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

[F8L]

Originally Posted by RedDevil

The sidewall on the 17" tires is an inch less high than on the 15"s.
On impact with the road they have to flex deeper than the 15", and it also takes more force to flex them in the first place.

The 17" rim has a much wider open gap, and the thin spokes do little to prevent the air from flowing in. The 15" rims have thick spokes and little gaps between them, so less drag.
4 big bucket sized holes generate more drag than 20 tea cup sized ones.

My guess is that setting the pressure to max sidewall PSI will have a big effect on rolling resistance, as the sidewalls will have to flex much less then. Steering will be lighter and more precise. Grip and comfort stay behind in the parking lot.

Covering the rim with a plate would help reduce drag at higher speeds.

Indeed but even at 55psi the loss is still there.

[F8L]

Originally Posted by RandomFact314

This inspired me to look up the Ecopia tires, are they seriously $235 a tire? The LRR Goodyear Viva II tires I have been using the past (since I've been here) years are only about $70 a tire and I've never had any issues with them.

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Update: I actually re-put in my tire size and it went down to $114 a tire. After 4 tires I dont think they will pay themselves off in extra FE over the VivaIIs

What is your tire size? I looked up your car and the OE tires size of 185/60/15 the Ecopia EP422 is only $80. The 16" tire is $108. You can also get them at Costco with a $70 rebate every other month.

The key to purchasing any premium LRR tire is to wait until the rebates are offered. There is a $70 rebate for both Michelin and Bridgestone. There is an $80 rebate for certain Goodyear tires but not all qualify. Discount Tire also runs a $100 rebate for any 4 tires but they only do this twice a year or so.

[mcrews]

really need to have all the tire sizes to have a better understanding. Also the diameters.
Is the rpm at 60mph lower or higher with the 15s?
were the 17' 45s and the 15's 70s?

[F8L]

Originally Posted by mcrews

really need to have all the tire sizes to have a better understanding. Also the diameters.
Is the rpm at 60mph lower or higher with the 15s?
were the 17' 45s and the 15's 70s?

I stated all of the tire sizes for myself and the OP.

The 17s were either 45 series or 50 series. Both sizes were tested. The 15s are a 65 series. Revs/mile were also listed.

RPM is too difficult to monitor because of the power split device and how it regulates RPM.

Speedometer and odometer effects were monitored, however.

[F8L]

To recap.

GenII (2004-2009) Prius tire sizes:
185/65/15 - 24.5" dia, 855 rev/mile average
215/45/17 - 24.7" dia, 844 rev/mile average

GenIII (2010-2013) Prius tire sizes:
195/65/15 - 25" dia, 829 revs/mile average
214/45/17 - 24.7" dia, 844 revs/mile average
205/5-/17 - 25.1" dia, 828-829 revs/mile

[mcrews]

sorry, f8l, I had refered to the op's first couple of pages.
somehow i MIssed the middle pages.
but it was alll muddled by then.

[F8L]

Originally Posted by mcrews

sorry, f8l, I had refered to the op's first couple of pages.
somehow i MIssed the middle pages.
but it was alll muddled by then.

Oops, sorry for the confusion.

[silverdelight]

I haven't seen anyone mention the new Michelin Defender tire. I'm trying to figure out if they are responsible for about a 5 MPG loss on our 2007 Prius. We bought this car about three weeks ago and put new tires on it a day after purchasing it. Since we had only driven the car for a short time while trying it out, and then about a 2 hour drive home (mostly highway miles) we can't actually say what the "normal" MPG is for us. The car said the average for the person that had it before us was 42, and we seemed to continue to get that on our drive home. But since putting the Defender (185/65/15) tires on, I am lucky if I get an average of 34 MPG!

Now most of my driving is 10 minutes to work and back, or 5-10 minutes running errands from work, so I'm probably not going to get the best MPG's with that type of driving. But does that seem normal? To me it seems like I have lost considerable MPG when we put the Defenders on. I have about 7 more days to decide if we want to keep these tires... I'm thinking of going back and having them put the Michelin Energy Savers on which were spoken of in an earlier posting.

One more thing... I did read that my MPG is expected to drop due to winter gas, and cold temps. But again, could that be responsible for the loss we are experiencing, along with driving mostly short distances? Or do my tires have something to do with it too? I only saw one other posting on these tires from another Prius owner (after we bought ours), and he stated he lost 5 MPG when he put them on. A few other postings mentioned they thought they got the same, or a little better, but they didn't say if they were Prius owners, so it's hard to go by their comments. There isn't much feedback on the Defender tires yet.

Looking for any advice that will help us decide what to do.

[F8L]

The Michelin Defender is not quite as fuel efficient as the OE 15" tires on the GenIII. I'm not sure how they compare to the Integrity on the GenII but I'm sure they are not more fuel efficient. It seems most people lose a few mpg when switching to the Defender BUT losing a few mpg is typical when you swap a worn tire for almost any new tire unless the new tire is the Energy Saver A/S or Ecopia EP422.

Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires

The Defender is a good tire. It's just not the most fuel efficient choice. If it truly lasts 90,000 miles then some of that inefficiency will be made up for compared to the Energy Saver A/S which is rated for 65,000 miles. The Energy Saver A/S is good for 3+mpg more than the Defender when equipped on a Prius.

[silverdelight]

Would either of the two be better on wet/snowy roads? I did take it on the highway today for a 60 minute road trip and managed to average 45 MPG for the trip. I was surprised at that. It was another 10 degrees warmer today (47), if that had anything to do with it. At least now I know I can still get at least 45 MPG with the Defender tires, even if it's only on the highway. I was worried I'd never see that kind of mileage again