Bicycle Mechanics - tire pressure ???

I have contenental 3000 ultras... they are rated on the tire at max 120 psi... so what is best to have them at??? 90? 100? can ANYONE help me out??? sorry if this is a stupid question...
thanks so much
Ryan

up to a point, the higher the tire pressure, the lower the rolling resistance. but you can vary your pressure depending on your ride. if you're going for speed, pump 'em up to the max rating. however they tend to ride like rocks, relatively speaking, so you feel every bump. if you want a softer ride, or need traction in slippery conditions, do 10-15 psi less.

cool thanks... so what you all doing personally???:)
thanks again
Ryan

I have Conti GP3000s and they're similarly rated for 120PSI. I pump them to about 125PSI figuring [1] they'll lose a little bit of pressure over the course of the ride, [2] they can handle much more than 120PSI and more importantly, [3] I like a nice firm ride. It's all about your comfort level. If you prefer a cushier ride then go with a lower pressure. Play with it a bit and see what feels best.

There is a recent thread on the Road bike forum about this. 120
psi is the max the tire is rated at. Most people feel this is a harder tire than feel comfortable riding at, especially if you have a lot of chipseal roads. A few feel it is a good level to ride at. My opinion is that 90-110 is adequate, try various levels for your self and see how they feel for comfort and then for perceived rolling resistance. Steve

Originally posted by sch
My opinion is that 90-110 is adequate

Yup, that has been my experience also. I feel that I get a better grip on the road running psi lower than the max.

Ryan
All rims have a max pressure rating, check to see what it is for your rims and you should not exceed that pressure no matter what is on the tire, for example, Mavic T-520 has a max rating of 105 psi.

Pete

I'm rollin' Huthcinson CArbon Comp tires on my Lemond... they are rated as max psi 120... I generally run the back tire at 110, and the from around 105... I have noticed zero effect of rolling resistance and speed, going from higher pressure tires down to this... actually the guys at roadbikerider.com seem to think you should never inflate over 100psi... the debate rages on, but they said that you can actually increase rolling resistance by using lower pressure.... if anything, less psi will give you a more comfortable ride, just don;t go too far down, or you risk a pinch flat

JEff

Of course you INCREASE the rolling resistance by LOWERING the tire pressure. A softer tire will create more friction with the road surface. If you want to go faster, at the expense of comfort, you want LESS rolling resistance. I run Panaracer Stradius Pro 700x20 at 120psi. They are fast, but a little bumpy when the road surface turns rough. I just stay out of saddle over the big stuff.

DEMON

I generally pump them up until they explode, and then back off the pressure a little.

i'm riding on pretty smooth surfaces, and for usually under two hours...actually during the week i get about an hour a day so i'm just busting my hump as fast as i can, on really smooth roads. so comfort is less important than zippiness. i keep 'em near the max rating on my tire (120-125 psi)...actually i pump a little less into the front tire, just to give my arms a break from the vibrations. but that's probably about as useful as a good luck charm.

So is it better to have the back tires pumped highter thsn the front?

That depends on the bike. If you have a carbon fork, it will soak up a lot of the vibration anyway, so you can keep both tires fully inflated to minimaze your rolling resistance and maximize your speed. If you have a carbon frame or even just parts of the rear triangle, vibration shouldn't be a problem anyway.

DEMON

yeah, what demoncyclist said. i should have mentioned that i'm riding an aluminum bike, which is a bit 'firm' in the vibration department. the fork is cromoly, which should be taking up some vibes...but yeah, if you've got an all-steel or lots-of-carbon frame/fork, the tire pressure might as well be the same. and i'll be the first to admit i haven't really noticed much difference either way. i do it because in theory it makes sense.

My tires have a max psi to 120- I pump my tires to 120. Is there a problem with doing that?

Koffee

I'm a big clydesdale rider, entering into rhino class. My conti's are also rated at 120, and I pump them up to 130 the night before my ride the next a.m. Never had any problems!

