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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.
@jivehoneyjive that looks really interesting!
Any more details, or do you have an old thread?
Single pivot, steel.. similar to a Murmur!
I can't be arsed to trawl through 5 pages...but has anyone mentioned that the back end of the Flaremax and Rocket Max are actually aluminium?
Regardless - I demoed a Flaremax and it was one of the most fun full suss bikes that I have swung a leg over.
I just love the look of steel-framed bikes, with skinny straight tubes - that was my main reason for getting a Stanton Sherpa. It definitely feels flexy compared to the aluminium frame it replaced, and I like it.
I've taken two things away from this thread:-
1. I really want a Starling Murmur - that's the nicest looking FS bike i've ever seen. Factory version will be fine, what do I know about custom geometry?
2. I really want a Barefaced Bass Cab
As mentioned before - my best cornering frame was a Cannondale Prophet that I ‘enduro-ised’ before bailing out of 26”. It flexed to buggery but was awesome on long foot out fast sweepers. I replaced that bike with a 27.5 Cannondale Jekyll which has a massive substantial frame and is marketed as such. It is too stiff. In Morzine this summer it was pattering sideways into corners when lent over as there is no give in the frame whatsoever. It's not the shock setup - I raced and spannered in MX for years, I know suspension.
The front triangle/head tube area is another place that will allow flex as the fork tries to 'lever' the front triangle under loads.
The only issue with introducing flex into frames is that the loads need to be isolated from feeding into the shock as binding/wear occur.
Hols2, when you say you do simple stuff with excel and studied philosophy and political science, do you mean you're quite high up in the Brexit department? Because that would make a **** of a lot of sense of all this.
Are you suggesting that a bit of flexibility may actually be a good thing in international diplomacy.
Utter bollocks!
I like that bike JHJ - well what I can see if it!
The massive stiffness is what’s making it harsh and lose traction when leaned over.
That's your assumption, it's not what the reviewer says. What it says is that the rear shock wasn't set up properly (basically that he couldn't find a setting that worked for him on that trail) and that he thinks a coil shock might fix it. At no point does he say anything about the rear suspension being compromised because the chassis isn't flexing. That's you imagining what you want to hear.
That’s your assumption, it’s not what the reviewer says. What it says is that the rear shock wasn’t set up properly (basically that he couldn’t find a setting that worked for him on that trail) and that he thinks a coil shock might fix it. At no point does he say anything about the rear suspension being compromised because the chassis isn’t flexing. That’s you imagining what you want to hear.
*cough.
The new Cube Stereo Two15 that I've been testing recently has a similar-looking silhouette (but a different Horst-link suspension design) as well as the same wheels, tires, fork, and shock. The Session is stiffer in all directions, and much more efficient under pedaling. The longer frame size, slacker head angle, and longer chainstays of the Session definitely give it a more balanced and stable ride. But, when things get rough and the terrain is trying to throw you around, the Cube tracks better and is easier to handle.
Also: Cons Possibly too light and stiff
He directly says the a not-as-stiff bike is easier to handle in rough terrain and tracks better.
The Session is stiffer in all directions
Including vertically? So you're saying that a bike with stiffer suspension jumps around more on rough stuff. Astounding!
After I broke my old Spesh FSR, I bought a Giant NRS, which took the harsh riding XC thing to its extreme (they were designed to be set up with zero sag so they pedaled like a hardtail). It wasn't particularly stiff laterally, but the only direct comparisons I have are to generic aluminium hardtails and a first generation Giant Reign. The Reign felt laterally stiffer, the NRS felt flimsy, but really fast in a straight line. Over rough stuff, the NRS was bloody horrible, the Reign was like riding a magic carpet in comparison, it would just go where you pointed it and tracked really well in comparison. Having good vertical compliance and lateral stiffness is much better over rough stuff than lateral compliance and vertical stiffness, IME.
How many of you have actually spent any time riding a Session?
Im not sold
i see knackered bearings and frame rub! I do not believe that he has designed that amount of stiffness in!
Starling owners do you constantly have to change your bearings, shock bushings and suffer terrible wheel rub?
How many of you have actually spent any time riding a Session?
Does it count if they've ridden something that looks like a Trek?
How many of you have actually spent any time riding a Session?
I've ridden a hardtail that was really stiff laterally and sucked on rough descents, exactly the same (well, not exactly, but slightly vaguely similar) to the Session. Then I converted to tubeless and let the tyres down until they squirmed like crazy laterally and it was much softer riding on descents. Therefore Trek should make the Session out of steel and it will breathing with the trails.
Ten out of ten for tenacity on this thread hols2 🙂
Yes, it feels like Theresa May and Brexit...
