The Thule Racks Xadapt 9 adaptor kit will work. This is the adaptor Thule specs for mounting the Thule 517 Peloton to their Thule Rapid Aero bars (which are nearly identical to your Audi bars). As a matter of fact, Thule makes the racks for most the European brands sold in the US. Sometimes these european model factory roof rack systems go by the name of Votex racks. They include a t-slot channel in them just like the Thule rapid Aero load bars do. This allow many Thule gear carriers, including the Thule 517 Peloton bike rack to mount to bars of this type by inserting a Thule Xadapt kit into the t-slot and then mounting the gear carrier to the Xadapt.
A handy compatibility list that shows what gear carriers fit Thule Rapid Aero bars (as well as any Votex / european car model factory racks) and if they require an Xadapt kit can be found here...
Thule Racks Gear Carrier to Roof Rack Compatibility Chart
mounting thule pelotan to audi tt factory rack
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