Rear End Gear Suggestions

-
jerkyboy

jerkyboy

Well-Known Member
Joined
Apr 30, 2010
Messages
192
Reaction score
2
Location
Upstate NY
I am currently running 3.23s and am considering going with 3.55 or 3.73s. I have a gen. III 5.7 hemi and a Tremec 5 speed that the prior owner installed. I'm less than 2,000 rpms going 65. Anyone run running this same setup with 3.55 or 3.73s, and if so how do you like them and what are you running (rpm wise) at highway speeds?
 
Hit the online RPM calculators that take you transmission gearing into account and enter different the rearend gearing as well. You then can compare what gear you will like the most.
 
I went from the stock 3.06 in my magnum to a 3.55 for a while and it made a massive difference. Think about it, that's basically 16% more force to the ground.

3.23 to 3.55 is around 10%, to 3.73 is around 15%. I think you'll notice. It's also a 10 or 15% increase in RPM, so you'll pick up a couple hundred.
 
a lot depends on how tall the rear tires are,,,,the reason for O,D , is lower RPM when cruising,, how tall is the tire ?? whats the 1st gear ratio in that tranny and whats the OD reduction in 5ft ??
 
they either have a 2.9 or 3.3 1st and the od can be .63, 68, 72, 83...unless if he got it from a truck....then it's different..
 
SuperShafts makes an excellent point. We really need a tire size with this. And the intended purpose of the car. 3.90's or 4.10's with the overdrive ratio( what ever the ratio is) would be of help and then a final drive RPM can be known.
 
the tremec TKO, first gears are either 2.87 or 3.27,the OD choice depends on the tko model,,, 500 or 600

wit ha short rear tire the 3.27 will wind up to quick in 1st with a 3.91 or 4 series gear,,, and if you go to deep on the OD reduction figure the car may be cruising way under the sweet spot of the RPM range and not have enough power to pul it self out wit hout down shifting,,, lots to consider when choosing a rear gear and OD,,
 
C'mon.... 3.2 1st gear is nothing.... i have a 4.10 and i have a 6.6 1st gear and it just means that clutch is dropped, and 2nd is crashed way sooner..
6.6 ratio 1st into 3.3 ratio 2nd...let me tell you 2nd is perfect with a 4.10

550 ft lbs x 6.6 = 3630 frame twisting ft lbs , 550 ft lbs x 3.3 = 1815, 550 x 2.4 = 1320

I wouldn't go any less then 3.90
 
My TKO has the 3.27 first. With a 3.55 rear and 245x60x14 tires, it cruises 70 MPH at about 2400 or so. I bolt on a set of 275x50x15 MT ET Streets and run high 12's. The gearing seems perfect for the street but only because I have the stock small cam in there. With a big cam or larger diameter tires 3.55's would be too tall.
 
First through fifth gear ratios are 3.27, 1.98, 1.34, 1, and .68. My rear tires are 245/40/18s. I drive the car on the street and highway both and I definitely like to romp on it, as we all probably do(?), from time to time. I also have a stock GenIII hemi rated at 375 hp.

I was on the highway the other day and at 60 I was running about 1,800 rpms. I'm starting to think that I'll get my best bang for the buck out of 3.73s, which I had in my Nova and hated because I had a Turbo 350 with no overdrive.
 
I think I'd want 4.10s with what you have. It's pretty economical, pulls well, but won't go to 7Krpm. I think a set of 4.10s would be fine and allow it to get up some speed with that 375hp.
 
moper said:
I think I'd want 4.10s with what you have. It's pretty economical, pulls well, but won't go to 7Krpm. I think a set of 4.10s would be fine and allow it to get up some speed with that 375hp.
Click to expand...

I installed 4.56 gears in my Dodge Ram with stock wheels. I like it and my fuel economy got better. Of course the truck has overdrive is why I can get away with such a steep gear.
 
mullinax95 said:
I installed 4.56 gears in my Dodge Ram with stock wheels. I like it and my fuel economy got better. Of course the truck has overdrive is why I can get away with such a steep gear.
Click to expand...

What size tires, final gear ratio, and rpms @ 70 mph with the 4.56 gears????
 
jerkyboy said:
What size tires, final gear ratio, and rpms @ 70 mph with the 4.56 gears????
Click to expand...

