Errors in Judgement - fine and costs waved

[PDQSHIP@aol.com]

In a message dated 96-01-02 16:56:46 EST, you write:

>>
>Difference in tire diameter would screw up the computations of the ABS
>computer, I've ben told...
>
>

No, the abs is stupid, it senses only impending lockup of the driveshaft, not
the wheel....  Yes, in "track mode" most radar can be used to clock, yes,
Police speedos are "certified" for tracking purposes......   The 13 mph
difference is not tire error, but could be speedo sending or recieving (hall
sender)error.....

Some math:

STOCK

205/60 15 = 24.68 dia X 3.1415926 = 77.53 circum 

215/45  17 = 24.62 dia X 3.1415926 = 77.35 circum

5280 feet/ 1 mile X 12 = 63,360 inches /mile

63,360/77.53 = 817.23 tire rotations per mile on the stock 205/60 15 tire

63,360/77.35 = 819.13 tire rotations per mile on the  215/45 17 tire

So, 817.23/819.13 = .9997% difference.....  Per most car manufacturers a
variance of 1% @ 1 mile @ 60mph is most acceptable, and in fact, prolly a
great target......

So, either your speedo was off before the swap (MOST LIKELY), or the cop was
full of *%#t (given) or you just have your foot planted too close to the
floor (given).....  

I read a SAE paper on speedo error a while back and most car manufacturers
use 1000rpm cable speed = 60mph and a 10% variance in that cable speed is
most acceptable.  Sounds to me like your hall sender/converter on the speedo
is a LITTLE off.....  Also, remember tho, that a "non certified" speedo is
only calibrated (most manufacturers) at 60mph.

HTH 

Scott