Let's say I want to go down from the stock 215/60/15 tires on a car to 205/50/15. I would also drop the car so that I could hide the huge fender gap formed.
This would quicken up the gears a little bit, but I have also heard that it would cause the car to be squirly.
Why is that??

 

You want to go to a narrower, smaller diameter tire? Hmmm. IMO, that's not wise.

The smaller diameter tire will throw off your speedometer, odometer, ABS sensors, etc. because each revolution of the tire will move the car a shorter distance. Also, your car will be slower at any given engine rpm.

The narrower tire will have a smaller "footprint" (contact patch) which will reduce traction for acceleration and braking.

If you want a 50-series tire, I'd suggest you move up to a larger diameter wheel and get a tire that's wider than 215. That'll keep the overall diamer about the same. Most tire suppliers can give you the right numbers.


[Modified by bob01721, 12:25 AM 1/28/2002]

 

Correct on a couple of points, but the ABS sensors will be fine b/c they only come into play when there is a significant difference in wheel speed b/w corners....it's all relative.

The smaller wheel diameter will effectively lower the gearing, which helps acceleration. The smaller tires will also more than likely be lighter (providing that the manufacturer didn't need to beef it up more to have the greater stress of a lower-profile tire).

Yes the car will end up being a little more squirrelly b/c there's less compliance in the tire to take up the slack of the imperfections of the road, but this effect will be caused more by lowering than the tires.

While it is considered more reliable and wiser to use rim/tire combo's that yield the best likeness to stock wheel diameter, it's not gonna kill the car. Just so long as you do it knowing what the consequences are (good and bad).