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I'm still not totally convinced by all this "steep seat angle climbs better" business. Different people suit different positions, and I also think there is a smidge of marketing bs with lazy designers (wink at jameso but actually aimed at others not him) where longer stays and steep seat angles make it easier to package big wheels and fat tyres without more radical tube shaping.
I'm working on the 3rd iteration of my 29er frame, gradually tweaking the design over the last 8 years. I've got a clean sheet to make whatever I want, but constant features are an unfashionably slack seat angle and very short stays. Works for me or I wouldn't keep making them like that 🙂
Before starting this frame, I've gone out of my way to hire / try a variety of other hardtails. One thing I did notice was the tendency for stiff bb might make it slightly more prone to break climbing traction on the pedal stroke. More flex seemed to be a good thing in smoothing out the torque application at the tyre.
Out of interest what sort of head angle are "Iron Works" using? Mark 2 and mark 3
I've probably said but I think it is all very height dependent. For me short stays and a slack seat tube can have me over the rear axle with little weight on the front wheel.
I think the stiff BB and traction thing makes total sense
Are we saying that the stiff carbon frame on the Dude will transfer more energy per pedalstroke to the tyres, deforming them more and so less energy is propelling the Dude up hills?
In which case tyre pressures on the Dude should be higher than on the ICT, using the same tyres?
Are your times just taken from strava or a similar app? They are not always bob on...
I n r a t s
But op unless you are accounting for your power output or heart rate at least the comparison between the 2 bikes is pretty meaningless.
It really is about power to weight in the main, the rest is detail and unlikely to account for the difference
Sorry to digress, but for my friend mr ampthill:-
Ironworks Mk1 was rigid Singular Hummingbird fork 55mm rake (more than a standard sus fork of the time) and 70 degree head angle, 120mm stem (had to go with long stem for various boring down tube and e-stay related reasons). Frame still alive and now my fixie mudguarded fat slick tyred commuter.
Mk2 was suspension fork corrected 120-130mm travel, 51mm offset and 70 degree sagged (about 69.5 static). 90mm stem so front end correspondingly longer than Mk1.
Mk3 will only be half a degree slacker but about 40-50mm longer (so now 40-50mm stem). I don't like the floppy steering of super slack head angles - prefer the Mondraker Prime R method of longer frame / shorter stem / not crazy slack head. BB drop will be rather low 75mm but I'm not currently pedal clonking 65mm so will give it a try. Frame will be 29 plus capable so don't want bb too high if running bigger tyres.
Mk3 is my prototype for a 29plus I'm making for a tall friend in Portland (trading for a batch of Biciclista jerseys). I'm waiting for his saddle / bar / bb position to throw into CAD - will be interesting to see where the chainstay length and seat angle end.
You're running the same tyres, but are they really the same?
EG there's a huge difference in drag between the 120tpi surly Nate and the 27tpi.
It was the same set of wheels on both bikes (I swapped them over when I bought the Dude). The ICT ran 4.8" Jumbo Jim Snakeskin tyres. Again the Dude had the same (as in, just swapped from one bike to the other) tyres for some rides, but on others either the rear or both were swapped for the 4.4" version of the same Jumbo Jim snakeskin tyre. So, for a lot of the rides not only was the Dude lighter overall it had lighter wheels.
It's possible that the 4.8" JJs just roll much better than the (lighter) 4.4" version, but it seems unlikely.
Both bikes ran Surly Bud up front in the winter, but unsurprisingly I wasn't setting my fastest times in the winter.
Although there have been a lot of interesting discussions here, my own view is that it's probably quite simple. I was faster on the ICT because I was trying harder. What I don't understand is why I would consistently try a bit harder on almost every climb on one bike. My current theory is that the lively springy feel of the ICT just makes me want to push a bit more than the stiffer but more "dead" feeling Dude, but it's just a theory and I'm intrigued by the article by Jan Heine.
Other factors that could have an effect:
Chainstays: ICT 450mm Dude 439mm
Cranks: ICT 170mm Dude 175mm
Seat Angle: ICT 72.5 Dude 74
Gearing was 1x11 with a bottom gear of 26/42 on the Dude and 2x10 with a bottom gear of 22/36 on the ICT. So pretty similar with the ICT having a slightly lower bottom gear.
Effective Top Tube: ICT 630mm Dude 642mm
What tyre pressures do you use? The rolling resistance of JJs increases by over 50%, dropping from 20-8PSI https://www.bicyclerollingresistance.com/fat-bike-reviews/schwalbe-jumbo-jim-snakeskin-2017
On mostly tarmac, I run my 4" JJs at ~25/27PSI (front/rear), with total weight of me (with kit) and Wazoo of ~91KG.