L8R

Originally posted by Koffee Brown
My tires have a max psi to 120- I pump my tires to 120. Is there a problem with doing that?

Yes. I think if you don't need to pump your tyres that high then you're unnecesarily using precious oxygen. Please release that air from your tyres so that others in more need may have it. :D

Originally posted by Koffee Brown
My tires have a max psi to 120- I pump my tires to 120. Is there a problem with doing that?

Koffee

None that I can see, that's the way I do it. Seems simple, don't it?

I am running 100 in each right now, and seem to be fine... now... how to judge if my seatpost is too low/high...:) man talk about issues...
Ryan

In a semi related topic, what do people use to check their tire pressure? The pressure gauge integrated into the pump or some external air pressure gauge? The reason I ask is that yesterday as I was helping my sister set up her MTB I pumped up the tires and the gauge on the pump said 50PSI. Just for kicks, I then checked it with a digital air pressure gauge that I use on my vehicles and it read 41.5PSI. That's almost 20% delta! So which to trust? :(

Hmmmm I had always thought to run mine to the Max 125 psi also... but reading this taken from Roadbikerider.com.. makes me think.. maybe I will experiment for a while

Following is a quote from Uncle Al on Roadbikerider.com

"Most everyone I know runs too much pressure. Welcome to the club. Over many years of testing and talking to guys who live on their bikes, I'm convinced there is little reason to run more than 95-100 psi -- and there are compelling reasons to run 85-90 psi.

High pressure, say 100-120 psi, guarantees short tire life, poor cornering and lots of punctures. A rock-solid tire cuts/punctures more easily than it would at a lower pressure. Also, a softer tire can "smear" -- conform better to objects encountered on the road. Why make the ride even rougher on America's ever-crumbling road surfaces?

Admittedly, I weigh 210 pounds and ride on really poor road surfaces. These things influence my opinions. I run 85-90 psi front and 90-95 psi rear on 700x23C clincher tires. I do not have flats! Plus, bumps are less of an issue, and my bike corners as if on rails on high-speed descents. I get 1,000-1,500 miles out of a rear tire. When I ran much higher pressure many years ago, I got no more than 500 miles.

So, my advice is never to run smaller than 23C. Use good tubes, air them up before every ride and spend extra for premium tires -- they'll pay you back in extra mileage and better handling."

Hmmm... I have a 23C, and I'm happy with that. But still, I've done a lot of miles, and I've only had one flat, and that was from running over a really BIG obstruction- I couldn't avoid hitting it, and the flat came right away.

I kinda like my 120 psi. I really feel like there's a difference in speed, and I feel a lot faster at 120 psi than at 80- 90 psi. I also feel like I have to pedal a lot harder at 80- 90 psi, which is why I made the decision to run them at higher psi's. I first started at 85 psi, then moved to 100 psi, then 110 psi, then finally made the decsion to move to 120 psi. So I'm pretty happy here, but still wondering if I should drop down the pressure. The lowest I could possibly go is 100 psi. Any less, and I'll feel like I have to spend all my time stomping on the pedals to get the revolutions! :eek: I currently do at least 150 miles a week too, and I know I've done more than 500 miles on my bike since I've changed my tires back in June.

Koffee

I weigh about 205 and ride 700x20 at 120psi. Yes, they are rough on bad surfaces, but the rough is so much shorter at higher speeds. I agree with Koffee about not running at a lower pressure. It feels like you are riding through mud. I have had 1 flat tire in the past 3 years, and my commute takes me over 5 railroad crossings, only one of which has been upgraded with those new composite strips between the rails. The other 4 are rotting wood and have pretty large gaps. The roads around here have been in the news lately for their horrendous condition, but I still feel more confident on the bike with a fully pumped tire under my butt. A difference of 10 psi and I feel like the wheel is squishing under me when I maneuver the bike. I also had my last set of tires for 3 years, and I kept them for emergency replacements, so the high pressure really isn't killing the treadlife. As for my excessive use of oxygen, air is only 18% anyway, so I don't see myself as being a conspicuous consumer!!

