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For example, if I had a bottle on the bike I couldn’t tell (in a blind test) whether it was full or empty.
I could on some bikes I think - funnily enough on my rigid bike I think it's the most stark. Given the fashion for going packless and loading up one's bike I thought I'd try it. I put two bottles and a seat pack for tools on my rigid (steel) bike with carbon forks, whilst riding around the Ridgeway area. If you're not familiar, it's a by-word for tame non-technical riding which it is, however it's not quite that simple. The chalk dries rock hard, and ends up being very lumpy. So in places you get a lot of very small bumps, sort of like washboard but not. With the weight on me, I was able to hold the bars lightly and the bike would buck around under me and I could go faster; but with all the weight on the bike it was less able to buck and skip over the bumps so made it far more laborious. I felt like I was crashing into every bump rather than skimming.
Tangent anyway - it would have been more relevant if I'd compared an alu rigid bike alongside it 🙂
I could tell you what material the bottle cage bolts were 😀
coupled with your meandering career history
I don't really think of it as a career so much as random leaps towards whatever option seems to involve the least work. On the bright side, I have contributed massively to Wikipedia, so it's not like I've just been wasting time slacking off.
No, I said I studied engineering. I hated it and got a degree in political philosophy instead
Were the philosophy and politics classes done separately? It’s just that you seem to be much better at the latter than you are at former 😆
Is Wikipedia where you found that formulae you keep regurgitating to imply you are an engineering expert?
I am not a genius like you, I am an airline pilot (semi killed manual labourer) but I do know that steel bikes feel really great because they have bit of give in them. So when a frame designer that is infinitely more clever than me tells me the science behind it I tend to believe them.
I have a Starling Murmur , its nice really really nice .
HTH .
That point I missed earlier about road cars using rubber bushes to make them lesss noisy may be relevant in this case. Bikes generate very little rumble because they don’t have big resonant panels (apart from Orange 5 swingarms 😉 ) but they will vibrate. And you will feel that vibration through your hands and feet. Will a more flexible frame reduce that?
Fatigue really matters on long descents. That’s why we care about grips and handlebars.
hols2, I’m glad to hear you don’t work as an engineer because you’d be decidedly mediocre at it!
Incidentally, all my bikes bar my Brompton have alloy frames, the old 100mm XC hardtail with toddler seat and the modern 150mm hardtail and 160/140mm full-sus bikes.
I know that a lot of bike journalists write a lot of rubbish but not all of them do. And you will see a theme of them becoming aware of the effect of frame compliance (regardless of material) on bikes, to the point that the ones with more give (but enough stiffness to go where you point them) are highlighted as being better on rough gnarly trails whilst stiffer frames are great park or trail centre bikes but beat you up more on natural enduro style descents. All these journalists can’t be deluded, it isn’t a conspiracy!
And work the numbers out if you can be bothered - it’s pretty much all about downtube stiffness.
I'm starting to think poor hols is just after a bit of attention.
hols2, it is clearly a bit of copy for marketing, that bit about breathing with the trail, copy is copy, it's not claiming to be a bit of engineering is it? My issue with your output is mostly that you're contending that there is obective truth, only, and that poetry (as you put it), or even just description, doesn't express truth. Seems a bit bleak.
Perhaps have a look at some phenomenology - that messes all your claims of objectivity up in one fell swoop. Or read Prufrock, or even better, Four Quartets. That was pretty good at expressing truth when everything was upside after the last world war and no one knew what the point was - kind of like this thread.
Anyhow, my bike's better than your bike. And the OP should defo get one.
As someone that has the job of doing much of the engineering and writing the marketing copy for another business, if you want to sell a product to a wide range of customers then you can't describe it as you would to an engineer. And also, if you describe it in precise engineering terminology including giving all the numbers related to the performance, then you make it a damned sight easier for the competition to steal your ideas. It's a fine line to tread, being honest and convincing and appealing without giving all the proprietary but hard to protect info away: https://barefacedbass.com/ (thousands of words of me doing my best at that).
I like the "fatter warmer mellower and rounder with a nice edge and bite to the treble" bit. Mysteriously need a speaker that's taller than me...
what is a proper degree these days what are the talking bobbins useless ones where people go to university to study
The only things i have learned in four pages are.....
1: I still think steel full suspension bikes are the best based solely on my riding experience and the fact steel bikes are just plain prettier.
2: Some of you can't half waffle on.
