FMadridRN

I'm using the tube from the 35. Someone from the LBS said I could. Just not sure if I should use same PSi as the 35 for the 28.

northernlights

for tire pressure the tube doesn't matter. it depends on the tire.

FMadridRN

Ok thanks! I just saaw that on the side of the tire. 120 whew that's a lot of pumping.

Pendergast

That's probably the maximum pressure rating of the tire. My 28mm tires have a maximum pressure of 116, but the recommended pressure is 80.

SuperDave

Depends on total weight, to an extent. I had no problems for years, running my 28's at 65 rear/60 front, and 10psi less wouldn't have hurt. But that's at an all-up weight of about 170lb, me and the bike.

Igo

I went from 32 to 28s. My 32s called for 65 psi max and my 28s call for 105 psi. I like the sports car feel and the lesser roll resistance of the high preasure 28s so I run them max fill. Great handling bike.

GeorgeBMac

I agree that the pressure relates to the tire, not the tube. But the tire should have a range of recommended pressures like: 100 - 120 psi

I keep mine halfway between the two recommended pressures (for my Bontrager Race Plus that's 110psi).

Many people recommend running them at lower pressures, but while that improves the comfort, it will also increase the chance of a pinch flat -- plus it makes the bike slower and more work to pedal...

Also, if you carry a spare tube, get a smaller one. A large tube can make it harder to change a tire if you get a flat. I tied to put a 28-38 tube on a 700x28 tire and had a hard time getting the tire to seat where the valve was because the tube was 'spilling over' and blocking the tire from coming down all the way. I finally inflated the tube and that pushed it out of the way and the tire seated.

Bill G

The tires have a max recomended pressure rating on the side of them. About 5 to 10 lbs less than what is stated on the side is normally about right for general tire pressure. Max would only be needed if the bike was loaded down for touring. Most times a little less air pressure than the stated max of 5 to 10lbs gives a good ride while maintaining good rolling resistance with most all Bicycle tires as a rule of thumb.

Ride Safe,
Bill G

jsdavis

The difference in rolling resistance will not vary much between 32 and 28.

Igo

Seeing how I've already made the switch I'd say I know exactly how much difference there is in rolling resistance.

Igo

>It's all about roll resistance. I was riding road bikes to work with no dirt involved. Then on weekends I was riding a 35 mile paved national recreation trail that went way out in the desert. Over time I ended up with with lights, racks and panniers on my otherwise sleek road bike. It became a really quick commuter but a really clunky racer. That bike was stolen. I replaced it with two bikes, an even sleeker racey road bike and a sturdy, duty oriented hybrid commuter. Now I zip along the 35 mile route in a few hours on the stripped down road bike and I have a truck-bike for hauling clothes and lunches back and forth to work. That "truck" bike is the Giant Escape 1. As I refined my route to work it ended up that I had a 450 foot elevation climb in 5 of 7 miles but only 100 yards of hard pack dirt in the route off of asphalt. Since I can't wear traditional bike shorts to work I put a softer aftermarket seat on the Escape/commuter. What the fat 60 psi tires did for comfort is now the seat's job.
Not having to give great consideration to "all terrain tires" because the great majority of my ride was asphalt and in good condition, I started looking at what would be the appropriate tire for smooth asphalt and a 450 foot climb without giving up the "truck" capabilities of the hybrid/commuter bike. I'd rather go more miles or make better time than get all my exercise by overcoming mechanical resistance that was part of the OEM tire design. Three things had to be considered. Heavy tread is much like rough pavement, it had to be smoothed out. I wanted a tire that had some girth to it for puncture resistance and weight carrying capability but had to be smooth enough to level out the road contact patch under the tire. I wanted less patch on the ground to further reduce roll resistance and along with smoothing out the tread you reduce patch by using a narrower tire with higher air pressure. You also speed a bike up by throwing less centrifugal force so the Panaracer tires had 4 things going for them. Immediately I improved my time to work as by GPS my average speed increased by 1.5 mph (I always ride slow to work; went from about 7 mph to 8.5 mph) by riding the same cadence but in one and 2 higher gears. Switching from a 60psi 32c tire to a 105 psi 28c tire increased the efficiency of the bike by great leaps. Smoother tread, less weight, smaller patch and less flex = MUCH less roll resistance and increased responsiveness. If you are not going to ride in the dirt and you think you can be comfortable on a stiffer tire then get rid of the roll resistance that is a byproduct of the design of dirt oriented tires.

GeorgeBMac

+1 I agree completely...

My experience was at a Trek Demo: I road a Madone racer and then a Cronus CycloCross. When I got back I commented to the Trek rep that the Cronus felt so much slower and more work. His response was: "Swap the tires and the Cronus will be as quick as the Madone."

