Road Cycling - tire pressure, can this be true? I'm 115 in front and 120 in back

DEAR UNCLE AL: It's obvious that low rolling resistance is a good thing. Yet trying to find solid information about the rolling resistance of different tires is a problem. Do you
have a cluestick to point the way to some clarity on this issue? -- Michael R.

UNCLE AL FIRES BACK: When I opened your e-mail,
I cringed at the thought of the negative reactions I might get after answering your question.

I know some of you won't agree with me, and I pretty much know your reasons. You don't need to send long e-mails to dispute the way I look at this issue. Hey, it was Mike who asked, not you!

Rolling resistance is one of the most misunderstood elements of the bike. There will be those who insist that reducing it is all about running super-high tire pressure. That is
simply not the case.

Rolling resistance is dictated by several factors, one being tire construction. A top-quality clincher tire will have a threads-per-inch count ranging from 125 tpi to an astounding 440 tpi. Most companies use nylon for casing threads, going by names such as Aramid or Polyamide.

There will be 3-5 overlapping casing layers to give the tire strength, puncture resistance and good handling characteristics. The suppleness of the casing material is key to performance and reducing rolling resistance.

Another factor is the tread material. Most top-end clinchers are now using some form of silica compound, which lowers rolling resistance while increasing cornering traction. Sounds like magic, doesn't it?

Understand that the designers and engineers behind quality tires are some of the brightest lights involved with the bike industry. We are spoiled riding tires that are as good as the stuff used in auto and motorcycle racing, yet we can
buy them for just $50.

Remember this: The best tires cost what they do because of the technology and materials that go into making them. We are the lucky beneficiaries of this high science.

The last factor affecting rolling resistance, obviously, is tire pressure. If a tire is flat, it has a whole bunch of resistance and really doesn't handle very well.

A properly inflated road tire (700x23C) at 6bar/87 psi has about the same rolling resistance as the same tire at 8bar/115 psi. But at the higher pressure, the rider gives up some of the cornering traction and comfort so necessary to cycling.

There's a perception that running tires at 115-140 psi somehow makes a rider faster. What those maximum pressures really do is accelerate wear, compromise handling and give an extremely harsh and skittish ride.

Super-high pressure also compromises the integrity of your wheels and, in the case of a high-speed blowout, can assure you of a visit with the pavement. Heavy braking while descending will heat the rims and increase pressures wellbeyond the danger zone.

I've talked to pros about tire pressure. They universally agree that inflation to 85-100 psi is plenty, depending on road conditions. Pressures up to 110-115 psi are fine on a smooth time trial course without many corners.

Most riders who run super-high pressure will remain unconvinced about the benefits of lower pressure. I think it's their placebo.

mailbox:/C|/Program Files/Netscape/Users/User00/mail/inbox?id=200305151916.h4FJGdh06633%40host3.globalsecureserver.com&number=47274969&part=1.1

i saw this too and was a little surprised, i think even if this is the scientific answer most people will still inflate to high pressures if not just for a mental edge

After a nasty flat last week, I was only able to get 75psi in my tire. I usually run 115 in the front. Speed wise, my avg speed did not drop even a 1/10th MPH. Ride quality was up some...

However, as Seaman posted above, I'll keep 115 up front for the mental edge.

Lower psi and you will work harder to keep that mph up.I can sure tell when mine are lower.Like i am in mud.

Mud? Guess I like mud. Wonder what the pro teams use for pressure...nt..

mikemets5

Very interesting post. I have been playing with tire pressure and tire size for awhile. I have even switched to a 700X28 tire because of the large inflation range they offer. Have gone to apporx. a 80-90 pound inflation range. Fewer flats and have not really noticed a difference in preformance. More comfort on the bike and a greater safety margin should I be forced through some gravel of off the road a bit.
The tires are cheaper to and last longer.

Originally posted by mikemets5
A properly inflated road tire (700x23C) at 6bar/87 psi has about the same rolling resistance as the same tire at 8bar/115 psi.

As opposed to an improperly inflated road tire at 6bar/87 psi?

Call me shallow, but a road tire tire at 87 psi is improperly inflated.

Max it out, baby.

Lance Armstrong only runs something like 105 psig in his front tyre, so there goes the high pressure argument!
FWIW, I usually ride with anywhere from 100-110 in my front tyre (21mm tubular) and from 125-135 in the rear. I have 2 wheelsets, one made for comfort, and one for speed.
Recently, I bought a new Specialized Nimbus set of tyres for my fixed gear. Very stiff, smmoth tread, but very flexible sidewalls. Even at 75 psig they have very little rolling resistance, but they ride very nicely!

My LBS guy told me to keep my MTB tires, Panaracer 2.1's at 40 PSI, and to keep my Michelin 700X23's at 110 PSI for my road bike. Is he right? I am still new at this, and I pretty much have to take everything that the shop tells me as truth. - Ted

What ever inflation-pressure that decreases hysteresis to it's lowest point is the optimum tire pressure for a given load and tire.

