What was the CPI in 2023?

 

40.1 in 2023
40.8 in 2024

 

The tournament have changed the balls from Wilson to Yonex this year. The Wilson balls had been heavily criticised for fluffing up after only a few games, making it difficult for most players to generate pace and hit through the court. The Yonex balls are said to be harder and faster. Tennis TV commentators (Koenig and Lester) were saying that the tournament had made a deliberate decision to slow the courts 'slightly' (in their words) this year to adjust for the change in balls.

Worth noting the effect of the high humidity in slowing things down, and also the fact that the courts will speed up to some extent later in the tournament.

If you look at ace count so far, Cilic served 17 aces in 2 sets yesterday. Most other players are in single digits. I'm watching Cazaux vs. Martinez at present and they've just played a 27-point rally, the courts do look slow to the eye.

 

The tournament have changed the balls from Wilson to Yonex this year. The Wilson balls had been heavily criticised for fluffing up after only a few games, making it difficult for most players to generate pace and hit through the court. The Yonex balls are said to be harder and faster. Tennis TV commentators (Koenig and Lester) were saying that the tournament had made a deliberate decision to slow the courts 'slightly' (in their words) this year to adjust for the change in balls.

Worth noting the effect of the high humidity in slowing things down, and also the fact that the courts will speed up to some extent later in the tournament.

If you look at ace count so far, Cilic served 17 aces in 2 sets yesterday. Most other players are in single digits. I'm watching Cazaux vs. Martinez at present and they've just played a 27-point rally, the courts do look slow to the eye.

The bolded: Humidity actually speeds up conditions.

Humid or Heavy?: How Air Really Affects Tennis

Cool temperatures and showers during the first week of Roland Garros this year have had a mass of pundits and players talking about the “heavy” playing conditions. Some said those condi…

fogmountaintennis.wordpress.com

A Quick Introduction to Aerodynamics

First, we’ll need to understand a few basic things about how the air affects a ball’s flight path. Once it leaves a player’s racket, a ball naturally tends to fall due to gravity, but it also loses speed due to friction with the air. If the ball is moving anywhere near the speeds seen in a typical professional match, this drag force is greater than the force of gravity. It can be described by this formula:

where

CD is the ball’s drag coefficient
ρ is the air density
r is the ball’s radius, and
v is the ball’s speed, relative to the air

Notice that the drag force is proportional to the air density—a 10% increase in density, for example, causes a 10% increase in drag.

[...]

Humidity

When people in the sport talk about “heavy” playing conditions, humidity is the atmospheric variable they mention most often. It comes up during rainy weather like at this year’s Roland Garros, in the sauna-like conditions that often prevail on the US east coast during the hardcourt season, and has even been blamed for slowing down play when the roof closes at Wimbledon. Conversely, one popular justification for the widespread belief that balls tend to fly further than normal at Indian Wells is the dry desert air.

There are two problems with such theories. Most importantly, they’re backwards. Contrary to common intuition, humid air is less dense than dry air, and therefore creates less drag on a ball. This is a consequence of the ideal gas law, which implies that at a given pressure and temperature, a given volume of any gas contains the same number of molecules. Dry air consists almost entirely of nitrogen molecules (N2, molecular weight 28) and oxygen molecules (O2, molecular weight 32). Diluting it with molecules of water vapor (H2O, molecular weight 18) makes it lighter.

The other problem with blaming humidity for slowing down or speeding up play is that, in the conditions under which most tennis matches are played, the effect of humidity on air density is very small. At 70°F (21°C), a change in the humidity from 0% to 100% decreases the air density by a mere 1%, which increases the speed at which a fast groundstroke arrives at the opposite baseline by less than 0.3 mph (0.5 km/h).

At very high temperatures, the effect is larger because hot air at 100% humidity holds more water than cooler air at 100% humidity. But heat combined with high humidity is so hard on the human body that WTA rules, at least, require suspension of play under such conditions (see below).

The reason humid air feels heavy to our senses isn’t because of its density or viscosity—it’s because the more water is already in the air, the less sweat evaporates from our skin. That forces our bodies to sweat harder and do more work to keep cool, leaving less energy available for athletic performance. Taken to the extreme, it causes dehydration and excess body temperature, which can cause the body’s mechanisms to malfunction altogether.

Humidity does have some effect on the surface characteristics and mass of the ball, as well as the air density, but these effects turn out to be very small and largely cancel each other out. More on this later.

It seems Stephane Bohli described humidity’s effects on the game more accurately than most while playing a Challenger tournament in New York last year, saying “You feel like your racket is a little bit heavier… that your legs are a little bit heavier, everything is a little bit heavier.” It’s more about humidity’s effect on a player’s body than it is about the effect on the ball.

[...]

How Does Humidity Affect the Ball Itself?

