1M Diff and Transmission Specs

[Madozu]

You're right ... curb weight was too low. Just to mention: it was the same (wrong) value for both 1M simulations. Wrong but fair

I fully agree that the area under the HP curve is important.

What the CarTest simulations also don't take into account is the fact that an FI engine increases torque at a quite limited rate (turbos need to spool up) and therefore in low gears peak torque is more at the upper rev-band.

[swamp2]

Originally Posted by Madozu

Just played around with my (quite old) version of CarTest 2000. As Swamp showed, the 50Nm overboost doesn't make a huge difference ... but setting max. torque at 1500 rpm or 4500 rpm makes quite a bit of a difference. I was using identical data of a 1M with one exception:

• BMW 1M (LOW) has max. torque at 1500 rpm
• BMW 1M (HIGH) has max. torque at 4500 rpm

Cool. Keep in mind that the default values for both the parasitic losses and shift times for MT are all quite a bit off. Less relevant when you want to do A vs. B comparisons which is what CarTest is perfect for, but much more important if you want to get absolute predictions. Lastly the weights should be Curb minus driver since CarTest has a separate input for the driver weight. I actually had this wrong in my prior sims as well!

BMW has said 332 ft lb from 1500-4500 rpm. If you allow the actual peak to be all the way up at 4500 (or simply truly 100% flat across this band) you'll have a really hard time having a truly physically realizable power and torque curve and one that has the peak hp quoted by BMW.

[swamp2]

Originally Posted by Pete_vB

Good example of why the shape of the dyno curve is critical, as area under the HP curve, not peak hp to weight, is critical.

Sure it matters, but again NOTHING matters as much as power to weight. Not the peak torque to the wheel per weight nor shape of the torque curve nor anything else...

[tarheel91]

Originally Posted by swamp2

Sure it matters, but again NOTHING matters as much as power to weight. Not the peak torque to the wheel per weight nor shape of the torque curve nor anything else...

No. Power to weight gives you only an instant value, that is, power to weight at max power. You can derive power to weight throughout the entire RPM band using the horsepower curve. What's most important is definitely the effective torque under the curve, mostly in the upper part of the rev range (i.e. from whatever RPM you shift into 2nd at on).

Effective torque at the wheels is actually more useful than horsepower, as it considers the actual gearing and tire size. Horsepower is great for a rough idea of how a car with a given weight will accelerate, but it's not as precise as torque at the wheels.

P.S. Early on you were talking about centrifugal forces causing tire diameter to expand, but that has no where near the effect that deformation from the weight of the car (i.e. contact patch) and the longitudinal slip ratio (The tire bunches up right before the contact patch and stretches after it when being acted on by a longitudinal force). The tire size is actually always smaller than it's static diameter (although it gets closer the higher the speed). Calculating this stuff, though, requires much more info than you have, and ultimately it's not worth it when you're using such a basic simulator.

You're better off making sure you've got the basic stuff right; worry about the complicated stuff much later (same goes for parasitic loss; it's much more complicated than you're assuming it to be, and you'll probably be way off).

[Pete_vB]

Originally Posted by tarheel91

Effective torque at the wheels is actually more useful than horsepower, as it considers the actual gearing and tire size. Horsepower is great for a rough idea of how a car with a given weight will accelerate, but it's not as precise as torque at the wheels.

Exactly. And torque at the wheels divided by weight, as I posted initially, is my preferred why to compare, as- it quickly lets you visualize the important variables...

Originally Posted by tarheel91

P.S. Early on you were talking about centrifugal forces causing tire diameter to expand, but that has no where near the effect that deformation from the weight of the car (i.e. contact patch) and the longitudinal slip ratio (The tire bunches up right before the contact patch and stretches after it when being acted on by a longitudinal force). The tire size is actually always smaller than it's static diameter (although it gets closer the higher the speed). Calculating this stuff, though, requires much more info than you have, and ultimately it's not worth it when you're using such a basic simulator.

This is correct for radial street tires, which are designed specifically not to increase in diameter. Bias plys and especially drag tires are different, however, and do have some expansion with centrifugal forces. Hoosier has some stuff about this on their site- they can be talking inches for drag tires, however the car must have additional fender clearance, etc for this.

For street radials this isn't an issue, and I turned that off in my sim.

