Re: Tires causing torque-steer

["Rudy Consolacion" <rconsolacion@kumhotech.com>]

Ralph,
I'm watching. It is possible that there is a tire/vehicle interaction 
that may be causing your torque steer.  You say that you noticed this 
shortly after installing the Hakkas.  I would start the diagnosing by 
putting the 16" Yokos back on the car and seeing if the torque steer 
occurs.  If it does, then I would say it's the Torsen system acting 
up and transferring torque to one side. If not, then try running the 
Hakkas in reverse rotation by putting the rights on the left side and 
vice-versa (don't worry about the directional pattern). If the torque 
steer changes direction or goes away or even reduces in severity, I 
would say it's a characteristic of the tread patter giving you 
problems. If it doesn't change direction, then the tires have a 
conicity problem. Is anyone else in q-land experiencing this on their 
Hakka 1's?

Another test I would suggest while the Hakkas are on the car is to 
see if the car pulls the other direction under braking. This will 
determine if the tire tread pattern is torque sensitive.

Tire 101:
If the vehicle pulls at constant velocity, it can be attributed to 
RAT - Residual Aligning Torque. It's defined as the level of aligning 
torque at the slip angle where the lateral force of a tire is zero. 
What this means is that if a radial tire is allowed to roll at zero 
lateral force, the tire is not at zero slip angle which creates a 
moment (or aligning torque) which translates to pull. This phenomena 
is characteristic of radial tires.  There are two components that 
relate to the level of RAT, one is conicity and the other is 
plysteer.  Conicity is the lateral force generated by the tendency of 
a tire to roll as if it were cambered to the road surface. The force 
will not change directions when rotational direction is reversed. 
Plysteer is the lateral force generated by the tendency of a tire to 
roll as if it had a slip angle. Plysteer RAT is heavily influenced by 
the tread patter design and_will_ change when rotational direction is 
reversed. This is a very brief description and I'll understand if it 
doesn't make sense.

In summary, swap rights and lefts. If it pulls in the same direction, 
it's a conicity problem (tire manufacturing problem like off-center 
belts). I would swap fronts and rears. If it pulls in the opposite 
direction, it's a plysteer problem (tread pattern design). Nothing 
you can do about that except get different tires.

I mentioned above that it may be a tire/vehicle interaction thing. 
When going to narrower 15" tires from the wider 16", the footprint 
gets longer which increases the pneumatic trail. Pneumatic trail is 
the distance between the center of the contact patch and the 
"center-of-gravity" of the contact area pressure (or moment arm). 
This has an affect on RAT sensitivity.

Let me know the prognosis. HTH!
Rudy C.  

> Hi Guys:  I hope Rudy from Ohio is watching...  My car torque-steers with my
> new Hakka 1's.  I noticed this shortly after installing them.  The car went
> dead straight on the sumer tires (Yoko A-509s on 16" rims).  The Hakkas are
> on the 15" OEM rims and when I step on the gas, the car pulls to the left.
> Get off the gas and it settles out pretty straight.  My tire shop finally
> got a replacement tire in yesterday.  They put it on the left front and no
> improvement.  The shop said maybe it is a 'characteristic of these tires'.
> I can't believe that! I don't think it is an alignment problem since the car
> went straight on the other tires.  I'm thinking of rotating tires around to
> try to isolate.
> 
> Any opinions?
> Ralph Poplawsky
> '91 200TQ (keeps coming back to the same place)
>