hi there i was looking on line at dodge.com and was a little confused the rear gear ratio is 2.82 then it states that the final gear ratio is 3.55 whats the difference in the 2 numbers ?

 

3767,

Normally the two are the gear ratio in the differential. It has to do with the number of teeth on the ring and pinion gears.

2.82, 3.55, etc, is basically, the turns an axle will make with 1 revolution of the tranny's final drive (usually 1:1).

The higher the number the faster your axles turn with the same number of revolutions from the transmission.

Drag racers like lots of torque and like high numbers like: 4.11, 4.56, 5's or even 6's. Highway gearing is lower numbers like 3.06, 3.23, or 2.82. Towing trailers, campers, boats, like the 3.55 ranges.

The speedometer gearing or computer settings are a given formula (or specific gear set) to adjust the axle ratio to work with the speedometer correctly. When we start changing tire heights, we start changing the speedometer readings, and, actually, the final drive ratio that is driving the tires on the ground.

Hope this helps.




MN

 

ok i got that part but the read gear sets in the rt model is 2.82? and on the website dodge.com it says the final gear ratio is 3.55 so i ask this 2 part question is the rear gear 3.55 or 2.82 ,thats question 1 part 2 is and if its raised the rear gear set to say 3.55 which is what i would like to get would the final ratio be like 4.11 or even higher.............just wondering mainly if with the final gear ratio being 3.55 is that the actuall turning or is that something else,ex with the rear gears being 2.82 do the tires turn that speed or do they actually turn at 3.55 because of computer control or something in the tranny..just thinking that this info could become important down the road when someone actually makes a set of gears.so if for some reason the geating changes to higher numbers if we put in 3.55 gears will the gearing be a lot higher actually

 

I thought final gear ratio was the relationship with the crank shaft to the tires. This would be calculated by using the number of your highest transmission gear and your rear end gearing. With the OD trannys we have they should be lower than our rear gears. Warning- I am traveling and have been up for the last 26 hours, so if this is incorrect, I completely apologize. When I get home (someday) I can do the math to calculate our final drive.

 

3767,

I went to the Dodge site and looked for what you are saying. I didn't see it. I looked under Charger specifications. Frankly, I don't know what my final tranmission drive is, I assumed 1:1 which is typical, and my rear differential is 2.82. Changing differential ring and pinion whould change the final drive... put in 3.55's and you'd have 3.55's...

Seems like you are confusing something... (me ), but seriously, something isn't gelling.

For now, putting in 3.55 would turn the rear axle 3.55 turns per revolution of the tranmission 1 turn...



MN

 

OK THE INFO IS LOCATED AT WWW.DODGE.COM UNDER SPECS GO TO DRIVETRAIN AND THE VERY LAST STAT IS THE FINAL DRIVE RATIO IM INCLUDING THE LINK
http://www-5.dodge.com/vehsuite/VehicleCompare.jsp

 

3767,

You're right, I read it.

And, you're right again, after reading that, I am confused. Do I have a 2.82 rear final gear or a 3.55 rear gear?

Since I had 3.54's in my GTX with a 4 speed, I remember 4th gear being in the 3,000s at 70. My rear tires were 265/60-15", therefore, being 27.6" tall, close to my current 235/55-18" 28.2" tall tires -- so, if I take my Charger out in 4th gear, and drive at 70 MPH, my RPMs should be 3,000; but only 2,400 because of the magical 5th gear with a final drive of 2.82.

If I have 3.55s for a final gear, my RPMs at 70 would be 3,000.

It is going to storm shortly, but if I took mine out at 70 MPH, my tach would be near the 2,400 range, not the 3,000 range: therefore, I proclaim, , that I must have a final drive ratio of 2.82 not 3.55.

As far as the confusing information on the Dodge site, I have NO IDEA what they are trying to tell me...



MN

 

I suspect that this page was written by a marketing type who had too much/little caffiene or was not real familiar with the technical terms.

As BlackSRT correctly pointed out, the final drive ratio is from the crankshaft perspective and is the product of the rear axle ratio multiplied by the highest transmission gear ratio. In days of yore when high gear was 1:1, final drive and rear axle ratio were synonomous. With today's transmissions, high gear is an overdrive ratio so the final drive ratio is usually numerically lower than the rear axle ratio. If you divide 2.82 by 3.55 you get about .80 which is a common overdrive ratio used in today's transmissions. I would be willing to bet that the R/T series have a 3.55 rear axle ratio with a 80% overdrive high gear tranny to give an overall final drive ratio of 2.82.

If you want to verify this, have someone skinny lay under the car and count the driveshaft revs while you move the car forward one tire revolution. Almost 3 revs would be a 2.82 rear axle and 3 and 1/2 revs would be a 3.55 rear axle. If you don't know anyone skinny enough who trusts you , jack up the car and have someone hold one tire steady while you turn the driveshaft enough times for the free tire to make 2 revs (this extra revolution is due to the interaction of the spider gears in the differential with one wheel locked). Same driveshaft rev counts as above.

I also noticed that the SRT8 spec on that page has 3.06 for the axle ratio AND final drive ratio. Now the SRT8 is supposed to have the same tranny (according to the web page) as the R/T so how can that be. Must be true, though, because it's on the Internet.

Have a good weekend.

Redbeard

 

so let me ask you your opinion why havent they made new gears for the car yet . i was speaking to a rep from high horse power inc and i was told that the possibility was remote because there would have to be a special flash of the computer and etc.gsm motorsports has said there would be a tranny chip neccesary and that there still prototypes.i realize that the cars are new and still a lot of tinkering andf eventually im sure as the sun will rise someone some how will get all these probs worked out..

 

I talked to some Charger owners last night at the track that said that there is a transmission flash upgrade available The program is from the AMG version of the transmission, and does not have the torque management software programmed. The AMG transmission is a little different, it has a torque converter that can lock in any gear, but I understand that for our use it is not a hinderence. I can tell you it is being used, but not where to find it. I suspect that a company could not sell it, since it was appropriated, rather than developed. You will probably need to 'network' a little to find it. I would not want to be the one distributing it.... Sounds like a lot of liability.