Author Topic: Tire pressure  (Read 4611 times)

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Offline rwinot25

Tire pressure
« on: July 31, 2019, 12:36:38 pm »
I wonder what tire pressure others run when they are on tour. I am about to replace the tires on my Kona Sutra. I am going to install Schwalbe Marathon Plus 700c × 38. The bike loaded is 70 lbs. I weigh 170 lbs. Do you run high pressure (75-85 psi) for less rolling resistance, or lower pressure (60-65 lbs) for comfort? Does tire pressure affect rolling resistance that much? I know it effects comfort levels.

Offline jsieber

Re: Tire pressure
« Reply #1 on: July 31, 2019, 02:38:21 pm »
Recent studies have found that low pressures do not seem to add resistance. This article by Jan Heine is a good read on the subject.

https://www.adventurecycling.org/sites/default/assets/resources/20150801_MechAdvTirePressire_Heine.pdf

Offline driftlessregion

Re: Tire pressure
« Reply #2 on: July 31, 2019, 02:57:21 pm »

Offline Pat Lamb

Re: Tire pressure
« Reply #3 on: July 31, 2019, 05:16:14 pm »
Note that Heine's findings only apply to flexible tires.  Your typical Vittoria Randonneur or Continental Gatorskin are pretty stiff, and his early experiments showed extra resistance with those tires, and especially when run 10-20 psi below the labeled maximum pressure.

I'd say it takes some experimentation to find the best pressure.  If the O.P. is running Marathon Plus, there shouldn't be much worry about flats.  As heavy and stiff as those tires are, though, I'd suggest starting at the max label pressure.  Ride them a couple days without pumping them up, see if they feel any better, and then check the pressure (they'll probably drop 5-10 psi).  Repeat until you feel the tire is slowing you down (even more than at maximum pressure), or the ride starts feeling squirrely when climbing, accelerating, or banking into high speed downhill turns; then pump them up 10 psi, make a note of the pressure, and try to maintain that pressure for the rest of your tour.

And think about finding post offices in the first few days to mail some of the luggage home.

Offline staehpj1

Re: Tire pressure
« Reply #4 on: July 31, 2019, 05:18:11 pm »
In addition to the load, IME, it also depends on how smooth the surface is.  On a really smooth new surface higher pressures roll real well.  With chip seal a little lower pressure rolls better both for ride and rolling resistance.  How big the gravel in the chip seal is will vary how much that is true.

Offline driftlessregion

Re: Tire pressure
« Reply #5 on: July 31, 2019, 05:34:55 pm »
On my touring bike I ride Gatorskins 32 mm. They are rated to a max of 94 psi. I weigh 195# and even loaded touring would never run more than 80 psi. I want more rubber on the road through deflection and even at 80 psi the ride is harsh.

Offline John Nelson

Re: Tire pressure
« Reply #6 on: July 31, 2019, 05:56:30 pm »
I typically run near the maximum. E.g., if the tire says that the minimum pressure is 65 psi, and the maximum pressure is 85 psi, I'll probably put in 80 psi.

There are a lot of reasons to go high and a lot of reasons to go low.

Contradicting what Jan says, Schwalbe says this: "The higher the inflation pressure the lower the rolling resistance of the tire. The susceptibility to punctures is also lower with high pressure. If the inflation pressure is continuously too low, premature tirewear is the result. Cracking of the sidewall is the typical consequence. Abrasion is also unnecessarily high." Most riders agree with Schwalbe (right or wrong) and firmly believe that higher pressure results in less rolling resistance (what Jan calls the "placebo effect").

One reason I start near the high end is so that I don't have to pump them up so often. If I put in 80 psi, it'll be more days before the pressure drops below the 65 psi minimum.

But lower pressure (in my opinion and not based on any testing) transmits less shock to the spokes, and thus should make it less likely to break spokes. And in my experience, I typically have most tire and rim failures shortly after pumping up my tires. That's the reason I don't go all the way up to the maximum.

