FRAME STIFFNESS

[landsurfer]

Technology reaches a finite point in all applications, all " new" stuff is just embellishment of the original. Steel frames topped out in the 80's. 74/73 angles are still the norm even in carbon frames. Stiffness is a concept i think ... what is stiff to you is soft and flexible to me .... I'm 6 ft 3 and 110 kg , you may be 6ft 3 and 80 kg we both fit roughly the same frame but the dynamics are massively different ... to me the frame is complaint to you it is stiff ... same frame !!! ...... discuss ...

[531colin]

Nice looking bike Colin. Will the front fork be capable of taking a low rider rack?

The carbon fork won't but we are working on a steel fork for people who want front panniers or more than 300mm of steerer.

[531colin]

Thanks for that. It looks good, Ti always does and for ease of keeping clean and not fretting about stone chips or corrosion it's great. To some extent theres an answer to my question in that you have disc tourer and disc audax style bikes in steel as possible products too. You'll have to try and make the disc audax have clearance for 32mm tyres plus guards, then we can use reohn2's world renown vittoria voyager hypers . The Spa Audax I have may just fit gp4000s2's in 28mm with guards but I suspect I may have to file the slots in the guards to get 5mm closer to brake. But that's a future test, manufacturers quoted sizes are quite variable. To accomodate 32mm tyres with guards opens up interesting options without going into CX/touring style tyres.

The spa Audax is a nice-riding bike, but I don't want one because to me its just too limiting to have to choose between sensible size tyres and sensible mudguard clearance. Most people are so fixated on STI levers they won't buy anything else, so the bike has dual pivot sidepulls and the associated clearance issues.
Most people wont buy anything called a "tourer" which avoids the clearance issues. I think thats an image problem.
Disc brakes free you from the clearance issues, and all the disc bikes will have more clearance than the rim braked audax bike....it remains to be seen if that too causes an image problem.

[531colin]

Technology reaches a finite point in all applications, all " new" stuff is just embellishment of the original. Steel frames topped out in the 80's. 74/73 angles are still the norm even in carbon frames. Stiffness is a concept i think ... what is stiff to you is soft and flexible to me .... I'm 6 ft 3 and 110 kg , you may be 6ft 3 and 80 kg we both fit roughly the same frame but the dynamics are massively different ... to me the frame is complaint to you it is stiff ... same frame !!! ...... discuss ...

There is an old joke about an elderly man who works in his garden on a winter's day without wearing his scarf, and complains of a stiff neck. Next day his wife sends him out in the garden with no trousers on.
Frame stiffness is a bit like that, you want the frame stiff where it gives you pleasure, but you don't want it stiff where stiffness is uncomfortable.

[Brucey]

Technology reaches a finite point in all applications, all " new" stuff is just embellishment of the original. Steel frames topped out in the 80's.

well, kind of. In terms of 'frames that I like to ride, unladen,' I'd agree. But in terms of 'serving all shapes and sizes', not really. I think that there are many more good choices in steel frames that are suitable for loading up than there were back then. The other thing is that steel technology continues to develop; soon we may have frames made of superbainitic steel (or something) and that could be a game-changer.

Stiffness is a concept i think ... what is stiff to you is soft and flexible to me .... I'm 6 ft 3 and 110 kg , you may be 6ft 3 and 80 kg we both fit roughly the same frame but the dynamics are massively different ... to me the frame is complaint to you it is stiff ... same frame !!! ...

sure; frames need to be made stiff/strong enough in relation to the rider weight. The other thing is the effect of frame/rider size. In certain respects a frame 3" smaller (for a smaller rider) is likely to be about twice as stiff as the larger one. Thus if you are both tall and heavy, it is a double-whammy. Ideally frames for any given purpose would be built very differently in different sizes to allow for this, but that still leaves people whose weight doesn't scale to their height who are badly served.

Many OTP bikes are just built for the heaviest load/rider of that height, and these framesets are often a lot stiffer than you might otherwise choose. Years ago, the biggest guys looking for a 'road bike' would be steered towards a touring frameset or a custom build, because OTP road bikes in large sizes tended to be super-whippy. These days there are more OTP choices for these guys but this is usually at the expense of those who are lighter-built.

cheers

[iow]

The Spa Audax I have may just fit gp4000s2's in 28mm with guards but I suspect I may have to file the slots in the guards to get 5mm closer to brake.

great frame - i'd be interested to hear how you get on - I tried it on mine without filing the mudguards but it was too close for comfort. on 24mm external width rims my 28c 4000sii's measure 28mm high x 31mm wide. the brake arms (tektro r539) were the limiting factor as they sit lower than the bridge/crown. narrower rims would help as the arms move higher with travel, but butting the mudguard hard up against the brakes doesn't allow enough room for the quick release to function...
for the time being i've reversed the rear brake so that it sits in front of the seat stays and am running with 'half' length mudguards which stop at the bridge / crown.
maybe different brakes would help. also not sure of the build tolerance on the spa frames and forks, but both the front and rear brake blocks on mine only sit half way down the adjustment slots so there is quite a bit of wasted potential clearance.