DEMON

man...I didn't know this was going to start such an informative post...:) I just went out real quick and tested the 100 psi front and back and it feels great!!!:)
Ryan

so how much of this is psychological? i've put 125 psi in my tires, so therefore i'm faster...i'll be the first to admit that i haven't actually done any methodical experimentation on this.

so what we need to do is a proper test. for the next twenty rides, arrange to have someone else pump up your tires for you. they'll keep a record of the psi put in, and the amount will be random between 80 psi and max rated. then after each ride, you keep a little log of how the ride felt and what tire pressure you thought was in the tires. and no cheating by giving them a little squeeze during the ride! then see how your perceptions match up with the actual pressure.

i'm not sure my wife can be bothered to pump my tires for me, so i don't think i can do this test personally.

and for those of you reading too much into that last sentence, shame on you.

i think i'll try riding at a lower than usual pressure this weekend, just to see what i think of it all. but if i get a flat tire, can i send it to chaztrip for repair? :)

(added this later):

{Bobsled** In a semi related topic, what do people use to check their tire pressure? The pressure gauge integrated into the pump or some external air pressure gauge? The reason I ask is that yesterday as I was helping my sister set up her MTB I pumped up the tires and the gauge on the pump said 50PSI. Just for kicks, I then checked it with a digital air pressure gauge that I use on my vehicles and it read 41.5PSI. That's almost 20% delta! So which to trust?


trust no one.

remember you let air out of your tires every time you put on a gauge or a pump, so it'll likely keep going down. and precision isn't the same thing as accuracy...your digital gauge may just be very detailed about how wrong it is. but that still seems like a big drop. i doubt most of these gauges are better than +/- 5psi anyway.

In my humble experience, tire pressure has less of an effect on tire wear as quality of the tire itself. Flame suit on: Cheaper tires last longer! The rubber durometer is harder and thus doesn't wear as quickly, and better flat resistance. The trade off is a harsher ride, less traction (especially in the wet).

Plus, with my engineering experience, I know that the max rating is still well within the "Safety" zone of design, and exceeding that limit by 10% will have minimal ramifications.

L8R

In my humble experience, tire pressure has less of an effect on tire wear as quality of the tire itself. Flame suit on: Cheaper tires last longer! The rubber durometer is harder and thus doesn't wear as quickly, and better flat resistance. The trade off is a harsher ride, less traction (especially in the wet).

In reality this is far from the truth. Tires with harder durometers do not have the grip of softer tires. Because of this they are much more likely to skid or slid around. This movement acts like sandpaper between the road and tire causing increased wear. I experienced this on my old sports car. I bought the softest compound, most grippy tire I could find. Those tires had excellent tread wear because they were always gripping. They didnt slid so there was sandpaper effect.

So back to the topic of tire pressure. Once your tires are inflated to the point they support your weight without deforming you dont need anymore pressure. Tire size is very crucial in determining pressure. 20c tires need more pressure because there is less volume and vice versa. 32c tires need less pressure because they have more volume. Have you ever seen the tires on those big dump trucks? They run relativly low pressure because they make up for it in volume. Lower pressures, as noted earlier, will not puncture as easily.

Two riders, a female weighing about 110 and a guy weighing in around 200. Its quite obvious they need different pressures. In this scenario the lady could ride 19c tires at 90 psi while the guy has no choice but to ride 23's at 100.

Lastly, super high pressures do have the potential to roll more easily. How else do explain track and hour record riders running 200psi with helium?

Originally posted by rippo

i think i'll try riding at a lower than usual pressure this weekend, just to see what i think of it all. but if i get a flat tire, can i send it to chaztrip for repair? :)


HE HE :D just remeber that I was taking what I said from some one else's quote on another forum. I am a Road Bike Newbie:( :)

I did not even no what PSI was until 7 months ago:D

I want helium in MY tires!!!

