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best tire preasure for DH

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best tire preasure for DH
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flag manicmastiff
Posted: Jan 30, 2010 at 14:41 Quote
On my 40+lb DH bike with Michelin DH16's (2.5) I used to run around 18 - 20 psi. On my current set-up (37lbs) with Intense Tyres I run 28 - 30 psi as the minimum recomended pressure is 30 psi. I tried to run the Intense DH fro lites at around 18 psi and as I am running 29mm rims I found they didn't feel stable compared to the 33mm rims I was running before. So I have adapted to running higher pressures with softer compounds and softer suspension to compensate.
flag rideonjon
Posted: Jan 30, 2010 at 14:55 Quote
jonbikes wrote:
rideonjon wrote:
jonbikes wrote:


Hit the nail rite on the head. The only other thing you forgot to mention, is tire volume. 20psi in a skinny little 1.95 is a lot different than 20psi in a 3.0.

I usually try to run around 20psi front and rear, less if it is muddy and wet.


tire volume has nothing to do with PSI,tire pressure is a personal preference.i run 28 in the front 35 in the back at Whistler,but drop that by 10 psi for the more technical local trails.where traction is more of a concern than flatting.get a good tire guage,start with higher than normal and incrimentally drop it down until your happy with the traction to flat ratio.

Your kidding, rite?



please educate me!!
flag jonbikes
Posted: Jan 30, 2010 at 14:59 Quote
Think of a road tire; if you were to run say 30psi in a road tire and ride over something with a square edge, you would almost most definitely pinch flat. If you put 30psi in a 3" tire, you can put that tire through quite a bit of abuse without even coming close to hitting the rim on similar bumps.


4 wheeler tires, what, 2-5psi and you rarely hit rims on the ground? Look at the volume.
flag rideonjon
Posted: Jan 30, 2010 at 15:06 Quote
jonbikes wrote:
Think of a road tire; if you were to run say 30psi in a road tire and ride over something with a square edge, you would almost most definitely pinch flat. If you put 30psi in a 3" tire, you can put that tire through quite a bit of abuse without even coming close to hitting the rim on similar bumps.


4 wheeler tires, what, 2-5psi and you rarely hit rims on the ground? Look at the volume.

the volume remains constant but the PSI can change.so when i charge my air compressor with 100 PSI the volume of the tank hasn't changed from when there was 2PSI in the tank.get it.do you understand atmospheric pressure,it's a good place to start.
flag jonbikes
Posted: Jan 30, 2010 at 17:34 Quote
That's not what I was getting at at all.
flag rideonjon
Posted: Jan 30, 2010 at 17:39 Quote
jonbikes wrote:
That's not what I was getting at at all.

what were you getting at then.your basically trying to say liquids and gasses have the same qualities.volume measures liquids,psi measures gasses.
flag jonbikes
Posted: Jan 30, 2010 at 17:46 Quote
uhhh, no? I never said anything about volume being dependent or pressure or vice verse, and never once said anything about units.

I said a tire with a large volume compared to a tire with a small volume will withstand pinch flats better than the lesser volume tire on the same square edge bump. Sure I don't know exactly how it works, I'm not a scientist, but I know it works. As I said, a road tire with 50psi would still pinch flat relatively easy. A 4 wheeler tire with 50psi would be extremely hard to deform at all comparatively speaking. No need to start in on tire sidewall strength and thickness, we don't need to factor that in for a simple statement that you chose to strip down and change around; a simple yes or no with a reason would have done.
flag jonbikes
Posted: Jan 30, 2010 at 17:50 Quote
Something I forgot to add. Gasses can most definitely be measured in volume, no two ways about it. However, if you feel you can prove that statement wrong go rite ahead, and if you can I will gladly retract that statement.
flag rideonjon
Posted: Jan 30, 2010 at 18:06 Quote
jonbikes wrote:
Something I forgot to add. Gasses can most definitely be measured in volume, no two ways about it. However, if you feel you can prove that statement wrong go rite ahead, and if you can I will gladly retract that statement.


http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH5004
flag jonbikes
Posted: Jan 30, 2010 at 18:10 Quote
So you are saying gas can not be measured in volume? You are suggesting gas takes up no space in the universe?

Depending on the application, gas can actually be monitored by pressure, or as in a welding application, volume. If you are a welder (like I am) and try to weld while regulating your gas such as helium or argon or co2 by pressure you are not going to get far in that job. When welding, gas is measure in volume, usually CFH or CFM (cubic feet per hour or minute) and pressure is fairly irrelevant, it more or less tells you how much is left in your tank.
flag rideonjon
Posted: Jan 30, 2010 at 18:16 Quote
not what i'm saying at all but gasses can be compresses and liquids not so much.if your a welder you should understand PSI better.the weight of a cylinder of gas will change when you compress more gas into it.but your not increasing the volume of the cylinder.
flag TwistedBench
Posted: Jan 30, 2010 at 18:29 Quote
PV=nRT

I am bored on a Sat night so will through in my 2cts.

Gas is often measured in volume.. But the measurement will be in units such as standard cubic feet. That is cubic feet of gas at standard temperature and pressure (60F and 14.696 psia). As rideonjon stated, the weight of a cylinder of gas will change when you compress more gas into it.but you are not increasing the volume of the cylinder.

But the point jonbikes makes, that a wider tire has much more resistance to pinch flatting than a narrower tire, is correct, with both tires at the same pressure.
flag jonbikes
Posted: Jan 31, 2010 at 7:28 Quote
TwistedBench wrote:
PV=nRT

I am bored on a Sat night so will through in my 2cts.

Gas is often measured in volume.. But the measurement will be in units such as standard cubic feet. That is cubic feet of gas at standard temperature and pressure (60F and 14.696 psia). As rideonjon stated, the weight of a cylinder of gas will change when you compress more gas into it.but you are not increasing the volume of the cylinder.

But the point jonbikes makes, that a wider tire has much more resistance to pinch flatting than a narrower tire, is correct, with both tires at the same pressure.

Thats exactly what I was saying. Take a full sized tank of oxygen compressed at say 2300psi. The volume of the tank is only just a few cubic feet, but the contents of gas would be much, much more. Rideonjon or whatever just seems like like to make assumptions that I know less than what I am stating.
flag rideonjon
Posted: Jan 31, 2010 at 11:03 Quote
i didn't assume anything i asked you to explain and you couldn't.so tell me how is volume of a tire and PSI related.
flag jonbikes
Posted: Jan 31, 2010 at 12:47 Quote
TwistedBench wrote:
PV=nRT



But the point jonbikes makes, that a wider tire has much more resistance to pinch flatting than a narrower tire, is correct, with both tires at the same pressure.

Two against one.

I am not a physicist so I can't tell you why it works, but this guys seems to know his stuff and agrees with me.

I don't know how the sun works, so it must not work at all; I wonder where all our light comes from.

 


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