Importance of weight savings: Allan McNish - 45kg is 1sec extra on Barcelona F1 track

[Boss330]

The 80kg weight saved over the E9x has been debated, to the extent of wether it's feelable and makes a genuine difference to lap times/cornering etc.

Some argue that 80kg is a tiny amount, others that 80kg should make a difference.

I found this video where former F1 driver Allan McNish talks about the new F1 cars and turbocharged engines quite interesting. If you are interested in F1 and how it's different to drive a high torque engine on track then listen to the start as well.

But, look and listen to his response on the question wether the added 48kg to the minimum weight limit is feelable at 12:00

He says that 45kg is very noticeable on his 925kg Audi LeMans racer, so it will definitely be feelable on a 600kg F1 car. Goes on to say that if you add 45kg in the trunk of your car and "thrash it on the circuit, you will feel it".

And a added 45kg equals an increase of 1 sec in lap time (assume he is talking about a F1 car here).

So, according to a ex F1 racer I guess that 80kg saved should be of significance

[swamp2]

The difference in the new car is right about equal to a passenger. I think anyone will agree that one can feel the effect of a passenger in a straight line in just about all street performance cars. So the effect will be well measurable on a track.

45/925 is about 5%
80*(2.204)/3550 is also right about 5%

However, again, what really matters is power to weight and both power and weight are changing in the new car. From prior work here on the forum we've found that there is a 17X change in lap time on the Nordeschleife times the change in weight/power (kg/hp). Of course this does not count for improvements in CG, tires, suspension, etc. Thus:

((1678/414)-(1610/450))*17 = 8 seconds

Now that is on an 8 minute track so about 1 sec/min.

Hmmm what was BMWs claim, better than 10 seconds. No surprise given the variables not in this model.

[CanAutM3]

Tidbit: 40kg is the weight penalty of DCT over 6MT.

[RealStig]

Originally Posted by CanAutM3

40kg is the weight penalty of DCT.

Thats a lot. So you basically lose half the weight savings if you go with DCT? That's terrible

[ybbiz34]

Have the F80 M3 and F83 M4 been independently weighed yet?

Or are we just taking the manufacturer-provided numbers as the gospel?

[CanAutM3]

Originally Posted by ybbiz34

Or are we just taking the manufacturer-provided numbers as the gospel?

I believe that is the only info we have to go with...

[absoluteis350]

Good information... Because the lower weight will save me loads of time on my daily commute around the Barcelona F1 circuit.

[CanAutM3]

Originally Posted by RealStig

Thats a lot. So you basically lose half the weight savings if you go with DCT? That's terrible

Well, yes and no...

The weight penalty was 20kg on the E9X, it is now 40kg on the F8X. So in reality you are loosing about a quarter of the claimed weight saving (the latest info I have seen is -83kg/-63kg for the 6MT/DCT 2 door and -85kg/-65kg for the 6MT/DCT four door).

[ybbiz34]

Originally Posted by CanAutM3

I believe that is the only info we have to go with...

The reason I ask is that the manufacturer-provided dry curb weight numbers tend to be a little on the lean side.

I'd like to see what a well-equipped, fueled-up F80 or F82 ends up weighing.

[CanAutM3]

Originally Posted by ybbiz34

The reason I ask is that the manufacturer-provided dry curb weight numbers tend to be a little on the lean side.

I'd like to see what a well-equipped, fueled-up F80 or F82 ends up weighing.

Agreed, I am with you regarding the absolute weight of the cars. We'll only know for sure once somebody gets them on a scale.

However, using weight differences, we can still make good assumptions (DCT vs 6MT for example).

[solstice]

Given the details given of weight and having the numbers stated in the EU standards I would take them as accurate at this point in time. The 40kg difference between MT and DCT is eye opening though if it's 40kg. That's a lot of weight in a car where weight saving has been the number 1 goal. Luckily it's pretty much perfectly located for minimum negative impact, it actually helps with lowering CG but still.

[ybbiz34]

Originally Posted by CanAutM3

Agreed, I am with you regarding the absolute weight of the cars. We'll only know for sure once somebody gets them on a scale.

However, using weight differences, we can still make good assumptions (DCT vs 6MT for example).

Very true. We can only work with what we've got for now.

I hope the weight info. turns out to be accurate as it is one of the most appealing aspects of the new generation.

[RealStig]

In the other 6MT vs DCT thread a lot of people are saying how bad the MT is and how the turbo engine is not optimized for it. It has long throws and clutch is soft and so on. My point is, if this is the case, why didnt BMW improve the DCT weight? Whats the point of advertising 80kg weight savings when half of that requires you to use MT which is not suitable for the car? Am I missing something here?

[Boss330]

Originally Posted by RealStig

In the other 6MT vs DCT thread a lot of people are saying how bad the MT is and how the turbo engine is not optimized for it. It has long throws and clutch is soft and so on. My point is, if this is the case, why didnt BMW improve the DCT weight? Whats the point of advertising 80kg weight savings when half of that requires you to use MT which is not suitable for the car? Am I missing something here?

How can they say that when no one has driven the F8x MT...

And the MT in the F8x is NOT the same as in the E9x. It's a modified version of the one from the 1M.

[CanAutM3]

Originally Posted by RealStig

In the other 6MT vs DCT thread a lot of people are saying how bad the MT is and how the turbo engine is not optimized for it. It has long throws and clutch is soft and so on. My point is, if this is the case, why didnt BMW improve the DCT weight? Whats the point of advertising 80kg weight savings when half of that requires you to use MT which is not suitable for the car? Am I missing something here?

You have it wrong again. You don't loose half of the weight savings with DCT. Going from a DCT E92 to a DCT F82 there is an advertised 63kg weight reduction as opposed to a 83kg reduction from 6MT to 6MT.

