Prius 15's are better than aftermarket 17's! (Wrong wheels/tires can wreck your MPG)

[johnathanf1lm]

I"m sure this was mentioned but a Prius has a CVT which putting larger tires doesn't do anything besides add weight since the CVT adjust the gear ratio constantly. Now if the Prius had a fixed geared trans like most automatics this would add weight but would make the gears taller. Long story short wrong car to test and prove the larger tire theory.

[sidecar]

Originally Posted by johnathanf1lm

I"m sure this was mentioned but a Prius has a CVT which putting larger tires doesn't do anything besides add weight since the CVT adjust the gear ratio constantly. Now if the Prius had a fixed geared trans like most automatics this would add weight but would make the gears taller. Long story short wrong car to test and prove the larger tire theory.

we know all about that, there are hard working guys on the Prius forum that track all these features of potential LRR tyres in a database and account for correct rolling diameters.

Incidentally the US fit tyre is too small by a few percent. The 195/60-15 offers better diameter options, from memory 844 revolutions per mile. There are 17" options that fit this profile, and these are the ones recommended.

[RedDevil]

Originally Posted by johnathanf1lm

I"m sure this was mentioned but a Prius has a CVT which putting larger tires doesn't do anything besides add weight since the CVT adjust the gear ratio constantly. Now if the Prius had a fixed geared trans like most automatics this would add weight but would make the gears taller. Long story short wrong car to test and prove the larger tire theory.

Personally, I've experienced otherwise.
A CVT can adjust the gear ratio between its limits only. If the optimum lies beyond that, tires do play a role.

Driving at a constant speed between 30 and 60 mph, my CVT is at its top range all the time; revs = mph times 30.
I bet the Prius, with its bigger engine, will also have no trouble doing that.
So tires with a larger circumference will drop RPMs in the 30-60 mph zone.

[glasses]

I am really looking forward to seeing the difference the Ecopias we just bought today make on our Versa, 5mpg sounds amazing!

[CapriRacer]

Originally Posted by glasses

I am really looking forward to seeing the difference the Ecopias we just bought today make on our Versa, 5mpg sounds amazing!

Don't be surprised you don't get that.

First, you are likely taking off tires with low levels of rolling resistance. Changing to the Ecopia is a small step, not a big one.

Second, worn tires get better fuel economy than new ones because of the increased mass of the new tires.

So it is possible than your fuel economy will get worse initially - improving as the tires wear.

[wyatt]

And remember, I moved from 17's to the stock 15's, which I think also helped. This reminds me, I need to update my fuel log sometime .

[wyatt]

Based on my rough calculations:
Before I changed to the Ecopias, I had 15 fill-ups averaging about 44 mpg. Since then, I have had 28 fill-ups averaging about 50 mpg. That's over a 13% increase in FE, with no other changes made.

[royanddoreen]

I have 17"x 7" centerline storms that weigh 11.7 lbs not to many lighter.

[TexasCotton]

Originally Posted by wyatt

I will have to check what the tires were when I get back home, and report back. I do know the rims were 8" wide, vs the 7" wide Prius rims. The rim/tire combos are noticeably lighter when lifting. This is comparing between my wife's 15's and the 17's. I don't have a mass reading on both, so it's not a real comparison, but it is something I noticed.
Running the old tires on the back of the car would be an option, but we plan to sell off the 17" rims to someone looking to "upgrade" their ride. Anyone here looking for some 17's?
I agree, it could be a large number of factors that impacted the large change in FE. I am just glad it is up, way up .

The image you have is of a Gen Prius with non OEM rims. Just stating obvious
If you want custom rims and 17 that is fine too but that to me is custom . The FE/mpg is not a concern with different oem rim size.IMHO
I am looking to increase my 15 oem rims FE/mpg

[Frank Lee]

IMHO Capri Racer's advice to go wide makes sense if you are loading the tires to near max capacity. I would expect a tire engineer- who is always concerned with liability issues- to have that position.

However I think if your vehicle is always at the lightly loaded end of the spectrum, fe gains can be had from going narrower, to tires with fewer plies and thinner sidewalls and treads. I have yet to personally test that theory.