Question about Gear Ratios

[Mossimo142]

Ok I'm a noob when it comes to car stuff, but am trying to learn. I'm thinking about getting the 2011 Mustang and see that you have the option of different gear ratios 3.55 or 3.73, with stock being 3,31.

I know it involved the number of revolutions the (something) makes to turn the wheel 1 revolution, but what does that exactly entail? What types of differences will you see with a 3.73 opposed to a 3.55 or the stock 3.31.

Thanks!

 

[KMc]

This would be the rear end ratio, so this is the number of times the drive shaft turns compared to the rear axle. So one turn of the rear axle requires 3.31 turns of the driveshaft for stock and 3.73 or 3.55 for the others. In a nutshell, the larger the ratio, the quicker acceleration you might experience for a given torque output. However, a larger ratio could also translate into a lower top end speed and overall lower fuel economy.

 

[Mossimo142]

Thanks! I was thinking it had something to do with torque/top speed, but that seals the deal.

 

[JulesMaximus]

Get the 3.55. I had a Mustang GT years ago and put 3.73 gears in it which was great fun, coming from a 2.73 rear gear, but I ran out of first gear really quickly. Also, at 65mph on the freeway I was turning about 3,000 rpms (IIRC) which does nothing for your fuel economy. That car could be a handful in the rain too if you didn't know what you're doing. Speedo error was greater with the 3.73 gear also even though they replaced the speedo gear to compensate for the different rear end ratio. It read higher than I was actually going though which probably wasn't a bad thing. The car was red and I saw 140 mph on the freeway once with it...never got a speeding ticket in that car though.

 

[Zenmervolt]

Get the 3.55. I had a Mustang GT years ago and put 3.73 gears in it which was great fun, coming from a 2.73 rear gear, but I ran out of first gear really quickly. Also, at 65mph on the freeway I was turning about 3,000 rpms (IIRC) which does nothing for your fuel economy. That car could be a handful in the rain too if you didn't know what you're doing. Speedo error was greater with the 3.73 gear also even though they replaced the speedo gear to compensate for the different rear end ratio. It read higher than I was actually going though which probably wasn't a bad thing. The car was red and I saw 140 mph on the freeway once with it...never got a speeding ticket in that car though.

I'm going to have to disagree here because the primary (transmission) ratios have changed so much since your 1980's model.

The new 6-speed manual in the GT has a 0.65:1 ratio for the top gear; far taller than the 5th gear in your old 5-speed GT. Even with the 3.73 rear end, the 2011 GT only spins 2,000 RPM at 70 mph. See the "Specs and Performance" area in the sidebar of Edmunds' review.

ZV

 

[Saga]

The tires on the Mustang are def too small to use this (I think?), but it gives a general overview of RPM ranges for the sizes and gears:

http://www.4lo.com/calc/geartable.htm

I would probably be more worried about having too high RPM's in the usual drive zones of 45 and 65mph, etc.. as this will obviously effect fuel economy drastically. My truck has 4.56's, but it helped me normalize the MPG after putting 33's on it..

 

[Lotheron]

What's the difference on the wear and tear of an engine between 2000 and 3000 rpm highway speeds? I ask this because my Mazda6 V6 5SPD is right around 3000 RPMs at 70MPH. How much life (if any) do you think this would take away from an engine? I've never been able to come up with a good reason one way or another although I would assume that higher rpm means more wear and tear.

 

[Saga]

What's the difference on the wear and tear of an engine between 2000 and 3000 rpm highway speeds? I ask this because my Mazda6 V6 5SPD is right around 3000 RPMs at 70MPH. How much life (if any) do you think this would take away from an engine? I've never been able to come up with a good reason one way or another although I would assume that higher rpm means more wear and tear.

Not really an expert here but I'd guess that as long as it's below redline it's operating under "normal" conditions and the only obvious effects of cruising at 3000rpm over 2000rpm is slightly less gas mileage and more on-demand power from being higher on the power band.

You can cruise the highway at 1600rpm's in sixth in a Corvette and get 30mpg if you want, but it'll accelerate like a power wheelchair.

 

[JulesMaximus]

I'm going to have to disagree here because the primary (transmission) ratios have changed so much since your 1980's model.

The new 6-speed manual in the GT has a 0.65:1 ratio for the top gear; far taller than the 5th gear in your old 5-speed GT. Even with the 3.73 rear end, the 2011 GT only spins 2,000 RPM at 70 mph. See the "Specs and Performance" area in the sidebar of Edmunds' review.

ZV

Wasn't an 80's model, it was a 1994, but point taken.

 

[JulesMaximus]

What's the difference on the wear and tear of an engine between 2000 and 3000 rpm highway speeds? I ask this because my Mazda6 V6 5SPD is right around 3000 RPMs at 70MPH. How much life (if any) do you think this would take away from an engine? I've never been able to come up with a good reason one way or another although I would assume that higher rpm means more wear and tear.

It really depends on the engine. My bike is turning around 5,500 rpms at 70 mph...that's close to redline on many cars.

Honestly, I wouldn't worry about it in your case. Mazda has engineered that car to give you a good balance of performance and fuel economy and you'd probably be close to lugging it at lower rpms.

