Road Cycling - TIre Pressure

What is a good pressure to have for a trek 1000 that i ride on trails and roads...I want to kick up my training so i can get a faster avg speed.....Help anyone...?

What pressure are you running now? I typically run 115-120 psi but I stay on the road.

The best bet is run at the max recomended pressure that is on the tyre usually for road tires it is 110-12-psi.

I havent ridden in a while...so the pressure is prob inaccurate anyway...its been very cold, and i dont have the gear for that quite yet...im a newbie

This may be kind of obvious, but tire pressure will have little to do with your training...kind of like the weight of your bike.

If you're riding alone then neither factor will affect your fitness, rather they will only affect how far/fast you go on a given ride. Fitness will be determined only by how hard and/or how fast you are pedaling.

Now in either a group or race, that's entirely different. In a race you definitely care about weight and tire pressure and a host of other items. Because you're trying to be as efficient as possible.

In a group ride, as long as you keep up and do your share of pulling, then you will get a better work out as your bike gets heavier or your pressure is lower.

My own theory (for what little it's worth) is that on solo training rides you should lower your tire pressure until you run the risk of pinched tubes...that will give you the most comfort (at some slower speed) for a given ride/workout.

So why high pressure and or low weight for non-racers? CAUSE IT'S FUN! There's definitely a keener sense of the riding experience as you increase pressure and lower weight.

So what's more fun to you? Comfort on the ride? (lower pressure) or the feel of the road and speed? (higher pressure)

Have fun!

What is a good pressure to have for a trek 1000 that i ride on trails and roads...I want to kick up my training so i can get a faster avg speed.....Help anyone...? What it says on the tire sidewall. Depends on your weight too. Try running to little and you get pinch flats.Too much and there are other issues.

There's pro's and con's to tire pressure.I'm big on max psi but sooooooooooooo many said thats not right,lower psi wont effect anything but will be a better ride.Well i lowered my psi and it doesnt ride any better.Maybe this would work on 25's or bigger but on 23's or 20's,i dont think so,imo.I'll keep mine at 115-120

Got this from Vittoria tyres , remember it´s a GUIDE not a rule of law .

rider weight pressure
50 kg 95 --105 psi
57 kg 100- 110 psi
64 kg 105 - 115 psi
77 kg 110 - 120 psi
84 kg 115 - 125 psi
91 kg 120 - 130 psi
105 kg 125 - 135 psi

Do remember this is a guide and the BEST pressure will depend on tyre choice , type of tube etc.
ie you may not want to use less than the minimum but not to exceed the max .
Hope this helps .

Got this from Vittoria tyres , remember it´s a GUIDE not a rule of law .

rider weight pressure
50 kg 95 --105 psi
57 kg 100- 110 psi
64 kg 105 - 115 psi
77 kg 110 - 120 psi
84 kg 115 - 125 psi
91 kg 120 - 130 psi
105 kg 125 - 135 psi

Do remember this is a guide and the BEST pressure will depend on tyre choice , type of tube etc.
ie you may not want to use less than the minimum but not to exceed the max .
Hope this helps .

I am not sure thisa applies to all tyres if I could put 135psi in my tiyre it would blow or it could even damage the rim. As I posted before follow the recomended psi on you tire sidewall.

I think rims are rated but dont they use bars instead of psi?

The discussion of tire pressure from Road Bike Rider, Uncle Al's Rant (http://www.roadbikerider.com/ua4.htm#The%20Case%20for%20Lower%20Tire%20Pressure)

Page down some to find the discussion.

I don't find what Uncle Al to say true at all I get more slide when I run my tyres low than I do at proper PSI. The last non related ice fall I had was because my rear tyre went out from under me in a turn. Why? not enough air in the tyre and when I made the turm the rear end slid. Yes I feel the bumps more but I get a faster ride and almost totally flat free. Your road tyres are designed to ride up on the smallest surface posible they pivot better giving you better control of your bike. If you want to touch more road surface buy a wider tyre

The discussion of tire pressure from Road Bike Rider, Uncle Al's Rant (http://www.roadbikerider.com/ua4.htm#The%20Case%20for%20Lower%20Tire%20Pressure)

Page down some to find the discussion.Uncle Al needs a good flush.

