Hitch Bike Rack's Effect on Vehicle Efficiency

[BTOR]

Curious if anyone out there has experience with using a Yakima Hitch Bike Rack with their R1S? The hitch rack model is the "Double Down". I've attached two pictures showing the model behind a vehicle folded down, without bikes, and with bikes loaded.

I will be doing an out and back trip. Each way is 1,100 miles. It is Interstate the entire way. My bikes will be inside my R1S so the rack will be in the folded down position and empty. On my old ICE SUV, it had little to no effect on mileage when folded and unloaded. But I suspect on an EV there will be some impact to efficiency (but hopefully not) and I've run out of time to experiment.

My question is can I expect a drop in efficiency with the rack "unloaded" without bikes on it? And if there is a drop, should I plan for a 0.1 miles/kWh or something more like 0.5 miles/kWh? I used the Rivian Trip planner to map out my charging sessions. However, it does not factor a hitch bike rack attached. I think there is plenty of margin with most of the stops that even a significant drop in efficiency I will be okay. However, there is one or two where remaining SOC is in the 20-30 mile range.

If there are any owners out there with experience and have done a trip with a similar rack (empty or loaded), was there a noticeable difference in your typical freeway efficiency?

Thank you!

Sponsored

 

[Redmond Chad]

I haven't done any testing with a bike rack on my Rivian.

But many years ago, a bunch of Roadster owners compared notes after a group trip, and the energy efficiency of all the vehicles were extremely close together...except the one carrying a bike on a rack was 15% higher.

That's WITH a bike on the rack. And the Roadster is about twice as efficient as the Rivian, so that efficiency hit would probably only be half as much on the Rivian...if the bike was just as high above the rear of the Rivian.

I'd guess it's only going to be a 5% hit carrying a bike on a Rivian, and unmeasurable if you just have an empty rack.

But happy to see numbers if anyone has them!

 

[dleepnw]

Haven't done any real testing with data but anecdotally, i think it does decrease efficiency slightly at higher speeds but its pretty negligible below 30-35mph.

 

[cbrcanuck]

Someone on here did some great testing fairly early on and posted great data/graphs from some road trips with their hitch rack. I'll take a quick look to see if I can find it, but it's buried in here somewhere. From what I remember, it wasn't as bad as feared...

I'm thinking you probably won't have to make any dramatic changes to your route/planning...

 

[cbrcanuck]

Yup, check this thread out:

https://www.rivianforums.com/forum/...r1t-road-trip-range-vs-temperature-data.8782/

 

[Budman]

Somebody else already directed you to a previous thread of mine documenting the efficiency I've experienced with my R1T, now R1Ts as I'm onto a 2nd Gen R1T.

Attached is an up to date graph of the data I've collected. With regard to your question of the effect of a bike rack, look at the 2 green data sets. This is data from Gen 1 in Conserve mode with and without a hitch mounted bike rack with 1 or sometimes 2 bikes. There was about a 10% hit on the efficiency.

As am always careful to point out, this data is not a 75 mph freeway range/efficiency test. It's a repeated route of mine that is about 50% 70 mph freeway and 50% 55 mph rural roads/small towns. It's a route that is close to the EPA combined cycle and I do see numbers very close to the EPA range estimates for the R1T.

 

[Redmond Chad]

Budman's data (and presentation) is fantastic. Note, though, that it's for an R1T...the OP asked about R1S. I would expect the hit to be smaller on an R1S because the bikes don't sit up in the airstream as much. But of course there's a large number of factors involved so don't take my word for it.

 

[BTOR]

Budman, thank you for the data. This is great info. Although it is for an R1T, it does prove, as you would expect, a loaded bike rack has an impact on efficiency. Although I agree with Redmond Chad, I would expect less impact on the R1S since the rack sits in the low pressure zone or "draft" of the vehicle and this will result in a much lower drag coefficient than the R1T. However, it will disrupt the airflow and therefor change the aerodynamics. I suppose any "aero disturbance" will impact the efficiency and of course that disruption will be a negative one, not positive. But it could be small enough (I hope) that I won't even notice it due to other factors like temperature (air density), wind, terrain, etc. playing a bigger role in my overall efficiency variability.

Anything I learn or discover that may be of interest during my trip, I'll be sure to post comments.

