Tires and rolling resistance have been a hot topic in Lennard Zinn’s tech column at VeloNews lately. I suspect that the topic has such legs because it’s so misunderstood – if there were definitive facts about tires all arguments would cease. Here’s my attempt to clear up some misconceptions.
#1: Contact patch size
I’ve always heard that contact patch size is easily calculated. If you put 120 pounds on a tire pumped up to 120 psi, then your contact patch is 1 square inch. 60 pounds on 120 psi, 1/2 square inch. Simple math. Is this true? I set up a tire on a piece of glass, then blasted it from 4 sides with lights. I took pictures of the patch using a mirror on the floor. A one inch square was placed next to the patch for reference. Area was calculated by counting pixels in the photos and comparing the patch size to the one square inch reference.
I measured 3 tires at 50 to 120 psi in 10 psi increments. The tires were a Vittoria Crono, a Schwalbe Milano, and a Hutchinson Tubeless Fusion 2. The Crono tubular is essentially a glorified condom of a tire, about as thin as can be. The Milano is a thicker training tubular. The Hutchinson is a heavy tubeless clincher. 27 pounds of weight were put on the tires, which were inflated with the weight in place.
Here’s the caveats. Distortion in the photos would make the area calculation inaccurate. The pressure gauge in my pump may be off. Even though the image of the contact patch is pretty clear, I still have to make a judgement call at some point and guess where the edge of the patch is. As with all my home experiments, be skeptical.
I graphed the results and compared them against the numbers the mathematical equation predicts. As you can see, the lines follow the curve of the predicted values, but are higher. My guess is that there’s a column of air that supports the weight, with a wall of rubber on the perimeter. The thicker the tire, the thicker the wall, the bigger the contact patch.
Now, 27 pounds isn’t a realistic weight for a cyclist, so I beefed up my setup and ran the Vittoria only again at 39.5 and 48 pounds. This is still less than what you might expect from a typical rider and bike, but I’m just too scared of the glass shattering to go beyond 48 pounds. As you can see below, the same pattern still holds.
To test my wall theory I drew ellipses that matched the sizes of the Vittoria contact patch at 50, 80, and 120 psi when under the 48 lb weight. With trial and error I arrived at 1.3 mm for the thickness of the wall of the contact patch. The percentage of the air column vs. the total patch size in the diagrams are 59%, 64%, and 70%. The percentage of the mathematically predicted contact patch size vs. the actual patch size in the corresponding instances are 58%, 69%, and 82%. Given my massive margin for error I think my theory might be correct.
So what does this mean? I guess the formula for contact patch size applies to a theoretical tire of no thickness. Actual contact patch size is a sum of the mathematically predicted size and the tire’s thickness. It seems that a thicker tire would yield a bigger contact patch, which means it should have more rolling resistance, since the larger patch is farther from the centerline of the wheel and has more leverage to push back against the axle of the wheel. In other words, thinner, presumably more expensive tires, should be faster. I know, I know, what a shocker.
Coming up: do nicer tires conform to bumps better?
Â
OK, so since you conclude that thinner tyres are faster due to smaller patch and less rolling resistance, can we also conclude that using higher pressure is also generally faster?
Of course, this is a whole separate argument and there is evidence that has shifted conventional wisdom to conclude that moderate pressure is faster, but that is what I conclude from your summary.
http://rouesartisanales.over-blog.com/article-1503651.html
I think smaller is better on a perfectly smooth surface, just based on logic and no testing. Aside from the smaller contact patch, the tire flexes less, so there’s less energy loss to hysteresis. That’s why trackies go so high. High pressures would cause too much bouncing on the road.
Higher pressure is faster when you’re riding on a glass plate.
ask Carmichael, he knows it all, tomorrow in Central Park…
Do you prefer nerd or geek?
I can see these theoretical differences being important for a tt. However, how and when does handling trump rolling resistance? I like 105 psi max for say a technical crit. Or how about a tricky circuit race. high speed descent, or fast cornering?
How does this relate to the sweet Aerospoked skipatch I’ll lay down in the Alleycat this weekend? Does the skidpatch go deeper if my lock is worn around my waist or wrapped around my seatpost? Does the addition of a hanky tied to my stem increase drag or does the turbulent air drag from my chopped riser bars cancel that out?