It is in fact true that since loads vary between the front and rear wheel, pressures (in theory) should vary also. (as well as rider's weights )

This ISN'T rocket science, just pump your tires up so they don't look "low".

Another true "Richard Cranium" post.........

i dunno about everything else, but i LOVE being able to feel everything in the road when my tyres are up to 110 - 120psi

Gee! I run my fortezzas at 140-145 and I think they ride better than the stock steel beadede 700x25s that come on the bike! I have had very few flats and seem to get at least the same milage from the fortezza as the stock tires. I read that same Uncle Al so just for kicks I put on my other set of wheels with the 700x25 already mounted and pumped to 80psi and I just can't tell that much difference in the way the bumps in the road feel. Maby it's just what you get use to?:confused:

I run about 100 psi -105 psi in both my clincher tires (my pump isn't the most accurate gauge in the world) I do notice however it is a bit harder to spin tires that are lower than 90 psi (hard to inflate a commuter tire with a hand pump!) but then again I'm still spinning :)

I wouldn't ever ride a clincher pumped to
140 or 145. Tubular, not a problem
but not a clincher.
Just my grouchy $.02 worth.

Marty

Lotek, Can you give me a reason? I have been riding this for about 6 months now and haven't noticed any problems.

well I have this thing about clinchers blowing off the
rim. . . won't happen with a tubular.
Of course both clincher tires and rims are better than
they used to be so this shouldn't be much of a problem.
Like I said, I was being a bit "retro grouchy".

Marty

Tubulars are a heavy pain in the but.Never heard of or seen a clincher blowing off a rim.You would think that would be a problem in the tdf if that happened.Do they use tubulars there?

Lance Armstrong only runs something like 105 psig in his front tyre, so there goes the high pressure argument!

and we all know that if Lance does or says something, it's gotta be true!

shokhead: yes, they do use tubulars in in the tour. not everyone, but quite a few teams do. if you want to find heavy use of tubulars look to the track. there's nothin like a tubular pumped up to 220psi.

Tubulars are a heavy pain in the but.Never heard of or seen a clincher blowing off a rim.You would think that would be a problem in the tdf if that happened.Do they use tubulars there?

Negative, o ye of little knowlege. Tubulars are always lighter than comparable clinchers, and the rims are also lighter. And, yes. Ive seen a clincher blow off a rim. Used to be much more common, but it still does happen. clinchers are also much more likely to pinch-flat, too.
And, since you are clueless about the equipment that teams in the TdF use-about 90% of all riders are using tubulars, all the top riders are riding tubulars, and every single TdF ever run has been won on tubulars. Any more questions or ignorant comments?

I run Fortezza's at around 110/120 This is not for speed but to prevent pinch flats. There are a lot of gravel driveways out here and it is hard to miss every rock. If you run a heavy loaded bike(touring) you should run more pressure because it is easier on the tire. It does not flex cycle as much when it comes around to the contact patch. Kind of off topic but I believe that contributed to failures of Firestones on Explorers. Ford reccomended a lower than optimum pressure to improve ride quality and it reduced the load capacity of the tires to the point where heat failure was possible. Every time the tire flexes there is friction, which generates heat, within the casing, Flex it enough and it will get hot enough to fail. A bike tire is unlikely to fail but I have seen some damaged side walls from low pres.
If you think the pressure does not make a diffirence thenhop on your mountian bike with the tire at the low pres. marked on the sidewall, ride it around on the street for a while. Then pump it up to the max and ride it again.
The pressure given 87psi is really pretty arbitrary any way. Optimum pressure depends on casing, durometer, rim width,air temp., and load.
uciflylow If you stay within the gudelines on the side wall of the tires you should have no problems, the engineers who designed the tire put those there to keep you out of trouble. Off road if you need more traction try dropping your tire pressure. If you are just riding fire roads then up it to reduce your pedal work. On the road, if you are on roads made with coarse aggregate then you might want to run at the lower end of the pressure reccomendation to give a smoother ride and if you find it comfortable and it does not feel like it is slowing you down leave it there all the time.

One factor that is frequently overlooked regarding high tire pressures is the rim.

Everybody knows what pressure their tires are rated for. It's printed on the sidewall. Practically nobody knows what their rims are rated at. Rims change over time too. As your brake surface wears, high tire pressures will gradually cause your rim flanges to flare outwardly. Eventually, you will find the point at which the forces trying to blow your tire off of the rim will exceed the ability of your tire and rim to resist them. It usually happens in the middle of a turn.

Your so smart d*alex that it must hurt.So i have learned something,thanks.Never had a pinch flat but you knew that,right?

