5 speed vs 6 speed?

[bratboy]

The cool thing is you can always put together a gearbox here with the gears you want. At least hopefully it won't be too much of a hassle. And if you have to change the final drive gears then it wouldn't be too much to change a couple of the other ones if you can find them. I'm not too worried about Towing and I don't know why a 5-speed would be better for towing than a 6-speed. If anything I think the six speed I'm thinking of can take more power than the 5-speed. What is an EOC?

[oil pan 4]

Typically 5 speed transmissions have a 0.7:1 top gear almost universally. 6 speed transmissions usually have a 0.6 or 0.5 to one top gear, with 5th gear being a 0.7:1 OD.
EOC is engine off coasting.

[bratboy]

Originally Posted by oil pan 4

Typically 5 speed transmissions have a 0.7:1 top gear almost universally. 6 speed transmissions usually have a 0.6 or 0.5 to one top gear, with 5th gear being a 0.7:1 OD.
EOC is engine off coasting.

I'm not sure anybody caught it in my previous posts, but the two Transmissions would have the same first gear same 6th Gear and same final drive. I could change the upper two or three gears to drop the Rev a little bit more if I wanted to.

[Ecky]

Repeating what others have said, in the 'states many 6 speeds have the same top and bottom gear, just more ratios in the middle. I feel that for a majority of vehicles I'd rather have one more gear on the top as a "super overdrive", but my Insight is probably one of the few exceptions to that - I could definitely use another in the middle. 5th is so tall that it will do 70mph in 2nd gear.

[oldtamiyaphile]

If we're talking about NA engines, you're best off with a 3 speed, assuming the same rollout.

Skip shifting 1-3-5 has the effect of increasing the average load on the engine for reduced pumping losses, remembering that BSFC is over 3k rpm for most engines anyway. I skip shift my NA's unless towing/ hill/ need the acceleration.

My best tank ever was recorded skip shifting, if nothing else it reduces clutch and shift linkage wear.

The term 'overdrive' is meaningless. Various cars in the 90's had double overdrive five speeds. A lot of cars today have triple over drive.

Less gears= less friction

Don't be fooled by today's 10 speed autos. They're more about the driver not noticing when the computer shifts the wrong way and less about economy.

[pete c]

I think the difference is largely marketing. All the 6 speed gains is slightly closer ratios. Given todays VVT engines that have board flat torque curves, I just don't see the advantage. You might even see a bit of an advantage with the 5 speed as you spend less time shifting.

It really gets ridiculous when you go to 7 speeds, particularly in the vette which makes roughly 12 metric **** tons of torque right off idle to 6 grand. A reviewer for one of the car mags said the vette needs a 7 speed like it needs square wheels.

[Ecky]

Originally Posted by oldtamiyaphile

If we're talking about NA engines, you're best off with a 3 speed, assuming the same rollout.

Skip shifting 1-3-5 has the effect of increasing the average load on the engine for reduced pumping losses, remembering that BSFC is over 3k rpm for most engines anyway. I skip shift my NA's unless towing/ hill/ need the acceleration.

My best tank ever was recorded skip shifting, if nothing else it reduces clutch and shift linkage wear.

The term 'overdrive' is meaningless. Various cars in the 90's had double overdrive five speeds. A lot of cars today have triple over drive.

Less gears= less friction

Don't be fooled by today's 10 speed autos. They're more about the driver not noticing when the computer shifts the wrong way and less about economy.

The Insight's 1.0L delivers best economy between 1750 and maybe 2250RPM, with 1500 to 2500 still delivering "reasonably good" economy. In practice, when I accelerate at high load up to 3K RPM there are noticeable economy losses. Taking it up to 3-4k on a highway on-ramp might drop a trip with 10 miles of cruising afterward from ~95mpg down to 75-65mpg, when compared with keeping it below ~2250 when getting up to speed.

In order to get a highway cruising RPM of ~2000, the gear ratios are so wide that you're going both above and below this range, and the tiny 1L doesn't have the torque to climb some steeper hills even in 2nd gear once the battery is depleted, so moving all of them up isn't an option.

Another gear in the middle would definitely improve economy when accelerating, and give more options when climbing hills. As-is, in 5th gear I can only maintain lean-burn on nearly level ground. Any hill I can't climb in 5th, I generally can't in 4th either; I imagine 4th would be more useful in an area with longer, more rolling hills. 3rd is often too far in the other direction and I end up with low-load, high-RPM when climbing hills - 3rd is a good passing gear.

I'll grant that an extra gear would add friction. I'm not sure how much of a real-world effect this would have. I'd guess that Honda put a 5 speed in this car more to save weight though - the gearbox only weighs ~57lbs.

EDIT: Here are my available gear choices if I want to stay at peak BSFC. Going outside of the range basically prevents me from getting 90+ mpg trips:



Could definitely use another gear in the 1-2-3 range.

[oldtamiyaphile]

Originally Posted by Ecky

The Insight's 1.0L delivers best economy between 1750 and maybe 2250RPM, with 1500 to 2500 still delivering "reasonably good" economy. In practice, when I accelerate at high load up to 3K RPM there are noticeable economy losses. Taking it up to 3-4k on a highway on-ramp might drop a trip with 10 miles of cruising afterward from ~95mpg down to 75-65mpg, when compared with keeping it below ~2250 when getting up to speed.

Yes, but that's why I said NA engines. I perhaps should have said 'standard' NA engines. Pretty much every NA 4 cylinder car is over powered and under geared and really only needs three speeds for our needs.

My 875cc (turbo) Fiat needs all it's 5 speeds, as does my 1.6 Renault (turbo diesel -six speed triple overdrive). Both of these sit on 2000 at 60mph, but have a relatively narrow sweet spot.

The gains of gutting a 5 speed into a 3 of course wouldn't be worth the effort, but if you were building a car from the ground up, every little bit adds up, especially when we start talking about 60mpg+.

[Frank Lee]

The forum is analyzing how much power an oil pump draws; surely boatloads of gear meshes draw more power than, say, a 3-speed direct-drive manual transmission. Put a tall final drive behind it too and there's no need for overdrive. Of course it will lack urgency in acceleration but that's what fast bikes are for.

[Gasoline Fumes]

Originally Posted by Ecky

Could definitely use another gear in the 1-2-3 range.

Yeah, me too. The way I drive, I could even see a 7-speed being an advantage. I use a very narrow RPM range (1200-2000). After swapping out my original transmission for the CRX HF one, I ended up raising my shift points in the lower gears due to the wider ratios. 20 MPH school zones are tricky for me. The engine lugs in 3rd, revs higher than I'd like in 2nd. So I try to coast the school zones.

I'd hate a 3-speed! My car would barely be drivable. I've driven older 3-speed trucks. I was always wanting a gear that didn't exist.