Why can't manufacturers standardise frame sizes.

[Gravity Aided]

Why?

I buy a great many used bicycles, over the course of time. Sizing information is not always readily available on the bicycle itself, and there are variances among frame styles.

 

[avalon]

A cyclist's life was much simpler when the majority of frames were made from steel tubing. Although you could have a made to measure frame built to your personal specifications you still knew what size frame suited you without having to try it out. If you rode a 24'' frame you could be fairly sure that you could buy another 24'' frame and it would be ok. Having a made to measure frame would only mean making adjustments to angles and top tube lengths, but the seat tube length (giving you the frame size) would remain the same.

 

[deptfordmarmoset]

For bike fit, perhaps it would be better to measure the lengths the triangle between the 3 points of contact on the bike - crank, saddle, handlebar. Those are the essential points. And yet we measure just about everything else instead.

 

[martint235]

Most (I have found some that don't) bike websites publish the geometric sizing. Get a tape measure and it's easy. My last 2 bikes have been bought based on the measurements of my old Giant commuting bike so I now have an XL Giant bike, a 58cm Planet X Ti and a 59cm Mango bike.

I did try to buy a Merlin bike but they insisted that their 59cm wouldn't fit me but couldn't provide me with a geometric diagram.

 

[User6179]

I buy a great many used bicycles, over the course of time. Sizing information is not always readily available on the bicycle itself, and there are variances among frame styles.

Yes but all that tells you is the distance from BB to seat clamp , I do not see how the measurement would help you as BB height from the ground differ and the seat clamp distance from the top tube differ ,top tube length and stand over height are better measurements for frame size , personally I put seat in neutral position and measure from back of seat to the handlebars .

 

[Judderz]

IME Cannondale do tend to use a slightly longer top tube than others. Suits me perfectly though.

For us tall people

 

[youngoldbloke]

It would be helpful if there was a standardized system of listing dimensions. For example what does centre (of bottom bracket) to top mean? Sometimes it means to the point level with the top of the top-tube where it meets the seat-tube , often it means to the very top of the seat tube (seat clamp) - without specifying how much seat tube is above the top tube. The useful dimension is the virtual top tube length of course, as many frames have a sloping top tube, to a greater or lesser degree. Standover height is also important to know, as is bottom bracket height if you are trying to compare frames.

 

[Dusty Bin]

It would be helpful if there was a standardized system of listing dimensions. For example what does centre (of bottom bracket) to top mean? Sometimes it means to the point level with the top of the top-tube where it meets the seat-tube , often it means to the very top of the seat tube (seat clamp) - without specifying how much seat tube is above the top tube. The useful dimension is the virtual top tube length of course, as many frames have a sloping top tube, to a greater or lesser degree. Standover height is also important to know, as is bottom bracket height if you are trying to compare frames.

The definitions are already standard. 'Centre to top' or 'C-T' means centre of BB to top of seat tube. It always means 'top' of the seat tube. The other measurement is 'C-C' which is centre of BB to centre of TT.

 

[youngoldbloke]

The definitions are already standard. 'Centre to top' or 'C-T' means centre of BB to top of seat tube. It always means 'top' of the seat tube. The other measurement is 'C-C' which is centre of BB to centre of TT.

If that is the case - it would be extremely helpful if manufactures could give BOTH measurements, so that you could determine exactly the position of the top tube junction on a 'compact' frame.

 

[youngoldbloke]

The definitions are already standard. 'Centre to top' or 'C-T' means centre of BB to top of seat tube. It always means 'top' of the seat tube. The other measurement is 'C-C' which is centre of BB to centre of TT.

You are very likely correct - to put it another way, my point was that the length (if any) of seat tube above the top tube is never specified.

 

[ShipHill]

I'd like to see them standardise shoe sizes first... my feet are 10.5" long, but my wide variety of footwear includes size 9, 10, 11. Logic suggests, they all should be 10.5 ... do cobblers use elastic tape measures?

I made this same suggestion to a lady who worked in a shoe shop once many years ago. She said it was "a stupid idea that would never work. What a load of nonsense."

I asked if she drove a car.

"Yes I do," she informed me.

"Well if it takes 14 inch tyres I hope they fit the 14 inch tyres, not the ones that are a bit under 14 or even a bit over. Bye."

 

[martint235]

You are very likely correct - to put it another way, my point was that the length (if any) of seat tube above the top tube is never specified.

Do you mean seat tube or seat post? Centre to top means the centre of the BB to the top of the seat tube regardless of where that is in relation to the top tube. The seat post is, ime, never included in the frame measurements (apart from I suppose monocoque TT frames.)

 

[avalon]

This whole thread is highlighting how complicated frame measurements have become.

 

[youngoldbloke]

I refer to the seat tube.

Do you mean seat tube or seat post? Centre to top means the centre of the BB to the top of the seat tube regardless of where that is in relation to the top tube. The seat post is, ime, never included in the frame measurements (apart from I suppose monocoque TT frames.)

Exactly. Many modern frames have a length of seat tube extending above the top of the top tube. Some extension is necessary to accommodate the seat post clamp, unlike a 'traditional' lugged steel frame where the centre to top measurement (usually) was the same as the centre to top of top tube measurement. Perhaps Sheldon Brown puts it more clearly than me:

A further complication is that nobody knows how to measure a bicycle's seat tube any more. Even leaving the inches/centimeters question out of things, there is the question of where the seat tube ends:
The old standard system was to measure from the center of the bottom bracket to the very top of the seat tube.

• Some manufacturers have decided that this is too easy, so now many bikes are measured instead to the intersection of the centerline of the top tube with the centerline of the seat tube.
• Some other bikes that have seat tubes that protrude farther than normal above the top tube measure as if they were measuring to the to the top of a seat tube with normal protrusion.
• Some bikes are measured to the top edge of the top tube, even though the seat tube protrudes higher up.
• Some bikes with slanting top tubes are measured as if there were a level top tube, they use the length that the seat tube would be if it was as high as the head tube.

 

[perplexed]

Piffle to bike sizes.

I always have a nightmare with slippers...