Jeff Winchell wrote:
[...]
> Some people feel the suspension and weight distribution advantages of
> the M3 give it the ability to launch quicker.
The multi-link rear suspension helps it put down power in a corner or
over bumps better than a solid axle. It actually hurts acceleration in a
straight line on relatively smooth pavement. Nothing better for hard
launches than a solid axle which yields no camber and toe changes under
acceleration. Of course, that's _IF_ you can keep the axle under
control. If you're getting axle tramp there's a flaw in the setup of the
car or suspension design. If you're getting excessive wheelspin, you're
launching too hard or not getting enough weight transfer (shocks too
stiff?). Weight distribution I can buy, but a solid rear axle in and of
itself is not a liability for a drag launch - in fact it's a benefit.
> My car has 3.37 first gear ratio, 3.27 ring and pinion gear ratio, and
> depending on the RPM, 250-300 lb-ft of dyno measured SAE corrected
> RW torque. That comes out to between 2750 and 3000 lb ft of torque
> available to my 315 tires.
I get ~3300 for your car (300*11.02), but no matter.
> I don't know what the transmission and ring and pinion gear ratios are
> on the typical ESP M3s out there (can you fill me in?), but I have to
> believe that the torque #'s come out WAY less.
1st gear is a steep 4.20. Only legal gear sets in SP are 3.15, 3.23, or
3.38. The max multiplier would therefore be ~14.2. Max RW torque in SP
trim is ~220 giving a max applied torque of 3124. Bob's car weighs about
3150 w/driver? That's almost 1:1... slightly better than your car on
paper. I don't think Bob uses the 3.38 much though... guess it depends
on the course. With the 3.15 (stock on a '95 M3), the raw numbers are
about the same as your car. 2nd gear drops off to 2.49, BTW.
The shape of the torque curve is overlooked with simple number crunching
though. That 220 lb-ft comes at about 4400-4500 rpm. Below that, the
pushrod V-8 will have the advantage.
Tire height also matters. That lb-FOOT torque figure is not at the axle,
it's at a theoretical point 12" from the axle. Bob's tires are about 25"
tall meaning the arm for the applied torque is over 12". The torque felt
at the tread is therefore somewhat less than the total 3124 lb of
available force at one foot. We're talking effective gearing here. If
you're running shorter tires, you may still have an advantage. In either
case, it's pretty close.
> So maybe other people's theory about suspension and/or weight
> distribution is making up for the differences I'm seeing.
Looks to me like it's more a classic power/weight/gearing thing. There's
no magic in the M3's suspension.
I'll surmise that the secret to the M3's good launch is that its
powerband is very linear. Unlike a peaky S2000, or a low end torque
monster V-8, the US M3 has a powerband that is well balanced between low
end torque and high end HP. It doesn't tend to bog _too_ badly if you
are too aggressive on the clutch, yet it won't get excessive wheelspin
(it doesn't have the torque) if you're too aggressive on the throttle.
Yup, it still takes some practice, but I just think it's an easy car to
launch because of a nice linear powerband.
Having owned and drag raced both an '88 5.0 and the M3, I can say that
the M3 is far easier to get consistent launches with. It's been my
experience at the track that mildly modified F-bodies are not faster
than mildly modified M3s in the 1/8 mile, but will pull away after that.
That's the last part of this equation - traction. You can add power all
day long, but you only get to use as much as you have traction. Once on
a roll, I'd rather have the low end torque. That's why Bob is more
dominant in Pro Solo than Solo-II. The good launch of the M3 is
nullified in Solo-II by the V-8s superior low end torque on the roll.
You'll notice the DSM cars, which launch like rocket sleds, also
dominated the top spots in ESP at the Pro Solo. Different story today.
--
Ron Katona
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