Elysium32

I have just bought a new 700C*32C tyre and it says 5.5-7.5 bars. I uset to do 6.5 bar in the previous 700C*38C tyre so I have decided to stick to that with the 32C tyre too, but what is the difference and how does it affect the tyre when I pump only 5.5 bars/or when I pump 7.5 bars into it?

With 6.5 it is not flat at all....it seems to work just fine. I only use it in the city at this stage and I am wondering if I am shortening the tyre's life or something.

UPDATE: I have had both my tyres changed for a schwalbe Marathon Original. 700*32CC. It says 4.0-6.5 bar. What shall I go for if I use my hybrid mainly to get to work and back home. I weight 80 kgs (177 pounds). My main goal is not to have my arse shaken into pieces as I ride some of the dodgy bike lanes in Barcelona.

rpenmanparker 

The larger the tire, the less pressure it needs to avoid pinch flats. The larger the tire, the more comfortable it will be at the minimum safe inflation pressure with regard to pinch flats. The larger the tire the less comfortable it will be at exactly the same pressure than a smaller tire. The larger the tire, the less rolling resistance it will have at the same pressure as a smaller tire. Heavier riders need more pressure to avoid pinch flats in any size tire than lighter riders. Front wheels need less inflation to avoid pinch flats than rear tires, because rider weight is unevenly distributed.

Within a given tire size it is desirable to have lower pressure for comfort, while avoiding pinch flats and still minimizing rolling resistance. Hence the range of suggested inflation pressures. The top of the range is for blow-off safety. The bottom is for pinch flat avoidance. You are likely to be happiest near the bottom. Actually, unless you are very heavy, you can probably go WAY below 5.5 bar. Those numbers look very high.

Elysium32

Thanks a lot for your reply.

So, in the city....I am okay with the lowest range to avoid snake bites from curbs?

I am about 20 pounds lighter than the top weight limit of the wheel. So, I guess at low pressures with my weight the sides of the tyres wont get worn out. Right?

Doesnt also the lower end of the pressure mean that I can easily lose control over the bicycle? Or that's the case with lower pressure than the lowest recommended pressure?

I am so new to this topic and it seems to be pretty complicated.

znomit

You want to lower the pressure as much as you can without getting pinch flats.
Heres a good place to start:

Elysium32

Thanks a lot for the chart. Do you happen to have the same with 700*35 and 700*38 too?

Willbird

I'm riding 700x25 right now at 178lbs, I run both at 90 and have had zero issues , they ride a lot nicer at 90 than at 125 (sidewall maximum) 90 is under sidewall minimum, due to not being super attentive at first I have ridden them to 80 with zero issues . I'm thinking the "sidewall minimum" deal on the chart is just butt covering liability wise ? The tires I am presenting wearing out are specialized turbo pro. Next in line are roubix pro and turbo pro 700x28...the roubix pro they call a 25/28 I think. Grabbed them up on the 2 for 40 sale. I have put 800 miles on them at 90...I do not run over curbs and stuff like that though :-). Get a little rough stuff that makes me picture cobbles, and a few pavement seams. Rear wheel is 32 spoke bhs xc-279 rim with dlite spokes if that matters.

blacknbluebikes 

Vittoria has an interesting app out there named iTire Pressure that calculates a suggested psi/bar for their tires, road or off-road. The intro clearly states that the app suggests a starting point, while ideal pressures are discovered via personal experience. Notably, the suggestions from the app are not really aligned with the chart above.

Factors in the road algo are: casing (material and TPI), clincher v. tubular, total weight (bike&rider), road conditions.

Example road calc: nylon/220, clincher, 80kg, dry/smooth => front 7.6 bar/110psi, rear 8 bar/115psi
another road calc: nylon/110, clincher, 80kg, wet/rough => front 6.9 bar/10psi, rear 7.3 bar 105psi.

Factors in the off-road algo are: tire version(tube,tnt,tubular), size, total weight, terrain.

Example off-road calc: inner tube, 26x2.25, 85kg, mixed (hardpack/loose) => front 2.3bar/34psi, rear 2.5bar/37psi.

One might note that the off-road calc does use tire width but the road calc does not.

Basically, tires can be expected to function properly between the boundaries on the sidewall, and the rider finds a preferred trade-off. Smoother ride versus reduced resistance. Tires are in a constant process of deforming and reforming upon contact. Pressure determines the amount of deformation and the size of the contact patch. (Informative article regarding rolling resistance in automotive tires)

Nothing miraculous with the Vittoria app, but it's neat and worth the time if you like exploring those types of things. Of course, most folks know after a few bazillion miles just what pressures what we like for ourselves and can feel it with a thumb press.

Willbird

I found an ap somewhere and it told me I should be at like 105, but 90 works great, and rides nicer :-).

The stock wheels on my bike are a lot like the BHS XC-279 really, it is a 23mm wide rim...and that may play into the minimum pressure too ?? Had another look at sidewalls, it actually says 115/125 psi.

The ap gave me 120 front 125 rear.

bikemig 

I'm curious, where did this chart come from?

znomit

The chart is from Michelin.
Personally at 73kg I run about 85-90 and almost never get pinch flats.

blacknbluebikes 

Heck, a flat is still just a $5 problem. As long as you're not descending at 35mph, anyway...