They just need better ratio splits.
Are mainstream cars geared too tall?
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ls1mike
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The Buick must have a tall gear, not sure what it is but at 70 it is under 2000 RPM with the 4T65E-HD. With the blower it is nice. I won't downshift unless I hit a large grade, even before the modifications. Now with modifications I still see right around 28 MPG cruising on the highway, but it is nice lay into it.
I wish my 2003 Civic MT was geared a little taller. It turns 3,400 rpms at 72 mph.
My Jeep is about 33mph / 1000 rpm in 4th (4 speed auto) with the TC locked. If I had the money, I'd love to have a gearset made to make 1st and second in the tranny a bit lower, and gear the axles a bit taller, which would drop a little over 100 rpm at 60mph. From anywhere 1200 rpm on up, it pulls well, and it pulls great from 1500 and up.
If I really had cash, I'd regear the axles from 3.73 to 4.56 and have the mounts, etc fabbed up to swap in a stick (Tremec 6060). With the lower axle gears and 2.97 1st in the tranny, I'd have at least as much off the line as the auto + TC multiplication. Plus, with the 0.5 6th gear, I'd be down from just over 1800 at 60 to about 1600, which would only require downshifting on the steepest of hills, and would keep the engine loaded a bit better, giving some extra mpg on the highway. That would be 37mph / 1000 rpm.
If I really had cash, I'd regear the axles from 3.73 to 4.56 and have the mounts, etc fabbed up to swap in a stick (Tremec 6060). With the lower axle gears and 2.97 1st in the tranny, I'd have at least as much off the line as the auto + TC multiplication. Plus, with the 0.5 6th gear, I'd be down from just over 1800 at 60 to about 1600, which would only require downshifting on the steepest of hills, and would keep the engine loaded a bit better, giving some extra mpg on the highway. That would be 37mph / 1000 rpm.
Originally Posted By: levi
Originally Posted By: eljefino
The decent torque band and wider ratios preclude the need for more than 4 speeds. IMO automakers are shooting themselves in the feet for moving away from this simplicity.
Well said.
Its not just about CAFE to the auto makers, IMO.
Complexity breeds downstream maintenance revenue.
Lots of it.
I have a 30 mile commute and my 3 spd auto shifts about 32-40 times total getting to work depending on the lights. And I do 90% of my passing without even unlocking the TC, let alone downshifting. At 70mph+ it would be nice to have a 4th gear for mileage but I rarely drive that fast.
There must be some common parts wearing on a 5 speed auto on every shift? I bet some would make 30 shifts driving for 4 blocks in town...
With the new high torque turbo engines coming, a 4 speed auto is all they should ever really need IMO. Especially if the computer is going to control the throttle and trans together as well.
Originally Posted By: eljefino
The decent torque band and wider ratios preclude the need for more than 4 speeds. IMO automakers are shooting themselves in the feet for moving away from this simplicity.
Well said.
Its not just about CAFE to the auto makers, IMO.
Complexity breeds downstream maintenance revenue.
Lots of it.
I have a 30 mile commute and my 3 spd auto shifts about 32-40 times total getting to work depending on the lights. And I do 90% of my passing without even unlocking the TC, let alone downshifting. At 70mph+ it would be nice to have a 4th gear for mileage but I rarely drive that fast.
There must be some common parts wearing on a 5 speed auto on every shift? I bet some would make 30 shifts driving for 4 blocks in town...
With the new high torque turbo engines coming, a 4 speed auto is all they should ever really need IMO. Especially if the computer is going to control the throttle and trans together as well.
Yup. A wide ratio 4 speed auto coupled to an engine with a broad torque curve will give good mpg and driveability, without adding too much complexity. 8 speed autos are just overkill, and only desirable if working with an engine with a very narrow powerband.
My CRV 5AT turns 2500rpm at 80mph.
Originally Posted By: Vikas
Originally Posted By: CBR.worm
My G35 has a 6 speed stick and in 6th gear on the highway I am at 3,500 rpm or higher for hours a day.
