if having to buy a bike on frame measurements alone, whats MOST important?

[reohn2]

Different length top tubes, so seats postions are adjusted accordingly.

This is the bit that I (and many others) can't do.
I need to sit a fairly precise distance behind the bottom bracket (although in reality I suspect plus/minus 5mm is close enough, as I move about on the saddle anyway).
Having set the saddle setback, reach is adjusted with different stem lengths.
Saddle setback is critical for me because it governs how much weight is on my hands, and what proportion of pedalling "work" is done by quads vs. hamstrings.
I'm sure I'm much fussier over this in my seventies than I was in my thirties; in my thirties I think I could jump on just about anything and ride it.

I agree,as I've got older(not quite 70 yet)saddle position has become more critical for comfort,especially on longer rides not just that but saddle shape and type though that's a subject for another thread.

[Manc33]

I had the saddle on a seatpost with 50mm setback so it was 34mm further back than I had it on my Thomson - but it felt weird. There were also times it felt like I could accidentally pedal backwards, which seems odd considering the saddle position, I would have thought it would be the other way around (positioned to feel like pedaling forwards more) but no. I swapped back to my Thomson (it has 16mm setback) and all of a sudden it feels a lot better.

I'm sure my legs are short compared to my reach (going off the knee at 3 O'Clock plum line rule, with the line about an inch behind the pedals on a 16mm setback seatpost). Meanwhile I am always messing about trying to make the reach big enough.

I have seen people say the further back your saddle is, the comfier it is (because of weight on your hands?!) but to alleviate weight on my hands I just put a higher handlebar on and try to not mess with the saddle.

Other times I have had that 50mm setback is when the frame is too small for me (putting flat bars on a bike I had drops on etc).

You can experiment, but I have found deviating away from how it's always been done is always a step in the wrong direction.

The other problem is, bike manufacturers seem to think we are all racing, I mean if you buy a carbon frame, it's tailored to racing usually. What if we just want a lighter bike that soaks up the road vibration a bit better... they never thought of that? The days of people not being able to afford these "racy" frames is long gone!

[reohn2]

Manc33
The seatpost doesn't matter it's the saddle position in relation to the BB that does I find KOPS to be a good place to start with saddle position,only needing to tweek it slightly for optimum.
Once the saddle's set to optimum then and only then do you set the handlebars(whether drops or flats)to their optimum in relation to the saddle position.

[Jamesh]

Manc33

There are carbon bikes that are slacker geometry and handling usually called endurance bikes synapse, Roubaix, etc.

It does seem counter intuitive that having a saddle futher back reduces load on the hands when a shorter reach would also reduce loads on the hands.


Cheers James

[martinn]

I put the measurements into the bike geometry calculator and then used the measurements from the spa site for the 58 and 56, tried to aim to have the saddle nose to BB distance, and the saddle nose to the end of the stem.
fading the one bike geometry over the other until the saddle and end of stem position were the same and didn't change, when toggling between the two.
the 56 seemed the better match, interestingly i then tried the 54...... that seemed to be an even better match, as long as I didnt mind a large amount of seat post showing, 20+cm, and 130cm stem..

think I will go for the 56

Martin

[Paul Smith SRCC]

I put the measurements into the bike geometry calculator and then used the measurements....

If you like playing around with data you may enjoy composing each in BikeCAD free. It's quite easy to find data for the bars, seatpin and headset and even luggage; so you can play around with it quite a bit.

54cm

56cm

58cm

If that appeals before you do anything create your free account so that you can save your drawing when finished. You can start with either their quick start drawing, or any from their design atchive that includes mine above (I composed 52/54/56/58, note I used Spa's Audax frame geometry for those drawings as I could need see one listed for their Mono bike, I assumed it would be similar; I have emailed them for clarification as the geared version lists 52-58 and the mono 50-60cm. If the geometry I used is correct I'm not surprised you found what they call a 54cm fitted OK, it has an effective top tube of 564mm. Whatever drawing you start with in each case you can edit and save to your free account as your own drawing and keep it 'private' or make 'public' as desired. When you have found the drawing you want to start with simply click on the green "open in BikeCAD' tab, note as they correctly state "it can take several minutes to load"; it does.

Normally the free version works best if you do not display the chain and rear derailleur, plus even though technically you can I would not try and upload any brand logos as it is inclined to crash; adding text to frame and components as I have done in the example above is not a problem, being a single speed I had no issue composing the two drawings above as there is no rear derailleur anyway!

[martinn]

Thanks Paul

I have already built it up... i purchased a 56 in the end, and have set up the position, and then modified it.
I will try bikecad to see what reach and stack that gives me

many thank

Martin

[531colin]

Reach and stack are in this geo. chart for one of the "Audax" bikes https://spacycles.co.uk/m1b0s223p3203/SPA-CYCLES-Titanium-Audax-105-R7000-Double