What is your effective gear ratio?
03-15-2005, 08:20 PM
#11
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Originally Posted by CHarris
Just go 75 mph in 3rd gear and see what your tach says. That is your effective gear ratio. mine said 3000 so it is 3.00 to 1.
03-15-2005, 08:52 PM
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Originally Posted by mzoomora
That is kind of a useless piece of info. Not to sound like an ***, but not all cars have the same o/d ratio, so you would be comparing apples to oranges. If you were comparing 3rd gear(1:1), it would make more sense. What they consider a "effective" gear ratio and "actual" gear ratio is when changing tire size. Another use for it is people multiply the first gear ratio of the trans by the rear end gear ratio and call that the effective first gear ratio. People do it a bunch of ways - tire diameter / rear gear, tire roll out / rear gear, trans ratios in overdrive or firrst gear, there are really too many variables to apply any of them to all vehicles. They do work when planning changes on any one vehicle, just to see where the change will take you.
Everyone with an automatic has a 1 to 1 third gear. Now a five speed would need to use 4th gear. And it is useful... I can clearly see that I need more gear. Others might as well.
03-15-2005, 09:17 PM
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Yes that works good...Assuming, you don't have a big verter with hills around and you do know, for a fact what gear is 1 to 1....Like Cory said 3rd for most autos and 4th for most manuals.....I used this for years figuring out what gears were needed for big tire combos....Got the info from a car mag (like hot rod) years ago... 
Never really thought about it before....
Jimbob
Never really thought about it before.... Jimbob
03-15-2005, 09:36 PM
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Originally Posted by Naked AV
So once you get your number, what does it mean? 
In my case I'm hitting third gear and the truck "lays down" at the end because it doesn't have enough gear ratio to keep the RPM's high up in the powerband for max acceleration. I can see that I either need shorter tires or more front and rear gear (I'm full time 4wd). To be quick you have to have the best gear ratio possible.
Think about it this way... lots of F-body guys go to 3:73 to 1 gears or 4:10 gears to get better acceleration. As we have much taller tires we have less gear ratio and might want to do the same (increase gear ratio) to maximize acceleration capability.
03-15-2005, 09:41 PM
#16
Originally Posted by CHarris
Well, for starters if you are interested in drag racing it can help you select the right gear for maximum rpm in the traps.
In my case I'm hitting third gear and the truck "lays down" at the end because it doesn't have enough gear ratio to keep the RPM's high up in the powerband for max acceleration. I can see that I either need shorter tires or more front and rear gear (I'm full time 4wd). To be quick you have to have the best gear ratio possible.
Think about it this way... lots of F-body guys go to 3:73 to 1 gears or 4:10 gears to get better acceleration. As we have much taller tires we have less gear ratio and might want to do the same (increase gear ratio) to maximize acceleration capability.
In my case I'm hitting third gear and the truck "lays down" at the end because it doesn't have enough gear ratio to keep the RPM's high up in the powerband for max acceleration. I can see that I either need shorter tires or more front and rear gear (I'm full time 4wd). To be quick you have to have the best gear ratio possible.
Think about it this way... lots of F-body guys go to 3:73 to 1 gears or 4:10 gears to get better acceleration. As we have much taller tires we have less gear ratio and might want to do the same (increase gear ratio) to maximize acceleration capability.
hmmm
03-15-2005, 09:42 PM
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Ok...
I did not explain it too good (oops)... If you go 75 mph in a 1 to 1 tranny gear (auto 3rd usually) or (manual 4th gear usually) and look at your tach, The rpm you see (example 3000 rpm) now equals your effective gear ratio. In this case 3000rpm = 3.0 gear. This means that you have effectively have a car with 3.0 rear gear and 26 inch tall tires. My last big truck tires was 38.5 inch so we put in 5.13 gears to equal about 3.4 gears in a car. In Cory's case he would either need to get smaller tires or re-gear to 4.56's to equal about a car with 3.4 gear ratio....I hope this doesn't screw anybody up.....
