"25 inch frame. That means the same geometry on any 'Audax' frame?"

[P Walsh]

Zigzag is of course right to point out that you have to make sure the frame will allow enough adjustment to get the seat and bars in the correct position relative to the bottom bracket. But I would still be aiming to replicate the exact position on the previous good bike, with the saddle the same height and the same distance behind the bottom bracket and the bars at the same reach, etc. (A Brooks saddle will limit saddle adjustment severely).

[citoyen]

You can't always trust the geometry advertised on the website to be accurate though, so best take a tape measure and protractor along to the shop when buying. I'm not entirely convinced the length of the head tube or top tube are critical, since bar height can be adjusted with spacers (albeit upwards only, and only if you haven't cut down the steerer) and reach can be adjusted with choice of stem. Main thing is to get a bike that broadly fits your needs (ie don't get a full on racer when what you want is the relaxed geometry of a tourer) but unless you buy a fully custom frame, there's always going to be some degree of compromise - standard sizes are based on average-sized people, and really, who among us has truly average physical proportions?

You should be able to tweak the set-up to suit your individual dimensions though. I'm the same height as my colleague but he tends to ride a 54cm frame or larger, while I tend to err on the smaller side (52cm frame for preference) because I have little legs. He's also a lot more supple than me, so if I'm riding a bike after he's been on it, I have to drop the saddle and raise the bars, but that's usually enough for me to get a comfortable ride.

Mind you, I wonder if I have more forgiving physiology than some people. I didn't spend much time at all on setting up the bike I used for WCW - just made sure the saddle height was right for me and got on with it. I realised, several hundred km into the ride, that the bars were far too low, but I couldn't be bothered to make the adjustment (it was also apparent by then just how stiff the bars were compared to those on my own bike). I also realised that they were slightly off centre - one of those things you may not notice on a short test ride (I'd only ridden the bike about 20km prior to the event) but becomes very apparent when you've been on the bike for 20+ hours. Still, I came through the ride in pretty good shape - developed a bit of knee pain late on but I think that was more down to the hills than the bike set-up.

[vorsprung]

I'm not entirely convinced the length of the head tube or top tube are critical, since bar height can be adjusted with spacers (albeit upwards only, and only if you haven't cut down the steerer) and reach can be adjusted with choice of stem.

headtube length is directly related to bar height because it gives the relation between the bars and the ground

Although it is true that reach can be adjusted by stem length (or saddle lay back) the way that steering feels is related- and also rise- so it is fairly important

Spacers and stems are there for adjustment, the head tube length and VTT are the gross metric

[citoyen]

Sure, I wouldn't want to be using stem length to make major adjustments to reach, but if your off-the-peg frame gets you within +/-10mm, that's probably good enough.

Within those parameters, I'd say (based on purely anecdotal personal experience) that trail is a bigger factor in steering feel than stem length.

I guess you can't take any of these individual measurements in isolation though - it's how they all add up (or maybe multiply) that dictates how the bike feels to ride.

[GrahamG]

I do wish everyone would adopt the stack/reach approach - every other measurement is worthless without an understanding of how seat angles etc. impact on TT measurements.

Even if you think the frame is identical it's worth checking as I've got two custom frames made to exactly the same fit requirements by the same builder but the second time around he built it slightly differently with 5mm longer on the TT, it still fits great, but that's because the only measurements I use are saddle set-back from BB spindle (tip of same brand/model saddle!), saddle height, reach to bars and drop from saddle to bars. None of these measurements involve the frame, the frame just has to be within the necessary parameters to allow me to get all those components in the right place.

[P Walsh]

Graham is right. I too have no idea how long my top tubes are (though I did know when I bought the frames) and I don't think about angles. I just try to get the saddle the right distance behind the bottom bracket and the right height above it, then I get the bars the right distance in front of the saddle and the right distance below the imaginary horizontal line from the saddle. With all that done, my position is almost identical on all my bikes.

[Ningishzidda]

"get the saddle the right distance behind the bottom bracket" is more 'mythamatics.

