MrCjolsen

How much difference does pumping my tires up from 110 to 120 (max) psi make?
Can higher pressure actually increase rolling resistance, especially on rougher roads?

It seems like I had a marked increase in vibration and little or no (or perhaps a negative change) in rolling resistance.

Is this a correct assumption?

NealH

There is not going to be any difference in rolling resistance. There have been several studies performed on this in the past and, the conclusion was that the higher pressure did not decrease rolling resistance. The differences were insignificant. You should always ride the pressure that you are comfortable with. I ride 90# because above this figure the ride noticeably degrades. If you have found that lower pressures cause flats then you need to change tires. I am 200# and ride Conti Force/Attacks and, don't have flats.

MrCjolsen

I never got any flats at 100 or 110. I just thought I would go faster at 120. But I thought wrong. And the vibration was much more noticable on bad roads.

I ride conti gatorskins, so flats shouldn't be an issue.

skydive69

I'd love to see the physics explanation of that one!

Brett 12

Rolling resitance will decrease with increases in pressure. However, the improvements in rolling resistance begin to plateau at a certain point. The point at which it plateaus is related to the load on the tire.

THe higher the load on the tire, the higher the pressure required to reach the plateau. In other words a 130 lb rider is not going to need nearly as much pressure as a 210 lb rider. In fact, the 210 lb rider needs roughly 50% more pressure to achieve the same size contact patch.

Size of the contact patch determines tire sidewall deflection and thus influences rolling resistence.

P.S. You don't need that much pressure in the front. You should consider dropping front pressure to enhance ride quality.

Climbing is about power to weight ratio, but damn it is so much nicer not having to fight the extra rolling resistance when you put a heavier load on the rear tire (more power goes to fight gravity than goes to fight tire deflection)

I never realized how nice it was to have high pressure in the rear tire till I got my Tufos. 180 psi in the rear tire and I could rocket up hills so much easier.

2Rodies

I ride Vredesteins TriComps which have a max pres of 145psi. On smooth roads in good weather conditions I'll run 145psi. On bad roads or if it has been raining I'll run 120-130psi. The tires roll better at 145psi than they do at 120psi. I've used four high end clinchers (Michellin ProRace/Hutchison Carbon Comps/Conti Attack-Force/Vreds TriComps) this year and found the Vreds to be the best rolling tire and second best against cuts/flats.

skydive69

How do you measure "best" in regards to rolling?

keevohn

In contradiction to many of the above statements, a Zipp rep. wrote an article for Velonews a while back:

https://v1.velonews.com/tech/report/articles/7507.0.html

Essentially, he's saying that tires have "...optimal rolling resistance between 105 and 125psi depending on load and road surface condition."

This is because tires "...increase in rr at higher pressures due to the tread rubber beginning to fail in shear as it locally deforms to meet the contour of the road imperfections when the casing is too rigid."

He goes on to mention about comfort: "It may be that by increasing tire pressure by 20-25 psi, you feel faster as your tires are transfering more of the high frequency vibration to your body (you're feeling a higher frequency 'faster' vibrations' so it really does 'feel' faster) but are actually expending more energy to do it, while simultaneously wearing out the tires faster and inducing fatigue."

Believe what you want, I'm just relaying a counter viewpoint from a seemingly reliable source.

skydive69

Interesting information. That "feeling" of being faster is analgous to those idiots who put straight pipes on their vehicles with no further tuning. They believe that because they are noiser they are making more power when in fact the dyno will illustrate quite graphically that they are making less power.

Machka 

Increasing tire pressure will reduce rolling resistance.

But that minimal a difference in tire pressure shouldn't make much difference in speed - it's not like you'll suddenly be travelling 5 km/h faster!!

Yes, of course the vibration will be much more noticable - your tires are harder.

And also don't blindly assume that a particular brand of tires is flat-proof. I've heard of people getting flats with every brand ... some quite to their surprise.

I prefer to ride with my tires slightly flatter (95-105 psi) ... it's more comfortable.

Brett 12

As the pressure drops the contact patch gets longer I thought.........because at lower pressure the contact patch has to be bigger. Since there is no way for it to get wider the only way to increase size is to go longer.

One reason why wider tires may have less rolling resistance is becasue a short and wide contact patch has less rolling resistance than a narrow long one. This is due to greater sidewall deflection with long narrow contact patch.

Weight of the rider vs. tire presssure is the key concept to understand here.

