Thorn Cycles Forum
Community => Non-Thorn Related => Topic started by: JWestland on January 28, 2013, 03:33:00 pm
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http://janheine.wordpress.com/2011/02/27/a-journey-of-discovery-part-5-frame-stiffness/
Another bone of contention on cycling forums...does one feel the material? Does it matter? Etc.
I can only say a frame with 0,0 flex feels "dead" and a frame with mad flex (never happened to me...) probably gives more excitement than one wants!
The XTC definitely "moves" a bit unladen with the long stays and stiff but slender frame it's very, very subtle but compared to my mixte steel fixie (which is very stiff as...mixte. Also, cheaper tubing so probably thicker) I do feel it a little on very rough roads or going Full Mash.
Goldielocks problem I guess, heavy rider = need less flex, heavy load = need less flex, but a little flex adds to the feedback (frame tells you on what road is like, preloads under flex, takes out worst of roads) and comfort.
This may explain why one forum member here said the XTC flexed too much for him but his missus loved it: Weight/power differences made it too flexy for him, but just perfect for her :)
(and if it's a 490S I want it lol)
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I wonder if cadence figures into the equation. Certainly for a given power a higher cadence implies lower torque and that must produce less flex. But I am thinking that the frame plus rider system could well have some kind of side-to-side oscillation resonance at a frequency not too far off a cycling cadence, so if you are spinning near that frequency you will lose a significant amount of energy, while either higher or lower cadence will avoid the coupling and the loss.
I, on the other hand, find myself at low cadence *and* low torque, so these problems just don't happen to me!
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I've a terrible habit of gearing up instead of spinning up...
52/18-16 on the winter tires, 56/16-14 on the summer tires on the XTC.
They mentioned cadence in another article if I read their blog post right...stating that if a certain cadence + flex is optimal the rider can feel less fatigued. But unfortunately cogs and a lot of other stuff also factor this aside from frame.
Hence maybe the "magic" when a bike is just right.
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I would say the control of flex on a bike is the key ingredient to getting a bike which feels right. It is getting the right mix of comfort and efficiency and a lot of that does depend on the rider style / luggage if any and the types of road surface.
In a race bike I tried all manner of materials from steel to aluminium to carbon fibre and severel makes of each and always kept coming back to my 1983 Gazelle Champion Mondial made from 531c. The geometry and material and thickness of tubes was just right for me.
My Thorns are perfect for loaded use (and with the high volume tyres very comfortable) and are extremely rigid but I ride much differently now to how I used to and I think they feel best under high cadence / low torque (especialy when loaded)
Andy
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Ohhh, Jawine! You've stirred up a potential hornet's nest of theoretical discussion with this topic -- thank you! ;D
By coincidence, after a couple hours' sleep, I was re-reading this very article a few hours ago. For more information tangentially related to the topic, Google-search "What is a planing bike?"
Not that it affects any Thorns -- and especially not TiG-welded ones -- a dirty little secret of many production bikes in the 1980s and 1990s is the tubes would sometimes come through unmitered and two key joints (where the seat tube and downtubes entered the bottom bracket) often had really skimpy amounts of braze.
How do I know this, firsthand?
A friend of mine for 35 years owned a busy secondhand bike shop for 25 of those years. Knowing my interest in hobby-framebuilding, he culled all the damaged frames and set them aside for me to cut up, rebraze, repair, or rebuild into other creations; tens of frames numbering very close to a hundred over the years. Those I didn't want went to the local steel recycler's where he was paid by the pound (usually covered the fuel cost to haul them there in his pickup truck) A good part of my Dan-built full-sus Folder came from this source...Ishiwata seatstays, Tange Prestige chanistays, True Temper seat tube, Reynolds steering mast, and a pretty rare Phil Wood elliptical tandem keel tube set on edge for the main frame spar (new from another source, but accidentally cut too short for its intended use; I got it cheap). All the tubing past the HAZ (heat-affected zone) was good, provided it had not been crash-damaged (mostly head-on curb strikes and crashes into parked cars that wrinkled the undersides of the top- and downtubes) and good cheap fun with the torch (full tubesets are very not-cheap). I used to be very active on the early iBOB listserv shortly after it was founded by Piaw Naw (this in the days following the paper version of Grant Petersen's Bridgestone Owner's Bunch), and a few members graciously mailed me their cracked and crash-damaged frames so I/we could find out what made them tick internally that might account for some of their noted ride qualities.
