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

define typical 😉

I think the point is that even straights aren’t straight, nor necessarily upright, I know on my local trails the vast majority is ‘a bit bendy’ rather than ‘a corner’, and also has cambers, banks, etc. that mean even when riding them in a straight line while upright that there’s enough variation to mean your bike* is actually doing neither for most of the time, and significantly enough for the non-vertical components to matter a lot.

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

I hardly spend any of my descending time going in straight lines with the bike upright. If there is a straight bit on my local trails it invariably has a jump or drop or chute/bombhole or is off-camber.

Although the net forces on a bike have to balance to stop it falling over, it’s standard cornering technique to weight your outside foot and inside hand and shift your centre of mass outwards relative to the centre line of the bike. Those forces alone will cause frame torsion, regardles of the forces coming through the tyres.

@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.

If you look at this test, different source, same test, substantially similar outcome, it was 47.5lbs I think in both front and read rear ‘triangles. The vertical was not tested, I assume as it wouldn’t move as much as we would imagine! Thus suggesting that vertical flex only comes in during periods the frame is canted over? Reading through this thread, thinking logically and reading these tests does suggest vertical compliance to be non existent. But, on an MTB, the bike is rarely being ridden bolt upright on pan flat territory.

Looking at that ‘fact’ alone would suggest that how carbon, alu and steel are affected by pedalling, suspension bumps and frame deflection whilst leant over or swinging from side to side (honking down or uphill) would en masse affect the riders enjoyment and comfort
http://www.sheldonbrown.com/rinard/rinard_frametest.html

If you read the commentary from Damon Rinard he says “I ignored any vertical loads on the frame, as I believe a traditional diamond frame resists such loads easily due to its truss design in the vertical plane.” and he also links this interesting piece from the old rec.bicycles.tech usenet discussion group (it’s well worth reading the whole post). I certainly remember discussing all this stuff on there many, many years ago and there’s no surprise that I’m saying much the same thing as Rinard and Bob Bundy.

Sure the loads there are the same for both parts of the test – both lateral deflection tests. However the other test you linked does have lateral and vertical deflection parts with similar deflection for both parts, which implies very different loads must have been used.

So maybe you should have written “no I don’t” – though I’m intrigued as whilst I don’t really ride downhill, thinking about all of the trails I’ve ridden, which includes lots of trail centres as well as natural, I can’t think of a single trail where the majority isn’t straight or close enough to straight that you’re not leaning off the side and the bike is very close to upright. I’m sure that the vast majority of the totality of riding is with the bike close to upright.

Thing is when a bike is lent over then the wheels will deflect, so will determine what you feel. Plus I’d be surprised if many people are sitting down when cornering so any ‘comfort’ of the frame becomes a moot point.

Am I the only person who thinks comfort on a bike outside of key contact points is a bit of a stupid concept anyway? If I wanted comfort I’d take a car or train. On a bike I want maximum efficiency and hence stiff, light bikes (with decent suspension if an mtb) win.

So maybe you should have written “no I don’t” – though I’m intrigued as whilst I don’t really ride downhill, thinking about all of the trails I’ve ridden, which includes lots of trail centres as well as natural, I can’t think of a single trail where the majority isn’t straight or close enough to straight that you’re not leaning off the side and the bike is very close to upright. I’m sure that the vast majority of the totality of riding is with the bike close to upright.

If you ride a bit faster you’ll find the straight bits turn out to be curves! 😉 Also, longer, slacker and bigger wheeled bikes have to be leant over more to turn than old school bikes.

I have to admit I’m curious where you’re referring to because I seem to spend most of my time on the bike going around corners, wherever I go! My local trails are the woodlands of the South Downs but a few weeks ago I was in FoD, Cwmcarn (that does have more straight bits) and BPW.

I’d assumed this thread was about flex in full-sus bikes, following Dirt’s Starling review. If that’s the case then it’s not about comfort, it’s about control.

dragon – Member

Am I the only person who thinks comfort on a bike outside of key contact points is a bit of a stupid concept anyway?

no, plenty of other people are wrong too.

😉

FOD is fairly local to me, and I’ve ridden there a lot. I’ve no idea about the DH tracks, but Verderers and Freeminers certainly consist mostly of straight bits punctuated by corners – I reckon that even if you look only at the bermy bit at the end of Verderers that’s more straight than corner. I’m wondering if this is another perception thing where the impression isn’t the reality and a lot of corners leaves people with the impression that you’re continuously cornering (strangely enough when I was trying to think of places which might be more continuously cornering I wondered about Cwmcarn, but then it’s a long time since I’ve ridden there!)

Let me get this straight, we started off discussing if steel bikes are becoming more popular among the run of carbon based designs. And via Ducati frames have agreed compliance is non existent in the vertical plane and all mountain bike trails are straight?