It seems like every day another review is posted where stiffness is not the be all and end all. Here we have a 170mm full-sus 29er:
https://m.pinkbike.com/news/first-ride-scott-ransom-900-tuned.html
It seems like every day another review is posted where stiffness is not the be all and end all.
Vitus review on BR today too. Apparently it 'shimmies' through the rough, reducing fatigue, but also listed as a con.
Commencal frames have been on a stiff-flexy rollercoaster. from the Meta 55 to the V3 and then V4. The press release for the V4 specifically mentioned it being less stiff than the V3 (which I guess was built for strength to recover from the snappy, flexy 55), for the better.
Utter bollocks
[radio 4 voice]
Are you a victim of marketing speak, do you feel the need to lash out, or you back pedalling furiously? Help is at hand at
www.ivemadeatitofmyself.com
Charges my apply
[\radio 4voice]
Are you a victim of marketing speak
We all are, but only some of us are woke enough to recognize it. You will thank me later.
I think Hols is now in full on trolling mode, he's dug a hole so deep that he may as well keep digging and see where it goes!
Either that, or he's a flat-earther. That's the only other group of people I know of who, despite overwhelming facts, multiple theories, and scientific/engineering proof, still manage to twist information and ignore all facts to prove the world is flat, the sun is a few thousand miles away, gravity does not exist, the earth is the centre of the universe, and yet all other planetary objects are spheres...
Are you, Hols2? 😀
It's an interesting question. On the caeser rojo podcast he talked a lot about this issue. It seemed that on moto gp the consistency of track surface and amount of data mean they have a value for lateral stiffness that they know is fast and can design the frames to. Cotic are making frames for riders between 7 and 20 stone, for railing world cup tracks and braking down blues. The perfect amount of lateral stiffness to balance, precision, grip and pump will vary on different corners on the same track. There isn't data available to pick a number, all cotic can do is base it on feedback from riders on old frames and protos and guess a compromise. So for what it's worth "breathing with the trail" is both rubbish and the truth and we'll never know which, we can't even pick a wheelsize how can we get this right? I've got a flaremax because the wheelbase seemed decent for an xc bike and the kit on it was solid enough, although I like the idea of cornering grip through lateral compliance I've no idea how I'd decide which bike does it best. I also like that cotic clearly aren't big enough for super slick press releases, some of the hyperbole does make me cringe but I'm happy my cash goes into bikes rather than words.
gravity does not exist
People have been lying about gravity for millennia.
Ah... Ok... so as i thought. none of you have even ridden a Session.
Makes sense. As if you had you might have have known the detrimental suspension traits detailed by cheif were present on even the first superlight (and def not all that stiff) Mk1 Aluminium Session frames.
It's not because of the stiffness.
The Session definitely doesn't suit every rider but what Paul Aston said about them only suiting a heavier stronger rider is also nothing more than journalist bollocks. Reviews are full of that sort of shit. It's cyclical and whatever minutae to detail happens to fashionable at the time.
Sorry guys, much as I'd love to show you that bike in full, the simple fact is that it's toooooo sexy for youze and would likely blow you mind.
It’s not because of the stiffness.
Damn you, spoiling a perfectly good thread with pesky empirical facts.
/a>”
This is worth reading.
Regarding old Trek Sessions vs current ones, there’s nothing empirically accurate about assuming that the kinematics of the new 29er are identical to much earlier bikes with the same name.
You only have to move a pivot point a few mm to have a signicant change in behaviour - and if you have a 26” and 29” DH bike with the same BB height and chain stay lengths then you’ve inevitably moved the rear axle pivot by over 30mm (due to the much larger wheel radius) which will change everything.
I didn't say they had the same kinematics. I intentionally didn't mention kinematics at all. I said they all have the trait you were getting your knickers in a twist over.
Try actually riding the bikes you like to disect and fret over to "princess and the pea" levels of worry instead of reading motocross suspension physics manuals in an attemp to make yourself sound clever on the internet.
If you were paying attention I also didn't say it was necessarily a negative trait
Im not sold
i see knackered bearings and frame rub! I do not believe that he has designed that amount of stiffness in!
Starling owners do you constantly have to change your bearings, shock bushings and suffer terrible wheel rub?
No issues here. I know (I think) what Andy is saying but the bike in question was one of the first that Joe built and it was run ragged by testers.
Mine has been fine though - had one experience where the bushes for the shock were a few mm out and there was a bit of flex but once it got sorted it’s been as solid as I need. It’s not as stiff as my Turner was but no heel rub / noticeable flex and it feels good
Btw - offset bushings were able to knock up what I needed as the Fox plastic bushes weren’t strong enough. It needed the strength of the metal bushings to support it
"I didn’t say they had the same kinematics. I intentionally didn’t mention kinematics at all."
"you might have have known the detrimental suspension traits detailed by cheif were present on even the first superlight (and def not all that stiff) Mk1 Aluminium Session frames.
