Rear Gears
- Thread starter vobraman
- Start date
It doesn't matter what I or anyone else runs, what matters is your combo. The gears need to compliment the engine and transmission to help keep you in your torque curve for maximun perfomance. If you have a stock engine and stock tranny then 3.50 are even too much in my opinion. It also depends upon whether you have an overdrive tranny or not.....4.11s on the street without OD are punishing at best.
mfp4073
Founding Member
It seems that most folks that have changed out their rear gears are either 3.50 or 3.89(ish). I am running 3.89s and they are too much for my power tire combo. 80 mph is 4000rpms for me. The car is not a daily driver anymore, but with street tires I can roast them in second gear without using the clutch. Every once in a while I can get a chirp out of my 3rd to 4th shift. Thats all well and good, but traction off the line at the track under full power is pretty much none existant. I am going to drop back to 3.50s one of these days when I get around to it.
6Stang7
New Member
My vote is for 4.11's. DON'T FEAR THE GEAR!!!! 
It will be pushing it though if you don't have an OD, but the gain is worth it.
It will be pushing it though if you don't have an OD, but the gain is worth it.
WORTH
20+ Year Stangneter 
I think everyone missed the obvious question. What do you want your car to be? 3.00 makes a nice cruising machine, but you sacrifice 0-60 acceleration, 411 will get you off the line nicely but you'll toast your engine if you like the hyway.
The best all around gears are probubly in the 3.50 range. You just have to decide what you want it to be?
The best all around gears are probubly in the 3.50 range. You just have to decide what you want it to be?
Ronstang said:
Why do you think traction would be more of a problem with higher (lower numerically) gears? That makes no sense. It is MUCH easier to roast the tires with a lower gear ratio. My old 89 Mustang couldn't squeal a tire when I first got it with 2.73 gears. And I tried a lot! A switch to 3.73's and I could burn them off very easily. Traction was now difficult to find at the track where before I could just floor it from the line with no worries.
ratio411
Founding Member
We cannot tell you our thoughts unless we know alot more about your car.vobraman said:
Year?
CID?
Tranny?
Cam?
Intake?
Carb?
Tires?
Daily driver?
Racing?
Anything else with the info we have, zero, is all pointless.
mfp4073
Founding Member
Vinyl66 said:
yeah, that was what I was thinking. Lets say that I cannot take advantage of the 3.89s in any way buy making the tires spin. At least a 3.50 would give me dig, but also give me better top end.
You guys are thinking about the traction/gear relationship all wrong, HP/torque does play a role but it is much harder to get the tires spinning with a low gear ratio because the tires have to spin more times per 1 revolution of the driveshaft and the spinning is also harder to maintain up to high rpms for the very same reason.....think about it. If you couldn't spin the tires with a 2.80 gear but you can with a 3.89 that proves nothing but the fact that your cam is too big to produce enough low end touque to get the tires spinning in the first place with the 2.80 gears but the 3.89 gears put you in your torque curve so you can. Highway gear ratios put very little load on the drivetrain and once you get them spinning they just keep spinning if you have enough HP but 4.11s definitely will not do the same.
LMan
Founding Member
Ronstang said:
No. It is MUCH easier to spin the tires with a low gear ratio like 3.89 or 4.11's.
The fact that the tires have to turn more times per one revolution of the driveshaft is exactly why it IS easier...Torque Multiplication!
The fact that I couldn't spin the tires with 2.73's and could with 3.73's is because of the torque multiplication advantage the lower gears gave me. You get the final drive ratio by multiplying the tranny first gear ratio by the rear end ratio. For good takeoff in a Mustang you should be around 9 or 10:1. Here is a good chart of many different combinations.......
http://www.ultrastang.com/Rearinfo.asp?Page_ID=4
My cam in my stang was the stock small 5.0 cam which made best power from idle to around 5000rpm. It was definitely not too big. The reason why it would now scorch the tires is because the first gear final ratio went from 6.552 to 8.952. All from a simple gear change.
blown65
Founding Member
Ok, put your car in first and roast the tires. Now do it in second, now in third. You tell me which is easier to burn the tires off.
Lower gears makes it easier depending on your HP level, obviously if you have 200hp and 2.80 gears it wont be such an easy task as 200hp and 4:11's. Now lots of HP it wont matter much.
Yes I know, its actually TQ but all the same you get my point.
Lower gears makes it easier depending on your HP level, obviously if you have 200hp and 2.80 gears it wont be such an easy task as 200hp and 4:11's. Now lots of HP it wont matter much.
Yes I know, its actually TQ but all the same you get my point.
Route666
Active Member
Ronstang said:
Exactly! Since I.C.Es inherently produce more power with higher rpms (to an extent) it is easier to get the tyres spinning with performance gears than highway gears. Only a stupid or truck (semi) cam would give you more torque at low rpm than high rpm, this isn't an issue. (EDIT: I should say moderately high rpm, and very low rpm. What I mean was that noone would build an engine with max torque at 1000rpm, and petering off from there)
Think about this - rolling along in 2nd, lowish speed, 4.11s, put the foot down, tyres turn to smoke. Try the same with 2.80 gears at the same speed in 2nd, and the engine and drivetrain load quite a lot, while tyres do not (because of the ratio) and hence, you do not go forward as fast as you would if you had traction with the 4.11s.
Not only do the 4.11s put you into a zone with more torque and hp, but they multiply it more as well. Hence the tyre-frying nature of the gears. It is easier to fry tyres because the engine is able to accelerate faster. That is, the engine can increase in rpm faster because it isn't loaded like it would be with 2.80s.
Sure gears have nothing to do with tyres' tractive ability, but it sure does have a lot to do with traction.
Route666
Active Member
I've looked over the numbers, with an overdrive, 3.89 would make a good compromise between accel and high-speed, low-rpm cruising. Without OD you have to really decide which is more important, accel or highway use. You can compromise of course.
ratio411
Founding Member
Think of the gears as a lever...
If you use a 5' lever to move a rock that weighs 1 ton, you struggle and eventually roll it without fan-fare.
If you use a 12' lever to move the same rock, you have more mechanical advantage, so the rolls quickly and easily without you pulling your back muscles.
That is what lower gears do. They give you a longer lever to move your weight. They multiply torque, so you put more torque to the ground with less effort... that is why the traction is lost with lower gears.
See, I do remember some automotive schooling! To think I was so chemically altered that time of my life, I barely remember my wedding day.
Dave
If you use a 5' lever to move a rock that weighs 1 ton, you struggle and eventually roll it without fan-fare.
If you use a 12' lever to move the same rock, you have more mechanical advantage, so the rolls quickly and easily without you pulling your back muscles.
That is what lower gears do. They give you a longer lever to move your weight. They multiply torque, so you put more torque to the ground with less effort... that is why the traction is lost with lower gears.
See, I do remember some automotive schooling! To think I was so chemically altered that time of my life, I barely remember my wedding day.
Dave
WORTH
20+ Year Stangneter
ratio411 said:Think of the gears as a lever...
If you use a 5' lever to move a rock that weighs 1 ton, you struggle and eventually roll it without fan-fare.
If you use a 12' lever to move the same rock, you have more mechanical advantage, so the rolls quickly and easily without you pulling your back muscles.
That is what lower gears do. They give you a longer lever to move your weight. They multiply torque, so you put more torque to the ground with less effort... that is why the traction is lost with lower gears.
See, I do remember some automotive schooling! To think I was so chemically altered that time of my life, I barely remember my wedding day.
Dave
Ah,,, Dave,,, your not married
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