# Windshield Damage

#### MolaKule

Staff member
During thunderstorms, hail the size of ping pong balls can damage vehicle sheet metal and windshields, since they have a free-fall velocity of up to 91 feet/second (27.34 m/s). Two identical windshields of the same material are canted at two different angles; one with a 15 degree slope and the other with a 30 degree slope. Q1: Which windshield has the greater probability of being damaged and Q2: Why? This question is open to all.

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#### oldhp

Well, my head says 30Â° because it's closer to being flat, which would be the perfect 90Â° for the hail to hit straight on.

#### JimPghPA

Is the vehicle moving, and if so how fast?

#### Vern_in_IL

15 degree slope will receive less damage. Why? because of redirection of the energy. assuming the hail is coming strait down at 90 degrees, the momentum of the fall of the ice, is slightly redirected by small angles. The greater the angle the more energy has to be deflected or absorbed by the glass. Max impact would be sunroof glass, at a 90* angle to the projectile trajectory.

#### 14Accent

Your question is missing too many variables. What is the relationship between the angle of the incoming hail stone and the windshield? IE, what is the EFFECTIVE angle. If the windshield is placed on level ground and canted at a 15 degree angle relative to the ground, is the hail stone striking the windshield at a perfect 90 degrees from level? I highly doubt it. Wind shear and rotation of the hail stone will greatly vary the results. You state that the hail stone could have a velocity UP TO 91 MPH. That's fine, but what is the actual speed? This will most certainly change the likelihood of damage to said windshield. Is the vehicle moving, or stationary? Again, this will affect impact velocity and force. That being said, I will throw out that a 15 degree slope will likely incur less damage than a 30 degree slope. Why? Not a clue.

#### Revving2Redline

30 degree.Flatter surface to increase impact radius?

#### CharBaby

I'm just shooting from the hip here because I really don't know. A1: The 30 degree windshield has a grater probability of being damaged. A2: Because it is angled more upward toward the "INCOMING"!

#### joegreen

I'm going to guess the 30 degree windshield will have a higher chance of being damaged due the higher impact angle

#### bullwinkle

I would say the 15 degree (assuming it's 15 degrees from horizontal) would be more likely to be damaged because the hail will strike directly on the glass, more energy exerted on the glass. The 30 degree (more vertical?) one will receive a more glancing blow, allowing the hailstone to have enough energy to cause a nice hood dent...

#### Vercingetorix

Voting 30 degrees because the closer the angle to vertical the thicker the glass will be to the hail. AKA sloped armour.

#### brages

When viewed from above, the steeper windshield presents a smaller "target area". A perfectly vertical windshield would be completely safe from hail, assuming it falls straight down. Even with hail that's not straight down, the same concept applies.

#### Kira

Upon reading the question and the answers it appears that there is confusion over which axis the 15Âº and 30Âº is taken from. Are these angles measured up from the X axis or to the left or right from the Y axis?

#### gfh77665

Moving, 30 degreee. Stationary, 15 degree. Why? Effective angle of impact closest to 90 degrees.

#### Nukeman7

I will go out on a limb and say that both windshield angles have an equal chance of being damaged in a real-life thunderstorm <span style="text-decoration: underline">if the vehicle is stationary</span>. This is based upon my (uneducated) suspicion that the angle of the hail impact is random due to factors such as wind speed and direction of the incoming stormfront.

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#### NO2

What Nukeman said. If you hit hail when driving at 70mph , the angle with least damage is going to vary. Small diameter hail falls more slowly than large diameter hail because of different surface area to mass ratios. The difference might be somewhere between 40 mph (small with damage unlikely), and your velocity having a greater effect vs 90mph (large and possibly damaging to the glass and sheet metal).

#### opus1

Anecdotal experience, but my Sonata has been assaulted by damaging hail twice. First time, I was in stop and go traffic, mostly stopped, and IIRC, quarter-sized hail. \$7300 in damage, including windshield, multiple dings where the paint was broken, and one dent in particular that could have held a chicken egg - on the curved part of the fender. Last May I got caught on the expressway during golf-ball sized hail, but there was little traffic so I was moving. I have a number of dings, but no broken windshield and no damaged paint. I can't prove it scientifically, but I'm convinced that the fact that I was able to keep moving helped divert some of the energy of the falling hail.

#### MolaKule

Staff member
Originally Posted by 14Accent
Your question is missing too many variables. What is the relationship between the angle of the incoming hail stone and the windshield? IE, what is the EFFECTIVE angle. If the windshield is placed on level ground and canted at a 15 degree angle relative to the ground, is the hail stone striking the windshield at a perfect 90 degrees from level? I highly doubt it. Wind shear and rotation of the hail stone will greatly vary the results. You state that the hail stone could have a velocity UP TO 91 MPH. That's fine, but what is the actual speed? This will most certainly change the likelihood of damage to said windshield. Is the vehicle moving, or stationary? Again, this will affect impact velocity and force. That being said, I will throw out that a 15 degree slope will likely incur less damage than a 30 degree slope. Why? Not a clue.
The hailstone is assumed to be coming down vertically with no vehicle movement, i.e, vehicle is stationary, there is no horizontal wind component, no relative motion or I would have included those variables. The velocity vector is Z = - 91 ft./sec, indicating a pure free fall of the hailstones.

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#### spasm3

15 degree. That angle absorbs less energy and allows the hailstone to continue moving imparting less energy to the glass. Seems to me the closer you get to 90 degrees, the more energy is absorbed by the glass.

#### spasm3

Too add to my previous post, think of a stone skipping on the water vs dropping straight down in to the water.

#### zorobabel

Are the windshields identical in size?