confused about ratios

[Hillbilly Deluxe]

If you run a high ratio do you run higher rpm ?

If you run bigger tires how this affect your ratio and rpm?

 

[Gotta_gofast]

If you run a high ratio do you run higher rpm ?

If you run bigger tires how this affect your ratio and rpm?

A numerically higher ratio will yield more torque multiplication at the expense of speed. I think it will be easier to use an example.

A common ranger gearset is 3.73:1. This means, that the pinion gear (the drive gear) will make 3.73 turns for one turn of the ring gear (the driven gear). In our test truck, this means the driveshaft will turn 3.73 times for the tire to complete one turn. How does this translate into torque at the wheels and speed of the vehicle? Well, lets apply 1 lb-ft of torque to the driveshaft. With a 3.73:1 ratio, we will effectively produce 3.73 lb-ft of torque at the wheel. As far as speed goes, we turned the driveshaft one complete revolution but the axle only turned 0.268 turns. If you were to upgrade to a 4.10:1 gearset (also common for rangers) then you apply the same 1 lb-ft to the driveshaft, then the torque at the wheel will be 4.1 lb-ft. This will result in faster acceleration and better towing, but we are going slower now, because for one turn of the driveshaft we are only turning the wheel 0.244 of a turn. This is why your vehicle must run at a higher RPM to maintain the same speed if you install a numerically higher gearset, because you are multiplying the available torque while decreasing speed.

The size of your tires will also affect final speed and performance. The bigger the diameter (height) of the tire, the larger the circumference (distance around the tire), right? Another example. A 31" tire has a circumference of 97.4". This means that when the tire makes one complete turn, the vehicle has move 97.4". If you were to increase the diameter of the tire to 33", the circumference would be 103.7". This means, that for every one complete turn of the tire, the truck will travel 103.7". So, by upgrading to a larger tire size, you will effectively go farther per rpm than with the smaller tire. If you were to maintain the same engine RPM with the larger tires, your speed would increase. But, you will lose "leverage" by increasing your tire size. Likewise, if you were to run a smaller diameter tire, the axle has more "leverage". It is similar to the gears mentioned earlier. By increasing the distance, you decrease the applied force, and vice versa.

This is why you should consider running numerically larger gears in your truck when you run bigger tires.

 

[86ford]

A numerically higher ratio will yield more torque multiplication at the expense of speed. I think it will be easier to use an example.

A common ranger gearset is 3.73:1. This means, that the pinion gear (the drive gear) will make 3.73 turns for one turn of the ring gear (the driven gear). In our test truck, this means the driveshaft will turn 3.73 times for the tire to complete one turn. How does this translate into torque at the wheels and speed of the vehicle? Well, lets apply 1 lb-ft of torque to the driveshaft. With a 3.73:1 ratio, we will effectively produce 3.73 lb-ft of torque at the wheel. As far as speed goes, we turned the driveshaft one complete revolution but the axle only turned 0.268 turns. If you were to upgrade to a 4.10:1 gearset (also common for rangers) then you apply the same 1 lb-ft to the driveshaft, then the torque at the wheel will be 4.1 lb-ft. This will result in faster acceleration and better towing, but we are going slower now, because for one turn of the driveshaft we are only turning the wheel 0.244 of a turn. This is why your vehicle must run at a higher RPM to maintain the same speed if you install a numerically higher gearset, because you are multiplying the available torque while decreasing speed.

The size of your tires will also affect final speed and performance. The bigger the diameter (height) of the tire, the larger the circumference (distance around the tire), right? Another example. A 31" tire has a circumference of 97.4". This means that when the tire makes one complete turn, the vehicle has move 97.4". If you were to increase the diameter of the tire to 33", the circumference would be 103.7". This means, that for every one complete turn of the tire, the truck will travel 103.7". So, by upgrading to a larger tire size, you will effectively go farther per rpm than with the smaller tire. If you were to maintain the same engine RPM with the larger tires, your speed would increase. But, you will lose "leverage" by increasing your tire size. Likewise, if you were to run a smaller diameter tire, the axle has more "leverage". It is similar to the gears mentioned earlier. By increasing the distance, you decrease the applied force, and vice versa.

This is why you should consider running numerically larger gears in your truck when you run bigger tires.

since we are using math to describe gearing i will add another factor

every pound of rotating weight you add at the wheels=7 pounds of weight inside the vehicle. so if you get 4 31s to replace your 205s that in total weight 100 lbs more than the stock ones that hundred pounds = 700 pounds in cargo or 3-4 fat chicks, which ever makes more sense to you.

i do not know off hand a good calculation to factor in rotating resistance of taller tires.

the people that "off-road" or hardcore mall crawl in many cases, re-gear to help offset the weight and rotating resistance added by larger tires.

3.73 gears dont get along well with 38s unless you have a motor with enough power to push them (7.3 turbo, 460, other built motors).

86

 

[pssnmn1]

i made a chart in windows excel

but have no idea how to post it

 

[Dishtowel]

i made a chart in windows excel

but have no idea how to post it

when your in excel hit the PRINT SCREEN button on your keyboard

open up PAINT, hit COPY. save as a JPEG, post on photbucket/wherever

 

[Mac]

Go up in the Tech Library for good chart.
Dave