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Stealth.Pilot
09-30-2010, 09:26 PM
I was reading a recent review of the 750i comparing it to the LS460 Sport.

The stats on the 750i were impressive: 0-60 in 4.9 seconds, and 0.89G lateral acceleration on the skidpad (which is the same as the old 550i, and much better than the 0.84G I've seen in recent 2011 535i tests). The 750i beat the 535i in both acceleration and cornering grip!

Does anyone know if the 550i would beat the 750i, or the 750i really the sportier drive?

richschneid
10-01-2010, 05:11 AM
I was reading a recent review of the 750i comparing it to the LS460 Sport.

The stats on the 750i were impressive: 0-60 in 4.9 seconds, and 0.89G lateral acceleration on the skidpad (which is the same as the old 550i, and much better than the 0.84G I've seen in recent 2011 535i tests). The 750i beat the 535i in both acceleration and cornering grip!

Does anyone know if the 550i would beat the 750i, or the 750i really the sportier drive?

I have read 550i lateral g forces from 0.87 to 0.88. The 550i should outperfrom the 750i because it weighs less with the same tires. I think the differences you cite are related to the fact that the tests were performed by different people. The only way to accurately compare the two would be a head to head test by the same organization. In terms of the 535i test, check to see what tires were on the car. Lateral g force is highly dependent on the size and type of tires on the car.

BTW, 0.89g is pretty impressive for Goodyear Grand Touring run flat tires. Don't you think?

Munich77
10-01-2010, 06:36 AM
I totally agree - the 550i should have better performance than the 750i. The 550i has the same power train as the 750i and is lighter.

Stealth.Pilot
10-01-2010, 02:24 PM
It's a shame the 550i hasn't been tested by car and driver. I'm going to write to them and tell them their loyal subscribers want to see a 550i vs. Infiniti M56S vs. MB E550 test, and a 750i vs 550i test.

tadtaggert
10-01-2010, 02:48 PM
It's a shame the 550i hasn't been tested by car and driver. I'm going to write to them and tell them their loyal subscribers want to see a 550i vs. Infiniti M56S vs. MB E550 test, and a 750i vs 550i test.

You mean this? (http://www.caranddriver.com/reviews/car/10q3/2011_bmw_550i_automatic_and_manual-short_take_road_test)

Stealth.Pilot
10-01-2010, 05:19 PM
Exactly. So if we take the C&D test of the 550i you have these:
C/D TEST RESULTS (auto):
Zero to 60 mph: 4.8 sec
Zero to 100 mph: 11.0 sec
Zero to 130 mph: 19.0 sec
Street start, 5***8211;60 mph: 5.3 sec
Standing -mile: 13.1 sec @ 109 mph
Top speed (governor limited): 155 mph
Braking, 70***8211;0 mph: 170 ft
Roadholding, 300-ft-dia skidpad: 0.86 g

Then you look at the R&T test of the 750i:
http://www.roadandtrack.com/var/ezflow_site/storage_RT_NEW/storage/original/application/dfcc793dddc5338d9c596a2d5eb514e1.pdf

Maybe the R&T people are just better drivers. The C&D people did say that because of the lack of steering feel they had difficulty exploring the limits of the 550i.

Munich77
10-01-2010, 08:19 PM
There could be other variables as well - such as the temperature and location where the tests where conducted. Also, the mileage on the cars at the time of the test could make a difference. Let's not forget engine tolerances. Also, it looks like outside of 0-60, the 550i is alot faster.

chrischeung
10-01-2010, 10:34 PM
I totally agree - the 550i should have better performance than the 750i. The 550i has the same power train as the 750i and is lighter.

That's not true. The 550i has an 8 speed tranny, whereas the 750i is a 6 speed.

Stealth.Pilot
10-01-2010, 10:45 PM
That's not true. The 550i has an 8 speed tranny, whereas the 750i is a 6 speed.

I wonder why the 750i has a 6 speed. Seems totally insufficient for a 400hp 155mph car. I would never buy a car with a 6-speed again.

enigma
10-01-2010, 10:51 PM
I wonder why the 750i has a 6 speed. Seems totally insufficient for a 400hp 155mph car. I would never buy a car with a 6-speed again.

Please do share and enlighten us why 6 speed isn't enough? And how many gears would be considered enough? 8? 10? 20? 60? How about bazillion?

solstice
10-01-2010, 10:52 PM
With the level of torque the TT V8 produces and the broad band where it's available I think a 6-speed might be faster due to less interruption while shifting. An 8-speed will be more fuel efficient though.

tadtaggert
10-01-2010, 11:00 PM
With the level of torque the TT V8 produces and the broad band where it's available I think a 6-speed might be faster due to less interruption while shifting. An 8-speed will be more fuel efficient though.

