Sorry to state the obvious - I’m always amazed at the number of riders who leave their suspension open when they’re climbing a fire road or on pavement*. Bouncy bouncy bounce.
Is it actually clear that if a bike with suspension is bobbing a bit while pedaling it requires more power to keep speed up, or is it just being assumed?
I have no idea whatsoever…just curious. I’ve been on a mountain bike once in the last 20 years, and didnt even notice it bobbing, not that that means a thing lol. I take that back actually…I definitely did notice it when out of the saddle. Seated though…it seemed rock solid…same as my cross bike.
You’re putting energy into the suspension instead of the drivetrain/tire. That’s why it took many years for the XC pros to switch to FS bikes - between the bobbing and the weight penalty, they didn’t want to risk the change.
But today’s suspension designs are so good that a well-tuned suspension isn’t going to bob much under seated spinning. And any losses due to bob are more than recouped in less fatigue and better traction.
I’m not arguing the logic behind the reasoning…but I’m asking if this has been actually tested. This just seems awfully similar to the talk about watts being lost to frame flex in road bikes that has gone around in circles for years with no clear answer. I mean pardon me if this is in fact known and not assumed…but just because a suspension bobs does not necessarily mean power is being lost IMO.
It feels like bobbing matters but on some hill climbing testing with powermeter and hr we didn’t see any difference between wide open and locked out. I’d like to recheck it by doing it again….and that energy has to come from somewhere right?…but I couldn’t show bobbing was slower.
Well yes and no. I mean obviously if you’re compressing suspension, that takes energy. But compressed springs give energy back as well. If the suspension rebounds before the end of your downstroke, I dont see why there would be any measurable power loss.
Like I said I have no idea if this is figured out or not. But IMO the answer certainly is not clear to me without testing…
I wonder if you could compare Power at the hub (trainer) and crank/pedals and find the loss.
There is some energy being lost, that’s how it’s designed, but I actually think I’m more efficient in open or traction mode than locked. Nothing worse than the bike jumping up and launching you forwards whilst you’re trying to spin up a lumpy climb.
No because there’s a lot of loss in the drivetrain. I think what you’d want to do is standardize power on the hub, then see if there is a difference in power required at the pedals to create say 250 watts at the hub with the suspension locked and unlocked.
My GUESS is that there will be a difference…but miniscule. Like a fraction of the overall wattage, then multiplied by the efficiency of the spring. So say 50 watts is being used to compress the suspension…but the springs are 95% efficient or something…you’re losing 5% of 50 watts…2.5watt loss overall.
Exactly. A modern FS bike that’s tuned properly might lose 1W in bob (made up number), but the gain in traction and reduction in rider fatigue more than makes up for it. It’s mostly a non-issue unless you’re riding a soft long travel bike.
Open vs “traction” vs locked is a good question. FWIW, I almost never lock out my suspension (Fuel EX, 140mm F/130mm R, no remote lockout). It’s open 80% of the time and in trail/traction the remainder (only on sustained, smooth flat or uphill sections).
I could see using a remote lockout in an actual sprint situation, but I’ve never run into that as a mid-pack masters racer.
And for most of us posting here in the middle of the day, it’s all within the noise of our day to day performance variance. So, interesting to ponder but not going to make us suddenly move from mid-pack to elite.
The damper transfers kinetic energy to heat energy and therefore there is some amount of efficiency loss there. How much, don’t really know.
But again, if you are measuring power from the crank/spider/pedals that efficiency loss is already accounted. So if your power meter is reading, say, 200 watts that’s the power turning your back wheel.
Mmm. I’m not sure that’s right. The suspension compresses when you pedal…that’s a result of the force you’re putting into the bike at the pedal. I think a portion of that would be lost.
The dampers are something I hadnt thought of…that probably works against the rebound force of the springs I imagine. Of course ultimately the same work is done by the springs so I’m not actually sure how much it matters…if at all. This stuff gets complicated pretty quick…
I’ve been real interested in researching this and testing what I have available. There isn’t quite 100% confirmed hardtail vs full squish that I’ve seen. I’ve seen a few YouTube tests that all have been debunked in the test methods. Dylan Johnson did some testing that showed there is no effect of a shock lockout, the problem is that the inefficiency of pedal bob essentially happens before the crank, so it doesn’t get measured. 300w at the crank is going to equal 300w minus drivetrain loss at the hub, no matter the suspension type, but the rider may be working harder to produce 300w at the crank. Imagine the pedal stroke being a perfect circle, as in a hardtail or fully locked full squish. If the suspension is bobbing, that now becomes an oval, with the minor diameter equaling the diameter of the hardtail circle (aka crank length times two), and major diameter equaling the minor diameter plus pedal bob. You may be making the same torque at the pedal and the cadence sensor reading the same RPM, but the oval scenario is going to have your feet traveling on a longer path to produce that same power, meaning your body has to exert more energy to make those 300w. The complicated way to say, it is true that pedal bob means your body/feet are moving without all that power going into the pedals, that inefficiency just isn’t captured by the power meter. The hard part is that the rider would need to be instrumented in some way to actually capture this, CO2 rates in breaths, or something like that.
