Kai and all,
Go for whatever you like, but remember the following:
Overall rolling diameter - if you increase the diameter, your speedo will read low and you will effectively be making your rear-end have a taller ratio, which will give you a decrease in RPM at a given speed in gear. Unfortunately, this means that you will lose some acceleration performance. If you decrease the overall diameter, you will do the opposite. Your speedo will read high and you will have a shorter rear-end ratio. So, although you will be accelerating faster, you will have a higher RPM at any given speed in gear. You can do the math yourself, or go to a number of diameter tools (like the one in the rims section "about tires" at
www.veloce.nu to figure out the size/diameter thing.
In terms of width, a wider than stock tire (besides making it a bit harder to steer at slow speeds) will also increase wear on your steering box and other steering components and will also change the overall handling characteristics of your car. Most of the changes with a wider tire are good, but remember that you are adding a significant amount of additional stress to the suspension and also to the body/frame. I guess that if you had a rusty early Spider (which already has a pretty soft structure to begin with), you could cause stress fractures when cornering quickly. You also need to think about how they fit. In a Giulia Ti (sedan) or early Bertone coupe for example, the rear wheel-wells are tight and large tires mounted on short offset wheels will rub the inner fenders. Finally, remember that unsprung weight is important to handling. A larger tire almost always weighs more, which also increases the stresses on your suspension and steering systems.
For the 105/115 series, I recommend the following:
Giuliettas, Roundtails, early Bertone Coupes and Giulia Sedans (with stock 15 inch rims): 155R-15 (stock), 185/70-15 (street), 195/65-15 (street & track) (for race - switch to a 14 X 6 or 7 inch rim and use a 205/60-14 race tire, requires a change in brakes of course).
ATE brake-equipped early cars (with stock 14 inch rims): 165R-14 (stock), 185/70-14 (street), 205/60-14 (track & street). I don't recommend going any larger than that.
Later Spiders (post '82 when they stiffened the structure a bit): If you must, you can switch to a larger diameter and width wheel like the 16 inch wheels available from Serpent or other manufacturers and go nuts. Just remember that you will be changing suspension and steering components more often. Also, be careful about your wheel offset and how it will fit before you spend lots of money needlessly. In the later Spiders, the larger than stock wheels and really wide tires can actually rob you of overall cornering speed because of increases in unsprung weight and because you are using power to drive the rubber.
I hope that helps.
Cheers,
)
Linear Mode
