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Old 04-21-2022, 03:34 AM   #1 (permalink)
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Got a prius, should be interesting to mess with....



Been a while since I've poked around here. Went from a camry (around 30mpg), to a corolla (38-44mpg), then went the opposite way to a Lexus LS400 v8 car (15-20mpg, it needs work, o2 sensors and such). I got a matrix and the mpg was horrible for what I expected, 30-33mpg, maybe there's an issue with it I didn't pick up on, but the old corolla engine I liked a lot more. Anyway, now I have a 2006 prius. It's a bit of a beater, banged up, ugly, city beater car.

Main focus for it is short trips for my business ~10 miles round trip in the country (55mph limit). Secondary use case is longer trips on the expressway likely around 60mph (75mph limit).

Rear spoiler is cracked a bit, front "hub caps" or rings are broken a bit, and there's a chunk of plastic hanging down in the front I need to fix up. Looks like it hit something in the front, some of the front plastic is messed up.

I'm thinking a kammback will give a bit of a gain. It's a base model, so no backup camera (or it doesn't function). Clearly blocking off the front end some will help things a bit. I haven't gotten under it to see what the belly pan situation looks like. Any other low hanging fruit for mpg I'm missing?

For the prius only stuff, I suspect taking the hybrid battery apart and balancing the cells would be a good idea, maybe capacity test them or whatever process to detect under performing cells and replace them.

I only recently got the car legal, so haven't done much testing with it. Just a few short trips so far and I'm only seeing around 45mpg so far. Instant mpg I see hangs around 50-70mpg at around 55mph, most of the time around 50-55mpg. The engine seems to run a little off at idle, maybe a slight miss. I have some basic "tuneup" parts coming for it, spark plugs, air filter, doing an oil change soon and cabin filter.

My last mpg based car was the corolla, I could give it a lot of throttle and hit around 70-80% load while taking off and it seemed to do quite well. Since the prius automatically adjusts the gear ratio to what it thinks you want to do, I'm not sure what the optimum take off pattern is for them. I assumed light take off would be best, but maybe pulse and glide logic is better on the prius (aka almost floor it and get up to speed asap as I understand it)

Tires are already at around 45psi. I have a broken strut spring in the rear so have new rear struts coming as well. It rides about like a skate board right now lol. The design is good where there's effectively no risk of the spring touching the tire. I bought the car as "non running", even though the seller jumped it with a 12v battery and had it running. It wasn't too happy about anything, abs, brakes, everything was on basically except check engine light. I've gotten all of the warning lights off except tire pressure, and the 12v battery should be about charged up all the way. I'll have to see if it holds a charge or not since it sat dead for who knows how long.

Anyway, not looking to go super crazy extreme or anything, hoping to hit at least 50mpg average for short trips, and maybe 55-60mpg for longer trips which from what I've read and watched on vids, should be very solid goals with my driving style and slower average speeds.


I've looked around for some mods on Prius cars, but I didn't see a whole bunch.

I did see a device that spoofed the engine coolant temp once the engine was warmed up to keep the engine running less. I might build a micro controller to do something similar if there's an easy way to detect when the engine is being started by the computer. Like say the engine is fully warmed up so the engine doesn't go through the warm up process till I'm already crawling down the road on battery only long enough for it to want to recharge. Maybe that's less efficient though since it would be charging while cold. I always just started up my corolla and started moving right away and drove lightly and could hit good mpg in the first mile or so.

I've also played around with aftermarket computers a little for "race" use. It would be interesting to toy with building my own control system, but that's probably out of my scope for the time being.

I also want to use the Prius as an efficient generator since it seems my area has really unreliable power for the last few years (10-20 outages a year). On the stock inverter system I've heard it's rated for about 1500w but the car being in ready mode draws something like 300w. I assume not much can be done about the extra draw unless I tapped into the high voltage battery with a dc to dc converter and somehow controlled the start button on the car based on the hybrid battery state of charge. Haven't thought about this too much yet, but I've ran over some numbers people have stated and it's about as efficient as a backup diesel generator at an ideal load, much better than any gas generator.


