More info will help considerably.
1) Wheel width and offset you are running, to wide a tire on a given wheel size is not usually faster and less precise.
2) Tire specs, real specs are far more important as the sidewall markings are not accurate except in wheel diameter.
3) Familiar with checking and adjusting the tire pressure? This is critically important.
4) Camber setting you are running
5) Budget
6) Life expectancy goal
7) Street and track, any autocrossing as well or dedicated track set of wheels and tires?
8) Driving style, all out all the time, late brake, or more mellow driving, TT type where looking for a clear lap to run the best lap time, let it cool down, do it again....
9) Sliding in the turns, if so which end of the car?
10) Consider 15's or 16's to get wider wheels and more tire choices?
There is a lot to consider when picking tires and wider is not always better, the more you let us know the more we can help you decide
Rick
I can certainly offer my reasoning!
1) Wheel width and offset you are running, to wide a tire on a given wheel size is not usually faster and less precise.
In autocross, it isn't possible to get the RE71R's in a size that will work with the OEM 17" rims. Therefore you have to do the (-1") rim diameter (which is allowed by SCCA) and go with either a 205/45R16 or the 205/50R16.
In my case, I've run both sizes. They both have advantages and disadvantages:
The 205/45R16 is beneficial for initial acceleration as it has a smaller diameter, and it is 2lbs lighter per tire than the 205/50.
The 205/50R16 on the other hand actually had a wider profile by around 3/8"~1/2" even though it is still a 205. Being a taller tire, it gives a little more top end speed in each gear, and finally it is significantly cheaper.
Personally I found the two tires to give similar performance, and really the only place I found a noticeable difference was the 205/45's did tend to break away a touch sooner than the 205/50's did. The big thing for me is the cost, it saved nearly 200$ for me... and that is hard to ignore.
2) Tire specs, real specs are far more important as the sidewall markings are not accurate except in wheel diameter.
This is true. Both the 205/45R16 and 205/50R16 are actually just as wide as their 215/45 and 215/50 main competitors. In fact if you stack them beside a set of 215 Dirreza's, they stand the same height. Don't be fooled by the 205 rating, they are wide tires!
3) Familiar with checking and adjusting the tire pressure? This is critically important.
Optimal pressure for autocross was around 50psi in the front and 47psi in the rear
4) Camber setting you are running
Stock
5) Budget
These tires run from around 130$ up to 160$ USD depending on size, dealer, and demand
6) Life expectancy goal
I get between 40-50 runs by flipping them front to back at each event, and after that I get a tire shop to flip them inside out... and another 40-50 runs after that before they cord.
A typical practice event usually get us around 12 runs, and main day events are 8... give or take a few. So usually we do a Saturday practice, and Sunday competition day. That means I burn through a set of tires every 4 to 5 events. I usually have 6 rims, so that I have 2 extra tires ready to go in case I cord them before I expect.
7) Street and track, any autocrossing as well or dedicated track set of wheels and tires?
I was driving between the event and my house with the tires, which was a 2 hour drive each way. Other than that, no driving on my racing tires.
8) Driving style, all out all the time, late brake, or more mellow driving, TT type where looking for a clear lap to run the best lap time, let it cool down, do it again....
I overdrive the crap out of my car. It takes 1 run to get heat into them, and then they get nice and sticky for the next 2 to 3 runs that occur shortly after that. I am not trying to save tires, I am trying to push out tenths of a second from my run.
When it starts to get hot out, these tires basically start melting away, so it is a good idea to keep a spray bottle handy to use between runs
9) Sliding in the turns, if so which end of the car?
I will occasionally induce a rear slide, I never have any plowing issues even when I overdrive it
10) Consider 15's or 16's to get wider wheels and more tire choices?
16" is the only way to go with these tires if you want to do AutoX