acceleration times

[aotiko]

On BMWs website they have 0-60 times. I was wondering with the automatic transmission times is if those are made by just accelerating normally or if they are using the tiptronic system. Because I thought that manual runs the same times as tiptronic.

[Ohrid]

The major difference for acceleration times is the gearing ratio.
Due to the leasuirly nature of an auto, the usulally have taller gearing, thus the spread between each shift is greater.

[jinmon]

Sport mode on the steptronic also makes a significant difference in 0-60 times with the automatic.

[GRD-4-3L]

As Ohrid mentioned above, manual is faster than automatic.

For 0-100km/hr,

330Ci Specifications:

Manual is listed in BMW brochure as 6.8 seconds.

Automatic is listed as 7.4 seconds.

Automatic as also 35kg heavier than manual.

Manual gear ratios are 4.35 > 2.50 > 1.66 > 1.23 > 1.00 > 0.85 (2.93 final)
> 4.35 x 2.93 = 12.7

Automatic gear ratios are 3.67 > 2.00 > 1.41 > 1.00 > 0.74 (3.38 final)
> 3.67 x 3.38 = 12.4

Manual will definitely be faster in 0-100km/hr or 0-60mph

[Ohrid]

Manual gear ratios are 4.35 > 2.50 > 1.66 > 1.23 > 1.00 > 0.85 (2.93 final)
> 4.35 x 2.93 = 12.7

Automatic gear ratios are 3.67 > 2.00 > 1.41 > 1.00 > 0.74 (3.38 final)
> 3.67 x 3.38 = 12.4


hey GRD-4-3L, can u explain what you meant by these figures (12.7 and 12.4)

I understand the gear and final ratios, and how to calculate at what speed the vehicle travels at certain RPM and gear.

Thanks

[GRD-4-3L]

12.7 = every 12.7 engine turns, rear wheel will turn once for manual gear. This means more engine torque is available for acceleration.

12.4 = every 12.4 engine turns, rear wheel will turn once for automatic gear. This means although torque available for acceleration is slightly less than manual gear, you will reach slightly higher speed before changing to 2nd gear.

If you want to calculate vehicle speed,

Say, at maximum 1st gear speed or engine RPM of 6500.

Engine speed is 6500.

Through gear box, you have 6500/4.35 = 1494 RPM

Put 1494 RPM through final drive ratio = 1494 / 2.93 = 510 RPM at wheel or 8.5 tire rotations per second (makes sense). If you want to do this quickly, 6500/12.7455 = 510 RPM.

Now, 18" wheel with 255 wide 35 profile will give you 18x25.4 + 255x0.35x2 = wheel diameter of 457mm+179mm=636mm or 0.636m

Rotate 0.636 m diameter wheel 510 times per minute or 510x60=30600 times per hour = 0.636x3.14x30600=61109m/hour or 61 km/hr. Fun, eh?

Now take the torque curve of the engine, put it through gear, calculate the force pushing on the car (taking into account rotational inertia of the wheels, suspension jounce, frictional losses, aerodynamic losses, etc) and you can estimate 0-60mph time!

I'm sure you could put the formulae into Excel sheet and do it much faster . . .

[Ohrid]

yeh, i actually did put it in excel a while ago, but used a slightly different formulas. its mad fun, working out each cars' speed at a certain rpm/gear.

[Gulelin]

Remember too that the numbers on BMW's website are conservative; actual tested numbers(for manuals anyway) for 0-60 are lower.