3: I really want a go on that Slingshot Ripper
it’s pretty much all about downtube stiffness.
According to the bike designer, it's about the toptube, not the downtube.
You seem to have overlooked my point, which is that a frame cannot flex to the same order of magnitude as a 6" rear suspension. I'm not saying steel bikes don't feel nice to ride, just that a frame cannot flex enough to help a wheel track the ground the way multiple inches of suspension travel do.
So when a frame designer that is infinitely more clever than me tells me the science behind it I tend to believe them.
He's not telling you anything scientific, he's spouting marketing bollocks. The next frame designer will tell you the exact opposite and quote some other made up "science".
Love a bit of steel and really looking forward to a visit to the Stanton HQ to try out and order my new Switcher FS frame. Just got to decide on the colour
And you are missing the point hols. Its that few mm of lateral flex that makes a bike feel less harsh and track the ground better when leaned over because at high lean angles the suspension cannot work effectivly
“You seem to have overlooked my point, which is that a frame cannot flex to the same order of magnitude as a 6″ rear suspension. I’m not saying steel bikes don’t feel nice to ride, just that a frame cannot flex enough to help a wheel track the ground the way multiple inches of suspension travel do.”
I didn’t overlook it - I clearly stated that frame flex does not have to be of the same order of magnitude as suspension travel for it to have an impact on handling.
Let me put it another way - what if we make the frame far too flexible? According to your logic, as long as the frame flex is not at the same order of magnitude then it will have no impact on the feel of the bike. So on a DH bike with 200mm of travel the rider will not notice if the bike flexes sufficiently to cause 20mm of vertical movement at the wheels.
Does that sound logical?
I remember ages ago there was an excellent article regarding how frame feel was influenced by resonance and harmonics, but I can't for the life of me find it.
That said, this article might provide a few clues:
https://www.tms.org/pubs/journals/JOM/0511/Burleigh-0511.html
TJ, this is just the first video that popped up so feel free to link to one that does illustrate your point, but I'm afraid I don't see where the bike is leaned over so much that the suspension is locking up and the rider is relying on frame flex instead.
Think there's something along those lines on Jan Heine's blog jivehoney, he talks about the bike 'planing'.
More roadie related.
I'm no scientist like some of the Profs on here, but I do know that karters will use different torsion bars on different tracks. Almost as if the flex had some bearing on handling...
So on a DH bike with 200mm of travel the rider will not notice if the bike flexes sufficiently to cause 20mm of vertical movement at the wheels.
We're talking about the frame twisting so the wheel can move laterally, not vertically. My point is that that much lateral flex would feel absolutely horrible. Or so I imagine, the only experience I have had that is remotely similar was when the chainstay on my old FSR cracked. It wasn't too hard to notice that the back wheel was off doing it's own thing.
karters will use different torsion bars on different tracks. Almost as if the flex had some bearing on handling
Karts don't have proper suspension, so they use chassis flex instead. In a regular race car, the aim is to have a very rigid spaceframe or monocoque to mount the suspension to, then use springs, dampers, and swaybars to adjust the suspension characteristics. Karters can't do this so they adjust how the chassis flexes instead. Completely irrelevant.
In any wheel size discussion on FS bikes it's everyone shouting about racing results, but not so in this thread. Is the enduro/DH racing scene awash with steel framed bikes at the upper levels?
It all gets a bit complex when steel is 3 times stiffer than alu though; I had a steel full suspension bike with a burly steel rear end...
Even though it had a puny by modern standards 135QR axle, it tracked like a downhill bike, with a noticeable improvement in holding a line on off camber sections compared to the alu enduro bike I had before it.
Nonetheless, despite this stiffness, it also had a pleasing level of compliance.
Wasn't the lightest mind...
The fastest bikes are the ones with the fastest riders. And the fastest riders are the ones riding for the teams with the biggest budgets. And the teams with the biggest budgets are connected to the companies selling the most bikes. Material choice is way down the list.
BUT it's well established that you can't improve a full-sus bike by making the frame infinitely stiff - there is a tipping point where more stiffness is detrimental to handling.
"We’re talking about the frame twisting so the wheel can move laterally, not vertically."
Well in that case, why are you saying that the amount of frame flex has to be of the same order of magnitude as the suspension travel? You really aren't thinking about this very logically! It's very easy for frame flex to be of the same order of magnitude as suspension flex in the same direction because a good fork and good rear suspension design is pretty stiff and good at moving how it's meant to, which is up and down, not laterally.
