Adjusting the Clutch Knob tension on the Saris M2 Smart Trainer

Goodbye to the Tacx Vortex

My Tacx Vortex packed up. I was a bit surprised. Five years it’s been turning round and round with various degrees of resistance and I’ve always taken it a bit for granted. Then recently, when trying to pair it to Rouvy, I noticed nothing was happening. No lights, no connection.

I was in denial for a while. When something has worked fine for 5 years then doesn’t, it’s a bit of an adjustment. After changing the power and plug and digging around with a multimeter, it was clear it really was dead.

I lifted the hood, had a google, and it looks like it’s a thing. A thread on reveals a few people with tantalisingly dead Tacx trainers. I don’t fancy prodding the PCB with a soldering iron – my soldering skills were never that good – but I might one day revisit this.

The R64 resistor gets a few mentions and the one on my PCB looks like after 5 years it’s decided to call it a day.

I was discovering how much I’d taken the trainer for granted. The Tacx Vortex is a really simple affair, with a straightforward lever that presses the roller against your back wheel. I liked it a lot. Smart Trainers are hugely variable in price and the Vortex hit a nice entry-level sweet point when I bought it in 2015, and now it was dead.

Or, more precisely, dumb. Clearly I could use it as a dumb trainer, like in olden times. But I was surprised how quickly I’d adjusted to, and taken for granted, having real virtual resistance, or virtually real resistance, as I slogged up an alpine pass in the comfort of my garage. I needed another smart trainer.

Looking for a new Smart Trainer

Time for another shock or two, or three. The Vortex was no longer available. And Smart Trainers are pretty expensive. Even cheap ones are expensive. And as we pedal virtually through the post-Covid apocalypse, they are very hard to find.

I was quite keen on a wheel-on trainer. Mostly because they’re a lot cheaper, but also because you can use it to road-test, or pseudo-road-test, an old bike. During lockdown I’d rebuilt two old steel bikes and learned a lot on the way. Mostly about the joys of trying to adjust a cup and cone Campag bottom bracket. And I was discovering that the best place to discover that you hadn’t adjusted it very well, was not somewhere a long way from home.

I bought the Saris M2 Smart Trainer. I wanted to stick with Tacx, but price and availability were against me. Despite many of the alarming reviews for the M2 I decided to take a risk. It was the only one around my budget, in stock, and available to pick up.

There’s a good review, or non-review, of the M2 by Jeff Whitfield on the website. I have to say my experiences almost exactly reflect his. He mentions adding the bolt action tube was difficult. My experience was identical. Initially I assumed that I was doing something wrong and I kept checking and re-checking the documentation until I was convinced I was right, and eventually it jostled in. It was in the right place but the engineering felt a bit rough.

Same story for the resistance unit. After many “this can’t be right” moments I tentatively tapped the bolt through the frame, having constantly checked the alignment and kept everything lined up. There isn’t a huge amount of thread to be engaged on the bolt and I spent a few minutes fruitlessly using a socket wrench turning a small amount of empty space mistakenly assuming I’d finally managed to get the bolt far enough along to engage the thread.

But I got there in the end. And then, the adventure really begins. The Clutch Knob.

The Saris M2 Smart Trainer Clutch Knob

It’s hard to find a review of the M2 that doesn’t mention the Clutch Knob. It is, as they say, a fine idea. In principle, you might add. But it scares me. So much tension in such a delicate looking piece of metal. So much so, that on my first attempt, I lost my nerve. I’d read so many reviews mentioning so many bent frames and so many clutch knobs not clicking, that I really didn’t want to end up with a bent 2-day old trainer. The last one the shop had in stock.

It was very frustrating. After spending a lot more time assembling the frame than I expected, and thinking I was finally getting somewhere, I wasn’t sure I wanted to risk turning, and turning, a yellow piece of plastic hoping, waiting and praying for it to click. What I hadn’t been able to find out from my searches was a ball-park figure for how many turns, how much pressure, would be required to get to the click. How much should the tyre be squashed?

One article suggested 2.5 to 3 turns, but that was for a black knob. The M2 was yellow. Did this matter? Another support article suggested the tyre should be squashed in about a 1/3 to get the required resistance, with the tyre inflated to just a little of maximum. And a thread on shows that I’m not the only one to be uneasy about the level of deformation or turning required.

Having lost my nerve and resigned myself to never knowing, and then discovering the joys of software calibration, I was feeling pretty dejected. Compared to the simple engagement mechanism used by the Vortex to apply pressure to the wheel, I was finding the M2 pretty inelegant. I visited the Saris website, registered the product, and put in a support ticket explaining my sad story.

Waiting for the click

To set things up I was using a 1983 Alan bike with a wheel and tubular of similar age. The tubular is pretty frayed but it would fine to test things out.

Alan Super Record with old tubular

Next after the Alan was to try it with my road bike with a dedicated Tacx trainer tyre inflated to the recommended 120psi.