[old_windbag]

and all the disc bikes will have more clearance than the rim braked audax bike....it remains to be seen if that too causes an image problem.

Hopefully they'll look fine and not "gappy" or ungainly. I have a Dawes super galaxy that sits in retirement with rust on the bb and cable ends. It'd be quite low cost to renovate that frame and have a large tyre clearance bike...... but it's just a little bit of a "bus" to ride. Something lighter and more flexible tyre-wise would be good and with the benefits of discs. The Spa Audax is a nice frameset and it let me use up parts that were sitting idle and have an all weather road bike. I'm thinking of the bike to replace my Kona Jake as the on-road, off-road( well gravelly sustrans/ bridleway ), tourer. Jack of all trades master of hopefully some .

the brake arms (tektro r539)

I've just checked my tektro's... they are the same, I thought I had R737's but I believe they are dimensionally the same anyway. So from your experience it looks as though I may be limited to the conti in 25mm . It's too much of a ball-ache having to fiddle with brackets to make things fit if it's all in vain. Perhaps best to simply cut losses and accept it's limits. My rims are 15c and my vredesteins( 28c ) measuring around 27mm( rim to tyre edge ) have a good 10-15mm clearance at the guard ends but probably 10mm under the brake. This seems to be a pinch point in robbing of space. Ho-Hum. The vittoria graphene range are one alternative to gp's that may fit at 28mm and offer similar performance( particularly Corsa but bit pricey at present ), plus schwalbe one v-guard( but think some said poor in the wet ).

[fastpedaller]

Nice looking bike Colin. Will the front fork be capable of taking a low rider rack?

The carbon fork won't but we are working on a steel fork for people who want front panniers or more than 300mm of steerer.

That's good to know..... it's nice to have a choice as a customer, and hopefully it gets more sales for the shop. Having only carbon forks would have ruled it out for me (and maybe many others?)
Talking of choice, I asked PlanetX about the Kaffenback frame (which has good following and reviews), - it is now only available for disc brakes. I suggested they could re-introduce the mk1 as "Kaffenback Classic", as the costs of doing this would be minimal (ie already done before, all drawings etc available) and may get them more sales, but of course my idea fell on deaf ears

[Samuel D]

In fairness to Planet X, I think sales of non-disc-brake frames are falling off a cliff.

Given what Colin has said about the trend to tapered steerers with 1-1/2" bearings at the bottom, I also wonder what will happen to the availability of conventional 1-1/8" threadless headsets and forks. The ancient 1" threaded system may yet outlive them all!

[fastpedaller]

In fairness to Planet X, I think sales of non-disc-brake frames are falling off a cliff.

If they only supply frames that use disc brakes then it is inevitable!

[531colin]

I'm having another go at this.
Brucey says that when just pedaling normally, seated, all the reaction is at the saddle. I can see that to keep the bike upright needs either balance or steering input to counteract the changing weight distribution between left and right pedals; so some riders steer a wavy course, others (presumably) adjust their weight on the saddle. I can also see that when you start working harder it gets more complicated because you are pulling on the bars.
Riding along, I can watch the bottom bracket sway from side to side under the top tube. When I push down on the right pedal, I can see the bottom bracket move left, and it moves right when I push on the left pedal. This is because the pedal is to one side of the midline of the frame, and pushing the pedal down gives a sideways force on the bracket. I take that to be self-evident, and not controversial.
If there is a sideways force on the bracket, for the life of me I cannot see how the chainstays can do anything other than transmit that to the back wheel.
If a frame is stiff, then the rider's input pressing the pedals is directly turned into forward motion. (Jan Heine's theories about "planing" and anything involving recouping the energy put into flexing the frame seem speculative to me.)
There is more to it than that. Brucey somewhere mentions "resilience" as being a better concept than "stiffness", and I had one bike that was rather too stiff when it was crashing through the potholes, and yet at the same time it was totally unrewarding to ride, try as I might, it was just slow to accelerate.
On one occasion, some numpty built some steel audax prototypes with oversize top and down tubes, so I had the opportunity to ride these back to back with correctly-built steel and titanium audax bikes......same carbon forks, same wheels, same tyres, same pressures. The titanium bikes are a shade more comfortable than the steel ones. The bikes with the oversize tubes were very unpleasant to ride on 25mm tyres over stuff like granite chip road surface, there was an awful lot of vibration which I felt mainly through my feet. I never found a smooth enough bit of road to tempt me to investigate whether or not they were any quicker.
I'm not of the opinion that any and every degree of stiffness is good, however I think that it would be difficult to make chainstays that were "too stiff" laterally because there is only so much room between the tyre and the chainwheel. I think there are opportunities to maximise the stiffness of some of the tubes in particular places by ovalising the tubes instead of increasing the diameter, oval tubes are stiffer in one plane and more flexible in another. Ovalising the downtube where it joins the bracket will make it stiffer laterally. Similarly ovalising the top tube at the head tube might reduce shimmy. Vertical ovalising of the downtube strikes me as counterproductive, except for big downtubes which otherwise wouldn't join standard head tubes.