 

[LindaI]

I regularly drive 500 miles with my MTB on the back of my R1S. I used to drive a Model Y with the same bike and bike rack. The R1S keeps the bike shielded from the wind, and does not have a huge impact on range, maybe 10% if that. With the model y the bike was in the wind, and cut the range by about 30%.

 

[BTOR]

Thank you for your feedback. So far ~ 10% seems to be the general consensus.

One note for what it is worth, both you and Budman have wheel mount racks which position the bike lower relative to the vehicle than my frame (top tube) mount type which places the bike higher and probably a little closer to the vehicle. I think it will center the bike in the back of the vehicle a little better too.

From bike transport perspective, I much prefer your style (and Budman’s) rack. Much easier to load/unload the bike and no contact with the frame.

 

[Seano]

I would support @Lindal 's estimate of around 10%. I don't have as good a data as @Budman , but to my memory its a hit without being major. While its true that the R1S somewhat shields the bikes on the back, I'm pretty certain messing up the flow of air at the back of the vehicle still slows it down / reduces efficiency.

Never notice it around town - but 230mi trips from Bay Area to Truckee seems to show the reduction.

 

[BTOR]

I would support @Lindal 's estimate of around 10%. I don't have as good a data as @Budman , but to my memory its a hit without being major. While its true that the R1S somewhat shields the bikes on the back, I'm pretty certain messing up the flow of air at the back of the vehicle still slows it down / reduces efficiency.

Never notice it around town - but 230mi trips from Bay Area to Truckee seems to show the reduction.

I found a technical paper on the aerodynamics behind an SUV. It was quite interesting if you’re in to these types of things. Having a MechE background I am ?.

The study used a Land Rover Defender or a slightly earlier model of the Defender with a different name. They were able to reduce the drag coefficient by 10% by mounting the spare tire on the rear door (removing it from underneath, and adding a “diffuser” on the underside of the bumper in the center. They also said having the spare tire on the door disrupts the vortexes that are created behind the vehicle. These create low pressure behind the vehicle creating a force in the opposite direction of travel (this force is essential pushing on the vehicle in the opposite direction of travel and it takes energy to overcome that force). With the vortexes disrupted, the magnitude of the force is reduced, thus reducing the drag coefficient.

So, my thinking is the drop in efficiency by adding a hitch bike rack may be more due to removing the hitch cover and not the rack itself. In fact, the rack may improve efficiency by disrupting the vortexes. But because it is attached by means of the hitch located in a critical area under the center of the bumper it has a major influence on the drag coefficient (increases it).

So, I wonder if there is a noticeable difference in efficiency with the hitch cover removed but nothing mounted in the hitch? ?

 

[Budman]

The tent on the back of my R1T seems to cut my range 10% to 15% or so. Just a guess, no rigorous testing.

 

[Seano]

I found a technical paper on the aerodynamics behind an SUV. It was quite interesting if you’re in to these types of things. Having a MechE background I am ?.

The study used a Land Rover Defender or a slightly earlier model of the Defender with a different name. They were able to reduce the drag coefficient by 10% by mounting the spare tire on the rear door (removing it from underneath, and adding a “diffuser” on the underside of the bumper in the center. They also said having the spare tire on the door disrupts the vortexes that are created behind the vehicle. These create low pressure behind the vehicle creating a force in the opposite direction of travel (this force is essential pushing on the vehicle in the opposite direction of travel and it takes energy to overcome that force). With the vortexes disrupted, the magnitude of the force is reduced, thus reducing the drag coefficient.

So, my thinking is the drop in efficiency by adding a hitch bike rack may be more due to removing the hitch cover and not the rack itself. In fact, the rack may improve efficiency by disrupting the vortexes. But because it is attached by means of the hitch located in a critical area under the center of the bumper it has a major influence on the drag coefficient (increases it).

So, I wonder if there is a noticeable difference in efficiency with the hitch cover removed but nothing mounted in the hitch? ?

Super interesting! I can maybe look at our last trip since I popped of the hitch cover (using the hitch for a little while) and promptly ran over the hitch cover ? and we then drove home with the hitch cover removed (4hr trip)

 

[BTOR]

Super interesting! I can maybe look at our last trip since I popped of the hitch cover (using the hitch for a little while) and promptly ran over the hitch cover ? and we then drove home with the hitch cover removed (4hr trip)

Yes, let us know if you find anything interesting.

Sponsored