Calculating mph

[steffen707]

Hey guys, i'm trying to find out how to calculate mph on my scooter for various gear ratios.

I was searching around but I can't find the math behind it. I found the ratios here viewtopic.php?f=5&t=10334 and on the wiki link at the end of the thread. I'm sure wheel size, rpm, variator and the rear gears are in the math.

I saw an excel file screen shot on this link viewtopic.php?p=224589#p224589 that shows a 9.19:1 ratio would yield 68.5mph at 11,000rpm.

Today I maxed out my corsa 9:1 setup at 11,100 rpm and i only hit 57mph. Not sure what my tire size is off hand, but i doubt it can be 11.5mph different.

[steffen707]

Is this it:
Tire Circumference in inches / 12 = tire circumference in feet

Engine rpm / (rear ratio * variator max overdrive) = wheel rpm

Tire circumference in feet x wheel rpm = wheel feet per minute

Wheel feet per minute * 60 minutes = wheel feet per hour

wheel feet per hour / 5280 = wheel miles per hour



And a 90/90-10 tire is 51.45 inches in circumference, so
(11000 / ( 9*0.8 ) * (51.45/12) * 60 / 5280 = 74.4mph? Now that seems far off

and a 80/90-10 tire is 49.23 inches in circumference and at 10,800 rpm should be 69.9mph i'm also nowhere near that. ugh

[Trafficjamz]

your math looks like it is correct.

Your assuming a .8:1 ratio from your drive to driven pulley.

If you are running a zx trans, that ratio is more like 1:1 or less depending on the belt.

I did all this math a while back on an excel speadsheet.

viewtopic.php?f=4&t=17752&p=149980

[steffen707]

your math looks like it is correct.

Your assuming a .8:1 ratio from your drive to driven pulley.

If you are running a zx trans, that ratio is more like 1:1 or less depending on the belt.

I did all this math a while back on an excel speadsheet.

viewtopic.php?f=4&t=17752&p=149980

i was looking for that excel spreadsheet.

I took your advice and assuming a 10,800 rpm, a ratio of 1:1 (i'm using a 654 belt) and i still forgot to check but a 80/90 tire would yield 55.9mph

SO, either my tire is bigger, the tach is off, or the belt is making a better overdrive than 1:1 and is closer to 0.8:1

Perhaps i'm right around the possible max that you can get out of 9:1 gears and a stock tire with ZX trans.

I'm going to fiddle with the stock trans tomorrow and see what the best I can get is and report back.

[maddog]

R-U trying my dio theory, the master engine builder that i deal with knows it can be built....