Don’t wrap your chain around the seatpost, it’ll throw off your handling. Aerospokes are way too expensive for a street bike, keep it real with some deep dish Velocity rims; they last forever. Lose the hanky, you’ll look too trendy.
Why the attacks? Do we really have to promote the all too truthful label that we are elitist dorks that are too cool for anything…
When my wife came to one of my city races she mentioned everyone’s attitude. She asked me what everyone’s problem is and why is the vibe so intensely arrogant? I wondered that myself and then I had a flashback to my first ‘Roadie’ days and the ‘you’re not worthy’ vibe that almost everyone gives off. Check yourselves…
Some dopey hipster grrrl passes me on the bike path this morning. Fixie, over sized messenger bag, colored aero wheels, lock on the waist– the whole nine. As she comes by, she gives me the Lance/Jan glare. My bliss was ruined, so I ride her wheel on my commuter bike for a while. As I pass her, she yells all agro and shit, “What’s your problem dude???” I return the favor, “Uh,You.”
Why dont you cover some of the great cross and fall mtn bike races on the calendar? Similar to the NE road scene, this site is really stagnant lately…
‘Cover’? Why don’t you send in reports? Anyone can post content to the site.
It’s really just the road scene and it (the arrogance) seems to be heavily concentrated in NYC (compared to other regions in the US). MTB and CX events don’t really have this negative attitude issue. Roadies are just way too self-important.
“if there were definitive facts about tires all arguments would cease”
You ought to know by know that definitive facts don’t cease arguments:)
So here’s a worthless opinion. Unless we’re talking about a straight time trial, handling is more important. I find 22-23’s with 90-100 psi handle much, much, much better than 19-21’s or anything inflated to 120 psi or above. How often do we lose races on a straight? It’s in the bends and pack positioning that we lose most of the time. Everytime it rains we see these guys slipping and crashing because they put too much pressure in their tires to minimize rolling resistance:(
Why ride on air at all for that matter? Ride right on the rim with only some glued on tread for the optimal contact surface patch??? Maybe the deflection of a soft sidewall actually make you more efficient by smoothing the inherent oscilation of the pedalstroke?
Copy what Lance does, works for the rest of us!
Aged 3 years, massage daily, and then get the best that modern medicine has to offer…
MORE DRUGS! $10,000 bicycle that is essentially a lightweight cruiser, versus the same resources into better “healthcare”…Does not (local hospital) have a bike shop next to the gift shop for all of the “global cancer burden” junkies? Someone wrote in to another cycling website, why not do RAAM? or for that matter a global cancer ride? From Arctic to Antarctic? from London to Sydney???
I hope he rides for Team Borat, “I like…”, just imagining Lance Alberto Levi and the other German from T-Mobile days gone by riding TTT up the mtns and GC…I digress…
(breathe)
(pause)
(mental eureka)
Lance, Jan, Ivan, Floyd, Tyler, Roberto, Frigo, Pantani, (other caught/known drug cheats) will ride the Tour side by side the people-ton, shouting out against the ASO…
(bllpp, bllpp, bllpp…and then I woke up…)
“It’s really just the road scene and it (the arrogance) seems to be heavily concentrated in NYC (compared to other regions in the US). MTB and CX events don’t really have this negative attitude issue. Roadies are just way too self-important.”
Exactly, I am a part of almost all scenes (mountain/cross/street) and the NYC Road sector makes me sick. It will never grow with that kind of attitude.
http://www.cyclingnews.com/photos.php?id=/photos/2008/sep08/giro_toscana08/giro_toscana082b/2B_WC1_4319
yup. I can’t wait for the annual powercrank push…
I started off racing BMX and Mtn bikes. The atmposhere was nothing but fun and good vibes. Guys did not care what kit they had, it was all about pain and fun. The local road scene is depressing. Great races and great talent but the attitudes are just too much to stomach. Guys who are decent cat 3s thing they are 1 win away from landing a spot on Healthnet. Forget about the shite Cat2s who race the occasional NRC and DNF to then tell everyone how good they are.
