While browsing tire rack I found this little bit of info, I gotta try this out





Follow the speed measuring instructions below:



1. Travel at a constant rate of speed on an open highway and have someone record the number of seconds it takes to travel exactly one measured mile.



2. On the chart, locate the number of seconds it took your vehicle to travel one mile. The speed indicated next to the number of seconds is the true average road speed of the vehicle.



3. Repeat the measurement several times and average the results. Recalibration of your speedometer is recommended if significant inaccuracy is noted.



Seconds Per Mile / Road Speed



50 72



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51 71



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52 69



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53 68



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54 67



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55 65



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56 64



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57 63



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58 62



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59 61



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60 60



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61 59



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62 58



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63 57



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64 56



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65 55.4



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66 54.5



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67 54



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68 53



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69 52

 

Nice... good post!

 

try this:



http://www.miata.net/garage/tirecalc.html

 

i need a min was 60mph