The real question is, do you want to buy an extra set of wheels or not? If you buy extra wheels then I would get the 10-inchers so you can run the wider tire. Or you could daily drive on drag radials, it's pretty fun . There must be a small gain to be had with the wider tire, and the 305/35 is slightly shorter so there would also be a little gearing advantage to be had.

 

The real question is, do you want to buy an extra set of wheels or not? If you buy extra wheels then I would get the 10-inchers so you can run the wider tire. Or you could daily drive on drag radials, it's pretty fun . There much be a small gain to be had with the wider tire, and the 305/35 is slightly shorter so there would also be a little gearing advantage to be had.

These won't be daily drivers. I already have a set of 9" for the 275's. If the track difference is negligible, I'd rather stay with the 9's. If it's worth tenths of a second, that will nag at me.

Thanks

 

You might want to try the new 275/40/20 Mickey Thompson ET Street S/S tires:

Mickey Thompson 3401, Mickey Thompson ET Street S/S Radial Tires | Mickey Thompson

The 275 MT ET Street S/S should give you better traction then the 305 Nitto 555r's due to the R2 compound.

 

I'm reading that they are well-liked. How long will those last if they are mostly a track day tire?

I'm still curious about the same question, performance results 275 width vs 305? I guess that could be very different from the tire chosen?

Thanks

 

If you are going to buy some 10" wheels , go with the 305/35-20 MT ET S/S's...
They will give you maybe 3 years of use ... if you drive to and from track only...
I've got them and really like them...

 

No need for the wider tire in stock trim. See my signature below on my best time with the 275/40/20