how much does a closed racket face contribute to topspin?

dominikk1985

Legend
the conventional way of generating topspin is swinging low to high with a vertical racket face.

the WW forehand looks different but actually the across is generating a steep racket path too because the swing becomes parallel to the chest (like a windshield whiper) and at ball contact the movement is mostly up and then after contact across (maybe a tiny bit across already at contact so that a little bit of sidespin is added).

we have also established that the racket face is not rolled over the ball, the racket face angle remains constant unless you hit the stringbed below the center.

however when watching highspeed video of top players we can see that the racketface is usually closed 5-10 degrees. they also brush up on the back of the ball but the face is slightly closed.

is that closed face just to control launch angle (to counter the incoming spin and ball rise) or does it add to the spin of the ball?

OTMPut

Hall of Fame
Sometime, as in Physics, it is useful to look at the "inverse" problem.

Does the open face and high to low path produce under spin on backhand slice? Or do you roll the the racquet under to create spin?

Chas Tennis

G.O.A.T.
This seems like one possible explanation.

Entire video with a discussion of TS aerodynamics.

I believe it may have come about by trial and error during practice after learning that a certain feel was associated with stronger forehand drives. The angle used by players with strong forehands starts showing up in high speed videos and 'slightly closed' catches on. ?

Any idea as to when this slightly closed impact forehand caught on?

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Chas Tennis

G.O.A.T.
This popular instructional video underestimates the angle of racket face closure on forehand impact.

Is 5-10° the best estimate for what is being used in most current forehands?

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dominikk1985

Legend
This seems like one possible explanation.

Entire video with a discussion of TS aerodynamics.

I believe it may have come about by trial and error during practice, and learning that a certain feel was associated with stronger forehand drives. The angle used by players with strong forehands starts showing up in high speed videos and 'slightly closed' catches on. ?

Any idea as to when this slightly closed impact forehand caught on?

great video. I think that the closed face slightly adds to the topspin but the main reason is probably launch angle control.

that is also the reason why rec players are well adviced to hit with a less closed racket. the more spin the incoming ball has, the faster you swing up and also the more the ball rises at contact the higher the launch angle will be. because of that pros need to depress the launch angle to create the desired flatter flight path.

rec players are facing less spin, swing upwards less/slower and also usually hit the ball more while it is falling. that means the launch angle is lower and they often need to lift the ball more than "push" it down like the pros.

while for pros 5-10 degrees are used rec players would probably not use more than 2-3 degrees or so or they would dump it into the net.

maxpotapov

Hall of Fame
^^That is a really good explanation, thanks!

fuzz nation

G.O.A.T.
I didn't look at the video - sorry if I'm repeating anything - but the pros and some stronger amateurs can often do a better job of hitting the ball on the rise more often than mere mortals such as ourselves. I think this is a consideration in terms of the racquet face angle necessary to deflect the ball not-too-high and also not-too-low to knock it back in the other direction with topspin.

Once the ball has bounced and topped out, the racquet face has to be a little more open (or a little less closed) to "lift" through the ball, make that angular contact to produce topspin, and also carry it over the net. That angular contact requires a certain swing path together with a certain racquet face angle (along with the proper timing) to meet the ball, make it spin, and send it in the desired direction at a certain height.

By comparison, hitting the ball on the rise requires meeting the incoming ball that's moving into the racquet at a different angle - it's rising instead of flying level or falling. If we used that same racquet angle and swing path with a rising ball that worked with the descending ball, it would deflect more upward off the racquet and likely sail long.

So in semi-basic terms, I think that the closed face works together with the appropriate swing path to make topspin on an ascending ball. It doesn't work as well when the ball has already turned over.

dominikk1985

Legend
not only hitting on the rise but also the spin of the ball. a topspin ball tries to "roll up" the strings and thus deflects higher.

Chas Tennis

G.O.A.T.
.......................................
So in semi-basic terms, I think that the closed face works together with the appropriate swing path to make topspin on an ascending ball. It doesn't work as well when the ball has already turned over.

