# Am i getting screwed by the dealer? **URL:** \ **Category:** NYSpeed Automotive\ **Created:** [December 7, 2007, 7:26am UTC](https://forums.speedlife.net/t/am-i-getting-screwed-by-the-dealer/39904 "2007-12-07T07:26:58Z")\ **Posts on this page:** 1\ **Showing post:** 47
**Author:** ![Rx3](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/rx3/32/7194_2.png) [@Rx3](https://forums.speedlife.net/u/Rx3)\ **Post date:** [December 7, 2007, 4:31pm UTC](https://forums.speedlife.net/t/am-i-getting-screwed-by-the-dealer/39904/47 "2007-12-07T16:31:09Z")
[quote=“newman,post:16,topic:39904"”] Here is WHY it is true. Given: 235/84/16 tire diameter (Tn) = 31.7 Assume: 9/32 tread depth At 50% wear, tire diameter (Tw) = 31.7 X 2(9/64) = 31.42 Assuming you are traveling at 70mph: w = th/t s=r\*th then th= s/r so w = s/ (r \* t) but since v = x/t or in this case v=s/t w= v/r so w = v/r since r=d/2 w = 2v/d (radians) 1 rad = 180/pi degrees so w= 360v/(pi\*d) Angular slip (As) will be defined as wn-wu SO at 70mph = 73 920 in/min As = 360\*v/pi (1/dn-1/du) As = -2381 degrees per minute. since 1 ROT = 360 degrees As = -6.61 rpm **So, for every minute you drive, your differential is SLIPPING 6.6 times every minute. I’m sure you can see how this would be BAD for any differential.** EDIT: I LOVE MATH. [/quote] Does weight ever come into play or is it strictly overall rolling diameter (being equal)? --- _[View the full topic](https://forums.speedlife.net/t/am-i-getting-screwed-by-the-dealer/39904)._