The importance of frame compliance over rigidity

[james-o]

Interesting read. My take on it is that frame flex is mainly felt as twist in the front triangle so a bike with larger tyres can still benefit from that 'steel feel'. How much flex is the big Q - it varies by frame size and rider strength, loaded or unloaded etc so I think 'stiffer is better' has come about because an absolute is easier for mass produced bikes than an optimum for each rider. Too much twist / lack of lateral stiffness and the frame can shimmy and I'm not a fan of bikes that are built that light or flexible.
I think a (non-road race) bike benefits from some twist in the main frame, it's subjective though and my lugged trad OS sized 631 frame that rides beautifully also isn't as reassuring on a fast descent as my larger-tubed Genesis Equilibrium. In a perfect world I'd have tubesets matched to use, tyre size and whether it's a 1-5hr or 3-12+hr sort of bike. ISO tests now make it harder to go as light-tubed as I'd like to see on some bikes.

Fairlight's approach is interesting. They have the now almost standard tapered carbon forks (or 1 1/8" steel fork) with accompanying oversized headtube and an oversize downtube, but the top tubes are 1" Reynolds 631 and 853, which are ovalised for their entire length. (So the 853 tubes have to be ovalised in the UK, heat treated by Reynolds, and then shipped to the contract manufacturer in Taiwan, rather than just being drawn down from whatever general stock of tubing Reynolds and/or the manufacturer have in Taiwan.)

More interestingly perhaps, the use of 'flat' oval tubing in a frame for stiffness and flex optimisation reasons was patented in 1939 iirc (edit, no, it was 1928) by Frederick William Evans, FW Evans the builder and then bike shop, eventually Evans Cycles ltd.
I worked at Evans in 2012 when we made a couple of frames using ovalised to spec 853 and 631 tubes based on his ideas, just out of interest really, we were interested in the FW Evans patent. The bikes rode well. Cotic were also using oval Reynolds top tubes at the time.



https://kitesurfbikerambling.wordpress. ... -fw-evans/

^ fully ovalised top and down tube FW Evans project bike. Made by an ex-RSP framebuilder at Pashley.

[Barrowman]

Reynolds used to do a plethora of different tubes, and I am sure they did a 'Designer Select' Range where framebuilder could have something they wanted ( from the range) rather than a set of 531, 531c , 531pro, 531 Special Touring, 531 Speed Stream, 753,653 (all this from memory think I have most if them)
And some framebuilders had interesting ideas about mixing tubesets . Plus those 'pushing the envelope' such as :
Bates Cantiflex ( specially drawn 531 with a bulge in the centre section. And diadrant fork)
Hetchins with Curly Seat and Chainstay
Paris Galibier : Oversize 'down tube' that goes nowhere near the bracket and effectively a 'floating' bracket
Hetchins Hellenic ( I know a lot more builders did an Hellenic design) Seatstay overlaps the seat tube and junctions with the top tube.
Joe Cook Imperial Petrel Super Rigid : Curved tube let in behind the head between top tube and down tube.
And curved tube between seatstays and chainstay at the bottom of the seatstays.
Flying Gate . 2 sets of seatstays , seat tube not much longer than seatpin in the usual place then the rest of the seat tube vertical to the top tube ( where it meets the second set if seatstays)
Thanet Silverlight. Marginally undersize tubes, silver soldered not Brazed, bottom bracket cradled above the tubes (rather than the tubes entering the bracket)
Saxon twin tube : 2 seat tubes that allow the back wheel to overlap the seat tube by fitting between them.

And there are other tubing makers too, Vitus, Columbus etc etc .
And fork shape ( of the tubes and the 'bend' ) Ther are just so many variables.
If you are struggling to visualise these have a look at Classic Lightweights think most are represented there.
You probably need something to do now the Olympics are over

[james-o]

A frame with actual, visible vertical compliance / spring -

[Orbit531C]

A frame with actual, visible vertical compliance / spring -

And an example of steel forks flexing visibly vertically:

"We designed a simple test to measure the flex of fork blades. By combining a small bag-support rack with the hoop of a low-rider, we could easily visualize (and measure) the flex of the lower fork blades: The two racks will move against each other only if the fork flexes between their attachments – in the lower 2/3 of the legs. (If the flex occurs higher on the fork, both racks will move in unison.)

