Tire Pressure, How much??

[Mikebike125]

My old tires had a max pressure (witten on the sidewall of 110psi. The new tires I just got have a pressure written on the sidewall of 150psi. I know the tires go up in pressure with the heat of the day so I know to back off a little from the max. Am I safe using say 130psi?

I am just not sure if there is some sort of limit on the pressure in reguards to the tube. Can you clear this up for me?? I like the idea of running higher pressures to cut down on rolling resistance, I just don't want anything to blow up.

Thanks!

 

[sogood]

Don't forget that wheels/rims also have a max pressure spec.

In any case, you really should choose the psi based on your weight. For an average weight of 70kg, 100psi front and 105psi rear is in the ball park. There are charts around that matches the rider's weight to ideal tyre pressure.

When you push the pressure up too high, the wheel would bounce around and lose grip. And the ride would be uncomfortably harsh without performance benefits. Track riders on perfectly smooth surfaces may have a different opinion on this.

 

[Mikebike125]

I am 200 lbs.

 

[sogood]

I am 200 lbs.

On 23mm tyres, I'd think most would suggest 110-115psi front-rear pressures or perhaps 5psi more. Try a few ranges and see how you like it.

 

[Mikebike125]

Try a few ranges and see how you like it.

So with a tire maximum of 150psi, then it kind of gives me more range to experiment with different pressures and how I like the ride, correct? I guess also higher pressures make for lower rolling resistances?

 

[Sikhandar]

Humm very difficult to answer for me (damn american measurement system!)

I am light, 132 lbs (something like that), and I pump up clinchers (on training wheels) to 116-123 psi (front-rear) Their stated pressure is 123 psi. I pump up tubulars (tufo tires, on racing wheels) to 9.5 bars, that is...around 137 psi.

 

[Sikhandar]

So with a tire maximum of 150psi, then it kind of gives me more range to experiment with different pressures and how I like the ride, correct? I guess also higher pressures make for lower rolling resistances?

...and more "straight turns" during a descent ;-)

 

[ScienceIsCool]

So with a tire maximum of 150psi, then it kind of gives me more range to experiment with different pressures and how I like the ride, correct? I guess also higher pressures make for lower rolling resistances?

When you look at the maximum pressure ratings of the tire and rim, the lower number is the one that guarantees the tire won't blow off the rim while just riding along. It says nothing about the ride quality.

The minimum rolling resistance does not often occur at the maximum pressure because the surface you ride on is not smoothe. For the average rider (150-170 lbs) the minimum rolling resistance occurs somewhere between 95-110 psi (according to Continental). The added benefits of running at lower pressures are increased comfort and improved handling.

At 200 lbs, I'd suggest going to 105-120 psi.

John Swanson

 

[Mikebike125]

For the average rider (150-170 lbs)
At 200 lbs, I'd suggest going to 105-120 psi.

John Swanson

Hey, you callin' me fat? I'm sure I've got a few to lose, but at 6'-3" I'm pretty sure most of it is from the height.

Thanks for the response John. I'm cust curious as I have never had a tire that had such a high pressure rating on it. I think I might try 130psi just to see what it feels like and then see how it handles.

 

[anth]

I think I might try 130psi just to see what it feels like and then see how it handles.

How it feels isn't a good enough indicator if you're trying to get the best performance. Overinflated tyres feel fast, but actual measurements of the speed say otherwise.

Reading the following might be useful:
http://sheldonbrown.com/tyres.html#pressure

 

[mikesbytes]

I don't know, you kick the brits out in 1776 and the frogs are your friends and what do you do, you keep the brits measuring system when the frogs have a better one.

200lbs = 90kg, now I can think.

Front 110 - 115 psi
Rear 115 - 125psi (don't make both 115psi)

130psi is defently too high. The odd thing is that it will actually feel more efficient when it is actually not. The problem with over inflated tyres is that the don't fold around the micro bumps on the road and therefor waste energy going over them.

BTW, it isn't a case of sogood, scienceiscool or me being right or wrong, there are a number of factors that influence optimum pressure, of which weight is the major factor and there's a reasonable range where there is little difference in the rolling resistance.

 

[Sikhandar]

I don't know, you kick the brits out in 1776 and the frogs are your friends and what do you do, you keep the brits measuring system when the frogs have a better one.

They're crazy but also you use the psi (POUND per square INCH...)

USE BARS or ATMS!!!!!!!

130psi is defently too high.

