Sy Reene

Here's a better chart that emulates a real road a bit better, taken from this article.
https://blog.silca.cc/part-4b-rollin...-and-impedance

Think of the blue line being the rollingresitance.com result; Green line = excellent smooth new road; yellowline = typical not great roads.

ZHVelo

It feels much better. I like it hard for some reason, so front is back to 8 and rear just above that. Felt so much cleaner, smoother

But I have been reading a lot and will actually try to lower the pressure and see how that works. But I will keep the balance, with the rear slightly more than the front.

kenshireen

On the green line... how can RR be less at 120 than 100 yet the Watts are higher at 120 than 100. What am I missing here.. I thought the Watts were a measure of RR

Sy Reene

Read the linked blog article. Basically RR.com uses a steel roller that doesn't terribly well emulate a real road. Lots of little microbumps on a real road mean that once past a threshold PSI, overinflating is detrimental to your rolling resistance/speed.

jefnvk

No, its not. I've got a pressure gauge for my fat bike that reads to the quarter pound, and I don't have any issue with air loss when using it. As others have said, get one with a bleeder, pump a bit extra in, and let it out til its where you are at. I've got AccuGage, both for my fat bike and race car.

Or do what I do, and pump it up til it says something between 80-100 psi on the pump gauge, and call it good. Outside the fat bike, everything I have has a wide tolerance on tire pressure.

greatscott

It seems to me you're using too much PSI, if you like it that way then fine, but I think you're saying you use 25mm tires, with your weight of 140 psi plus 20 pounds for bike and stuff, your psi should be around 55 front and 85 rear. That's according to PSI calculators, there is some leeway there depending on roads, weather, and how you want the bike to ride, but the pressure the calc provides is for max tire wear, best cornering and braking traction.

Scan down to the middle (2nd) calculator: Bicycle tire pressure calculator

greatscott

I want to be you when I get older! Congrats for riding for so long.

WizardOfBoz

Agree with above: read the article. To answer one question, though, watts is a unit of power (energy per time) and the plot shows the power lost to rolling resistance AND impedance.

If roads were smooth as glass then impedance wouldn't come into play and you could ride on tires inflated to any pressure they could hold. But the tire deformation and vibration induced by rough surfaces takes up rolling energy, too. Think of it this way: you're riding along and hit a bumpy patch. You feel your bike vibrating as it goes over the bumps. Where is the vibrational energy coming from? That's right, your kinetic energy is being transformed into vibrational energy. High pressures are more efficient, apparently, at making this conversion. So as tire pressure rises, at some point the additonal vibrational energy loss (called impedance) becomes signficant.

What's so striking about this figure (Thanks very much for posting, Sy Reene) is that it confirms Jan Heine's point. For riding on real roads with bumps and such, the inflation has only minor impact over a very wide (60-110psi or so!) range. So, find a pressure that's comfortable for you and ride without too much concern for rolling resistance.

(Unless you ride a track bike on a very good velodrome- then, pump 'em up).

himespau 

I know this isn't the most accurate of explanations, but I always thought of part of the reason that overinflated tires results in increased rolling resistance as, if the tire is so hard that you're bouncing, you aren't able to maintain consistent contact with the ground, which results in 2 sources of lost power: (1) when a portion of your forward horizontal momentum gets converted to vertical displacement as you bounce upward, energy that would otherwise be used to push you forward is wasted, and (2) when you lose contact with the ground (or decrease your contact with it) as you bounce, the energy you are transferring to the pedals isn't further converted to speed because your tires aren't pushing against anything. Neither of these are actually causing resistance in the most traditional of senses in that they're not increasing friction and making it harder for the tire to roll but they're causing energy input to turn the wheels to be wasted and not directly converted to force pushing you in the forward horizontal vector, so they count as resistance.

Kapusta

The phenomenon of losing pressure when hooking up a guage happens will ALL gauges. When air moves into the gauge, pressure in the tire drops.

