Bicycle Mechanics - Tire Pressure Question
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06-22-06, 11:33 PM
Today I purchased a new floor pump with a pressure gauge. The tires, Specialized 700x28, have a psi range of 115-125. I knew I needed more air in my tires, but had no idea I needed that much. Is there a rule of thumb for tire pressure regarding the low end or the high end of the psi range? I am still new at this and have replaced only two tubes due to a puncture and one new tire. Thanks in advance for your responses!
I have had 28, 25 & 23s in specialized All Condition Sport, Pro & Armadillo. All these tyres are rated 115/125. The 125 is obviously recommended max, but as for the 115 assumable min makes no sense to me. The 28 tyres, for a given weight should be able to be run at a slightly lower pressure than the 23/25s. I am currently using 25s with a front tyre pressure of 100 spi & rear 110 psi. My weight is 78 kgs These pressures are more comfortable & possibly less rolling resistance for the type of road surfaces I ride [a bit bumpy] than max pressures. BTW I notice you ride a flat bar road bike [so do I]which by all reports can be a little hard on the wrists so max pressures will jar more. I know you did not ask but while I'm "talking" I may as well add that riding flat handed with fingers resting on the brake levers also lessons jaring & fatigue.
06-23-06, 08:41 AM
I use 100 psi front, 110 psi rear on my tandem with 700 x 28c Continental Gatorskin tires and don't get pinch flats. I used to run higher air pressures but I've found that the lower air pressures ride much better and don't seem to extract any performance penalty that I can tell.
06-23-06, 10:40 AM
Al f R wrote: I am currently using 25s with a front tyre pressure of 100 spi & rear 110 psi. My weight is 78 kgs These pressures are more comfortable & possibly less rolling resistance for the type of road surfaces I ride [a bit bumpy] than max pressures. BTW I notice you ride a flat bar road bike [so do I]which by all reports can be a little hard on the wrists so max pressures will jar more. I know you did not ask but while I'm "talking" I may as well add that riding flat handed with fingers resting on the brake levers also lessons jaring & fatigue.
Hey, that's great information. I never thought about a higher psi for the rear tire, but that makes total sense. I weigh just about five pounds more than you. I will try that combination of psi's when I go on my 64 mile ride tomorrow morning. Oh and thanks for the tip on the hand positioning.
Do a search on snakebite and pinch flat. These are impact caused flats that tell you that you need more tire pressure. (or need to steer around obstacles) Lots of us started out having one snakebite after another before getting the pressure up high enough. Heavier riders will need more pressure to avoid snakebite failures for a given tire width. Pressures higher than this limit will ride more harshly. I am heavier than you and need more pressure...I use 115-120psi in 23 wide tires and 85psi in 32 wide tires.....I haven't used 28's lately.
06-23-06, 12:06 PM
I am looking forward to riding with the higher pressure tomorrow. I am very glad I bought the floor pump with the gauge. Is there a general guideline for pressure and a person's weight. My wife rides the exact same bike and tires that I do, but she is only 5'5" and 120lbs (54kg).
06-23-06, 12:29 PM
And those are just that, guidelines - especially what is printed on the tire sidewall. There is no way that pressure is suitable for all the different loaded weights that is imposed on it. Experiment and find out what works best for you.
If you're getting snake bites - pressure too low. If you can feel every nook and cranny of the pavement - too high.
There are many other signs obviously.
06-23-06, 03:13 PM
Having no snakebites is the key. I'd bet your wife could use 95# front and 100# rear and never have any unless she hit a hole at very high speed. The lower the pressure, definitely the more comfortable the ride. Many say that the lower the pressure, the less the rolling resistnace.
06-23-06, 03:50 PM
As you can see at this page, rolling resistance doesn't change much at the high end. Going for comfort is just fine:
Note that bigger tires have LOWER resistance at a given pressure. Granted, that doesn't hold for % of max pressure (skinny tires go to higher pressure). Still, it's nice to know you can have MORE traction, MORE comfort, and MORE flat resistance with a bigger tire -- possibly with LESS rolling resistance. The only disadvantage is weight -- and aerodynamics, as rim and tire width closer together is more slippery in the air.
06-25-06, 05:54 PM
Did my ride yesterday and put in 100 miles with the new tire pressure. I went with 100 in the front and 115 in the rear. It was so much better and faster! Thanks for all the advice!
06-26-06, 07:18 AM
Sheldon Brown on the subject: http://www.sheldonbrown.com/tires.html#pressure. Look for the sections on "width and pressure" and "pressure recommendations."
I definitely agree. for the last three years I have been doing 20 miles per day commute on 700x23 Specialized Armadillos pumped up to 115psi for fear of flats. Today for the first time I decided to use 95psi on both the front and back. Speed, comfort and handling was unbelievably better. My only concern is opening myself up to punctures. I weigh 130lbs so I am hoping I will be ok.
Yeah, at that weight, you're fine with 95psi. When I weighed about 250lbs, I'd use 28mm tyres at 120psi. Certainly pounded me less than 23mm tyres at 150psi! :eek: Now that I'm around 180lbs, I can get away with 100psi on 25mm tyres. :)
06-26-06, 04:00 PM
I'm about 140# and ride anywhere from 95-120 on 20's and 23's. 95-105 when I am just tooling around and training. 110-120 for races depending on road quality. I can't remember the last time I pinched and I think I am more towards the rough side. I even do some light trail riding on the 20's when I am out with the kids.
06-26-06, 07:17 PM
Call me crazy but I ride 32mm tires with 60-80psi. I weigh about 155lbs. I have never had a pinch flat and it's pretty comfortable. I noticed on Sheldon Brown's site that was linked earlier that I'm right in his range of size/pressure so I feel like I did a good job! Of people I know who ride, I have really low tire pressure. It seems like there's a huge window.
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