Your point would be true when going from a 6MT E9X into a DCT F8X, but that is not an apples to apples comparison.

The 6MT in the E9X is a carry over from the E46 which dates back to 2001, a rather older design. My guess regarding the the 6MT evolution is that BMW probably figured it was time to modernize the gearbox; hence the reduced 12kg. As for the DCT, I believe that for cost reasons, they use the same unit as on the F1X M5/M6, which needed a rather beefed up version of the DCT to deal with the extra torque; hence the added 8kg.

[solstice]

Originally Posted by RealStig

In the other 6MT vs DCT thread a lot of people are saying how bad the MT is and how the turbo engine is not optimized for it. It has long throws and clutch is soft and so on. My point is, if this is the case, why didnt BMW improve the DCT weight? Whats the point of advertising 80kg weight savings when half of that requires you to use MT which is not suitable for the car? Am I missing something here?

The rumors has it that BMW contemplated an even heavier DCT by adding gears but shelved that idea just because of weight and size concerns. A DCT is not easy/cheap to rebuild, it's also not a BMW design, they source it and it was just recently updated for the M5. I'm sure we'll see lighter versions in the next iteration M3s.

BMW MTs are traditionally not very crisp. They often have long trough, rubbery feel and a very long high clutch engagement. I've learned to like them in the 5 BMW MTs I've owned but never loved them. The MT in the 1M is supposedly and reportedly a whole different story with crisper shorter troughs and quicker more authorative clutch. This is what they've worked and improved for the F8X. I have high hopes. Don't mind the "doesn't fit the engine" talk. It's more about an overall fit for the car. The F8X is supposedly a rather light car with some race character, it should fit like a glove. Also if it fits the 1M it should fit the F8X, very similar cars.

The DCT is just great in any car except for luxury cruisers and utility vehicles where a silky smooth AT is better IMO.

[CanAutM3]

Originally Posted by solstice

The rumors has it that BMW contemplated an even heavier DCT by adding gears but shelved that idea just because of weight and size concerns. A DCT is not easy/cheap to rebuild, it's also not a BMW design, they source it and it was just recently updated for the M5. I'm sure we'll see lighter versions in the next iteration M3s.

BMW MTs are traditionally not very crisp. They often have long trough, rubbery feel and a very long high clutch engagement. I've learned to like them in the 5 BMW MTs I've owned but never loved them. The MT in the 1M is supposedly and reportedly a whole different story with crisper shorter troughs and quicker more authorative clutch. This is what they've worked and improved for the F8X. I have high hopes. Don't mind the "doesn't fit the engine" talk. It's more about an overall fit for the car. The F8X is supposedly a rather light car with some race character, it should fit like a glove. Also if it fits the 1M it should fit the F8X, very similar cars.

The DCT is just great in any car except for luxury cruisers and utility vehicles where a silky smooth AT is better IMO.

The 1M was mostly a parts bin car and I don't think it had a unique/bespoke transmission. IIRC, the 1M used a 135/335 transmission (same gear ratios) with better synchros and improved components. IMO, the 6MT in the F8X is simply an evolution of the current BMW 6MT.

[Boss330]

Originally Posted by swamp2

The difference in the new car is right about equal to a passenger. I think anyone will agree that one can feel the effect of a passenger in a straight line in just about all street performance cars. So the effect will be well measurable on a track.

45/925 is about 5%
80*(2.204)/3550 is also right about 5%

However, again, what really matters is power to weight and both power and weight are changing in the new car. From prior work here on the forum we've found that there is a 17X change in lap time on the Nordeschleife times the change in weight/power (kg/hp). Of course this does not count for improvements in CG, tires, suspension, etc. Thus:

((1678/414)-(1610/450))*17 = 8 seconds

Now that is on an 8 minute track so about 1 sec/min.

Hmmm what was BMWs claim, better than 10 seconds. No surprise given the variables not in this model.

Interesting! As you say, CG etc will also influence lap times. But according to your estimate it seems that the overall improvement won't be much more than the 10 sec quoted by BMW (even though 10+ sec isn't bad in itselves).

[solstice]

Originally Posted by CanAutM3

The 1M was mostly a parts bin car and I don't think it had a unique/bespoke transmission. IIRC, the 1M used a 135 transmission (same gear ratios) with better synchros and improved components. IMO, the 6MT in the F8X is simply an evolution of the current BMW 6MT.

As long as it has evolved passed the issues of the past I'm perfectly fine with that. I.e it doesn't matter if it was all new or improved from that perspective. That said, it's like the EPS, when you never experienced a really good one from BMW you would be a fool not to test it before ordering. It needs to be very good not just acceptable to lure me from the DCT.

[CanAutM3]

Originally Posted by Boss330

even though 10+ sec isn't bad in itselves.

10 sec on an 8min lap would roughly translate to 2,5sec on a 2 min lap.

If I can get 2.5 sec at my local track, I'll be very happy

[CanAutM3]

Originally Posted by solstice

As long as it has evolved passed the issues of the past I'm perfectly fine with that. I.e it doesn't matter if it was all new or improved from that perspective. That said, it's like the EPS, when you never experienced a really good one from BMW you would be a fool not to test it before ordering. It needs to be very good not just acceptable to lure me from the DCT.

I am with you, I also ordered my M4 with a DCT.

I am just pissed that I now have an 89lb penalty compared to a 6MT. You'll probably hear me grumbling for a little while before I finally get over it

[/// M sa]

Originally Posted by CanAutM3

10 sec on an 8min lap would roughly translate to 2,5sec on a 2 min lap.

If I can get 2.5 sec at my local track, I'll be very happy

2.5 seconds doesn't sound much does it? Until you get your tail handed to you and the 2 seconds feel like an eternity. Been there done that :-)