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Originally Posted by ps2fixer
The CVT in the prius still has a max high gear ratio. I'm not sure how the computer calculates what gear ratio it runs at, but it assumes stock sized tires. My thinking would be it would use higher gearing while in cruise when it should be in the highest effective gearing already. I've read the gear ratio of it is 4.11, I suspect that's the sun gear ratio. The "CVT" effect is just engine vs electric motor rpm to simulate the lower gears. A side effect of this is the 41mph max speed to kill the engine and have the electric motors be happy (regen or driving on electric only) can be increased by the % of the oversized tires as the rpm's for the engine/motors wouldn't change besides the effective final drive gear ratio.
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Ah I see - the larger tire size should trick the car into thinking you're only going 40mph when you're really going 42 (or whatever).
As far as I can tell, the effective gearing is pretty similar between gen2 and gen3 despite large differences in final drive & MG2 rpm:
NHW20:0.620m(185/65R15)
ZVW30:0.635m(195/65R15)
NHW20: 6400rpm / 4.113 = 1556rpm (max wheel rpm)
1556rpm*0.620m*3.1416*60min/1000 = 181.9 km/h (113.0mph)
ZVW30: 13500rpm / 2.636 / 3.267 = 1568rpm (max wheel rpm)
1568rpm*0.635m*3.1416*60min/1000 = 187.6 km/h (116.6mph)
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I'd hope the tire size change doesn't make the computer use higher than ideal ratios for taking off and such, but who knows if the prius's programming is based purely on best mpg figures for a given acceleration rate.
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I think the computer just tries to set the ICE at the most efficient rpm for the given load and lets MG1/MG2 figure out how to make that happen for whatever speed you're currently at.
For the Gen2, you can stay at the 1000 rpm "idle" until about 66mph and hit 110mph at ~3,000rpm so I don't otherwise see a benefit from the tire gear change. You can play around with MG1, ICE, and MG2 speeds here:
Toyota Prius - Power Split Device
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I liked my corolla because I could give it a lot of throttle but the transmission wouldn't down shift, so I could load the engine well and put it in the more efficient range. It wasn't a fast take off since I'd let off and get it to shift basically as soon as possible. The prius seems to rev up the engine more than ideal, it doesn't sound like it's loaded as much as I'd like, but I don't have direct control over that either besides what I tell it via the gas pedal.
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Look again at the BSFC graph:
The prius ICE is meant to operate on that thick black line - varying rpm to match the desired power.
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My battery testing was done at 30mph on pavement, my house is 1/4 mile on dirt and I travel 10-20mph depending on road condition. Thanks for the extra details about the actual speed you traveled at, I think roughly speaking that should be a reasonable way to test the hybrid battery, 15mph should have very little areo effect and the loads should be more or less linear as long as the road start and end points are roughly the same elevation (perfectly flat would be ideal of course). My dirt road can be pretty smooth and just a few loose stones on top but otherwise about as hard as pavement, other times it's loose like right after it's graded, and of course when it's wet it can be muddy. The road as a lot of sand/dirt not much rock. I suspect the scan gauge or the app suggested before would give a solid value as well, but sometimes real world testing is nice since the other numbers should be more theory based (calculated, but effectively a guess based on past performance).
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Yeah, road surface can have a huge effect on how well it rolls. Hardpack dry dirt is probably even better than asphalt. Smooth concrete is probably the best you'll encounter. Potholes and water and gravel and mud all add resistance - sometimes 2 to 3x the rolling resistance which is all the really matters at battery speeds...
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Based on a little searching, your 2010 should have a 1.6kwh battery, while mine seems to be around 1.3kwh which is about 23% difference. That should mean if I have the same usable % of the battery as you, I should be able to go roughly 1.5 miles at 15mph. I know the 2010 is a bit different from the 2004-2009 era. I suspect mph on pure electric mode effects the efficiency point of the electric motors (rpm vs torque output). I haven't studied electric motors a whole lot, but peak levels if I remember right are around 90% efficient (1000w of electricity in for 900w of mechanical work output). I'm not sure how much that drops at less than ideal rpm's though and these cars have a bit of a unique electric motor in them.
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I'm new to motors and batteries so I'm learning as we go. My understanding is the gen2 and gen3 both have 28 7.2v cells totaling 201.6 V with 6.5 amp-hours capacity. 201.6V x 6.5Ah = 1310 watt-hours, or 1.31 kWh.
From my reading gen3 cells were slightly improved and had less internal resistance for better efficiency.
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Anyway, the gravel road is only 1/4 mile (1/2 mile per round trip), so the overall effect it has on mpg shouldn't be much. All the other roads are paved even if they are bumpy. I can really feel the bumps, but I'm guessing that's more because of the broken strut spring lol.
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Yeah, I just hate when my ICE is on while I'm poking along on a dirt road because my mpg plummets. I prefer the engine warm up and/or charge the batteries while I'm driving 30-40mph...