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Old 04-22-2022, 07:41 PM   #2 (permalink)
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Well I think I found why the vehicle was sold for scrap. The gauge cluster went blank on me today. Center screen still worked but no mpg figures. It still drove normal. I left it off for a while and when I turned it back on, the screen worked again and I think the trip was still counting up.

Going off of the in car indicators, I'm averaging about 47mpg so far. I'm sure I'm doing some things wrong for best mpg. Taking off real easy letting it take off on electric only generally to about 20mph before the engine kicks on and cruising at 55mph. Once the battery is charged and the engine is warmed up, I'm seeing around 50-60mpg in cruise. For fun today I dropped my speed down to 45 and it bounced around 60-80mpg. Seems like this car really likes going slower speeds.

With a cold engine, I'm not sure what the best method of driving is. It seems like the first 5 mins I'm seeing around 25-30mpg average as indicated at least, so I'll have to work on getting that better. From what I've seen other people driving the car more or less normal is beating me there but I'm not sure what speeds they are traveling out, the videos are always later in the drive which I'm seeing good mpg at those points.

For the hybrid battery, I drove to my dad's house on his road 30mph electric only and parked it. It started off 2 bars from full, and parked with still 2 bars from full. When I left I went 35mph which seems to be mostly electric even though the engine was running for warmup mode. By the time I got to the corner I noticed the battery's state of charged dropped suddenly to 2 bars of charge. People online were saying with a healthy battery they can get about 2 miles on purely electric mode, looking like I'm around 1 mile, but it has 263k miles, so if it's at 50% capacity, or needs balanced, I think that would make perfect sense.

Anyway, I'll have to research the gauge cluster issue, I suspect it's bad capacitors which are easy enough to fix. I probably should have gotten a pic of it, basically everything was out except check engine light (tire pressure light went out, but check engine replaced it lol), cruise didn't work either.
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Old 04-22-2022, 07:55 PM   #3 (permalink)
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You generally want to avoid running on battery just for the sake of running on battery because the Prius electric-mode returns only about 67% of the energy that the internal combustion engine put into it.

Your engine makes power very efficiently at fairly high loads (say, 80mph cruising speed), but much less efficiently at low loads (creeping around a parking lot) so at slow speeds the car may switch back and forth between ICE & battery because even with that 33% energy loss, the engine might be more than 50% less efficient creeping at idle. The car is pretty smart about managing the hybrid system, but you can do even better by pulsing and gliding - accelerating at that fairly high load (pulse) and coasting at no load (glide). See:

The Gen2 prius will completely stop the engine when coasting below around 38mph (Gen3 will completely stop the engine coasting around 42mph). This speed fluctuates a bit depending on whether you're coming at it from below the threshold or above (kind of like automatic transmissions where you can coax an upshift at a certain speed, but hold that higher gear as you drop back down a couple mph below the upshift). Anyway, above that speed the engine spins 1000rpm which wastes energy. It doesn't burn fuel (directly) during the 1000rpm coast, but it is drawing power so for best pulse & glide mpg stay below that threshold.

As far as the bars or pips on the battery display - they are nearly useless. I'd just ignore them, but if you want to monitor battery life/usage you should use a scangauge to see a more accurate accounting of the current state of charge or, more preferably, get an OBD2 bluetooth adapter and the Dr. Prius app to see the individual battery cells.

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Old 04-22-2022, 08:18 PM   #4 (permalink)
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Here is the brake specific fuel consumption map for the Prius 1.5L (Gen 2 & Prius C) and 1.8L (Gen 3, V, & Gen 4):




That dark grey "island" of peak thermodynamic efficiency occurs between about 20 & 35 KW of power (~27-47 horsepower). Here is a ballpark of the power required to overcome aerodynamic drag and rolling resistance at steady speed on flat ground for the gen 2 prius:

MPH HP
5 0.4
10 0.7
15 1.2
20 1.7
25 2.4
30 3.2
35 4.2
40 5.5
45 7.0
50 8.7
55 10.8
60 13.3
65 16.1
70 19.4
75 23.1
80 27.2
85 31.9
90 37.2
95 43.0
100 49.4