Off-road, I know you probably wouldn't want to run anything like that pressure, but an extra ~10-20% boost to your normal pressures on the Dude might transfer more of your pedalling power to moving you uphill rather than the stiff frame squashing the tyre into the terrain.
Got any Strava segment analysis links comparing the two bikes up a hill?
Effective Top Tube: ICT 630mm Dude 642mm
Why do you keep mentioning this?
If you are in the same position over the bottom bracket, what would it matter?
And different length cranks. Might make a difference of the longer one is actually too long for you to use comfortably.
GCN experiments on stiffness of frames. Sweetspot and grey area come to mind as said above. Suitability of material for one's weight and power?
FWIW I found my relatively stiff carbon hardtail was short on traction. That's where of a lot my energy went as it skipped about.
Ride the Dude, do 5 miles with a few hills and a heart rate monitor. Check your segment times.
Get home, fit the bits to the ICT and do the same, let's see.
No point basing this on "4 months ago, "
2 bikes, same day, same route, same conditions
I guess I keep mentioning top tube because I'm interested to know whether the longer bike, which I prefer descending, is having a negative effect on climbing. I'm looking to replace my trail bike this year and wondering whether to go longer. I can see that position of hips over the BB is crucial but just wonder whether being a bit more stretched out could be causing a loss of power somehow.
Doing the experiment properly would probably never work. There would always be some element of the experiment that could be criticised. As soon as you start to consciously measure the effect you get into the problem that you know which bike you are on and I wouldn't put much faith in a single run anyway. That's why I've not published any segments and have tried to avoid talking about any one climb. What I'm doing is looking at the results from a dozen different climbs then (using veloviewer) looking at the history of all my efforts, which shows time and which bike I'm on. What I like about this approach is that I wasn't thinking about which bike was faster when I did the rides. Most of the time I wasn't even thinking about the segment, just enjoying the ride. So I'm hopefully taking my bias out of the equation. Yes, conditions vary, but it's unlikely that conditions were always better on one bike compared with another. To be clear I'm not placing too much weight on any one climb. It's more that when I look at the spread of all the times with multiple efforts for each bike over multiple segments I'm not (as I'd expect) seeing a clear advantage for the lighter stiffer bike on the climbs. In fact there seems to be a clear advantage for the heavier more flexible bike, which is strange to say the least. I'm not claiming the result is definitive (or even statistically significant) but it's probably as valid as most if the other deeply flawed "experiments" that are done with bikes.
As as for tyre pressures; mine are much lower. I run 8psi in the rear and 6 (sometimes 7) psi in the front as that seems to work best for me on my trails. I might experiment a bit more with that now though.
Crank length is important to me - others, not so much.
Riding position has caught me out a few times.
Check your knee position relative to the pedal spindle and saddle hight with a tape measure.
Even a really small difference has a huge effect. Ever had a slipping seat post? You can feel yourself getting slower and your smoothness, power and cadence go to pot.
With regard to stiffness, I find a little flex helps with smoothness when tired at the end of a long day. I have to concentrate more with an ultra stiff frame, which in itself is tiring.
And if you really want to try an ultra stiff road frame, try one of the older bonded aluminium examples. Just solid, incredibly distracting after a couple of hours.
That 'Planing' article is weird.
Why measure power? it seems to suggest that putting out more power is a good thing. Surely you want a frame to use less power to go the same speed. Measuring power is measuring effort isn't it? So it took more effort?
So is the conclusion that the flexier frame somehow made it easier for the rider to expend more effort?
I must be missing something.
I can see that position of hips over the BB is crucial
It's not crucial. Afterall, it's constantly changing as it depends on the gradient you're riding up.
Ignore any comments regarding knee position, saddle position etc. Spoken by people who've got no further than MBUK bike fit articles.
Very funny, but both wrong and unhelpful.
☺
It’s not crucial. Afterall, it’s constantly changing as it depends on the gradient you’re riding up
Exactly. The basic idea behind Keith Bontrager's 'KOPS - Debunking the Myth' essay, worth a read for anyone that cares enough about all this stuff.
As as for tyre pressures; mine are much lower. I run 8psi in the rear and 6 (sometimes 7) psi in the front as that seems to work best for me on my trails. I might experiment a bit more with that now though.