Originally posted by Phatman
I want helium in MY tires!!!

But then you'll have to carry around one of these instead of a CO2 cartridge or minipump... :eek:

http://www.balloontime.com/images/20-helium-balloons.jpg

trust no one.

Alright Mulder.

Love always,

Scully

;)

Originally posted by a2psyklnut
I know that the max rating is still well within the "Safety" zone of design, and exceeding that limit by 10% will have minimal ramifications.

L8R

I agree.
I prepare my tires to 125psi religiously every time before I go for a ride. I don't really feel the stiffness of high pressure. I think most of the vibrations are absorbed by the frame(mine is steel) and my legs. Faster I go, the more it seems that way.

I always pump my 120psi tires to 110-115psi. Usually by the end of a long ride they are down to between 105-110psi.

"clydesdale rider, entering into rhino class." I like that.

Currently, I weight in at 220, and run 25's at 90/95 psi F/R. Being an engineer, I set up a rolling resistance test on a hill. I measure max speed coasting from a full stop, from a mark at the top of the hill to a mark at the bottom of the hill, while adjusting tire pressure between runs. Anal? Oh, hell yes, but I wanted to personally settle the question of tire pressure. Now I roll faster, tires last longer, and better ride & cornering.

FYI, Conti ran tests on various gases to fill tires, and nitrogen won.

FYI, Conti ran tests on various gases to fill tires, and nitrogen won.

Its funny you mention that, at work we use nitrogen to power the compressed gas tools. Supposedly it shuttles faster. Helium is used primarily used because of its low mass and I'll assume it easier to get.

Da Tinker: Thats a test I've always wanted to do but never did. I was going to mine slightly differently than you. I was going to start at the top of hill and see how far I could coast up the next one.

I run both tires at their max rated pressure. One side benefit is that i almost never get flats.

Originally posted by Da Tinker
"clydesdale rider, entering into rhino class." I like that.

Currently, I weight in at 220, and run 25's at 90/95 psi F/R. Being an engineer, I set up a rolling resistance test on a hill. I measure max speed coasting from a full stop, from a mark at the top of the hill to a mark at the bottom of the hill, while adjusting tire pressure between runs. Anal? Oh, hell yes, but I wanted to personally settle the question of tire pressure. Now I roll faster, tires last longer, and better ride & cornering.


just for clarification, your 90/95 psi is better than what? higher psi's of 120 or so?

no this isn't anal, this is exactly the sort of thing people should do, rather that believe old wives tales without research!

and to report back, i road 23 miles today on 100 psi f/r rather than my usual 115/125. didn't notice any difference!

What about my tires on my very old roadie, which have a max psi of 75?
None of my mountain or hybrid bikes I've had over the years have had any higher either. Maybe higher psi's start at higher prices?
After reading this post, I'm probably going to pump them up to 75 - 80, at the risk of bursting them, and then I'll have a good excuse to buy new ones, thats my method of thinking. By the way, how much will a pair of new high pressure and good quality tires and tubes set me back?
Or wait, do modern road bikes still use tubes, something tells me they don't?

What about my tires on my very old roadie, which have a max psi of 75?
None of my mountain or hybrid bikes I've had over the years have had any higher either. Maybe higher psi's start at higher prices?
After reading this post, I'm probably going to pump them up to 75 - 80, at the risk of bursting them, and then I'll have a good excuse to buy new ones, thats my method of thinking. By the way, how much will a pair of new high pressure and good quality tires and tubes set me back?
Or wait, do modern road bikes still use tubes, something tells me they don't?

If your tires are rated for 75psi, chances are your bike has straight sided rims rather than more modern hook bead rims. I'd make sure my dental coverage was paid up before experimenting with tire pressures much higher than 75psi. Tires sometimes have a way of waiting until you are on a downhill curve before they decide to blow themselves off of the rim.

