Re: CONS of putting 17" wheels on 86 16v Scirocco? (Road America)
Quote, originally posted by Road America » |
Ok, yea, I goofed being in the wrong section. Guess I was too caught up in reading ads. Ok, let me explain here.
1. I'm not worried about my shop scratching my wheels. He's got the equipment to do it right.
2. I'm not buying bigger wheels to get bigger brakes, but bigger brakes because the stock brakes will look silly.
3. Handling? I'm really confused here. |
Perhaps.
Quote, originally posted by Road America » |
I think people are confusing handling with ride quality. |
Maybe you are confusing absolute lateral grip and sidewall stiffness with real world handling. As soon as you find a bump on the road in the middle of a corner, they aren't the same thing. In a bumpy turn, some compliance in the sidewalls is a very good thing. It allows the tire to soak up some of the bumps entirely, and to absorb a significant portion of larger bumps, too. That keeps the movement of the unsprung weight to a minimum and keeps the tread in contact with the road better.
With stiffer, shorter sidewalls, more of the energy of the bump is transfered to the wheel and unsprung weight of the suspension (and brakes). If you increase the spring rates and stiffen the dampers (shocks) to handle the added spring, you get more roll stiffness (and often more understeer in our VW's). You also get a more significant temporary spike in the loading of the tire when you hit the bump (and more lateral slide from the overload, just like from a more roll stiffness). So you get less lateral force on the rising side of the bump. Going to a softer spring and shock package to increase compliance will keep the load lower on the rising face of the bump, but it will fail to control the unsprung weight once you cross over the top of the bump, and the tire will unload on the back side of the bump and lose some lateral grip. Basically spring and shock adjustments will allow you to choose which side of the bump you lose the most grip on, but the only way to get more grip on both sides of the bump is to have more compliance in the tires.
Back in 1994 or 1995, I ran an improved touring 1986 Golf GTI. Just for the heck of it, I took several different wheels to a Porsche club high performance school (I was an instructor for the school). I ran 13" wheels, 14" wheels and 15" wheels on my car with basically the same tires (all the same make and model of tire, 205/60-13, 205/55-14 and 205/50-15 sizes). The tires were DOT race compound tires. My Golf GTI had the best lap times with 14" wheels. It had the highest speed at the end of the straights with the 13" tires, but it was really "squishy" in the corners with the taller sidewalls. It felt a lot like an A1 car without a lower stress bar. Perhaps if I had taken a few more sessions and made some tire pressure adjustments, I could have worked around that a little more, but I didn't try. It had the slowest speed at the end of the straight with the 15" wheels and tires.
A friend who was also at that event had a set of 16" wheels that fit my car as well. Those wheels had racing slicks on them. I tried those wheels and tires, too, and they were even slower on the straights, and the lap times with those 16" wheels and slicks were only slightly faster than the 15" wheels, and still not as fast as the 14" wheels.
With the bigger wheels on the car (the 15" and 16" wheels), it felt very skittish through the bumpier turns on this track (there were two long sweepers that had some rough spots in the middle of the turns). Through most of the other smooth turns, the shorter sidewall resulted in a sharper feel to the car, and this helped speed through the smooth corners slightly. Still, it wasn't enough to make up for the losses on the straights and the bumpy turns.
IIRC (and it's been a long time, I could probably dig up my notebook entries on this if you really wanted the exact times), the 13" wheels (VW Tarantula wheels) were about 1.5 seconds per lap slower than the 14" wheels (VW Snowflakes), and the 15" wheels (Ronal turbos) were about 2 seconds slower. The 16" wheels with the racing slicks were about 1 second slower than the 14" wheels. That's from 7-8 year old (possibly faulty) memory, though, so take it with a small grain of salt. I'm certain that the fastest times came with the 14" wheels, though.