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Old 19th November 2007, 12:58   #1
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Default Speed calculator from ratios etc

I came across this - Wallace Racing - Calculate Speed for given RPM, Rear Gear Ratio and Trans Gear Ratio

Now, RPM : no issues

Tire diameter : Tyre + rim or only Rim? for eg, if a bus has a 295/80 R22.5 tyre, then total dia will be 63.5 inches right ( .80 x 295 + .80 x 295 ) mm - convert to inches + 22.5 in + 22.5

Gear ratio : If a bus' 6th ratio is 0.83, i will input .83 for this ?

Trans gear ratio : the specs of bus say the rear axle ratio is 4.1 : 1 (shall i write this?)

HELP..
I m talkin abt this bus - http://www.ceritamotors.com/ceritamo...d_brochure.pdf
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Old 19th November 2007, 13:09   #2
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Thats one hellava find Bunny.

Am just getting used to auto calculations ( they are a lot doff from the P/E ratios used in Audit firms, I guess !!! )

How did you arrive at the 4.1 : 1 final calculation. Am working it our for an Indica Turbo DLG model, incase that helps my case.

Also, am assuming that this table can be used to caliberate the ideal running speads for the rpms.

If so..under what conditions and does engine power bear no influence here..??

Any clues, please.

Cheers
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Old 19th November 2007, 14:34   #3
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Quote:
Tire diameter : Tyre + rim or only Rim? for eg, if a bus has a 295/80 R22.5 tyre, then total dia will be 63.5 inches right ( .80 x 295 + .80 x 295 ) mm - convert to inches + 22.5 in + 22.5
295 x .8 = 236mm = 9.291 inches

(9.29 x 2) + 22.5 = 41.08 inches (overall diameter).

Quote:
Gear ratio : If a bus' 6th ratio is 0.83, i will input .83 for this ?
Yes

Quote:
Trans gear ratio : the specs of bus say the rear axle ratio is 4.1 : 1 (shall i write this?)
Yes

Shan2nu
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Old 19th November 2007, 14:36   #4
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295/80 R22.5 => 2*295*0.8+25.4*22.5 = 1043.5 mm dia of wheel

If engine RPM 1000, then wheel RPM in 6th gear

1000*(1/4.1)*0.83 = 202
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Old 19th November 2007, 14:44   #5
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Quote:
If engine RPM 1000, then wheel RPM in 6th gear

1000*(1/4.1)*0.83 = 202
Is it 202 or 293.85rpm (18.39kmph)?

Shan2nu
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