Sure is funny to have this crossover between my “real job” and my core hobby after all these years 
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“Welcome to the forum thread dedicated to making a better vacuum seal”
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This is what led me to getting a Seasucker.
In the past worked with a ton of these suction lifts in situations where more is on the line than even an expensive bike. I bike weighs nothing. The vacuum cups on the Seasucker are pretty substantial. I don’t even worry much if one of the three cups on my Seasucker is loose. 1000lbs of glass 50+ stories up is scarier than a bike on a roof.
A single Woods vacuum cup is good for 100lbs of glass or so. I only ever had one fail and it was the glass that actually failed and not the vacuum cup. A 20lb bike on three or four vacuum cups is pretty solid.
The only issue I’ve had with mine is with a rental car a couple months ago. It was a Hyundai Santa Fe (I think) and the roof had ribs molded in for some reason. The cups were just a little bit bigger than the space in between the ribs and didn’t really work. Other than that a Seasucker is one of the most universal racks you can buy.
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I’ll add another edge case, my old Toyota Yaris (200,000+ miles) roof’s paint got a bit rough. While it wasn’t flaking, looking at it closely revealed it was no longer a smooth surface—kind of hard to describe but up close it was loaded with tiny little cracks that gave it a subtly rough feeling. As it worsened over the years, my Seasucker was no longer able to work on it.
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I wonder if you could have polished the paint enough to have a working interface again wittout polishing too much paint away.
If it were my old car I’d either polish it, or just sand it down and spray-bomb a new paint surface onto it.
My old truck had enough scratches and rust on the roof that it didn’t work everywhere but I could still find a spot.
As you both touch on, the actual surface condition for the base material is super important. Any imperfections like scratches, pitting and such can lead to issues. Some vacuum pads will have enough pliability in the sealing edge to properly seal those, but some conditions result in an imperfect seal. That will lead to vacuum loss over time and eventually show the “Low Vacuum” warning mark on the pump if it is left alone.
I thought about it, but I wasn’t using that car to travel long distances to races and it was perfectly easy to just throw my bike in the trunk when I did use it.
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@mcneese.chad a couple of questions if I may:
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For car roof use, does it matter what the material is so long as it’s smooth?
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how much small amount of ‘curve’ in the surface can these cups cope with and still work well? (E.g: Any/none or v-minor or lots?)
Reason for asking is my current car is an Estate (station wagon for US peeps) with Thule racks but I’m planning (funds allowing) to buy a sports car which has a carbon roof and I know there is an ever so slight curve to shape of the roof as well.
Thanks 
For clarity, my direct experience is with “materials handling” and not bike racks. I have experience with our products and a handful of the SeaSucker products we got in for short testing, but I have nothing directly connected to use on the roof like these racks. That said…
The material to support the rack should likely be smooth, clean and able to support the load in question.
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Most metal roofs are likely fine. I do suspect there could be some with thinner or less sturdy roofs that could lead to flex in the metal. This can lead to odd performance of some vacuum pads on those surfaces as they change shape.
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Glass roofs may be fine as well. Typical glass used for these panoramic roofs is quite sturdy. The main concern I have with glass roofs (most specifically movable “moon” roofs) is the support of the glass to the car. These are generally strong, but I doubt that most car designers have considered people strapping a rack and bike to them and loading them with wind and dynamic motion. I could see some systems working better than others due to differences in designs and materials used.
I have to check with what SeaSucker specs for any curve allowance. We offer a number of “curved surface” vacuum pads that work well with non-flat surfaces. We list a “minimum curvature radius” for our products like this. The SS ones copied one of our common pad designs, so likely follows that it will work with some curved surfaces.
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Generally speaking, if you can set the pad on the surface, activate the pump and get a properly buried vacuum indicator, you are good to go.
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Considering the marketing info that SS uses, I suspect most cars without major surface irregularities, grooves and such will be fine. Some body lines can even function with the pad if they aren’t too “sharp” or deep.
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Good timing on this thread. Using my Seasucker for the first time today and this thread may make me stop to check one less time on my 17 mile drive. 
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Unless you drive a bowling ball I think you’d be hard pressed to find a roof panel on any vehicle that has too much curve. The cups conform pretty well and the “deck” of the rack also has flex to it to bend to any contour.
I won’t outright say that it will fit every car but I wouldn’t bet against it.
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It took a pretty hefty whack on a barrier to pull my MTB off the roof of my Mini. The cups creased the roof upwards from being ripped off… I’ve got a video somewhere.
For reference, I went for the Rockbros mount and was and still am very pleased with it.
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I have a Seasucker Talon and never had any issues with it. Even “accidentally” driving in excess of 100mph when I forgot the bike was on the roof.
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You’ll quickly stop worrying about it. 17 miles is nothing. I drove from close to 500 miles with 2 bikes on my seasucker (at highway speeds - 70-80mph) and only stopped to re-pump when we stopped for gas or food. Also then took it to Iceland and drove around at 90kph with some strong crosswinds with no issues. The product works very well. I just don’t personally love it. Can be a a little bit of a hassle to load by yourself - but easier the shorter your roof is. It’s also noisy but you will get that with any sort of roof mounted rack.
For curvature the problem isn’t with the cups themselves - it’s the platform they are mounted to (with Seasucker specifically). I assume this might be less of an issue with the single rack (the talon?). But I have the mini bomber which holds 2 bikes. It has 4 suction cups that are mounted to a stiff platform that has no curvature. So almost every car roof is curved so you can’t always get “full” suction with all 4 cups. But you get enough force with the ones you can pump all the way that it’s not really an issue. Maybe if someone’s roof has a crazy curve it would not be the rack for you
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Update: Bike didn’t fall off.
Only downside is I got more compliments on the Seasucker than my bike at the group ride.
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I have the mini bomber as well. I used it on a 2002 Miata hardtop for two 5-hour drives at highway speed in the summer, with two mountain bikes on the roof. If you’ve seen the Miata hardtop, it definitely has some curvature in it.
No problems, even though I stopped to check multiple times on the way
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Curious that you can’t make them all work. I haven’t seen this issue. I own the single but have used the double and triple. The platforms are stiff but still have some flex.
Also strange that you can seemingly get them partially working but not fully. Once you have a seal and a vacuum there shouldn’t be much to prevent a full seal.
How do you mount your cups? In sequence or with the outer ones first? What kind of car do you have?
I’ve found that depending on the rack and the roof shape that sometimes you sometimes need a specific sequence to get the cups to all work. I’ve also found in some situations you really need to give the rack and the cups a good push down to get an initial seal.
This is definitely one of the downsides to the rack though.
I’ve noticed this this too- typically I find it’s easiest to start on one end and work across the rack, so to speak, instead of doing one end and then the other. By adding suction in sequence across the rack, it naturally flexes the platform down and holds it there, making it easier to conform to a curved roof. If you start at one side and try to jump right across to the other end, you have to physically push it down all the way, which isn’t easy.
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