Eibach Springs and KYB Struts REVIEW

The other day I swapped the 15s back on to test out the MPG loss with my 17s and new tires. The car felt very stable and the body roll was still much reduced. I expect the 15s to feel like mushy marshmellows but they didn't. Obviously I couldn't corner as hard as I can with the 17s but the ride was very nice and not bumpy. Having driven on the 15s with the lowering springs I will retract my earlier recommendation to not lower the Prius if you value comfort. With the 15s at high pressure the car rides very smooth if a bit stiffer than stock and the improved handling is not compromised.

On the 17s I was averaging 45mpg if I tried really hard. Today I drove the same route (which includes a 1200 foot elevation gain) during my commute and achieved 55mpg and the day before I was at 58mpg but I didn't run my normal route so no hill climbing. Hell if my commute was flat then 60mpg wouldn't be a problem. Boy those 17s kill my MPG.

 

I'm still laughing at the last sentence.

I agree. The ride is not really compromised unless you enjoy the "riding on marshmallows" feel. The car just feels more stable and safer. By safer I mean if you have to perform and emergency maneuver the car is much more stable and less likely to wind up out of control.

I think I may have to sell the 17s. This 7-10mpg loss is ridiculous. lol

 

I guess we are fortunate enough to have the option of swapping back and forth but damn it would be nice if we didn't have to.

The MPG difference is so vast despite the monetary cost being small that I cannot be happy unless I am getting 50+mpg. Being stuck in the low to mid 40s makes me feel like I should be driving a VW turbo diesel instead. lol

What id the difference between your OEMs and your Kyowa's?

 

Sidecar, I think you have it right.

My wheels weigh 15lbs and the tires weigh 22lbs according to the manufacture. Unfortunately i never weighed this combo but I did weigh my old 17" combo and they were between 37.5 and 38lbs each. The stock combo were approx. 31.5-32lbs each. I have not weighed the OEM wheels and my current tires.

My commute is around 98% highway. I live about 1mile from the freeway and my work is less than 1 mile off the freeway. This is the route I have been basing my MPG figures on. I do drive around town but I leave that out of the calculation for the most part as it is highly variable and doesn't really help determine the MPG difference between the 17s and 15s. I will say that even with city driving the MPG doesn't change much. I still get much worse MPG with the 17s. In fact I would say that the MPG difference is worse in the city because it is easier to pulse and glide with the 15s despite the fact that the Michelin MXM4s roll really well. There is also the penalty for having to stop and go over and over with such a heavy tire/wheel combo.

 

That sounds about right. I think if I performed the same kind of driving I did today with my 17s then I may have pulled off a 45mpg trip but I doubt I could have gotten any better. I think this 15" tire just rolls really well. Ah well, I'm just happy to be above 50mpg again.

 

Indeed, sidecar. I think rolling resistance and the larger rolling diameter of the 17s are the main culprits.

The 17" tire is taller than the 15" so part of the gain in mpg when swapping from the 17s to the 15s is due to increased tire revolutions per mile than the 17s. When I ran my worn down 17s the tire size was much closer to the 15s and the MPG difference was about 4-6mpg less with the 17s. So I expect the new Michelins would close the gap in MPG once they wear down a bit like the Yokos have.

See picture below.

 

I agree. i talked about this in my tire review thread for the Michelins. With these 17s the speedometer is actually dead on now as compared to GPS readings. Normally with the 15s it is 2mph too fast compared to GPS.

The tire calculators show that my tire size 215/45/17 should be very close to the diameter of the 185/65/15 but it is obviously not. The 205/50/17 would be off ever further. I could have paid more attention to the revs/mile specifications but I really didn't have many choices in tire and mpg quirks aside the MXM4 is an awesome tire.

 

The Michelin tires have 2000 miles on them now so they should be broke in but the fact they are so much taller, wider and have a higher rolling resistance is the main problem. I really like them though so I'll just wait until winter to run them because they are much safer than my 15" summer tires. The true mpg loss is probably around 6mpg which isn't that big of a deal economically but it hurts my hypermiling ego lol.

 

I just noticed that the new tires do not scrape the wheel well like the older Kumhos did. I think it is the design of the tire that keeps it from hitting the wheel well. The Michelin sidewalls are shaped such that they curve inward toward the wheel as opposed to the Kumhos which had a very flat sidewall.

 

Yup, you'll love it.

 

Just a quick update...

When cornering hard and fast AND hitting small bumps during cornering the tire front tire scrubs the wheel well ocassionally. This situation will be determined by your wheel specs, tire specs etc. With the 15" tires this does not happen yet I cannot corner nearly as hard soooooo.