Physics of rollers/rock n roll trainer

So I’ve been wondering recently above if using rollers or a rock n roll trainer makes sense.

Usually the perceived advantage is that they help with the stabilization and balance.

I question if this is practical because in the real world you would be moving forward while turning your legs. Let’s say you are going hard on a flat stretch of road doing like 350 watts. That would be approx 35-40 km/h. The forward momentum would help you stay stable and balance is not really an issue.

On rollers however at 350 watts you are still going 0 km/h so a lot of balance work is involved. I have tried a friends kinetic rock n roll a couple times and it seems you are moving side to side way more than on the road.

So do these type of trainers actually make sense given the differences on the road?

I am happy to keep my KK road machine and do some gym work and swimming to work on the core.

I am likely the most biased person in the group related to this subject (as the leader of rocker plates and motion platforms for training), so take my opinion with a massive grain of salt.

  • Having said that, I also take a very realistic approach to reviewing the many aspects of motion for trainers. I know they aren’t perfect, and will not be for everyone. But i see far more benefits to be gained when looking at the full picture, as compared to fixed.

The points you raise are interesting. But if we oversimplify and offer motion or no motion as two pure choices, I see motion as a clear winner.

  • There is nothing natural about riding a bike that is locked in position, if you care about riding outside.
  • Seated is close, but still not as realistic as many want to think. Watch a buddy from behind on a road without them knowing. You will see a lot mot movement than they realize. It is subtle shifts even when in a straight line.
  • Then add in slight lane changes for positioning and eventually cornering. We move the bike under us more than we keep it perfectly still and upright.
  • As you note, straight line stability increases with speed, so the bike is more resistant to lane changes. But we are still leaning the bike for all position changes left and right.
    When you then consider what happens when standing, there is no contest. Standing for regular cadence climbing efforts leads to a very different upper body motion when on a fixed trainer.
  • It is totally natural to slightly rock the bike back and forth when standing outside. Our upper body stays center in space, roughly over the contact patch of the tires under the rider.
  • Watch the same rider fixed inside and they adopt an awkward sway at the head and shoulders. It’s totally unique and not at all like riding outside.
  • Now bump that up to a standing sprint and it is even worse while fixed. Just plain wrong to me.

I think we have a way to go in search of the best feel and motion. But I feel that we are improving and will get there some day. Some in my group and elsewhere have tried rockers and disliked them or been indifferent. But the wide majority I have seen (admitting to total anecdotal evidence here) have been more than happy with the rocker and state they will never go back.

I find that my rocker plate increased my comfort on the trainer for long rides. This is reason enough to use it. I think the rock’n’roll trainer is going to be more similar to rocker plates than rollers.

IMHO, rocker plates are the answer to improved comfort on the trainer, especially for longer rides. For rides under 90 minutes people may not notice a difference. Do 3-5 hours, and I’d be surprised if the vast majority of people didn’t think rocker plates improved the experience.
I don’t think they are the answer to ‘make indoor like outdoor’, especially regarding out of the saddle efforts.
It all depends on what you want to get out of it.

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At the risk of hurled tomatos for being an Inside Ride evangelist, I hafta evangelize.

I have a KKRM, and when I decided to upgrade last fall, I determined that I wanted either rollers or a trainer that rocked (either by design or with a rocker plate).

I ended up getting these.

Though I’ve never ridden a rocker and can’t compare from experience, I can say that I love the engagement these rollers provide. There’s no collapsing over the bars at the end of an interval, and the forward-and-back gliding both is pleasant and keeps you smooth (transitioning in and out of the saddle and “humping” while seated will both show up as movement in the rails). I also noticed my abs being a bit more sore after a workout vs. the RM.

As an added bonus, I don’t have to worry about exacerbating the delamination on the inside of my DS dropout, which I suspect came from clamping in the RM, but saying that is just asking for more hurled tomatoes (unless @mcneese.chad wants to back me up on that). :rofl:


Agreed on the fun and engagement of motion rollers. I moved from simple wind trainer to Nashbar rollers for something new to try. I soon found the motion rollers from InsideRide, but couldn’t afford them. So I made the DIY version after researching them.

They are the closest reproduction of real riding that I have tried, bar none. Then I wanted to move on to a smart trainer, and ended up with a CycleOps Powerbeam Pro. Great trainer, but the lack of movement after so much time on the motion rollers was terrible.

I started another round of research on making a smart trainer into a Rock and Roll style trainer. I ended up making my first rocker plate around December 2015. After making several versions and testing dozens of springs, I got the feeling wanted

It has nearly the same freedom as my rollers, but I don’t have to worry about falling off at the end of those massive anaerobic efforts when you want to collapse.

As to the dropout wear, and related bike stress, I think a rocker will likely reduce the wear and risk when compared to a rigid setup.

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Great feedback all, thanks!

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I’m a big fan of the Inside Ride E-Motion rollers. They’re silky smooth and with the resistance unit set to Level 2, it feels like riding the road and gives me all the range I need for any TR workout by just shifting gears.

Here’s a post where I shared my reasons why I like rollers over fixed trainers:

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These points all make sense but like Shane Miller said on one of his videos, all the rockers he’s seen tilt the wrong way??
Have you seen this?

