RE: E36: Maximum Tire Size

[michael_kohlbrenner@xxxxxxxxxx]

- -----Original Message-----
From: Serge Maillet [mailto:serge.maillet@domain.elided]

> I'm thinking about upgrading my stock 16" alloys to
> 17" rims but before I do, I would like to know what
> is the maximum tire size I can put on front / rear
> or what is the best combination? I'm looking for the
> maximum rubber contact for the best traction. Also,
> should I go 17" or 18" ??? Thanks to all replies!

Here's my opinion...

Is your suspension still stock?  If so, and if you are
truly interested in maximum cornering traction above
all else, you should simply stay with 16" and get the
best tires you can afford in the widest size that fits
(keeping overall diameter the same of course).  This
also happens to be the cheapest solution and won't
hurt your ride quality like short sidewall tires will.

Contrary to popular belief (and boy is it popular!),
most cars with stock suspensions will actually lose
some cornering traction by going to a wheel/tire
combination with a significantly lower profile than
the car was designed with from the factory.  There is
simply too much adverse camber gain during cornering
in stock suspensions to keep the inside of a very
stiff tire from lifting off the pavement.  That wide
tread won't do much good if half of it isn't touching
the pavement.  Stock sized tires with some sidewall
height will have more compliance in the carcass and
will tend to keep more of the tread on the pavement.

If, on the other hand, you have PROPERLY uprated the
suspension including dialing in some extra static
negative camber, then your car should be able to make
use of the stiffer, lower profile tires.

With all of that said, the performance improvement most
folks perceive when they "Plus-size" their wheels/tires
is better steering response, and for many that is
arguably more important than ultimate cornering
traction.  If you are willing to sacrifice a small
amount of absolute cornering traction and ride quality
to get this, then go ahead and get those low profile
tires.

There was actually a Road & Track test around 2 years
ago that supported this.  They tested various sized
wheel/tire combos on a stock 5-series that came with
15" wheels.  The data from the test with the stock
15" setup was invalid, since these stock tires weren't
as aggressive as the tires used with the other wheel
sizes.  The data from the 18" wheel size was similarly
flawed since it was again a different tire model.
However, the tires used with the 16" and 17" wheel
sizes were the same model in essentially the same
width.  The 16" had better skidpad numbers, while the
17" had better steering response.  The 17" just pipped
the 16" in the slalom and "Auto-X" times, showing the
value of steering response.

Regards,
Mike Kohlbrenner

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