Spider Speedo

[LEN_LEEB@domain.elided]

Debbie writes:
...Does someone have a speeds in gear chart available on the web, I don't
trust this speedo too much.

Congratulations on the new Spider purchase. May it serve you long and well.
I realize you are right not to trust the speedo too much, by why do you think 
the tach is right?
That being said, the speeds per 1000 rpm in each gear are:
1st gear ..... 5.27
2nd   "  ..... 8.73
3rd   "  ..... 12.73
4th   "  ..... 17.46
5th   "  ..... 22.0
the above numbers assume standard rear axle ratio (4.1) and 185-70x14 tires 
(851 revs per mile)
The formula is 1/tire revs per mile  *  1/gear ratio   * 1/axle ratio  * 
1000*60 = mph/1000 rpm

I usually round off the numbers to the nearest mile per hour to figure speeds: 
5, 9, 13, 17, 22.
Try to find a measured mile on the highway, and hold 60 mph. Time the mile, and 
you should drive it in exactly 60 seconds. If your time is LESS, than your 
speedo reads LOW. If time is MORE, the speedo reads high. Within 2 or 3 seconds 
error, the error is 1 mph/second. i.e., 58 seconds = 62 mph.
Enjoy your Spider.
Len

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