I’m currently looking into changing frames.

The Pike RC which came with my bike is 150mm. The two frames I’m looking at are based around either a 160mm travel fork or 140mm. Just wondering if the travel is adjustable on the fork?

Yes. You need to change the air shaft. Its pretty straight forwards if your used to working on your bike. Lowers service plus open up the air side (just removing a circlip).

You should look to buy a 2019 Debonair shaft if it’ll be compatible as its deemed an upgrade on the air spring. TF Tuned or Ben @ Bird Bikes will know for certain.

Approx £40 for the Air Shaft.

Expensive? – Answered above

Trying to stay 27.5 to keep costs down but if the fork issue became expensive I might just take the plunge and go 29er.

The air shaft to change the travel is likely only £42 – that’s how much I paid for a 2019 debonair one for my Lyrik. Fitted it myself – as long as you’re methodical and follow the SRAM tech documents it’s pretty easy.