Mountain Bike for my girlfriend...

[mimitabby]

sub, that's not how it works.
it's like this.
Each major brand has several different models.
The cheapest
a little better
even better
a lot better
THE BEST

don't buy the cheapest (unless it's an on sale last year's model)!! don't be tempted. go for a little better, even better or a lot better.

the bikes that range from $500 - $1000 are the best bang for your bucks. (a little better, even better and a lot better usually can be found in that price range)
now these are road bike prices, but i am sure it's very much the same with MTB's

further, if you buy her a bike that is THAT much bigger than she needs she will NOT enjoy riding, she will suffer pain and you will have wasted your money.

[subharmonic]

I realise it's not as simple as that, as it never is.
The problem I've got though, is that at this auction, I will likely not have access to t'internet to check potential value of items, so a broad understanding of the good brands and stuff would be very handy.
It's an auction, so there may well be some right good bargains...

[tiffany Hart]

Get her a bike helmet with a gift certificate inside. That way she can get a bike that fits her frame and that she likes. She also has a present to open.

[Grog]

I realise it's not as simple as that, as it never is.
The problem I've got though, is that at this auction, I will likely not have access to t'internet to check potential value of items, so a broad understanding of the good brands and stuff would be very handy.
It's an auction, so there may well be some right good bargains...

Well the thing is that among the major bike-shop-bikes manufacturers (let's say: Trek, Giant, Kona, Specialized, Marin, DeVinci, RockyMountain, Jamis, Norco... there are probably a few others), as explained above, the bikes are roughly the same in terms of range of quality. They all have entry-level bikes all the way up to super-duper-high-quality bikes. They don't really make bikes with crappy parts (compared to bikes you'd find at Walmart and cie.) but they sure make some that are better than others.

The BIG difference is the geometry of the frames, which varies between manufacturers AND between models. There is also a significant difference in the various configurations: some will have this kind of wheel with these components, others will go for a different mix, some put a specific kind of handlebar that one may like, etc. That becomes more of an issue as one gets some experience with bikes and starts knowing what one likes. However the geometry and the size are VERY important. If one's bike doesn't fit, it will just stay in the garage, end of story.

So buying a bike at an auction is a risky move. Sure you might get a really good deal... but if the bike doesn't fit her and is painful and/or scary for her to ride, you'll have wasted your money.

Otherwise, if you really want to do it, and are adamant on getting a "deal", you'll need to become familiar with the main series of each manufacturer (some have numbers, others have names) and be ready to think on your feet on the day of the auction.

Sorry for rambling; there isn't a simple answer to that question.

[elk]

seems the route with the most success will have either to do with

1. givin up the idea of surprising her with a bike and having her get involved with the process or
2. look up how to fit a mountain bike, get her measurements, do a ton of reading and take a best guess.

one place you can learn about mountain bikes is mtbreview.
http://www.mtbr.com/
another place you might learn about fit is wombats
http://www.wombats.org/tips.html

she'll love you for the thoughtfulness it takes to make sure it fits.
IF it doesn't fit...she'll feel all guilty about being honest, you'll feel like a heel for being so impatient. been there.

[subharmonic]

The solution is that I'm going to take her to the auction!!!
There's a fair few items on her "want" list so if I can kill that bird with the auction, I'll be able to get her a few other bits n bobs. As it stands if I was to take her to a 'proper' bike shop, and get her a decent bike, I won't have much change left to get anything else for her...