Sadly, some of the more supple frames -- the ones that might be described in current online literature as "planing frames" -- came by that characteristic because they were barely glued together with braze and/or the tubes had unmitered or crudely mitered ends! I won't name names, but I could cite examples nearly equally from all major marques sold in America over two decades (Centurions and Miyatas were notable exceptions, as were early Nishikis; all the ones I examined were made with great care and extremely close miter-tolerances and had their full fill of brass). Occasionally there would be a tube-butting flaw resulting in a break at the end of a butt, though most of these surprisingly "bad" frames were held together only by the lugs or in some cases by the brazing pins used to locate the joint. Some tube ends weren't mitered at all, being cut-off straight. Others were only crudely mitered, still showing ragged ends in the cut-open lugs where aircraft tinner's snips had hacked crude half-circles that didn't even reach the head tube.
It was an education and a revelation all in one, especially for someone like myself who had always valued the functional artistry of nicely done lugwork. Some semi-custom (small-run production) bikes with high-zoot tubing and silver brazing were not immune from lug flaws either; in those cases, the problems were largely caused by failing to get the joints really clean before brazing. Being a lower-temperature process with different flux, silver-brazed joints just aren't as tolerant of grease and contamination as brass. silver doesn't fill gaps as well as brass, so if the tolerances were generous, the joint was weak. One joint had pulled loose in use, causing a shimmy that made the bike unridable. A number of brass-brazed bikes I cut up had cracked seat tubes, consistently about 1-2cm above the BB. Many would last forever under the lower stresses of spinners, while mashers could expect more problems caused by the cyclic loading of heavy pedaling. In each of the cases I saw, the seat tube had broken just above its lower butt due to inadequate brazing of the BB shell resulting in excess flex with every hard pedal; a classic fatigue failure secondary to poor brazing. The BB is a big heat sink, and it is hard to get the shell hot enough for brass to flow adequately without cooking the ends of the seat-and downtubes. Under the pressures of high-production, some just spent too little time in the autobraze fixtures or too little time under the brazer's hand torch before the next example came down the line.
One late American brand of overseas-sourced randonneur/porteur bikes suffered from tube-butting defects that caused cracks or had cracks that initiated secondary to an interference-fit of the fork crown-downtube. They were designed so the custom front racks bolted to threaded sockets atop the fork crown. When the front wheel turned, the allen bolts holding the racks dented the downtube right below the top butt; cracks followed about 18-24 months After. Oops. Owners oozed rhapsodic over their bikes' ride qualities...till the bikes literally fell apart.
After some teething problems, production TiG welding did solve a lot of these problems because it required good miters for each joint and there were no lugs to braze. So long as the weld beads were nicely lapped and not undercut, the joints generally held well (exception: right-rear dropout; Thorn's socketed, brazed dropouts plus some touring models' additional 'stay bracing neatly address this issue from the start). Hard to go too far wrong with fillet-brazing unless the tubes are cooked.
The lesson in all this is sometimes Bike Feel is/was not the result of obvious things like tube diameter or wall thickness, geometry or design, but came down to workmanship and the presence or absence of errors relate thereto. A bicycle is a complex system of factors and components that all work together -- or not. Pays to have a good designer and good workmanship first. Once that is established, there is a level playing field for comparison.
Oh! What a great topic for the propeller-beanied gear-heads among us...
Best,
Dan. (...who actually has a propeller beanie*)
*note the snazzy Aussie product labels shirt as well: Australasian Jam, Uncle Toby's Oats, Arnott's Biscuits, Billy Tea and good ol' Vegemite.
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Dan, LOL it the best way possible ;D
I think here when they see that hat they won't know what to make of it...and either crash into you or just give you a mile extra space ;D
The only other steel bike I had was a Raleigh roadster from 80s (when they went a bit...poo...) made out of gas pipe tubing. VERY heavy...it finally gave the ghost when the bottom bracket weld went. My brother noticed more and more pedaling effort going in and less and less being transferred. We all started laughing as he recounted how his slog up a hill got worse and worse every day *yes we got tiny hills in NL* until he noticed the bottom bracket was...moving. Not in a good way...
Me dad wasn't impressed. Must've been poorly done as many ghosts of ancient roadsters haunt Amsterdam, unaware bikes are supposed to be mortal ;)
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I'm not surprised Jawine's mixte feels stiffer than her diamond frame bike. It's probably the triangulations.