Aracer, you said ‘close to’ upright so this is being a bit pedantic .. but based on how we ride a bike, all of our time riding is cornering to some extent. More so off-road as we’re pushed further out of balance by uneven surfaces. So if we’re continually generating varying levels of cornering force you could say how much lateral twist a frame has can be a significant part of how we perceive a bike’s ‘feel’ or reaction to input, at a similar level to steering geometry.

Thank you JamesO!

In FoD we were riding the off-piste stuff and finished over at the DH with GBU. When I’m following my quicker mates they’re usually swooping about even more than I am – compared to a slower rider corners start earlier and finish later and you’re leant that far over that you just pass through vertical before immediately leaning the other way for the next corner.

I don’t have any particular dog in this race – both my MTBs are alloy and pretty stiff. I have a cheap steel BMX – stiff. And a steel Brompton – bendy bendy bendy. But I’m an engineer and oversimplification annoys me. My old hardtail was more flexy in a good way – but the forks were more flexy in a bad way!

I have a hypothesis that with full-sus bikes you want stiffness around linkages, bearings and bushes so forks and rear suspension work as designed. You want some lateral give in rims. You want some torsional give in the front triangle between head tube, bottom bracket and rear pivots but not too much – that’s the difficult area because you need to feel that when you push and pull the bike around it responds like you expect. But if the bike kicks back too harshly you’ll lose some control. You want as much longitudinal stiffness as possible so forks don’t judder under braking. Vertical flex is basically irrelevant on a 6″ travel full-sus, so it matters not that it’s usually triangulated down to negligible.

Down some of the rougher bits on the Cwmcarn DH and at BPW there are definitely moments where you are going in a straight line but the bike is suffering lateral forces from rocks on the ground.

An interesting observation from my part is that at BPW I was quicker on the straighter rougher trails and slower on the bendier smoother ones. My bike is slightly shorter travel than most of my mates’ bikes (150F/140R vs 160/170F and 150-165R) but slacker (64 deg HA). But I’m pretty certain the difference was that I’m not bendy enough as individual (working on it!) but I am fairly strong, so I can hold the bike on course through the gnarr but not whip it around tight berms well enough.

I guess some manufacturers have slapped sensors all over a frame and measured the strain as it rattled down a trail. But they probably regard that as valuable and confidential information. It would be interesting data anyhow.

dragon – Member

Am I the only person who thinks comfort on a bike outside of key contact points is a bit of a stupid concept anyway?

TBH I do think it’s weird that comfort seems to be such a big topic when talking about materials. I mean, apart from extremes like my wrist-destroying fatbike setup… My mmmbop was stiff/harsh as a mother****** but I never felt any difference in comfort compared to my noodly doodly Soda. Handling, sure.

Now to be fair, I have a cast iron arse so ymmv but most bikes are pretty much equally comfortable in material terms, to me.

I found comfort on a HT was improved (when standing up too) by fitting some of On One’s ‘chewy’ (flexy) carbon bars.
Much nicer on my wrists.

I do think it’s weird that comfort seems to be such a big topic when talking about materials. I mean, apart from extremes like my wrist-destroying fatbike setup… My mmmbop was stiff/harsh as a mother****** but I never felt any difference in comfort compared to my noodly doodly Soda

On a long day out on the Mmmbop I’d definitely feel more shaken up and therefore more fatigued than I would on the Ti version.

dragon – Member
Am I the only person who thinks comfort on a bike outside of key contact points is a bit of a stupid concept anyway?

no, plenty of other people are wrong too.

it depends on how, where and how long your ride for though as much as anything.

As a road bike example, I run the same contact points on all my road bikes, they all have the same saddle, same bar tape (well OK one bike is different) and one of either two models of bar across 6 bikes, 3 of them even run the same tyres so theres enough consistency there to say the contact points are fairly constant, but theres enough variation in comfort between them that its noticeable, on anything between 100-150k its enough to make a difference and anything over 200k it makes a big difference to the point that I simply wouldn’t use a couple of them*. One of them became noticeably more comfy after a stem swap to a flexier one, but I don’t know if you consider the stem part of a key contact point on not, I certainly don’t hold onto it while riding…

It’s similar on MTB, I run the same saddle and grips on all of them, bars/stems/seatposts vary, on longer rides or on 12 and 24 hour races there’s a lot more to comfort than just the bits you touch, but on the vast majority of short rides I can put up with anything for an hour or so and be ‘comfortable’ (as long as it doesn’t grate my palms off or make my bottom bleed)

The thing is comfort isn’t just about not initially being in pain as such, but fatigue as well, long term comfort comes not just from the interface with the bits you touch, but how battered, shaken and vibrated the rest of your body gets along the way, all my bikes are comfortable to sit on and ride, but not all of them are still comfortable hours and many miles later when muscles have fatigued and you are struggling to prop yourself up, all that micro trauma and action to the muscles mean it’s about more than just sitting on the thing and not saying ‘ouch’.