This dimension completely depends on what type of cycling you intend to be doing. It is coupled with the position of the lumbar vertebrae for the type of cycling to be done.

KOPS is a good start, but not the 'be all and end all' of it.

What's required is for the saddle to be in a position where the heart rate is lowest for sustained exertion in the power range most often used.

[P Walsh]

Ningishzidda, I agree with your comments, but my own comment about getting the saddle the right distance behind the bottom bracket was for someone who has already established that distance on previous bikes and just needs to replicate their tried and tested position.

[Ningishzidda]

Can’t speak for anyone else, but my skeleton has shrunk in the last twenty years.
I used to be comfy on a 57 cm Peugeot.
Then I bought a 22” Raleigh.
Then I got a 55 cm Dawes, and then a 54 cm Spesh.
I’m now looking at a 52 cm Whyte disk road bike.

When I’m eighty, I’ll be on an Islabikes. 

[P Walsh]

I must admit my calculations had not taken into account shrinkage!

[mzjo]

I do wish everyone would adopt the stack/reach approach - every other measurement is worthless without an understanding of how seat angles etc. impact on TT measurements.

Even if you think the frame is identical it's worth checking as I've got two custom frames made to exactly the same fit requirements by the same builder but the second time around he built it slightly differently with 5mm longer on the TT, it still fits great, but that's because the only measurements I use are saddle set-back from BB spindle (tip of same brand/model saddle!), saddle height, reach to bars and drop from saddle to bars. None of these measurements involve the frame, the frame just has to be within the necessary parameters to allow me to get all those components in the right place.

This is all very well but for some of us some very popular frame geometries are not at all within the required parameters. Add to this that when one is young the body is a lot more supple so a far wider range of potentially incorrect geometries and riding positions can be tolerated. Incorporate the changes in body shape as we get older due to vertebrae closing up and the increasing number of age pains and it becomes obvious that frame geometry is not something that can be generalised - without counting extremes like my dad who had the same back length as me but was 9 inches shorter in height. Long backs and long thighs rapidly put stock frames into the "poor compromise" category.
I used to be able to ride anything and everything (usually did), now any frame with modern race geometry seems to be outside the limits. I have shrunk about 1.5 inches (which seems reasonable for a 58yr old) with disc wear.
My set-up procedure always involves getting the seat lay-back right first (with an approximative saddle height), then selecting stem length and finally tweaking the saddle height and bar height after road testing. If I can't get the set-back right then the frame doesn't get past step 1. From experience I know I need the back of the saddle 32cms behind the bb spindle, otherwise I push back over the back. This is remarkably difficult to achieve on quite a few frames (especially if the budget does not include buying new saddles and posts).

[Fab Foodie]

If I can't get the set-back right then the frame doesn't get past step 1. From experience I know I need the back of the saddle 32cms behind the bb spindle, otherwise I push back over the back. This is remarkably difficult to achieve on quite a few frames (especially if the budget does not include buying new saddles and posts).

Exactly the same situation I have had to put up with until Rourke got the message and second time around built the bike as I requested.  The difference is immense.

[Hummers]

Thanks for all the comments and offers of help. Yup Jamie, we are the same height and inside leg but I am trying to persevere with this. After 2  200k rides, the shorter stem and moving the saddle back was a mixed blessing:

• Far better saddle position/tilt for hills and for general ride comfort. It feels like I am riding the Mercian again.  When it was further forwards it made the bike feel jittery and you felt all the bumps.
• Sadly, my leg and arse muscles have morphed to suit the position I have been riding for the last 10 months so it like starting from scratch  I will just have to persevere on this one
• The shorter stem somehow puts more pressure on my hands and numbness occurs within 100k rather than normally ....errr...never 

I have a slightly longer stem which is still shorter than the original stem. Will see if that is a compromise between power up hill and comfort on the flattish bits.

What is also apparent is the effect of riding in the warmth again. It needs discipline to drink and eat - something I have not been good at paying attention to. I am just glad there are a few DIY 200k rides between now and 16th August.

H