Well, that's not obvious. First of all you have to distinguish between tubulars or clinchers. Clinchers should not be over pumped: there are some tests, reported on a german journal of cycling (and also on some websites) that show that by over-inflating CLINCHERS you may also have even more attrictional forces than if you use the pressure stated on the clincher! This is an experimental evaluation, the motivation is still debated.

Moreover, you can damage a wheel with a clincher over-inflated: the lateral pressure on the rim could be too stressing for the aluminium of light-weight rims. (you take a hole on the ground -> the clincher exits from the sides or can damage irreversibly the rims).

In a tubular wheel the situation is quite different, and you can pump up to 10 bars, mantaining a god level of comfort. Well, ok: it depends strongly from the tubular you are using (tufos are very hard, vittoria are quite soft, conty are quite...expensive etc etc).

 

[mikesbytes]

They're crazy but also you use the psi (POUND per square INCH...)

USE BARS or ATMS!!!!!!!

Well, that's not obvious. First of all you have to distinguish between tubulars or clinchers. Clinchers should not be over pumped: there are some tests, reported on a german journal of cycling (and also on some websites) that show that by over-inflating CLINCHERS you may also have even more attrictional forces than if you use the pressure stated on the clincher! This is an experimental evaluation, the motivation is still debated.

Moreover, you can damage a wheel with a clincher over-inflated: the lateral pressure on the rim could be too stressing for the aluminium of light-weight rims. (you take a hole on the ground -> the clincher exits from the sides or can damage irreversibly the rims).

In a tubular wheel the situation is quite different, and you can pump up to 10 bars, mantaining a god level of comfort. Well, ok: it depends strongly from the tubular you are using (tufos are very hard, vittoria are quite soft, conty are quite...expensive etc etc).

Yeh BARS are better, I was keeping it US and you are correct, down here in Aus not only did we keep the Brits but we still seem to use PSI.

I've seen the Zip recommendations on tyre pressure and its a fair bit higher. Why do they recommend higher pressures for singles?

 

[Camilo]

How it feels isn't a good enough indicator if you're trying to get the best performance. Overinflated tyres feel fast, but actual measurements of the speed say otherwise.

Reading the following might be useful:
http://sheldonbrown.com/tyres.html#pressure

+1 on the sheldonbrown pressure chart. This just makes sense to me. Every other tire in the world has inflation pressure recommended on the basis of the size of the tire, the weight on it and intended use, not across the board inflations.

I use his general guidelines as a starting point and have found the tires perform great.

 

[Mikebike125]

I don't know, you kick the brits out in 1776 and the frogs are your friends and what do you do, you keep the brits measuring system when the frogs have a better one.

Don't get me going on this friend. I LOVE the metric system and cannot understand WHY we haven't converted yet. I am simply baffled on this. I went to Canada where they are metric and LOVED it. Metric is cool!

 

[Mikebike125]

First of all you have to distinguish between tubulars or clinchers.

Sorry, I have Clinchers.

 

[mikesbytes]

Don't get me going on this friend. I LOVE the metric system and cannot understand WHY we haven't converted yet. I am simply baffled on this. I went to Canada where they are metric and LOVED it. Metric is cool!

Australia is still a sinner too, we can't let go of PSI and I'm guilty too. Sometimes baby weights are quoted in pounds, but thats disappearing too. Oh yeah, I just remembered, we are still using inches to describe track and fixie gearing.

 

[Mikebike125]

mikesbytes,

I just read that Sheldon Brown article and from what he is saying, the weight on the tire also determines the pressure that should be in it. Do you or anyone else have a good idea as to what percentage of weight the front and rear get? If I am 200lbs (sorry about the non-metric) and my bike with waterbottles and all weighs 25 lbs. That's roughly 225. Are we looking at 60% on the rear???? 70%??

 

[mikesbytes]

A while back a bloke I know did a comparison between the recommended tyre pressures guides and we could see that there was quite a difference in opinion between the "experts". What I can say as that as you get to higher pressures, the gain in forward rolling resistance dimishes and the energy wasted going over the micro bumps increases, also you tend to get more flats at higher pressures as the objects can cut thru the rubber easier.

One way to decrease rolling resistance is to fit wider tyres. Yes wider tyres have less rolling resistance than narrower tyres. However wider tyres have poorer aerodynamics. Oh and you run wider tyres at lower pressers than thinner tyres.

BTW, which tyres do you have?

 

[Mikebike125]

BTW, which tyres do you have?

I got a set of Panaracer Stradius Pro 700x23c Min pressure 100psi max pressure 150psi 127TPI 210 grams each.

I've been thinking that I may run 115psi in the front and 125psi in the rear. Just for a start, maybe 130psi in the rear....