Jimbob
I did not explain it too good (oops)... If you go 75 mph in a 1 to 1 tranny gear (auto 3rd usually) or (manual 4th gear usually) and look at your tach, The rpm you see (example 3000 rpm) now equals your effective gear ratio. In this case 3000rpm = 3.0 gear. This means that you have effectively have a car with 3.0 rear gear and 26 inch tall tires. My last big truck tires was 38.5 inch so we put in 5.13 gears to equal about 3.4 gears in a car. In Cory's case he would either need to get smaller tires or re-gear to 4.56's to equal about a car with 3.4 gear ratio....I hope this doesn't screw anybody up.....
Jimbob
03-15-2005, 09:45 PM
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Originally Posted by jimbob
Ok...
I did not explain it too good (oops)... If you go 75 mph in a 1 to 1 tranny gear (auto 3rd usually) or (manual 4th gear usually) and look at your tach, The rpm you see (example 3000 rpm) now equals your effective gear ratio. In this case 3000rpm = 3.0 gear. This means that you have effectively have a car with 3.0 rear gear and 26 inch tall tires. My last big truck tires was 38.5 inch so we put in 5.13 gears to equal about 3.4 gears in a car. In Cory's case he would either need to get smaller tires or re-gear to 4.56's to equal about a car with 3.4 gear ratio....I hope this doesn't screw anybody up.....
Jimbob
I did not explain it too good (oops)... If you go 75 mph in a 1 to 1 tranny gear (auto 3rd usually) or (manual 4th gear usually) and look at your tach, The rpm you see (example 3000 rpm) now equals your effective gear ratio. In this case 3000rpm = 3.0 gear. This means that you have effectively have a car with 3.0 rear gear and 26 inch tall tires. My last big truck tires was 38.5 inch so we put in 5.13 gears to equal about 3.4 gears in a car. In Cory's case he would either need to get smaller tires or re-gear to 4.56's to equal about a car with 3.4 gear ratio....I hope this doesn't screw anybody up.....
Jimbob
03-15-2005, 09:56 PM
#19
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Okay, so what is the "best gear ratio possible" and how do I figure out what that is? Is there a table or something? I understand the principle, but would like to see some application.
Originally Posted by CHarris
Well, for starters if you are interested in drag racing it can help you select the right gear for maximum rpm in the traps.
In my case I'm hitting third gear and the truck "lays down" at the end because it doesn't have enough gear ratio to keep the RPM's high up in the powerband for max acceleration. I can see that I either need shorter tires or more front and rear gear (I'm full time 4wd). To be quick you have to have the best gear ratio possible.
Think about it this way... lots of F-body guys go to 3:73 to 1 gears or 4:10 gears to get better acceleration. As we have much taller tires we have less gear ratio and might want to do the same (increase gear ratio) to maximize acceleration capability.
In my case I'm hitting third gear and the truck "lays down" at the end because it doesn't have enough gear ratio to keep the RPM's high up in the powerband for max acceleration. I can see that I either need shorter tires or more front and rear gear (I'm full time 4wd). To be quick you have to have the best gear ratio possible.
Think about it this way... lots of F-body guys go to 3:73 to 1 gears or 4:10 gears to get better acceleration. As we have much taller tires we have less gear ratio and might want to do the same (increase gear ratio) to maximize acceleration capability.
03-15-2005, 10:06 PM
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Here is a good example of not enough gearing
http://highspeedproducts.com/randomp...ideo/corey.wmv
Cory's rig is barely in 3 rd for end of quarter mile. He goes like 45 in 1st 88 in second (now) and who knows in third.....You can see how this effects climbing low grades, accelleration and low speed rock climbing....when your way out of your power range.
Jimbob
http://highspeedproducts.com/randomp...ideo/corey.wmv
Cory's rig is barely in 3 rd for end of quarter mile. He goes like 45 in 1st 88 in second (now) and who knows in third.....You can see how this effects climbing low grades, accelleration and low speed rock climbing....when your way out of your power range.
Jimbob