the rack seems to reduce MPG by like 8mpg on my prius
adding two bikes doesn’t seem to make it much worse
.
Similar experience with a roof rack on a Dodge Truck, though not quite 8mpg. The Prius was specifically designed with a low drag co-efficient which I’m sure is drastically altered with the roof rack, adding a couple of bikes afterwards probably doesn’t matter after the initial loss. I think most people would save a ton of gas taking off their roof racks when not in use…
I haven’t noticed that much of a difference on my Civic. Gas mileage is down a little with the rack on all summer, but more like 1-2 mpg, not 8. Bikes don’t seem make much of a difference beyond the rack, but I don’t have any empirical data to back that up.
…old design Scion XB, I think the roof rack is about 2-3MPG loss at most. I haven’t noticed a drop off with the bike but never really paid close attention. Of course the Scion was never really designed with Aerodynamics in mind so my guess is that a roof rack can’t hurt that much.
throw a zipp sub9 up there and your car will refill itself as you drive down the road.
'03 Jetta. 2.0 and 5 sp. Leave the rack on all the time, because it’s too much trouble to take it off. Average 30 most of the time. 32 for a 2 hr or longer trip. Fueleconomy.gov says 29 on the highway, so it’s hard to complain. Guess that it may cost me 2-3 mpg. Not much difference with the bike on it.
I would guess that it is mostly the rack based on the noise, which is the reason I take it off when not going to a race etc. I like my sunroof. Noise doesn’t change much w/ bikes. Not noticed mpg more than 1-2 w/ rack.
Mine go inside, but on my other car (wife’s Audi wagon), only about 4-5 mpg less. 8 does seem like a lot, but maybe not for a Prius with that Kamm/phantom trailing edge or whatever that shape is called.
Do you have the wind-deflector? That made a MASSIVE difference on the aero-ness of my rack.
Put a P3C on it and it will certainly improve your mileage
Seriously now, given that the Prius is a highly efficient vehicle where aerodynamics is optimized, it is possible that the roof rack is causing the 8MPG deterioration… If you think in percentage terms, it would be similar to a regular car getting 3-4 worse MPG…
I would try a wind deflector which has already been suggested here
Part of the problem is that mpg is “backwards.” Volume really should be in the numerator and distance in the denominator.
A Prius that suffers an 8 mpg loss goes from, say 46 to 38 mpg, is going from 5.1 to 6.2 liters of fuel per 100 km.
A car that gets 25 mpg and loses 4 mpg is going from 9.4 to 11.2 L/100 km and actually loses more fuel economy.
Put P3C on it… Definitely the reply of the day!
Thule roof rack with a wind fairing on a Durango. No difference in noise or mpg.
With two bikes added, it costs 2-3 mpg.
Before I put the wind fairing on, the noise was pretty bad. I never took a trip with just the rack without the fairing.
I have a Camry hybrid and this is roughly what I get:
No rack interstate - 38
Rack only interstate - 33-34
Rack & 1 bike, town & highway - 30
Rack & 2 bikes highway - 26
It’s a huge difference for me and if I’m traveling to a race by myself I take the rack off and put the bike in the back seat. Most of the time the back is occupied with 2 carseats though. I drive normally, no pump & coast or crazy hyper-miling granny take offs.
Your car is gay, and far more damaging to the earth than a Civic…but.
On my Audi I get about 34 hwy @ 80mph with one bike on.
When I am at 80mph with three bikes, three wheel mounts, wind deflector I am more like 25 or so. I was far less when I had five bikes on the roof with five wheels (yes, I have wide cross bars and you have to put bikes front and rear facing).
Is that with the flying-pigs mounted or without?
seriously people are still taking that hummer/prius earth damage article seriously?
it was based on 1970s battery manufacturing tech and ignores the toyota battery recycling program.
and my car is gay?
I will, publically announce, that I will meet you at any autocross event in the Texas (or sufficiently nearby), and race against you, head to head in your own daily driver.
if you beat me I will pay you $250
if I win you owe me nothing except to admit you are an idiot.
i am kinda ok at triathlon but im a lot better at performance driving and car setup. I wont even bother to set the prius up to go fast though.
=)
Your car is gay, and far more damaging to the earth than a Civic…but.
On my Audi I get about 34 hwy @ 80mph with one bike on.
When I am at 80mph with three bikes, three wheel mounts, wind deflector I am more like 25 or so. I was far less when I had five bikes on the roof with five wheels (yes, I have wide cross bars and you have to put bikes front and rear facing).
On topic: I see almost no drop in the city with roof rack/bike on but about 1-2 on the freeway.
Frankly I share in RC10’s comments. A hybrid who’s aerodynamic and yet barely gets more than diesel powered engines with more hp? As for it being bad for the environment; I believe there’s exact numbers showing that the increase in fuel efficiency of the Prius is far outweighed by the carbon footprint of making it(versus purchasing the thousands of used vehicles)
Where do you live btw? I might take you up on the autoX offer with my Mini 
(which gets 38 in the city and 45 in my last road trip this past weekend)
What kind of audi is this?
I get 34 @ 80 with 2 bikes,with a TDI Jetta. Unless it is a TDI how are you evengetting 34mph without a roof rack?
We’ve actually gotten decent mpg w/ the bikes on the roof of my wife’s car on the hwy, but only if we are driving at a consistent speed (of course; this always makes the mpg better, but the effect seems to be magnified w/ the bikes up there).
Slightly OT - we took my car w/ a trunk rack and 3 bikes (2 road, and my daughter’s little boat anchor) up to VT for va-ca recently.
OMG, it totally destroyed my mpg!!! I normally get uppper 20’s on the hwy in my car, and even loaded down w/ all of us and our stuff, I’d still expect at least mid-20’s.
I think we averaged at or just under 20 mpg that trip. So, at least for that car, w/ that rack and those bikes, it was a good 5-6++ mpg lost.
(which is much worse than what I’ve ever experienced w/ the bikes up on the Thule roof rack)