I have had this discussion several times with road tire industry guys. They all seem to agree that running a road tire at it's rated PSI is the best idea. They designed the tire to perform at it's best at that PSI.

That said, I run my road tires at the rated PSI or a tad under. But never over.

And contrary to what one poster said about running them soft, I don't agree that they are less prone to flats. Soft tires pinch flat easier.

I am not sure about Low PSI. I ran my specialized all condiciotn tires on 110-120 for most of the summer. I weighed at the time about 235. I had so many flats that I got quite angry. I use specialized tubes, tried others and still flat city. I am now a nice 218 lbs and run my tires at 125-130psi. I feel like I am crusing through space, but yes cornereing is a bit of a problem. Sometimes slip out of the pitch and then yeow. My tires are 700X25. Just bought Ultra Gator Skins and run them at 125 and they seem to grip better on corners. I was worried about loosing speed, but so far no problem. Anyone care to tell me who makes a tire liner and I will go to Conti-Racers. I hate flats. Clarification, all pinch flats at lower PSI. Just my two cents! Wait I need that to save for the Roubaix Comp, mind giving my two cents back.

Whenever I've pumped continentals to their rated pressure, I get sidewall failures in very short order. I use 90 psi max on my 28 C's.

I have been inflating the tires at 120 psi for purpose of avoiding flat. Lately I'm experimenting at lower pressure, like 110, 100(recommended by MFG.). At 20 psi difference, I can feel a little bouncy feel but not by much. It may make a big difference on the long rides. So far I haven't had a flat at 100 psi yet.

I weigh 140 lbs and using 700x20 both front anf rear.

Here is a long answer from Leonard Zinn on this topic. Runs contrary to conventional wisdom but I would assume his reponse to be true.

"PSI too high?
Dear Lennard,
I've been reading some of Zipp's comments on tire pressure and rolling resistance attached below. When you really sit down and talk to them about tire pressure they're recommending pressures of 100-120psi (sometimes less) depending on the tire, casing, and environment. I am including comments from Josh at Zipp on this topic. One thing I quickly noticed was the absence of weight in his recommendations. A larger rider running 120 psi compared to a lighter individual (say 30 pounds difference) would exhibit a larger contact patch (resistance or traction however you look at it) due to weight so I'm really not jiving on his basic psi recommendations.

Leaving road conditions out (rain, etc.) what are your thoughts on tire pressure? The common theme of tubulars is the advantage of both weight and tire pressure. The ability to run pressures of 180-200 psi. I know for myself I feel faster (have never tried to test this with rollouts or anything) when running pressures of 140-160 psi (clincher) and 180-200 psi (tubular). I've ridden a number of tires and prefer the ride of higher psi tires such as Vittorias, Vredestein and Tufos.

Do you know of any numbers or tests that prove these thoughts on tire pressure? I've had a number of lengthy conversations with Biomechanists interms of rolling resistance (friction) and don't know how a general recommendation on lower pressures can be faster especially not taking weight into account. It goes against everything I've read about rolling friction. It's pretty easy to point out that the average pro in the peloton only weighs about 150 lbs., so of course it's common sense that they wouldn't need to run similar pressures as you or I, but 100-120 psi seems a bit low when you're talking tire pressure for the most efficient rolling resistances.

I've also been reading your blurbs about tubulars, Tufo and their clincher tubulars. Taking Zipp's tire pressure recommendations in mind where do you stand in regards to Tufo and their clincher tubies and other high pressure tires?
Tom

Dear Tom,
I agree with Josh, and yes, there are lots of test numbers to back it up. It is the same reason a suspension bike (or car) is faster over rough ground - less mass must be accelerated when bumps are encountered, thus saving energy and reducing momentum loss. Every little bump that gets absorbed into your tire (another reason that supple, handmade casings roll faster than stiffer, low-thread-count casings) is a bump that does not lift the entire weight of you and the bike.