I hit a hole in the asphault, actually a place the semi trucks had wallowed out, that wasn't there the last time I rode this down hill strech so hard that it almost caused me to chip some teeth!:eek:
No pinch flat or rim dammage. I was just wating for the flat and wobble while I was trying to get stopped! I have ran over other assorted trash that I know would have flatted the Bontrager select tires that came on the bike. I also know that while ridding the same roads I have had much fewer flats and I think those are just small holes that appear in the cheep tubes I'm using!

Can a tube just, get a hole in it? The last holes I have had where microscopic and there was nothing in the tire. I even went around it with a cotton ball!

uciflylow, sometimes tubes do just get holes in them, from a little piece of grit that was in the tire or from a small flaw in the tube like a little air bubble. One of the reasons to line up your valve with the tire logo is so that when you find a hole in the tube you can use the valve and logo to find the area of the damage. If you pinch there will be two small holes close together. A snake bite.
While the Tour is won on tubulars, the team leaders get new tires every day, the rest of the team every other day.That means there is a guy who does almost nothing but glue tires. While glueing tubulars is therauputic there are other things I would rather do. I have regulars that ride them and do about twenty a year, that is plenty. Also while tubulars weigh less, you lose the benefit if you carry a spare because they do weigh more than a tube and take up a lot more room. And, unless you like to sew once you flat one it is trash. I use Continental Sprinters and while they don't flat often when they do there goes sixty bucks(I don't sew). That is another thing, Tour riders don't pay for their tires. They also have a car following them with about fifty tires on the roof in case they flat.
If you blow a clincher off the rim(A modern rim that is) then you mounted it wrong, with the tube under the bead or did not check as you inflated it that it was seating properly and not creeping off the rim. Another reason to fully inflate a tire is to make sure that it has seated fully on the bead.
Oh, yeah, tubular rims are much lighter, ask any old timer about the time their GEL280s shattered.
One more thing, while clinchers are more likely to pinch flat, tubulars are more likely to roll off the rim. You can see if a clincher is mounted right, there is a guide line for the bead molded into the tire, you can follow it right around the rim. A tubular however requires your faith that you or the person you had do the work, glued them on properly and you can't tell until that first hard turn. Glueing takes longer to, first you mount it dry. This is to let it stretch and make sure it won't go flat before you get a chance to glue it. Then you apply glue to the rim and to the cotton tape on the tubular, let it set a bit, then stretch it into place with out getting glue everywhere.( A guy I work with mounting his own tires managed to glue his brakes to the rim, we don't let him do customers stuff). Now, it is on there, you made sure it is perfectly straight, you can go ride, whoops, you need to wait overnight so the glue can set. They do ride nice.

Shokhead, as I said rims and tyres are better, haven't seen
one blow off in a while.
Rev. I agree that Tubulars are a pain in the tush, but for
me its worth it (and keep 1 spare set rims/tires). there
is an outfitter in Fla (?) that will repair tubulars for $15 each
$10 for more than 2 (I think thats right) so you don't need
to trash them if you don't sew.
haven't seen a tire rolled in a while either, and
thats down here with the texas heat!

Whole heartedly agree concerning pro teams.
I'm not going to get into the tubular vs clincher thing,
it makes about as much sense as steel vs everything else
or campy vs shimano. Its all personal preference.

Marty

Oh come on lets argue. Clinchers are heavy, tubulars are expensive, Shimano wants to rule the world, Campy is clunky, steel is heavy, alluminum is dead, Ti is whippy, roadies are snobs, mtbers are potheads. There, it's all out in the open.

Thanks rev,i feel better now.

ok Rev. you hit the nail on the head but you forgot
one very important item (but nearly touched upon it)
STEEL is REAL.
fwiw nothing rides like a Clement Seta Silk, however the
last ones I saw for sale went for $175 the pair (NOS). yes
tubulars are expensive, even on the net.

Marty

low tyre pressure rules!!
try it discover the new world open to you.

95psi in the front, 105 in the back. Smoooooooooooth

Haven't had time to read all the posts, so sorry if this has already been addressed. With the low volume of air in higher pressure, low profile 700C tires, running with even lower psi should result in more impact flats, no?

Interesting thread.

I had never given tire inflation any thought whatsoever...my bad.

I have allways just followed the tire inflation suggestion and gone a few pounds light.

Can we agree that the rear should be inflated more than the front?

:D

Max them both.

Lower pressure will notmean more pinch flats if you keep the inflation pressure above the recommended minimum.

check this link...

click here (http://www.physics.helsinki.fi/~tlinden/rolling.html)

an experiment on rolling resistance on various bike tires.

Interesting post. I've been riding around 110 psi, with that same mindset that higher is faster and better. Going to try dipping it a bit and check out the difference.

Less psi=more tire on the road=slower- More psi=less tire on road=faster What am i missing?

that friction is independant of surface area perhaps....

