Sorry for asking this as I'm sure it's been asked hundreds of times but I've struggled to find an answer online.
I am wanting to by a new mountain bike frame and I'm a bit confused by info I have read online and my own personal experiences.
I am 1.66cm (5' 4.5") and currently have a 16" frame. I use it mostly for road riding and getting to work etc but do use it for off-road mountain biking fairly often. I have the seat raised quite a lot and although I do lower for parts of off-road stuff, I never put it all the way down.
So my confusion is this. I have seen a second hand frame which I am very keen on getting and from my own experiences with my current frame I assumed an 18" would be what I would need. However, everything I read online suggests my current frame is the one I need.
In case anyone is wondering I got my current frame (bike) when I was about 13 (I'm now 24) and clearly haven't grown much as I am short . I have upgraded most parts on it and was now looking at changing the frame and putting the new parts onto that, but I've hit this road block.
Help and advice appreciated.
Thanks

Bike sizes are confusing, the top tube length is the important part. You can get the seat higher by using a longer seatpost.

But an 18" frame would certainly be to big

Infact, I'd have thought smaller than a 16" might be even better for you.

Your best bet is to try some.

At your height 18 would be too big. I'm 5'7" and a 16" is perfect.

I could go a little larger but that size fits really well. I would use 16" as your max size.

I am the same height as u, I ride between a 15-16 inch frame..

I'm surprised you all think 16" is fine. Just measured my seat post and it's raised by almost 7" for road riding! Seems like a lot to me. I'd never lower it more than 3.5" for for any type of riding I don't think either.
On th frame it is actually marked as 16" but I measured it and it's 16" from centre of BB to the very top of the seat post tube - not just the crossbar but the bit that sticks up above that, not sure what that's called. Is that the usual measurement that is taken or is normally up to the crossbar and no further?

I would stick with a 16" as a maximum to be honest.A smaller frame with saddle adjustment is always nicer that a larger frame without.A smaller frame offers much more stand over height which i prefer over largers frames that bring the top tube height up quite abit.

As mentioned,check the top tube length of both.

My Turner Flux (trail /xc)
size: 15


My Custom AM Ti HT
size: well, measuring from bb centre to top of seattube.. 16


My Carbon weight weenie XC
size: 15.5


My Kona Kula XC
size: 16

so yea, all abt 7" of seatpost sitting proud of the top-tube
and all an awesome fit.

In a nutshell: A bike has three contact points. Pedals, saddle, handlebar.

As long as they are where they have to be and the bike still handles well, you don't have to care about how they got there.

_________________
"Nothing compares to the simple pleasures of a bike ride," said John F. Kennedy, a man who had the pleasure of Marilyn Monroe.

I take it you're the same height as me then?
It just seems to me that if you have the seat raised by 7" then surely I (or even yourself) would be ok with an 18". Anyway, I'm going to go to a bike shop to try out an 18" so I know exactly what I should be looking for and if I should be sticking with the 16".

There is top tube length that comes into play,
plus when riding on trails, the stand over height is much needed.
and when dropping bigger drops and railing down some of the gnarlier downhill runs, dropping that seat is gonna save ya family jewels.

Plus smaller frames always look alot nicer in my opinion.