Where to go to buy this? Bike rack amendment

Bump for the early weekend engineery types...

My non engineering thought is that you are trying to make a professionally designed item do something it wasn't designed for.

I'd be worried about my bike and the car behind me.

A fair point...which is why I'm thinking the extension needs to be full length of the current bracket plus the extra 20mm as well as being thicker.
I have contacted Atera and they don't do a longer bracket...
The 3rd bike would be occasional use, so I'm too concerned about a 20mm protrusion failing (if it is thick enough).
However, as you've flagged this concern, I won't discount it completely, but think a thicker piece would counter that valid concern.
The 2 inner racks (or the standard racks as it is a 2-bike rack +1 extender) are 230mm apart (wheel track to wheel track), the middle rack to the extender is about 190mm space between wheel racks. I'd like a longer bracket but Atera don't do them so I think a plate, bolted to bracket would work as that would make the gap wider.

I appreciate it is easier said than done, but a picture is worth a thousand words.

Good point, I'll need to get photos and work out how to show them here...

Hopefully this link will work - https://photos.app.goo.gl/azpLn3MK3Pxj6Nxp7

Main rack spacing is 23cm (230mm), the extra rack spacing is 15cm (150mm), so I'm thinking I need a 5cm (50mm) extension.

My thinking is the current bracket is 18cm (180mm) long (the flat surface that mounts the extra rack), so I want a flat length of something that is 23cm (230mm) long - with 3 holes drilled in it. I'll then bolt the extension piece to the top of the bracket (2 holes will bolt to bracket and the 3rd will then bolt to the extra rack).

I've no idea where to get flat metal bits and also not sure what to ask for...I'm sure this will be perfectly doable, just unsure what I'm asking for.

You can get all sorts of steel strip and box section at B&Q. You can also get hacksaws, nuts and bolts and metal drill bits there too.

I'd discounted B&Q as figured it would be a bit 'special' (in the sense it would need to be a reasonably thickness)...I'll take a trip there and see what they have, thanks.

As with so many things in life the easiest answer is probably just pipe lagging...

Nope, tried pipe lagging but there isn't enough space for both bikes to fit...it is incredibly tight (actually touching) and with pipe lagging on, the bikes won't sit close enough for the clamp to reach the 3rd bike...with a good push that then fits, but the pipe lagging then breaks as it is fully compressed.

I was at B&Q an hour ago and that section was full of sturdy 1m lengths of steel strip. It also had a pre-drilled Varnished Cold-pressed steel Flat Bar, (L)1000mm (W)40mm (T)2mm

Sorry about the link - all the insert options have vanished.

https://www.diy.com/departments/varnished-cold-pressed-steel-flat-bar-l-1000mm-w-40mm-t-2mm/254559_BQ.prd?storeId=1169&&&&&gad_source=1&gclid=Cj0KCQjw8J6wBhDXARIsAPo7QA9yMnPsHYlcn-_nlRvDVlXrX6bTtedWQdwNfPqbb238xJgB5JglJbUaAjdNEALw_wcB&gclsrc=aw.ds

The answer is probably that you're playing with fire legally / insurance wise messing with a rack and extending it rearwards.  Accessories need type approval for a reason.

It's not just the raw static strength you have to think about it's the dynamic loads applied to all the fittings.  The hitch connector was designed with a certain set of loads on it.  You're increasing those by moving part of the rack back giving it more leverage.

The attachment point for the extension and it's own attachment to the rest of the rack structure have all been designed with certain loads in mind.

Extending it rearwards and putting a heavy bike there might be fine but if it isn't it might be messy beyond just a mangled bike.

Good point. The 3 bikes come to just shy of 45kg, the rack is about 19kg (with the 3 racks). The towbar is rated to 75kg...so aware the static loaded weight is under the limit, but as you've pointed out, the dynamic load is going to be greater.

Ok, another email to Atera to ask if they have plans to offer an extended bracket that would still be safe.

Kind of glad I'd asked and got that answer, thanks.

I was in b&q earlier and saw that strip but it didn't feel very solid, so I didn't bother with it.

The manual for my car states that the max weight on the towbar is reduced for bike racks clamped on to it. Max load is halved if the centre of gravity is 600mm behind the towbar.

I always try to load heaviest bike first to keep the CofG forwards.

I don't think there's any specific legal issue with modifying a bike rack, provided that the end result is legal. Your insurance may have stronger views on modifications, but I think those generally relate to the car itself.

Bolt together frame fixings would work, they’re generally galvanised, but I’d probably want them powder coated on top to limit corrosion in the atera ally bits.  Considering you can get an atera 3 bike rack and then add on a 4th bike adapter I doubt it’ll muck up the tow ball loading, however the loading of the holes in the atera’s structure might be more of an issue.

does your car’s manual have anything like this in it?
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Yeah, again, all makes sense... although the rack is for ebikes, it carries 3 non-ebikes, so the weight isn't such an issue...lightest is about 13kg and the other 2 are about 15kg.

I've abandoned the idea of me 'fixing' this and have contacted Atera to ask if they have longer brackets or are likely to do some.

If they can't, I suspect I'm going to have to find a new bike rack.

I'll need to check the manual...got the new car (Skoda Enyaq) on Tuesday, and it all seems to be online via the touchscreen...suspect there is a paper manual somewhere but I've not had a look round all the storage bits.

I suspect, if I did have an extended 3rd carrier then it would be very close to the 70cm limit in that print, so something else to consider (and again, convinces me abandoning my idea of a DIY fix is now the sensible thing after all the issues and considerations flagged here).

Bear in mind that the distance is the CofG, so to a first approximation it's the middle of the rack, not the back.