Re: Need Wheel/Tire Help (archive)

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Also, weight transfer has nothing to do with the width of the tires. What you have to consider is that the taller the sidewall, the more movement it will have. For example, take a brush with long bristles, versus a brush with shorter bristles. If you press down and to the side, you will see the brush with the longer bristles flex and move more than the shorter bristles of the other brush. This is what happens with the sidewall of a tire in cornering. And this is what you feel when the tire is scrubbing along in a corner. You "feel" the wallowy-ness of the tire sidewall flexing. A bigger tire, and thus smaller sidewall, reduces this flex and gives better handling and feel. But, because there is less sidewall to compress, road irregularities and harshness gets transmitted more easily to the suspension, the car, and you (i.e., a bigger sidewall has more room to flex if you hit a pothole, whereas a smaller sidewall has less room to flex).

Weight transfer is a much more complex topic that needs discussing mostly in extreme handling conditions. You will not need to worry about this, but a simplified explanation for the layman's terms, weight transfer is the movement of downward the force that the car puts on the suspension, wheels, and tires from front to back or side to side. Let's assume that a car is perfectly balanced at rest, and it's putting 800 lbs on each tire at rest (for argument's sake). In a right hand corner, what happens is that the car will lean over to the left, and the left-side (or ouside) tires will have MORE weight on them, than the right side (or inside) tires will have Less weight on them. (Let's say 1000 lbs on each outside tire, and 600 lbs on each inside tire). The same applies for braking and acceleration. You only need to worry about weight transfer when you start talking about handling conditions, suspension travel/movement, and other suspension topics. For tires, all you need to make sure is that the tire can handle the maximum load it will be required to handle. Nowadays, tires are made well enough that you don't have to worry about load ratings. But for example, if you add weight to the car (you, your 3 other friends, and a trunk full of stuff), say 150 lbs each, you're adding 750 lbs of weight to the car that say weights 3250 lbs. This means it now weighs 4000lbs total, and if the car has perfect distribution (which in reality it doesn't but for argument's sake let's assume it does), then each tire will need to handle a 1000lb load. This load rating will be written on the tire, and often time it is high enough that you will not need to worry about it.

H-rated tires are rated for speed. Any letter rating is a rating for the maximum speed those tires can go without failing. This rating means nothing if you're looking at all-season H-rated tires versus summer only H-rated tires. What counts there is the compound. Snow tires, all-seaons tires, performance tires, high performance summer tires, all have different compounds made to work in certain conditions (such as low heat, low grip for snow, or high heat, high grip for summer tires). The speed rating is more a by product of what these compounds can handle. It all matters on how the tires are made. Usually a snow tire won't be able to travel as fast as a high-performance tire because of the compound and the "job" it has to do. Of course you can find V and maybe even Z-rated snow tires, but they will cost a LOT more than the "regular" snows because more development was needed to make that tire work well in the snow AND go fast.

What you need to do is consider the conditions you drive in, and figure out what you want your tires and wheels to do. Then you can start looking for the set-up that you will need. These requirements can range from snow/winter driving, to track and driver schools. And more often than not, you will need certain tires to do certain jobs (i.e, snow tires for winter, and performance tires that are good in the wet for spring, summer, and fall driving).

Now that we're done with all the math,in practical terms a 205/60/14 will act better than the 195's you have now.Using a 225 size tire on a 14" rim,with the weight of your car, will cause too much weight transfer in corners,and be worse,not better.
If you plan to keep the car,invest in 15" or 16" wheels,and use a 50 or 55 series tire.Far better handling,safety,and stability.Otherwise use a GOOD "H" rated or better 205/60/14 tire.
I specialize in setting up BMWs for street/track,mostly stock and/or extreme mods.,and will be glad to discuss it if you can catch me here.

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