Atmospheric factors alone simply cannot explain the perception that “balls fly” at Indian Wells, or the association of humidity with “heavy” conditions. It has been suggested that humidity might make the fuzz on the surface of the ball fluff up, increasing the ball’s effective diameter and therefore the drag it experiences.

I conducted my own experiments to test this idea. I opened cans of Wilson US Open Extra Duty balls at low and moderately high humidity levels and tumbled them in a clothes dryer, on the no-heat setting, to simulate the surface wear they experience during a match. I maintained the initial humidity inside the dryer throughout each test, and took high-resolution photographs of each ball before and after the tumbling process. After carefully measuring the effective diameter of the fuzz on each ball, I found that balls used at 61% humidity were effectively 0.6 mm smaller on average than balls used at 25% humidity. This difference is small, and just barely statistically significant—it’s only slightly larger than the typical variation between the individual balls I tested. But to the extent it affects balls’ behavior in the air, it only adds to the density-reducing effect of humidity, making balls travel further and faster.

Here are images and measurements of typical balls from the test. (The differences in color are due to different lighting conditions and the fact that I processed the images to optimize contrast of the fuzz fibers, not due to any difference in wear between the balls.)

High humidity has other effects, beyond this surprising reduction in the effective diameter of balls measured at rest. In humid conditions, the fuzz on a ball absorbs a measurable amount of water, increasing its mass slightly. At 27% humidity, I shaved as much fuzz off a ball as I could and gathered it into a small container. I weighed it on a high-precision scale, and then exposed it to 93% humidity for about 15 minutes, sealed the container, and weighed it again. It absorbed 0.04 grams of water, increasing its mass by 7%. This represents a mere 0.07% increase in the mass of the entire ball, which by itself isn’t enough to have a noticeable effect on the ball’s flight.

But it does affect the way the fuzz interacts with the air as the ball is in flight. Wind tunnel tests have shown that spinning balls have higher drag coefficients than balls with no spin. This is because the centrifugal effect makes the fuzz stand up off the surface of a spinning ball, creating extra disruption in the air flow around it. There are dramatic high-speed-camera photographs of this effect here (see Figure 12 in the link). By making the fuzz heavier, humidity enhances the centrifugal effect and makes the fuzz stand up higher.

I modified my computer model to take this into account and see how much it affects balls’ flight paths and speed in a match. The effect is measurable, but small. It’s just enough to nearly cancel out the effect of humid air’s lower density. The net result of all of these effects is that at 75°F (24°F), changing the humidity from 10% to 90% makes a deep topspin groundstroke land less than 11 inches (27 cm) deeper in the court, and increases its speed at the baseline by less than 0.6 mph (1 km/h). Other shots are affected significantly less. Once again, the results disprove the popular perception that humidity makes playing conditions slower, but the effect is so small it’s unlikely to make much difference in a match.

The author also notes that air temperature as well as altitude are more notable factors impacting air density and thus drag and speed of the ball:

Temperature and Pressure

As you can see in the diagram above, temperature has a much stronger effect on the air density than humidity does. A change in temperature from 50°F (10°C) to 100°F (38°C) reduces the air density by 10%. That makes a fast groundstroke arrive at the opposite baseline traveling a noticeable 2–3 mph (3–5 km/h) faster, depending on the spin and depth it’s hit with. The effect of the cool temperatures this past week at Roland Garros dwarfs the small opposing effect of the moderately high humidity, and is undoubtedly the main contributor to the slow playing conditions many have observed.

Another significant contributor is an atmospheric variable I’ve never heard mentioned in tennis, whether by a player, coach, or commentator: the barometric pressure. The ideal gas law tells us that the density of a gas is directly proportional to its pressure. For most locations on Earth, the barometric pressure (corrected for altitude) stays between 29 and 31 in Hg (980 and 1050 mb) the vast majority of the time. (Much lower pressures have been measured, but in places like the eyes of hurricanes and typhoons, circumstances under which tennis is unlikely to be played.) Typical variations in pressure lead to a potential variation of nearly 7% in the density of the air.

Pressures have been moderate during Roland Garros so far this year, staying between 29.74 and 30.19 in Hg (1007 and 1022 mb), but particularly in the first week, they were higher than the pressures usually seen during wet weather, and that may have contributed to the perception that conditions have been unusually slow.

Altitude

The biggest differences in air density from one tournament to the next are caused by altitude. Tennis commentators talk about altitude most often in reference to Madrid, the only Masters 1000/Premier Mandatory level tournament held at significant altitude. The Caja Mágica in Madrid is at 1860 ft (567 m), where the air density is more than 6% lower than at sea level, but it’s far from the highest venue on the tour. Here are the altitudes and relative air densities of the actual tournament sites for every currently- or recently-held tour-level event above 1000 ft, or 300 m:

[...]

