Are we posting pictures of fatbikes with thin steel tubes now then? Count me in, I’ve got dozens of these 🙂

I was very specific in what I said – as I always am when discussing this – and it wasn’t that. How much vertical flex is there in a steel frame?

Reading Steve Jones’ rant/interview with Starling’s Joe McEwan, it seems like there’s a lot of assumptions/jumping the gun going on.

I like steel bikes, I like built-by-man-in-a-shed bikes, but to time a few downhill runs and then declare steel as the reason seems a big leap.

It’s a long low 65-degree slack 29er – there aren’t many of those about.

Still nice though!

I should just reply to this one: you’re talking about fork rigidity there, which isn’t something I was covering – there certainly is significant vertical flex in a fork (mostly bending at the top of the crown AFAIK), and I wouldn’t be at all surprised if a fat bike fork is significantly more rigid than one on a “normal” bike. I’m still surprised it isn’t overwhelmed by the difference in tyre flex, but then it seems from other answers that there are also other factors at play – I never have and never will suggest that there aren’t differences in handling between different frames, which might impact on wrist fatigue. It’s all about the design rather than the materials used.

Though I’m also amused to note that in this discussion about the wonders of steel, the forks on the pics posted of fatbikes appear to be carbon 😉

It’s completely irrelevant ,the future of the bike is electric.

Electric bikes aren’t inherently direct

They can alternate tho

I’m conflicted on this one. Logically (and I do love a bit of logic) it’s hard to believe that the differences in flex between different frames amounts to a hill of beans once you slap a 5″ tyre on at 6psi. Yet there does seem to be something “different” to the way my steel fatbike feels. Springy? Lively? I don’t know. I’ll accept that it could all just be in my head though, or at least that I can’t prove it’s not.

And thinking about it, I went from an Mmmbop to a Ragley Ti- identical geo, different material and construction, identical build- and the difference was pretty big. Not comfort but handling- the bop amplified every bump and the rear end kicked around constantly at speed, the Ti was constantly more controlled and composed, had more grip too.

Identical journey and findings. Loved the mmmbop, though it felt a bit harsh. Moved all the bits to the Ti version of the frame, same geometry, same tyres etc and it was a completely different ride.

Reading Steve Jones’ rant/interview with Starling’s Joe McEwan, it seems like there’s a lot of assumptions/jumping the gun going on.

I like steel bikes, I like built-by-man-in-a-shed bikes, but to time a few downhill runs and then declare steel as the reason seems a big leap.

It’s a long low 65-degree slack 29er – there aren’t many of those about.

I’d like to know what bikes it was up against. He suggests they were all modern 29ers – so maybe the new Trek Slash, the new Enduro 29, maybe the Jeffsy (Dirt do love a YT) but what else?

It could be the Starling had an advantage if the other bikes were either longer travel or shorter in reach, eh?

No significant difference in vertical flex. There undoubtedly is a difference in lateral flex, and probably also in twist, hence it’s certainly possible to feel the difference between frames when riding. Doubtless some people like the feel of a frame with some flex in, and others translate that feeling of lateral flex into an assumption of vertical flex (possibly subconsciously). Clearly there are also all sorts of other factors at play like the fat tyre self steering issue mentioned – I don’t think anybody is claiming bike handling is a simple thing!

Though I’m also amused to note that in this discussion about the wonders of steel, the forks on the pics posted of fatbikes appear to be carbon

Probably a nod to weight shedding more than anything. Was in my case anyway. The steel fork on my fatbike weighed more than a sack of spuds so I fitted a carbon one.

I don’t know why it’s so hard for people to believe that the flex of a frame affects handling. And it’s handling we’re talking about, not comfort when pedalling for hours in essentially straight lines.

Consider a bike being cornered hard – you have upwards and lateral forces from the contact patches which are levering the wheels around the hubs. Those forces then act upon the frame from the axles. Meanwhile you have a rider putting most of their weight through the pedals, often a dropped outside pedal, generating leverage around the bottom bracket with big downwards and lateral forces. The wheelbase is more than a metre long. The bike weighs about 20% of what the rider weighs and is not a good shape for torsional or yaw stiffness.