This is insane or your definition of the highway speed is 85mph+
I have Maxima 3.0 5spd and it is not tall enough i.e. I never need to downshift. I think I cruise around 3100 or so.
- Vikas
Yep, I had a 97 Maxima SE 5speed. The G35, even with a 6 speed seems to be geared lower overall - I also never need to downshift. My office is 100 miles away. When I go up during the day the CC is set at 82 to 85. On the way home at night it is frequently 92 (which is the max the cruise will hold) or faster - The beauty of totally deserted 6 lane highways.
What is interesting with the G35 is that I get the same bad mileage at 70 or 100. Tank after tank.
Originally Posted By: CBR.worm
My G35 has a 6 speed stick and in 6th gear on the highway I am at 3,500 rpm or higher for hours a day.
This is insane or your definition of the highway speed is 85mph+
I have Maxima 3.0 5spd and it is not tall enough i.e. I never need to downshift. I think I cruise around 3100 or so.
- Vikas
Yep, I had a 97 Maxima SE 5speed. The G35, even with a 6 speed seems to be geared lower overall - I also never need to downshift. My office is 100 miles away. When I go up during the day the CC is set at 82 to 85. On the way home at night it is frequently 92 (which is the max the cruise will hold) or faster - The beauty of totally deserted 6 lane highways.
What is interesting with the G35 is that I get the same bad mileage at 70 or 100. Tank after tank.
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FYI, My 1995 BMW 525i 4-speed automatic has a 4:10 final drive ratio. The engine is a 2.5 liter, 24 valve, double overhead cam with vanos. factory HP is 189 at 5,900 rpm with 184 max torque at 4,200 rpm
At 60 mph in 4th the rpm is about 2,500-2,600. At 70 MPH about 2,900 to 3,000 rpm. It loves to cruise at about 80 mph. Seems to run better the faster I go. Feels lazy at low rpm.
The car is redlined at 6,500 rpm and has a top speed of about 128 mph. IMO,it is slow to 60 mph. Per bmw it takes 9.1 seconds with an automatic.
At 60 mph in 4th the rpm is about 2,500-2,600. At 70 MPH about 2,900 to 3,000 rpm. It loves to cruise at about 80 mph. Seems to run better the faster I go. Feels lazy at low rpm.
The car is redlined at 6,500 rpm and has a top speed of about 128 mph. IMO,it is slow to 60 mph. Per bmw it takes 9.1 seconds with an automatic.
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My '08 Merc GMQ "has" to cruise at 86mph to hit 2,000 rpm on the tach at HWY speeds "reportedly anyway" 
It is also reported to have a very-healthy top-end for a big girl
It is also reported to have a very-healthy top-end for a big girl Originally Posted By: Summerwind
My '08 Merc GMQ "has" to cruise at 86mph to hit 2,000 rpm on the tach at HWY speeds "reportedly anyway" It is also reported to have a very-healthy top-end for a big girl
2139RPM @ 86MPH.
2000RPM @ 80MPH.
Off just a couple hundred.
My '08 Merc GMQ "has" to cruise at 86mph to hit 2,000 rpm on the tach at HWY speeds "reportedly anyway"
It is also reported to have a very-healthy top-end for a big girl 2139RPM @ 86MPH.
2000RPM @ 80MPH.
Off just a couple hundred.
Originally Posted By: rslifkin
Yup. A wide ratio 4 speed auto coupled to an engine with a broad torque curve will give good mpg and driveability, without adding too much complexity. 8 speed autos are just overkill, and only desirable if working with an engine with a very narrow powerband.
The only thing NARROW here is your thinking!
BMW, Audi, etc., are ALL switching into the new 8 speed ZF gearbox. Smaller, lighter, better fuel economy, hybrid adaptable, etc.
You may want to live in the dark ages but many manufacturers are currently disproving this statement!