Tacx dedicated trainer tyre

After my first failed attempts I decided to man-up and try again. But this time I decided to video my attempts so that I had something concrete to show to Saris.

The twenty minute adventure is available for viewing but you might have some paint you need to watch drying somewhere, so here’s my key discoveries.


  • Old tubular at approx 120psi: Start tightening clutch-knob (06:47).
  • Old tubular at approx 120psi: Clicks after 8 and a bit turns (08:27).
  • Deformation in tubular (09:34).
  • Old tubular at approx 130+psi: Start tightening clutch-knob (12:50).
  • Old tubular at approx 130+psi. Clicks after 6 and a bit turns (13:25).
  • Tacx trainer tyre at approx 120psi: Start tightening clutch-knob (17:10).
  • Tacx trainer tyre at approx 120psi: Clicks after 6 and a half (18:00).

So that’s between 6-and-a-bit and 8-and-a-bit turns. To me that feels like a lot of turns, even if the tyres are slightly under-inflated. I get that you need decent thunk of pressure to get that potential 15% of slope, but even so, it doesn’t feel right. Perhaps I could inflate the tyres a smidgen more and it’d bring the number of turns down but I’m not so sure. There feels like a lot of tension in that L-bolt. I’ve had one training session on the M2 and the jury’s out. Time will tell.

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8 thoughts on “Adjusting the Clutch Knob tension on the Saris M2 Smart Trainer”

    1. Hi Alex, I’m pretty happy with it. It was available and at an affordable price when I suddenly found I needed a replacement smart trainer. When I can afford it, I’ll go for a direct drive trainer. Perhaps the Tacx Neo T2 will drop in price in the spring and there will be bargains to to be had. But for the time being and until I can afford a direct drive trainer, the Saris M2 does a decent job.

  1. Thanks for this article- I had the same issues with installation and am wrangling with the clutch knob to no avail, so it’s somewhat reassuring that I’m not alone. I’ve tried pedaling it a bit without the “click” and the tension is already quite high. Not sure if this is for me, but wondering what your experience is on the tension once you had it all set up and calibrated.

    1. Thanks Michael I’m glad you found the post useful. Yes it was pretty unnerving at first but it’s all settled down for me now. In one of my email chats with Saris support they said you don’t really need to tighten it until you get to the click, as long as it’s tight enough that the tyre doesn’t slip, and then you calibrate it after. I found the calibration app on the iPhone pretty hard work although I believe you’re meant to give it 10 minutes or so pedalling to get things warmed up. I must say I never bother with calibration now unless I’m doing a race on Rouvy and then I usually do it. I had a couple of Tacx trainer tyres but they were a bit disappointing. I’m now riding a Vittoria Zaffiro and it’s fine. I’ve written about that in another post and there’s a few comments on that you might find useful.

      One thing I would say is that tyre pressure does seem very important. I have a trainer tyre and I inflate it to 120 psi. I’ve not done any organised test but I’m pretty sure that even a modest bit of under-inflation results in requiring more turns to get to the click (which I still find a bit counter-intuitive).

      But I’m pretty happy with it overall. It’s settled down and it’s fine for the time being. It was the only thing I could afford when my old one packed up but when I can afford it I’ll definitely get a direct drive trainer.

    2. What is the click you guys are discussing- when I turn my yellow knob it is a smooth turn- I am just wondering how tight the wheel should be to the drum and does that effect the performance- I found initially that the tire was slipping on steep up hills so I tightened it and that went away but now I fear it is to tight- they have some nice set up videos on line which without I would still be trying to put the thing together-none of the videos discusses tire pressure or proper tension

  2. Hi,

    I have the exact same issue with the Saris M2 – the yellow clutch does not click. Saris customer service mentioned the tire will be 2/3 of the way pressed in. I feel it would be way too tight in terms of resistance…
    I’m just not sure how many “turns” of the yellow clutch are required following the initial contact with the wheel. (1 turn? a quarter of a turn?)

    I also tried to calibrate my trainer with the Saris APP – unclear if it really works? I ended up biking for a very long time at 175W and yet the screen text continually mentions “coast, test in process” without any perceived end. The message only stops when I stop biking and then it mentions “calibration successful”. Is this normal?

    1. Hi Leanne,
      I can’t really add much to what’s in the post or in the related posts ( I’m afraid. How many turns? More than you’d expect – for me it’s about 5 or 6 turns. I use a dedicated trainer tyre and fully inflate it to 120psi and that seems to make a difference.

      I agree with you over the Saris smartphone app (I’m on the iPhone one). I rarely calibrate the trainer now because I find it so hard! I do the calibration occasionally if I’m doing, for example, a race in Rouvy, but I find the app a bit unpredictable and I find it hard to maintain the effort before it tells me to coast.

  3. I got my M2 not too long ago and was concerned after reading about people not getting the click and bending things. I ended up reading somewhere that you have to make sure you’re not pushing on the knob as you turn it. Pushing as you turn the knob makes the click later risking damage. Hope this helps others.

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