Add another ~1 hp to run all of the computers, another 2-8hp to run accessories like the water pump and air conditioning. But basically the load you put on your engine holding a steady ~80mph is the load you want to drive at when accelerating. And if you're not accelerating you should try to be coasting.
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Old 04-22-2022, 09:22 PM   #5 (permalink)
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I've done a touch of pulse and glide, it's a bit too active of a technique for me even though sometimes the roads are open enough to do it closer to my house. I live way out in the country so all roads are 55mph, in town it drops to 45mph for most of the roads. There's not much for 35mph and less besides really busy drives to stores and such. I messed around with that a tiny bit in my corolla, and from stopped to stopped, best I could get was around 60mpg while steady state I was able to get about 45-50mpg for the same area. My tank averages were 38-44 including winter driving, never quite hit 45mpg in a tank, but sometimes I couldn't drive for max mpg. I think my best trip steady state driving was 52mpg on the scan gauge.

The way I got good mpg in my corolla was keeping the engine rpm as low as possible basically, it was an automatic so I couldn't control the gearing myself. The prius seems to go too low gear for max mpg, it seems to want to really rev the engine. Based on that pic it looks like prime rpm for the engine is around 2000-3800 rpm. My corolla's peak torque was at 2800 rpm, and if I kept it in lockup the best mpg I could get was around 40-45mph (45mph is min to get lockup, it comes out about 40mph). I drove those speeds since I worked midnights and traffic was reasonable. Now there's a lot more section of the road that people can't pass now, dumb left turn lane that doesn't help much, but that's a different story lol.

Anyway, sounds like I'm driving the car almost exactly opposite from the ideal setup. I'll have to try driving on the engine more and see how that does. I guess for parking and leaving my drive way it makes sense to run on electric only, but once on the road I should be using the engine.

I figured the round trip efficiency from engine, to battery, back to electric motor was a bit better than 66%, I think that explains why my mpg seems low, just driving it wrong lol.

The coasting tip in the vid is a good one, I kind of had the thought that coasting w\o charging the battery and with the engine off was more ideal than charging the battery and shortening the coast distance.

I need to dig up my scan gauge some time, I have it around, but my last car I was driving is a 1990 so no OBD2 port. There's a check engine code set, I'm guessing it's for a misfire as it seems to have a very slight miss at idle. Under load it seems fine, got new plugs and such coming to see if that fixes it. If not I'll have to hook my scope up and see if any of the coils are starting to fail.

Anyway, thanks for the info and write up. Everything I was finding was basically drive like a grandma and coast as much as possible.

I mess around a bit with electronics and programming and such. For under 45mph, it might be good to do a minor pulse and glide, say 5mph speed range or so. I know more is more ideal but in traffic I think a 5mph change in speed would be acceptable. Would be interesting to intercept the accelerator pedal signal and automate the setup, set the "cruise" at the peak speed, and it drops to 40mph and speeds back up to 45mph automatically. Not sure if/when I'd have time to play around with it, but could be a fun little project.

It would be nice to be able to cost down from 55mph with out the engine spinning or the battery charging. Guessing putting the Prius in neutral isn't ideal while moving, but I haven't tried it either. That use case is pretty situational for me, if no one is behind me, I don't mind coating a farther distance, but if someone is behind me, I try to be reasonable on coasting, more than the average person, but less than ideal.
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Old 04-22-2022, 09:39 PM   #6 (permalink)
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You can put the prius into and out of neutral all you want. If you put it into nuetral when the engine is stopped, the engine will stay stopped even if you then exceed the normal engine-on speed. But you don't get any regenerative braking in neutral, so put it back in D before braking.

Above ~10mph the prius will regen slightly if you take your foot all the way off the accelerator so you have to give it some pedal to truly coast. If you wanted another electronic project - automating a true pedal-off coast would be nice. Neutral works, but again if you suddenly have to brake you don't recapture any of that energy.

An automated pulse and glide setup would be awesome too - set a high & low speed and have it accelerate optimally between the two and coast down...
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Old 04-22-2022, 09:59 PM   #7 (permalink)
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Yea I've thought of ideas similar to that back when I had my corolla going. I wanted to throw a small computer in the car with a GPS and wifi antenna so I could track elevation (up hill vs down hill) and also track the fuel usage, TPS reading, gear, temps, etc. The idea was to collect enough data just driving the car where it could predict the best route based on my driving habbits, and also it should be possible to have it suggest better ways to drive. Clearly coasting more is always a plus, but maybe just minor throttle changes on hills and such would be a help.