BTW, climbing is the place where rolling resistance hurts you the most. On flat ground rolling resistance is overshadowed by aerodynamic drag.

steveknight

on my bent it came with tires that could only take 35 PSI. I repaced them with armadillo's at 100 PSI. I ahve a hill I coast down right in front of my house I gained 2 MPH on the coast changing the PSI. now this what you need to smooth out those tight tires https://www.pantourhub.com/products.html#wheel I went from 25PSI in the front to 100 PSI and it feels even better the nthe 25 PSI.

terrymorse 

When climbing, rolling resistance is overshadowed by the work required to lift the bike plus rider.

You might find these rolling resistance graphs interesting.

alanbikehouston

The graphs are educational, because they illustrate the point that one tire design can have LOWER rolling resistance at 85 PSI than another model has at 115 PSI. A few years ago, some tire companies would include such graphs in their advertising. Recently, ads seem rather short of any "facts".

Brett 12

OK, but you are assuming the the load hasn't exceeded the tire's pressure.

Inflating to high pressure will not result in a "V" if pressure is still trying to catch up with load.

Like I said before the key concept is rider weight vs. tire pressure, Most these tires are designed for 160 lb rider so pressures need to be adjusted up or down. Likewise, the front tire pressure should always be lower than the rear if tires are same size.

Stretch

All these V's and U's are only half of the story. The contact patch is not a V or U shape, it is an area. Not only width, but also length. (someone else already hinted at this)

Brett 12

Yeah that why wider tires sometimes have lower rolling resistance because at the same pressure the wider tire's contact patch will be shorter and wider vs. longer and narrow for the skinny tire. Wider and shorter contact patchs beat long/narrow ones if they are the same size in total area.

ajst2duk

Just a "seat of the pants" view from this newboy - I was pretty fussy about keeping my tyres up around 120psi (vittoria corsa's & conti GT3000's) thinking that I wanted the bike to be as fast as it possibly could be. A couple of weekends ago I was lazy, went for a ride after coming back from a two week holiday, and didn't pump up my tyres. The ride was smoother, but also to my surprise quicker than usual. I have tried varying pressures since and discovered that 100psi is about the optimum for me 195lbs 'Dale R600 Conti GT3000's. I will no longer blindly pump tyres up to the max reccomended pressure witout first experimenting.

TimB

At last someone who is beginning to understand Rolling Resistance
Lowest rolling restance for any tyre is that pressure at which it can be run with the contact patch as designed. The weight on the tyre is therefore important.
Bigger riders will use higher pressure to achieve this and smaller riders a lower one.

The optimujm pressure is the LOWEST pressure at which the contact patch is optimised for shape and size.

Long narrow contact patches = high rolling resistance
short round ones = low rolling resistance

ewitz

When the tire is at a lower pressure it is able to deform to aborb irregularities in the surface of the road. At higher pressures these irregularities are not absorbed by the tire and cause the bike to hop and skip more. This hopping and skipping is a source of power loss since the energy required is coming from somewhere. Unless the road you are riding has a glass like finish the lower pressure is actually more energy efficient. Contrary to what I have always felt, yet true. That being said I still run at higher pressure.

ngweimin

Does the discussion so far cover common tire sizes or just 700x23C in particular. I'm running Vittoria Diamante Pros in 700x20c and I was inflating my rear to 140psi and front to 130psi. The result was a pretty harsh ride which no doubt felt "fast" but I'm not sure if it has done any real good. I'm interested to know if running 700x20C at about 110psi would maximize both rolling resistance and comfort?

Doid23

This seems intuitive, so why don't tire manufacturers provide recommended pressure by weight so that riders can determine the pressure that optimizes the contact patch? Is their a general chart out there that does something like that (understanding that tires from different companies will have different optimization pressures)?

Brett 12

When you say higher pressure.......you mean over inflated. Higher pressure may not be overinflated if rider is heavier (key concept to realize).

If say the ideal contact patch (to optimize rolling resistance and comfort) is one square inch for a particular tire design.

A 100 pound load would require 100 psi (pounds per square inch)=1 square inch contact patch

A 80 pound load would require 80 psi (pounds per square inch)= 1 square inch contact patch

A 120 pound load would require 120 psi (pounds per square inch)= 1 square inch contact patch

Notice that all three inflation pressure gives exactly the same size contact patch.

So all this nonsense about some particular psi being the most effective pressure for everyone is nonsense...straight nonsense.

Brett 12

narrow tires require higher pressure to work. The hard ride is what you put up to use the lightweight narrow tires.

Bontrager

When you sit on your bike, the pressure in your tire increases. 100 PSI unloaded != 100 PSI with a 150 lb rider.