rearend gear?
- Thread starter slx70
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SirDan
Well-Known Member
great street gear ratio. 3.90 gears are too much for street and 3.23 gears are just a bit long for performance. 3.55 gears are rite in the middle a good match of performance and drive-ability.
unless you have overdrive and that throws everything I said out the window.
unless you have overdrive and that throws everything I said out the window.
fishy68
Tyr Fryr's Inc.
I have 3:55's and love them. Tire height plays a lot in the "final drive ratio". With 25" tall tires like you have (real short) even 3:23 gears aren't bad.
mopardude318
Well-Known Member
hey fishy, whats the actual ratio with 255's and a 25 in. tire as i have the same...
fishy68
Tyr Fryr's Inc.
Final drive ratio is really just a term and is a combination of the tire height and gear ratio. If you have 3:55 gears you have 3:55 gears so that's your actual gear ratio.
Here's an example of how tire height and gear ratio affects the "final drive ratio". With 3:55's and 27.5" tires (like my car) it spins approx. 2750 rpm at 60 mph. According to my calculator your car with 3:55 gears and 25" tires will spin right at 3000 rpm. If I kept the 27.5" tires I'd have to switch to 3:91 gears to equal the rpm yours spins at 60. That's figuring we are both running identical automatics with a converter efficiency of 95%. A stick shift will run slightly lower rpm at the same speed. Hope that makes sense..
Here's a link to a visual calculator that you can play with to see what rpm difference tire height and gears make
http://vexer.com/automotive-tools/speed-rpm-calculator
dodge freak
Well-Known Member
I agree with all said, 3.55 are a great all around gear.
I'm on the fence if I want to switch my 3.90 gear to 3.23 which I have already. My tire is 26.80 inches tall, that brings the rpm down to 2414 @ 60 mph--however traffic on the expressways goes an honest 70 mph now, that would be 2800 rpm @ 70, perfect for long hauls, just try to keep it 3,000, even 80 mph would be only 3,200 before converter slip.
I'm on the fence if I want to switch my 3.90 gear to 3.23 which I have already. My tire is 26.80 inches tall, that brings the rpm down to 2414 @ 60 mph--however traffic on the expressways goes an honest 70 mph now, that would be 2800 rpm @ 70, perfect for long hauls, just try to keep it 3,000, even 80 mph would be only 3,200 before converter slip.
Good post fishy. To many people over think the tire changes my gear ratio thing to much and then enter it into the mix which ends up causing problems.
dodge freak
Well-Known Member
That is why I wounder if 29 inch tires-which would fit with the 3.91's it has right now is the way to go ? 70 mph would be 3,200 rpm
Burntorange70
Well-Known Member
That calculator Fishy posted is a good thing to play around with.
I got 3.23's and around a 24 tire on my car. Runs around 60 @ 3000 RPM. Kind of wish I had less gearing on the freeway and more at the track.
My car is more of a street car so I am thinking of going to a 26 tire when it comes time to change them out.
fishy68
Tyr Fryr's Inc.
Thanks Rumble. That calculator sure comes in handy to give you an idea of what will really happen
mikesduster
Well-Known Member
I wouldnt say a 3.90 gear is too much for the street. It all depends on your combo,tire height and what your understanding of a street car is...Is it a daily driver?? A street/strip car?? I have a nice SB,28" tall tire and 4.56's and it is fine on the street for ME. Maybe not for everyone.
For your tire size,yes,3.55 would be a good gear for you.
For your tire size,yes,3.55 would be a good gear for you.
dodge freak
Well-Known Member
Its the engine also, short stroke engines like the 318 / 340 love rpms'. If you forget about mpg and have a nice quiet exhaust-which few do, lol--3.90's can make a good street gear. This is why I can't decide, get some 29 inch tires or just switch to 3.23 gears. Now I'm leaning again to the taller tires. I do know I need some quiet mufflers
dodge freak
Well-Known Member
Is that the car with the 4.56 gears ? If so why is it on a trailer if its fine on hte street ? Not knocking you--peace--just 4.56 can be a bear on the freeway for a few hours
fishy68
Tyr Fryr's Inc.
Can you get 29's in your car? Most A-body's (I assume your talking about an A-body?) have to be modified in one fashion or another to accept anything taller than a 28 cause the tire hits the front lower section of the wheel well.
abodyjoe
Well-Known Member
it depends on what you want to do with the car.. i had 3.91 and 3.55 in my car with a 28" tire and hated it. it was fun around town but up on the highway it sucked. i'm running a 2.94 gear and the same 28" tires and love it. still want overdrive though..
abodyjoe
Well-Known Member
with a 3.55 and a 25" tire you'll be doing 62 mph at 3000 rpm.
dodge freak
Well-Known Member
i'm running a 2.94 gear and the same 28" tires and love it. still want overdrive though..
