Kmanestor - you're right, but it's virtually negligible for small angles.
Remember that 5-6 degrees is the optimum entry angle to the pocket for most bowlers. (Mathematically, this equates to a breakpoint of the 2-3 board at 45 feet downlane for a right hander. If you diagram this as a right triangle, the dimensions are 18 in. lateral x 15 ft. long. Theta, the included angle of the right triangle is found by atan(1.5ft/15ft), or 5.71 degrees.)
The error in the speed sensor downlane will be a ratio of the hypotenuse to the adjacent side. If you have a 6 degree entry angle to the pocket, your speed measurement will be off by {[1/cos(6)] - 1} x 100 = 0.550%. Yes, that's only 1/2 of 1 percent!
For pin-chaser -
Most higher average bowlers only lose 1 to 2 mph from the time of release to the pins. 4 mph seems a bit high, unless the backends are long and completely toasty! Friction (dry and hydrodynamic) accounts for most of the loss in velocity.
This concludes todays math/physics lesson.
--------------------
======================
Dan
======================
Engineering * Bowling = a fun and practical application of rotational kinematics.
Bowling Nerd Herd (TM) Member
