I'm looking to buy one of these:

https://www.evanscycles.com/products/...le%20bad%20boy

I was wondering if any of you guys have one (or something similar) and could advise me of which frame size to choose?

I'm 5 feet 9 inches with an inseam of just under 32 inches (31.75). I feel a medium may be slightly too small whilst a large slightly too big!

Any help would be much appreciated as I'm completely new to this!

If you can't test ride before riding then email the supplier with your details and ask which size they think. Make it their responsibility, not those of Random People On TheNet, because that way you get legal comeback on bad advice. You won't be between sizes - they overlap. With a 32" inseam I'd expect you to be a medium fit.

Inseam is not really a measrement that means anything as far as bike fitment goes. There are a myriad of methods to determine the proper size of bike for any one person. Here is one discussion of the topic:

https://www.rivbike.com/article/bike_...izing_position

Here is another:

https://www.competitivecyclist.com/za...LCULATOR_INTRO

There really is no hard and fast rule of fitment that holds true in every case. But these sites will provide some useful info.

- RG