So you have big forces acting on a long skinny lightweight structure. So what if the tyres have some give? Cars tyres run at equally low pressures and its unheard of for convertible versions of coupes to handle the same – the main reason being the reduction in torsional stiffness.

The Starling is a fairly light and long single pivot design – it will definitely exhibit more torsional flex than a multi-pivot steel bike like a Rocket or something with huge carbon tubes like the Slash. I wonder if Dirt had any Strange 29ers in for testing at the same time?

Rocket is linkage driven single pivot – the old 26″ one was Horst link

It’s also a lot heavier than a starling

PS- it does but its not unpleasant

^^Good post.

Apply those same forces and logic across different materials and the feel will change with each, has to. I had a Scott Endorphin that Scott claimed had 3/4″ vertical compliance at the rear. I dont understand why other frame materials cant allow vertical compliance as well as flex

Edit: answered my own question, apparently they flex vertically and horizontally 1:1. Its all down to tube shape/size/geometry 🙂

Stiffness & Compliance

http://www.sheldonbrown.com/rinard_frametest.html

Right. Got it now. There is a lot more to feel than vertical flex.

Thanks.

I wonder if Dirt had any Strange 29ers in for testing at the same time?

I was thinking these might be the closest thing to the Starling in ride feel – rather than the Cotic being comparable just because it’s steel.

Though Cotic were talking up the flex in their bike as a positive in a recent email IIRC.

You also need to consider that lateral flex and movement also influence comfort, as well as handling, grip, and the intensity and frequency of impacts that make it further up the structure and to the rider, whether that movement comes from tyres, frame, bars whatever, the point being that even ‘vertical’ input forces are not totally vertical in the dynamic system that is a bike and rider being ridden, leant and moved in the way it does.

If lateral flex allows some component of the impact/input force to be absorbed or deflected than it lessens or diverts the remaining forces and can have a profound impact on feel, handling and comfort, you certainly mustn’t think of it in such a rigid 2-dimensional way as vertical=comfort, lateral=other

It’s also wrong to think that because tyres are big and squishy that they absorb forces to the point of them not making it through the the frame, it doesn’t work like that in real life. Sure they have a BIG impact on all aspects of handling and comfort, but forces will still be transferred, tyres are not a perfect suspension, and the frame and all attached contact points are then ‘in play’ as well.

As others have said, the vertical flex in frame is actually pretty small and irrelevant compared to the other aspects, it’s there for sure, but not to the degree some people think, and a bike is rarely vertical, even in a straight line there is leaning and such going on, but throw in a corner, a camber, a root, rocks, anything ‘real life’ and it’s a different matter entirely, and that’s where other aspects of flex and stiffness really start to come into play.

None of this is specific to a particualr material by the way, but the application of the material and how it’s all strung together.

Is the Starling CEN-tested?
Wouldn’t surprise me at all if avoiding CEN produced a better steel bike.

Edit: Good discussion at the time here:
http://singletrackworld.com/forum/topic/cen-safety-regulations-and-the-demise-of-the-steel-hardtail

It’s also wrong to think that because tyres are big and squishy that they absorb forces to the point of them not making it through the the frame

I think there’s only one person trying to argue this, and he’ll probably claim that he wasn’t.

In all the chat about vertical/lateral flex & compliance, nobody’s mentioned the materials’ different damping abilities have they? That’s a big advantage for carbon or steel vs aluminium IMO. Less unwanted feedback = less distraction = possibly riding faster.

chakaping – Member

In all the chat about … nobody’s mentioned the materials’ different damping abilities have they?

there might be a good reason for that.

kayak23 – Member

I think it’s the slight self-steer on a fatbike Northwind. I had it with the wrists on my Wazoo, then less so on the Dune. Did you not change tyres near the time too?

Nah, tbh it was so night and day it could only be the bar- I was getting hammered going down a single descent, swapped bar, next ride soloed the glentress seven without so much as a twinge.

I added a bottle cage at th same time so it could be that 😉 But no other changes.

I added a bottle cage at th same time so it could be that

Aha! it was definitely that, you altered the resonant frequency of the frame and stopped the vibrations, to be honest you could have done the same by sticky-taping 3 2pence coins under the BB shell and saved the cost of that bottle cage.

