Bike Forums

Bike Forums (http://www.bikeforums.net/forum.php)
-   General Cycling Discussion (http://www.bikeforums.net/general-cycling-discussion/)
-   -   Thule revolver bike rack installed with hitch adapter - safe? opinions needed (pics) (http://www.bikeforums.net/general-cycling-discussion/577835-thule-revolver-bike-rack-installed-hitch-adapter-safe-opinions-needed-pics.html)

mindleftnumb 08-24-09 05:55 PM

Thule revolver bike rack installed with hitch adapter - safe? opinions needed (pics)
 
I just installed a Thule Revolver on my Mazda CX9 with tow package using a Hidden Hitch 1 1/4" to 2" hitch adapter. This is what it looks like:

http://i25.tinypic.com/ka0dvl.jpg

The rack itself is great because of the revolving capability but what I also like about it is that (due to the use of the adapter) the liftgate can open without even needing to revolve the rack as you can see here: http://i30.tinypic.com/souy5d.jpg

The problem is, I just don't know if this is safe. There's a significant amount of wobble where the adapter attaches to the hitch mount (no wobble on adapter to rack due to threaded pin). I am considering an anti-wobble clam from Hitch-Vise to help with this. Even after eliminating wobble, however, I may be pushing the limit with tongue weight. I am told that using the adapter cuts the tongue weight limit from 350lbs to 175lbs. With the rack weighing 55 pounds that leaves 120 for bikes before hitting that limit. I am also reading that torque also due to the use of the adapter may be a problem. I'm a non-engineer noob when it comes to this, and therefore am looking for opinions on the safety of this setup. Thule says it is not advisable, but I've also ready this is a standard response for rack manufacturers when it comes to the use of adapters. If anyone out there has any advice or has used a similar setup I'd greatly appreciate your feedback. Thanks,

Here also a few other photos of the connections:
http://i28.tinypic.com/2h7kvb4.jpghttp://i27.tinypic.com/wjxtp5.jpg

mindleftnumb 08-28-09 01:43 PM

I thought I'd post an informative response I received at another forum:

*****Warning long explanation******

Trailer hitches are designed for a variety of road loads that occur at the hitch ball during use. The most damaging road loads to the trailer hitch are the vertical and horizontal. Bike racks mostly generate vertical loads on the hitch. The problem arises when the loads are placed far away from the hitch. The force times the lever arm generates a moment or torque. Road loads measured by Auto manufactures in North America typically result in vertical hitch ball loads of +/- 3 g's for weight carrying operation.

So - a typical 1-1/4" class 2 ball mount for your Mazda will measure ~10" horizontally from the center of the ball to the center of the receiver pin hole. Using the guidelines mentioned above, your Mazda receiver was designed for durability loads for its class 2 receiver of:
350 lb. tongue weight x 3 g's of vertical acceleration (road induced) x 10" horizontally from the center of the ball to the center of the receiver pin hole = 10,500 in -lbs. torque capacity.

Now your Thule 964 was designed to induce the following loads:
See - http://www.thuleracks.com/charts/Thu...Dimensions.pdf for dimensions
55 lb. rack weight x 3 g's of vertical acceleration (road induced) x 11.75" horizontally from the center of the mast to the center of the receiver pin hole = 1,938 in -lbs. torque induced for the rack load.
140 lb. bike weight x 3 g's of vertical acceleration (road induced) x 24.25" horizontally from the center of the bikes to the center of the receiver pin hole = 10,185 in -lbs. torque induced for the bike load.
Total torque induced = 12,123 in-lbs. This would be a 15% overload. That is a very significant number when dealing with repeating fatigue loads. This is why Thule requires you use a 2" receiver with this rack.

Now, let see what the adapter does to the rack's capacity. It adds 6" to all the lengths mentioned.
55 lb. rack weight x 3 g's of vertical acceleration (road induced) x 17.75" horizontally from the center of the mast to the center of the receiver pin hole = 2,928 in -lbs. torque induced for the rack load.
140 lb. bike weight x 3 g's of vertical acceleration (road induced) x 30.25" horizontally from the center of the bikes to the center of the receiver pin hole = 12,705 in -lbs. torque induced for the bike load.
Total torque induced = 15,633 in-lbs. This would be a 48% overload. Wow! Ok, let us reverse out the racks capacity.
10,500 in -lbs. desired max torque - 2928 in-lbs from the rack leaves 7572 in-lbs divided by moment arm of 30.25" = 250 lbs divided by 3g's = 83 lbs.

So 2 bikes, no problem, maybe 3 bikes if they are light.

Bianchigirll 08-29-09 09:10 AM

UH UM WOW. that technical stuff has my head aching this early. however I do agree. personally I would try and see if I could the hitch changed (is this a new vehicle?) to a 2"


All times are GMT -6. The time now is 06:32 AM.