Don't add more air based on that rolling resistance website test. The drum they use is so smooth it's of zero use to tell you anything about how a tyre works off-road. Having a constant for all tested tyres is fair enough but it just tells you that a fat bike tyre is a better on a track/tarmac at 30psi than 6psi ... no 5hit : )
I don't think anyone has mentioned KOPS?
Relative position is important.
In this case, the two crank lengths complicate the matter somewhat, but everyone has a seat position and crank length that is best for them.
"That ‘Planing’ article is weird."
Indeed so, but it definitely ties in with my experience. Although, that's on lightweight racing bikes which is a somewhat different kettle of fish.
The planing article is just weird. I did try googling frame flex and efficiency. I did see that Greg Lemond was a believer, apparently.
But the bold claim that the more flexible frame allows 15% more output can't be true. I mean did Sky and British Cycling really miss something that big
Bring it back to a small % then maybe. It is certainly true that when I was allowed out on a rigid titanium mountain bike (when rigid was normal) it did pedal beautifully. Boy was that bike bendy round the bottom bracket. But at the moment I can't see why a bendy bike should allow us to output more power
Because it smooths out the pedal stroke, allowing and encouraging a more efficient action?
"if you don’t think frame flex is an issue, try this: Grab your frame and pull hard on the bb, see it flex. Now do this once a second for five minutes, reckon you’ll get tired? You’ll have used up a noticeable amount of energy, and gone nowhere."
No, the energy does go back into the drivetrain. Losses will be negligible, just so small you could not measure it and not the reason for the OP's apparently loss of performance.
https://www.globalcyclingnetwork.com/video/are-you-faster-on-a-stiffer-bike
Anyway its all academic in the OP's can as he's stressed a few times he climbs seated, so no or minimal frame flex and the forces are all in line.
The fastest times up climbs in the TDF have been clocked on steel 'flexi' bikes. OK the riders were all doped upto the eyeballs, but they probably are today. But modern technology advances of modern bikes (stiffer and lighter than ever before) and better understanding than ever before in the science of human performance still has not delivered someone up, say Alpe D'huez any quicker than the old steel bikes of the '90's. You can't get away forth fact it is 99.9% about the engine and not the bike.
I think even seated I'm flexing the frame a fair bit. The steel bike certainty feels more "springy". It's the first thing I notice when I jump on it after riding the carbon fibre one for a while. That surprises me given how big the wheels are and the low pressures I'm running. I'd expect frame material to be largely irrelevant when it comes to the feel of a fat bike.
I can accept that frame flex might not be as bad a thing as I thought. I've always believed that stiffness was key for climbing. Maybe the losses aren't as bad as I thought though and maybe it does smooth out the power delivery a bit. But I still can't see how I can be faster on the more flexible bike. No slower, yes I could buy that. But faster means I'm putting out more power and I still can't see how a bit of flex is making me work harder. I suspect that's what's happening though and it's why I put "psychology" in the title. For some reason that I don't understand I think I just work harder on the ICT.
There are two climbs that I've only ever managed to get up on the rigid fat bike. Never managed either of them on any of my hardtail or full suss bikes (although I'm sure lots of fitter people have). I'd cleared both of them on the ICT, but in both cases on my first attempt (different days) on the Dude I just gave up before the top. In both cases I went back out again the following week and forced myself to ride up them, so I know I can. I'm sure it's psychological and may have nothing to do with the bike (just the was I felt on the day) but there seems to be a bit of a pattern of me just not wanting to push myself as hard on the Dude.
I don’t think anyone has mentioned KOPS?
No, but they did mention seat angle and climbing efficiency, it's all related. KOPS is based around seat angle and pedal efficiency on the flat and the way it varies in climbing is what Bontrager's article was about.
I guess I keep mentioning top tube because I’m interested to know whether the longer bike, which I prefer descending, is having a negative effect on climbing.
ETT has no bearing on how stretched out you are. Reach is the dimension you should be looking for. Given that your saddle position isn't different between the two frames.
I thought ETT was the important number when sitting down. It always used to be in my road riding days. Reach matters more when standing of course, but if I'm sitting down and the ETT is longer then surely I have to bend forwards more to reach the bars (assuming the same bar height and stem length of course).
Nope.
You position the saddle relative to the bottom bracket.
Seat tube angle is irrelevant to your position. It's also irrelevant to how much you need to bend forwards. (unless you go from one extreme to another and the range of saddle positions is compromised, which is unlikely in this case.)