The video (link below) shows this test on my ‘Mule’ with its flexible Kaisei ‘TOEI Special’ blades. As the camera zooms in, you can see how much the fork blades actually flex. That is what takes the edge off bumps that are too large for the tires to absorb."


https://www.renehersecycles.com/myth-9- ... dont-flex/

In comments he replies to the person who says it only shows that the tire [sic] is flexing:
"You are right, the tire flexes, too. That is where most of the shock absorption comes from. But on larger bumps, the fork blades flex as well. The two racks wouldn't move against each other if just the tire flexed. They clearly show that there is significant movement in the lower 2/3 of the fork blades."

[peetee]

Reynolds used to do a plethora of different tubes, and I am sure they did a 'Designer Select' Range where framebuilder could have something they wanted ( from the range) rather than a set of 531, 531c , 531pro, 531 Special Touring, 531 Speed Stream, 753,653 (all this from memory think I have most if them)

Yes, they did offer 531 Designer Select. I took advantage of this in 1989 to design my MTB which I still ride and enjoy.
It was also known that certain bespoke builders would mix and match tubes from different tubesets.

[joshua3]

To answer your question; ''What ‘gems’, simple steel frames that ride with comfort, do members have or have had?''

For me it is an FW Evans touring bike with a 531c frame and 531 fork. Even with the 25mm gatorskins at 90psi it absorbs the poor surfaces of the fenland back roads where i live.

Just a question, why did they select 531c for a touring frame? I thought it was 'competition' for road bikes? In any case it is very light and comfortable.

Regards

James.

[531colin]

To answer your question; ''What ‘gems’, simple steel frames that ride with comfort, do members have or have had?''

For me it is an FW Evans touring bike with a 531c frame and 531 fork. Even with the 25mm gatorskins at 90psi it absorbs the poor surfaces of the fenland back roads where i live.

Just a question, why did they select 531c for a touring frame? I thought it was 'competition' for road bikes? In any case it is very light and comfortable.

Regards

James.

I think you answered your own question.......they chose 531c because it makes a light, comfortable bike.
It might be a bit less suitable for 4 pannier touring.

[531colin]

You have to love Rene Herse and his theories........LOOK the forks flex! (when somebody puts their whole weight on the bars)

In the short bit of video before he zooms in on the movement between the 2 racks, you can see the handlebars flex, the tyre bulge, and the straight bit of the forks flex forward......but theres a point to prove here......

[531colin]

A frame with actual, visible vertical compliance / spring -

Heres an earlier one with a claimed 5 inches travel.....I wonder how it tracked?
https://theradavist.com/1998-ibis-bow-ti-mtb/

[Brucey]

...... an FW Evans touring bike with a 531c frame and 531 fork.....

Prior to '531c' it was known as '531DB' and actually the earlier tubeset is higher quality. In 531c they used a cheaper seam-welded steerer tube, instead of the draw/seamless tube used in older tubesets. IME small/medium frames in these tubesets make excellent touring bikes, but are a little heavy for racing. For many years my 'go to' touring bike was built using 531 DB.

FWIW your bike is clearly designed for cantis, not V's. If you must use v's, STX ones will probably fit better.

In standard tube sizes, for good comfort in a steel frame, the lighter the better.

[joshua3]

I agree about the V's, I have a set of NOS retro Shimano cantilever brakes off of Ebay ready to go on.

Can I ask will my 531 fork also have a welded steerer tube? Should I be worried?!

Thanks.

[Barrowman]

Wasn't 531 Double butted the only tubeset available for a few years ?

