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X3 F25 (2011 - current)
The latest X3 brings some added style and some new features to the BMW SUV family. Talk about the new F25 now!

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  #1  
Old 10-11-2010, 12:43 PM
X3forlife X3forlife is offline
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8 speed automatic transmission

I guess the F25 will have 8 speed auto transmission.

Can somebody explain in English what an 8 speed auto transmission is and if it is so much better than a 5 or 6 speed auto transmission? Is it something we would notice or just a gimmick?

Thanks
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  #2  
Old 10-11-2010, 01:18 PM
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raleedy raleedy is offline
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It has 2 more speeds than a 6 speed, and 3 more than a 5 speed. You're welcome.
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  #3  
Old 10-11-2010, 01:56 PM
wallymn wallymn is offline
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the purpose of adding gears to the transmission to to provide the optimal engine speed for any driving speed..

Once upon a time an auto had 2 speeds.. The engine had to work very hard at some speeds when first gear was too short but 2nd gear was still too tall. as such a engine might spin at 4k RPM, but if another gear were available the same road speed could be held with only 2k RPM.. Adding a gear which delivers a 2K RPM at this road speed cuts fuel costs.

Over the years many gears have been added the but the goal is the same , provide a gear which allows the engine to work as little as possible to provide the desired road speed.
(the ideal would be a CVT , but there are power limits to this transmission type).

the positive of adding gears...
1. better fuel economy.
by making the engine work less for a given speed

2. possible longer engine life.
If the engine doesn't work as hard, it should last longer..
Bad trans program can lead to engine "lugging" which can cause wear...

Negatives of adding gears..

1. cost
Up front and maintenance if something goes wrong..

2. gear hunting....
with so many gears available a transmission might switch gears frequently
good programing avoids this...

I personally don't see the point of the current 6 spd I drive... the shifttronic mode shows that 5th gear isn't really ever used....
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  #4  
Old 10-11-2010, 03:37 PM
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AzNMpower32 AzNMpower32 is offline
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Under normal driving, there isn't as noticeable a benefit. Having more steps allows the engine to operate the best rpm for optimum efficiency, emissions, and power.

Under sportier driving and hard acceleration, the difference can be appreciated. This is especially true in Germany where speeds are higher.

When one floors it from a standstill, a shorter 1st gear allows the vehicle off the light quickly and get into the powerband and maximum horsepower. Gears 2 3 4 5 and 6 can be geared much closer together, so the revs do not drop as much with each upshift, so the engine does not fall to "lower revs" and continues to produce near-peak to peak power as it runs through the gears.

So pretend I am in Germany, driving the new 8AT in an X3 xDrive28i. As I go around a cloverleaf ramp, I am coasting around 50km/h. As the ramp straightens out, I need to merge onto a derestricted zone of the Autobahn, with average traffic speeds around 150-160km/h. I slam down the throttle, the gearbox shifts into 2nd. I can rip off gears 2-3-4-5-6 without the revs ever falling below 4750rpm and speeds quickly climbing to 200km/h.

Gears 7 and 8 are intended as overdrive gears for cruising, so higher speeds translate into lower rpms. Also, lower revs at cruising speeds reduce emissions and fuel consumption, and provide a quieter ride.

The 8AT in BMWs has been designed so that it can perform direct multiple-gear downshifts, so the engine can skip many gears to get into the powerband quickly when sudden acceleration is needed. BMW touts it can perform an 8-2 downshift, skipping 6 gears instantly.

__________________________________________________ ____________________
Another example is readily apparent in my X3 2.5i with the older 5AT. Gears 1 2 and 3 are spaced closely together, providing strong acceleration from 0-130km/h. However, with only 5 speeds and to accommodate an overdrive 5th gear, the revs drop off precipitously beyond that speed. The 3-4 gap is huge (6500rpm down to 4000rpm) and as a result, there is not much passing acceleration beyond 130km/h no matter where the throttle pedal is. Floor my X3 at 140km/h and it takes a while go climb up to 160km/h, worse if there's a gradient. 5th gear is tall but not very because modest power is still needed to maintain speeds, so as a result, the revs are a bit high for extended cruising. The 3-4 gap is not a problem with the 6MT or the 6AT in later model years, based on the published gear ratios.

