Frame geometry question - one for a frame builder ?

[Farrina]

I am looking for some advice as regards frame geometry and my new frame as something appears odd.

Scenario thus - sorry it's a bit of a novel ...

I approached a local frame builder to build me a bespoke 853 steel frame based on my existing (25 year old) bespoke 531c frame. This old frame is what might be called an Audax frame i.e. a compromise between an out and out racer and touring frame. It has served me well and will continue to be used as a winter and foul weather bike. It is a big frame being 64.5cm

The brief for my new frame was no mudguards and for slightly tighter handling - my expectation being that it would have snappier handling at the expense of reduced ride comfort.

At the suggestion of my frame builder I decided to use a 12 cm handlebar stem as compared to the existing 10.5cm stem on my old frame. Note that new frame is A head, old is the traditional type of stem. I doubt this is relevant to my query but is included for completeness.

I took delivery of my new frame on Saturday but have yet to build it up (headset was fitted by frame builder so forks are on).

Measuring the dimensions of my new frame as against my old frame I noted the following

Seat tube 64.5 cm on both frames - so far so good.

Wheelbase ( measured from vertical dropouts on back to fork dropouts

Old frame 99cm
New frame 104cm

Top tube length (note this may not have been measured the way a frame builder would measure but has been done like for like on both frames so should be a comparable measurement)

Old frame 54 cm
New frame 61 cm

Now my expectation re the above would be that a bike with a longer wheelbase will be more relaxed and comfortable to ride but will not handle as snappier as a racing frame (I am aware that the height of the bottom bracket above the ground also influences this)

Given that my old frame fitted me and was comfortable the total top tube length plus handlebar stem length should be approximately the same length. I accept that the angle of the seat tube may marginally affect this.

I am confused as I seem to have ended up with a racing frame with a wheelbase 5cm longer than my old Audax frame and a top tube considerably longer than my existing frame which means I will be stretching to reach the bars.

Old frame (54 + 10.5) = 64.5cm
New frame (61 + 12) = 73cm

The frame builder used my existing frame as the basis of sizing my new frame but looking at the above it appears miles out.

I have spoken to him today to express my concern and have suggested that he compares the two and explains. So far he has made noises about me being a big bloke (true I am 6-4) but I don't see these being of any relevance as my old frame was the template (no measurements were taken of me during the pre order consultation).

I am endeavouring to keep matters polite but having spent the best part of £800 ( and waited 5 months for a job that was estimated to be 6 to 8 weeks my patience is running extremely thin.

Would anyone care to comment as to my observations as regards wheelbase and top tube length above and advise me if I am missing the point or am otherwise misinformed. Alternatively would you confirm that my observations raise cause for concern.

Cheers

Alan

[531colin]

I think that in these days of BikeCad etc. any builder should provide his client with a proper frame drawing with dimensions. The customer approves the drawing, which is then the basis of the legally binding contract between builder and customer. If the frame is built to the drawing, thats it, the job is right.
The time to decide the spec. is at the drawing stage, not the built frame stage.

Unfortunately in this case there is very little information to decide what actually was the arrangement between builder and customer.
"based on my existing frame" and "no mudguards and slightly tighter handling" in a verbal discussion is not much to go on.

For the technical matters, is the extra wheelbase in the seatstays or the front centres? Wheelbase itself is not a measurement I attach much significance to (Heresy!!)
The new frame probably has steeper head angle and less fork offset than was normal 25 years ago**.....this will give brighter handling, but also a longer top tube if front centres and seat tube angle are kept the same, but its difficult to see where a longer stem would figure in this scenario.

**Edit...now we have a photo, this doesn't seem to be a major factor

[Farrina]

Forgive my ignorance but what are "front centres" ?

Regards

Alan

[Brucey]

I don't wish to get overly involved in what might well turn out to be a contentious discussion, but 54 cm is an unfeasibly short top tube for a 64.5cm sized frameset, almost regardless of the seat angle. 61 cm might be ridiculously long or 'about right' , or something else again for you depending on what the seat angle is and how well your old frame really fitted you. Each degree of seat tube angle difference makes about 1" difference to top tube length using the same riding position.

The wheelbase is a bit of a red herring; it is subordinate to steering geometry, and there are various combinations of head angle and trail which give comparable handling at somewhat different wheelbases.

People go to framebuilders for several reasons, including;

1) the customer knows exactly what they want and just need the framebuilder to build it
2) the input of the framebuilder regarding frame fit and geometry is valued.

If there is any misunderstanding regarding which applies, disappointment for someone is the inevitable net end result. Whenever I have had frames built, I've agreed a dwg with the builder, including realistic tolerances, and we've each had a copy. That way there are no stupid arguments once it is built; it is either to the dwg or it isn't.

I find it hard to believe that a 54cm top tube is a sensible length for such a large frame; I ride a frame that is almost 10cm smaller than that and most of them have longer top tubes than that.

I'd suggest that you have two main points to address;

a) is the frame as agreed, and was the nature of this documented?
b) does the frame fit you or not?

Re b), I'd go to another builder and get them to recommend a riding position for you, starting from scratch. You might find you are folded up like a cardboard box with your old position, it is all wrong, and what you really need is the new frame.

Or not.

hth

cheers

[Farrina]

I seem to be causing confusion by talking about a top tube length of 54 cm .... I did say in my original post that my measurement as to this might not be correct but as I was using the same methodology it should not matter as I was comparing like with like.