.. even ‘vertical’ input forces are not totally vertical in the dynamic system that is a bike and rider being ridden, leant and moved in the way it does.

^ good points and why I think most of what we feel is twist, or deflection due to twist is what can vary most between frames. Thinking about actual vertical forces only, a parallelogram and a triangle, one will have the ability to deform much more than the other. Some bike frames tend towards a parallelogram and are less like a triangle than others so shape is one way a frame can have more vertical give. It’s not a lot in displacement terms compared to lateral flex and twist but it’s enough that a front wheel on a ~480mm fork/lever can move back and forth enough to make a difference to how we feel the shocks from the wheels, or in a similar way for a seatpost to deform the seat cluster area (seat tube and top tube plus some stay flex) more than another frame. Think about how some very rigid forks feel harsh, it’s from that same lack of flex and movement fore/aft at the axle.

FEA for an average steel MTB frame under a high forward load at the front axle (part of an ISO test) shows top and down tube centres deflecting 3mm or so and a head tube moving enough to give clear movement at the front axle. You can see it happening when a frame is tested. That’s a large load to apply but we’re quite capable of perceiving fairly small changes in how load or shock is felt, so although most of what we feel or describe as ‘vertical compliance’ is probably lateral twist and seat post flex, frames will vary in feel due to vertical flex.

I think there’s only one person trying to argue this, and he’ll probably claim that he wasn’t.[/quote]

I presume this was aimed at me – go on then, where have I made such an assertion? Though I’m impressed at your attempt to disparage any clarification from me before I’ve even made it 🙄 Maybe you should try and understand better exactly what it is I’m saying.

The point is that the amount the tyres deflect compared to the amount the frame deflects is so large as to make the frame deflection essentially irrelevant. Of course that doesn’t mean that forces don’t make it through the tyres (and straight through the frame).

BTW you have to have deflection to get damping – it doesn’t really matter how much material damping there is in an essentially rigid structure.

The point is that the amount the tyres deflect compared to the amount the frame deflects is so large as to make the frame deflection essentially irrelevant.

Irrelevant or less significant, not sure, depends on how much force and how much variation in frame design there is. Over most bumps on most rides tyres do most of the job, agreed, there’s times when there’s enough force through the wheels that the frame is moving in that plane, some more than others to a point that it’s something a rider could feel. It’s just another subjective point of bikes surrounded by variables and degrees of perception, with some mechanics stuck in there 🙂

Damping .. frames deflect for sure but steel and ti make good springs so I’d assume damping is minimal to zero, carbon fibre has some damping properties apparently (or the resin does) but I have no idea whether it’s really enough to help swing the decision on what material to use. It can’t be that much otherwise we wouldn’t have ‘Zertz’ inserts .. !

Jonesy’s test of the Starling Murmur was against some top level bikes, Trek Slash, YT Jeffsy, Cotic 29er and others.

I think overall he just loved the ride feel and the times were consistently quicker.

Is steel the right material for bikes, maybe. Luckily (for bike manufacturers) the problem is so complex and difficult to get definitve answers for, that it will fuel interest and debate for years to come.

The motorbike track test with 3 different stiffness swingarms(mentioned in an earlier post) is a good example. Laps are timed to small margins and riders can consistently put those times in. The variation between tracks are not massive. This allows some difference between swingarm effect to be quantified.

To try to replicate this test with offroad bicycle with so many other variables is nearly impossible. Hence opinion and debate rule.

Personally I belive my Starlings are great because they have a solid silent ride character and are simple to ride. Riding a bike down a technical tracks is quite a brain intensive activity (in my case anyway). A rider that can concentrate and relax will be a quick rider. If your distracted by noise and quirky riding characteristics, your gonna be rubbish!

The difference in the ride feel the first time I had a go on the Ti was astounding- I’d been a sceptic until that point. It there’s nice little trail int eh woods nearby that rewards being able to hold a line across roots on an off camber section- at the time I couldn’t keep up with him down there, swapped bikes and suddenly it reversed. The bike somehow hugged the trail and hovered over it- I actually checked he wasn’t running the tyres insanely soft but they were a good 5psi harder than mine.

