[s-cars] Quattro - What Don't I get?

[Theodore Chen]

--- Taka Mizutani <t44tqtro at gmail.com> wrote:

> Teddy-
> At least with the solid axle, you don't destroy CVs- the Mustang Cobra
> is known to eat CVs if you don't set up the suspension to prevent axle
> hop.

it's true that CV joints are probably more vulnerable to damage from
the shock loads created by wheel hop, but wheel hop is bad for any car.
there are plenty of solid axle cars destroying axleshafts, ring and
pinion gears, transmissions, etc. due to severe wheel hop.

i think the real problem is that the mustang cobra's CV joints are a
little undersized for what people are doing to it.  stock mustang
cobras are quite rare.  most of them are making considerably more power
than stock, and 400-500 hp supercharged cobras are common.

the cobra also uses more ride-oriented bushings, because ford was trying
to lure some would-be import coupe buyers.  those bushings are used in
a semi-trailing IRS, which makes the car more prone to wheel hop.

> Reading about how the Cadillac CTS-V behaves, I wouldn't be surprised
> if it does the same thing.

cadillac softened the bushings to make the car more comfortable.
performance upgrade is to use stiffer bushings.  some people go so far as
to replace all of the bushings with spherical bearings - and then they
complain about the ride and noise.

> I have not heard that about the Pontiac GTO or the Chrysler 300,
> though. Axle hop can be a problem with the supercharged AMGs, so it
> might with the 300.

the devil is in the details.  that's what engineering is all about.
i wouldn't be at all surprised if the mercedes and chryslers had different
wheel hop tendencies, because tuning counts for a great deal.

in the case of the CTS-V, i suspect that ride and road course handling
were higher priorities than stoplight drags.  i've driven the CTS-V,
and didn't have any issues with wheel hop.  but i didn't rev the engine
to 6k and dump the clutch, either (not my style).  i loved the car, BTW,
and wouldn't touch the bushings if i owned one.

there are a lot of other factors - even tire pressure and shock damping
can have a big influence on wheel hop tendencies.  cadillac could, for
example, mitigate the wheel hop issue by tuning the rear shock absorbers
to increase damping at the resonant frequency of the wheel hop, but that
might affect ride and handling.  i don't know if the regular CTS has
a wheel hop issue.  if not, that suggests that the package that cadillac
put together for the CTS-V has created the wheel hop tendency - a 
combination of spring rate, bushing durometer, compression/rebound damping,
wheel mass, tire profile, etc.  but maybe that package made the car
very fast at the nurburgring while retaining a comfortable ride, so cadillac
decided to use it.

-teddy


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