It’s not because of the stiffness."
"If you were paying attention I also didn’t say it was necessarily a negative trait"
Well that's a lot of contradiction in a short space of time!
A detrimental suspension trait is by definition a negative trait. The two words are synonymous.
And if it's not because of the stiffness, then this can only be caused by the kinematics - that's what describes the suspension behaviour. And if they're suspension traits then that has to be talking about the kinematics. QED.
I don't need to prove I'm clever on the internet but I can use my ability to understand and explain complex things and shoot down some of the misinformation that abouts across the web. I'm not worrying about anything, I just don't like people shouting "bollocks!" when actually they're the ones talking bollocks.
Stiffness is a multi-factorial kind of thing. flex in the shock linkage could cause side-loading and stiction, resulting in poor perceived performance, whilst in other respects the frame could be relatively stiff. Or vice-versa.
What would be interesting would be to see some actual measurements for stiffness. I am sure reviewers do their best, but I would be wary of reading too much into a reviewer's bald statement that a frame is stiff, or not. Did they measure it, or are they simply reacting to ride characteristics which they believe to be associated with stiffness, or what the manufacturer said?
Calm down wee man. There's no contradiction in anything I said. I didn't say they I thought they were detremental. I said "detrimental suspension traits detailed by cheif" :rolleyes:
I intentionally didn't mention kinematics because you tend to become a complete tool over the mere mention of the word. As witnessed above.
Of course it's a suspension trait but the actual kinematics of each new Session design from OG to curent model are not identical.
Did you ever stop to think why the fastest TREK riders in the world don't complain about the same things you and Paul Aston do?
Ride your bike moar. (Any bike)
"Did you ever stop to think why the fastest TREK riders in the world don’t complain about the same things you and Paul Aston do?"
I know why that is and that's why they're professional athletes. I know I wouldn't make a great professional athlete because I haven't got the right brain for it but many of the aspects that are detrimental to my athletic performance help make me a very good engineer, product designer, teacher and coach. I earn a living designing products that (within my small sector) are internationally acclaimed, ground-breaking and award-winning. I don't earn a living from riding my bike, it's just one fun aspect of my life.
"Ride your bike moar. (Any bike)"
I'm fine thanks, I'm riding my bike just the amount I want to at the moment. I'm playing my bass a lot more. I'm moving heavy barbells in the gym. There's only so much one pair of legs can handle!
Sorry, I had to do some stuff at work for a few days, absolutely no time for anything else.
Paton's links are interesting. Basically, Moto-GP bikes are leaned over at extreme angles, up to 60 degrees from the track surface. They are also extremely fast, so even small undulations become high-frequency bumps. If a bike is laid over that far and hits a bumb, the lateral load absorbed by the tyre greatly exceeds the vertical load absorbed by the suspension. Thus, the main compliance (i.e. spring) is provided by the tyre, not the suspension. The frame of the bike cannot provide compliance at the same order of magnitude or else the bike would be too flexy. The suspension damper cannot damp oscillation at 90 degrees to it's axis, so the lateral tyre oscillations need to be damped. Part of this will come from the tyre itself, but designing a tyre to be the primary damper would compromise its performance in other ways, so some sort of lateral damping is needed. Until recently, there was enough flex in the frame to damp this lateral oscillation, but as materials and design improved, this flex was reduced to the point where lateral damping was insufficient. Therefore, some sort of damping needs to be incorporated into the design of the chassis.
Some key points:
This seems to mostly be an issue with the from suspension, not the rear, as on the Trek. The Trek seems to have a problem with the leverage curve and shock tune. There's no evidence that it's related to chassis stiffness.
Having flex in the forks, swingarm, and suspension mounts is detrimental. The damping needs to be provided elsewhere. Stiffer forks, swingarm, and suspension mounts are better (that's what Paton's link says, anyway).
This lateral damping is only applicable when a bike is cornering at extreme angles. The MotoGP bikes are apparently hitting about 60 degrees. In that case, the lateral bump force will be twice the vertical (the inverse of the cosine of the lean angle). MTBs cannot lean that far because they don't generate sufficient cornering G force. Railing around a berm doesn't count for this, the relevant angle is the angle that the tyre leans in relation to the track surface. At a lean angle of 30 degrees, the lateral bump forces will be small enough that normal suspension travel can take care of them and the regular damper should be enough.
So, to summarize. Very high speed motorbikes racing on very smooth tracks seem to need some lateral damping to stop front wheel oscillations. This is not relevant to MTBs because we can't achieve the lean angles or speeds where this is a problem. Having flexy suspension linkages and mounts is undesirable. Breathing with the trail is marketing bollocks.
Having flex in the forks, swingarm, and suspension mounts is detrimental.