Anyway- frame stiffness, in my experience, can make a difference. Not sure if you can say for better or worse without a specific case in mind.

I had a Mk I Ti Switchback which was a fabulous bike to ride – it reminded me of a really old school steel frame. It was awesome but was stolen.

I replaced it with a second gen version which is also brilliant but has lost some of the magic feel of the previous one. It’s a lot stiffer because the of fancy chainstay yoke and the tubes being thicker to cope with the internal routing. I really, really like it but don’t love it like I did the previous one.

I think overall he just loved the ride feel and the times were consistently quicker.

This might be all there is to it. I do believe that the quickest bike we can ride is often simply the one we engage with most, the one that has the right feel and handling balance to suit the rider, rather than anything that can be quantified or packaged and sold. Level of flex is a big part of that feel so why not.

The point is that the amount the tyres deflect compared to the amount the frame deflects is so large as to make the frame deflection essentially irrelevant.

I disagree.

Tyres have a big impact, but they do not render the flex in a frame irrelevant.

I’ve back-to-backed enough bikes down familiar trails, often with the same wheels/tyres to feel the differences in flex characteristics of the frames (not material, the frame), often more than jsut feel, you cna visibly see the flex in some circumstances, if the tyres where acting as you say then this would not be the case.

I’ve got two Cotics which are a great example of this, built with identical components, the same geometry, and essentially the exact same back end, the only differences being the diameter of the seattube that the back ends join to, and the tubeset on the front end of one of them being much lighter, they ride very very differently, one is a lot flexier, and a lot more comfy and less fatiguing, and it’s very much down to the frame and not overshadowed by tyre deflection.

Break it down to it’s most basic => force acts on tyre, some* of that force is transmitted through the system of tyre/wheel/axle/fork etc. and then on to frame, of which there is no dispute**, it happens. Regardless of how big or soft your hypothetical tyre is, there is a remaining force that gets to the frame.

If you keep the force and the wheels/tyre combo constant in this scenario you still have force ‘X’ getting to the frame, then how the frame/system responds to that force IS relevant***.

The tyres can and do play a massive part in how much force is trasmitted, and to a big degree in what direction it acts, but they do not have such an impact as to render frame flex irrelevant in either handling, feel or comfort.

All of this discussion is also skipping over the fact that input forces come from the rider as well as the terrain. Flex in a frame or bicycle system isn’t just important when considering inputs from below, its important when considering inputs from above, and how the frame reacts to your pulling, pushing, twisting and thumping great muscley body acting upon it, a bit of give and or flex between contact points can make a big difference in how your body fatigues when working hard, and sometimes it can be worth sacrificing a bit of efficiency in power transmission for a bit of comfort and feel, especially if you prefer it.

*how much, and in what direction is complicated and dependant on the dynamics of the situation.

** there is not really some magic value below which the tyres absorb it all and nothing gets further through the system, there is always transmission, and under normal circumstances it is significant.

*** I know we are discussing MTB here but this is so much more relevant on the road where it’s a lot easier to swap wheels between bikes and feel the difference in handling comfort and ‘feel’ between very stiff frames and flexier ones while keeping other variables constant.

I disagree.

Tyres have a big impact, but they do not render the flex in a frame irrelevant.

I’ve back-to-backed enough bikes down familiar trails, often with the same wheels/tyres to feel the differences in flex characteristics of the frames (not material, the frame), often more than jsut feel, you cna visibly see the flex in some circumstances, if the tyres where acting as you say then this would not be the case.

Break it down to it’s most basic => force acts on tyre, some* of that force is transmitted through the system of tyre/wheel/axle/fork etc. and then on to frame, of which there is no dispute**, it happens. Regardless of how big or soft your hypothetical tyre is, there is a remaining force that gets to the frame.

If you keep the force and the wheels/tyre combo constant in this scenario you still have force ‘X’ getting to the frame, then how the frame/system responds to that force IS relevant.

The tyres can and do play a massive part in how much force, and to a big degree in what direction it acts, but they do not have such an impact as to render frame flex irrelevant in either handling, feel or comfort.