Here is a video where the ball can be seen to be descending and not 'on the rise' but the racket face is closed at impact. I believe that it is representative of the current TS forehand.
https://vimeo.com/63687035

Do you have HS videos where the racket face is more vertical on balls that are on a downward path?

It would also be interesting to compare to some videos of balls on the rise and see how closed the face is on those.

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dominikk1985

Legend
Here is a video where the ball can be seen to be descending and not 'on the rise' but the racket face is closed at impact. I believe that it is representative of the current TS forehand.
https://vimeo.com/63687035

Do you have HS videos where the racket face is more vertical on balls that are on a downward path?

It would also be interesting to compare to some videos of balls on the rise and see how closed the face is on those.

the rising is only ins factor generating lift. The upward brushing and incoming spin also generate lift.

Topspin Shot

Legend
Closing your racket face adds topspin because topspin is generated by swinging upward relative to the racket face angle. So swinging upward with an open face may not generate any spin at all. But you can't close the racket face angle very much if at all on a groundstroke, or you will dump the ball into the net because racket face angle is the main factor controlling launch angle. On a serve though you can close the racket face a significant amount because you're aiming down into the box, which is how you can generate heavy topspin on a serve without swinging as radically upward as on a groundstroke.

TennisCJC

Legend
Closed face makes spin easier. Twu has research on hitting topspin serves and it indicates you get higher spin rates if you hit top of ball. But,I think you have to be careful with using this. I never think of changing angle during a match. I use a e/sw fh grip and close the face in backswing and as swing starts forward. But I only think about shot direction and height as I go into contact.

dominikk1985

Legend
Closing your racket face adds topspin because topspin is generated by swinging upward relative to the racket face angle. So swinging upward with an open face may not generate any spin at all. But you can't close the racket face angle very much if at all on a groundstroke, or you will dump the ball into the net because racket face angle is the main factor controlling launch angle. On a serve though you can close the racket face a significant amount because you're aiming down into the box, which is how you can generate heavy topspin on a serve without swinging as radically upward as on a groundstroke.

yes. what really matters is how "thin" you hit the ball. the more the force vector goes through the center of the ball the flatter the ball will be and the "thinner" you hit the ball, i.e. the more tangential you hit the ball the more spin you get.

theoretically a horizontal swing with the racket face pointing to the ground will give you the same spin as a vertical face swinging straight up but in reality of course friction and physics will play a role too (that ball would go like straight down into the ground).

in this picture every racket face and swing combination in the left pic will produce a flat ball and on the right a TS ball. of course not all swing directions are good to produce a ball that goes in

ChicagoJack

Hall of Fame
I don't think anybody is hitting top spin groundies with a perfectly vertical racquet face. Slight alterations in racquet face angle, by even a few degrees, has a profound effect on outgoing RPMs. There's an article published in RSI Magazine written by Rod Cross, (Sydney University, Co-Author of The Physics and Technology of Tennis) that gives us some insight on the relationship between spin, racquet face angles, swing path angles, head size/width, and racquet head speed. These are all inter-related factors. What follows is a snippet from that article.

[..]

Quote : "Players were given an inch in the 1970s and they took a mile. The ball now spins 4 or 5 times faster than it did before the 1970s. An increase in just one inch allowed an amazing increase in spin due to steeper, faster swings and a tilting of the racquet forward by up to 5 degrees, all without clipping the frame. An example will make this very clear.

Five Times the Spin

When a ball bounces off the court it acquires topspin, even if it had no spin before it hit the court. In fact, it spins faster than most players can generate themselves when they hit a topspin return. In order to return the ball with topspin, a player needs to swing the racquet both forwards and upwards and fast enough to reverse the rotation of the spinning ball. If the player doesn’t reverse the direction of the spin, then the ball will be returned with backspin—it is still spinning in the same direction but traveling in the opposite direction back over the net.

