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Thread: Effective Gear Ratio
11-30-2012, 05:55 PM #11I'm starting to confuse myself thinking about it more and more trying to make sense of it and how to explain it.
ta=t0*gr: ta is torque on axleshaft, gr is gear ratio
F=ta/r: r is tire radius (=1/2 diameter) F is Force between wheel and ground (this is what makes you go).
solve for t0: t0=F*r/gr
for comparing when something changes:
t0=F1*r1/gr1=F2*r2/gr2 (remember that t0 doesn't change for our purposes)
if we assume 1 is the "stock" configuration, then to compare 2 to 1
Example: stock gear ratio 3.55 with a 30 inch diameter tire
new is 3.73 with 35 inch diameter tire
F2/F1=(15/3.55)*(3.73/17.5)=.90 so the new configuration will put 10% less torque (F2=90%*F1) to the ground and will thus feel more sluggish than stock.'98 K1500 Suburban LS 5.7 L 4L60E NV246 ARB
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11-30-2012, 06:46 PM #12
Also some things the math does not take into consideration is if your lifting your truck you will have more wind resistance and also if your adding any extra weight from larger tires and rims. It might not be much but it is a factor. So my recomendation is to always round up to the next available gears or even the next after that. Just my .02.
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11-30-2012, 07:22 PM #13
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05-10-2013, 04:44 PM #15
wait, im confused... so...
(33 / 29) x 3.55 = 4.03
to run 33" tires, i should have at lease 3.83 gears for the axles?
i have 265/75 (about 29") and i want to go to 285/75 (about 33") .... i still dont know what gears i should have...Gas was $1.83 when Obama took office.....
05-14-2013, 01:29 PM #16
look at it this way as well
(29/33) x 4.10 = 3.608 effective gear ratio so real close to 3.55
(29/33) x 3.73 = 3.28 effective gear ratio so taller than stock by a decent margin and a little more effort required to get things rolling.David
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05-14-2013, 09:29 PM #17
ooooo-k cool thanks! =)
im gonna stick with my 265/75R16s
31" looks, and handles well with my 3.73 axle
05-16-2013, 12:06 PM #18
although, 32 would almost be 3.55.... just a little under!
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