Since the prius is DBW, it's a lot easier to electrically control the throttle. With that control also comes a massive liability if I ever sold anything like that. An open source project might be interesting though. Tapping into the gear select switches and pedal shouldn't be too hard. ODB2 could get most of the other data needed, but reading directly off injector #1 I think would be more accurate for fuel usage.

I've been building harnesses for derby cars lately, they want to delete as much wiring as possible, remove protections for the engine, and all of that kind of stuff. That's why I've been looking into the micro controller stuff a fair bit. A speeduino should be able to control the Prius engine no problem, but it doesn't support the DBW pedal and throttle plate control. If those issues were solved, you could have more control over exactly when the engine started, and how it responded to throttle inputs. The hybrid computer will still control the regen and such if I'm understanding the wiring right. I've looked a little at it since there's a couple people out there want that to try to derby a prius. I suspect the car would hold up well in a derby, but the electronics up front would probably need to be relocated inside the car and then there's high voltage wires to deal with and such. Not exactly a friendly car to build for derby use lol.

The stock cruise control switch should be possible to be used for the automated pulse and glide computer, but I'm thinking it won't be possible to be able to switch between them too easily besides adding like a toggle switch somewhere. Clearly would need wiring tied into the brake pedal and such so it can be canceled, and all of the basic safety concerns solved. I'm fairly new to hardware designing, but I've programmed most of my life and get the basics of hardware design well enough to have an idea of what's going on at the circuit board level. This might be a good little project for around winter time when business is slow.

The board with all the lights is to show injector control and ignition control and such. The screen is the data from the speeduino, TPS % and such. Everything there is simulated, but there's quite a few people running engines off that project. It seems to be common over in the EU and AU more in the racing scenes. It might not be legal to run a car under 25 years old on a speeduino if it's for on road use (EPA/DOT regulations). Not sure how likely someone would get caught in a state with no inspection, or if it's like removing the catalytic converter where most people don't care. My state doesn't have inspection, for anything older probably 50% of the cars are missing the cat since the scrap prices for them have been crazy.

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Old 04-23-2022, 01:11 AM   #8 (permalink)
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I probably should have reset the trip for going to town and back, but it does seem to be slightly better mpg in the first 5 mins driving it on the engine when cold at least. Seems like I'm averaging around 45mpg with the 55mph driving.

I used the neutral costing a lot more, it didn't seem to effect the mpg too much, I did always put back in drive to slow down if I overshot the speed for the corner. Target was to coast to it around 25-30mph. With my corolla, it seemed like it coasted just as good as this car when I put it in neutral. There's a few marker points I'd coast at 45mph and hit the corner speed perfect. The prius might have slowed down a little less but I don't think it's a massive difference. Clearly have a lot to learn yet since I want to hit 50+ mpg with this car.

There is some front end damage on the passenger side, the plastic down there is messed up. I zip tied it up to make it a bit better, but I'm thinking a lower grill block might be in order, similar to my corolla had (upper + 1/2 lower for summer, 80% lower blocked for winter). The other factor is the rear strut spring is broken, so the rear end sits much lower than normal, maybe it's too low and is throwing the areo profile off.

Looking at quite a few ecomodder Prius cars 2004-2009 range, it looks like around 47-55mpg is the main range people are getting with a fairly unmodified car. Clearly the car's reported mpg isn't going to be perfect, but it seems to be pretty accurate for most people.

Anyway, I suspect lower grill block and fix up the belly pan and I'll see some reasonable increases. Fix the rear strut, and getting the engine running as best as it can with some fresh new full synthetic oil and it might be a bit happier. It's nice beating my Corolla's mpg while going 55mph while I had to do 45mph with the Corolla. I also tried out a Matrix and wasn't impressed at all, 30-33mpg with an unmodified car across a few tanks. I didn't hyper mile too much in it, but I tried a little. That car performing so bad is basically why I thought about trying a Prius. Basically wanted a good mpg vehicle with a hatch. Yaris was another car on my radar.