This is probably the best article I've read on the
subject.

http://roadbikerider.com/ua4.htm#The%20Case%20for%20Lower%20Tire%20Pressure

www.belfastandbeyond.com

Thank you all for your responses....much appreciated....

I am not sure thisa applies to all tyres if I could put 135psi in my tiyre it would blow or it could even damage the rim. As I posted before follow the recomended psi on you tire sidewall.


The max pressure on the tyre wall is usually a trade off between the lawyerswho want it low ( product liability ) and the pr weenies ( publicity ) so a NEW and properly instaled tyre will not blow if taken a bit above the max rec pressure ; but it´s liable to be a very rough ride , it´s mix and match as always .

High pressures ride rough , grip less but are less ( in theory anyway ) liable to cut .
Low pressures are more comfortable , grip more but can be more vulnerable .

It´s all on the one hand but on the other type of into , track and time trial very high , touring low / medium .

A good test for rim wear is a pressure test at about 200 psi ( but I would not want anybody to try that at home , sounds scary , waiting to see if the rim cracks ............. )

The max pressure on the tyre wall is usually a trade off between the lawyerswho want it low ( product liability ) and the pr weenies ( publicity ) so a NEW and properly instaled tyre will not blow if taken a bit above the max rec pressure ; but it´s liable to be a very rough ride , it´s mix and match as always .

High pressures ride rough , grip less but are less ( in theory anyway ) liable to cut .
Low pressures are more comfortable , grip more but can be more vulnerable .

It´s all on the one hand but on the other type of into , track and time trial very high , touring low / medium .

A good test for rim wear is a pressure test at about 200 psi ( but I would not want anybody to try that at home , sounds scary , waiting to see if the rim cracks ............. )
Remind me why max psi would grip less?Doesnt grip have to do with rubber compound?

It is a function of compound and contact patch. Lower pressure means a slight, and I do mean slight, increase in the contact patch, especially when we are talking about road tires.

interesting...I believe tire pressure can depend on many factors. One must consider road conditions, terrain, weather conditions, brand of tire, weight of the rider, wheels (rims), and frame material.

If the road is rough, I would use lower psi for comfort and control...but not below the recommended psi. On smooth roads, I would push the psi to the upper limit of what is recommended. On mountain rides with technical decents and smooth roads, I would run box rim wheels with the rear tire about 10 psi higher than the recommended. This gives good roll resistance while climbing in the seat and good steering control for the decents. On fast sweeping decents, I like semi-aero wheels with the front tire about 10 psi higher than the recommended.

Tires that are too soft slide around in turns and handling is poor. Tires that are too hard not only give a rough ride, the handling can also be unpredicable. It may not be apparent from the start, but if you take a fast turn and encounter some rough road, it can bounce you into oncoming traffic.

Most people like to drop their psi when the roads are wet...call me careless, but I like to keep the psi on the high side. When its wet I tend to stay off the tricky decents and the higher psi give an edge over everyone else running at lower psi.

Okay, I'm getting a little esoteric...

I did some calculations based on the Vittoria pressure figures posted previously in this thread. I looked at rider weight (pounds) and pressure (psi) and calculated total contact patch area (square inches). I think contact patch is the important factor in tyre pressure considerations. This is what I got:

rider lb max patch min patch
100 1.05 0.95
114 1.14 1.04
128 1.22 1.11
154 1.40 1.28
168 1.46 1.34
182 1.52 1.40
210 1.68 1.56

Thus a 100lb rider has a contact patch between .95 and 1.05 square inches, and a 210lb rider has a contact path between 1.56 and 1.68 squ inch which is heaps different

The mean of all these contact patch sizes is 1.30 square inches. Assuming this average is some kind of optimum, working back to pressure gives optimum pressure according to rider weight as follows:

weight 'optimum' press
100 76.92
114 87.69
128 98.46
154 118.46
168 129.23
182 140.00
210 161.54

Hence a 100lb rider would have an average pressure front-back of 77psi and so on, giving all riders the same contact patch size of 1.30 square inches.

