[sfair74]

Thanks for the replies. I'm a long time lurker and huge geek.

I forgot to mention I also upped the tire PSI to 40 after the first couple weeks to get a baseline.

As far as grill block and engine temperature I don't have a scan gauge yet. I guess I could use one of my ELM23 sensors and Torque pro android app. The Yaris doesn't even have a temperature gauge. It has a blue engine temp idiot light that is on when it's cold and a red light if it's too hot. On my 2001 Insight I just shoved a coroplast yard sign between the grill and the radiator during the winter.

I live in Michigan and winter tires are a must in my book. I have recently been a big fan of Nokian's all-weather tires. They are different and not to be confused with all season tires. They are a softer winter compound but they were designed to hold up to heat and can be run year round. The are heavily siped and feature aggressive winter tire patterns. They aren't the best for noise vibration and harshness but if I was too concerned with that I wouldn't be driving a Yaris. I prefer the all weathers vs having to switch a dedicated set of winters and all season tires. If my car didn't have TPMS or had indirect TPMS I would probably just buy a separate set.

I would really prefer to stick with the Nokian WR-G4 tires so my size selections are a bit limited.

185/65-R14 (Stock -2.04%) *Honda Insight Rims $250+ w/ moving TPMS
175/65-R15 (Stock tire size) *Stock 15" steel with OEM Hubcaps
185/65-R15 (Stock +2.14%) *Stock 15" steel with OEM Hubcaps
195/65-R15 (Stock +4.27%) *Stock 15" steel with OEM Hubcaps
205/65-R15 (Stock +6.41%) *Stock 15" steel with OEM Hubcaps

14" rims will fit fine. I have found a few posts detailing that 13" rims should fit the Yaris. Unfortunately there's not much good information out there on what size taller tiers fit in the Yaris without rubbing. There's a good deal of information about going to wider tires with a lower sidewall ratio but the diameter is usually pretty close.

I have run the Yaris specs through a spreadsheet that I use to analyze any vehicle I'm interested in regarding gearing and piston speed. The gearing is quite pathetic and I think should either have a couple more gears or a taller final drive. The engine stroke is 84.7mm. The forward gears are 2.847, 1.552, 1, and .7. With a final drive of 4.237. The stock tires are 175/65-R15. In top gear the speed the piston reaches 5 m/s is 43.01 MPH and the speed it reaches 6 m/s is 51.91 MPH.

I think my mostly steady highway driving could benefit from taller tires but it inevitably will come with wider tires and more ground clearance.

How tall of a tire is too tall provided that it will fit? Has anyone gone to drastically larger tires with good results?

I'm not concerned about the speedometer. I use a GPS as a heads up speedometer. On top of that the Yaris speedometer is trash. It has numbers every 20 MPH and a line every 10 MPH. But don't worry they decided to use the space for some weird dot pattern on the outside that doesn't associate with MPH vs the standard line pattern used on most every other car.