All of this discussion is also skipping over the fact that input forces come from the rider as well as the terrain. Flex in a frame or bicycle system isn’t just important when considering inputs from below, its important when considering inputs from above, and how the frame reacts to your pulling, pushing, twisting and thumping great muscley body acting upon it, a bit of give and or flex between contact points can make a big difference in how your body fatigues when working hard, and sometimes it can be worth sacrificing a bit of efficiency in power transmission for a bit of comfort and feel.

*how much, and in what direction is complicated and dependant on the dynamics of the situation.

** there is not really some magic value below which the tyres absorb it all and nothing gets further through the system, there is always transmission, and under normal circumstances it is significant.

POSTED 1 MINUTE AGO # REPORT-POST

Heres an eye opener for you someone who is fast on a bike is **** fast on a bike…end of

Must admit, I really love the look of the Starling.

In regards to KTMs steel trellis frames, I heard they stuck with these at its easier and cheaper for non factory race teams and KTM (who dont have R&D budget of Japanese teams) to get the flex right.

You can either reweld or weld up a steel trellis frame with slightly different tubing, alu frames require new casts etc.

tldr; but this thread is making me want to replace my trek budget alu 26″ ht for commuting with a 26″ cotic bfe and still use it for commuting. Can’t imagine commuting on any bike that I couldn’t just have a bit of fun chucking around when the impulse strikes (ie most days). I want a cotic bfe. I want a cotic bfe. I want a cotic bfe. I want a cotic bfe. I want a cotic bfe. I want a cotic bfe. I want a cotic bfe. Just try talking me out of it.

Just one question, will I be allowed a 48-36-26 triple on the front of it?

Heres an eye opener for you someone who is fast on a bike is **** fast on a bike…end of

eh? has anyone said different? I was disagreeing with the assertion that tyre deflection is so great as to render frame flex irrelevant the the way a bike handles and feels.

but yes, fast people gonna be fast, no disagreement there.

Well you sure as heck aren’t going to see vertical frame flex, so you must be talking about some other sort of flex!

As I’ve made clear all along, there are significant differences in lateral flex and twist between different frames (though frame material can’t be used to define what and how much on its own, it’s more down to design). Which makes a significant difference to how frames feel, and even if none of that is down to differences in absorption of bumps it’s easy for the subconscious brain to assume it is.

Of course the tyres don’t absorb all the force and some (most?) gets through to the frame, I don’t think that has ever been in dispute (it does sometimes seem in such discussions that people want to argue with points which aren’t being made*). It’s simply that the ratio of deflection in a vertical direction between the tyres and the frame is >20:1, probably >50:1 at which point the deflection in the frame is essentially irrelevant to the total deflection.

*edit:

Now you see I don’t think anybody has ever made that assertion

Taking this from my link earlier, the deflection in either direction is almost identical. Accepting this, placing in the real world with forces coming from above, below and (HT) from the front as the forks get knocked back before riding over obstacles, its quite clear to me that being able to adjust material dia, thickness and ‘shape’ i.e. butted tubes etc. will make a difference to handling. Its the same as laying carbon up in different ways in different areas. Re. steel, the clever bit is having the correct tube for the job in the correct geometry and its that that makes the frame come alive I think.

Torsional Stiffness of the Rear Triangle: This test applied pressure to the frame’s rear triangle side-to-side and measured how far the frame deflected in inches (moved) under a set pressure. The lower the number, the stiffer the bike is side to side, the less flex it will have, and the more direct the rider’s power will be transmitted to the drive train.

• Cannondale CAAD 3 Oversized Aluminum: .038”
• Softride Rocket R1 Aluminum: .039”
• Serotta Legend Ti OS: Oversized Butted Titanium down tube and chain stays: .045”
• Marinoni Lugged Butted Reynolds Chromoly: .045”
• Trek OCLV 110 Carbon: .052”
• Klein Quantum Pro Oversized Aluminum: .054”
• Seven Axiom Butted Titanium: .057”
• Kestrel KM40 Carbon: .060”
• Generic Welded Butted Chromoly Frame: .066”
• Litespeed Tuscany Production Titanium Frame: .074”

Vertical Frame Compliance: This test was conducted in a similar fashion to the torsional stiffness test, but it measured vertical deflection in inches. The numbers directly relate to a frame’s comfort and ability to absorb vibration. In this case, the higher the number, the more flexible, compliant and comfortable a frame’s rear triangle will be up and down.

