Math guru's step in please!!!!!!
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From: Mason Mi
Math guru's step in please!!!!!!
The difference from a 4.10 gear to a 3.90 is about 5%.
So, does this mean that a 4.10 gear car will act exactly like a 3.90 if it is using a 5% larger circumference tire?
So, does this mean that a 4.10 gear car will act exactly like a 3.90 if it is using a 5% larger circumference tire?
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From: Mason Mi
First of all why would a radius be better?
Secondly, why do you use the term "perceived". Is it because it will not affect the actual final ratio of the drive axle but will affect the final result at the pavement, which to me is all that counts.
Thanks, Randy
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From: Mason Mi
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From: At the beach in little Rhody
Exactly. Larger diameter tires will effectively lower the overall ratio. I didn't see the part about the circumference. If you compute the rotation distance per RPM for each combination, assuming you know the circumference of each tire, you should be able to come up with a tire that provides the same distance per motor revolution.
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From: Mason Mi
Exactly. Larger diameter tires will effectively lower the overall ratio. I didn't see the part about the circumference. If you compute the rotation distance per RPM for each combination, assuming you know the circumference of each tire, you should be able to come up with a tire that provides the same distance per motor revolution.
My stock rears are 275/40/18 at 83.76". 295/30/18's are 78.44".
This tire change should be close to the same as changing from a 3.90 to a 4.10 rear gear. Right?
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Yes, in theory going to a 5% smaller circumference tire is the same as a 5% steeper gear ratio just like you asked.
However, in practice they aren't the same thing. With the wheels, you will get a higher torque multiplication but you could also get a lower inertia tire which is easier to accelerate. With the gears, you will likely get higher torque multiplication and a slightly higher gear loss. Makes lighter and smaller wheels look like the better option.
Peter
However, in practice they aren't the same thing. With the wheels, you will get a higher torque multiplication but you could also get a lower inertia tire which is easier to accelerate. With the gears, you will likely get higher torque multiplication and a slightly higher gear loss. Makes lighter and smaller wheels look like the better option.
Peter
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From: Mason Mi
Yes, in theory going to a 5% smaller circumference tire is the same as a 5% steeper gear ratio just like you asked.
However, in practice they aren't the same thing. With the wheels, you will get a higher torque multiplication but you could also get a lower inertia tire which is easier to accelerate. With the gears, you will likely get higher torque multiplication and a slightly higher gear loss. Makes lighter and smaller wheels look like the better option.
Peter
However, in practice they aren't the same thing. With the wheels, you will get a higher torque multiplication but you could also get a lower inertia tire which is easier to accelerate. With the gears, you will likely get higher torque multiplication and a slightly higher gear loss. Makes lighter and smaller wheels look like the better option.
Peter
So I can put a bigger diameter 18/19 set of wheels with a 4.10 gear for the street. This, if sized correctly, would give me a 3.90 equivalent for the streetability and manners I'm looking for!!
I could still have my old 17/18 combo for the 1320 and times I want a little more punch :o.
I don't understand why this isn't more common
Melting Slicks
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From: Nashville TN
Hmmm
So I can put a bigger diameter 18/19 set of wheels with a 4.10 gear for the street. This, if sized correctly, would give me a 3.90 equivalent for the streetability and manners I'm looking for!!
I could still have my old 17/18 combo for the 1320 and times I want a little more punch :o.
I don't understand why this isn't more common
So I can put a bigger diameter 18/19 set of wheels with a 4.10 gear for the street. This, if sized correctly, would give me a 3.90 equivalent for the streetability and manners I'm looking for!!
I could still have my old 17/18 combo for the 1320 and times I want a little more punch :o.
I don't understand why this isn't more common
Melting Slicks
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From: Rochester Hills MI
all you have to do is set up two different dummy scenarios to find the speed the car is travelling with the two different setups and the same input speed from the transmission:
SCENARIO 1 (3.9 gears):
given:
1000rpm input from trans
3.9 gear ratio
25in dia tire
final drive rpm = 1000/3.9 = 256.41 rpm
distance per tire rotation = 25in * pi = 78.54in/rotation
256.41rot/min * 78.54in/rot = 20138.4 in/min
(rotations cancel out leaving units for velocity in in/min)
velocity = 20138.4 in/min = 19.07 mph
SCENARIO 2 (4.1 gears and 5% larger tire):
given:
1000rpm input from trans
4.1 gear ratio
26.25in dia tire
final drive rpm = 1000/4.1 = 243.9 rpm
distance per tire rotation = 26.25in * pi = 82.47in/rotation
243.9rot/min * 82.47in/rot = 20114.4 in/min
(rotations cancel out leaving units for velocity in in/min)
velocity = 20114.4 in/min = 19.05 mph
RESULTS:
the resulting velocities are only slightly different because 3.9 to 4.1 isnt EXACTLY a 5% difference. You would be better off with the smaller tires and 3.9 gears though. The larger wheel/tire setup has more inertia and requires more power to get up to speed.
Last edited by SaberD; Dec 29, 2009 at 05:12 PM.
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From: Mason Mi
"You would be better off with the smaller tires and 4.1 gears though. The larger wheel/tire setup has more inertia and requires more power to get up to speed."
Understood, that's why I would use a smaller ( stock or smaller ) for the strip and larger diameter for the street because 80% of my driving is on the highway. Plus my 490rwhp has me kinda traction challenged with the current 3.90 on stock dia. wheels and tires.
Understood, that's why I would use a smaller ( stock or smaller ) for the strip and larger diameter for the street because 80% of my driving is on the highway. Plus my 490rwhp has me kinda traction challenged with the current 3.90 on stock dia. wheels and tires.
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From: Katy Tx
when switching to the 4:10 gears then using the smaller circumference tires on the strip, you'd also lose some traction.. smaller contact patch for the tire coupled with higher torque multiplication of the gears.