gen2 wheels vs.gen3

They are effectively the same. One may have slightly better aerodynamic properties but because the tuck into the well so much I doubt you could measure the difference.

 

yes same size

 

Isn't the second gen base tire something like 185/65R15? Vs 3rd gen's 195/65R15. The cosequential smaller od would change your gearing, throw the odometer off, and so on. Not a lot, but some.

 

The question was about wheels not tyres.

 

Assuming the computer/parts are all the same ratios between Gen II and Gen III the difference is 855 revolutions per mile (RPM) on the Gen II OEM tire vs 829 to 836 RPM. Using 855/836 it's roughly 2% difference in speed/mileage/etcetera. In another thread I laid out the reasoning why I'm assuming 845 is the most accurate RPM but it could be 850 or some other number.

15" Rims (standard aluminum rims in the US 2004-2009)
185/65/15 (2004-2009 Standard U.S. OEM tire size for Goodyear Integrity at 855 RPM)

15" Rims (standard alloy rims in the US 2010+)
195/65/15 (2010+ OEM tire size 1 Goodyear Assurance Fuel Max at 836 RPM)
195/65/15 (2010+ OEM tire size 2 Bridgestone Ecopia EP20 at 833 RPM)
195/65/15 (2010+ OEM tire size 3 Yokohama AVID S33D at 829 RPM)

But since every tire brand has differing RPM / outer diameters for each line of tires it's easy to find the correct RPM / OD in tires of varying xxx/xx/15 sizes such as

RPM "Size" Brand/Model
851 185/65/15 Nokian eNTYR
850 185/65/15 Yokohama AVID ENVigor
848 185/65/15 Continental ProContact with eco Plus#
847 205/60/15 Goodyear Assurance Fuel Max
844 205/60/15 Kumho eco Solus HM KR22
843 185/65/15 General Alimax HP
842 195/65/15 Michelin HydroEdge w/ Green X (All-Season)
842 185/65/15 Continental ContiProContact#
841 205/60/15 Continental ProContact with eco Plus#

### Please note that the "ContiProcontact" and the "ProContact with eco Plus" are confusingly similar names with differing sizes to get the same accuracy.

In some lines like the Assurance Fuel Max you can easily put several sizes on your Prius such as

185/65/15
195/65/15
205/60/15


The Pirelli P4 Four Seasons it grouped even tighter by RPM adding one more size to the mix (sorted by OD / RPM)

195/60R15
185/65R15
205/60R15
195/65R15

In other tire lines the RPM are so far away from standard you can't get it on a Prius at all or are restricted to one tire size that is right on the edge of usable or they don't even make that tire in the size that would be in the correct range.

fwiw I'm going on the assumption that 845 RPM is "right" for both the Gen II and Gen III Prius no matter if it's a 205, 195, or 185 tire. And since I'm targeting 845, I avoid recommending a tire outside of the 835-855 range. In fact if it weren't for the highly rated Hankook Optimo H727 being at both ends I'd probably not push outside that at all.

Hankook Optimo H727
195/60R15 858 (closer to Gen II OEM tire RPM)
195/65R15 831 (closer to Gen III OEM tire RPMs)

 

I concur with dhanson865 for the most part.

The original Integritys and my dB Super E-Spec sport an RPM of 855 and 848 respectively. They both created an approx. 2mph too fast condition on the speedo. When I had checked the speedo accuracy on the dB Super E-Spec they were already worn down at least 75% if not 50%. This would have increased the revs per mile.

My 17" Primacy MXM4's sport an RPM of 844. These tires when brand new would almost fully correct the 2mph speed error such that when compared to GPS (with a min. of 30' accuracy) the speedo read exactly the same as the GPS. I still feel the speedo was a tad too fast but that could be GPS error.

So I cannot pinpoint an exact number of revs per mile that would fully correct the speedo error but it is very close to 845 or a little below that.

 

It's looking like I might have to eat crow. Mark57 was nice enough to do a pretty thorough test with his Gen III from 25 to 75 mph and it looks like Gen III likes 835 RPM.

See http://priuschat.com/forums/gen-iii...-fast-have-you-taken-prius-2.html#post1399436 and there abouts.

I'm still not certain if Gen II wants different RPM than Gen III. I either need someone to do a similar test with fresh tires of a known RPM on a Gen II or I need to get a GPS so I can do it with mine.

 

I wish I had performed the test when my dB's were new but it just didn't occur to me at the time. At least we know how the 844 RPM works on the GenII.

Darelldd is buying new tires for his GenII soon. I'll ask him to test it.

 

I am using 831 Hankook 205/55/16 tyres in the UK and still find my speedo reads slightly fast, some ware around .5 to 1 MPH at 30 MPH but I do not know how the UK and US cars differ if any. This is on a GEN2 Tspirit witch I think is similar to your touring version of the Prius.

 

SWMBO's Gen2 T4 has 16" rims with 195/55/R16 tyres, would she benefit from changing to the Gen3 15" rims, mpg wise.

 

In theory yes but if the 16" wheels have LRR tires and the 15s use a high performance tire then probably not. It all depends on the setup but generally speaking, the 15" wheel with a LRR will get better mpg than a 16" wheel with the same tire as long as there are not other differences like the 16" wheel being substantially lighter.