For my trip I made, probably should mention that was mostly with the heat off, no ac, no radio. It was raining both ways, 45F both ways and with headlights on both ways. I had to turn ac on a couple times to keep the windows cleared.

Just read an interesting post linked below. The person suggests using the battery as much as possible at the end of the trip, the concept is when the engine is cold started, it's charging the battery up for a quicker warm up and such. They claim 60+mpg averages. Kind of funny, there's so many little things that can be done differently, but the MPG effect is so small on these. Back when I was driving my corolla, first trip with it was only 33mpg, bad alignment, blown struts, pre-tuneup, junk rear tires, etc. Deleting the passenger mirror, belly pan, and grill blocks and I saw 20%+ gains.

https://electricvehicleforums.com/fo...tml#post135465

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Old 04-23-2022, 11:53 AM   #9 (permalink)
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Just FYI, the heat exchanger for the power inverter is in the lower section of the radiator. So if you block the lower grille, the inverter will run hotter. I don't think the car gains any benefit from the inverter warming up faster. But if you block the upper grille instead, it will warm up the engine faster.

I'm also trying to mod a Gen2 Prius for more fuel efficiency. But I'm not very good with electronics. So I'm focusing on the mechanical & aero stuff instead.

I noticed that sometimes my car turns on the gasoline engine when it really isn't needed (engine is warmed up, battery has good charge, coasting along). But if I let off the throttle just a tiny bit, the engine shuts off. So IMO the "engine turn-on" algorithm could use some fine-tuning. But I'm not sure if there's any way to adjust the ECU programming.

So I developed a tactic of getting to a coasting speed, then letting off the gas pedal to turn off the gas engine. Then I get back on the throttle to maintain coasting speed (and hopefully not turn the engine back on). I call it "gaming the gas pedal". And I've been able to achieve coasting speeds up to 40 mph with the engine off (level road, minimal wind, etc).

But it would be nice to have a switch or a button to force the gas engine off. Or tweak the ECU programming to make the gas engine usage more conservative. Anyway, I'm looking forward to what you accomplish with the electronics.
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Old 04-23-2022, 03:43 PM   #10 (permalink)
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The data from Drifter's posts works well. While cruising, say 55mph in my case, push the shift control left and hold it, about 0.5-1 sec it will be in neutral. I do the action at the same time and the car coasts and the engine turns off. I only have one 30 mile round trip under my belt with that trick, but so far that seems to work. I think it's best to put it back in drive under the 42mph upper limit so the engine isn't needed to be on. Basically there's 2 electric motors, and pure electric motor mode (regen or electric power) max speeds are around 42mph. Above that it needs the engine spinning to keep the electric motor rpm's within spec.

I didn't know where the heat exchanger was located for the inverter. I should be able to at least do a 50% block off easily with no problems, unless the Prius's cooling system isn't massively over sized like basically every other Toyota I've owned. I think I left my scangauge in my dad's Lexus when we was working on it last. Is there a gauge to show inverter temp by chance? I really don't like the fact the prius doesn't give any real gauges. I'm used to 90's era vehicles I guess where you could see voltage, coolant temp, sometimes oil pressure, rpm, etc.

Another factor for kicking the engine on is the hvac system, if you demand heat from it, defroster, ac, etc it's another reason for the engine to kick on. Like when I very first got the car, the 12v battery was dead, so I put the heater controls to max heat, rolled the windows down and in around a 10 mile trip I'm pretty sure the engine didn't turn off while on the car dolly. The battery seems to be doing well so far, last time I checked it was at 12.55v which isn't quite full charged, but it's 90%+. To check the 12v state of charge, it needs to sit long enough so the flash charge goes away, letting it sit overnight is the easiest way I've been going. You could put a load on it w\o turning on the charge system if you recently drove the car, but it's not as accurate. In a "normal" car you can crank the engine a little but not start it to eat up the flash charge.