Another aspect is how the tires interact with the road. It’s the same phenomenon as to why lower pressure tires can often be faster (https://silca.cc/blogs/silca/part-4b-rolling-resistance-and-impedance). If the tire pressure is too high, the tire is almost sending high shock waves back at the bike when hitting bumps, slowing it down. Same is true for suspension, hitting braking bumps with a rigid fork/frame really slows the bike down, just from that impact force pushing back through the tires. If you have front/rear suspension, the tires are able to blow-off, letting it float over the bumps. Then with full squish, the pedal stroke is also smoother and easier to put power down as the trail gets more bumpy. There’s a straightaway that’s mildly rooty in which my buddy and I have probably ridden a hundred times between the two of us. We’ve both concluded that not only is the full squish fastest (despite being a few lbs heavier), but can actually put more power down.
So the high level formula would be:
[Power exerted by rider] - [Pedal bob inefficiency] - [Impedance of road surface into bike] = Output
On a perfectly smooth road, impedance will be low and not matter much, so optimizing pedal bob efficiency and weight is most important. As it gets bumpier, impedance goes up, as well as a less efficient pedal stroke. At some point, the full squish will be faster. In my experience, my 25lb full squish is faster on every MTB trail I’ve ridden than my 23 lb hardtail with the same tires, even smoother XC style trails, so even though it’s less “efficient” (as in exerted energy vs power meter reading), the rest of the equation makes up for it and then some. I rode a hardtail this past weekend at a race, because it was 50% gravel and the singletrack is smooth flow trail, only a handful of roots.
In reply to the OP, using the power pedals on both bikes won’t give quite the same results, because of the fact that there’s some power loss pre-pedals. If you average the same power and are faster on the full squish, you may be exerting more energy and not knowing it. Without having expensive laboratory equipment to instrument your body, I think just doing a bunch of laps with each bike will show the true story. At least for me, I do my bike/suspension/tire testing at a local trail that I’ve ridden over 80 times. I have enough lap times that if I know I’m fresh, go when there’s no/low traffic, and really give it a go, that within a few laps I’ll have a pretty good idea whether the new bike/tire/setup is better or worse. Also using Strava’s “compare” feature is great for seeing where each bike is faster.
Nitpicking a bit… 300W is 300W. A rider exerts the same energy to make 300W regardless of suspension. What matters is how fast that 300W makes the bike. The more losses you have due to drivetrain, suspension, tires (and whatever else), the slower the bike will be for a given output from the rider.
But, your main point is correct - if the rider made the same power, and one bike was faster, then that bike was more efficient transferring that power into forward motion.
This may be true…but I’m inclined to disagree. I think what happens is that the suspension compresses as ypu start your downstroke, then rebounds before you get to the end of that stroke, so your foot is not actually traveling a longer distance.
I think the effect would be similar to how an oval chainring operates…the force changes for a portion of the pedal stroke, but the path is the same.
What’s your reasoning or proof that a rider exerts the same energy to make 300w, regardless of suspension? Tested: Does Suspension Lockout Make Climbing Faster? Anti-squat, efficiency & power meters. - YouTube Here’s one of the YouTube videos that basically shows 300w (or whatever constant power he uses) will equal the same speed, regardless of suspension. He explains that the inefficiency happens before the power meter. The power meter only measures the torque times cadence, but as I explained, that doesn’t always capture how much energy the rider is exerting.
That’s not true for most suspension bikes. Unless you’re talking about a graph of force, but you can pedal squares on a hardtail too.
Because if the rider is making 300W, he’s making 300W. :shrug:
That 300W may be transferred into motion. Or it might get lost to wasted motion/heat of some sort (suspension, tires, etc). But the rider still made 300W.
Damn. The more I think about this…the more complex a question it really is. IF (a big it) the suspension creates a longer travel for the foot on the downstroke…that would not be reflected in pedal or crank based power meters.
Wait. It may though…there would be a longer time at any given force…which would be recorded. Good grief I have no idea. Somebody with a mountain bike needs to test this shit 
You need to do it with a met cart.
And/or some sort of ridiculously sensitive temperature measuring devices to see exactly how much energy is transferred to heat at the shock.
Yep that’s exactly the point. If you exert a given force for a longer period of time (because of longer travel with the suspension bobbing), but the cadence sensor still reads the same RPM, then the reported power is the same, yet real power is higher (force times time). There’s just so many variables and no way to measure.
and to AlistairSH: “Because if the rider is making 300W, he’s making 300W.” But we don’t know the rider is making 300w, the rider is pushing the cranks and all we know is that 300w is measured at the crank. So far everything I’ve read/researched points to the fact that suspension efficiency affects prior to the power meter, and my reasoning above is why. There is a pretty clear theory as to why that is.