Contradicting tire pressure

[novetan]

Currently am using Vittoria Zaffiro tire. Yesterday I chanced upon a Vittoria tire pressure chart from a bike shop and then only I realized basing on my weight of 65kg, the pressure shld be bet 90 to 95 psi. But the imprint stated on the tire itself mentioned bet 100 to 120 psi. I still have a new box of the same tire and the instruction so clearly stated “never allow the pressure to be less or more than the indicated pressure”. For my case is already less.

So what is your advise. Shld I pump to the min. 100psi or follow the chart which is less than 100 psi.

 

[daveryanwyoming]

The imprint on the side of the tire refers to maximum tire pressure for safety reasons, not ideal tire pressure for rolling resistance and comfort reasons. It is best to not exceed the maximum tire pressure, particularly if you're going to do things like ride down long technical descents with a lot of braking on hot days as that maximum pressure is intended to avoid things like tires blowing off the clincher rim due to excessive pressure.

Technically rolling resistance on smooth surfaces continues to decrease as you increase tire pressure. But on real world roads with irregularities you reach a point where additional pressure actually slows you down as the energy of all the micro-deflections caused by road roughness is no longer returned to the road and is instead transmitted up the frame and fork into your body. So it's a double whammy, you lose some energy efficiency (go slower for the same effort) and you feel all the road vibrations and get tired out and are less comfortable. Tires pumped up excessively hard also don't corner as well with their reduced contact patch area, especially in wet conditions.

So go with the lower tire pressure recommendations based on weight at least as a starting point. You can go up or down a bit from there but tune into comfort and road feel and add or subtract a bit based on what you learn. One simple rule of thumb is to do some test rides starting from the low end of the recommended pressure and increase a bit for each test until you find the point where you feel the road buzz and micro-vibrations at speed. IOW, find the point where the tires 'feel fast' then let out a bit of air to the point where they actually ARE fast and are more comfortable as well.

Also if you're running wide clincher rims like the newer 23mm wide rims (HED C2, Zipp Firecrest, Kinlin XC-279, Velocity A23, Boyd Vitesse, Latest Neuvation wide clinchers, etc.) then drop the pressure further from what the charts recommend. HED suggests at least another 11% drop in pressure for their 23mm wide C2 rims. FWIW I ran tires on 19mm rims up at 115 to 120 psi for years but run tires on my HED C2 rims at ~95 psi on dry roads and ~85-90 psi for fast racing in the rain. It felt funny at first to run such low pressures but the tires roll fast, corner really nicely and don't pinch flat at those pressures on the wide rims.

-Dave

 

[novetan]

Originally Posted by daveryanwyoming .

The imprint on the side of the tire refers to maximum tire pressure for safety reasons, not ideal tire pressure for rolling resistance and comfort reasons. It is best to not exceed the maximum tire pressure, particularly if you're going to do things like ride down long technical descents with a lot of braking on hot days as that maximum pressure is intended to avoid things like tires blowing off the clincher rim due to excessive pressure.

Technically rolling resistance on smooth surfaces continues to decrease as you increase tire pressure. But on real world roads with irregularities you reach a point where additional pressure actually slows you down as the energy of all the micro-deflections caused by road roughness is no longer returned to the road and is instead transmitted up the frame and fork into your body. So it's a double whammy, you lose some energy efficiency (go slower for the same effort) and you feel all the road vibrations and get tired out and are less comfortable. Tires pumped up excessively hard also don't corner as well with their reduced contact patch area, especially in wet conditions.

So go with the lower tire pressure recommendations based on weight at least as a starting point. You can go up or down a bit from there but tune into comfort and road feel and add or subtract a bit based on what you learn. One simple rule of thumb is to do some test rides starting from the low end of the recommended pressure and increase a bit for each test until you find the point where you feel the road buzz and micro-vibrations at speed. IOW, find the point where the tires 'feel fast' then let out a bit of air to the point where they actually ARE fast and are more comfortable as well.

Also if you're running wide clincher rims like the newer 23mm wide rims (HED C2, Zipp Firecrest, Kinlin XC-279, Velocity A23, Boyd Vitesse, Latest Neuvation wide clinchers, etc.) then drop the pressure further from what the charts recommend. HED suggests at least another 11% drop in pressure for their 23mm wide C2 rims. FWIW I ran tires on 19mm rims up at 115 to 120 psi for years but run tires on my HED C2 rims at ~95 psi on dry roads and ~85-90 psi for fast racing in the rain. It felt funny at first to run such low pressures but the tires roll fast, corner really nicely and don't pinch flat at those pressures on the wide rims.

-Dave

Hey, tks so much Dave for the detail explanation.

 

[mpre53]

How wide are your tires? 23 mm? 25 mm? Wider?

Regardless, at your weight, you should be fine at 90 psi, even on 23 mm.

 

[dhk2]

That Vittoria table looks good to me. I like that it recommends 5 psi higher pressure for the rear tire, as well as different pressures for the different tires they market. Last year I was running the Diamante Pro Lites, and found they needed more pressure to feel closer to my usual GP4000s. At 200 lbs, I use 100F/110R in the Conti's, but pumped the Diamante Pro Lites up to 110F/120R. Even with more pressure, the Diamante tires felt softer, with a slower steering response than the GP4000s. My guess is that the thinner casing and softer compound rubber made a difference in the ride feel and handling response.

The sidewall on the Diamante Pro Lite said Min Pressure 130 psi, Max 160, which seems way over the top. I used the 110/120 psi in them and enjoyed the ride. Being thin and lightweight race tires, they didn't last long and picked up cuts in the rubber, but that's to be expected.

 

[jaretj]

I'm near your weight...slightly lower

I've run 95 psig many times but for training my roads have some holes and I like to run 105 to keep from pinch flatting.

If you are in an area that has pretty good roads 95 will most likely be a bit faster and more comfortable than 105+

jaretj

 

[CAMPYBOB]

90 to 110 PSI should be fine, depending on road conditions and ride quality desired.