Suppose, for example, that the ball spins at 3,000 rpm (50 revolutions/sec) after it bounces off the court. That is a typical amount of spin when a ball hits the court at around 30 or 40 mph. Returned with a wood racquet, a player won’t be able to swing up at a very steep angle without clipping the frame. He will still be able to reverse the spin, but he will get only 200 rpm or so of topspin by swinging the racquet upward fairly rapidly at about 20 degrees to the horizontal. A change in spin from 3,000 rpm backwards to 200 rpm forwards is a change of 3,200 rpm, which is a relatively big change, but it is only enough to return the ball with a small amount of topspin.

Now suppose the player switches to a 10-inch-wide racquet and swings up at 30 degrees to the ball. The player can do that and can also tilt the racquet head forward by about 5 degrees, with even less risk of clipping the frame than with a 9-inch-wide wood racquet being swung at 20 degrees with the head perpendicular to the ground. In this way, the player will be able to change the spin by about 4,000 rpm instead of 3,200 rpm, with the result that the spin changes from 3,000 rpm of backspin to 1,000 rpm of topspin. The result is therefore a factor of five increase, from 200 rpm to 1,000 rpm, in the amount of topspin. That’s an amazingly big effect considering that the racquet increased in width by only one inch, or by only 11 percent.

Why Width Matters

A 9-inch-wide racquet swung with the strings in a vertical plane has about 8 inches of string in the vertical direction and about one-half inch of wood above and below the strings. A 10-inch racquet swung in the same way has about 9 inches of string in the vertical direction. The ball is just over two and one-half inches in diameter, so 3.1 balls can fit across a 9-inch racquet and 3.5 balls can fit across a 10-inch racquet. If the 10-inch racquet is tilted forward 27 degrees, then the strings extend 9 inches diagonally and 8 inches vertically, as shown in Figure 1. The racquet can therefore be swung upwards at 27 degrees or tilted forward by 27 degrees, and it will then present to the ball exactly the same area of string as a 9-inch racquet. No one tilts the racquet forward by as much as 27 degrees, but they now swing up into the ball at angles of 30 degrees or more to generate topspin. Tilting the racquet head forward slightly generates even more topspin.

Giving a player an extra inch of width allows the player to swing up at a steeper angle or faster or both. In that case the ball slides farther across the strings, so you really do need that extra inch. A change in 4,000 rpm rather than 3,200 rpm is therefore not surprising given the extra speed, angle, and tilt made possible by the extra one inch of width.

Going from a 10-inch to an 11-inch racquet does not deliver another huge increase in topspin. The reason is that if players tried to increase the upward speed of the racquet any more than they do now, the ball would sail over the baseline. They can do that for a topspin lob, but the forward speed of the racquet and the ball remains relatively small for a topspin lob. An 11-inch racquet will work better for topspin lobs but not for any other shot. On the other hand, 9-inch racquets were only just over the limit of being able to generate any topspin at all. Give a 9-inch graphite racquet to a player today and the result would be some serious clipping of the frame every few shots, though perhaps not as many as “old-timers” might expect because modern players are so practiced and skilled at steeper swings. "

--The Inch That Changed Tennis Forever, By Rod Cross
http://www.tennisindustrymag.com/articles/2006/01/the_inch_that_changed_tennis_f.html

[..]

Also, might want to check out this tool here, which was created by a longtime research partner of Mr. Cross, Crawford Lindsey. You can input all sorts of parameters: racquet face angle, swing path angle, among others, and get estimates for RPMs, net clearance, distance, and shot speed. Not saying that the tool is the Gospel Truth, it just that this is one of the things we can look to for guidance as the which factors play a big role and which factors play a small role. When it comes to estimating RPMs I know that I'm really not very good at discerning the difference between say 2800 RPMs and 3200 RPMs. I can see trajectory, and ball height, but that's not spin, that's just my guess at spin. So I tend to trust the instrumentation that CAN measure this stuff, such as that Wilson Doppler thingamajiggy, or the tightly controlled lab studies more than I trust my guesswork.
http://twu.tennis-warehouse.com/cgi-bin/trajectory_maker.cgi

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