Fuel economy with Thule rack/bike attachments

[czvekslak]

Hi All,

I am planning on purchasing a Prius either used or new in the spring. I work as a bike industry sales rep in Metro NY driving over 30k miles a year. I have been driving a Subaru Outback, while the care is very durable, plenty of space I average aroud 22-23MPG and gas is back to $3. I often need to carry sample bicycles on the roof. I use a Thule rack with 3-4 fork mount attachments. What kind of fuel economy drop can I expect while there are no bikes on the roof? I would have a fairing on. I know the hitch mount would be a better choice but getting to the trunk with bikes on the back is a pain and I will need to put a Thule storage box on top here and there.

My main goal is to cut my gas bill in half, I hope this can happen even with the rack on.

Thanks for help on this topic.

[omgitsroy326]

<div class='quotetop'>QUOTE(czvekslak @ Nov 17 2007, 10:50 AM) [snapback]540914[/snapback]</div>

Hi All,

I am planning on purchasing a Prius either used or new in the spring. I work as a bike industry sales rep in Metro NY driving over 30k miles a year. I have been driving a Subaru Outback, while the care is very durable, plenty of space I average aroud 22-23MPG and gas is back to $3. I often need to carry sample bicycles on the roof. I use a Thule rack with 3-4 fork mount attachments. What kind of fuel economy drop can I expect while there are no bikes on the roof? I would have a fairing on. I know the hitch mount would be a better choice but getting to the trunk with bikes on the back is a pain and I will need to put a Thule storage box on top here and there.

My main goal is to cut my gas bill in half, I hope this can happen even with the rack on.

Thanks for help on this topic.
[/b]

There's really no real formula to calculate your exact mpg.

1) If you're driving mainly local at low speeds.
You will use your electric motor more. Drag will be minimal (since it's grow in the second power). Getting 45 mpg is realitic.

2) Mainly highway at speeds high as 70mph average. Then it will be harder to achieve 45mpg.

3) Temperature also matter. If you're in the snow all day long..

There's a lot of things to consider. But getting double or close to double... i'd say give it a shot.. I drove 8 miles today and averaged 99mpg. Then i drove more local aggressively uphill and got 37mpg. So again it depends on everyone's driving style and commute.

So guys are gettin 600 ish with one tank of gas (10gallon). I'm a little over 300 and i'm going to probably fill up at 360. I have a new car so there's probably a break in period

[HappyPig]

At lower speeds, I never saw a huge hit in mpg, but I found that my MPG went down dramatically when driving at 70mph with a bike on the top of my '04 Prius. Specifically, I had a fairing with my Thule rack system (one of the fork locking ones), and was using a bike bra to protect from chips. Driving down a familiar highway showed a drop in MPG from what was typically 44 mpg to about 32 mpg. Once I realized this, I took the bike off the top and stowed it inside, and eventually removed the rack for good.

[JimboK]

I ran some numbers for you using the Prius MPG Simulator. I assumed based on your annual miles that most were on the highway, so this assumes 55 MPH. It also assumes steady speed, no hills, smooth dry pavement, outside air temperature 60F, no winds, no climate control use, and Goodyear Integritys inflated to 44 front/42 rear.

• No rack: 56 MPG
• Empty roof rack with deflector (as the Simulator calls it, presumably the same as your fairing): 52
• Roof rack with one bike: 47
• Roof rack with two bikes: 44
• Roof rack with three bikes: 41

If you drive more slowly, the aerodynamic impact of the rack will be less, as you might guess. At 45 MPH:

• No rack: 62
• Empty roof rack with deflector: 59
• Roof rack with one bike: 54
• Roof rack with two bikes: 52
• Roof rack with three bikes: 49

[czvekslak]

<div class='quotetop'>QUOTE(JimboK @ Nov 17 2007, 01:22 PM) [snapback]540962[/snapback]</div>

I ran some numbers for you using the Prius MPG Simulator. I assumed based on your annual miles that most were on the highway, so this assumes 55 MPH. It also assumes steady speed, no hills, smooth dry pavement, outside air temperature 60F, no winds, no climate control use, and Goodyear Integritys inflated to 44 front/42 rear.

• No rack: 56 MPG
• Empty roof rack with deflector (as the Simulator calls it, presumably the same as your fairing): 52
• Roof rack with one bike: 47
• Roof rack with two bikes: 44
• Roof rack with three bikes: 41

If you drive more slowly, the aerodynamic impact of the rack will be less, as you might guess. At 45 MPH:

• No rack: 62
• Empty roof rack with deflector: 59
• Roof rack with one bike: 54
• Roof rack with two bikes: 52
• Roof rack with three bikes: 49

[/b]

[czvekslak]

Sorry about the previous posting error. Those simulation numbers are impressive. I would say about 1/3 of my miles will be with a bike or two on the roof. At least 1/3 of my driving is in traffic at low speeds - from what I have learned on this board that is good for gas mileage. When I am on the highway I try to keep it under 75mph as much as I can. I wonder what the data would be like with bikes on a hitch mounted rack. Still some aero resistance but the bikes are a lot more out of the wind.

Can't wiat to get my Prius! Still debating if I should look for something used for aroudn 15k or just jump in when toyota does some financing deales.

[JimboK]

<div class='quotetop'>QUOTE(czvekslak @ Nov 18 2007, 09:12 AM) [snapback]541196[/snapback]</div>

I wonder what the data would be like with bikes on a hitch mounted rack. [/b]

Well, since you asked .... :P

At 55 MPH:

• Empty hitch rack: 55
• Hitch rack with one bike: 53
• (Edit) <strike>Roof</strike> Hitch rack with two bikes: 52

Since you mentioned 75 MPH, here are those figures:

• No rack: 43
• Empty roof rack with deflector: 39
• Roof rack with one bikes: 33
• Roof rack with two bikes: 31
• Empty hitch rack: 42
• Hitch rack with one bike: 40
• Hitch rack with two bikes: 39

[ScottY]

I have the Thule roof rack and snowboard carriers. Last winter when I was driving around 75MPH with 4 snowboards, my mileage was in the 30's. Jimbok is pretty accurate!

[JimboK]

<div class='quotetop'>QUOTE(ScottY @ Nov 20 2007, 12:36 AM) [snapback]541815[/snapback]</div>

Jimbok is pretty accurate! [/b]

Thanks, but it's Wayne Brown and his MPG Simulator that are due the credit. I'm just the messenger.

[usbseawolf2000]

<div class='quotetop'>QUOTE(JimboK @ Nov 20 2007, 07:29 AM) [snapback]541897[/snapback]</div>

Thanks, but it's Wayne Brown and his MPG Simulator that are due the credit. I'm just the messenger.
[/b]

I don't remember seeing an option for the bike rack. Do you have the newer version or am I not looking hard enough?