Bike Size help

matt_wright

When a company say their bike is a 58cm frane size, what are they refering to?

I only ask as i am looking at buying a boardman bike size L. On the halfords website it says the large is a 55.7cm frame. When looking at the baordman website it doesnt mention 55.7cm anywhere for measurements on a large bike. It says the Seat tube is 55.5 and the effective top tube is 57.
[/url]http://www.boardmanbikes.com/pdf/Boardman2010_Road.pdf

i have been told by 2 differnet people at halfords that i am a Large sizem but after looking at the geometry and fram sizes of other bikes i am left very confused!!!

However i know for a Trek bike that i am a 58cm size (as i went to a Local bike shop and they said it would be the 58). But what measurement does the 58 refer too?

I am just conscious i want the correct size bike

i am 187cm tall (73.6 inches) with an inside leg measurement of 90cm (35.4inches).

Many Thanks

Matt

jonmack

You'd be fine on a Large, i'd trust the Boardman catalogue over the Halfords site (which is more likely to have typos).

To my knowledge the 58cm will be the effective seat tube measurement, same as on the Boardman. However that 58 doesn't necessarily mean it will be 58cm, is the Trek geo not on their website?

Slow Downcp

Different companies have different methods of measuring - seat tube length is less relevant than top tube IMO.

If you're unsure, a decent bike shop (admitedly not Halfords) should provide a proper measuring service, rather than the cursory "Yeah, that looks about right. It may cost £50 or so but you'll get a proper service and be guaranteed a bike that fits.

matt_wright

Thanks, i found some more info


the boardman (large) has a ETT of 57 and the trek (58cm frame) has a ETT of 57.3cm
Seat tube wise the boardman has 55.5 cm and the trek 55.3.

These seem very similar and would suggest that if the trek 58cm is the correct fit, than the boardman one should be fine?

Out of interest, what are the main measurements on a bike to be concerned with, from a newbie point of view it looks like ETT and Seat tube, or am i missing something complely?

Thanks

Matt

seanoconn

The top tube and seat tube are the important measurements. I'm 6ft, with an inside leg of 34.5 inches. The Boardman size large is plenty big enough for me, i even had to get a smaller stem. You can't really judge the size just by the seat tube as the geometry & way bikes are measured vary. If you got the extra large, the seat tube wouldn't be a problem but the longer top tube would probably mean you're too stretched out. I'd pop into a halfords if you can and try a large.

matt_wright

Thanks, i have tried a large already and i am trying a XL today. the problem is i do not know what the correct position is. e.g. should the arms be locked out, or just slighty bent etc?

given what ive read i think im happy the large is correct size, but no harm in trying both today and getting the opinions of a different halfords store

thanks

matt

Theomerchant

Arms slightly bent is the correct way to ride, if you ride with your arms locked out you risk injuring your back, shoulders,elbows & wrists and the ride would be extremely uncomfortable after 30 mins or so.

Do you have to get the bike from halfords? (is at a cycle to work scheme?)..If not I'd advise not using halfords..they do sell reasonably good bikes and decent prices i.e the boardmans, but there after service is atrocious, I would liken them to a back street car MOT centre so for example if you had to take your bike into halfords for a wheel truing they'd tell you you need an new groupset / wheels & everything else on your bike...there complete ar*e to be honest.

If I could give you any advice to go away with try looking in LBS's such as Evans or Leisure lakes...or even smaller more independent stores!!.

seanoconn

if your arms are locked, the bikes too big or stems too long. You need a slight bend in the elbow with your hands on the hoods to feel comfortable and absorb the impact of bumps as you ride. Maybe you should do a bit more research into what a good fit should be before forking out for a new bike. A test ride is the best way to find out but halfords don't normally let you.

Wheelie Bin

I disagree on 'most important measurements'.

Within reason, you can adjust a seatpost for height and saddle for position relative to the cranks, and you can adjust bars and stem for reach.

What you can't adjust is the bike's head-tube. So, to me, that's the most important measurement; it fixes the 'attitude' of the bike.

Having said all that, you've then got seat and head tube angles to consider...

... so to answer your question OP - I only really found the right position on a bike and therefore right size (one size bigger than I had assumed for 10 years previously), after a professional bike fit and that's what I'd recommend to you.

Burghley

+1 for head tube length being an important measurement.

It is often overlooked by people when buying a bike, but it can have a significant impact on handling and comfort.

Boardman road bikes seem to have quite race orientated geometry - suits some people but not others.

What sort of riding do you want it for, as this will help define the frame geometry and size?

Rgds

Pete