JollyJake99 Posted February 10, 2009 Report Share Posted February 10, 2009 Followed a Jeep Wrangler-type into C-back last week. "He" had two pairs of skiis carried vertically on a rack mounted on the spare tire or rear bumper. The one pair was bagged in a nylon ski bag(!); the other pair was in the open. What really attracted my attention was the violent oscillation(sp?) that was being set up in the forebody of the bagged skiis at anything more than 10 mph. I'm fairly sure that it was not just the flapping of the ski bag as a similar but smaller oscillation was seen the forebody of the unbagged skiis. Perhaps the flapping of the bag was what was propagating the oscillation. Anyway, it seems to me the such violent flexing the the bagged skiis was shortening their useful life. Quote Link to comment Share on other sites More sharing options...
JibHonk Posted February 11, 2009 Report Share Posted February 11, 2009 wtf did you just say? i do not want to have to read a post and then have to google half the words please dumb this down Quote Link to comment Share on other sites More sharing options...
phillycore Posted February 11, 2009 Report Share Posted February 11, 2009 I'm not sure exactly however I had similar feelings about putting my skis on my roof (horizontal obviously) Whenever I use the rack I put the bases up so that the air will travel along the base of the ski rather than make the tips get pushed upwards due to the air hitting them from underneath. Not to mention that I figured that it would probably be better for gas milage as it was more aerodynamic. Some of those drives back and forth from the pokies get long and watching the skis on other cars bounce around it made me start thinking I hope mine aren't doing that.... That's why I thought they'd be much better off with the bases up rather than down.. Quote Link to comment Share on other sites More sharing options...
backcountry_rider Posted February 11, 2009 Report Share Posted February 11, 2009 (edited) Guy would feel like a true dumbass if he was able to find the correct speed to induce the natural frequency in the skis, creating a more violent oscillation. I think that the big issue here would be de-lamination. Also have to wonder if the oscillations will propagate into the rack and bust one of the connections free. Let's assume it's a two door, regular size wrangler with the hard top installed. Considering the relatively poor coefficient of drag on the jeep (probably peaking at speeds of around upper 30s and cooling back down thereafter) the fluid (air) probably wants to push back down to fill in the "draft" pocket and the skis are creating unintended interference therein. The bag most likely acts as a sail and easily propagates the oscillatory force into the skis inside. This is probably also a primary factor of the unshielded skis oscillating at a lower, but related, rate since the air resistance on them is most likely small, given their "windshield" (the bagged skis). The guy could probably avoid some of this by installing the soft top **edit** and opening a rear window **edit**, since it creates such violent fluid entropy near the roof, thereby allowing more lower velocity wind to fill the gap between the truck and the skis. (any fluid dynamics pros out there correct me if I'm wrong) So yeah, driving fast and creating "wind" that shakes your skis violently is bad. Avoid it. Phillycore has the right idea. The only bad shit from that is what comes off the road; not wind (unless there is a big gap between the tip and the roof). Edited February 11, 2009 by backcountry_rider Quote Link to comment Share on other sites More sharing options...
sexkitten Posted February 11, 2009 Report Share Posted February 11, 2009 I'm not sure exactly however I had similar feelings about putting my skis on my roof (horizontal obviously) Whenever I use the rack I put the bases up so that the air will travel along the base of the ski rather than make the tips get pushed upwards due to the air hitting them from underneath. Not to mention that I figured that it would probably be better for gas milage as it was more aerodynamic. Some of those drives back and forth from the pokies get long and watching the skis on other cars bounce around it made me start thinking I hope mine aren't doing that.... That's why I thought they'd be much better off with the bases up rather than down.. Don't you think the air damn channels most of the air over the skis? Mine don't seem to rattle all over the place and I think that's why. Quote Link to comment Share on other sites More sharing options...
poconoceancity Posted February 11, 2009 Report Share Posted February 11, 2009 I've used racks since the early 90's on 5 different vehicles. I have never had a problem and drove 3 hours each way. Some years I think my boards never made it off the roof unless they were in use. Road grime is more of an issue on cars than higher sitting SUVs. When I had a Sub wagon, my skis would be covered with grime. Now with an Expedition it's not an issue. Quote Link to comment Share on other sites More sharing options...
phillycore Posted February 12, 2009 Report Share Posted February 12, 2009 Don't you think the air damn channels most of the air over the skis? Mine don't seem to rattle all over the place and I think that's why. No air dam on mine.... Quote Link to comment Share on other sites More sharing options...
sexkitten Posted February 12, 2009 Report Share Posted February 12, 2009 No air dam on mine.... Ah ha! I know when I bought my rack the clips for the dam weren't available but Bob fabricated some. I was soooo glad because there was a noticeable increase in my gas mileage after he put it on. Quote Link to comment Share on other sites More sharing options...
JollyJake99 Posted February 13, 2009 Author Report Share Posted February 13, 2009 wtf did you just say? i do not want to have to read a post and then have to google half the words please dumb this down A stereotype's not a stereotype if it's true. Quote Link to comment Share on other sites More sharing options...
First Grade Teacher Posted February 13, 2009 Report Share Posted February 13, 2009 It will turn the skis green from the violent oscillation affecting the color spectrum adversly. Quote Link to comment Share on other sites More sharing options...
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