i went to the strip with 18's with 215/35/18 tires
how much of a difference would it make on my time by putting on light 15's like slipstreams?
this is on my 4th gen prelude with h22

 

well if they are lighter, you will accelerate faster, if they are shorter, again you will accelerate faster. but if they are shorter you sacrifice a little top end, but as long as you are trapping at the top of a gear you are ok. and with the bigger sidewall on the 15's, you should hook better.

 

what does your best timeslip look like from this last trip to the track.
i bet you would cut at least .5 in ET easy