As you can see, events like Kitzbühel, São Paulo, and Bad Gastein are at significantly higher altitudes than Madrid, and the air density at these tournaments in very cold temperatures is as low as it would be in very hot conditions at sea level. Bogotá, Colombia and Quito, Ecuador host by far the highest events on the main tours, with air nearly three times thinner still.

Such altitudes make enough difference in the flight paths of tennis balls that we can easily see the effects visually, as well as in quantitative measurements. Using an evolved version of the computer model I developed for my analysis of court surface speeds, I examined how high altitude affects groundstrokes with varying kinds of spin. First, a flat shot with no spin (with the vertical scale magnified to emphasize differences in shape):

[...]

And the summary:

Summary

Like a lot of tennis lore, prevailing beliefs about how atmospheric conditions affect the game are a combination of truths, half-truths, and delusions made credible by repetition and recirculation. Scientific analysis reveals that many effects are more complicated than they appear, and often subtler than we expect. Often quantifiable reality differs from the tactile perceptions of players in the rush of battle. High altitude, high temperatures, and low pressures can all speed up play, in that order. Humidity has very little practical effect. Heavy balls, especially if they’re heavy because they’re wet, can make playing conditions heavier in a very real sense. But that’s a different kind of effect, sapping the strength of players more than it changes the flight of balls.

 

Are there 31°C in Shanghai? Jeez it's October 🙄

 

I checked the weather forecast and it's gonna be unbearably hot and humid in Shanghai. Days with max temperature of 34-35°C 🥵. If the courts are slow, this tournament will be a mess worse than Cincinnati 💀.

 

CPI of 32.9, it has slowed down an incredible amount as in 2024 the CPI was 42.2…

Across the whole tour organizers are tweaking surfaces and making it slow in order to guarantee a spectacular Sinner vs Alcaraz final. Which is really sad IMHO (it's unnecessary to adjust the courts to only one matchup. Especially since the two players are in fact best at adapting to surface conditions than other players. So it's (A) totally redundant and (B) a net-loss to the overall sport.

 

OK Roger.

 

They slowed down for Alcaraz and he didn't even bother showing up.

 

I watched Sakamoto play in qualies and it looked fast as usual

 

I wrote about this in Live Scores thread. Seeing so many winners in 1st set who usually prefer slower courts and watching a few matches, I also think it is slower than 2023/2024.
It does not seem they did it on purpose though.

 

Disgusting piece of news. The fall of tennis continues.

God forbid people for once play with an ultra fast court and ultra fast Yonex balls.

 

J.M. Cerundolo was returning every single shot today. 20-shot rallies all the time.

 

No wonder the king of pushers Djokovic has shown up.

 

GOAT won Shanghai (fastest court at the time)4 times!!!!and even grandpa version made final last year.
Get help

 

Can asalty make a post without desperately trying to diminish Djokovic?

 

I did not diminish him at all, lol.

 

Has such a slowdown between two following seasons happened before? I don't remember any tournament that was at a certain speed one year and was slowed down more in the following year than this one.

 

The picture OP posted not from CC.i am watching Novak match tomorrow,usually they show speed index at the beginning of the day,but its too early for me.
I am hearing alot of aces in matches,so it can't be slow.

 

Damn, Alcaraz should have pulled out of Tokyo to play here. He’d absolutely smoke Sinner in these conditions.

 

Main court CPI by the way

It’s slow

 

This means Djo has no chance. He needs to be able to servebot to be relevant

 

The picture OP posted not from CC.i am watching Novak match tomorrow,usually they show speed index at the beginning of the day,but its too early for me.
I am hearing alot of aces in matches,so it can't be slow.

Center court:

Main court CPI by the way

It’s slow

 

Todays match showing that most important thing in tennis is BALLS and not CPI.
Yonex balls are flying through the air,that even slow court is not issue.
Novak clocking 210 km/h flat serve(his usual serve under 200km/h) is unreal.
They slowed down the court to balance the balls.
32,8 is IW cpi,and we know how you can't penetrate there.

 

Fritz gave a good description of the conditions and balls at this year's Shanghai and compared to last year.

"They slow the courts down, the balls aren't as slow (as last year's) but they are still pretty slow, you play three balls into the ball change and they are massive, feels like the ball isn't going anywhere".

 

It’s considerably hotter and more humid this year for early October as well.
Shanghai normally changes season by now.

 

I think Draper likes this kind of surface most

 

 

 

 

Fritz is somewhat correct but getting a bit muddled here. The balls are actually faster this year, but the courts are consideray slower.

 

The courts should be very fast in the end of the season, because players are tired. That's why there are so many surprises by lower ranked players in this tournament. I agree with Fritz, but not with Zverev who is blaming Sinner and Alcaraz.