DP.
Nice bike JHJ, do you pics of the whole thing?
steel is 3 times stiffer than alu though
The problem with saying things like that is that an aluminium tube of the same weight and wall thickness will have a much greater diameter, and it's the diameter of the tube that gives the stiffness. This is really what people mean by "aluminium is stiffer". It's perfectly possible to make a really, really stiff steel bike, it's just that if you took the same weight of aluminium, you could make an even stiffer bike. You could also make a really flexy aluminium bike if you wanted to.
No, you were talking about the frame moving in the same order of magnitude as the suspension.
My point was that the frame cannot possibly flex vertically because the seattube would have to compress. Therefore the flex has to be twisting, so if the frame twisted so much that it was comparable to a 6" travel suspension bike it would be like riding a bike made of soggy noodles. But apparently "breathing with the trails" takes care of it all.
My point was never that steel frames don't feel nice or have different resonance properties than aluminium. It was just that a frame that twisted that much would be bloody horrible. I think we have agreed on that.
Karts don’t have proper suspension, so they use chassis flex instead. In a regular race car, the aim is to have a very rigid spaceframe or monocoque to mount the suspension to, then use springs, dampers, and swaybars to adjust the suspension characteristics. Karters can’t do this so they adjust how the chassis flexes instead. Completely irrelevant.
We agree on one thing, a car and bike tyres and suspension are designed to work in entirely different ways.
But car suspension carries on working vertically mid corner, keeping the tyre in contact with the ground.
Bike suspension doesn't, because it's no longer vertical, but a little bit of frame compliance is. I'm not entirely sure why you find that so hard to grasp.
And you've got the magnitude issue the wrong way around as well. a 200mm downhill fork doesn't just iron out everything <200mm, it's designed to take the edge off much bigger impact or give a little bit over smaller ones, so if you hit a ~50mm square edge the fork is only supposed to give 15mm (made up number, depends on the speed you hit it and how firm you set the damping up). So to track over the same 50mm undulation mid orner only needs 15mm of frame flex, or in reality probably less as you're balancing the opposing constraints of "some flex is better than no flex" with keeping the frame stiff enough to go in the direction the rider want's it to.
We agree on one thing, a car and bike tyres and suspension are designed to work in entirely different ways.
The point about car suspensions came up in the context of engineers wanting a very rigid structure to hang the suspension off. The same thing applies to MTB rear suspension, including the Cotic. The Cotic is heavy because they had to put a lot of material around the suspension pivots to make it rigid enough. Same principle applies.
The disagreement is about whether a steel top tube will twist enough that "breathing with the trail" will make a significant contribution to keeping a 6" suspension bike attached to the trail. My view on that is that "breathing with the trail" is marketing bollocks.
very sorry but looking at this
Im not sold
i see knackered bearings and frame rub! I do not believe that he has designed that amount of stiffness in!
The point about car suspensions came up in the context of engineers wanting a very rigid structure to hang the suspension off.
Which is a sweeping generalisation because they dont.
Which is a sweeping generalisation because they dont.
Cotic did, that's why their bike is so bloody heavy. All the other bike reviews I read seem to go on endlessly about how they've done some clever thing to make the suspension mounts and links more rigid. Please link to bike reviews where the designers emphasize how flexy their suspension mounts are.
Generalizations are things that are generally true. An exception to this is road cars, where the priority is on isolating the cabin from the road. Production car racers bin the rubber suspension bushes and replace them with rose joints to eliminate the flex.
You would be unwise to try and school mickmcd about what happens in the world of racing machines with engines in them.
As for the world of riding bikes for fun… spout off all you want. No one minds… it's entertaining to read, to some degree.
edit: not really that entertaining to me really, as it happens, but some like the odd armchair engineering rant, always a periannial favourite on this forum.
I thought you were done with this thread kelvin. Welcome back, I missed you.
"My point was never that steel frames don’t feel nice or have different resonance properties than aluminium."
Really? If you agree that a steel frame feels different to an aluminium frame then I don't know what we've been arguing about? If it FEELS different then it has to be flexing differently. It's impossible to separate those two statements.
"It was just that a frame that twisted that much would be bloody horrible. I think we have agreed on that."
I think what we've agreed on is that you've been missing the point about how a small about of frame movement can have a significant effect on the feel and handling of a bike.
"Cotic did, that’s why their bike is so bloody heavy."