You feel fast on a rock-hard tire for a similar reason that people like the feel of stiff brakes (V-brakes with the levers set on low leverage). The brake feels good and stiff because you are doing more of the work. If you increase the leverage, the brake feels spongy, because the extra mechanical advantage allows a modest pull to squish the pads.

When you ride a tire at 170psi, the bike feels really lively and fast. That is because you are being bounced all over the place by the surface roughness of the road. However, every time you are bounced, energy you applied to the pedals to get you up to speed is lost. Also, you have less control of the bike, so it feels like it is going faster, even though it isn't. Ever notice how driving down the highway at 75mph in an old Jeep feels crazy fast, and you can cruise smoothly along at 100mph in a nice Saab or BMW and feel like you are going maybe 60mph unless you are looking at stationary objects passing by?

There is simply no question about it; rolling resistance tests conducted with bicycle tires rolling over surfaces akin to normal road surfaces always indicate the lowest rolling resistance at pressures a lot closer to 100psi than to 170psi! Years ago, for example, I saw results like this at the Continental tire factory. I was told of similar results at a number of other tire factories I have visited.
Lennard "

If you want incentive to push the lower pressure limits check this out from Bicycling Magazine 1986:
http://www.precisiontandems.com/photos_files/tirechart.jpg

Also read up on what Sheldon says (stuff about pressure is about 2/3 the way down, but all is usefull):
http://www.sheldonbrown.com/tires.html

For commuting I run 28c conti gatorskins (rated at 120psi) at 110psi rear, 100psi front.

As to loosing pressure - in the cold (40-50dF) months I loose at most 5psi over the course of a week. In the hot (>110dF) months I can loose up to 5psi a day.

Al

Technical Q&A with Lennard Zinn - PSI, nasty roads
By Lennard Zinn
VeloNews technical writer
This report filed February 2, 2005
PSI too high?
Dear Lennard,
I've been reading some of Zipp's comments on tire pressure and rolling resistance attached below. When you really sit down and talk to them about tire pressure they're recommending pressures of 100-120psi (sometimes less) depending on the tire, casing, and environment. I am including comments from Josh at Zipp on this topic. One thing I quickly noticed was the absence of weight in his recommendations. A larger rider running 120 psi compared to a lighter individual (say 30 pounds difference) would exhibit a larger contact patch (resistance or traction however you look at it) due to weight so I'm really not jiving on his basic psi recommendations.

Leaving road conditions out (rain, etc.) what are your thoughts on tire pressure? The common theme of tubulars is the advantage of both weight and tire pressure. The ability to run pressures of 180-200 psi. I know for myself I feel faster (have never tried to test this with rollouts or anything) when running pressures of 140-160 psi (clincher) and 180-200 psi (tubular). I've ridden a number of tires and prefer the ride of higher psi tires such as Vittorias, Vredestein and Tufos.

Do you know of any numbers or tests that prove these thoughts on tire pressure? I've had a number of lengthy conversations with Biomechanists in terms of rolling resistance (friction) and don't know how a general recommendation on lower pressures can be faster especially not taking weight into account. It goes against everything I've read about rolling friction. It's pretty easy to point out that the average pro in the peloton only weighs about 150 lbs., so of course it's common sense that they wouldn't need to run similar pressures as you or I, but 100-120 psi seems a bit low when you're talking tire pressure for the most efficient rolling resistances.
I've also been reading your blurbs about tubulars, Tufo and their clincher tubulars. Taking Zipp's tire pressure recommendations in mind where do you stand in regards to Tufo and their clincher tubies and other high pressure tires?
Tom

Dear Tom,
I agree with Josh, and yes, there are lots of test numbers to back it up. It is the same reason a suspension bike (or car) is faster over rough ground - less mass must be accelerated when bumps are encountered, thus saving energy and reducing momentum loss. Every little bump that gets absorbed into your tire (another reason that supple, handmade casings roll faster than stiffer, low-thread-count casings) is a bump that does not lift the entire weight of you and the bike.

