There are SO many reasons not to put oversized rims on a car. The 400/CGT came with 14" rims so 20"s would be a +6 fitament. That's insane. First you will absolutely kill the ride. Second, you'd have a SMALLER contact patch...the size you would need is 165/30/20 (yes, 165)...and even that would throw a 3% speedo error into the mix. If they made them, the "perfect" size would be 195/20/20 (yes, 20 aspect ratio), but they don't make tires that low profile.
Now, lets assume for a second you decide that you are OK with 165/30/20s...the unspring weight of a 20 is going to be a LOT more than a 14". Every 1# of unsprung weight is = 10@# of sprung weight, so it's adding a TON of weight to an already slow car. You thyink your CGT is slow now? Count on the 20s adding at least 1-1.5 seconds to the 0-60 run. Also due to rotational inertia, your braking distances with by exponentially longer (to the point of being dangerous unless you do a big brake upgrade at the same time).
OK, so 20s are a BAD idea...so whjat's a good idea? Well, for performance, you want 15s or MAYBE 16s...anything bigger is 100% pure BLING. Now, if you really like the looks of chuck wagon wheels with rubnber bands...then go for 17s. With 17s you'd be ruinning a 205/35/17 tire, you can't getmuch lower profile than that..
But beware of that even to equal the performance of a 15"...you need a VERY light 17". Why The polar moment of inertia increases with proportion to the square of the radius. So given the same weight, the smaller radius wins. If the 17" wheel is a factor of 1.28 lighter however, they would be even (again, ignoring the moment of the tire). So to equal a 15" wheel which weighs 20 pounds you would need a 15.625lb 17" wheel.
So, if you are looking for best performance, go for 15", best ccombination of looks/perfomance go with 16" and for bling bling looks, go for 17s...
Now, lets assume for a second you decide that you are OK with 165/30/20s...the unspring weight of a 20 is going to be a LOT more than a 14". Every 1# of unsprung weight is = 10@# of sprung weight, so it's adding a TON of weight to an already slow car. You thyink your CGT is slow now? Count on the 20s adding at least 1-1.5 seconds to the 0-60 run. Also due to rotational inertia, your braking distances with by exponentially longer (to the point of being dangerous unless you do a big brake upgrade at the same time).
OK, so 20s are a BAD idea...so whjat's a good idea? Well, for performance, you want 15s or MAYBE 16s...anything bigger is 100% pure BLING. Now, if you really like the looks of chuck wagon wheels with rubnber bands...then go for 17s. With 17s you'd be ruinning a 205/35/17 tire, you can't getmuch lower profile than that..
But beware of that even to equal the performance of a 15"...you need a VERY light 17". Why The polar moment of inertia increases with proportion to the square of the radius. So given the same weight, the smaller radius wins. If the 17" wheel is a factor of 1.28 lighter however, they would be even (again, ignoring the moment of the tire). So to equal a 15" wheel which weighs 20 pounds you would need a 15.625lb 17" wheel.
So, if you are looking for best performance, go for 15", best ccombination of looks/perfomance go with 16" and for bling bling looks, go for 17s...