I also go with Jim and Jawine and AndyBG's idea of various cadence rates influencing the amount of flex/vibration in the bike, at least in a certain speed range.
My own opinion, gathered over a period of years riding a beautifully brazed French bike built with overly heavy tubes and/or on tyres too hard for it, then a couple of very stiff ali frames, and now a mixte (actually a cross frame that looks like a mixte, but the same triangulation plus some more) built in steel with properly proportioned tubes, is that what really matters in a competent bike (all of these were bikes in the upper price range that most cyclists would consider competent) is how the microvibrations are handled. My Kranich, which probably has 5000 pounds of twist resistance between the top of the steering tube and the rear frame ends (that's Rolls-Royce sedan quality stiffness) rides like a dream on Schwalbe balloon tyres. I haven't tried it but on the Marathon Plus I used before (a very good tyre for city commuters and bad roads) I think my hands would be tired after a couple hours, even if I picked roads without jarring potholes. On the Kranich with its Big Apples at 60kph I ride right through the pothole on a curve and the bike is not disturbed at all, and my hands just feel a ripple, enough for road feel, not enough to irritate. But, as I've said before, it isn't so much the big bangs that need fixing -- you get fatter tyres and run them softer, it's the small microvibrations all the time. I'll probably be shouted down for lack of scientific "proof", but I really think a steel bike is superior in this regard.
Andre Jute
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Back on the XTC again today, put the slicks back on as the ice is gone. For now.
So compared to the lighter/stiffer mixte it's not as fast a beast to get started. It's heavier, and supposedly a springier frame/longer stays slow down acceleration.
Couldn't resist a wee sprint at 52/11 and the frame is compliant at that torque too, no grumbles or vibrations.
However, even with the hard tires on it atm the XTC is much, much comfier than the fixie which is very stiff/fast accelerating but this comes at the price of feeling every f-ing pothole there is. We have a lot of f-ing potholes ;D
The only thing I found on XTC that requires wider tires is rollsplit roads. That lovely stuff can develops cracks and micro potholes EVERYWHERE The vibrations after an hour or so on hard tires are just too much for the frame. But I cycled on them on hard 1.3 sportcontacts, a 1.5 or 1.7 tyre running at lower pressure no doubt sorts that issue.
Crabon is supposed to be the best of both: Light AND deals with micro vibrations. But...crabon and communal cycle parking areas...I wouldn't. One good knock of another bike and you may be in for a nasty surprise.
Crabon touring bike anyone? ;D
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I have had a couple of carbon bikes and although fantsticly light I still prefer the feel of steel. I cannot knock the speed of these frames or the comfort but there is something "dead" about the feel of them. You dont quite have that "alive" feeling you get from a good steel frame.
The only time I would rate a carbon bike over anything else is on the track. In the real world and certainly for touring I think it would be utter madness.
I think a lot of it comes down to what you are used to riding. I rode steel for 20 years before trying anything else so am probably a bit set in my ways.
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Commuters in NL as steel (at least student bikes are) and generally have Gas Pipe Tubing. So I was glad to find out you can get light steel too ;)
Aluminium I find dead...my mum's Koga is Alu a fine bike but dead as a doornail.
Crabon I don't know, it doesn't suit my commuting, so never tried it. And don't get out in weekends due to other things to do.
Have a steel columbus 1978 italian Ciocc frame/forks waiting to be build my first road bike ;D
Wonder how that feels VS XTC which is also steel, but newer material (725/853 VS unknown columbus) and totally different geometry.
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Well the Ciocc (1978 Columbus SL) may be a tad "noodly": The front derailleur rubs on 52/16 but only when I push down hard due to having to accelerate/ride out of saddle.
Need to investigate if it's flex.
I am not using it for racing and the Belfast Roads are full of potholes/bits missing so I can't say I mind. The flex doesn't feel annoying to me if it's even there, I haven't noticed anything bar ultra comfort (also tx to tubulars) and I rather have something that doesn't beat me up than an ultra hard track frame.
Either way, don't put a 100 KG person on it! It's a 50x51 frame so it's only for short people anyway.
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Good points all, Jawine, and much is to be said for a frame that is comfortable! Before criteriums began to shape road-race bike design, comfort in the saddle was a priority in frame design.
