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working out top speed in each gear 

 

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 Post subject: working out top speed in each gear
Posted: Thu Aug 17, 2006 8:58 pm 
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gday,

Is there a formula for working out top speed in each gear with a given gear ratio and diff ratio?

basically im trying to work out my top speed in first gear with an EA T5 and 3.73:1 diff gears, with 15" rims and 205*65*15 tyres.

cheers

 

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Posted: Thu Aug 17, 2006 10:09 pm 
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umm you can

get the circumfrence of each wheel

the max rpm of engine
and all the ratio's of gears and away u go :)

 

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Posted: Thu Aug 17, 2006 10:26 pm 
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yeah but what is the actual equation???

oh and does anyone have the ratio for first gear in an EA T5??

 

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Posted: Thu Aug 17, 2006 10:28 pm 
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Disco Frank wrote:
umm you can

get the circumfrence of each wheel

the max rpm of engine
and all the ratio's of gears and away u go :)

. . . . . and then put them in a spreadsheet to make it easier.

Edit what you need in the yellow cells, and then click on a vacant cell for your figures. Bear in mind this calculates rolling speeds, obviously speed limiters come into as well.

 

 

Attachments:
File comment: Speed calculator
Speed_calculator.xls [13.5 KiB]
Downloaded 104 times

 

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Posted: Fri Aug 18, 2006 1:06 am 
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EA 1st is 3.5 from memory.
With 3.73's it'll be off tap dude, f**k burnout machine!

 

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Posted: Fri Aug 18, 2006 9:30 am 
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yeah back in the day I wrote my first flash application, http://users.bigpond.net.au/mikgan/flash/carcalc.swf and I think its got them values in there somewhere..

 

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Posted: Fri Aug 18, 2006 9:31 am 
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I only got the auto ratio in there 2.39, ahh well, was a while ago that thing...

 

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Posted: Fri Aug 18, 2006 4:27 pm 
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thanks for that,

judging buy that snap, my top speed will be 51 km/h at 5500rpm in first gear....


doesnt sound right considering ARM said that an EA T5 redlines at bout 40km/h with a 3.45 diff...?

 

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Posted: Fri Aug 18, 2006 9:42 pm 
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mrnasty wrote:
judging buy that snap, my top speed will be 51 km/h at 5500rpm in first gear....doesnt sound right considering ARM said that an EA T5 redlines at bout 40km/h with a 3.45 diff...?
I think you'll find it's reasonably close - my XH calculated 105kmh in 5th at 2000RPM - this is spot on in reality.
I did measure my wheel diameter, and compared with the spreadsheet, the diff is around 12mm less in calculation - rolling distance will calculate on the conservative side. Also I suppose the actual rolling distance will be slightly less due to the tyre sitting flat due to tyre pressure.

 

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Posted: Fri Aug 18, 2006 9:51 pm 
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doesnt matter how flat they tyre is it will still be the same distance all around the tyre. Dont forget about torque converter slip in the autos either.

 

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Posted: Fri Aug 18, 2006 11:01 pm 
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Andrew J wrote:
doesnt matter how flat they tyre is it will still be the same distance all around the tyre.
an example from http://www.southmainauto.com/tires.htm . "Rolling Circumference = The linear distance traveled by a tyre in one revolution. This can vary with load and inflation."

 

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Posted: Sat Aug 19, 2006 12:59 pm 
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thats just made my day :D

mint. Thanks dude!

 

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Posted: Sun Aug 20, 2006 9:14 pm 
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well its a goer. Pick the gearbox up tomorrow night, and then i have to collect a few more EF specific parts and a new clutch over the next month or two. :D mint

 

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Posted: Sun Aug 20, 2006 10:31 pm 
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nice work!

 

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