Totally Confused on Bike sizing

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EYE-TYE-MAD

New Member
Been looking at the Carrerra Subway Limited 2012.
My inside leg is 31ins and I am 6ft tall. According to the Halford Guide I should have a 17 in frame.
But looking at other guides. On a hybrid, stood aside it, there should be 2in clearance and on another guide its 3in clearance from crutch to top bar.
Others give a formula inside leg - 2in -10in ( bottem bracket to floor = 10ins so they say)
Here's my problem - I have a 21in Raleigh MTB which I am comfortable on, the distance
from centre bottem bracket to the floor is 13ins :wacko:
If I went to Halfords and stood astride the bike what should I be looking for ?
Any Member bought a bike from Halfords Altrincham ?

Any help would be welcome Ta
Bike sizes are now given vertually, that is, as though the top tube was straight, that is, parallel to the ground as all bike frames used to be. So in effect the size the manufacterer states doesn't really exist, it's imaginary, or at best an indication of what size the frame would have been when measured traditionally. Stated sizes also differ considerably from manufacturer to manufacturer because of frame geometry, degree of slope etc. In the old days it was simple, frame size was measured from the centre of the bottom bracket to the centre, or top of the seat tube. I'll try to make things simple by basically dividing frame sizing into three groups, 1. Traditional road bikes. 2. Mountain bikes. & 3. Road race & Sportive bikes. So,1. traditional bikes. Stand over the bike with both feet flat on the floor. Size wise, there should be about 2cm of distance between your crotch & the top tube. 2. Mountain bikes. For a number of reasons these need to be smaller, i.e, strengh, more manoeuvrable on rough ground, & you may need to get off in a hurry. For these reasons there needs to be at least 5-8cm of clearance. And so to 3. Race & Sportive bikes. Well, this is where things can get a bit tricky, as both are a direct development by borrowed virtue of both the road & mountain bike . Sizing in this category can be a nightmare even for the most experienced. However, I would, if pressed, be more inclined to use as my criterion for sizing the 2cm distance of the traditional road bike. Hope this helps!
 

kishan

Active Member
Location
London - Harrow
you probabbly wanna get 26inch wheels x18 inch frame size
 

al-fresco

Growing older but not up...
Location
Shropshire
It is a complete minefield - I'm 5ft 7 and a 50cm Surly Cross Check is a good fit but so is a 54cm Specialized Langster. The reason they both fit is that the manufacturers measure the frame differently - if you measure the Surly the same way as the Specialized it becomes a 53cm bike. And then there's the geometry - as gavintc pointed out the reach to the bars is also important and that's mainly down to the length of the top tube.

It's not that I can't ride a bike which is a couple of inches bigger but when you get a bike that fits just right it just feels part of you - not something you're 'on.' Definitely worth taking your time and getting it right.
 
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