No it isn't - it's pretty much the same weight as my alloy full-sus.
"All the other bike reviews I read seem to go on endlessly about how they’ve done some clever thing to make the suspension mounts and links more rigid. Please link to bike reviews where the designers emphasize how flexy their suspension mounts are."
Making suspension mounts and links more rigid is a good thing - it allows the suspension to work as designed. But that's not what we're discussing. Or maybe you are, because yet again you've missed the point!
Reviews that talk about stiffness as sometimes being a negative or flex being a positive - here's a few:
https://www.pinkbike.com/news/trek-session-99-29-review.html
https://www.pinkbike.com/news/cotic-flaremax-review.html
https://www.pinkbike.com/news/norco-aurum-hsp1-29-review.html
https://www.pinkbike.com/news/commencal-supreme-dh-29-review.html
https://www.pinkbike.com/news/nukeproof-mega-275c-rs-review.html
https://www.pinkbike.com/news/btr-pinner-review.html
https://www.pinkbike.com/news/starling-murmur-review.html
Generally you'll see a link between a certain amount of flex being seen as a positive thing and a bike being used for really gnarly natural riding - big, fast, rough descents where fatigue is a serious issue.
steel is 3 times stiffer than alu though
It is, but typically frame builders use much less material so the stress is higher (per/mm^3) and the effect is that you see more percievable "Flex"...
853 (that the flaremax is made from) is 3+ time Stronger than say 7005 (UTS of 1250 mPa+ Vs 400 GPa), and yes it's stiffness is also about three times more (E= 207 GPa for 853 Vs 70 GPa for 7005)...
853 is also almost 3 times denser, so for frame construction if you can use 1/3rd of the amount of material (by volume) you can achieve similar strength to weight for such a steel structure, The percieved difference in stifness comes from the fact that you not only tend to slim down wall thicknesses but also tube diameters and so you are applying more stress over a significantly smaller cross section with a reduced section modulus... basically for a skinnier steel frame you'll be putting the same amount of stess and strain through about 1/3rd of the volume of material you'd use in an aluminium equivalent...
Of course there is a limit to how thin you can make a tube wall and still be able to weld it...
Interestingly the young's modulus for 853 isn't all that different from the sort of (much lower UTS) structural steel you'd use (in much bigger sections) for more 'standard' applications (200-210 GPa), so that degree of elasticity is clearly desireable in the types of applications (Bike frames and motorsports) that Reynolds sell their materials for...
*all based on interweb poking and partial datasheet information...
"Generalizations are things that are generally true"
If only! Generalisations which have to bridge the gulf between engineering truth and consumer understanding are often inaccurate oversimplifications.
In my line of work the most common one is the assumption that the nominal diameter of a loudspeaker is the most critical factor determining how it sounds. It's like the unstoppable myth!
If you agree that a steel frame feels different to an aluminium frame then I don’t know what we’ve been arguing about?
That's what I want to know. My point was never that the frames don't feel different. It was that the lateral flex in the frame cannot be of the same order of magnitude as 6" of suspension travel so the idea that the "springiness" of a steel frame helping the wheel to track the ground in a 6" suspension bike is nonsense because the contribution of the lateral flex will be so small compared to the suspension travel, tyre flex, plus all the other sources of flex. I'm not saying they won't feel different, just that they ain't going to be flexing several inches.
Plus, "breathing with the trails" is marketing bollocks. I think we all agree it's quite pretty, but it is marketing bollocks.
I don't have time to read right through all those reviews linked to above. I skimmed the first one, looking for mention of stiffness of the suspension mounts. I couldn't see any mention of that. What I did see was this:
The combination of the bike's light weight, suspension design, and massive stiffness makes the Session pedal and accelerate very well. It also rails fast, smooth berms exceptionally well, and it's easy to see why some riders have had success on the World Cup circuit with this bike under them.
That said, heading into the rough stuff I found the Session noticeably, well, harsh. Tracking across off-camber sections and carving flat corners didn't inspire confidence - the rear wheel had a tendency to lose traction when the bike was leaned over. Despite the 'Active Braking Pivot' design keeping the rear triangle active under braking, I found the braking traction lacking, with the bike skittering into rough corners when I was most looking for grip.
The harshness I experienced may have been affected by settling on slightly less pressure than recommended by Trek, with the theory being that I could have been running deeper in the travel than necessary. That said, for the terrain I tested on I generally prefer a softer setup and the Session was set up similarly to the other bikes I tested. Alternatively, a coil shock could be the ticket here, which could improve the sensitivity and tracking of the back end of the bike.