Nope, we can go through all the gear ratios if you want and see how much of the power is getting to the ground. You're still moving >4000 lbs.

Stealth.Pilot
10-01-2010, 11:05 PM
My impression of the 8 speed is that it adds higher ratios. Doesn't affect 0-60, but it allows you to cruise at 125mph at 1700 rpm. At least that's the way it works on my car.

solstice
10-01-2010, 11:11 PM
Nope, we can go through all the gear ratios if you want and see how much of the power is getting to the ground. You're still moving >4000 lbs.

I'm not saying that you aren't getting more power to the ground while in gear but for an instant there is almost no power to the ground while shifting and if you need to shift one more time to reach 60mph you can loose more than you gain from slightly higher power output when in gear.

tadtaggert
10-01-2010, 11:19 PM
If you remember the 550i vs S6 vs E550 vs XF test by AutoBild some time ago, most of these questions came up, were argued and answered.

550i Ratios - 1st: 4.71, 2nd: 3.14, 3rd: 2.11, 4th: 1.67, 5th: 1.29, 6th: 1.00, 7th: 0.84, 8th: 0.67
S6 Ratios - 1st: 4.171, 2nd: 2.340, 3rd: 1.521, 4th: 1.143, 5th: 0.867, 6th: 0.691

The BMW 8speed does not just add a gear or two.

tadtaggert
10-01-2010, 11:20 PM
I'm not saying that you aren't getting more power to the ground while in gear but for an instant there is almost no power to the ground while shifting and if you need to shift one more time to reach 60mph you can loose more than you gain from slightly higher power output when in gear.

That will be true with a manual, or even to a lesser extent with the non-sport auto. But going 0-60 in the 550i, how many gear changes do you think there are?

solstice
10-01-2010, 11:29 PM
That will be true with a manual, or even to a lesser extent with the non-sport auto. But going 0-60 in the 550i, how many gear changes do you think there are?

Why don't you tell me? I know that the Veyron does 0-60 in about 2.5s in first gear. I think they would have made that 2 changes if it improved the time. So tell me how many changes there are in the 550i and the 750i to 60mph?

tadtaggert
10-01-2010, 11:36 PM
Why don't you tell me? I know that the Veyron does 0-60 in about 2.5s in first gear. I think they would have made that 2 changes if it improved the time. So tell me how many changes there are in the 550i and the 750i to 60mph?

That was a rhetorical question actually.

solstice
10-01-2010, 11:39 PM
This is what I've been tought, narrow power band -> many gears since the ability to stay in the power band trumps the loss at shifts. Broad power band -> fewer gears needed to stay in the power band and shifts within the power band is loss.

tadtaggert
10-02-2010, 12:15 AM
This is what I've been tought, narrow power band -> many gears since the ability to stay in the power band trumps the loss at shifts. Broad power band -> fewer gears needed to stay in the power band and shifts within the power band is loss.

So let's assume that we have a different engine in the 5, it has an even broader power band and has max hp and max torque from 500 rpm to 8000 rpm. Car weighs the same. Max HP is 100 hp and max Torque is 200.

While what you say is generally true, you still have to take into account the reality of the physics, where acceleration is a function of both force and mass. Mass we can't change, force is a function of the output of the engine, the transmission and final drive ratio.

400 hp may seem like a lot of power, but in an M3 it's one thing and in an F10 it's another.

I will grant you that you could design a transmission with 6, hell even 4 gears that would give you 0-60 faster, but it's still dependent on the ratios, and anything past 60 would suck eggs. There are a lot of fairly technical posts on germancarforum.com, people many times smarter than I, take a look.

For the 550i the transmission is pretty much where it needs to be.

solstice
10-02-2010, 12:48 AM
I don' think we are discussing if the transmission is "where it needs to be". It's raw performance numbers that are discussed and for outright acceleration a six speed like in the 750i might give an advantage to a torque monster as the TT V8 in some categories vs. and 8-speed which I suspect is mainly designed for EPA numbers when it comes to the 550i and not to optimize drag race performance.

richschneid
10-02-2010, 05:21 AM
Acceleration is determined by the fundamental laws of physics including.

Force = mass times acceleration
Work = Force times distance
Power = Work per unit time
Torque = force times radius

Low speed acceleration is mostly determined by engine torque and torque multiplication by the gears and the final drive. At higher speeds the torque multiplication is less and the negative forces acting on the car are greater, ie wind resistence is greater because the air molecules have to be accelerated to a greater velocity and the kinetic energy imparted to those molecules is dependent on the square of the velocity. This is called drag. In addition at higher speeds all the frictional forces opposing acceleration are increased. So, at high speeds maximal hp becomes the determining factor in acceleration.