But, conversly, I switched from a Cannondale road bike with 700x28 tires to a Trek DS with 700x38 tires because I ride almost exclusively on crushed limestone rails-to-trails and the wider tires give me more stability in soft stuff and gravel and they do a little better with ruts that sometimes cross the trail... So, I like them -- but they are definitely more work. (But part of that is the loaded DS is 35# compared to the 22# for the stripped down Cannondale.)

Paul Barnard

There can be an appreciable difference depending upon make, tread pattern, composition and ACTUAL size.

Igo

The Panaracer T-Serv tires I used to replace the OEM tire weigh 281 grams, have a very slight tread pattern, are sized smallish for most 28C and air to 105 psi.



The Giant SX-2 700x32 weigh almost 1000 grams, have a much more aggressive tread pattern, are a 32C tire and have a maximum inflation rating of 65psi were like spinning bricks comparatively.
You cannot deny the science of physics and physical properties. The proof is in the pudding.

jsdavis

Well no **** Shirlock. If you go from knobbies to smooth, then of course the roll resistance goes down. But making a blanket statement saying there is a huge reduction in rolling resistance going from from 32 to 28 is incorrect. For one thing, you cut 700g from each tire, that's HUGE in terms of rotational mass, but the biggest effect you will notice is due to rotational inertia, not rolling resistance. Even removing as little as 50 or 100 grams from any spinning component is very noticeable.

Igo

No ****!

Dunbar

I'll make another guess that if you back the pressure on your 28's down to ~80psi you won't notice a reduction in average speed. I pick a pressure that results in about 15% of tire deflection when I'm on the bike. Some tires like my 28c Gator Hardshells run narrow (closer to 26mm wide) so it's hard to make blanket recommendations about inflation pressure. I weigh 195# and run the 25's on my road bike at 90-95psi and they don't slow me down one bit.

GeorgeBMac

No, the proof is in how much sweat you expel!
Remember, even Neuton had to be hit on top of the head to get him to understand gravity!

GeorgeBMac

I use 700x28's on my road bike and keep them inflated half between the range recommended by the manufacturer (110PSI). If I forget to inflate them before I ride and they're down 10, 20 psi, I feel it. The bike is slower, sluggish and more work to peddle. It feels like I'm pushing it through molassis instead of air.

I know that there are a LOT of people who advocate the 15% / lower inflation pressure rule. But, I find that it slows down the bike and makes it harder to peddle. I can't see paying for light, highend components and then running soft tires. it's self defeating...

But, that's on my road bike. I should try the 15% rule on my hybrid with 700x38's. I again run them half way between the high & low manufacturer's recommendations (70psi). Perhaps a lower pressure would not affect them as badly as it does to the high pressure road tires???

Dunbar

The other variable is rider weight, the heavier you are, the more pressure you need to run. The 25's on my road bike are hardly soft at 90-95psi, just not hard as rocks. The cycling magazines have done tests on rolling resistance to show that, above a certain point, higher pressures become counter productive. The puncture resistant tires I ride all become unbearable if you run them near max inflation pressure. They would have the compliance of a solid rubber tire...

GeorgeBMac

I've heard that arguement before... So there has to be some logic in it. But it goes against my own experience. No, my 700x28's are in noway soft at 90-95psi -- but the bike is slower, more sluggish and harder to pedal.

Plus, it doesn't make sense to me that the manufacturer would recommend higher pressure. Why would they recommend pressure of 100-120psi on the sidewall if 90-95 were better?

Dunbar

No idea, the 25's on my road bike say 85-115psi on the sidewall. The OEM 32's on my 7.5FX say 55-85psi. My understanding is that the high number is the max inflation pressure, above which you risk blowing the tire off the rim or catastrophic failure. It should not be used as a guide to set the tire pressure (other than not exceeding it.)

GeorgeBMac

True, but I was talking about using BOTH the high and the low numbers as a guide. Not just using the high number and ignoring the low number.

From what i have read, going below the low number increases the risk for pinch flats and other problems. But, it also decreases the speed of the bike and increases the amount of work to pedal it.

melvinator

Just purchased CST PRO 700cc x 28c tires and had originally 35c. I weigh 270 and have to pump up the tire every other ride to about 95psi, if it gets under 87ish i feel a big difference and my average speed drops. I pump them up to 95 and i am back and ready to ride. 35c to 28c was a big diffference for me overall in speed and distance (2mph).

(My tire states max PSI 100)

GeorgeBMac

Yes, i find the same (about 2 or 3 mph) difference between my 700x38 and 700x28's. But then the bikes are different as well: the hybrid with 700x38's weighs in at almost 35# as opposed to a little over 22.5# for the road bike with 700x28's. But, partially offsetting that are the high-end, modern shfters on the hybrid -- the road bike is 20 years old and uses downtube shifters -- so I tend to just power through small hills without shifting.