I weigh about 128lb and I run 95psi front and 105 back so that fits with the above figures. Of course I'm around the middle of the range, where you'd expect it to work. If I weighed 210lb I wouldn't want to be putting 160psi in a clincher.

This information could be completely up the creek, but I'm bored at work and it was interesting to do. I have no idea whether in a dynamic situation the same contact patch size at different weights and pressures behaves the same; it could be interesting to think about that one some more.

cheers,
Ants

Remind me why max psi would grip less?Doesnt grip have to do with rubber compound?

Grip is related to the working temperature of the tread compound , just like on race cars . The lower the pressure the more tread deformation occurs , the more heat builds up and stickier the rubber becomes - too much heat and the tyre falls apart , too little and it don´t grip .

Here in the summer the road gets very hot and tyre wear gets silly if you don´t raise the pressure a tad BUT if it rains it don´t grip at all ( water cooling the tread , ) look at GP Motorcycles for example ; slick tyres will work on a wet road until the tread cools then ........... but rain tyres fall apart on a dry road because of the lack of cooling .
It´s the same for us , that happy balence between grip , rolling resistance ( or lack of it ) and comfort , difficult to find , but do try having the front tyre slightly softer than the rear , 3-5 psi and see how it feels in the turns .

Oh and too much pressure will tend to make the bike more nervous in it´s handling so take care .
Funnily enough there seems to be very little difference between 20 mm and 23 mm when it comes down to rolling resistance ( at same pressure ) but the 23 mm is much more rider friendly .

Yikes, I usually try to stay out of the religious debates like air pressure vs. rolling resistance/traction, so I'll just add a few more things to consider in this holiest of debates...

Traction is dependant upon rubber compound, contact patch size, compliance, and downforce. (We'll consider all roads as being equal for the sake of comparison...)

Modern, high-hysteresis rubber grips more as downforce is increased even if the footprint (contact patch) remains the same (downforce being a rider's weight, since we don't have downforce-generating airfoils like on a Formula 1 car.)

(As a sidenote, this is why the front tire performs the bulk of braking duties; under braking, most of the rider's weight is transferred forward onto the front tire, thereby increasing it's traction potential and decreasing the rear's traction potential...)

Traction goes up as the contact patch is increased (but there's a catch, see below.)

The size of the contact patch increases until the tire reaches equilibrium of air pressure vs. load. That is to say, with an equal load carried, the tire with push against the ground with the same net force regardless of air pressure. This is measured in pounds per square inch (but not as in air pressure).

Think of it this way: A 100 lb weight on a 2" sq. footprint is pressing into the ground with a force of 50 lbs/sq. inch. Reduce the footprint to 1" sq. and the force goes up to 100 lbs./sq. inch. So our high-hysteresis rubber should grip better with a smaller footprint since we have effectively increased it's load, right?

Erm, no... We lost some of the traction with the loss of the footprint size. It's all give and take, and different tires will react differently... Besides, the total load hasn't changed.

So let's add another factor into the mix: Compliance. Compliance is a tire's ability to absorb road irregularities without transfering them (or as much of them) to the bike and rider. It's the suspension for a road bike.

If a bump is big enough (or compliance is low enough), the bike and rider is pushed upward in order to go over the bump since it wasn't "soaked-up" by the tire. No biggie, but it takes a very brief moment for this upward momentum to end, even though we're past the bump. It's this upward momentum that causes the tire to leave the pavement. You could call that a zero traction situation. But even if the tire doesn't completely leave the pavement, it has less downforce on it. And as we've seen above, less downforce equals less traction.

This is where that "skittery" feeling comes from when you're hard in a corner. It's a little "traction-no traction-traction-no traction" dance that happens at the contact patch.

Compliance is mainly determined by air pressure and carcass construction. It is air pressure that makes a tire's carcass take on its final shape. More air pressure will add stiffness to this shape. It is important for a tire to be able to maintain this basic shape, too. The first reason is to avoid pinchflats. The second reason is to maintain the shape of the contact patch (more on this later).

