Postby europa » Sun Aug 05, 2007 10:35 am
G'day Perception,
Welcome to the nuthouse.
Now to your question. Measuring bits of you and then trying to make them fit bikes sizes is an approximation at best. I'm sorry, but there is no way to get around sitting on the bike in person.
For starters, this business of 'frame size' varies between manufacturers and sometimes varies within the same manufacturer. It's a number, no more than that.
Then you need to consider Tally's comments - there are a lot of components that go into giving a human a certain height and each of these can impact on the final bike setup.
Your inseam measurement will help your standover height ... but that's it. For example, I seem to need my seat set back further than the norm and am beginning to wonder if this is due to my thigh bone being a tad longer than the norm.
Seat height is affected not only by the length of your leg bones but by how you rotate your ankle when riding, though fortunately, we're only talking a cm or two there.
Your flexibility also affects bike fit, both in seat height but also in reach. My Trek520 which fitted when new, no longer fits 1,500 kms later because I'd become fitter and more flexible. Mind you, it does fit now because I went to the trouble of changing various parts of the bike but that doesn't alter the fact that I've made the best with a bike that is one frame size too small.
So, although bike fitting seems simple to start with, it gets complex very quickly and will change with your body.
This isn't to say you're going to be faced with an endless chase for new bikes and bike parts. Fortunately, it's only fussy buggers like me that do that (and a lot of that is just the joy of the hunt), but you do need to get a good heart for the set up, and that heart is the bike frame.
So, here's the easy part of the advice.
- Go sit on the bike in person. If you don't, you will be guessing.
- Stand over the bike, feet flat on the ground. You need a gap of a couple of fingers between the top tube and your PELVIC BONE. Not the soft tissue (as most people advodcate) but the bone. If the bike is a traditional diamond frame, you may find the top tube touching the soft tissue but I can assure you that after 20 years riding the Europa where this is the case, this hasn't been a problem. If the bike has a sloping top tube, like most modern bikes, you'll find this gap is much larger.
- Get the seat set to something like a good riding height - it only needs to be rough, and look at how much drop there is from the seat to the bars - how much below the seat are they. The modern racing fashion is to have the bars very low. This is great for aerodynamics and works with fit, flexible people but for still old gits like me, it places a lot of weight on the hands and can become torture. I like my bars at the same height as the seat. Bars can be raised but it can be frustrating and expensive to do it these days if you have to raise them more than a cm or two. So try to buy a frame that puts the bars up near where you would like them eventually.
- Now look at reach. Don't buy a bike on which you feel cramped. You shouldn't feel like you are stretching out too far either but as you get fitter, your back and abdomen muscles will strengthen and your reach will increase. The trick is to find something that isn't making you stretch too far.
If you can get a ride on the bike, so much the better because it's amazing how what feels good stationary (even on a wind trainer) feels horrid on the road - handle bar position is a good one here.
I know this sounds like a lot and I understand the attraction of saying "I'm so high, I'll buy that", I understand the seduction of internet sites with fancy programs and lots of numbers. Mate, they're not worthless but you need to apply them to the above physical try out.
You're buying second hand so I'm guessing the money is a bit tight. This to me means that you want to get it as close to right as you can so I offer you this single piece of gospel - if you can't ride it, don't buy it.
Richard
I had a good bike ... so I fixed it
:):)
) is to leave your fixie unlocked in a public space, then wait for some idiot to try to steal it 