Finding a Replacement Ball Bearing

J.D. Longboards

Jon DeAmicis

Problem

We are ready to expand!!

Increase customer satisfaction

We don't make cheap beginners boards

We agree with our customers. We need Change!!!

The Possible Replacements

We want to upgrade the bearings without breaking the customers bank.

CEO has has chosen Bones Reds and Abec 5 bearings.

A Little Background

Longboarding is, cool college kids do it!

And cool dogs!!

Rain is lame!

A little more background

Ceramics are better, but expensive.

Keep bearings clean!!

It prevents scarring and cold welding

A little clarification

Scarring is caused by debris

Cold welding happens when two peaks collide

Now for some experimenting!

Place bearings in 76mm wheels.

Dropped a 453 gram weight attached to a rope (more like a string) wrapped around the wheel 4 times.

12 trials for each brand, 3 per wheel.

Calculating...

Open Office

Mean (average)

Median (middle number)

Mode (most common number)

Standard Deviation (average distance from mean)

Pearson's Index of Skewness

Results for Bones Reds

Mean 28.3s

Median 31.9s

Mode None

Standard Deviation 7.7s

Pearson's Index - -1.4

Results for Abec 5

Mean 33.8s

Median 40.5s

Mode None

Standard Deviation 21.3s

Pearson's index - -0.9

Comparison

Bones RedsAbec 5

28.3sMean33.8s

31.9sMedian40.5s

NoneModeNone

7.7sStandard Deviation21.3s

75%Within One Standard Deviation75%

100%Within Two Standard Deviations100%

-1.4Pearson's index-0.9

v

Assesment

Bones reds had smaller standard deviation of 7.7s

Abec 5's had higher mean (33.8s) and higher median (40.5s)

Abec 5 has smaller skewness by Pearson's Index. (-.9)

Recomendation

I recommend Abec 5 bearings for use in J.D. Longboards longboards.

TrialDuration of Spin in SecondsAbec 5

149.9

257.8

360.1

46.2

58.1

67.8

717.8

816

932.7

1048.2

1151.8

1249.6

TrialDuration of Spin in SecondsBones Reds

119.3

215.6

314.7

435.3

534.2

633

724.2

830.7

933.2

1033.7

1130.8

1234.6