There's a lot of talk about Urethane now and frankly, I love this topic.
I won't fully repeat things I've said previously, but instead here is a link to an article on Urethane I wrote on my site:
http://tamerbowling.com/index.php/urethane-evolution-revolution-or-devolution/ Here's a link to my review on the Storm Natural:
http://tamerbowling.com/index.php/storm-natural/ In my personal experience, it did take a game or so to understand the reaction. I've been bowling for a long time, but I couldn't remember how it would react after using reactive since the early 90s. I thought I was playing a tighter line, but I simply wasn't tight enough causing some weak 7s and buckets. Once I tightened and rolled it up 3-7 to the same breakpoint, depending on the shot, it was money.
If you're THS is 40ft or longer, you may struggle a bit on the fresh with carry unless you really go down and in. I like to use it for 3rd game of 1st shift. If your house is on the drier side, you may be able to use it all night.
Here was my own personal test. For 3rd game, I average over 230 with it, easy. I tested it out from 1st to 3rd games and I found that I average 10 pins higher with it, the further into the night I get.
I agree with Charlest, I haven't seen a "hook set" motion. The urethane equipment is much more continuous, because Urethane reacts earlier on the lane and slowly to dry. This is opposed to Reactive where generally speaking, very little reaction early, but reacts very quickly when it encounters dry.
Whenever I am struggling to find a line, "I play for nine". Meaning, I take out my urethane ball and simply get it to the pocket every shot. If I strike great, if I don't it's a makeable leave.
Also, I will agree with Charlest about carrydown. Urethane will mess up the line for reactive balls much more quicky, but not because of carrydown but simply pushing oil out of the way. It "parts the seas" if you can envision that as it goes down the lane. You can make small adjustments, i.e. 1/1 or 2/1, with the urethane, but since reactives react very quickly to dry, if they encounter dry or spotty areas created by the urethane ball, they will become a little unpredictable. Carrydown happens, but not more than any other bowling ball.
I will be writing another article soon about Urethane for spares. I much prefer using urethane as compared to plastic, but I'll save that for another time...
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