Offline BikePacker

Re: Tire pressure
« Reply #7 on: July 31, 2019, 08:52:14 pm »
I spent a number of years running on maximum specified pressure (fully loaded touring on mostly pavement; 26"x about 1.8").
I concurrently had what seemed to me to be an atypically high number of inner tube failures. 
After a couple of years of this I started using only the highest quality inner tubes that I could buy .... yet, to my further consternation, that did not change the frequency of my tube failures.
It was not till I dropped the pressure to about 80-90% of the maximum specified pressure that I quit have tube failures.

Offline HobbesOnTour

Re: Tire pressure
« Reply #8 on: August 01, 2019, 03:31:07 am »
I'm far from an expert on tyre pressures but I do recall reading of a loaded tourer being advised not to fill his tyres to maximum as this added extra stress to the rim,increasing the chance of splitting the rim.

Sorry, I can't supply a link - I think it was on CGOAB. The idea is worth considering, any way.

Personally, I choose comfort over speed and tend to believe that the middle of the road approach works well to most aspects of cycle touring - except for road positioning  ;D



Offline BikePacker

Re: Tire pressure
« Reply #9 on: August 01, 2019, 07:30:19 am »
I'm far from an expert on tyre pressures but I do recall reading of a loaded tourer being advised not to fill his tyres to maximum as this added extra stress to the rim, increasing the chance of splitting the rim.
Where were you when i needed you? :o .... Above and beyond my previously posted tube failures, i eventually also experienced your above mentioned rim failure, to boot.

Offline misterflask

Re: Tire pressure
« Reply #10 on: September 08, 2019, 09:39:25 pm »
I follow Jan's writing, but defer to https://www.bicyclerollingresistance.com on all tire matters.  I think they pretty consistently find higher pressure correlates to lower rolling resistance. 
I run about 75psi in 700x35s.  Did not put a lot of thought in arriving at that number.

Offline misterflask

Re: Tire pressure
« Reply #11 on: September 09, 2019, 06:08:41 am »
This is also worth reading: https://www.bicyclerollingresistance.com/specials/grand-prix-5000-comparison
The TL;DR is that while wider tires have lower resistance than narrow at a given pressure, we are not likely to run our 35mm tires at the same pressure as our 25mms as they would run rock-hard.  Adjusted for the likely operating pressures, the narrow tires still had an edge. 

Offline DarrenBnYYC

Re: Tire pressure
« Reply #12 on: September 11, 2019, 10:13:23 pm »
My take is that while the experts quibble about which tire inflation pressure achieves the highest performance, the average commuter or touring cyclists probably can't even tell the difference because the differences are so small. However, a small drop in tire pressure often makes a very significant difference in comfort.

I don't race bikes, so I am more than happy to take an insignificant hit in performance to achieve greater comfort on the road.

Offline staehpj1

Re: Tire pressure
« Reply #13 on: September 12, 2019, 07:44:32 am »
My take is that while the experts quibble about which tire inflation pressure achieves the highest performance, the average commuter or touring cyclists probably can't even tell the difference because the differences are so small. However, a small drop in tire pressure often makes a very significant difference in comfort.

I don't race bikes, so I am more than happy to take an insignificant hit in performance to achieve greater comfort on the road.
I will say that when I was servicing the bikes of my companions on the TA they definitely complained when their pressures dropped even a little a bit.  They said they were working harder.  I think it is possible they had incorrectly learned to associate the feeling high pressure with performance, but they definitely felt like they were working harder when their tires weren't at the high end of the pressure range.

I find that I like my pressures very high when the road surface is smooth and lower when there is something like chip seal.  The coarser the chip seal the lower the pressure at least to a point.  It seems to benefit both comfort and rolling resistant in that case.

Offline froze

Re: Tire pressure
« Reply #14 on: September 27, 2019, 07:30:06 pm »
According to a inflation calculator you should be running 48 psi in the front and 58 rear, supposedly that's idea for traction and wear, but you do have up to a 5 psi above and below depending on whether or not you like a firmer or softer ride.