Cross and Mtn biking now are coming back and growing and I believe its due to many roadies just getting sick of the road scene. Also, many guys travel out of town to race road simply to get away from the PP type atmosphere. Too each his own but for me the dirtier you get/wider tire you ride = the more fun and better vibe at the races…
actually you pull/lift and kick forward with PC, while standing;
not push…
Can we just get over the ‘NYC road scene is this, cross scene is that – ‘ BLAH BLAH BLAH you’re on the frigging web site, you’re sucked into this world just like everyone else, you pompous multi-tool.
There is no pride in what I said. Actually I’m calling you on yours and you responded exactly as predicted.
I would just like to add my two cents about the NYC road scene as a newly minted member, and recent outsider. I would say that, like everywhere, there are jerks in road cycling in NYC. There are guys who ride like a**holes and talk smack and exclude newbies in cloud of smug. however, by and large, i have found the scene to be remarkably welcoming and fun. This was my first year of racing, something that I had wanted to do desperately since I saw the Tour du Pont go past my house when I was in kindergarten. I came to this City a year ago without expectations to ever ride my bike. Lo and behold, I found a wonderful community of riders who were willing to let me in, encourage me and allow me to indulge my fantasies of being a “bike racer.” My first year in this city would have sucked without racing. I have tried my best to smile and be friendly to as many people as possible and most of these people have returned the favor. Its all about expectations and attitude. Sure, the Mengoni race ended in some ugliness, but that happens everywhere. Most races end with a bunch of people hanging out and smiling–what am I missing?
(count down to flames in 10,9,8,…)
You seem like a good guy though I haven’t actually met you at races, but I think its hard for you to judge the scene. At the level of talent you displayed from the get go, the scene is pretty welcoming.
This is the darkenss of pain and disconnectivity…
We are all interconnected infinitely…
LA FORCE!
Stop thinking about it so good damn mush!!! MUSH!!! MUSH!!! MUSH!!!
Yeah, we’re basically man-crushers and dick-riders to the talented.
should we start big-upping the losers? the cat 4-lifers? what kind of motivation is that. of course colin gets props, he killed it this year.
This kid is a beast and deserves lots of praise. I do not know him and have not raced him. I will be a 3 for life and I suspect he will be a Cat1 by the end of 09. The problem many have with NYC racing is that for every Colin P there are 100 ave joes just trying to have fun and learn the ropes., We need to be more welcoming to these people if the sport is going to grow. In cross and mtn bike you hang and talk to everyone. Ex., I was at Windham East Coast NORBA Nats this year hanging with Todd Wells and Adam Craig. This does not happen in the road scene… They were very open to talking about the course and equipment choices.
Why are we so concerned with this again?
This sport will never grow like triathalon because it requires so much more to participate. In cycling we are not trying to beat ourselves (“I PR’ed this week”). Instead it requires a serious commitment to even step into the ring. The scene is pretty vibrant, there seems to be plenty of R&D and bikes available, and more races than I can handle. Does it need to be a huge, lovefest, participatory sport? Go see mom if you need a hug.
Ask the Mtn bike racers why… In the 80s and 90s they had lots of races and trails. Lance came along and everyone went to the road. They lost their races and many of the trails. Now that people are post Lance and sick of the a-holes that flock to road racing they are going back to Mtn or just plain old riding to ride. Look at the races this year out of town – All the big ones (with the exception of Battenkill) were down in registration. The economy had some play in this but so did the fact that many are just bored and tired with the scene. So if the sport does not grow and suffers what Mtn biking did in the past 10 years you will get – less racers = less races = less racing.
No, just not a hatefest. Kind of like here….wow, I think I’m on to something. Maybe if I don’t race in the city and don’t frequent certain sites I could stand it…
Road cycling is a bit more intense I think by nature, and that reflects the serious time and work commitment that we make to the sport to participate at a competitive level (ie. not just to play, but to play well and compete). Guys have fun at Mtb and Cross, and its a more chill scene, simply because they havent invested months into the sport and expect to judge themselves critically by a result. They mostly go for the fun and to maintain fitness – a different though very valid goal. So, you get what you get because its simply an accurate reflection of seriousness.
