Taller Tire Test (5.7% MPG increase observed on Honda CR-Z @ 55-65 MPH)

[oil pan 4]

Taller tires it is then.

[2000mc]

capriracer- on the rolling resistance coefficient chart you have on Barry's Tire Tech it seems generally, taller and wider is better.
however the exact order that the 14" tires in sizes i might switch to seems inconsistent 185/75, 185/70, 195/70, 185/65, 175/65, 175/70. i have 175/70-14 tires.

195/70 out performed by a 185/70, 175/70 outperformed by 175/65, and 215/75 outperformed by a 3 sizes smaller tire 185/75.

do you think that overall rule of thumb, wider, taller is better works, and the specific tires used caused this? or do you think that there are certain sizes that cause an inherent disadvantage somehow?

[CapriRacer]

Originally Posted by 2000mc

capriracer- on the rolling resistance coefficient chart you have on Barry's Tire Tech it seems generally, taller and wider is better.
however the exact order that the 14" tires in sizes i might switch to seems inconsistent 185/75, 185/70, 195/70, 185/65, 175/65, 175/70. i have 175/70-14 tires.

195/70 out performed by a 185/70, 175/70 outperformed by 175/65, and 215/75 outperformed by a 3 sizes smaller tire 185/75.

do you think that overall rule of thumb, wider, taller is better works, and the specific tires used caused this? or do you think that there are certain sizes that cause an inherent disadvantage somehow?

What I did was run a regression analysis on all the data to derive a generaized formula that covers the 3 dimensions used in the tire sizing. The formula has an r squared value of 66% - which is NOT very good - meaning the formula doesn't explain the numbers very well. I would need to add more factors to get a better fit.

However, the data is what it is. It is the ONLY data I have seen that compares tires only by size. I have my doubts that this is EXACTLY true - and that may be why the data doesn't fit very well. I am pretty sure there are OE tires in that mix, but they do not jump out as outliers.

So I stand by the analysis. It is the best information available.

A side note: While you looked at 14", the same principle ought to work in 15". That why I did the regression. It looks at ALL the data.

[oil pan 4]

I almost forgot about the wiki page I made on this subject.
Consider this added to the forum links.

[Cobb]

I drove a crz with stick and I think the IMA gives it a great win for such modifications. Maybe even better if you had more power to supplement the IMA charge?

I found the crz didnt mind 6th gear at 35 mph and it was difficult to really lug the engine. I was rather disappoint at the performance at the 50-70 mph range of accelerating for merging in 4-6th gear.

I drove the cvt model too and just didnt like how the cvt shifts or should I say slide like you got a clutch going bad.

It is amazing though how the Insight can do 55mph at under 2 grand.

[F8L]

Be careful when comparing the average tire or other LRR tire to the Energy Saver A/S. in my testing I have found the Energy Saver A/S 195/65/15 to be 2-3mpg more efficient than the Prius OE Yokohama S33D and aftermarket Yokohama AVID Ascend. All tires had similar tread depth and conditions were very similar. TireRack.com also tested the Energy Saver A\S and showed it to be up to 3.8mpg more efficient than non-LRR but efficient tires like the Michelin Hydroedge and ComforTread tires. It's and extremely efficient tire!

[UltArc]

Originally Posted by royanddoreen

I went to 5% higher od tires and I am feeling it may be high enough gearing. I'm sure when they design a car they gear a car to suit the majority of people.Still think there should be some options in the gearing when you buy a new car.

As Secondwind has brought up the valid point before (either here or in person), that the Standard is more so aimed at younger people as a sports/sporty car, with gearing being aimed at performance.

I have to say, the CRZ might just be my favorite production car right now. No doubt at all if you don't include front rears. A nice splitter, maybe some performance mods if she needs and, and taller tires. Perfect. (in my opinion)

[royanddoreen]

Glad to hear you!! I noticed your 90 day avg same as mine, similar car and drivers I guess.

[YeahPete]

I have to add this. When I switched to smaller tires on my cavalier the mpg and the speedometer were effected. It showed me as getting better mpg and my speedometer shower me as going 2-4 mph faster.

So if a larger diameter tire actually shows mpg gains, the gains are also multiplicative because it should decrease your mileage because it shows as your speedometer registering a slightly lower speed.

Anyone understand what I am getting at?
Larger tire shows a decreased speed and decreased miles on odometer.
Smaller tire shows increased speed and increased miles on odometer.

Was this factored into the mileage gains?

[mcrews]

If you are going to change tire size and then trying to use the odometer or speedo (w/o recalibration) is silly.
You have to calibrate for the difference in doing the math for mileage.

All of my posts concerning larger diameter tires are based on:
1. Garmin gps for true mileage
2. calibrated ScangaugeII
note: SGII is calibrated in the metric mode w/ gps in the metric mode. this gives a more accurate reading when switched back to miles.