smd4

Why would I want to feel very little? I want to feel as much as possible!

mdarnton

I'm skeptical of ALL of the tire info I read. Riding sewups I never used a gauge, then when I recently switched to a bike with tubes I started following the various charts, all of which put me under max by quite a bit. I read all of the advice, followed it, felt that my bike was really draggy. One day I pumped up to 100% and dropped 5 minutes off my daily half-hour commute. Immediately and consistently, not a one-up. It's a little stiff, but I came from sewups to 35mm tires, so c'mon, how bad is it really? Screw the charts, screw the people who are saying my tires aren't in contact a lot of the time and therefore I'm losing and don't know it: the clock don't lie, and I'm less beat when I get there.

shelbyfv

Enjoying the way a bike feels is as good a reason as any to choose a pressure. We don't all need optimal speed, grip, tire life or whatever factors the mavens consider when coming up with charts. It's smart to start with the expert advice, then run with the subjective as far as you like.

smd4

amen!

smd4

I’m not the one who brought speed into the discussion. I merely addressed the subject by the guy who did.

Iride01 

Some people think all roads are chip seal with 3/4" or bigger aggregate. In such conditions and even with 1/2" size aggregate, I do lower my tire pressure. However most of the roads around here are made with very much finer aggregate, not much bigger than just sand, in the top layer. So I too have found that higher tire pressure than the "never wrong" tire pressure calculators that don't take everything into account, lets me be ever so slightly faster with less strain on my leg muscles.

Sy Reene

One reason I like the Silca pressure calculator, which allows you to choose the road surface. Though I still add 5psi to whatever it tells me :-)

elcruxio

Why don't you ride an aero aluminum frame with high profile carbon rims then? That would maximize the road feel to the nth power.

elcruxio

But you did, by claiming your tires weren't slow. Yet if you ride them hard as solid rubber tires, they are going to be slow.

JohnDThompson 

No; the reason solid tires are slow is because of hysteresis losses in the tire material. A pneumatic tire has far less solid material, and correspondingly lower hysteresis losses. A high pressure can lower rolling resistance, but depending on the road surface, at the expense of comfort and control.

Russ Roth

Not true any more, wider, low profile tires use higher pressures. The wife's minivan with 17" rims uses 40psi, tires say 44psi but the door panel says different. Mine minivan (same make/model) with 16" wheels uses 35psi, 3psi below the tire recommendation. While my miata's tires say max of 50psi on 17" wheels, car says 40, but the usual driver recommendation is 30psi since the car weights 2300lbs and literally bounces around the road at higher, and screw tread life, its all about the handling.

at 280lbs even I don't run my tires that high anymore, 35/30, all about tires conforming to the surface. Interesting to me is that I used to run 26x1.95 at 50psi in my 20s and dented so many wheels, had lousy times in races and really poor handling ability. Didn't mtb in my 30s except on the cross bike from time to time. Picked up a modern 29er running 2.25 and not only do I have faster times but I ride much more technical terrain and have yet to dent a rim. I find MTBing much more enjoyable now.

Kontact 

The 2020 and 2023 Mazda Miata manual says 29 psi. What do you mean "the car says 40?"

The pressure you use is the one on the door panel and in the manual. Not the one on the tire, or some fictional third pressure you've invented between the two.

As with bikes, tire pressure is set in proportion to the weight on the axle, adjusted for tire volume. So a 4000lbs minivan will have a higher psi than a sports car for the same 225R17 tire size, just as a heavy rider will use a higher air pressure in his 700x19c tires than a lighter rider. Larger volume tires require lower pressures to create the same pneumatic 'pre-load' as a smaller tire.

Beyond that, I don't have a clue what you are talking about. But I suggest you read your car manual.

mitchmellow62

One of my conundrums: I feel there is conflicting evidence for lower tire pressures being beneficial. These two sources seem to indicate that higher pressures create less rolling resistance.
https://www.velonews.com/gear/resist...ce/?scope=anon
https://www.bicyclerollingresistance...-tr-comparison
Additionally, in all of Bicycle Roiling Resistance's road tire tests resistance is reduced with increasing pressure. I'm not a subscriber and some of the results are shielded but that's true from their extra high to ultra high pressure categories.

Thoughts?

Kontact 

Rolling resistance is lower on smooth surfaces at higher pressure.

Bikes don't ride on perfectly smooth surfaces. Recommended real-world pressures are designed to give the tire about 15% deflection when loaded, which is enough spring to absorb minor bumps and not force the entire suspensionless road bike have to go up and over every pebble, and subsequently decelerate from having to do so.

That's just the rolling resistance aspect, ignoring braking and cornering traction.

Riding on an Olympic track? By all means, increase your pressure over road recommendations.

base2 

True. And solid freight train rolling stock has the lowest rolling resistance of all. The whole discussion is about finding the balance between competing nominals.

Maybe SMD has unusually high quality, clean streets. Like those of a velodrome or the surface of a swimming pool. In which case, he might be on to something. For the rest of us, the balance between tire load, width (height, really) and pressure is a moving target based on ever changing use cases.

mitchmellow62

I understand what both of you are saying. I've read about the 15% deflection and the idea that the tire conforms to the irregularities in the road rather than lifting the entire load. Yet, all referenced tests were on a diamond plate surface which is not smooth. In fact, the Outside article chose it to simulate asphalt roads. In these controlled studies on a irregular surface, higher pressure was less resistance. I need to dig back to some of the counter articles to study their methodology.

I'm not really sure why I care. I don't even attempt to ride fast anymore and at my speeds the effect is probably so small it is negligible on my shorter rides.

Kontact 

The diamond plate simulates the road, but does the wheel holder simulate the bicycle? Or is the wheel held mechanically in rigid contact with the plate?

elcruxio

This article explains it pretty well
https://silca.cc/blogs/silca/part-4b...-and-impedance

In short: the drum doesn't simulate the rider and so the drum will keep showing lower rolling resistance at higher pressures even with an uneven drum surface.

Kontact 

That breaks it down clearly. Thanks!

smd4

My Cinelli Super Corsa works just fine for me, thanks.

smd4

Maybe you don't understand how this works. In post 38 Kontact said that my tires were slow. He brought up the concept of speed. I responded--as I am allowed, and how discussion goes--in post 39, by simply stating they weren't slow--and that I also liked the road feel. I also provided a quote to back up that assertion, which stated that narrow tires--which I use--aren't "slow."

And again--anyone who thinks high-pressure pneumatic tires feel anything even remotely the same as solid tires must have no experience with either.

smd4

I'm happy for you and your low pressures. I don't plan on owning a mountain bike anytime soon.

elcruxio

If you're running your tires at 140psi, the only place they're not going to be slow, is at a parquet velodrome. The tires at 140psi are likely slower than if they were pumped to 60psi. And that's on a brand spanking new baby bottom smooth tarmac. If the road surface gets any rougher, well, you'd probably be better off at 40psi. Of course that's all conjecture as only you know how much your bike + rider combination weighs, what's the weight distribution etc.

All that being said, you'd likely be much faster below 100psi. But as you prefer to be slow, I'm sure that doesn't matter to you.

Chuck M 

I wonder what would happen if everyone on a group ride discussed tire pressure and chain lube before starting out.

Kontact 

There would be no bike forums.