When do gears lose their advantage?

[WydOpn]

Ok so i'm definatly an idiot when it comes to gears, but being that i just bought 3.73's for my car i gotta ask.

if im rollin down the street and the same car with the same mods rolls up next to me, but he has 3.27's and i have 3.73's, if we race from 2nd gear to third gear, is he going to beat me or will i accelerate faster and outrun him?

if i ever race from a rolling start i always start in second is why i ask. cause the one time i tried it from third it felt like the car didn't want to go and i definatly lost that one.

You'll win - not by much, but you'll win. You have to remember that the only thing you're changing with the 3.73s is the ratio of the number of turns of the driveshaft to the number of turns of the rear wheels. You aren't magically creating more torque - torque transfers are limited by the efficiencies of your powertrain - you're just simply trying to keep your engine in the powerband by changing what RPM you're at for a given speed. Think about the situation you proposed: Two cars with identical mods and torque curves - one with a 3.27 and one with a 3.73. If you're both running at say, 40mph, then the car with the 3.27 is at ~3400RPM and the car with the 3.73 is at ~3780RPM (assuming both cars are running a 285/35/18 tire). So the instant you both go WOT, the car with the 3.73s will be putting slightly more torque to the ground - assuming 1: the tires don't spin, and 2: the engine creates more torque at 3780RPM than at 3400RPM - which is obviously true for our 2V 281s.

The thing that's interesting about that situation (and the thing that always creates controversy about proper gearing) is that now the guy with the 3.73s has to shift into 3rd earlier than the guy with the 3.27 - and that shift is going to drop his engine RPM to a point where he's making less torque than the guy with the 3.27...but to answer your original question: yes, from a roll in 2nd, you'll beat him to 3rd.

 

[Stan Weiss]

You have to remember that the only thing you're changing with the 3.73s is the ratio of the number of turns of the driveshaft to the number of turns of the rear wheels. You aren't magically creating more torque - torque transfers are limited by the efficiencies of your powertrain - you're just simply trying to keep your engine in the powerband by changing what RPM you're at for a given speed.

So you are saying that lower gearing does not do any torque multiplication. Than why is it easier to move the car from a standing start in first gear 3.37:1 than in 4th gear 1:1 at 1000 RPM as you let the clutch out?

 

[CatmanJJ]

I had 4.10s in my GT loved them but stock Goodyears are a joke if you are tryin to launch aggressively from a dead stop, talkin spin city unless you seriously feather it outta the hole. But with 4.10s it was nice having more acceleration in 3rd and 4th gear shoot even 5th on the highway. Pretty much the same thing with my Mach with 3.55s right now ha.

 

[WydOpn]

So you are saying that lower gearing does not do any torque multiplication. Than why is it easier to move the car from a standing start in first gear 3.37:1 than in 4th gear 1:1 at 1000 RPM as you let the clutch out?

I think we're trying to say the same thing using different terminology. Saying 'torque multiplication' suggests (to me anyways) that changing from a 3.27 to a 3.73 somehow magically makes your engine produce another 100ft-lbs, and I guess I just didn't want anyone to think that...But however you want to say it, yes; engine torque is amplified through the drivetrain due to gear ratios.

As for starting off in different gears, I've had this explained two different ways to me: First, what youre saying Stan:

1st gear: 3.37:1 + 3.73 gear + say, 200ft-lbs @ 1000RPM = 200*3.37*3.73 = 2514ft-lbs of torque at the axels - as opposed to 4th gear: 1:1 + 3.73 gear + 200ft-lb = 3.73*1*200 = 746ft-lbs. 2514>746 = car moves easier in 1st.

Another way to think about it...

1st gear: 3.37:1 with a 3.73 gear means youre asking one turn of the engine to rotate the rear tires .079 times (1/3.37/3.73 = .079). In 4th gear (1:1), you're asking one turn of the engine to rotate the tires .268 times (1/1/3.73), which is too great a load (stall). Like someone else said - its like riding your ten speed...you have a tough time starting off from a dead stop in high gear because each rotation of the pedals needs to turn the rear tire a greater amount than when you're in a lower gear.

Please feel free to correct me if I've made any mistakes here - I'm on this site to learn just as much as anyone...I just happened to take a class on this type of stuff this spring and feel that I have a pretty good handle on it :SNSign:

 

[Stan Weiss]

We are both saying the same think only with different words. I always like to talk about torque where the tire meets the track, because the tire diameter / radius also factors into the equations.

 

[cronin49]

steeper gears will help you accelerate much quicker but kill your top speed as you cannot drag out the gear as long. you hit the rev limiter alot faster in 5th with the 3.73 and 4.10.

you can't "hit the rev limiter" in 5th.
With my supercharger I can hit 150 mph @4500 rpm in 5th.
If I was able to redline it in 5th I'd be able to hit 200+ mph...
I don't think that's gonna happen.
Not a flame, I'll just assume that you know this, that's all.

 

[Bluffing024]

you can't "hit the rev limiter" in 5th.
With my supercharger I can hit 150 mph @4500 rpm in 5th.
If I was able to redline it in 5th I'd be able to hit 200+ mph...
I don't think that's gonna happen.
Not a flame, I'll just assume that you know this, that's all.

+1

Yes, you lower your theoretical top speed. Thing is you can't even hit your top speed with the 4.10s let alone 3.27s.

Now when do they lose their advantage? I would say if you are a drag racer then when they make you run out of gear right near the line. But you could always go even steeper to utilize that next gear too, as long as you have the supporting traction mods.

 

[tomustang]

With stock 245-45-17 tires 3.27:1 rear and 5750 RPM top sped is 200.6. The problem is with the stock HP and torque the force need to push the car though the are greater at around 150 MPH, so that is your top end. With stock 245-45-17 tires 4.1:1 rear and 5750 RPM top sped is 160. With 4.1's the real top end is about 148 but it takes less time and a shorter distance to get there.

That is why I said theoretical, not actual, and you can push the limit to 6250rpms which should come to about 240 or something

 

[tomustang]

Ok so i'm definatly an idiot when it comes to gears, but being that i just bought 3.73's for my car i gotta ask.

if im rollin down the street and the same car with the same mods rolls up next to me, but he has 3.27's and i have 3.73's, if we race from 2nd gear to third gear, is he going to beat me or will i accelerate faster and outrun him?

if i ever race from a rolling start i always start in second is why i ask. cause the one time i tried it from third it felt like the car didn't want to go and i definatly lost that one.

Just think, you would always beat him to the next gear since yours are shorter now

 

[blackfang]

Ok, let me add to this. Steeper gears will allow your car to be faster, granted other factors can change this. It allows the vehicle to accelerate faster and puts the motor in the powerband faster than a 3.27 gear.

Top end will also increase because steeper gears make the 4th and 5th gears more usable and can help overcome the resistance you hit at 140+ mph. I have ran both my 99 and 97 Cobras on a lone road with stock gears and with 4.10's and 4.30's and each time I was able to pull easily to 160, where the car struggled to hit 150 and took longer with the stock gears.

When do they become a disadvantage? Dragracing, when you have too much gear for your engine/trans setup, but a simple tire swap to a bigger tire fixes that.