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PostPosted: Thu Jul 26, 2012 9:41 pm 
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Joined: Tue Jul 24, 2012 7:05 pm
Posts: 2
Hi,

I have a G2X (red). Although I can monitor my speed via GPS, I am interested in setting
up the gear ratios in order to see which gear I'm in. I know I can do it "automagically"
in Setup2, but would rather do it the manual way.

Have done a search, but can't find a "method" to to calculate them properly.

I have a 944S and my current gear ratios are:

1 - 3.500:1
2 - 2.059:1
3 - 1.400:1
4 - 1.034:1
5 - 0.829:1

I'm running 235/50/15 tires which gives me a circumference of 73 inches (if I measured correctly)

This might be a really basic question.....but.....How do I calculate the ratios for proper entry? Or do
I simply enter them as they are?

Thanks,

Jim


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PostPosted: Fri Jul 27, 2012 4:37 am 
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Joined: Wed Jul 25, 2012 6:19 am
Posts: 11
Location: IL
I get 76 in for your tire diameter (=pi()*(235*0.5*2/25.4+15)). If you actually measured 73 in, then use that. The best number to use is the revs/mi number that the tire manufacturer provides. If you don't know this number, see if Tire Rack has this number for your tires. If you still can't gets revs/mi, then you can calculate it.

revs/mi = 5280*12/Tire Circumference

Once you have the revs/mi number for the tire, you can calculate the required ratio as follows.

ratio = GearX*GearFinal*revs_per_mi/60

Where Gear final is your final gear and GearX is the gear ratio you are calculating for.

_________________
Jared Cromas
SCSCC Race Steward / Pointskeeper
'12, '11, '10, '08 ITA Champion
2008 Driver of the Year
#111 ITA 1990 Gold Acura Integra


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PostPosted: Fri Jul 27, 2012 11:27 am 
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Joined: Tue Jul 24, 2012 7:05 pm
Posts: 2
mc-integra111 wrote:
I get 76 in for your tire diameter (=pi()*(235*0.5*2/25.4+15)). If you actually measured 73 in, then use that. The best number to use is the revs/mi number that the tire manufacturer provides. If you don't know this number, see if Tire Rack has this number for your tires. If you still can't gets revs/mi, then you can calculate it.

revs/mi = 5280*12/Tire Circumference

Once you have the revs/mi number for the tire, you can calculate the required ratio as follows.

ratio = GearX*GearFinal*revs_per_mi/60

Where Gear final is your final gear and GearX is the gear ratio you are calculating for.


Excellent. Although I'm totally math challenged, I think I can figure this out now. TireRack did have the revs/mi for my tire
so that makes it easy.

Thanks for the help!!!!

J


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