Touring Modification

After going to work for 60 miles one way here in Southern California M-F, I decided to take the Hybrid road and purchased myself a Touring (Package 6). I wanted to get some stiffness on the Prius, hence decided with the Touring. I have rented Prius (non-Touring) whenever I travel to NY and Sacramento. I like the feel of the suspension of the Touring, but I think it can benefit a little bit on the looks if I replace the touring wheels.

The present Touring wheels is 16" and weights around 16 lbs I believe. It has the Bridgestone Turanza P195/55R16 86V and each tires weight around 19 lbs. I decided to do some research (and I am pretty sure a lot of the folks here have done so as well). With this touring setup, you have a calculated Revolutions per Mile of 851 using this set ot tires. The overall diameter is 24.4", V-Rated tires, and a UTQG of 260 AA (may last up to 22,000 miles per tire ave).

At first I decided maybe just add an inch on the rims and up the ante to around 17". After researching for tires, the closest tire sizes available without affecting too much my RPM & Speedometer are 205/45/17 or 225/45/17. After calculating I found out that the 205/45/17 will have a factor of .74% faster on my speedometer reading and .74% diameter difference. Pretty close to touring stock compared to 225/45/17 giving me 2.173% slower on the speeadmeter read and 2.13% diameter differences compared to stock. At this point I was set on a 17" rim, until I saw another Prius (non-Touring) by our parking lot that has 18" Rims.

Hmm, However the tire size installed was 225/40/18. I did some computation and found out this size tires actually will make the speedometer reading 2.616% slower and has a diameter difference of 2.56%.

I did further digging and found out that the best tire that will result as close as Stock without modifications (assuming the total weight per tire + rims are the same) is using 205/40/18. This will have a speedometer reading of .035% slower and diameter differences of .05%. If the stock has a RPM of 851, this one has a RPM of 850.7 - cannot get much closer than that. This is just like a deflated tire. Depending on the Brand of tires you get, you can get up to max psi of 51, similar to stock Bridgestone. Also, stock weight of Bridgestone is 19 lbs. Just find a tire close to its weight.

Here's my question - anyone out there used this tire size - 205/40/18? What 18" rims did you get? I am thinking of Zigen but it is around 19 lbs, 3 lbs heavier than stock.