Cycle wings - best way to mount them?
 

Hi everyone, so ever since I finished my Fiorano kit I've been constantly having problems with my wheel arch supports.
They are currently made from steel tube that's welded together, and they seemed pretty strong, but it seems that almost every time I drive the car one of the welds snaps off and the other day the tubeitself actually sheared off.

Does anyone have any ideas of what the best method of attaching the wings could be?

Pics would help so we could see the current set up and make suggestions

Ok I'll try and sort some out

Should you have a good library around, you may try this reference:
Sports Car Bodywork: Construction in Timber, Metal and Plastics
B.W. Locke, 1960 or 1961.
Great old reference, with fold out blueprints. Dreadfully expensive even used.
He shows a foolproof method for exactly what you are looking for.
I (insanely) gave away my copy to a kit manufacturer in Michigan.

It's unlikely that tube will be strong enough. It may appear to be stiff, but will inevitably tear at the welds. My Marlin uses solid round bar about 10mm as I remember. Done about 6000 miles with no problem. My Pembleton has 8mm round bar. Too soon to tell if its ok though. But mudgaurds much lighter than Marlin so I am hopefull...

Mudguards that move with the wheels get a lot of pounding. Its a common problem area.

Cheers, Robin

Thanks guys, yeah someone said solid bar might work better, also do you think it might help to have a layer of rubber sheet between the brackets where they bolt onto the hubs?
Would this help dampen the vibration?

Perhaps, but I see it as adding a lot of additional bouncing on the wings.

Seen this ?

http://www.hotrodders.com/scratch-bu...Running_Boards

of course no one has asked who did the welding ? and with what ?

regards Paul

It can depend on how you are attaching them as to how the design pans out. My experience with stays that clamped on the hub (mgb based kit) was similar (ie welds failed.) To cure it I made some solid round 'plugs' about 4" long which I heated up red and flattened the end and drilled for mounting. The other end of the plug had the last 1.5" turned down so it was tight fit in the steel tube (seamless gas tube) and the parts were brazed together. The logic being that cycle frames (very thin and light) take enormous stresses (think bike forks) and have been traditionally made this way. At the top end I also used a tube bender to bend to 90 degrees so no 'corners' as stress raisers. It worked.

Ok, here's some pics.
first one is the hub where the tab that supports the arch bracket is welded. (there's one on the other side of the hub too that's hidden in this shot)
https://c8.staticflickr.com/6/5541/3...dbd0b6b5_z.jpg1DSC_0505 by paul ward, on Flickr

and this is the arch support itself - the 'nodular lump at the bottom is the latest temporary repair where the tube sheared off.
https://c1.staticflickr.com/6/5795/3...765a7e4d_z.jpgDSC_0026 by paul ward, on Flickr

https://c6.staticflickr.com/6/5836/3...79d3c570_z.jpgDSC_0025 by paul ward, on Flickr

Hi Paul are they braking at the weld or across it ? and what method of welding are you using ? could you mount them on rubber bushes to absorb any vibrations ,I had to use this method on a Westfield.

Both, they have broke several times, sometimes the welds snapped off and also the tube sheared off

Are they tube or solid? I think the welding is causing embrittlement of the steel, leading to the tube breaking in the heat affected zone (ie close to weld). If solid (or tube) you could slot them to take a 6mm plate (nice tight fit in slot) and braze them - look at chainstays or seatstays where they meet the rear dropout on a quality brazed cycle frame. Brazing acts at a lower temperature so doesn't cause the embrittlement problems that welding does - that's why it's been used in bike frames for over a century! Good old-fashioned simple engineering is sometimes the best:icon_wink: You may have to replace some of your metal that is already heat affected?

Welds Fracturing
 

Totally agree with the above ,stress due to heat is likely causing the brake especially in thin wall tube ,brazing or solid inserts at the weld will solve the issue ,good luck keep at it !

You don't say what welding method is being used also what is the thickness of the tube compared with the bracket thickness ?

It is possible you are getting undercuts which reduce the wall thickness at the point of maximum stress i.e the tube/bracket interface ?

If you put a internal sleeve into the tube and tapered the inside end to spread the stress you would double it's thickness at the point of the weld ?

Don't forget if you make one part stronger and unable flex you just move the forces somewhere less strong , sometimes flex is best

Thanks for the input everyone