right tires for a good MPG

michelin energy saver a/s.

 

whatever is already on there, 195?

 

The OEM spec for the 2007 is 185/65/R15, but in the UK the 16" rim are fitted with 195/55/R16 and here in NZ we fit 195/55 R15 on 15" rims. I'm not sure what effect the wider tires would have, but of much greater importance is getting tires that have low rolling resistance (LRR). As the name implies an LRR tire will roll further before it stops due to a lower resistance.

The Michelin mentioned by Bisco is one that comes up a lot. Other manufacturers also make LRR tires:

• Michelin Defender
• Bridgestone Ecopia 422 Plus
• Bridgestone Ecopia 422
• Continental TrueContact
• Continental ContiProContact
• Goodyear Assurance Fuel Max
• Goodyear Assurance ComforTred Touring
• Yokohama Avid Ascend (T-Speed Rated)

The Goodyear Integrity are the OEM tire, but not a lot of people have anything good to say about them.

If you want opinions about any of these tires do a search in the Gen II Fuel Economy forum using any of the tires listed above and read until your eyes hurt.

Once you have your new tires fitted, be sure you run them 4-6 PSI higher than the door placard (35F/33R) so at 39F/37R - 41F/39R. Any higher than this yields diminishing returns in my experience.

Hope that helps.

 

Patience, grasshopper!!

 

Look on TireRack. You can set it to show only LRR.

 

That would be correct.

 

185 Michelin Energy Saver A/S. We consistently knock down 50+mpg in mixed driving conditions inflated to 42F/40R. This car does 100+ mile daily commutes most of the week as well.

 

195, bigger, better mpg's
More accurate speedometer

 

I wouldn't do ANY of the above.

 

Anyway, to answer the op's question, the 195's will save more fuel, what of the above btw, wouldn't YOU do?

 

The stock tire width is 185. Going to a wider 195 tire will invariably lower mpg.

Speedometers read slightly high due to international agreements, in the hopes of slowing drivers down a bit. Odometers however, are accurate. Going to larger outside diameter tires to "correct" the speedometer seems overkill, and it will cause the odometer to read low. Larger tires will also be more expensive, and (albeit only slightly) reduce wheel well clearance.

 

Ah, I see

Yes the width of the 185 is 7.4 inches vs 7.9 inches for the 195, the 195 has a 25" circumference vs the 24.5" circumference for the 185 series tire, I'm saying the 195 gives better mpg's because of the larger circumference, irregardless of the 1/2" larger width.
And the speedometer is almost exactly correct.

But...I'd be interested in seeing unbiased comparisons.

 

Not to mention probably even heavier and thus contribute more to unsprung weight.

 

Increasing the rolling circumference in a manual car can improve mpg by reducing engine revs for a given speed. With the Prius transmission this is not the case as engine revs are likely to increase with an increase in torque load that a larger circumference will produce

John

 

A 55 is a wider tire than a 65 for a given diameter. Typically, narrower tires give better mileage and poorer handling. If you drive typical Prius style, hypermiling and such, I'd select one of the LRR (low rolling resistance) tires in the 65 profile. If the recommended tire is a 195/55 then you could go to a 185/65, which should keep the diameter around the same while narrowing the thread footprint. I use the Bridgestone Ecopian 422 in the factory recommended size on both the Prius and am now putting some of them on my Odyssey van. I get around 59 in the summer and 45 to 50 in the winter, typically never exceeding 65 MPH. Again, this slightly reduces cornering and stopping effectiveness because you have less rubber meeting the road, the reason for the increased economy. The LRR tires accomplish similar by staying "rounder" (they are stiffer in the sidewall), I understand. Others may elucidate a bit more.

 

Assuming 55 and 65 are tire profile heights (the number after the slash) I think you jumped the tracks there. Not 100% sure, the coffee hasn't kicked in yet. Take tire designations:

195/65R15 and 205/65R15

The second's wider than the first is all.

 

I agree. Same profile, bigger size. The second is also taller. (The 65 is a percentage of height vs. width.) But if you compare a 195/65R15 with a 195/55R15, the second one is again wider (and also shorter). Make the first a 205/65R15 vs 195/55R15 and I believe that they will be around the same diameter with the 55 still wider. Do we need a tire person here????