Rear Hitch/Bike Rack, Drop in MPG?

<div class='quotetop'>QUOTE(ryogajyc @ May 23 2006, 02:48 PM) [snapback]259916[/snapback]</div>

I am a mechanical engineer and I have experience with both the Yakima roof and rear hitch rack.

I purchased the Coastal receiver hitch since it was the only one with a 2" receiver that I found, and yes, you can get more accessories for a 2" then 1 1/4" receiver. I can now use the same 2" receiver bike rack that I already owned and used with my 4Runner on the Prius.

I know they make 1 1/4" to 2" adapters but they increase the length of the rack behind the hitch and significantly increase the load/moment on the receiver. Some of the hitch manufacturers I talked to when researching my hitch purchase said that if you use an adapter they reduce the receiver load rating by 50%. They also can increase the motion of the bike rack relative to the car since you now have 2 connections (hitch to adapter, and adapter to bike rack) vs. one connection (hitch to bike rack). Each connection will have a small amount of play to enable the parts to be inserted into eachother.

I do see a 1-2 mpg drop when driving with the roof rack unloaded. With 2 bikes loaded on the roof, it drops about 10 mpg depending on wind. The roof rack is easy to use and securely mounts the bikes using a fork mount so the bikes do not move at all on the car. My wife is only 5'2" and she puts the bikes on the roof without any problems. The biggest risk with a roof rack is driving into a garage or other low clearance area with the bikes loaded!

The receiver rack doesn't decrease the mileage when unloaded, and when loaded probably only decreases the mpg by 3-5. The bikes do definitely move around on the hitch rack, but I've been using a hitch rack for years and have never had any incidents related to the motion. The visibility is partially blocked by the bikes, but you can still see fine out the back window. It's really hard for a car to hide behind a 1.5" dia frame tube. If you use a receiver rack you have to watch going up/down curbs or steep steep driveways to ensure your bike wheels don't drag on the ground when the front of the car starts going up. When backing down curbs, etc. the backup camera is nice as you can see if your bike wheels are about to touch the ground!

My wife and I mountain bike 3-4 times per week and we use the roof rack for short drives due to ease of quickly putting the bikes on the roof rack and not having to put the receiver rack on the car. If we drive more then an hour to a ride we'll put the receiver rack on the car and use it. Some people have suggested not using bike racks and putting the bikes inside the car, but after a dirty or muddy mtn bike ride, I certainly don't want the bikes inside the car where they can trash my interior.

 

<div class='quotetop'>QUOTE(steved @ Jun 27 2006, 03:19 PM) [snapback]277610[/snapback]</div>

Thanks for the wealth of info, Steve.

Poking around the web, it looks like there are 2" to 1.25" adapters that would not extend the length of the hitch, but play would probably still be an issue. I imagine that it would be possible to build or there might exist a 2" to 1.25" adapter with some sort of expanding/screw mechanism that would have no play. I'm an electrical engineer, so take my suppositions with a grain of salt.

Wow, that's a pretty significant difference in mileage between rear rack and roof rack. I'm mostly interested in a rear snowboard rack as opposed to the bike rack, which may block a bit more of the view b/c of bindings. The boards probably block very little (since the planes of the boards are parallel to the line-of-sight out the back). I imagine the mileage difference are probably comparable between snowboard and bike racks.

Interestingly enough, my concerns about the rear vs. roof rack fitting in a garage are reversed. With a snowboard roof rack, it fits easily in my garage. However, my garage is very short (it's convenient that my Prius is very short, since it actually leaves enough room in front of my laundry machines unlike most cars). A rear rack means I would not be able to close the garage door with the rear rack attached without potentially catastrophic results.

I actually just noticed this thread. While it details the Curt hitch, I was wondering if the Coastal hitch had a similar potential problem. While I probably won't encounter the problem since I won't be driving in such high heat, having the hitch block exhaust airflow is just plain bad engineering. It seems like this may cause undue wear and tear over the long term even if you don't drive in high heat, and not just to the rear plastic skirt. It seems like hot exhaust is probably not the best way to keep rear hitch from deteriorating. Anyone mind taking pictures of the Coastal hitch in relation to the rear exhaust to get an idea of what it looks like? Thanks in advance.

 

<div class='quotetop'>QUOTE(ryogajyc @ Jun 29 2006, 11:25 AM) [snapback]278699[/snapback]</div>

John/grasshopper was nice enough to post a pic to show the Coastal hitch clears the rear exhaust quite nicely. Direct link.