Confusing sizing help please :)

[Dr Imran T]

Hello chaps

Can anyone kindly shed some light on this frame sizing please. I have ordered a large based on the measurements of the top tube and other measurements given. However, it is the seat tube length that doesn't make sense to me.

It states 515mm but surely with all the other measurements given it falls in line with a regular 56cm 'large' frame.

Frame in question:

http://www.ebay.co.uk/itm/2016-Costelo-road-bike-b...

Thanks chaps

[jrb43]

Yep, road bike frames are typically measured along the top tube. This is in contrast to mountain bike frames which tend to quote the BB-seat clamp. Not unusual for a modern road bike frame to have a sloping top tube and therefore be shorter BB-seat clamp than the top tube length.

[Jimbo.]

Bike measurements are rubbish: no consistency, even between different sizes of the same model, never mind makes.

Ignore top-tube this and headtube that; look up "stack" and "reach" and work from that.

[Dr Imran T]

thanks chaps, yes I'm aware of the differences in frame geometry that give very different measurements.

Had not thought so much about reach and stack - care to elaborate further?

thanks

[NatAsp]

It's a compact frame. I.e. Shorter seat tube with a sloping top tube to compensate.

The seat tube length does not affect your position on the bike, you can pretty much ignore it. Just means you'll have more seat post showing based on your saddle height when compared to a semi compact or classic frame.

What model/size bike do you ride at present?

[Dr Imran T]

NatAsp said:

It's a compact frame. I.e. Shorter seat tube with a sloping top tube to compensate.

The seat tube length does not affect your position on the bike, you can pretty much ignore it. Just means you'll have more seat post showing based on your saddle height when compared to a semi compact or classic frame.

What model/size bike do you ride at present?

yes, my thoughts too. was thinking to bump the seat up a little more to get the correct height.

currently ride a 56cm ribble or whatever framed bike it is. It's my interim bike after my crash

I've gone on the basis of top tube length mainly, hoping I get then make minor adjustments to get the perfect fit.

I've noticed that different frame builders/sellers have measured the seat tube in different ways which makes it nigh on impossible to figure the correct size.

thanks

[NatAsp]

Dr Imran T said:

yes, my thoughts too. was thinking to bump the seat up a little more to get the correct height.

currently ride a 56cm ribble or whatever framed bike it is. It's my interim bike after my crash

I've gone on the basis of top tube length mainly, hoping I get then make minor adjustments to get the perfect fit.

I've noticed that different frame builders/sellers have measured the seat tube in different ways which makes it nigh on impossible to figure the correct size.

thanks

If you've gone with the same effective top tube as what you have now, then provided the seat tube angle and saddle height (from bottom bracket to top of saddle) are also the same then you'll be the same distance from the head tube as your current set up. If the head tube on the new bike is taller then the handlebars will be higher and if it is shorter then the handlebars will be lower. You will only have a "problem" if you currently slam your stem and the new bike has a taller head tube. Otherwise you should be able to adjust your stem to get the same position. I am making the perhaps incorrect assumption that your existing fit is good, if not then matching your current set up would be pointless.

One further point - this method of fitting is used by The Bike Whisperer who I spoke to at length on the subject during my fitting appointment with him. So anyone who tells you that you should ignore these measurement is effectively saying that one of the top fitters in the country, if not the world, doesn't know what they're talking about. I'll let you decide who to trust.

[Dr Imran T]

^^ thanks some great advice there. I had a quick read up on reach and stack height too so I better understand all this jazz.

I have indeed gone for the same TT length as my current bike, even the HT is the same length. It was the seat tube that threw me out as it measures just 52cm. However, I think this measurement was taken behind the seat tube whilst I've noticed some other geometry charts have measured ST length in-front of the ST.

AS you can see from the geometry chart the actual seat tube has a funny shape and a lot of the bike's tubing and general shape is quite different to your regular 'road racer/sportive type bike'

Anyway, I've ordered the frame now so I shall report back once I've got it. If it's too short then I'll go back to square one

Was a little risky buying the frame without seeing it in the flesh, plan is to put all my good quality parts on this new frame.

cheers