HOWEVER, how much it drops depends on a few things:

1- the volume of air in the pressure gauge (the bigger it is, the more pressure is lost in the tire.

2- The volume of the tire (the bigger the tire, the smaller percentage of air is lost)

3- The pressure in the tire - the greater the difference in the tire and atmospheric pressure, the more air needs to move into the gauge to equalize the pressure.

#2 and #3 go a long way to explaining why people may have a big issue with pressure dropping on a set of 23s pumped to 120psi, but with the same gauge could check the pressure a dozen times on a 4.8 fat tire pumped to 6 psi and not detect any change in pressure..

Reynolds 

A device that can be called gauge, gage or guage can't be reliable.

wle

allegedly, with presta, the escaping air is not from the tire, it is just the air in the pump hose (when using a pump with a gauge)

Road Fan

Back to the tire gauge and difficulty in removing some from the Presta valve - With the Meiser Accugage for Presta valves, I find it is very easy to apply the gauge and to remove it. It's much easier than the old Silca track pump head, and the dual head on my Cannondale track pump.

I don't really care about the accuracy, just ease of use. The Silca track pump matches the Meiser pretty well.

Road Fan

And for some designs the volume of air in the hose.

DaveSSS 

If a presta valve is filled with a pump that has a gauge, there will be no loss of pressure, when the hose is removed. The presta valve seals when the pressure on both sides of the seal is the same.

If a gauge is later used, the stem nut has to be loosened, something has to press down on the stem to allow air out and some small amount of air travels into the gauge, so a small amount of pressure may be lost, but it should be very little, if the gauges has a properly designed rubber seal around the stem.

Schrader valves are much more prone to losing pressure when a gauge is used.

Kapusta

Yes. The hose would be part of the gauge. Though I don’t know of many tire pressure gauges that use a hose, other than ones attached to a pump.

livedarklions

Who gauges the gaugers?

WinterCommuter

It’s called the observer effect. It’s quite profound with low volume/high pressure tires.

phillman5

I am not sure about joke, but part of the Heisenberg Uncertainty Principle is you can't measure a property of something without disturbing (or changing) it.

nhluhr

A Gatorskin at 80psi feels significantly stiffer to the thumb test than a GP5000 at 100psi.
I'm not saying you should be using a separate pressure gauge, but it's worth looking at your floor pump's gauge to at least get some consistency when you use it, especially if you have more than one bike or set of wheels with different tires.

Consider giving this a listen: https://cyclingtips.com/2016/08/cycl...and-pressures/
There is a strong tendency for you to *feel* like you are faster when your tires are pumped harder but aside from the increased vibration, there isn't really much to prove it and there are other factors at play such as the 'suspension losses' that they talk about in this podcast, but also the fact that tires wear faster when pumped harder (because you put more pressure on a narrower part of the tread), are more likely to get punctures (because the tread/casing can't deflect around the sharp object), etc.

Also, a recent GCN video tries to combine the effect of 'rolling resistance' and 'suspension losses' on a graph to understand how there might be a sweet spot:
https://www.youtube.com/watch?v=7dx_y0KVkj8

myisland

I test pressure with my fingers. When it softens I use a floor pump.

jjefferies

My motorcycle club held a wrenching session dealing with pressure gauges. The host provided a "CALIBRATED" pressure source and you could check your own gauges against it. I had four. None of them were within 5 lbs of the correct pressure. You could test at varying pressures to see. I just selected 35 lbs and then put the difference on a piece of tape on the gauge. Most of mine were indicating a higher pressure than what they were actually connected to, i.e. using them as they reported the pressure would result in underinflated tires. I don't know whether incorrect pressures are more of a concern on bicycles or motorcycles but in both cases it can be serious. Just an FYI.

halloleo

Interesting! Where do you got this info from? Has somebody done proper field experiments? I'm very curious!

freeranger

Here ya go-probably others, this is the one that I had prev.read: https://www.roadbikerider.com/the-ti...-jan-heine-d1/

halloleo

;-)