Steel Full Suspension Bikes

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

http://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? 😀