* great example there is one bike that I’m really prone to calf cramp on after about 100-130k, position wise it is set up to the mm the same as another bike that I’m quite happy on for 200 or more, same bars, same tape, same saddle, same pedals, same tyres, even the same cranks actually, it’s simply the other differences that mean on one I get vibrated, battered and generally worn out on, the other I don’t, it’s not as good at getting power to the rear wheel mind and is noticeably slower on short rides, but on long ones it evens out to roughly the same speed as I can work hard for longer, and they’re both steel BTW 😉

All this talk of frames and not much about forks.

Surely the long cantilevered bit of the bike is going to have more effect on feel than anything else?

An example is my early model Singular Swift. With the steel fork it was very comfortable, but when I put a carbon fork on – which turned out to be much stiffer – it felt like a completely different bike.

Yep it all makes a difference, I had 35mm Pikes on the front of my HT and swapped them out to 32mm Revs as they were too harsh….ditto the bars, swapped traditional stiff Alu ones out for flexy carbon ones…both changes made the front end much more compliant and comfortable to ride….let’s not forget tyres, my current Swalbe setup of Magic Mary front and Nobby Nic rear (both apparently 2.3) feel and look like larger tyres, certainly bigger than Maxxis 2.3 and 2.5 tyres….then you’ve got seat posts, if your bike is an old school 27.3 size it will flex moor than the 30.9 and 31.6 versions giving the impression of comfort when sat down peddling….wheel flex, the new wide and presumably stiffer rims hitting the market are likely to be stiffer and less compliant than old model narrower rims…etc etc….frame material is just one factor, I’ve managed to make my big tubed and apparently stiff Alu Dartmoor Hornet more comfortable than any of my previous steel bikes using some of the changes listed above.

All this talk of frames and not much about forks.

Surely the long cantilevered bit of the bike is going to have more effec

Absolutely, although in my mind its part of the frame(set), as ever though the more you dig the further down the rabbit hole you go… 😉

Just moving from a 45mm offset to a 60mm offset version of the same fork on my audax bike made a noticeable difference in both handling and comfort over longer distances.

Funny how we talk about stiff carbon frames but we also have flexy carbon bars

And steel frames that give flex but we don’t put steel handlebars on our bikes

Funny how we talk about stiff carbon frames but we also have flexy carbon bars

And steel frames that give flex but we don’t put steel handlebars on our bikes

Thats the great thing about carbon – you can tune it to be many things for basically the same weight. Steel bars are pretty heavy compared to alloy ones.

tmb467 – Member
…And steel frames that give flex but we don’t put steel handlebars on our bikes

The problem is trying to find a steel bar that isn’t gas-pipe thick these days.

I suspect it’s regarded as too hard a sell by the bike industry, so no one is game to spend the money on the tooling for a good lightweight steel bar.

Think my point was really that we’ve got pre-conceptions about so much … steel is a hard sell full stop, these days.

It’s expensive to make it in the strength and weight people want (and are used to) so any scale is much harder to achieve. There’s no right answer here – a good bike is a good bike no matter what it’s built from. Geometry, materials, looks all come together to make something special…and then we’ll spend ages arguing why the one we prefer is better

Bit of marketing (and magazine reviews to be fair) – selling something lighter and (possibly) cheaper in aluminium/CF isn’t hard. Thats really why the Treks/Specialized have gone that way.

Steel is now thought of as a bit more artisan. You can still find a bloke in a shed chopping and brazing R531 tubes together. I think the STW appeal of steel is a lot more to do with “look at me, I’m not a sheep buying mass produced goods” more than real material benefits. Not that I’m saying supporting local/UK builders is a bad thing per se. My ti frame wasn’t much different to my CF or my alloy frame to be honest, I was a little disappointed.

My mate has a Hetchins Curly framed road bike he uses a lot but I don’t think he’s ever commented about how smooth the ride it. He says ‘ow’ as much as me when crashing through the crappy potholed roads up here.

Though that Ritchey (steel) road frame is really tempting me at the moment…

And steel frames that give flex but we don’t put steel handlebars on our bikes

Steel is much stiffer than aluminium. But because it’s much stronger and much heavier we use smaller diameter tubes for steel frames – that reduces the stiffness compared to an alloy frame made from large diameter tubes. If you made a steel handlebar it would be far stiffer than any alloy bar because you can’t change the diameter significantly.