Yup. A wide ratio 4 speed auto coupled to an engine with a broad torque curve will give good mpg and driveability, without adding too much complexity. 8 speed autos are just overkill, and only desirable if working with an engine with a very narrow powerband.
The only thing NARROW here is your thinking!
BMW, Audi, etc., are ALL switching into the new 8 speed ZF gearbox. Smaller, lighter, better fuel economy, hybrid adaptable, etc.
You may want to live in the dark ages but many manufacturers are currently disproving this statement!
Kestas
Staff member
Originally Posted By: levi
Complexity breeds downstream maintenance revenue.
Lots of it.
One of the best-worded thoughts I've read in a while.
All the technology we throw into transmissions is supposedly to enhance fuel mileage. Unfortunately, I believe all the money we save on fuel eventually goes to a mechanic to repair the gas-saving features. I doubt our pocketbook is any better for this technology.
Complexity breeds downstream maintenance revenue.
Lots of it.
One of the best-worded thoughts I've read in a while.
All the technology we throw into transmissions is supposedly to enhance fuel mileage. Unfortunately, I believe all the money we save on fuel eventually goes to a mechanic to repair the gas-saving features. I doubt our pocketbook is any better for this technology.
CX7 turns ~ 3000 rpm @ 80 mph. My Subaru Forester turns 3000 @ ~ 70 mph and wish it had a 5th crusing gear.
Steve - If they were to apply all that new technology to a 4 or 5 speed with the ratio spread of the 8 speed, wouldn't it be even lighter, etc?
I rented a new Grand Marquis the other day. Top gear was really tall. Every gear was tall. 50mph in first. In top gear at 70 it was somewhere around 1,600 rpm. For me that was too tall. It actually ran well on the highway, but was slow off the
Line.
For the size of the car it was pretty well optimized. Got surprisingly good gas mileage and was a quiet and comfortable cruiser.
Line.
For the size of the car it was pretty well optimized. Got surprisingly good gas mileage and was a quiet and comfortable cruiser.
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Originally Posted By: rslifkin
Steve - If they were to apply all that new technology to a 4 or 5 speed with the ratio spread of the 8 speed, wouldn't it be even lighter, etc?
Indeed possible. But consumers demand more performance AND better fuel mileage.
With only one additional planetary they add a whole bunch of ratios. Then you get great acceleration in low gears and fuel economy too. That new 8 speed is also lighter and more efficient.
My whole point was that dozens of new models across many manufacturers are all using the same trans. This doesn't cost money it SAVES money. And standardization means easier to get repaired.
Steve - If they were to apply all that new technology to a 4 or 5 speed with the ratio spread of the 8 speed, wouldn't it be even lighter, etc?
Indeed possible. But consumers demand more performance AND better fuel mileage.
With only one additional planetary they add a whole bunch of ratios. Then you get great acceleration in low gears and fuel economy too. That new 8 speed is also lighter and more efficient.
My whole point was that dozens of new models across many manufacturers are all using the same trans. This doesn't cost money it SAVES money. And standardization means easier to get repaired.
How many planetaries are required for the 8 speed? 3? 4?
Originally Posted By: CBR.worm
How many planetaries are required for the 8 speed? 3? 4?
The ZF uses 4
How many planetaries are required for the 8 speed? 3? 4?
The ZF uses 4
Originally Posted By: bruno
That's what transmissions are for !
Downshift !
No kidding.
If anything, top gear in more cars is too short. My Accord has plenty of 60 MPH oomph, and could really use a 6th gear.
I've been running 5% taller-than-stock tires for a while. After correcting for the odometer error, I'm getting slightly higher freeway mileage. IMO, the car could benefit from a ~30% taller final gear.
That's what transmissions are for !
Downshift !
No kidding.
If anything, top gear in more cars is too short. My Accord has plenty of 60 MPH oomph, and could really use a 6th gear.
I've been running 5% taller-than-stock tires for a while. After correcting for the odometer error, I'm getting slightly higher freeway mileage. IMO, the car could benefit from a ~30% taller final gear.
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