As for your flex, I a key component in the mix for bikes of this era was often the BB spindle. If it is problematic, a switch to another model/brand can make a world of difference wrt the chain rubbing on the front mech cage.
Best,
Dan.
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I had a chat on Facebook with the guy that sold me the frame, he's had similar issues with his Campagnolo 11 speed setup. Apparently a noodly crank can cause it too.
Tx for tip :) BB is another common cause let's hope that's not it as I especially picked a titanium Super Record one!
Generation 2...first gen was hollow and as Titanium wasn't as strong those days one snapped during a pro-race. Which soured the marketing and the gen 2 one never really took off. Now titanium is part and parcel.
The XTC has clear flex in the stays (long stays) when you hammer down but it's stiff elsewhere. I really need to load it up, bring on a camping tour...
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jawine what tubs did you put on that beauti. i'm still hankering after the grand bios clinchers for my raleigh 753.can't make a comment on frame flex i always put preformance down to the pilot ::)
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It was a loose bottom bracket...phew.
I put on Continental Sprinter Gatorskins. So far no punctures even though Belfast is a public glassbin. Not the mega lightest tub at 300 grams a piece, but at least you don't have to walk home too often :P
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very good used to ride tubs all the time .
would any of your buddies happen to have a mavic exp 33 rear wheel 36 spoke blue rim only.
no harm asking i could get lucky ;D ;D
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Bar the mounting process as it's quite time consuming with waiting for glue and straightening the tubs on rim...they ride great actually. Very pleased. Cursing helps when pulling them on :P
Feeling blue Jags...? Sounds like an e-bay job to me...not easy to find blue rims.
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It was a loose bottom bracket...phew.
Whew, indeed!
So glad it was "only" this, Jawine. Now, you'll really be able to fly on that bike!
Best,
Dan.
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Except I picked up a p_nct_r_ in the front tire. Why ow why can people not put their glass in the bin, or take it home, instead of dump it all over the road!
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Except I picked up a p_nct_r_ in the front tire.
Oh! Unusual for it to be the front. Fate, Jawine. When it happens there, it is Destiny. Why ow why can people not put their glass in the bin, or take it home, instead of dump it all over the road!
Liege, BE is like that. I'm pretty well convinced they save on paving materials by recycling glass to do the job -- particularly down by the river. Worse if it rains. Like in science class, when we had to use razor blades to cut the gum surgical tubing to supply the Bunsen burners with gas. A person could saw away all day 'til the blade got dull, or! you could put a drop of water under the blade and it would cut like a hot knife through butter. Unfortunately, tires are the same when it is wet and pokey-sharp stuff is about.
Are you ready to partially unmount, unstitch, patch, and restitch? If so, be sure to test-inflate before restitching/regluing, as there can sometimes be more than one and then you get to do it all again. Don't ask how I know this, and it happened more than once when I was too eager to get things wrapped-up again. The phrase "haste makes waste" kept going through my head. Finding the hole is the worst part of the outside damage isn't obvious. I sometimes ended up unstitching more than I wished.
Good luck on a not-very-fun job; hope it goes quickly for you.
Best,
Dan.
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I will test with Ye Olden Bucket with Water before putting it back on.
Small pieces of glass, lotsof, rain...the perfect storm.
I can use sealant but I mentally prepared for this from day 1. It's unfortunate it takes time though...I LOVE that bike! It's a smidgen small (all my bikes have something lol) but it goes like greased lightning.
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ah i wish you luck trying to patch that tub up. i used to do it meself a right pain in the arse.
i remember years ago i punctured 3 times on a spin, lucky enough my brother was riding tubs as well it would have been a long long walk home .
no mobile phones in those days ;D ;D
the grand bios tyres clinchers are not a kick in the arse away from tubs so might be well worth concidering a new set of wheels.
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Have to see how this goes, I've another pair of Tub wheels which I need to fix and rebuild. I may get clincher rims for rainy days, as rain + glass = perfect storm.
Sealant works quite well I heard. I want to try this as an "experience" but most people use sealant then dump tub when it punctures again.
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I remember some very long walks back in my college days, getting a flat and then a flat in my spare, walking with very thin leather cycling shoes and those aluminum cleats you'd nail in. That Legnano flew like lightning but then too I had to true the rims practically every ride. Yeah life with a Nomad is a lot more boring!
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GP4 are supposedly bomb proof, they're 36 spokes and I am not too heavy. So far so good.
#waiting for repair kit...
:)