Everyone has said this. Haven't they?
It was in the long Cotic piece you selectively quoted from yourself.
You want the flex elsewhere in the frame.
Well, not 'you', obviously.
You want the flex elsewhere in the frame.
Not flex. The MotoGP bikes need some lateral damping to control tyre oscillations. Damping is not the same thing as flex.
Also, nobody has shown that what is relevant for a MotoGP bike cornering at 60 degrees is relevant to a MTB. If you want to claim that a flexy MTB full suspension frame is actually desirable, you need to actually produce some evidence. Haven't seen it yet beyond marketing bollocks.
This is getting a bit worrying hols.
Are you OK?
I’m not sure hols2 has even ridden a MTB down a rough rocky like the techier reds and blacks at BPW. Because if he had he’d know that this statement is, appropriately, bollocks:
”At a lean angle of 30 degrees, the lateral bump forces will be small enough that normal suspension travel can take care of them and the regular damper should be enough.”
And the rest of his arguments are equally full of holes. Like how a DH bike will often hit 40mph during a race and the surface is far rougher with much shorter wavelength high amplitude bumps than any track racing motorbike has to deal with. Yes the motorbike might be going four times as fast but the bump wavelength will be far more than four times as long or the track would be unrideably rough.
Anyone who’s ridden a full-sus bike off-road will know that the suspension can’t deal with high frequency buzz, however soft or long travel it is.
If you want to claim that a flexy MTB full suspension frame is actually desirable, you need to actually produce some evidence. Haven’t seen it yet beyond marketing bollocks.
A "flexy" full suspension frame is not desirable.
Some people think that means having no flex at all anywhere in the frame is therefore desirable.
When riders claim otherwise, and if manufacturers embrace that, perhaps the result is bikes that you don't like to ride. Oh well. If the manner of describing the ride characteristics comes across as bollocks to you. Oh well. That fun little one liner is framed by a long essay on the subject… it's a catchy and not entirely serious headline/tagline only. Read the rest.
http://www.cotic.co.uk/geek/page/SteelFullSuspension
IIRC SantaCruz did a nice long series of blog posts claiming absolute stiffness is all that matters … hunt it out @Hols2, I think you'd love it. Chimed well wth your view IIRC. Not the only view though.
Only time my bike gets owned over at 30 Deg is when it's leaned up against the wall I have to admit the suspension doesn't work at all
I haven't read the thread after page 2, and never rode a steel fs bike but my question would be, if they are genuinely better at providing grip, then why does not one pro on the wc down hill circuit use one? I'm sure if they were better manufactures would make them.. But for some reason they don't
Let's be brutally honest here, what's more likely ...
A small UK manufacturer has worked out that steel frames are a better material for a full suss bike than those produced by all the major manufacturers and everyone but them is doing it wrong
Or
Small UK manufacturer has always made steel frames, has the tools and expertise to make a full suss one, and reckons that by doing so they provide a certain niche that will appeal to some folks.
I'm sure they are great bikes, they look lovely. And I'm sure they may ride slightly differently, which some may prefer . But if you think they provide better grip then I suspect you are kidding yourself.
Are you OK?
Well, last week at work turned out a bit hellish. Mostly we don't have to do very much, but when we get busy, the deadlines are brutal. When I took the job, a guy who was on the way out told me that he trained himself to only take a dump twice a week so he wouldn't get distracted when things got busy. I thought he was a bit strange to be honest, he took a job in Viet Nam so he might be a communist, but I'm not sure. He was nice enough to leave a card on my desk saying "Enjoy the view, it's the only good thing about working here." Anyway, last week got really hectic so I didn't have time to take a dump for three days and the smell of my farts got really disgusting, but I got out for a ride on Saturday and the miraculous pre-ride dump materialized and cleared everything out. So now it all seems to be back to normal.
Small UK manufacturer has always made steel frames, has the tools and expertise to make a full suss one, and reckons that by doing so they provide a certain niche that will appeal to some folks.
Well, maybe. For some people being able to do the work 'in house' is going to be a big thing. Cotic made their first FS out of aluminium though, and all bar the newest rocket max are still made in the far east, where you could get it made in aluminium too.
Did we decide that frames can flex sideways? Because I can visibly flex my (steel) commuter just by holding onto the saddle and pushing on the bb with my foot. So, frames can and do flex from off axis loading. Given the relatively unconstrained position of the rider above the bike and the nature of the surface being ridden, almost all impacts bar riding straight at a curb seem likely to have an off axis component. Peak impacts from a rider+bike combined weight, moving at speed, similarly seem likely to be much higher than I can manage with my foot. The head tube is a pretty long way from the seat tube, so to say there isn't going to be a noticeable amount of flex or twist in-between seems pretty unlikely to me.
Whether that it is good or bad is a different thing.