You feel fast on a rock-hard tire for a similar reason that people like the feel of stiff brakes (V-brakes with the levers set on low leverage). The brake feels good and stiff because you are doing more of the work. If you increase the leverage, the brake feels spongy, because the extra mechanical advantage allows a modest pull to squish the pads.

When you ride a tire at 170psi, the bike feels really lively and fast. That is because you are being bounced all over the place by the surface roughness of the road. However, every time you are bounced, energy you applied to the pedals to get you up to speed is lost. Also, you have less control of the bike, so it feels like it is going faster, even though it isn't. Ever notice how driving down the highway at 75mph in an old Jeep feels crazy fast, and you can cruise smoothly along at 100mph in a nice Saab or BMW and feel like you are going maybe 60mph unless you are looking at stationary objects passing by?
There is simply no question about it; rolling resistance tests conducted with bicycle tires rolling over surfaces akin to normal road surfaces always indicate the lowest rolling resistance at pressures a lot closer to 100psi than to 170psi! Years ago, for example, I saw results like this at the Continental tire factory. I was told of similar results at a number of other tire factories I have visited.
Lennard

Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of several books on bikes and bike maintenance including the pair of successful maintenance guides " Zinn & the Art of Mountain Bike Maintenance" and "Zinn & the Art of Road Bike Maintenance."Zinn's regular column is devoted to addressing readers' technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn's column appears here each Tuesday.


Written by Josh at Zipp - Supplement to LZ Column
This report filed February 2, 2000
Written by Josh at Zipp: Here is an excerpt from a PM I sent to somebody a few weeks ago on this identical topic. I hope this helps clarify things somewhat...

The outer aluminum hoop in our clincher rims weighs only 200 grams, and therefore will get much hotter than a standard aluminum rim. Since the temperature of something is relative to the energy input/mass, a 200 gram rim will get twice as hot as a 400 gram rim for the same energy input. What happens is that if your descending a mountain at 70 degrees and you brake for 2 minutes and your standard aluminum rims heat to 220 degrees (an increase of 150) this same condition with a 200 gram clincher rim will result in a rim temp of roughly 370. Since the carbon is such a good insulator, the rims just have nowhere else to put the heat, so they get hot. This in itself is not the end of the world, except that tubes can melt at these temps, but considering that your tire pressure will rise at a rate of roughly 1psi per 10 degrees, you will see a corresponding tire pressure increase of 30psi.

Assuming your tire pressures are at 125, everything is fine almost regardless of the tire you are using, but if you were at say 160 and then had this same situation, your pressure could elevate to 190 which could be a terminal situation causing the tire to blow off of the rim.

We have seen temperatures intermittently hit 350-400 degrees in mountain testing in the Alps, so the case described here can actually happen. Since there is a pretty wide band of tolerance for tire fit, we can only guarantee that your tires will remain properly seated at their recommended pressures, and must recommend a pressure of our own. We make our rims at the large end of the diameter tolerance for ISO classification, meaning it is harder to get tires onto the rims and therefore harder for them to blow off, but air pressure is such a powerful and explosive force, that when combined with heat we must be very, very safe, not to mention that as tires age and stretch, their pressure capability is reduced, so there are numerous factors which must be accounted for here. Every rim manufacturer has a recommended pressure in this range in their literature, some just advertise it more than others, Mavic for example has a nifty sliding scale relative to tire width allowing for 135psi MAX for a 19mm down 115 psi MAX for a 25mm tire, and we have advised similarly, and for all the same reasons.