[Brucey]

I'm having another go at this.
Brucey says that when just pedaling normally, seated, all the reaction is at the saddle. I can see that to keep the bike upright needs either balance or steering input to counteract the changing weight distribution between left and right pedals; so some riders steer a wavy course, others (presumably) adjust their weight on the saddle. I can also see that when you start working harder it gets more complicated because you are pulling on the bars.
Riding along, I can watch the bottom bracket sway from side to side under the top tube.....
If there is a sideways force on the bracket, for the life of me I cannot see how the chainstays can do anything other than transmit that to the back wheel....

Well there is something I didn't mention before which is that the action of accelerating your left leg up and your right leg down does produce a small torque on the bike, even if you are just pedalling backwards. This is normally dealt with by some combination of the bike weaving and the upper body swaying slightly. Either or both can make the BB appear to move around under the top tube, in addition to any real movement there might be.

I don't think the loading and forces from 'normal pedalling' are much different from that which occurs when you are stationary with the brakes on (but not working the handlbars. Provided you are balanced on the bike, the chainstays are not heavily loaded in bending when you just apply normal pressure on one pedal, but the seat tube is!

Regarding where the forces go; imagine instead of a rider with legs, there were a couple of hydraulic pistons attached to the pedals that are anchored at the saddle. Extending or loading one piston does not load the chainstays; forces of that type (i.e. ones that are not inertial in nature) are always reacted somewhere; they cannot exist in isolation. If something on the bike is generating that force, it is also reacted on the bike as well. In this case the BB shell tilts and this twists the chainstays slightly, but they are not stiff in this plane; most of the loading and flex is in the seat tube.

You do get large lateral loads in the chainstays when riding out of the saddle, leaning the bike, working the handlebars, pedalling badly etc and then you can benefit from stiff chainstays. But when pedalling normally (still in the saddle, little load through the handlebars) the chainstays don't do that much. 'Normal pedalling' usually means loads in the low tens of kg for most folk.

BTW if the seat tube bends at all, you may see movement between the top tube and the BB. But this doesn't mean there is a large lateral load in the chainstays; it is just as (if not more) likely that the seat stays and seat cluster will deflect sideways w.r.t. the rest of the bike/rider.

cheers

[531colin]

I'm sure you are right, but I still have a bike where all I have done is ovalise the downtube horizontally and avoid flattening the chainstays, and it accelerates like stink.
I can only assume that I'm "working the 'bars" at a relatively low power output.....the bike is quick when I do ordinary things like "single out" to let a car go past.
My days of "sprinting out of the saddle" are gone....

[Brucey]

..I can only assume that I'm "working the 'bars" at a relatively low power output.....

That would be my best guess, but it is not as much better than 'just a guess' as I'd like; the reality of what is going on is probably a lot more subtle than anyone thinks.

I suspect that the stiffness is 'best' when it matches the pedalling effort of the rider in the most beneficial way, for the greatest part of the time. It becomes chicken and egg-ish because habituation quickly comes into play, but some analogies are;

- bouncing on a trampoline; a good trampolinist can expend a minimum of effort, timed just right, to either bounce high or stop bouncing at all. Exactly how they do that will probably vary from one trampoline to another.

- what happens when you (say) stamp on solid ground; you can expend the same amount of energy as the trampolinist uses, or that is enough to (say) kick a football fifty yards, or propel a bike forwards at some speed, but all that happens is that your efforts are turned into heat and noise. Something similar may more easily happen on 'frames that are too stiff' or 'frames that are not efficient springs' .

When I'm tuckered out (and too tired to think straight properly without what seems like a terrible effort) I've occasionally just caught myself 'pedalling badly' by which I mean that my pedal stroke is just less well timed than normal. If I can more easily feel when this is happening, or perhaps have a frame that makes the result of such slightly mistimed efforts less inefficient (less like stamping on solid ground, and more like trampolining...?) then that may be a good thing.

I have a feeling that I've most often caught myself 'pedalling badly' when MTBing, which usually means a stiff (overly stiff) frame and often the added complication of suspension, too. Pedalling correctly to get the best out of suspension is more difficult than many other sorts of pedalling, I'd have said.

BTW many folk who tap along at ~150W would downplay their 'sprinting power' but most happily manage 500W or more for a few seconds at least (which is not much different from (say) the amount of effort required to go up a short flight of steps more briskly than normal). Very few riders normally produce this amount of power on the bike without working the bars somewhat, I'd have said.

cheers

[samsbike]

What I am curious about is how the forks with discs and fat tires compare to the steel forks on your own bikes are? I am still curious to the perceived/ real difference in comfort. If this is a derailment I will start another thread.