In general an 8 speed transmission will be faster 0-60 than a six speed because the torque multiplication is greater in 1st and 2nd gears. This will be somewhat counterbalanced by a lower final drive ratio but even factoring in this the total torque multiplication in 1st and 2nd gear will still be larger with an 8 speed.

In BMWs the maximum speed in second gear is usually around 62-68 mph. Therefore in a 0-60 sprint there will be only one gear change. In the 8 speed sport automatic tranmission this shift is faster than either the 6 speed or the standard 8 speed auto. Since we know from multiple tests including the current C&D test of the 550i and prior tests of the E60 M5 with manual and SMG that the stick shift is slower, we can surmise that manual shifting prolongs the 0-60 times in high powered V-8 BMWs.

In addition, in high torque vehicles 0-60 is faster in cars with AWD because more of the useful torque can be applied to the pavement without wheel slippage. This is comfirmed by the already published tests comparing the 0-60 times in the 750i vs the 750i xDrive and the Porsche Panmera AWD vs the rear drive version in which the AWD versions with the same engine were faster 0-60 than the RWD versions despite the additional weight of the AWD versions. In other words, the maximum amount of torque that can actually be utilized to accelerate the car is limited by the coefficient of friction between the tires and the pavement and the size of those tires. Four tires can simply transmit more torque than two tires can. At higher speeds the torque multiplication is less and all the torque can easily be tranmitted by just the two rear tires without slippage. So, at higher speeds, the RWD drive cars will accelerate faster than the AWD cars because the RWD cars weigh less.

bklyn550
10-03-2010, 09:46 AM
.4 second diff in favor of 550i with the zf transmission....the 750 is over 5 seconds 0 to 60

nosnoop
10-03-2010, 09:48 PM
.4 second diff in favor of 550i with the zf transmission....the 750 is over 5 seconds 0 to 60

Official 0-100km/h for German specs BMW:
750i - 5.2s (6-speed auto)
550i - 5.0s (8-speed auto)

solstice
10-03-2010, 11:07 PM
I got curious and did a quick rough check on my F10 535i using the speedometer and manual shifts and it seemed to me ( didn't want to keep it at redline for more than a moment ) that my car redlines at around 57 mph in 2nd gear. That can hardly be optimal for 0-60 times. The 550i is probably differently geared so it doesn't mean much for 550i vs. 750i especially since I also don't know where the 750i redlines in 2nd.

tadtaggert
10-04-2010, 08:24 AM
I got curious and did a quick rough check on my F10 535i using the speedometer and manual shifts and it seemed to me ( didn't want to keep it at redline for more than a moment ) that my car redlines at around 57 mph in 2nd gear. That can hardly be optimal for 0-60 times. The 550i is probably differently geared so it doesn't mean much for 550i vs. 750i especially since I also don't know where the 750i redlines in 2nd.

What size wheels are on your car?

solstice
10-04-2010, 08:58 AM
What size wheels are on your car?

The 19' from ZSP with the run flats that comes with it.

tadtaggert
10-04-2010, 09:29 AM
The 19' from ZSP with the run flats that comes with it.

With the auto, 535i with 19" tires, you'll probably have to make two shifts, top speed in 2nd is somewhere around 50mph.

With the manual, top speed in 2nd is around 71 mph.

So an extra shift, but as we've already seen in the C&D numbers (550i auto and manual, same gear ratios) the auto is quite a bit faster.

So your post/position has more merit.

EDIT: To be precise, what does the 535i redline at? I just used the same as the 550i (6750) above, should be close.

solstice
10-04-2010, 10:27 AM
With the auto, 535i with 19" tires, you'll probably have to make two shifts, top speed in 2nd is somewhere around 50mph.

With the manual, top speed in 2nd is around 71 mph.

So an extra shift, but as we've already seen in the C&D numbers (550i auto and manual, same gear ratios) the auto is quite a bit faster.

So your post/position has more merit.

EDIT: To be precise, what does the 535i redline at? I just used the same as the 550i (6750) above, should be close.

Auto and manual are really hard to compare due to the big human factor. I.e who is doing the shifting. I'm not at all curious about that comparo. My 535i redlines at 7000 that's probably why it looks more like 55 mph than 50 mph at redline. To get back to this threads subject I wonder where the 6-speed auto in the 750i redlines in 2nd?

Stealth.Pilot
10-04-2010, 12:46 PM
What size wheels are on your car?

Actually tire size is more pertinent than wheel size, since often people reduce tire wall when increasing wheel size to keep overall radius constant and ensure speedo remains accurate, avoid rubbing, etc.