[Pete_vB]

Originally Posted by swamp2

Sure it matters, but again NOTHING matters as much as power to weight. Not the peak torque to the wheel per weight nor shape of the torque curve nor anything else...

Not true, as I think the exercise has illustrated.

As far as I can tell you had this concept in your head, and when I posted results showing otherwise you strongly disagreed. What this shows, though, is that it's the area under the curve in the particular gear you are using that is important. In 1st gear the whole rev range is used, so while the peak power to weight favors the M3, the average power to weight of what's used favors the 1M due to the huge low-end torque.

In higher gears a smaller and smaller slice of the rev range is used, and there the average and peak power to weight ratios converge, so there a car with a higher peak power to weight has a more of an advantage... Of course if you're driving a caterham with an awsome power to weight ratio, higher gears are also where aero begins to catch up, so it's not that simple either.

[tarheel91]

Originally Posted by Pete_vB

Exactly. And torque at the wheels divided by weight, as I posted initially, is my preferred why to compare, as- it quickly lets you visualize the important variables...


This is correct for radial street tires, which are designed specifically not to increase in diameter. Bias plys and especially drag tires are different, however, and do have some expansion with centrifugal forces. Hoosier has some stuff about this on their site- they can be talking inches for drag tires, however the car must have additional fender clearance, etc for this.

For street radials this isn't an issue, and I turned that off in my sim.

It occurs on any car, it's just not as much of an issue on street tires. The real issues are longitudinal slip under acceleration (or any kind of longitudinal force) and effective radius vs. rolling radius. The former can be responsible for up to a .5% reduction of radius (although it usually decreases up top as rolling resistance works in the opposite direction of acceleration). The latter depends on load, vertical stiffness, etc. There's way to many variables to count. It's effect is a little more obvious. Basically, the bottom of your tire is flat, and the distance between the road and the center of your wheel is shorter than the radius of the tire. However, the rotation doesn't work that cleanly (a point right at the edge of the contact patch is actually very close to the rolling radius in terms of distance from the center, whereas a point in the center is very close to the loaded radius), and it actually ends up working like the car is rotating around a point below the ground. Regardless, the effective radius is significantly shorter than the rolling radius, and this effect becomes more pronounced at higher speeds due to air resistance adding more load.

Oh, and the effective radius is closer to the loaded radius the fatter the tire (and both of these cars have relatively fat tires for street cars).

Long story short, this stuff has much more of an effect than tire expansion due to centripetal acceleration.

[Dackelone]

Since we are talking about the diff (LSD) and transmision... I wonder IF BMW will say that the 1M needs to have its trans and diff fluids (AND oil and filter) changed at 1,200 miles - first service.

BMW still requires this for other M models like the M3. I have also seen on the M3 forum where guys were doing ED with their M3's and had the service done at a German dealer. Even though its free in the states over here the dealers charge about 500 euros ($700) for this first "oil" service. I also saw where BMW NA will reimburse you IF you pay for this service over here while on ED.

So... I wonder what the //M stance on this will be? Since the car has a N54 but has a LSD and different trans. ?


Dackel

[technik330]

Originally Posted by swamp2

Sure it matters, but again NOTHING matters as much as power to weight. Not the peak torque to the wheel per weight nor shape of the torque curve nor anything else...

I've read several of your posts, in various threads, and it appears you're extremely skeptical of the 1M, even insecure about its very existence.

[Pete_vB]

Originally Posted by tarheel91

Long story short, this stuff has much more of an effect than tire expansion due to centripetal acceleration.

My point is that statement is not true of drag tires/ wrinkle walled slicks. They can grow in diameter 30% when designed too. For street radials I agree completely.

[tarheel91]

Originally Posted by Pete_vB

My point is that statement is not true of drag tires/ wrinkle walled slicks. They can grow in diameter 30% when designed too. For street radials I agree completely.

Oh, oh, I misread. I thought you meant the deformation due to the scrunching up right before the contact patch only happened on drag radials. My bad.

Drag radials are completely different beasts.

[Kurt_OH]

Originally Posted by tarheel91

No. Power to weight gives you only an instant value, that is, power to weight at max power. You can derive power to weight throughout the entire RPM band using the horsepower curve.

Exactly.

What's most important is definitely the effective torque under the curve, mostly in the upper part of the rev range (i.e. from whatever RPM you shift into 2nd at on).