A pliable carcass at a given inflation pressure is more compliant. A stiffer carcass at the same pressure is less compliant. Now if we keep the carcass constant, more pressure will make it less compliant, and vice versa.

Pretty straightforward, huh? Yes, for a change. But this is why it's difficult to discuss optimum inflation pressures unless you are talking about the same tires.

Now back to the reason why a contact patch's shape must remain stable... The bulk of a cornering load is carried by the outside (of the turn) of the contact patch, and the shape of the tire deforms until it no longer can due to air pressure or carcass stiffness. We need some of this deformation; it's what allows the tire to conform to the road. The problem arises when the tire is too soft from underinflation to hold its basic shape, and a ripple forms in the middle of the contact patch in-line to the direction of travel. The result is a quick drop-off in traction since part of the tire just left the road.

This is why high-tpi tires (which are very compliant) generally have more traction; they have the needed compliance and enough air pressure to maintain a stable shape.

That leaves the rubber compound... This is the easy part! Grippy rubber grips better... It just doesn't last as long. Such is the price of performace...

Rolling resistance vs. air pressure? I have my own religious beliefs, erm, preferred pressure, and suggest that you find your own. ;)

(Yeah... Did'ja notice me completely steer clear of that aspect of the discussion?)

Seriously, experiment within a safe range for your rim and tire combo and find what YOU like... Remember, you're the one who's riding your bike, and the inflation that I run may not suit your preference. And anything that makes you feel comfortable in how the bike handles will make you faster on that bike... Really!

The best part about experimenting with air pressures? It's free!

-Erik

Big Snip

Seriously, experiment within a safe range for your rim and tire combo and find what YOU like... Remember, you're the one who's riding your bike, and the inflation that I run may not suit your preference. And anything that makes you feel comfortable in how the bike handles will make you faster on that bike... Really!

The best part about experimenting with air pressures? It's free!

-Erik

This is one of the best discussions of tire pressure I've read. Thanks for posting it.

Hmm, I was hoping someone would bring up the compliance thing and provide some good info on that, but amongst his excellent analysis there are a couple of things Erik has said about friction that I think are not quite right.

Firstly friction is independent of surface area and depends on the coefficient of friction and on the force pressing the two surfaces together - those don't change with pressure (friction force=force between surfaces x coefficient of friction); secondly, modern tyre rubber is low hysteresis - it doesn't lose a lot of energy through its expansion/contraction cycle; and thirdly, we're talking about force measured in pounds in this case, pounds per square inch is a pressure. So to paraphrase:

'A 100 lb weight on a 2" sq. footprint is pressing into the ground with a PRESSURE of 50 lbs/sq. inch. Reduce the footprint to 1" sq. and the PRESSURE goes up to 100 lbs./sq. inch.'

Ignoring any effects of casing deformation, the friction between rubber and road will be unchanged since the force and the coefficient of friction are unchaged.

In my consideration of contact patch above, I deliberately left compliance out of the mix, since I don't know what happens to compliance as you change rider weight and tyre pressure. Contact patch is easy to calculate but compliance can only be assessed by changing things and riding. The important thing about contact patch is perhaps its shape - a long narrow contact patch will have greater rolling resistance than a wide short one due to the difference in tyre deflection and associated hsyteresis loss. Hence a tyre at high pressure has lower rolling resistance than the same tyre at low pressure. Perhaps any given tyre has an optimum contact patch shape? So what I tried to do was calculate

Anyway, Erik makes good points about compliance and deformation and I totally agree that everybody should play with tyre pressure and find what works for them.

cheers,
Ants

This is way to much for a few pounds up or down,air up and ride,man.

This is way to much for a few pounds up or down,air up and ride,man.

:) Got to agree with that. Like I said, I'm bored at work... rather be on the bike.

Let me start by pre-emptively defending Ants before somebody jumps all over him by misinterpreting what he wrote (like I've seen in previous discussions on this subject)...

When he says friction, he is referring to the beneficial friction between contact patch and road, a.k.a. traction.

He is not refering to rolling resistance.