As far as electrical mods, I'd have to look at the wire diagrams, but I don't think there's much direct control for the gas engine besides what the gas pedal and shifter does. I watched a vid about an open source controller for the inverter which drives the electric motors. According to that vid they can make 80hp or so but that's with the engine deleted, and the sun gear welded, not quite the route I'm looking to go. A pure electric car would be neat if the batteries didn't cost $10k+. I suspect most of the engine control and all of the automated functions in the care is communicated over the canbus, so maybe it's possible to intercept messages, or control things manually over that network. I have basically zero experience with canbus though, I just know it's a network designed for in the car, and of course the raw data is 1's and 0's. The new scope I bought recently is fast enough to read canbus though, so could be interesting to peek at some time.




Small update for the thread, I've done a fair bit of reading, sounds like 55mph trips people average roughly 45mpg so I'm slightly above what I've been seeing at around 47mpg. I'm sure fixing up the front end will help things a bit.

ABA testing is a bit harder with this car since the hybrid battery is a factor. When I get some spare time I might have to drive north a bit where there's basically no traffic and do some testing on driving patterns and such for take off. It seems like as long as I don't actually floor the car, or take off too light, it gets roughly the same mpg. I'd like to try higher speed pulse and glide and see how that effects things too. I'm pretty sure I could automate the setup with an Arduino. If the slight pulse & glide works well, then I'd want some way to automate it for long trips on the expressway and such since most of the time the traffic can get around no problem, unless it's a person not paying attention (lot of them around my area too lol).

An idea just dawned on me. I've been pulling up my driveway normally, but then I have to back out. Since my road is a dirt road, the last 1/4 mile is slow enough it's always electric only mode. I could back in and probably use slightly more battery than coasting in. I suspect puting a load on the cold engine sooner might be a benefit instead of idling and doing nothing. The trip to the first corner (1/4 mile) is again slow enough where the car wants to run off battery only even with the engine running to make the emissions systems happy and such. Too bad I couldn't control that a bit more, but that seems to be the nature of newer cars.

Another idea I had last night was the gear ratio. Since my driving is at higher speeds, I suspect having the gearing slightly higher should help mpg. At least my own experience has been larger tires give better mpg on normal cars roughly equal to the size increase if driven right. I don't need the car to be a rocket or anything. The fun thing is how well would the computer respond to the change though. Say a 10% increase in tire size gives 5% better mpg. If 45mpg is typical for 55mph speeds, then that would put me right in the 50mpg range for my goal. Sadly, it looks like the prius has a smaller 5 lug bolt pattern than the other vehicles I have in my yard, so I don't think I have a bolt on larger tire to just test the idea with. Has anyone else tried larger/smaller tires on a prius vs stock? Clearly the in car reported mpg and speedo will be off, have to offset the numbers based on the % difference in tire size (effective gear ratio change). City mpg will be worse most likely because of the higher gearing is harder to accelerate and the heavier tire.

Another idea that might be hard to aba test would be running a tire with a higher load rating. The whole tire would be heavier, but the max psi would be higher too. Like my truck's load range E tires are 80psi max and I run them at that pressure. I suspect "small" high load range tires are hard to find. Closest thing I can think of would be for a trailer which aren't designed for on car use, handling and such might suffer.


I found one mention going larger size got better mpg, but it's a person delivering mail... they went up one side on width and claim they got the best mpg that way. The ~4% larger size they lost 4mpg. Their use case is the opposite to mine though, so 4mpg drop in city driving might mean a 4mpg increase for highway driving. If you count 55mph+ as highway, that's 90% of my driving. I suspect once winter time hits, I'll be looking for some winter tires, so I'll look at going larger for the added ground clearance and ABA testing with 2 tires of each size and rotating the tires front to rear should be a reasonable test, same rolling resistance and such.



Just found this chart, looks really interesting. Looks like 14-27mph steady speed driving gives 100+ mpg on the prius. 55mph says 65mpg which doesn't match my car, but it's also 263k miles and needing some work, weaker battery, etc. The post/graph was posted in 2007 so likely using nearly new cars for the tests. On a warmer day I did a steady state 55mph test and the mpg readout said 53mpg if I remember right. I reset the trip while going 55mph, and looked at the average before I slowed down for the corner, engine fully warmed up clearly. That puts me down about 18.5% from what the chart suggests I should be getting on an effectively new car.


Source: https://priuschat.com/threads/most-e...-2#post-385271


Last edited by ps2fixer; 04-24-2022 at 03:42 AM..
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