The other issue to consider is that most every tire on the market runs at optimal rolling resistance between 105 and 125psi depending on load and road surface condition. We have seen data from numerous manufacturers and had enlightening talks with others to learn that nylon cased tires like Michelin or Continental tend to run optimally around 105-115 and cotton or bias cased tires like Vittoria or Vredestein tend to run optimally at 115-125 maybe as high as 130 for Vredestein, but all of them actually will increase in rr at higher pressures due to the tread rubber beginning to fail in shear as it locally deforms to meet the contour of the road imperfections when the casing is too rigid. Think of it in terms of heat input, as the over inflated tire struggles to conform to all the tiny surface imperfections to make the necessary contact patch, a lot of heat is generated. Not only is there higher rr, but faster tire wear as well at higher pressures, not to mention the tires decreasing ability to stay mounted on the rim as pressure increases. In an ideal world tire manufacturers would list a recommended pressure and not just a MAX pressure (the max pressure is simply a predetermined percentage of the bursting pressure of a given tire as set out by industry standards and has nothing to do with the pressure you should actually run) but they are between the rock and hard place as consumers continually push for higher and higher pressures feeling that ‘if some is good, more is better'. Of course none of this even mentions comfort, which we believe to be of increasing importance as more and more data has shown fatigue to be caused by vibration. It may be that by increasing tire pressure by 20-25 psi, you feel faster as your tires are transferring more of the high frequency vibration to your body (you're feeling a higher frequency 'faster' vibrations' so it really does 'feel' faster) but are actually expending more energy to do it, while simultaneously wearing out the tires faster and inducing fatigue.

Looking to pro road teams, most of them are running 100-110 psi in tubulars and 105-120 psi in clinchers, and this has been a bit of a knock against the clinchers from the pros, that they prefer the lower pressures for improved handling, grip and feel, but need additional air to prevent pinch flats. Especially of issue are rainy races, where they may even lower pressure to 95 psi or so for better grip and control in the corners. The only real exception here would be track racing, especially on wood, where the surface is so smooth that very high tire pressures can yield excellent RR results, but still generally reduce grip slightly, but even this is specific as a board track may run well at 220psi, but a concrete track favors 150-160psi, and some track surfaces are no better than most roads... For an analogous example, look to Inline Skate racing, where they carefully select the durometer (firmness) of their wheels to the surface they are racing on, this is nearly as critical as ski wax in ski racing as it can win or lose races for you. It is so critical as too hard a wheel will get you dropped like a hot rock on most road surfaces, whereas that same wheel is the only way to be competitive indoors on wood.
Josh

the tire pressure also depends on your weight, and front/rear tires.
Being heavy myself I pump my rear wheel to 140psi. The wheel is very hard, and wears out a bit faster (smaller contact point), but it rolls so much better. you can get tires that are rated to take 145psi (Conti supersonics, Vittoria, etc.), but I use the Conti 3000 Grand Prix (rated 120), and it is doing fine. By front tire I pump up to 120..

I don't know if this is actually true, but I go on the premise that the harder the tire is, the less likely you will get imbedded glass in the rubber. So I always run my Specialized Armadillos at the max, 125. I use an air compressor I got at Lowes for $50 -- it sure saves a lot of pumping when you have four bikes.

The Continental tire website lists both the "maximum" and the "best" PSI for each of their current tire models. "Best" PSI relates to the weight of the load on the tire (the rider's weight plus the weight of the bike), so the Continental "best" PSI is for some mythical "average" rider.

The interesting thing is how LOW their recs are. My favorite tire size is a size 28. Depending on the model, Continental sets the "best" PSI at 80 PSI to 95 PSI for a size 28 tire. Yet, I know guys riding these tires at 140 PSI "cuz my pump goes that high".

I'm heavier than any "average" rider, mythical or not, so I set my size 28 tires at about 90 PSI front and 100 PSI back. That level provides a good balance of handling, stability, braking, and protection against flats and road shock.

I've been riding bikes for over 35 years. Almost daily. I have never measured the psi.
I just always pump them up to what feels right. I like them "tight". For less rolling resistance.
And I've never popped one.
I use hand pumps, foot pumps, and when available, gas station lines.