If a bike is too small

[Longshot]

...what problems will you experience?

I have a 58cm Specialized Sirrus which I bought from new and was fitted for me at the store, albeit very briefly.

I've always felt it was a shade larger than ideal, despite the fact I'm 6', as I cannot get my saddle up to level or above the handlebars without flipping the stem. From my own uninformed point of view, I thought a slightly smaller bike would have been better as I could raise the seat height to fit but the bars would be that bit lower.

I also note that Giant suggest a 53.5 for my height and inside leg.

Anyway, I've seen a good deal on an Allez that I'd like but it's a 54. I don't see a problem but perhaps I'm missing something important?

Any advice would be appreciated.

 

[Rob3rt]

Depends how small it is. Going from a 58 to a 54 is a pretty massive change and at 6' tall, you most certainly do not want a 54cm frame! The most important measurement is the effective/horizontal/virtual top tube measurement. The 54cm frame will be too short and you will be sat bolt upright and look like a proper dork.

But to clarify this stem flipping. You are trying to get a greater saddle to bar drop? To do this you have to flip the stem over to lower the bars? Many people would have said you are installing it the way it should be and that for some reason it was already pre-flipped.

You will have to clarify.

 

[Peteaud]

...what problems will you experience?

I have a 58cm Specialized Sirrus which I bought from new and was fitted for me at the store, albeit very briefly.

I've always felt it was a shade larger than ideal, despite the fact I'm 6', as I cannot get my saddle up to level or above the handlebars without flipping the stem. From my own uninformed point of view, I thought a slightly smaller bike would have been better as I could raise the seat height to fit but the bars would be that bit lower.

I also note that Giant suggest a 53.5 for my height and inside leg.

Anyway, I've seen a good deal on an Allez that I'd like but it's a 54. I don't see a problem but perhaps I'm missing something important?

Any advice would be appreciated.

The Giant size guide would be a M/L (53.5) and that is what i have, i am 6 foot tall with a 32 leg and it fits perfect.
But, i do find the giant size guide odd as it does seem to read a frame that is smaller than they say.
A friend also has a giant, he is 5 foot 10 and rides a M frame, again fits him spot on.

Different manufactures, different sizes,

 

[potsy]

Maybe you need a road bike, not a sit up and beg hybrid?

 

[Rob3rt]

It is not that brands frames are drastically different throughout the range (although there will be geometry variance), it is that they use different measurement conventions.

Some use, centre of bottom bracket to top of seat tube, centre of bottom bracket to centre of top tube etc for the stated size, what this means is that a frame with a sloping top tube, like Giants and other modern bikes have, come up with small measurements. If you were to compare this stated value to the value a horizontal top tube would yield, you will find the bike to probably be equivalent to a 56-58cm frame, which sounds right for your size.

For the length of frames some measure centre of head tube to centre of seat tube along the length of the top tube. Others measure horizontal/virtual top tube, i.e. the measurement of what length a horizontal top tube would yield. The virtual top tube measurement on a sloping frame, and top tube measurement on a horizonal top tube frame would be the most important of all dimensions.

You need to learn to identify which convention is used and be able to approximate across conventions. You can calculate it accurately if you wish.

In general though if you reduce things down to one convention, in general sizes are fairly consistent IME.

 

[accountantpete]

The Sirrus was designed to put the bars at or just below seat height.

Road bikes like the Allez go in a different direction and aim to position the bars bars at a distance below the seat -with the ability to raise the height of the bars through a longer steerer if necessary.

I'd make sure that the forks on the Allez have a lot of steerer left to make any required adjustments.

 

[Mr Haematocrit]

Im on the edge of a 52/54 frame set and will always take the smaller frame, with a slightly longer stem and setback seat post you can make a smaller bike feel bigger, I find I have more trouble trying to make a larger bike feel smaller.

 

[Longshot]

I'm happy to listen to the advice of those with more experience but I'm surprised at some of the comments. It's 40mm we're talking about here and less if, as I suspect from my own experiences, I'm actually better suited to a 56.

Anyway, you've convinced me... I won't be looking at any 54s! Thanks for the help.