Extra gears: Not always better for FE

[theholycow]

I knew that it's common practice to add more gears to a car's transmission and not increase its gear range, instead just making the ratios closer...but I had no idea that a 1992 Toyota Tercel would get worse FE with the optional 5 speed manual than it does with the 4 speed manual.

According to fueleconomy.gov:
1992 Toyota Tercel 4 speed manual: 27/30/33
1992 Toyota Tercel 5 speed manual: 25/28/33

[IndyFetch]

The 4-speed has much taller gearing than the 5-speed. Honda did the same thing with the 88-91 Civics, if I am not mistaken. I test drove a 1990 Civic hatch with a 4-speed, and the 4th gear was taller than the 5th in another 1990 I drove.

GM is the king of tall gearing with fewer ratios (in their automatics). For example, a Buick Terraza reaches 89 mph in 2nd gear (4-speed auto). Wow.

[theholycow]

That's what I figured. Why would they do that?

GM is definitely the king of tall gears and wide ratios in automatics...I'm always amazed at how fast the engine in anything else goes at highway speeds. I found it amazing that my VW cruises along at 3000rpm and I was even more amazed when I found out that it's quite common. I was raised mostly on GM and Ford and my own vehicles have mostly been large GMs and when I drive anything else I keep wondering if I'm in high gear.

[thisisntjared]

that is weird... i noticed a similar trend in subarus. not between the auto and the manual but between the manual 5spd and 6spd. the top gear on the 6th (top speed ~=150) is substantially shorter than the top gear on the 5th (top speed ~=160).

i think gms tall gears are the secret to their success with any kind of efficiency. i mean how else are you going to get a 400+hp sports car to get 30mpg on the highway? slow down that motor.

[GasSavers_maximilian]

Are more gears associated with sportier driving? I have the vague impression they are, but where I got that from I have no idea, not being a performance enthusiast of any stripe.

[theholycow]

Wait a minute, the 4's 4th being taller than the 5's 5th doesn't make sense for those EPA ratings. By those EPA ratings, the top gears in both trannies are the same, but the 4 speed manual gets better city mileage.

More gears are associated with sportier driving. Sports cars got 6 speed transmissions before other cars (and you still can't find 6 speed transmissions in lots of non-sports cars). Standard practice seems to be that when they add a gear, they don't add a taller overdrive for the new gear; they just make closer ratios and/or a shorter 1st and 2nd. Closer ratios allows the car to stay in a narrower powerband while accelerating.

Eventually, additional gears will have to be for fuel economy. There's got to be a point where the extra time spent shifting is more than the time saved by staying closer to the optimum RPM.

Some new 6 speed automatics already don't use all their gears all the time. I don't remember which, but some manufacturer's automatics skip one gear on the way up which only gets used when downshifting, and it skips another when downshifting. The new Camaro SS doesn't use 1st except for when you first drive away while the engine is cold, and probably when you set the transmission in "Sport" mode. I don't know if the V6 Camaro does the same thing.

[Lug_Nut]

How do the final drive ratios compare? Transmission gearing is one of three major factors, final drive ratio and tire diameter are others.

[GasSavers_BEEF]

I was thinking the same thing. maybe they put a different differential gear ratio in it (not sure what you call the front wheel drive version of this).

[theholycow]

Lug_Nut, if you're talking about the Tercel, I have no idea what the gear ratios are OR what the final drive ratios are. I just know how many gears, and what the EPA ratings are.

I know my five speed 2008 VW runs the same RPM at 70mph in 5th as the six speed 2008 VW GTI in 6th.

[dkjones96]

It isn't the transmission that made the difference, it was the engine.

The 4-speed was paired with the base 1.5L 3E-E SOHC 3-valve, fuel injected 4 cylinder while the 5-speed was paired with the 1.5L 5E-FE DOHC 4-valve, fuel injected 4 cylinder.