However it is quite apparent that this is causing problems so if some kind soul would care to enlighten me as to where to measure it from I shall get my tape out and re-measure the fames.

Cheers

Alan

[Brucey]

for a horizontal top tube, centre to centre is the traditonal measurment. But without seat angle and bike fit information who is to say what is 'right'?

cheers

[Farrina]

So from centre of where seat pillar resides to centre point of fork column ?

.... Accepting this will be a rough measure but possibly more accurate than my original.

[Brucey]

yep that is it...

cheers

[531colin]

So from centre of where seat pillar resides to centre point of fork column ?....

Yes, thats it ..... measured at the centre of the top tube, so its centre to centre.....where a line in the middle of each tube would cross..

Front centres is BB axle to front wheel axle.....again, centre to centre.

[Erudin]

Why not build it up? At least put wheels, stem and bars, seat and seatpost on it, then you will be able to access whether you can get a similar fit with your other bike more easily. If you can not then take it back to the frame builder and give him a chance to rectify any issues.

See also: http://www.rivbike.com/v/vspfiles/assets/images/ttr_excerpt.pdf

"The Top Tube Ruse (sort of): The relative unimportance of top tube length on what you really care about, which is how far you have to lean & stretch & reach to grab the handlebars"

[Farrina]

Updated figures for top tube length - now properly measured as per advice kindly given

Old frame = 58cm
New frame = 65cm

So new frame my "stretch" to bars would appear to be 65 + 12 = 77cm as against 58 + 10.5 = 68.5 cm (second figure stem length)

Regards

Alan

[stewartpratt]

My personal opinion, which should hopefully count for little:

65cm is HUGE, at least unless you have a very, very slack seat angle. I'm a whisker taller than you and my top tubes are 60-60.5cm (with 12cm stems, albeit with a lot of saddle layback). It's rare to see a top tube over 60cm; I don't think I've ever seen one over 61cm. 65 is way off the norm.

I don't know what conversations you had or how your limbs and body are proportioned or how accurate your measurements are, but if you've genuinely ended up with a 65cm top tube with no mention of anything being out of the ordinary then... wow. It might work if the bike is designed to be used with the saddle well forward, eg mid-rail on an inline post, but if so I'd have personally expected that to have been part of the design discussions.

[reohn2]

My personal opinion, which should hopefully count for little:

65cm is HUGE, at least unless you have a very, very slack seat angle. I'm a whisker taller than you and my top tubes are 60-60.5cm (with 12cm stems, albeit with a lot of saddle layback). It's rare to see a top tube over 60cm; I don't think I've ever seen one over 61cm. 65 is way off the norm.

I don't know what conversations you had or how your limbs and body are proportioned or how accurate your measurements are, but if you've genuinely ended up with a 65cm top tube with no mention of anything being out of the ordinary then... wow. It might work if the bike is designed to be used with the saddle well forward, eg mid-rail on an inline post, but if so I'd have personally expected that to have been part of the design discussions.

IMHO that opinion counts for a lot from someone who is taller than the OP.
65cm T/tube is definately huge by anyones assessment,to ride such a frame with a 12cm stem is getting into Boardman/O'Bree superman riding position!

Farrina
Could you confirm that both frames are horizontal top tube construction.

[Farrina]

Yes both are what might be considered as traditional lugged frames with horizontal top tubes.

First one was built by Raleigh's specialist lightweight division circa 1986 (Gerald O'Donovan at SBDU - more here http://www.classiclightweights.co.uk/builders/raleigh-sbdu-builders.html) I have been happily and comfortably riding this frame since then.

The brief for my new frame (my old frame being used as a template) was for it to have slightly sharper handling and that I did not require any mudguards so (presumably) rear triangle would be built such that wheel would be closer to seat tube.

My frame builder suggested longer stem (increased from 10.5 to 12cm) as he thought frame did not look proportioned and I went along with his suggestion, obviously expecting given his expertise, that he would make necessary adjustment to the sizing. There was never any suggestion from me that my existing frame was uncomforable in any way. Indeed all measurements where taken from old frame and nothing from me! In my ignorance I expected a similar frame with possibly a slightly shorter fork rake and marginally shorter wheelbase.

What I seem to have ended up with is a frame with a longer wheelbase (104cm v 99cm) and a massively longer top tube. I can only assume that my builder has "boobed" in recording the measurements - he did offer the comment that he had to extend his jig to build it and it was the biggest frame he had built. With hindsight this should be flagged (to him) that possibly something was not right.

I intend to take it back to him with my old frame to discuss later in the week .....

Regards

Alan

[stewartpratt]

Again I don't presume to know the accuracy of your measurements or the details of the conversations you had prior to build (eg "racier handling" would likely be interpreted very differently to "a racier position"), but to take a frame that is known to be a good fit and to add 7cm to the top tube is, to put it mildly, an extreme change (assuming there hasn't been a similar change to the seat angle; the fact that the new frame is 7cm at the top but only 5cm longer at the bottom says the angles probably differ somehwere). To add 7cm and also propose an extra 1.5cm on the stem is... well, from experience I find an extra 1.5cm on the stem to be a significant difference in positioning in its own right.

Again, just my opinion as another punter, albeit a slightly geometry-obsessive one. But my (limited) experience of custom framebuilders is that not all are custom frame designers.