Yup. And I have my video that shows proper rocking direction.

I feel the majority of the issue is setup and usage. But I also know that doesn’t solve the issue for everyone.

Additionally, I am not a unicorn, as there are others who use rockers with proper timing.

We don’t have them “perfect” yet, but they can be used “correctly” in some cases. Part of my continued designs are aimed at better solving this issue.

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Yeah that looks better. That other video I linked seems to mechanically control the rocking with steering.

Indeed, and it’s one reason I dislike the IR fork stand. I just don’t think rocking should be that directly linked to drive the rocking direction. We do turn the bars a bit when we do a standing motion outside.

But I find it seems far less than the way the IR fork stand is designed. I like the pure concept, but I don’t think their execution seems right. I have not ridden it and could have a different impression after riding it, but I doubt it.

Yeah I couldn’t find any other comments on how well the fork stand works.

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Naturally, when you ride outside, your bike will tilt side to side and steer at the same time. You can’t ride without steering.

The problem with rockers and why so many do it wrong is the front wheel is locked in place and you end up tilting the wrong way. Even if you closely watch the video Chad linked, you will see a slight steering motion.

There is also that side to side motion that no stationary trainer can mimic.

IR looked at this whole motion differently and created this floating design to mimic what actually happens when you ride outside. So you got the side to side tilting and side to side motion.

It’s not perfect but found it to be pretty decent for an indoor ride.

I’m not sure that I agree about Inside Ride being so realistic. I rode a set for 5 years and I found them way better than standard rollers in terms of not falling off and things like that. However, I wouldn’t call them very realistic because the still suffer from the extreme lateral sensitivity to any motion of the bars or bike. This is because there is no lateral friction between the tire and roller nor momentum of the rider. You have to be super smooth compared to riding outside or you will be off the rollers. Same if you are really flogging yourself and dying during an interval. I stopped using them because I found that sensitivity distracted from the training experience. I have never tried a rocker plate but based on the videos they look way more natural.

Most of that stability does not come from “the forward momentum”, it comes from the precession moments resulting from the spinning wheels. Think of a bicycle as two spinning tops mounted sideways; those two spinning tops resist any angular input normal to their axes. A set of rollers spins both wheels, and therefore reproduces correctly the stability of a bike as far as wheel intertia is concerned. Of course, it does not do so as far as forward momentum is concerned (the moment of inertia of the roller system gets substituted to the rider + bike forward momentum), unless a pretty large and/or very high-gearing flywheel is used.

What really makes rollers twitchy is the small diameter of the rollers, which creates a set of steering forces that differ a lot from those experienced on the road. Those who have used treadmill-based bike trainers can attest that although the bike is not moving, you do not get the twitchy handling experienced on rollers, because the tire is rolling on a flat surface, as on the road.

The position of the front tire on the front roller has a large influence on the handling, by the way. The steering stability gets affected by moving the roller axis ahead, in-line with or behind the front wheel axis.


I don’t know about all these theories on rollers. If anything the rollers are too realistic. I have an older set of E-motions and to me they steer as natural as the road. But the problem is they are too narrow to ride hard without weaving. It’s like riding in a slot in the pavement…you’re gonna hit the sides. The slower you go under heavy resistance (climbing out of the saddle) the more swervy it gets. And some say they can sprint on them but I just can’t go as hard on the rollers without banging into the side wheels and bouncing around, so your output is limited on Zwift. I’m always looking for something better, but I’ve tried the Kurt RR and didn’t like it. I assume all these rocker plates are the same?

When I heard about the fork stand it made sense to me as one notch better than a rocker, but there’s limited first hand comparisons between them on the trainer forums.
They both claim to lock the bike in while still allowing it to move, but IR obviously doing it totally different and pushing the fact that the tilt is easily controlled. They also have the forward and back motion that’s built in to the E-motion base, so given what’s been posted, I’ll probably go ahead and take a gamble for $195. If it works as advertised I’ll be able to switch between a roller and a rocker.

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I have rollers, and I like using them. However, they have so little resistance that I can’t really go over 200 watts. Great for recovery and pedaling work, not great for actual work.

If you have aluminum drum rollers, its possible to add magnetic resistance to them. Several DIY vids on YouTube for it.

I modified the CycleOps resistance unit to work with my Nashbar rollers. I even added manual control via an old MTB shifter and cable.

I can get plenty of hill and light sprint resistance.

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There are “elliptical” rollers - the mathematicians will not be impressed as there is really no ellipsis to be seen there, but they have a larger diameter on the edges, which create a recentering force that’s a lot more gradual than rollers on the side. Never tried them, so I can’t say if that works, but in theory it would. Most roller users will tell you that the “narrow road” feeling you describe is what makes rollers good in developing handling: once back on the road, you can hold your line without swerving around.

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One thing I noticed recently is that tyre pressure has a huge influence on the power produced in my rollers
I would say that is because the contact is not done in a flat surface, a few psi might change the contact area a lot and friction also changes hugely.

With 23 tyres at 120psi, I cannot get more than 400w even in 53x11 gearing.
However, at 90 psi, I can reach 600w and still have a few cogs to go further.
I just cannot get there while sitting.