[Closed] Ooh - that's risky......

Have used suction ski mounts for 1200 miles apps trips before (with £2500+ worth of skis attached.)

Was a bit nervous, but they are seriously well fixed.

I never like the idea of mounting forks onto a rack by the dropouts like that.

Given that I continually check my bolted on rack, I think having that on the roof would bring on some sort of stress related illness before I got to the top of the road.

Don't really like bikes on the outside of the car anyway 🙂

Suction mount's good enough for Trainrider 8)

The story behind that train rider is fantastic.

From what I remember, the surfer was dying of some illness - so he literally had nothing to loose.

There's another similar system that was feature don here from the Sea Otter report or somewhere, not so long ago - caught my eye as a non-bodywork damaging solution for the Elise and better than having a stripped down bike belted in to the passenger seat, with sharp, pointy bits a few inches from face in the venet of nasty accident. Made by an American company who specialised in marine applications and it'd been tested with up to 250kg loads, still didn't ease any concerns - just made me think the bodywork would give up first and they'd take chunks of the fibreglass instead, so nevermind expensive bike in pieces, expensive car as well. And the things weren't cheap - about £350 for one bike/2 suction cups.

I bought a cheap runaround Golf instead in the end...

[img] [/img]

Suction mounts are how they install huge panes of glass on buildings... as long as you install the suction cups correctly job will be a goodun.

xiphon -
Member
The story behind that train rider is fantastic.
From what I remember, the surfer was dying of some illness - so he literally had nothing to loose.

It's even better when you find out that was just a cover story to try and get on the sympathetic side of the law 🙂 Nowt wrong with the lad (other than not being wired up right!)

Go-pro have suction fastened tripods that are rated to 200mph!

The story behind that train rider is fantastic.

From what I remember, the surfer was dying of some illness - so he literally had nothing to loose.

It is a very strong mount if installed properly but I would not fork mount wither as iirc it streeses the forks too much as they were not designed to flex like that

I know that a suction cup would easily hold my weight from the side of a skyscraper.... Just as I know that drinking apple juice from a potty is fine.
Neither would sit well with me, though!

DrP

serioulsy make sure you smell the apple juice first

HTH

Ps If you do it front of a patient can you film it

The sucker machine pictured above has a sensor to keep an eye on the pressure at the suction cups, if the pressure drops then the machine starts a small electric motor to increase suction, job done. With the better quality hand held glass lifters you get a gauge or similar on the tool to keep an eye on the pressure, again good stuff.

With the device at the top of the page there doesn't appear to be any way of checking the pressure when in use and because of this I wouldn't trust it.

if the surface is good the suction should hold, but you might end up with a wavey roof skin. the sun roof shown would stiffen it up a bit but a big bare roof might get a bit flexi.

they use suction mounts for all these kinds of things:

oh and if you want to try the above: http://www.toolstation.com/shop/Automotive/Suction+Pads/Suction+Pad+Triple/d60/sd3264/p93392

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ormondroyd - Member
I never like the idea of mounting forks onto a rack by the dropouts like that.

Junkyard - Member
I would not fork mount wither as iirc it streeses the forks too much as they were not designed to flex like that

Could you elaborate on these comments? I've been considering getting a Thule Outride fork-mounted bike rack instead of the usual downtube clamp one as they looked like a better solution.

I seem to recall reading that the forces on forks - it was possibly carbon forks on race bikes ???- were not great as you got a twisting motion on the forks/stresses they wer enot designed for - it could have been from years ago in a road mag?
Off for lunch and I will go a googling

Yup, dropouts aren't designed for that kind of twisting force - go around a corner and the whole weight of the bike is basically taken on one dropout, trying to yank it out. I'd trust the suction cups a lot more than the fork clamp.

Seem to remember that Pace wouldn't warranty forks that we're clamped on a roof race for that reason.

I used to use fork mount racks all the time and found them by far the most secure I've ever used, and the least damaging to bike/frame.

I've seen one, actually maybe two, reported examples (over 15 years or so I guess since I first used them) of someone attributing a dropout failure to using a fork mount rack - and neither of these were very convincing. I find it very hard to believe that the forces exerted on a dropout when a bike is on a rack are anywhere close to those exerted when being ridden, loaded with a rider, through hits, cornering and braking.

I do think that you should be very careful when loading and unloading bikes into them though - it's at that point that you could fairly easily put a very high load through one dropout if you accidental employ the bike as a nice big lever.

The manufacturer warnings are just the usual cover-their-arses statements I suspect, where they don't feel they have control of one side of the equation (the bike manufacturing) so make a blanket statement to cove themselves. Similarly the fork manufacturer warnings.

I find it very hard to believe that the forces exerted on a dropout when a bike is on a rack are anywhere close to those exerted when being ridden, loaded with a rider, through hits, cornering and braking.

The forces might not be as big. But they are in the opposite direction and unbalanced. Normally when riding a bike, the axle is being forced up equally into the dropouts - in this situation, the "axle" is being twisted down and out of the dropouts.

The closest similar example is those situations where a disc brake forced a wheel out of a dropout, causing a crash.

Interesting. I'd be using mine for road bikes and MTBs, most with rigid carbon forks including one of the MTBs, so now I'm worried.

Pretty much the only other way to fix a bike to a roof rack involves clamping the downtube. This surely also falls into the 'not designed to experience those forces' category?

But when clamping the downtube, the lateral forces (i.e the bike trying to 'fold' over to the side when cornering in the car) are taken up by the bike-rack, not the actual bike *.

DrP

*OK - there is a force of the downtube pushing against the clamp, but this wouldn't be enough to dent the radial tube will it...

More on Trainrider (he wasn't dying). I love the ticket thing. He'd be section 44'd here in no time.

Pretty much the only other way to fix a bike to a roof rack involves clamping the downtube. This surely also falls into the 'not designed to experience those forces' category?

That's clamping at pretty much the centre of gravity - it's fine. Clamping at the dropouts turns the bike into a big lever, trying to pry the forks out.

bencooper - Member
The closest similar example is those situations where a disc brake forced a wheel out of a dropout, causing a crash.

Or where it doesn't force the wheel out, and it's perfectly safe - i.e. most of the time - like a rear horizontal or slot dropout (see pedalling forces for another example*).

*whether the forces compare, I don't know!

Suction cups are used all the time for car photo and video rigs -

http://www.b-hague.co.uk/camera_suction_pads_vacuum_mounts.htm

http://www.filmtools.com/carmounts.html

Now the speeds are a lot lower but folk will happily plonk £000's of camera kit on them.

I personally would want decent pneumatically adjustable cups as opposed to the cheapy pos jobs andyl has linked to. - No offence but we have one of those here at work and let's just say you pay for what you get.

Or where it doesn't force the wheel out, and it's perfectly safe - i.e. most of the time - like a rear horizontal or slot dropout (see pedalling forces for another example*).

I was comparing it to the famous/infamous Annan effect:

http://www.kinetics.org.uk/html/disc_brakes_-_qrs.shtml

Disc brakes and QRs are perfectly safe - for a given level of "safe" 🙂

scuttler - thanks for the video - he's a bit of a nutter!

bencooper - Member
I was comparing it to the famous/infamous Annan effect:

which is the point I was trying to make (and most fork ends have safety dropouts anyway)

Most tracks won't let you use suction mounts these days because of the risk of them popping off under load. Or, if they do, the mount and camera both need to be tethered so that somebody else doesn't get a nasty surprise if it's an external mount/the driver doesn't get brained by a flying camera if it's an internal mount...