlatans. I can point you at the good stuff.

znomit

It's 2020, you don't need to back it up with data. If you identify as a faster rider we accept that.