It wasn't really important on road bikes either. Except for the fact that any comparably sized/frame would broadly have the same seat tube angle. Everything I've ever had (50 at least) has been between 73 and 73.5.
My current and recent mtbs range from 71 to 75. All cross country bikes.
Ett is irrelevant.
Unless you don't understand how to measure up a bike fit and transfer it from one bike to another
You’ve lost fitness. Or you’re not trying as hard as before.
OK, I get where you are coming from now. Thanks. You obviously feel that position of the saddle relative to the BB is key. I'm not sure I agree. Mind you, I spent a few years riding round on a recumbent ! I'm not going to argue the point though. You may well be right and if you can set the saddle in the same position relative to the BB on all your bikes then I can see why seat angle and ETT are irrelevant to you.
Positioning your saddle relative ONLY to the BB means all you can say is how far apart they are. I assume we mean in terms of vertical distance above and horizontally behind? (as some suggested up there, using gravity as a reference is arbitrary and fairly meaningless for seated pedalling efficiency (I'm guessing within at least 5-10 degrees either way - recumbent different in that they seem to have backrests to push against))
I'm not a fit expert or a racer but if I cared I'd want to position my saddle, BB and grips all relative to each other for best pedalling on a road bike (or for seated pedalling generally, I guess). "Fixing" those 3 points relative to each other should allow for a constant level of angle of bend at your back & pelvis, that you've arrived at [s]by many painstaking hours of turbo-based power testing.[/s]
[s]I suppose you might then choose to set the flatness of your back or whatever while still in that optimised "triangle" by, say, pushing saddle forwards and grips a bit forward and lower (or saddle back and grips up&back) and then confirm that it's all optimal by extensive aero and than timed-ride testing of that position and some others just to be sure you're still correct[/s]
... by luck with a bike that you really felt comfy & were fast on
Seat tube angle is clearly relevant to this but yes it can often be "corrected for" by sliding the saddle (unless you've also got combinations of layback on the 2 seatposts that exagerrate the differences between the frames).
ETT isn't totally irrelevant as long as you accept that it also needs saddle position (layback & rails), stem length/rise, bar width/rise and fork+headtube length before it really means anything. Most of those lengths and rises can be altered to get the fit you want, of course.
I'm a "meh" on crank length but seems it affects some people (and of course would alter the position of your saddle relative to your BB)
A Dude you say?
Have you taken to wearing a heavy cardigan and drinking white russians?
This really is getting down to mbuk level bike fitting now.
I'm out.
This really is getting down to mbuk level bike fitting now.
I’m out.
or you could be more helpful and say what you know?
We seem to have gone down a bit of a bike fitting dead end here. It was kind of fun to think about these things back in my roadie days, but I fail to see the relevance to mountain biking. I'm not interested in getting the most aerodynamic position on the bike and things like stem length, bar width and bar height are set to give me the steering feel I want (mainly for descending) based on the head angle etc. Since I was already running a 35mm stem on the ICT, moving to the longer Dude was going to give me a more stretched out climbing position unless I did things that messed up the feel I wanted on the way down.
There is far less consensus on the ideal geometry for a mountain bike and the whole point (for me) of trying different geometries is to see the effect. If I buy a bike with a steeper seat angle and a longer reach it's because I want to see the effect of being in a different position. Adjusting all my contact points to give exactly the same setup as my previous bike would make the exercise pointless (for me).
Getting back to my original point, I was interested to see whether a steeper seat angle and a more stretched out position might have been causing the slower climbing times, given that steeper seat angles are often marketed as a way to improve climbing. The fact that I could have compensated for the steeper seat angle by sliding my saddle back is true, but I didn't because I wanted to see the effect of being further forwards.
Adjusting all my contact points to give exactly the same setup as my previous bike would make the exercise pointless (for me).
I'd agree. Bike fitting to transfer or compare fits (seat over BB, or full contact point triangle) between bikes is largely pointless imo unless both bikes also have same wheelbase and potential F-R weight distribution, handling needs, etc.
Road bike fitting guides may work as all road bikes used to be 73/73, square frame ST:TT ratios, or very close to. That all goes out of the window for MTBs and other off-road bikes. I adapt my fit to the bike's handling needs as well as ride efficiency or comfort/balance needs - that's why it's complex, there's no formulas that really work and where my 'bike fitting formulas are BS' angle comes from. Some very good bike fitters work w/o formulas.
Bike fit and bike handling are linked and it's either something you don't need to care about or it needs experimentation and interpretation to get the balance right. It's a big topic with few reliable rules, as you're appreciating : )