Also equally important to point out are 1) most of the guys at RR that seem standoffish arent unfriendly – they are just focused and maybe even a bit nervous, which makes anyone a little quiet. This can be misinterpreted. I show up at races stressed out until I have number in hand, bike and clothes put together, and dump number 1-3 accomplished. After that I might be chill enough to greet people and chat, but likely busy warming up. Im not mean – just serious at that momement in time. I show up at a cross race and I likely could give a crap about warmup and other stuff.
2) I think the presence of amped up racers in road who have invested years of time and effort to get strong may inherently lend itself to an insular culture. Maybe its even a good thing that you need to show a similar commitment to be really accepted. That DOESNT mean you need to be Colin P or whoever (ie. fast), just that people know you have spent real time training and give a damn. That will result in mutual respect.
Of course at the end of the day, some people just suck. You dont see those people getting a lot of love at races though.
Oh, and if you were able to make friends easily and play with the other little boys well in school, chances are you will be well received in cycling. If not, dont expect to show up with muffin top under lycra to a RR and have it be any different. Welcome to Type A sporting – its not Romper Room. OK, Im a dick. Whatever.
..and Andy S rocks for this analysis. WAAAAAY cool and very helpful, actually. Go Andy!
You want to see a sport with a bunch of a-holes? Go play in any recreational softball game in the tri-state area. You’ll find 10x more take-themselves-too-seriously jerks than you do a month in bike racing.
in cycling the results speak for themselves. usually (most likely) there is a direct correlation between the work/discipline you put into this sport and the results you get in races. others will recognize that and respect will soon follow.
there is not enough love to go around for mediocre riders with mediocre results. get your name out there.
“They (Mountain Bikers,CX) mostly go for the fun and to maintain fitness – a different though very valid goal.”
I don’t know about you, but I race / train road for fun and to maintain fitness. Being competitive is fun. What else is there? Money? Chicks?
Chris M hits the nail on the head. The NYC road racing meritocracy attracts Type A “dicks”. So quit complaining. Train really hard, lose friends, get divorced, and get grumpy. Then, finally, you’ll get that special key to the cave with 20 guys who’ll laugh and smile with you while giving everyone else the cold shoulder.
But here’s the trick. Those guys are maxed out. Look at guys like Colin. He’s waltzing right past them with a smile on his face. He is young and energetic, and he doesn’t need cycling to smooth over a rough tri / mid life crisis.
For them, those hours and hours of training are just one big narcissistic reach-around. Cycling is a beautiful sport. It is playful and hard as hell. Insert Type A New Yorkers and you just suck the soul out of something great.
I’m not saying anything should change. But if you’re feeling put off, you’re not just training too little. You’re not riding training wheels. You’re spot on. The scene is whack. Unfortunately, you might have more fun in another part of the country, or with another group of guys.
and others suspiciously decline worlds invite when form is there…
VDV
Sastre
just wondering with the re-testing is all…
hmmm…
the idea that colin is exempt from being “maxed out” is a little absurd. he hasn’t raced out of town in months and gets burnt out like the rest of us.
I’m sorry, I don’t underatsand that post. I kind of thought I got some of it, but the wheels really fell off for me that last paragraph.
if you are feeling ostracized, it’s probably because you painfully are average. don’t feel bad. welcome to high school, except this time grades are more important than good looks.
(good looks doesn’t hurt)
“They (Mountain Bikers,CX) mostly go for the fun and to maintain fitness – a different though very valid goal.”
The top Mtn bikers and cross racers say the same thing about road. This statement above is so telling of the NYC road scene. Top Mtn bike racers and cross racers would be top roadies if they wanted to focus on the road. Ex. Christian Favata won the overall at Catskills 35plus and Galletta was 2nd. Favata is a pro mtn biker and Galetta is pretty much a semi-pro or now (Cat1/pro mtn biker based on new ranking system).
For some reason I do not think these guys or the 2/3s and Pro1s at UCI races such as Granogue, Whitmores, Mercer are a big fun fest for guys who dont care how they do. Us cross racers and mtn xc show up to those races ready to go. Lots of specific training, intervals etc. I use road to train for Mtn bike and Cross as do many others. Go to the top cross and mtn bike races in the country and the competitive fire is fierce but the atmosphere is much more positive.
