1) Older Bikes use a Non latching part, you can buy an Upgrade

Newer ones the way you turn the suspension bung can do that Or if turned otherwise will stay latched .

2) yes that is how they are the angle is for the Kickstand fold.

3) The Mudguard is a thermoplastic , maybe the struts are letting it bend inward , bend those first. Plastic will Break .

4) Your Lowest cost Brompton Bag is the basket.. I am clueless to your Backpack specifics .

Give more details

I have Used A Messenger bag with a waist Band, and clipped the waist belt around the bag frame .

Then I got a Brompton Ortlieb O Bag They are a specialist in Bags that keep stuff Dry.

5) so you figured out #1, already ?

Your Brompton Dealer will sell you all the spare parts you need ..






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