Just played around with tyre (note the spelling please) pressures today. dropped it around 100psi in the back tyre and 90 infront and the ride was silky smooth.

I'm curious, what was the suggested inflation on the tire?:D

suggested inflation range is 87psi min - 116psi max.

Pinch flats are enough of a hazard around here that I would need an honest-sized 700 x 28 to get away with 95 psi front and 100psi rear (I weigh about 170 pounds). That rules out the all-out racing clinchers like the Grand Prixs, relegating me to training tires that weigh more (and plow a wider path through the air).

Does it matter that much? Probably not really. If I can't keep up on a decent training tire, then I just can't keep up.

This has always been an issue with me for mountain biking too. I get my best traction in the 40psi area, but let me loose on a rocky trail and I'll get a pinch flat in a hurry, with 2.1" tires. Light, high-performance XC tires that are significantly larger than that are not too common. Here's the one I'd like to try next: WTB MutanoRaptor 2.4" at 565 grams (http://www.wtb.com/mutanoraptor_24.html)

The tyre pressure is variable thats why theres a range.
The minimum pressure is there to give the user a safe inflation pressure witha factor of safety to ensure the tyre does not roll off the rim. Since I only weigh in at 150lbs (70kg) I tend to run the tyre at close to the minimum pressure to get the best road feel. To much pressure and the rolling resistence increases.
And I run 700Cx23 tyres.

On my Mtb I use Michelin Wildgripper CompS USt which I run at 28 psi at the front and 32 psi at the rear.
Lower rolling resistence comes from the compliancy of the tyre over the terrain, not the contact patch.

To much pressure and the rolling resistence icreases?

Rolling resistance has little to do with rolling friction which is a function of the tyre compound and the grip offered by the running surface ie the cohesive forces (laws of friction not adhesion) between the tyre and the road.

Rolling resistance is the compliancy of the tyre or it's ability to absorb irregularities in the running surface with the minimum loss of momentum.
If you increase the pressure, the tyre casing cannot deflect to absorb the vibration. so the tyre/bike moves vertically to absorb the vibration. Now any vertical movement is clearly robbing forward momentum since the amount of effort applied by the rider is the same. This means you're slower.

If the tyre is run at a pressure where it's compliant enough to absorb irregularities yet still suspend the bike from the road, you will reduce the rolling resistance and convert more energy into forward momentum.

This is also true for a velodrome. In a velodrome however riders go for more tyre pressure because the running surface is super smooth and they want to maximise their acceleration effort but they still don't run them rock hard.

Rolling friction is independant of contact patch size because friction is independant of surface area.

So hard compound tyres run at minimum psi possible for riders weight will roll faster than same compound tyre running at maximum psi.

Also soft compound tyres will always roll slower than hard ones irrespective of contact patch size.

I really didn't know that tire pressure could be so boring.

LOL,but its fun.Hows this.Soft tires puncture easier,wear out faster,more difficult to pedal{gee really**dont brake as efficiently,easier to dent rim,increase the possibilty of pinch flats.When rolling resistance is critical,go as high as 140psi if the tires are rated that high.Stay at the lower end of pressure for comfort.Hows all that?

Originally posted by TimB
Rolling resistance has little to do with rolling friction which is a function of the tyre compound and the grip offered by the running surface ie the cohesive forces (laws of friction not adhesion) between the tyre and the road.

Rolling resistance is the compliancy of the tyre or it's ability to absorb irregularities in the running surface with the minimum loss of momentum.
If you increase the pressure, the tyre casing cannot deflect to absorb the vibration. so the tyre/bike moves vertically to absorb the vibration. Now any vertical movement is clearly robbing forward momentum since the amount of effort applied by the rider is the same. This means you're slower.

If the tyre is run at a pressure where it's compliant enough to absorb irregularities yet still suspend the bike from the road, you will reduce the rolling resistance and convert more energy into forward momentum.

This is also true for a velodrome. In a velodrome however riders go for more tyre pressure because the running surface is super smooth and they want to maximise their acceleration effort but they still don't run them rock hard.

Rolling friction is independant of contact patch size because friction is independant of surface area.

So hard compound tyres run at minimum psi possible for riders weight will roll faster than same compound tyre running at maximum psi.

Also soft compound tyres will always roll slower than hard ones irrespective of contact patch size.

finally.... someone with some sense is talking here!

haven't you guys ever noticed that when your pressure is too high the ride becomes really skittish---- you lose traction while going over the tiniest bumps in the road. there is a tire pressure "sweet spot" where you will minimize rolling friction while maximizing the amount of time that the tire spends planted on the road (ie, minimizing the vertical motion that TimB mentioned above).

on cars we have things like springs and dampers to make sure the tire moves up and down to conform to the shape of the road... but on rigid bikes, the tires ARE the suspension.