What did i do wrong here

[darederek]

okay the math part of my brain got curious so we are going to figure out the theoretical top speed for a blaster with 20 inch tires, 14/40 gearing, and in 6th gear at 7500rpm. however something is wrong here. this is my thought process so tell me whats wrong.

keep in mind that this is without wind resistance, friction, weight etc. just how much the wheels spin and how far you would get. here we go

okay so we say 7500 rpm. the primary reduction of the blaster is 3.227. so with the crank spinning 7500 rpm, the clutch output will be spinning 2324.14 rpm

next we will do what 6th gear affects. the 6th gear ratio is 0.905. so with the clutch output spinning 2324.14 rpm the output to the front sprocket will be spinning 2568.11 rpm.

now the secondary reduction ratio with 14/40 gearing will be 2.86 so with the front sprocket spinning 2568.11 rpm the rear will be spinning 897.94 rpm

now with 20 inch tires each revolution will move you 20 inches so at 897.94 rpm you will be moving 17958.8 inches per minute. or 0.28343 miles a minute which works out to roughly over 17 miles per hour??????

 

[Paulie B]

Measure the roll out of the tires. It's not 20"

 

[darederek]

Oops that would be it paulie. I need circumference not diameter. Thanks. I'm going to make a new thread with a different title when I figure it out right

 

[Paulie B]

NP brother ......

 

[darederek]

Its like 63 inch circumference so you would move 63 inches every revolution so 56423 inches a minute. Ill have to figure out the rest at home I'm on my blackberry so this is a little hard

 

[Paulie B]

Goin by your calculations I come up with roughly 53.4 mph.

 

[Awk08]

isnt that 7500 rpm's a little low ?????

 

[darederek]

idk im not sure what a blaster runs at. toomeys website dyno stops at 8750. im going to go through and do it for 8500 for the new thread im going to make now that i figured out my mistake. i got the same as paulie so im going to say the rpm was off some too