(Why do I want to clarify this? Because similar comments have gotten people needlessly flamed in this very forum. For shame! ;) )

Ants also wrote:

So to paraphrase:

'A 100 lb weight on a 2" sq. footprint is pressing into the ground with a PRESSURE of 50 lbs/sq. inch. Reduce the footprint to 1" sq. and the PRESSURE goes up to 100 lbs./sq. inch.'

Well, that's not quite what I said... In laymens terms, close. But I actually used the term force, not pressure. And as far as using the term "...lbs/sq. inch", it is a means of expressing the amount of force distributed over an area. I even tried to go so far as to make sure that I differentiated it from pressure, by writing:

(but not as in air pressure)

I guess when I begin to lose any sense of brevity, I should just embrace my verboseness! ;)

Ants further stated:

Ignoring any effects of casing deformation, the friction between rubber and road will be unchanged since the force and the coefficient of friction are unchaged.

I agree. Because I also wrote:

That is to say, with an equal load carried, the tire with push against the ground with the same net force regardless of air pressure. This is measured in pounds per square inch (but not as in air pressure).

...as well as:

Besides, the total load hasn't changed.

and was said in context to:

So our high-hysteresis rubber should grip better with a smaller footprint since we have effectively increased it's load, right?

Erm, no...

So, so far we seem to be in agreement.

Except on the subject of hysteresis...

Ants said:

modern tyre rubber is low hysteresis - it doesn't lose a lot of energy through its expansion/contraction cycle

And I would have to say that his definition of hysteresis is spot-on. Hysteresis is a measure of a material's elasticity, or its ability to fully recover once, well, "stretched". The percentage that a material doesn't recover is lost (converted) to heat. And yes, different tires will have different hysteretic properties.

But by and large, modern tire rubber is high-hysteresis rubber. This is one of the things that a tire designer uses to enhance a tire's traction, especially in wet conditions.

Two extremes of hysteresis? A high-milage touring tire would be comparitively low-hysteresis. A "one-day" race tire would be comparitively high-hysteresis.

Can you see this in action (in tires)? Yup. Dig your fingernail into a fresh one-day race tire... You'll see an imprint that goes away slowly, but not completely. Now do the same on a fresh touring tire. You can barely see the mark, right?

(As a sidenote, high hysteresis rubber suitable for tires was the breakthrough in the 1960's for tire technology. It's nothing new...)

But a bicycle tire as a whole is low hysteresis.

If nothing else, I hope that Ants and I have given some people a place to start in their own research... After all, the bottom line is that we're just a couple yahoos out in cyberspace. Why believe us? ;)

And yeah, I shoulda' been working, too... But at least I squeezed a wet, rainy ride in!

I was going to ask a question but i'm afraid to so i wont.So you run what psi in your tires?Not that it will change what i do but go ahead.

HAHAHAHAHA!!!

That's funny! Thanks!

And since you asked:
Tufo Tubular/Clincher Hi-Comp Carbon (700c 22)
Rated up to 175 psi, but I typically run 140 in the front and 155 in the rear.

And suprisingly, even at 170 psi (I had to try it, afterall) they feel cushier than Vittoria's Open Corsa CX at 140 psi and waaayyyyy cushier than Michelin Pro Race at 110. But I've never ridden "real" tubulars before, so I don't know if I even should be suprised.

But, yeah, I'm pretty sold on these Tufos...

This is probably the best article I've read on the
subject.

http://roadbikerider.com/ua4.htm#The%20Case%20for%20Lower%20Tire%20Pressure

www.belfastandbeyond.com

Great article, thanks for the link. Hadn't read this Uncle Al column before, but do agree with him on the benefits of running lower pressures.

Note, instead of just a max limit, Michelin Pro Race have a pressure range on the sidewall....6-8 bar (87 to 116 psi).

After all, the bottom line is that we're just a couple yahoos out in cyberspace.

I think it's safe to say this applies to everyone in cyberspace.

Good stuff gazedrop, thanks for the clarification :)

I'm going for a ride!

cheers,
Ants

Thank you all for your suggestions....i guess i will just do what feels right...thanks again