Need 5200 Mile Road Trip Advice

If you don't already own a 135/80-16 spare tire that fits your Prime, buy one now & practice mounting it under good daylight conditions...


Rob43

 

Expect to lose a lot of it, and get something closer to straight-gasoline MPG.

Expect to lose at lease at much as if you didn't use battery recharge mode while driving.

Any external carrier will cause a very significant loss. My rear bike rack, loaded, on a Gen3, does something like 15%. And that is at slower speeds than you will be using to achieve 1000 miles per day.

Just get over keeping your lifetime MPG rating for now, you can't keep a good number on a trip like this. Take the trip, then reset your long-term gauge and start over.

 

My experience has been...given i've run from Indiana to Nevada numerous times in the prime...your gas mileage will be less than your 86mpg on the interstate...At highway speed ...ie 70-85mph...your mileage will fall into the 55-60 mpg range...your ev battery range of 20-25 miles will be used very fast if your running in ev mode...I highly recommend only running in HV mode on the highway and EV mode in the towns and in slower speed areas...Running in charge mode will work but your mileage will fall into the lower 50s if you charge while running 75mph over a 30 minute charge time...(more-less)...Also as you go...leave a bit of EV charge on the display...like 6-10 miles of EV, while driving in HV mode...the car will try to add to it as you brake or slow down....etc...make sure you take your charge cable with you...you never know where you could plug into a 120V plug somewhere...(otherwise use 240V level 2 as you find them...) some hotels/motels and food establishments have 240V level 2 ...
Expect even lower MPGs with air drag on top as you highway speed increases...Overall my average MPG on the Indian-Nevada drives at Interstate speed and mountain climbs yield about 55-60mpg...YMMV and weather changes will cause decreases with higher use of AC as temperature climb...and rain drag on the pavement...etc...BTW if you sleep in car make sure it stays in the ready mode, and you dont need a full charge(80%) on the EV portion of the battery while stopped...while in ready mode the prime will act like a normal prius and kick in the engine as needed then off again...so an EV full charge isnt mandatory but it is ok if you do have it charged before stopping...

 

Good.

Both sizes are within a 1/10" of each other, so both will work excellent.

The reason I like the 135/80-16 over your 125/80-17 is because the 135/80-16 has a higher Max Load rating.


Rob43

 

That's good thinking if you're driving on brand new tires...

But as averages go, many Prime owners "might" be at ~25K miles (or more) when they get their first flat, thus the much closer overall diameter tire size will be the 135/80-16 at 24.8".


Rob43

 

So true , it took me about a good 12 months to get over that

 

My clean Prime typically averages about 56 indicated mpg in the highway at 73 mph, as one data point. That’s summer with A/C on, Interstates in the midwest.

With that roof box, I would predict that under similar conditions you would be in the mid 40’s max.

The battery in the Prime can absorb a lot of charge in the mountains. I would run in the mountains with about 50% charge to start. This will let you regenerate on downhills, and if the battery gets full or near full you can do some climbing in EV to make room for more regeneration. Look at a map of the terrain ahead and plan accordingly.

 

Like others have chimed in, the highway speed (anything above 65mph), AC use, heavy loads, rooftop container, no nightly charge, CHARGE MODE use, all will contribute to the lower mpg. My bet is that you will likely to loose substantial efficiency from your current 86mpg.

On my PRIME, I usually get 60-65 mpg on highway drive pure HV (no EV range) if I can keep speed below 65mph during summer. This is without using rooftop container nor CHARGE MODE, and with two occupants with minimal AC use. If I go above 70mph, the mileage drops to mid 50mpg. If it's winter time, the best I can get on highway is mid 50mpg. This is with modest AC (heat) use and with snow tires on.

 

This^

I did a similar trip in my previous car (honda civic hybrid) and, with the rooftop carrier, fully loaded, at highway speeds dropped my normal 40-45mpg down to the 20-30mpg range. I wouldn't be surprised if your Prime dropped down into the 30-40mpg under similar conditions.

That being said, any other vehicle would probably get far worse mpg for the trip. Honestly, I wouldn't worry about the mpg and focus on the drive. 1000mi/day is a pretty rough drive (something in the 12-14hr driving per day).

 

Is the roof box just for the spare?
If so, there are hitch mounted spare carriers that would have a smaller penalty than anything on the roof, though it might be higher cost.

 

The trick with HV mode on long trips is remembering to switch it on every time you startup.
The one time I remembered to switch on HV every time I got 70 mpg on a 900 mile trip and
had 90% of the initial charge still available at the end of the trip.
Others here might say that is not the way their Primes behave on long trips,
so you have to remember that the car adjusts to the drivers driving style somewhat.
And then there are things most of us don't really know for sure about how the car calculates everything.

The other two times I made the same 900 mile trip, i'd forget to switch into HV mode
after stopping for gas or food and I ran the estimated EV range way down. After that the EV range
never recovered fully for me during the rest of the trip and I ended the trips in the mid 50's mpg both times

I don't use charge mode too often, but I did run some tests and at hwy speeds 60 - 80 I've gotten 45 mpg.
At 35 mph I've gotten 55 mpg.

There are times when I've needed to charge and didn't have time to wait, even the 2 hours for Level 2 to finish.
So I switched to charge mode and got 80% charged, finishing off plugged into level 1 at home
and had a full charge when I needed it.

If you can figure out a way to streamline the roof you might not loose as much mileage as you would
with the wind blowing all around and through those racks and box.

Hope you have a great trip and get mileage you're happy with.

 

Well, some car manuals say using roof racks falls under extreme service in terms of maintenance. The how for why the reduce fuel economy also means the engine is running under higher load than normal.

 

That's a barn door up there. Not very aerodynamic.

Edit - the air coming off the windshield goes right to the bottom of the box and has to be compressed to go under the box. And add the turbulence from the blunt back of the box.

 

The coefficient of drag is just one part of measuring an object's aerodynamics. The other is the frontal area, which includes the gaps under the car, and between it and the roof rack.

Even if a roof box manages to not increase a car's drag coefficient, the increased frontal area means more total air drag that the car has to work against. So fuel economy will always drop with a roof rack, and the impact gets worse at higher speeds.