Here you go.... this will answer your questions a bit better than me just giving you my info. When you see "the gear" they are talking about the 4.56 gears.

http://www.dodgetalk.com/forums/showthread.php?t=113899&highlight=4.56+gears

http://www.dodgetalk.com/forums/showthread.php?t=114788&highlight=4.56+gears

http://www.dodgetalk.com/forums/showthread.php?t=99315&highlight=4.56+gears

http://www.dodgetalk.com/forums/showthread.php?t=65309&highlight=4.56+gears



"The 4.56 diff gears will improve your acceleration, and if you tow heavy trailers they will improve your truck's ability to hold speed up steep hills.

In city driving, your MPG mainly depends on how much acceleration you demand and how hard and how long you depress the accelerator pedal - also how much you end up using your brakes, and how much the truck weighs. The 4.56 gears will not affect City MPG too much if you continue to drive the truck the same way.

Despite what you might read here, a change from 3.55 diff gears to 4.56 gears will affect your Highway MPG. You can see this for yourself if you have the overhead trip computer. Drive on the highway at a steady 70 mph on a level stretch, preferably on a day without too much wind. Reset your trip compter while driving, then watch your MPG display and get a feel for what the MPG is in Overdrive top gear. Try to drive at least 20 miles this way to get a good average.

Now turn around and go back to the same stretch of highway. Turn off your OD button or press your 'Tow/Haul' button. Reset your trip computer again, then watch the MPG at a steady 70 while in the gear below overdrive, which is 1:1 ratio. The Overdrive is a 0.67 ratio. Driving like you are now in next to top gear is like driving in 0.67 Overdrive with a 5.29 diff gear.

(3.55/0.67) = 5.29

With newly installed 4.56 diff gears in OD gear your highway MPG will be a little better than the MPG you see in the 2nd test.

If you really want to be accurate, do this test in both directions on the highway to partially cancel out the effects of wind."
 
Use either the 3.90 or the 4.10....

Don't confuse your car and mullianax 32" + wheels on his truck for your possibly 26" tire at 55 psi...

Trust me you really want 3.90 or 4.10....

Trucks and cars run totally different tire heights and the same rules do not apply
 
Supershafts said:
Use either the 3.90 or the 4.10....

Don't confuse your car and mullianax 32" + wheels on his truck for your possibly 26" tire at 55 psi...

Trust me you really want 3.90 or 4.10....

Trucks and cars run totally different tire heights and the same rules do not apply
Click to expand...

I wasn't trying to suggest he needed 4.56 gears... I was just comparing what moper said since he chose the steeper gears of all that was mentioned. If you read my post where I quoted moper it says "Of course the truck has overdrive is why I can get away with such a steep gear."
 
You get away with the gear from the nearly 33" tall tire...

Put his tire height on your truck and the 4.56 won't be as perfect with the same O.D. ratio you have in your truck is what he also has in his tremec...

Your trucks OD is .69..... his is .68.... He has probably a 25" tire and you have more like 32"

The difference is in the tire, not the trans OD ratio.


If we were talking trucks, i would bring up 4.56 or 4.88 depending on overall wants vs needs...

In this case were dealing with a shorter tire and what would be a best overall gear with the 5 speed, atleast the 3.90.. or if not then the 4.10....
 
Supershafts said:
You get away with the gear from the nearly 33" tall tire...

Put his tire height on your truck and the 4.56 won't be as perfect with the same O.D. ratio you have in your truck is what he also has in his tremec...

Your trucks OD is .69..... his is .68.... He has probably a 25" tire and you have more like 32"

The difference is in the tire, not the trans OD ratio.


If we were talking trucks, i would bring up 4.56 or 4.88 depending on overall wants vs needs...

In this case were dealing with a shorter tire and what would be a best overall gear with the 5 speed, atleast the 3.90.. or if not then the 4.10....
Click to expand...

How about 4.30 gears then?

What he could do is get the gears that would put everything lets say 3000 RPM at 70mph in 4th gear.......then use 5th gear strictly for overdrive. He would have to find out each gear raito (4th and 5th gear)that is in the trans and do the math including tire size and gear. This will help keep that low end bang we all love without screaming down the interstate.

Make since?

Maybe not?

jerkyboy ... take your time and do the math with each type gear and see what you like the most. One thing is for sure math never lies. :read2:
 
4th is 1 to 1.... the Germans play/get into wild gear ratios in transmissions... Some of that German thinking could be taken into some consideration....

Imagine how great it would be to have a trans with ratios like 4.80 , 2.95, 2.15, 1.68, 1.39, 1.20, 1.00
 
You must log in or register to reply here.
-

Back
Top