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hat_man · 09-09-2012, 03:32 AM

This is just an idea I had regarding tire size and gear ratio.

Let's say that my Ranger has a stock rear end with 3:73 gears and stock 225/70/14 tires. If i wanted to keep my stock tires and go to a taller gear ratio I could change to a 3:45 just by swapping in another rear end. But let's say I need new tires anyhow. Is there a tire size that would give me the same (3:45) gear ratio or would it be so large that it just wouldn't fit in the wheel well? If there is a size that actually would give the desired results then you could fix the speedo at the same time by changing to a 3:45 speedo gear.

Something like taller tire (x)+3:73 gear=stock tires+3:45 gear.

Also swapping the rear end for better gears would mean more energy used from each stop sign/light. Would the loss be relatively the same if you changed the gear ratio by changing tire size instead of changing rear end gears?

Something like:

if stock tires+3:73 gears uses (=) a certain amount of energy (E)
and stock tires +3:45 gears uses (=) more energy (mE), then does a taller tire (x)+3:73 gears use more/less/same energy as stock tires+3:45 gears?

I guess what I am getting at is: is there an advantage to changing the final drive ratio with the tires rather than rear end?

For my driving situation the ultimate would be a rear end swap to 3:45's but I was wondering if there was a tire size that I could go to that would make the equation look like this:

Stock tires+3:31 gears=taller tires (x)+3:45 gears

I am planning a change to 3:45's, but when my tires DO wear out I would love to switch to a tire that would give me the equivalent of the 3:31 gear ratio. That is, if such a tire exists. Then all I would have to do is switch the speedo gear to a 3:31 and my speedo would be in sync and I would have effectively raised my final drive ratio again.

Is there a simple formula like:

Tire size(TS)+Rear Gear(RG)=Final Drive

or

Tire Diameter(TD)+Rear Gear(RG)=Final Drive

If there is then I could play around with different tire sizes and gearing to see what options are out there.

Thanks for the help.

09-09-2012, 03:32 AM	#1 (permalink)
hat_man Master EcoModder Join Date: May 2010 Location: Illinois Posts: 475 Oh Deer - '03 Ford Ranger XL 90 day: 33.97 mpg (US) Thanks: 55 Thanked 91 Times in 72 Posts	Need some help with the math This is just an idea I had regarding tire size and gear ratio. Let's say that my Ranger has a stock rear end with 3:73 gears and stock 225/70/14 tires. If i wanted to keep my stock tires and go to a taller gear ratio I could change to a 3:45 just by swapping in another rear end. But let's say I need new tires anyhow. Is there a tire size that would give me the same (3:45) gear ratio or would it be so large that it just wouldn't fit in the wheel well? If there is a size that actually would give the desired results then you could fix the speedo at the same time by changing to a 3:45 speedo gear. Something like taller tire (x)+3:73 gear=stock tires+3:45 gear. Also swapping the rear end for better gears would mean more energy used from each stop sign/light. Would the loss be relatively the same if you changed the gear ratio by changing tire size instead of changing rear end gears? Something like: if stock tires+3:73 gears uses (=) a certain amount of energy (E) and stock tires +3:45 gears uses (=) more energy (mE), then does a taller tire (x)+3:73 gears use more/less/same energy as stock tires+3:45 gears? I guess what I am getting at is: is there an advantage to changing the final drive ratio with the tires rather than rear end? For my driving situation the ultimate would be a rear end swap to 3:45's but I was wondering if there was a tire size that I could go to that would make the equation look like this: Stock tires+3:31 gears=taller tires (x)+3:45 gears I am planning a change to 3:45's, but when my tires DO wear out I would love to switch to a tire that would give me the equivalent of the 3:31 gear ratio. That is, if such a tire exists. Then all I would have to do is switch the speedo gear to a 3:31 and my speedo would be in sync and I would have effectively raised my final drive ratio again. Is there a simple formula like: Tire size(TS)+Rear Gear(RG)=Final Drive or Tire Diameter(TD)+Rear Gear(RG)=Final Drive If there is then I could play around with different tire sizes and gearing to see what options are out there. Thanks for the help.