Bags which strap on - do they scratch the frame?

[ScumOfTheRoad]

I have a little frame bag which straps onto the top tube, from Decathlon, using velcro straps. I have never seen it scratch the frame.
Just idly wondering if bags like that, or larger bikepacking bags, are prone to scratching the frame. Your thoughts and maybe fixes.

[Phil Hears A Who]

Depends on the attachments and conditions I think. I had a similar velcro tube bag that didn't scratch for about a year, then a single wet and gritty ride in Flanders helped it wear all the way through the paint. That's Belgium for you though I guess. Some bags have rubber straps that stop them rattling about which I think is supposed to help. Not sure about the types that have the elastic webbing style attachments. A common fix is just getting a load of 3M helicopter tape and popping that anywhere something touches the frame, like you would to stop shifter cables rubbing the head tube.

[jiberjaber]

Yes, even on a natural finished frame like Ti or Stainless they will polish the metal.

Helicopter tape is the usual fix, it's a clear adhesive thick tape originally used to protect the leading edges of helicopter blades.  It is even now marketed as bike (or frame) protection tape too.

example link: https://www.selfadhesive.co.uk/tapes/single-sided-tapes/helicopter-tapes

[ScumOfTheRoad]

I was part of a  Formula One aero engineering team (*) and helicopter tape was used.
Surfaces in F1 need to be a smooth as possible. I admit to never having seen it be applied.

(*) Computer nerd

[fruitcake]

I suspect the answer is 'notionally'. In the very worst conditions, over many hundreds of miles, the top layer of the frame coating (i.e. the clear coat) could be abraded by grit on the bag fabric or by the buckles. However, factory paint is very tough and it takes a lot to abrade it. I've used frame fit bags and seen no damage.

[ElyDave]

I've used heli-tape on the expected wear areas of the new Faran, and also on chainstays where I expect crap to be thrown around.
I've used a top-tube bag in the past and definitely seen wear on the paint

[BFC]

The primary wear mechanism is that a soft material picks up small pieces of abrasive materials which partially embed themselves in the soft material. Any relative movement then wears away the harder surface.

This is the failure/damage mode on old style rubber strip car windscreen fitment - grit embedded in the rubber seal wears through the paint then the metal goes rotten, performance vehicles went rotten quicker because of more body flex.

Helicopter tape gives good protection against this type of abrasion.