Think of gear ratios like this: You have to climb a embankment, You can have 5 widely spaced steps, or 8 smaller-spaced steps. Which one is easier for you to climb?
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  #5  
Old 10-11-2010, 03:54 PM
X3forlife X3forlife is offline
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Quote:
Originally Posted by wallymn View Post
the purpose of adding gears to the transmission to to provide the optimal engine speed for any driving speed..

Once upon a time an auto had 2 speeds.. The engine had to work very hard at some speeds when first gear was too short but 2nd gear was still too tall. as such a engine might spin at 4k RPM, but if another gear were available the same road speed could be held with only 2k RPM.. Adding a gear which delivers a 2K RPM at this road speed cuts fuel costs.

Over the years many gears have been added the but the goal is the same , provide a gear which allows the engine to work as little as possible to provide the desired road speed.
(the ideal would be a CVT , but there are power limits to this transmission type).

the positive of adding gears...
1. better fuel economy.
by making the engine work less for a given speed

2. possible longer engine life.
If the engine doesn't work as hard, it should last longer..
Bad trans program can lead to engine "lugging" which can cause wear...

Negatives of adding gears..

1. cost
Up front and maintenance if something goes wrong..

2. gear hunting....
with so many gears available a transmission might switch gears frequently
good programing avoids this...

I personally don't see the point of the current 6 spd I drive... the shifttronic mode shows that 5th gear isn't really ever used....
Thanks so much for taking the time to explain that. I never understood it. Brilliant explanation.
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  #6  
Old 10-11-2010, 04:04 PM
X3forlife X3forlife is offline
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Quote:
Originally Posted by AzNMpower32 View Post
Under normal driving, there isn't as noticeable a benefit. Having more steps allows the engine to operate the best rpm for optimum efficiency, emissions, and power.

Under sportier driving and hard acceleration, the difference can be appreciated. This is especially true in Germany where speeds are higher.

When one floors it from a standstill, a shorter 1st gear allows the vehicle off the light quickly and get into the powerband and maximum horsepower. Gears 2 3 4 5 and 6 can be geared much closer together, so the revs do not drop as much with each upshift, so the engine does not fall to "lower revs" and continues to produce near-peak to peak power as it runs through the gears.

So pretend I am in Germany, driving the new 8AT in an X3 xDrive28i. As I go around a cloverleaf ramp, I am coasting around 50km/h. As the ramp straightens out, I need to merge onto a derestricted zone of the Autobahn, with average traffic speeds around 150-160km/h. I slam down the throttle, the gearbox shifts into 2nd. I can rip off gears 2-3-4-5-6 without the revs ever falling below 4750rpm and speeds quickly climbing to 200km/h.

Gears 7 and 8 are intended as overdrive gears for cruising, so higher speeds translate into lower rpms. Also, lower revs at cruising speeds reduce emissions and fuel consumption, and provide a quieter ride.

The 8AT in BMWs has been designed so that it can perform direct multiple-gear downshifts, so the engine can skip many gears to get into the powerband quickly when sudden acceleration is needed. BMW touts it can perform an 8-2 downshift, skipping 6 gears instantly.

__________________________________________________ ____________________
Another example is readily apparent in my X3 2.5i with the older 5AT. Gears 1 2 and 3 are spaced closely together, providing strong acceleration from 0-130km/h. However, with only 5 speeds and to accommodate an overdrive 5th gear, the revs drop off precipitously beyond that speed. The 3-4 gap is huge (6500rpm down to 4000rpm) and as a result, there is not much passing acceleration beyond 130km/h no matter where the throttle pedal is. Floor my X3 at 140km/h and it takes a while go climb up to 160km/h, worse if there's a gradient. 5th gear is tall but not very because modest power is still needed to maintain speeds, so as a result, the revs are a bit high for extended cruising. The 3-4 gap is not a problem with the 6MT or the 6AT in later model years, based on the published gear ratios.

Think of gear ratios like this: You have to climb a embankment, You can have 5 widely spaced steps, or 8 smaller-spaced steps. Which one is easier for you to climb?
Thank you also. That was also a great explanation. Thanks for taking the time to explain that. I never understood how we are supposed to be using the RPM meter. lol I was wondering why they make it so big (as big as the speedometer) when I never look at it. I am guessing those who drive stick need to use it and they don't feel like changing the look for the 2 types.

