Gear ratio?

[Vagos]

Can anyone please explain to me the how the gear ratios work?In simple terms assuming we have two gearboxes which the first gearbox has a 1st gear ratio of 3500 and the second gear box a 1st gear with ratio 3600.Now which of the two has the longer gear the gear that will put out more mph than the other.thanks

[opelnut10]

Originally Posted by Vagos Can anyone please explain to me the how the gear ratios work?In simple terms assuming we have two gearboxes which the first gearbox has a 1st gear ratio of 3500 and the second gear box a 1st gear with ratio 3600.Now which of the two has the longer gear the gear that will put out more mph than the other.thanks

Gear ratio is simply multiplication, the gears in the transmission multiply the revolutions of the output shaft which drives the propellar shaft. In other words if the first gear is 3.50 then it makes the propellar shaft turn 3 and 1/2 times for every revolution of the input shaft of the transmission.

[namba209]

Theoretically speaking, the lower numbered gear ratio will produce the most MPH. That is, using your two ratios, the 3.50 will take 3.5 turns of the drive shaft to turn the wheels one revolution and the 3.60 will take 3.6 turns to do the same. This is presuming you have the horsepower to get the car to maximum MPH. Here's an example: My old Honda 90cc racing bike with a final drive ratio of 15:45, that's a 15 tooth sprocket from the transmission to a 45 tooth sprocket on the rear tire had a maximum speed of about 55-60 MPH. Changing the sprockets to 13:70, the top speed was above 70 MPH. This change is gears allowed the engine to get up into the higher RPM and horsepower range for what it was modified for. Max RPM with the lower numbered gearset was around 9600 RPM, with the higher numbered gearset the RPM was raised to about 16000 RPM. The lower numbered gearset would not allow the engine to reach the max horsepower range, while the higher numbered gears would put less work on the engine allowing it to get into that RPM range. HTH.

[Dmcbrass]

Opelnut10,
That's backwards. the input shaft must turn 3-1/2 times for one revolution of the driveshaft.

[GTJIM]

"3.5 turns of the drive shaft to turn the wheels one revolution"

Sounds right to me - I think Ron is speaking about the diff .....

[namba209]

You're right Jim, I was thinking about differential gear ratios. But the same holds true about the trannies 1st gears. 3.5 turns on the input shaft to get one turn on the output shaft, or 3.6 turns for the same thing on the other tarnny. So with all that being said, to answer the question posed, the lower numerical gear set at a given RPM, will produce a faster MPH than a higher numerical gear set, providing both will be able to attain the same RPM.

[Dmcbrass]

Vagos said 1st gear in the gearbox. I don't think he's talking about the differential.

Woops! Ron, I guess you beat me to it. We we're both responding to GtJim at he same time.

[jeff denton]

Remember, first gear isn't so much about mph. To study what trans to use for highest speed you should be comparing fourth gear (1:1) of the four speed to a five speed's fifth gear, which is turning the driveshaft faster than the crankshaft rpm. Final drive (differential) gearing needs to get involved here, too. Somewhere in this equation you want to consider horsepower available, the reality is that you may not have enough power to use the overdrive and gearing computed to go as fast as you want. Funny how this all goes hand in hand... Not to mention the brakes it might take to get it all slowed down or stopped.