• Softride Rocket R1 Aluminum: 1.4”
• Litespeed Tuscany Production Titanium Frame: .064”
• Generic Butted Chromoly Frame: .061”
• Kestrel KM40 Carbon: .060”
• Seven Axiom Butted Titanium: .057”
• Serotta Legend Ti OS – Oversized Butted Titanium down tube and chain stays: .054”
• Marinoni Lugged Butted Reynolds Chromoly: .052”
• Trek OCLV 110 Carbon: .052”
• Klein Quantum Pro Oversized Aluminum: .052”
• Cannondale CAAD 3 Oversized Aluminum: .049”

As I’ve made clear all along …. + it does sometimes seem in such discussions that people want to argue with points which aren’t being made

I think this is another one of those times were both sides are not explaining themselves as well as they think they are. 😀

And the more we discuss the more that becomes clear, as I’m not talking about vertical flex either, in all my posts I’ve been referring to flex in general, mostly lateral*, and how that impacts on what traditionally some people have attributed to vertical compliance when in fact it isn’t.

* refer back to my point about bikes rarely actually being vertical, so are we talking about ‘actual vertical’ forces on a leant over bike (therefore having a component acting laterally on the frame), or vertical as in ‘forces in plane with the seat tube’

damn the internet, it’s a hard place to have a chat sometimes!

Apology accepted 😉 – I did read back through my posts, and can see how it could have been interpreted that I thought there was no lateral flex, so I understand how we end up having arguments despite agreeing!

I’m trying to avoid getting into discussing what happens when a bike is leaned over for cornering as it all gets far too complicated, but will point out that the load is still pretty much straight down through the centre line of the bike as otherwise you’d fall off, and any effect of a bump will act in this direction. In any case we do mostly hit bumps when the bike is upright.

@buckster – there is no suggestion in that test that the loads for both parts were identical – and I’d be extremely surprised if they were, as a bike frame is clearly far stiffer in the vertical direction due to triangulation.

In any case we do mostly hit bumps when the bike is upright.

No we don’t.

What happens when the bike is leaned over for cornering is the main point of this discussion. And the torsional flex in that case is from the huge forces applied through the forks to the head tube, the bars to the head tube, the cranks to the bottom bracket and the rear wheel to the rear triangle/suspension.

Like in this review: https://dirtmountainbike.com/bike-reviews/downhill-bikes/devinci-wilson-carbon-vs-aluminium.html

I’m trying to avoid getting into discussing what happens when a bike is leaned over for cornering as it all gets far too complicated, but will point out that the load is still pretty much straight down through the centre line of the bike the system* as otherwise you’d fall off, and any effect of a bump will act in this direction. In any case we do mostly hit bumps when the bike is upright.

indeed yes it’s complicated, hence us lot wittering on! But it gets even more complicated when you consider that even when ‘upright’ there is a significant component of the force that is no in plane vertically as it’s very rare that the bike is actually upright**, there’s always dynamic change and leans going on.

On top of that, it gets even more complicate when you remember that the bike is moving forwards so that even at moderate speeds the majority fo the force is in a fore/aft direction, even the biggest bumps will input more energy in that direction than up down (discounting landings!), so if lateral flex, twist, deflection of any part, be that tyres, frame or otherwise allows for part of the system to absorb that by moving sideways to mitigate that force it has just as big an impact on what gets through to the rider as anything in the up/down plane, it also massively impacts on grip/traction, especially in marginal situations.

I guess it’s just trying to dispel this idea (mostly from poor articles and soundbite marketing) that comfort comes only from vertical compliance and that extreme lateral stiffness is key to handling, as ever it is lot more complicated than that in the real world!

* + ** the system being you and the bike, the bike doesn’t have to be upright, and rarely acutally is, the load may be down through the centre of the system, but that’s not necessarily in plane with the seat tube of the frame.

So how much of a typical trail is straight, and how much is corner?

Though as I wrote before, most of the forces are in the up/down plane anyway, as otherwise you’d fall off.