Similar to what I experienced with the Norco Aurum, there was also some vibration from the fork in the lower setting when riding mellow bike park trails with small stutter bumps. I'd put this down to the slack head angle and the 29" fork being long and riding high in the travel on flat terrain. I generally set the bike to tackle steeper terrain where this issue didn't appear, but flipping the Mino-Link to the high position helped, and if I was riding less steep trails more often I would be lower the front end of the bike through the crowns and raise the stem or handlebar to keep a similar riding position. I tried this in the Whistler Bike Park, where the trails aren't quite as steep, and it did end the vibration issue, but then I was in need of a higher rise bar or direct mount stem spacers to maintain my preferred bar height.
So basically, he couldn't get the rear suspension working as he wanted and this may have been related to setting up the shock. That's nothing to do with preferring a flexy frame.
If I missed something, or the other reviews criticize bikes for the suspension mountings being too rigid, please post the relevant quotes. Just posting a whole lot of links to that don't actually discuss anything relevant tends to make me question your understanding of the issue.
just that they ain’t going to be flexing several inches
No one has said that this happens, or that it would be desirable for this to happen.
Plus, “breathing with the trails” is marketing bollocks.
How many times must you use the word "bollocks"? You've made it pretty clear you don't like that phrase, enough already. Now, try describing how different bikes feel to ride… it's not that easy.
the other reviews criticize bikes for the suspension mountings being too rigi…
Enough strawman bollocks!
= ;87)
Suspension mounts need to be rigid… that doesn't mean ultimate stiffness is all that ever matters for the whole frame!
Stuck record time - no matter what materials frame designers are working in, many will look to tune different amounts of stiffness into different parts of the frame.
Cotic did, that’s why their bike is so bloody heavy. All the other bike reviews I read seem to go on endlessly about how they’ve done some clever thing to make the suspension mounts and links more rigid.
Err, I seem to remember Cy's argument is that they actually use less? Because a seat tube is a fixed size regardless of material (because seatposts are a certain size) then if you make it from steel the pivot's are actually stiffer. So when the whole bike is allowed to bend around that the pivots are still always in alignment.
It weighs more because the limiting factor in bike design is generally stiffness (if it's stiff enough it's already strong enough), Cy built a prototype Soul from 953 that was strong enough on paper (as 953 is stronger) but was too flexible, so there is a sweet spot where a material's stiffness and strength are balanced for the intended use. Whereas his background was in railway engineering where structures were generally built for strength and the stiffness was adequate*. Which was why you don't see aluminium railway bogies. Conversely an aluminium frame is generally too stiff in order to be adequately strong.
He gave a whole series of lectures at Sheffield Uni on the subject:
http://thisisheffield.co.uk/2011/cotic-lectures-cy-turner-from-cotic-on-bike-design/#more-1351
*All grades of steel are about the same stiffness, but different strengths. So cheaper steel used in the railways gave the stiffness required long before the component was strong enough.
Seriously Hols2, you are clueless.
Here it is:
”The combination of the bike’s light weight, suspension design, and massive stiffness makes the Session pedal and accelerate very well. It also rails fast, smooth berms exceptionally well, and it’s easy to see why some riders have had success on the World Cup circuit with this bike under them.
That said, heading into the rough stuff I found the Session noticeably, well, harsh. Tracking across off-camber sections and carving flat corners didn’t inspire confidence – the rear wheel had a tendency to lose traction when the bike was leaned over...”
The massive stiffness is what’s making it harsh and lose traction when leaned over.
You’ll read similar points (or the reverse on less stiff bikes) in all the other reviews.
“It was that the lateral flex in the frame cannot be of the same order of magnitude as 6″ of suspension travel so the idea that the “springiness” of a steel frame helping the wheel to track the ground in a 6″ suspension bike is nonsense because the contribution of the lateral flex will be so small compared to the suspension travel, tyre flex, plus all the other sources of flex. I’m not saying they won’t feel different, just that they ain’t going to be flexing several inches.”
The amount of movement in a bike’s suspension mid-turn, that’s providing the grip as opposed to dealing with larger bumps is often very small. That’s why frame flex matters! But you’re never going to accept what everyone on this thread is telling you, despite the evidence because you’re either too unintelligent or too closed-minded.