I would bet you’ve never been to a cross or MTB race. Riders train just as hard, and arguably the races are dramatically more intense than road races. The only difference is the CX/MTB riders tend not to have some up their ass.
we live in NYC, people.
a certain type of person chooses to live in NYC. you can apply the “type A” argument to a lot more than the road cycling scene. whether it’s the dating scene, academics, art, professionals, hipsters, elitists, blah blah.
we’re all nuts for living here. this is no news flash. it’s definitely reflected in the cycling scene–the NYC riders are brutally competitive, and it shows.
So mtb/cx races are as competitive and intense … but more positive. Why?
NYC. No matter how hard you try there is someone making more money, doing more for the world, making more art, and dating more beautiful women. People are competitive everywhere. We just have a bigger chip on our shoulder.
i prefer a shaven contact patch
Yes – these races are very competitve and a total pain fest for 60 minutes. Totally different racing but just as hard and to do well at the highest levels you need to train very hard. Why are they more positive? Well, during the races guys are not yelling stupid shit, and racing like jackoffs to gain 3 spots in the sprint. Before and after the race everyone is smiling and laughing and talking about the race. The atmosphere before and after these races a a big part of the race. You gotta be at the events to understand.
I recommend all the road snobs do the Darkhorse 40 this year and you will finally get it…
Ah, got it. Well said. Much clearer, thanks. (I’m not all that bright.)
“You ought to know by know that definitive facts don’t cease arguments” – except in the case that helmets save lives!
Huh?! None of the road racers I know are type A’s. The A’s are all doing tri’s or are running.
Who are some of the good racers here. Magarite? far from type A. Rashad? Definitely not type A? Zmolik? defines slacker. JKIA? works in finance but know way I’d classify him as type A.
Type A’s mostly don’t like road racing cause they’re is actually a team sport. Type A’s need to win, or at least beat a PB. Can’t do that while lettting a teammate win.
all those guys train obsessively their balls off, man. you don’t think they like to win?!
obsessively train
C’mon people now, smile on your brother, everybody get together, try to love one another right now.
And then Kurt Cobain blew his head off.
Question: why is it no one seems to want faster racing? Most seem satisfied sitting in and sprinting/crashing at the end?
I challenge this weekend the fields to set their fastest lap times possible and then only see what happens cat/mouse the final mile? It is technically a training race with nothing on the line except bragging rights until March, but at least try soemthing new, like going as fast as possible collectively? Who’s game? Meet me at the front…from the gun!
:)p)
We’re not talking about Mike and Rashad. Two contrasting examples …
#1
Riding through the park pegging a wattage target I approached two Foundation riders. I slowly closed in minding my business keeping a solid, consistent pace.
“EXCUSE ME! PASS US NOW!”
#2
Riding through the park on my way to Bear. Mike says …
“Hey man, nice to meet you”
There are a couple bad apples who just ooze stupid attitude. This isn’t about being competitive. It is about a couple stuck up people. Head out of town. The vibe is a lot better. The parking lot at Hilltowns reminded me of a mountain bike race. Laughing nice guys.
Agreed! Let’s make it The Race to Cuddle Kissena!!
MTB/Cross = Cross-Country Runners
Roadies = Soccer/Football
Both equally difficult groups of athletes, just wired differently.
the pace vehicle, or any field in front as many as possible…like a handicap that isn’t?
who gives a fuck what two foundation riders say to you
what does that even mean?
http://www.recumbents.com/home.asp?URL=wisil/whpsc2008
To Andy’s point about tires beingpumped too hard:
I believe Conti did some research a few years back on tire pressure. I bet you can google it and find…their conclusions were on mark with what Andy said in the comment section about tires being pumped too hard for road riding: it is slower due to bouncing.
NYC Bike scene:
There are certainly moments where the ‘tude of the guys in their kits certainly outweigh any real talent by miles. These are the guys that cut in front of you when you are doing a recovery ride to remind you that they are awesome cat 4’s and you are nothing.
But the flip side is the number of awesome people who I have spoken to over the years who have time to share a kind word. But in general I would agree the vibe is much cooler in the CX races and mountain bike races than that of road races. I agree with the guy who said roadies should come out and do the dark horse forty…a pretty easy trail for the skinny tire converts to have some fun on.
so- about that contact patch…