Since you did such a great job explaining, would you mind explaining what you mean by overdrive gears? Thanks.
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  #7  
Old 10-11-2010, 04:48 PM
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Overdrive gears are basically "highway cruising gears", intended to keep revs low at high speeds. The engine does not have to work as hard to maintain speed on the highway. Not the best for quick acceleration, but it's what allows one to achieve great fuel consumption when driving on the highway.

Think of a mountain bike with many speeds/gears. In the biggest front cog, you don't need to pedal as quickly to travel at a faster speed.
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  #8  
Old 10-11-2010, 04:55 PM
X3forlife X3forlife is offline
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Quote:
Originally Posted by AzNMpower32 View Post
Overdrive gears are basically "highway cruising gears", intended to keep revs low at high speeds. The engine does not have to work as hard to maintain speed on the highway. Not the best for quick acceleration, but it's what allows one to achieve great fuel consumption when driving on the highway.

Think of a mountain bike with many speeds/gears. In the biggest front cog, you don't need to pedal as quickly to travel at a faster speed.
Thanks.
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  #9  
Old 01-28-2011, 12:50 PM
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AzNMpower32 AzNMpower32 is offline
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Here's a vid that illustrates the close gear ratios possible with 8-speeds. I guess this person from Poland has already driven past the break-in of 2000km..........

By the way, the vid is of an xDrive20d, 4 cylinder diesel with 184hp. At 100km/h (62mph) the car is already in 4th gear, 6th gear by the time it hits 160 (100mph). The 4-cyl peters out above that speed but er........that's probably not very legal in the US.



By the way, it's kind of amazing. 8 years ago, getting 184hp meant 6 cylinder petrol engines. Now a 4-cylinder diesel makes that kind of power. Yeesh makes my X3 seem ancient.
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  #10  
Old 01-28-2011, 01:27 PM
cubed cubed is offline
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Thats pretty dang good for a 4 cy diesel. 120mph +/-
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  #11  
Old 01-28-2011, 04:51 PM
06BMWX3 06BMWX3 is offline
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Thats pretty dang good for a 4 cy diesel. 120mph +/-
A F25 with the 3.5D would be so much win
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  #12  
Old 01-28-2011, 10:39 PM
Lotus7 Lotus7 is offline
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For anyone who's interested, here are the "Speed in Gears" charts for a 35i (with Sport Activity Package) and a 28i with the same size wheels & tires. The 8-speed transmission ratios are the same, but the final drive ratio is different. The 28i engine turns 9.9% faster in each gear.
Attached Files
File Type: pdf X3 35i Speed-in-gears.png.pdf (105.9 KB, 187 views)
File Type: pdf X3 28i chart.png.pdf (110.6 KB, 134 views)

Last edited by Lotus7; 01-28-2011 at 10:43 PM.
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  #13  
Old 01-29-2011, 08:33 AM
UncleJ UncleJ is offline
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We are getting so many speeds that it is just a matter of time before the end all be all transmission is a CVT
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  #14  
Old 01-30-2011, 07:39 PM
Lotus7 Lotus7 is offline
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Originally Posted by UncleJ View Post
We are getting so many speeds that it is just a matter of time before the end all be all transmission is a CVT
Some manufacturers would have you believe that we are already there.

CVT's are available from many makers and most of them are using wide ratio spreads to boost low range acceleration as well as to decrease revs (and improve economy) at cruising speeds. It's a continuously variable field (no pun intended)* just like the numbers game of wider and wider zoom ratios on "superzoom" digital cameras.

Some examples are:

Chrysler (Dodge, Jeep) low to high ratio spread = 5.9:1
Subaru (Outback, Legacy) low to high ratio spread = 5.76:1
Ford (Freestyle, Five-Hundred) low to high ratio spread = 6.20:1
GM (various models) 5.9:1
Honda: (various models) 5.30:1
Toyota (various models) 6.859:1

The BMW X3 8-speed compares favorably with a low gear to top overdrive spread of 7.02:1.

Can anyone tell I'm getting bored waiting for delivery of our new red X3?

* Well, maybe a little pun

Last edited by Lotus7; 01-31-2011 at 02:41 PM.
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