[Carlton green]

..................
My daily ride is built from 18-23 which I had thought was likely not of any worthwhile quality. However research elsewhere says it’s perfectly fine (fit for purpose) and your post suggests to me that that should be the case too (if designed and built well). It glides along and seems to get me up the hills too … the fitter I get the better it climbs.

"18-23" is a Raleigh trade mark for tube; theres a (2007) post here from CJ viewtopic.php?p=30668&hilit=18+23#p30668 saying what it is and how its made; but to me more importantly CJ also says all varieties of steel have the same density and the same Young's modulus (stiffness); where fancy steels differ is in their strength, so you can have less of the fancy steels, this usually means thinner walled tube. The backside of this is that some frames made of cheap oversize tube (which is also relatively thick-walled) are really stiff; good for powerful riders' flat-out efforts, or a camping load; less good for light riders all-day comfort on an unloaded bike.

For several days I’ve been mulling this general concept of common material qualities over. Density and Young’s modulus (a ratio of stress to strain) is similar between steels but, importantly, the yield and ultimate tensile strengths differ and by a large percentage. I did find some data charts but can’t re-find them. Depending upon the loads on the frame the higher (material) strength (sustainable load per unit area) might or might not matter. However as loading has both static and dynamic (eg. variable shock loading) components the frame has to be built to sustain what the tube material (stress level) can manage without exceeding its yield stress.

Within the elastic range Young’s modulus is also a measure of springiness so if you double the thickness of a weaker tube to cope with its lower yield strength then you halve its springiness making it stiffer. Of course, if the loads are well known and stress levels are within the material’s yield strength then (with good design) the weaker material is fine - a point which the voiced practical experience of others confirms. Where that all leads us I’m not so sure, well other than analytic design is important and that using higher grade material leaves more scope for design error, extreme use and building in desired flexibility.

https://en.wikipedia.org/wiki/Young%27s ... 20material.

As a topic I’ve been glad that only frames have been considered in the compliance of the bike to the surface over which it’s ridden. However, whether necessary (for a decent ride) or not, the wheels and tyres must play a part in that compliance too. Over the years I’ve shifted away from (relatively) shallow section 27” tyres to 700c’s and gone from 1&1/4” wide (that might inflate to around 32mm) to 35mm wide; ride quality has definitely improved with those changes. Spokes have remained plain gauge and the wheels ungiving. Now, in terms of the bike’s overall conformity, I wonder whether - and specifically so with lower volume tyres - using butted spokes (for their greater springiness) might be significant. ‘Probably’ is the answer that comes to my mind along with: could I build better wheels and what relatively low volume tyres do you still use (so historically that might have helped me but for me now there’s little to no actual worthwhile gain). H’mm, so one might say that spring built into the (bare) wheel reduces the need for spring in the frame and spring in the tyre.

Whatever that topic (wheel build for conformity) is a diversion, it’s whole new can of worms that likely deserves a thread of its own and is probably only important where low / lower volume tyres are used.

[531colin]

Brandt, writing in the eighties, got 0.15mm movement in a wheel rim in response to an axle load of 50 kg., so there’s nothing to be gained there. Modern wheel rims are likely to be stiffer than Brandt’s rims.

The main gain from expensive steels seems to be that you can make a big diameter tube with thin walls which is very stiff but light; downside is they dent easily

[Carlton green]

Brandt, writing in the eighties, got 0.15mm movement in a wheel rim in response to an axle load of 50 kg., so there’s nothing to be gained there. Modern wheel rims are likely to be stiffer than Brandt’s rims.

The main gain from expensive steels seems to be that you can make a big diameter tube with thin walls which is very stiff but light; downside is they dent easily

Thanks. When I place my mass on my bike there’s a lot more movement (in the tyre) than 0.15 mm - too many pies.

To my mind making things ever lighter almost always has some undesirable drawbacks too. Similarly making everything as stiff as possible seems daft to me, a bit of spring - and sometimes a bit of give too - is almost always helpful.