 

[Lotheron]

It really depends on the engine. My bike is turning around 5,500 rpms at 70 mph...that's close to redline on many cars.

Honestly, I wouldn't worry about it in your case. Mazda has engineered that car to give you a good balance of performance and fuel economy and you'd probably be close to lugging it at lower rpms.

That's all well and good.

But technically it's a Ford engine

Although that's probably a true statement. I'm sure they engineer the components of the engine to operate at those RPMs for the amount of time expected.

 

[alkemyst]

With gear ratios there is a lot more than many people think about.

First if you are quarter mile racing usually the slightly higher gear (lower numerically) that keeps you from another shift is the best.

If you are doing highway pulls it's what's going to keep you in your power band the longest unless highest speed wins. In the latter case too high a gear may limit you by horsepower.

Moving 10-20% isn't going to really impact longevity...it could have a noticeable affect on MPG if going to lower gears (higher numerically)...most that are doing gears really aren't looking at that as a major downside.

I will say running high rpms all the time gets wearing in a daily driver.

My current car has a 4.08 in it...it's nice for the 4 cylinder I have. When I do my V8 swap I am going to a 3.64 gear set. The T-56 transmission I will use can use that gear set much better. With a 4.08, 1st and 2nd are useless.

 

[Saga]

With a 4.08, 1st and 2nd are useless.

For clarification sake, can you explain that?

 

[alkemyst]

In a T-56, with a 2500-2700 lb car...you can start in 3rd like it was first gear with a 4.08.

 

[zCypher]

You can cruise the highway at 1600rpm's in sixth in a Corvette and get 30mpg if you want, but it'll accelerate like a power wheelchair.

Yeah I dunno about that one. Obviously compared to revving higher, it's gonna be slower. A power wheelchair? Really? lol. My Aveo in 5th at 1600rpm's accelerates like a power wheelchair. I haven't driven a vette on the highway, but I'd imagine it's quite a bit better even at 1600rpm.

 

[zCypher]

In a T-56, with a 2500-2700 lb car...you can start in 3rd like it was first gear with a 4.08.

:biggrin:

 

[EightySix Four]

For clarification sake, can you explain that?

First and second gear are so short at that point, by the time you realize you've punched it, you already need to shift. Even if you do shift that fast, you'll likely have traction problems, that is a lot of torque to the ground.

 

[CurseTheSky]

3.31 if you want a daily-drivable car with a bit of punch, but still want to maintain traction, somewhat lazy shifting, and half-way decent fuel economy.

3.73 if you're going to be using it for "sporty" applications and general showing off.

3.55 if you want a good balance between the two.

4.11 if you want to...

I'd personally opt for the 3.73s or at least the 3.55s, but then again, I'd never buy a Mustang without the idea of chewing through tanks of gas, tires, and and pavement.

 

[Zenmervolt]

Wasn't an 80's model, it was a 1994, but point taken.

Crap. I'm too young to start losing my memory like that.

ZV

 

[jlee]

3.31 if you want a daily-drivable car with a bit of punch, but still want to maintain traction, somewhat lazy shifting, and half-way decent fuel economy.

3.73 if you're going to be using it for "sporty" applications and general showing off.

3.55 if you want a good balance between the two.

4.11 if you want to...

I'd personally opt for the 3.73s or at least the 3.55s, but then again, I'd never buy a Mustang without the idea of chewing through tanks of gas, tires, and and pavement.

Heh bingo, I would go with 3.73's as well.

 

[Mossimo142]

Is 3.73 the larger ratio or is it the 3.31? I know with maps and scales the "larger" scale actually shows less like 1:10,000 and small scale maps are 1:250,000.

Basically I'd like a lot of initial accelaration/torque as I don't plan on gonig 100+... At least for extended periods of time!

 

[fbrdphreak]

Lower number = taller gear

3.31:1 is taller than 3.73:1

 

[Throckmorton]

Get the tallest gear you can. You'll appreciate it on the highway. Unless you're going to race you don't need the shorter gears and will regret getting them most of the time.

 

[thedarkwolf]

Get the tallest gear you can. You'll appreciate it on the highway. Unless you're going to race you don't need the shorter gears and will regret getting them most of the time.

NEVER!!!!!

If he was going for a 4.56:1 maybe but a 3.73:1 isn't a problem on the highway. 3:73 is the perfect mustang gear.

 

[joutlaw]

NEVER!!!!!

If he was going for a 4.56:1 maybe but a 3.73:1 isn't a problem on the highway. 3:73 is the perfect mustang gear.

I agree.

My Silverado with a 265/75/R16 (around 31") is pretty solid with a 3.73. It's a nice balance b/t the 4.10s and 3.42s.

Some of the newer 6 speed automatics are negating the need for such short gearing. i.e. the new 6 speed in the Silverados with 3.42s is the equivilant to the old 4 speed with 4.10s as far as 1st gear torque and acceleration. You can get 3.73s with the 6.2L V8 and max trailoring package I believe... I would assume that is close the equivilent of the old 4 speed and 4.56s