I won't say your statement is wrong, but it's misleading/misled. HP is what matters at ALL RPM, at ALL speeds, and at ALL gearings. IN fact, HP is a MORE accurate measure - you don't even have to worry about, estimate or concern yourself with gearing - it is a constant from the crank right through to the tire.

The ONLY curve you need bother with is HP; torque naturally relates, but isn't "it".

[GotM]

Originally Posted by Kurt_OH

The ONLY curve you need bother with is HP; torque naturally relates, but isn't "it".

I think I would say, if you know one then you can figure out the other. Since Hp is a function of torque and rpm, if you know one you can calculate the other. Knowing this, is one really more important than the other?

[Pete_vB]

Originally Posted by Kurt_OH

IN fact, HP is a MORE accurate measure - you don't even have to worry about, estimate or concern yourself with gearing - it is a constant from the crank right through to the tire.

How do you calculate the HP at a given speed without taking into account the gearing? Do you have examples of the curves you're thinking about?

[Kurt_OH]

Originally Posted by Pete_vB

How do you calculate the HP at a given speed without taking into account the gearing? Do you have examples of the curves you're thinking about?

HP is not affected by gearing.

[Kurt_OH]

Originally Posted by GotM

I think I would say, if you know one then you can figure out the other. Since Hp is a function of torque and rpm, if you know one you can calculate the other. Knowing this, is one really more important than the other?

I agree with all of what you said: effectively you're talking about the same thing either way: area under the curve. The only real difference is that HP is the same measured at the crank and the wheel; torque varies based upon all the gears between the engine and the road.

So to say "torque matters for X, whereas HP matters more for Y" is absolute nonsense.

[GotM]

I think if you look at HP alone you are missing part of the information. Meaning, I think it would be hard to compare 2 different vehicles on a WOT run just looking at a HP curve as it runs through the gears.

[tarheel91]

Originally Posted by Kurt_OH

Exactly.




I won't say your statement is wrong, but it's misleading/misled. HP is what matters at ALL RPM, at ALL speeds, and at ALL gearings. IN fact, HP is a MORE accurate measure - you don't even have to worry about, estimate or concern yourself with gearing - it is a constant from the crank right through to the tire.

The ONLY curve you need bother with is HP; torque naturally relates, but isn't "it".

Nope. Horsepower is a made up value. It holds no real meaning. Horsepower is simply a trick way to take into consideration gearing (without actually knowing the gearing) because the higher the rpm "y" amount of torque is achieved at, the higher the gearing that can be used to achieve that torque at speed z. It's a relative measure of power, that's it. If you want to oversimplify things and argue that work/time is all that matters, that ignores that you're not just trying make power. You're trying to accelerate as fast as possible within a certain ranges of speeds.

F=ma. In a rotational sense, T=m*alpha (angular acceleration). For a given mass, it is instantaneous torque that determines how fast that object accelerates at any given second. Torque at the wheels = engine torque * gearing/tire size. Torque at the wheels, which is directly related to acceleration, is directly related to gearing. That means acceleration is directly related to gearing. Ultimately it's the area under the torque at the wheels curve vs. speed which determines how fast something accelerates.

[Kurt_OH]

Originally Posted by tarheel91

. . . the area under the torque at the wheels curve vs. speed

The definition of Horsepower.

[Kurt_OH]

BUT, we're kinda headed off topic anyway. Originally the discussion was about the gearing specs of the 1M. Then I commented regarding my preference for a higher numerical final drive ratio.

I've participated as much as anyone else in the tangent, but I'd prefer to get back to the prior discussion if possible. Another poster stated that the higher numerical gear would result in slower acceleration. I continue to disagree, especially when we're talking about WITHIN a gear, or across a contrived set of time/speed/distance measurements that favor the lower numerical gearing.

[Pete_vB]

Originally Posted by Kurt_OH

HP is not affected by gearing.

HP at a given speed is. I.E. what is the 1M's hp at 60 mph?

[Pete_vB]

Originally Posted by Kurt_OH

Another poster stated that the higher numerical gear would result in slower acceleration. I continue to disagree, especially when we're talking about WITHIN a gear, or across a contrived set of time/speed/distance measurements that favor the lower numerical gearing.

You may be referring to me? Start a now thread and we can discuss...