Be careful, too low of an rpm on the freeway can place heavy-damaging loads on the rod bearings. The bearings lose their crush and will spin.
You can safety go to 2.73--even 2.45 but with O.D @ .70 you be at 2.05, that engine is going to have its work cut out for it to push the car at speed.
abodyjoe
Well-Known Member
probably put a 3.55 in it if i go OD.
That is about the same as my 4.10's and a 28 inch tire (4spd car.) A few rpm more or less. (More I think)
dodge freak
Well-Known Member
No its a B body--i know but I signed up on FABO cause I like the the SBM, 29" will fit
dodge freak
Well-Known Member
Ugh, took the old Dodge out for a spin today--rained all week and raining again but was dry mid afternoon.
Gee 3.91's and 27 inch tires work great in 55 mph zones with traffic lights. slowing down for the light you just lift off the gas, car starts to slow, if light turns green and your at 35--40 mph, hit 2nd and it loves wot with that 10 inch converter/
If I go with 3.21 I be screwed right then. 1st gear would like 25--30 mph better. I would have more "dead" spots at certain speeds. Dead meaning the engine would lug more than it would scream. (that is how many cars are, lol )
I think I got it.
I need two sets of rear wheels. One pair of 26--27 inchers for around town and another set even 30--31 inches if it fit for longer trips. its got air shocks also. Might look a bit funny, maybe not. That old car will stick right out on the road, might be best to do 65 to 70 in the 70 zones. I like doing 75--80 and tapping the brakes when needed, I slip on pass but that is in a newer car
Gee 3.91's and 27 inch tires work great in 55 mph zones with traffic lights. slowing down for the light you just lift off the gas, car starts to slow, if light turns green and your at 35--40 mph, hit 2nd and it loves wot with that 10 inch converter/
If I go with 3.21 I be screwed right then. 1st gear would like 25--30 mph better. I would have more "dead" spots at certain speeds. Dead meaning the engine would lug more than it would scream. (that is how many cars are, lol )
I think I got it.
I need two sets of rear wheels. One pair of 26--27 inchers for around town and another set even 30--31 inches if it fit for longer trips. its got air shocks also. Might look a bit funny, maybe not. That old car will stick right out on the road, might be best to do 65 to 70 in the 70 zones. I like doing 75--80 and tapping the brakes when needed, I slip on pass but that is in a newer car
mikesduster
Well-Known Member
Dodge Freak...... My car is on the trailer because I was going racing that day and its a 2 hr ride each way. I dont like driving my car to the track because if something goes wrong,I can haul it home. Ive driven my car on the highway and only goes about 45-50 mph. I built my car as a street racing machine. I dont care about gas mileage or how fast I can go on the highway,its all about the 1/4!!!!!!!
dodge freak
Well-Known Member
2 hour expressway drives are no fun with 3.91's either. Its bearable, 3,000 to 4,000 rpms the 340's have no problems with, could run all day at those rpm's--if you can afford the fuel costs.
3.23 with 27--28 inchers are nicer for a steady 70--75 mph. Here I'm out of the car and thinking normally, ha ha
On the real roads with traffic lights timed as they are--sometimes you need to slow down for the 2nd light to turn green, those 3.91's in 2nd gear are like 5.67. Perfect to zip on past 60 mph and have great engine braking to slow on down back to 45, then its ready to hit again.
IF those 3.23 ever do go back in, its no more wot, unless its in 2nd gear on a straight away in a 70 zone. That be a 4.65 gear, that engine would scream pass 80 mph and it could go 80 in 3rd @ 3,200 before converter slip
3.23 with 27--28 inchers are nicer for a steady 70--75 mph. Here I'm out of the car and thinking normally, ha ha
On the real roads with traffic lights timed as they are--sometimes you need to slow down for the 2nd light to turn green, those 3.91's in 2nd gear are like 5.67. Perfect to zip on past 60 mph and have great engine braking to slow on down back to 45, then its ready to hit again.
IF those 3.23 ever do go back in, its no more wot, unless its in 2nd gear on a straight away in a 70 zone. That be a 4.65 gear, that engine would scream pass 80 mph and it could go 80 in 3rd @ 3,200 before converter slip
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