What difference does gear ratio make?
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From: Trophy Club Texas
What difference does gear ratio make?
I'm not a mechanic, don't play one on TV either....
I have a couple of questions that will probably sound stupid to those that know the answers.
I have an 05 F-250, 6.0 diesel 4x4. It has a 3.73 rear end. I'm not planning on getting a new truck right away, but was wondering if that was the 'best' rear end to have. I tow an 18ft bassboat fairly regularly and a 16 flatbed trailer now and then. I guess I'm looking more for 'general' information on what the different rear end ratios mean.
I also have a 1981 Ford Van (used for tailgaiting at football games). I'm fairly certain it was used as a school bus (or school VAN) originally. I have no idea what rear end it has, but top end speed is about 70. How can I find out what it has? Would a different rearend change that? Would it increase/decrease my mileage?
Thanks in advance,
dlp
I have a couple of questions that will probably sound stupid to those that know the answers.
I have an 05 F-250, 6.0 diesel 4x4. It has a 3.73 rear end. I'm not planning on getting a new truck right away, but was wondering if that was the 'best' rear end to have. I tow an 18ft bassboat fairly regularly and a 16 flatbed trailer now and then. I guess I'm looking more for 'general' information on what the different rear end ratios mean.
I also have a 1981 Ford Van (used for tailgaiting at football games). I'm fairly certain it was used as a school bus (or school VAN) originally. I have no idea what rear end it has, but top end speed is about 70. How can I find out what it has? Would a different rearend change that? Would it increase/decrease my mileage?
Thanks in advance,
dlp
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FOr the 05, 3.73s is about perfect, unless you put on huge tires. FOr the van, there should be a little tag hanging off the rear axle cover bolt. It will have a bunch of numbers, but the first set will be something like 3 55, 3L73, or the like. These are a ratio to one. Meaning that the driveshaft spins that many times for 1 revolution of the tire. Without getting too crazy, a tire has a circumference of pi D. This is 3.14159 times the diameter of the tire. Where this matters is that the tire covers a certain amount of ground per revolution. To make a certain amount of engine rpms per amount of ground covered, you have gears. All engines operate in a certain range, and must be kept here. That is why stock gears work for stock tires, but when you get bigger tires you need a larger ratio. Hope this helps.
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From: Trophy Club Texas
Thanks. If it warms up a little I'll crawl under the van and see what I can find. Based on your explanation, the larger the number, the higher the RPM's would be at a given speed. Correct?
So let's say for the sake of argument, that I find the van has a 4.30 rear end (not sure they made them back then, but know it's available now). With standard size tires, the 4.30 means my driveshaft has to turn 4.3 times to turn the tires once (I think that's what you are telling me). So if I changed it to a 3.73 rearend, it would require fewer RPM's to go the same speed.
Am I correct? Sorry for the silly questions....
dlp
So let's say for the sake of argument, that I find the van has a 4.30 rear end (not sure they made them back then, but know it's available now). With standard size tires, the 4.30 means my driveshaft has to turn 4.3 times to turn the tires once (I think that's what you are telling me). So if I changed it to a 3.73 rearend, it would require fewer RPM's to go the same speed.
Am I correct? Sorry for the silly questions....
dlp
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Joined: Jul 2005
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From: North Texas
Originally Posted by dlpinkc
Based on your explanation, the larger the number, the higher the RPM's would be at a given speed. Correct?
the 4.30 means my driveshaft has to turn 4.3 times to turn the tires once. So if I changed it to a 3.73 rearend, it would require fewer RPM's to go the same speed. Am I correct? dlp
the 4.30 means my driveshaft has to turn 4.3 times to turn the tires once. So if I changed it to a 3.73 rearend, it would require fewer RPM's to go the same speed. Am I correct? dlp
For passenger vehicles you want to be at the low end of your torque band at highway cruise speeds. Gives good fuel mileage. In work vehicles you want to be in the middle of your torque band or slightly higher. Helps ensure you can accelerate to, hold, and even exceed for passing highway speed when loaded.
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...at the cost of fuel economy. I would think you van has 3.55s in it. You can either swap in an OD tranny or swap out gears. Maybe 3.08s? Most people don't want higher gears, though. one final option is larger rear tires on the van to lower rpms.
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