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Running tires UNDER recomended pressure

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Running tires UNDER recomended pressure

Old 10-03-16, 05:37 PM
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Some tires say "Inflate Hard".

I went to Tufos (awful ride at anything less than rock hard) on the tandem cause I could run 160-180.
Never-mind - still an awful ride.
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Old 10-03-16, 09:55 PM
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Originally Posted by Doge
Some tires say "Inflate Hard".
Like the Dunlops on my old rod brake roadster...
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Old 10-03-16, 10:20 PM
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roads in the Santa Barbara/ Goleta/ Carp area are ****! and getting worse.
so, riding too low can be a problem with pinch flats, rim damage.
riding too hard is harsh and actually perceptively slower.
I'm 165 lbs. I've been riding 90 frt/100 rr for many years without any real damage issues.
just this July I started riding at 80/85 (and tried 75/80 without any problems) and this pressure is a great balance of smooth ride but very strong rolling performance. At this pressure 80/85 I can keep power to the pedals stronger than at a higher pressure.
I had inadvertently ridden a 45 mi group hammerfest without inflating for almost 4 wks - pressure was 50 frt/ 55 rr.
I honestly could not notice a performance hit - but I was lucky to not have a pinch flat...
When I get a flat I use a hand pump, not CO2, so the tire pressure rarely goes much over 65/70 before I say 'nuff'; and subsequent riding continues on as normal.
Experimenting will give you a better feel for what works for you. At your weight, unless you are really a leadass in the saddle, going under 100 or lower, should be no problem.
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Old 10-04-16, 02:26 PM
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Originally Posted by B1KE
Hey everyone,

I was reading some people run their tires in between 80-100 for a more plush ride. My current 25mm tires are listed as 110-125 PSI. If I run them under do I risk getting pinch flats, compromised speed/handling? What are the pros and cons of running below recommended tire pressure?
At 135-140 pounds, I've never pinch flatted down to 80 psi starting the week although that feels a bit squishy in back. 80-85 front 90 psi rear is better.

At 205 I never had problems starting at 90 psi front / 100 psi rear.

After six days they can be down 10 pounds and feel like they need air.

Continental GP4000SII tires roll well at those pressures. Less supple tires may not - pressure has a more significant effect as the carcass gets stiffer.

Obviously they feel better at lower pressures. Below the optimum pressure rolling resistance measures a bit higher, although too high costs you more than too low.

Dropping from 115 to 75psi here looks like .0005 Crr.

20 miles/hour is 8.9 meters/second; so a 75kg (165 pound) rider/bike combination would take an additional

8.9 m/s * 9.8 m/s^2 * 75kg * .0005 Crr = 3.2W which is about 1.5% of the 200W I use averaging that on a "flat" out and back course.

Most of your power is going into aerodynamic drag, with its force increasing with the square of velocity and power to overcome its cube. So at the same ~200W your speed would drop from about 20 MPH to 20 MPH * (197/200) ^ 1/3 = 19.9 MPH.

That's usually not interesting.



Last edited by Drew Eckhardt; 10-04-16 at 04:40 PM.
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Old 10-04-16, 02:42 PM
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Originally Posted by B1KE
Thanks for you opinion. I weight 180lb 79kg if that helps. Why are the labels in the tires listed with such high PSI and the range of 110-125 is so little when in fact you can run them at 90.

What tire pressure would you recommend for me based on my weight?
78psi front, 96psi rear for 15% tire drop. Experiment from there. With good quality tires, you'll notice a difference in comfort and (inversely) pinch flat resistance, but no noticeable change in rolling resistance.

The maximum pressure ratings are helpful for people who's frames can't fit wide enough tires to handle the weight of them and their luggage.
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Old 10-04-16, 03:00 PM
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Originally Posted by 79pmooney
I pay zero attention to the manufacturers' limits. I inflate them to the best pressure for my riding. It is a compromise between grip, rolling resistance and comfort and will be different for different both sizes and types of tires. Also different on different days (weather), roads and length of ride. (One piece of equipment I always have is a good frame pump. No gauge but plenty of oomph to get any pressure I want easily.)

Ben
Well you should pay attention to the maximum. Not saying you have to ride that, but I would not exceed it. Especially on gravel tires (and, of course MTB tires), as most have max pressures much less than typical road tires.
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Old 10-04-16, 04:57 PM
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Originally Posted by cthenn
Well you should pay attention to the maximum. Not saying you have to ride that, but I would not exceed it. Especially on gravel tires (and, of course MTB tires), as most have max pressures much less than typical road tires.
I pay no attention because I never ride anywhere close to the maximum. Now I might pump a skinny raod tire to its way high maximum someday just to demonstrate that this no-so-young guy can do it with an old-fashioned Zephal HPX.

I bring the pressures way down on the fatter tires. 70 on smooth roads with 32s, 60 on 35s. More than that and I find them jarring. (The other thing to think about if you have worn rims from brake shoes is that big tires apply MUCH more side force to the rims and can blow them right off.)

Ben
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Old 10-04-16, 05:13 PM
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Originally Posted by 79pmooney
I pay no attention because I never ride anywhere close to the maximum. Now I might pump a skinny raod tire to its way high maximum someday just to demonstrate that this no-so-young guy can do it with an old-fashioned Zephal HPX.

I bring the pressures way down on the fatter tires. 70 on smooth roads with 32s, 60 on 35s. More than that and I find them jarring. (The other thing to think about if you have worn rims from brake shoes is that big tires apply MUCH more side force to the rims and can blow them right off.)

Ben
Well I was just replying to "not paying attention to limits". If you underinflate all the time, it's not a problem, what I'm saying is pay attention if you want to go really high pressure.
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