Tire choice impacting power with Wahoo Kickr Snap?

Hi there,

I’ve recently joined TR and so far am really enjoying the more structured approach to training. I’ve just finished week three of the Sweet Spot Base, Low Volume I training plan.

I use a Wahoo Kickr Snap (the model with external LEDs near the flywheel) and had up until today been riding with just my standard road tire on the back wheel (GP 5000s 25mm clinchers to be precise). Realising that my indoor rides have been eating this (very expensive) tire rather quickly, yesterday I decided to change the tire to a Tacx indoor trainer tire (23mm clincher). Today I did Eclipse, which I was expecting to be really hard. However, I actually found it much easier than Carson from a couple of days before. And indeed, my HR stats were higher for Carson (avg HR 151, max HR 177), than Eclipse (avg HR 149, max HR 165). Whilst I’d love to think I got dramatically fitter in the space of a couple of days, I doubt that’s the case.

With both the old GP 5000s and the new Tacx tire I would inflate to 110 psi and turn the knob on the Kickr Snap two full turns. I then do a spin down via the TR app on my ipad ten minutes into each workout. The spindown time when using the old GP 5000s would generally be around 30 seconds, and this morning with the new Tacx tire it was around 17 seconds. Based on the information on Wahoo’s website though, I didn’t think this discrepancy mattered, as long as the tire pressure and roller tension was correct (though of course happy to be told otherwise!). I did notice previously that there would be a slight “squeal” when starting each workout with the GP 5000s, but not enough to cause any tire slippage. I should also say I ride my workouts in erg mode and my gear selection was the same for both workouts - small ring at the front and middle of the cassette.

I think that the new tire has made things slightly easier but would be grateful for views from others as to whether this is correct, or if there might be something else at play. I think my next step will be to do a ramp test before my next scheduled workout to ensure my FTP is accurate (I did my first ramp test three weeks ago on the old GP 5000 tire). Ultimately, what I care about is consistency and ensuring that my training stays effective and in the right zones - if my power is higher with the new tire then I don’t want to shortchange myself through workouts that are too easy.

Of course, any advice would be hugely appreciated.

Many thanks,


^^^^^^ This. ^^^^^ You’re not actually worried about absolute accuracy in power, you’re worried about setting your (indoor) training zones consistently. Do a spin down, do an assessment, go forth and improve.

I’ve had a trainer wheel for so long, I can’t remember any change in “power” between my road tire and my trainer tire (8 years or so at this point?).

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Thanks @kjdhawkhill! Did a ramp test last night. FTP went up by 17 watts from just under four weeks ago. I doubt that’s all fitness gains but it doesn’t matter much as you note. Now we go again! :slight_smile:

Something that I have noticed when my turbo tyre nears the end of its life is that the feel of the trainer is not the same. I’m certain that my legs tire a bit easier or at the least the RPE is higher. You then put on the new turbo tyre (i also use a tacx 23mm) and the whole experience just feels so much better. It’s almost night and day.

The functional rolling will most likely be changing with that wear. Spindown calibrations “should” take care of that, but I wonder how true that really ends up being in practice.

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I think different tyres take longer to warm up, perhaps do your calibration at the end of the workout to ensure the tyre is fully warmed up, Unless you are removing your bike from the turbo I don’t think it matters if you don’t calibrate every ride as long as your tyre pressure is consistent.

Thanks all. I did Tunnabora tonight. It felt easier than ordinary sweet spot work (even with my new FTP). My HR was around 10-15 bpm lower during the first two intervals than similar sessions last week (e.g. Ericcson, Carson), so I upped the intensity 5% for the last three. Will see how it plays out with other workouts later in the week.

The Kickr Snap is wildly innacurate in general.

Speaking from experience!

The calibration before each ride does matter on wheel-on trainers (or at least on most of them). One should not leave the tire pressed on the roller for a long time if the tire doesn’t move, as the constant pressure on one spot may, and very possibly will, damage the tire / wheel. If I remember correcly, for Kickr Snap it’s instructed that the best calibration is achieved when the spindown would is performed after about ten minutes of riding, ie. when the trainer has warmed up.

I would say it’s quite accurate as long as the tire pressure and the roller’s pressure against the tire is right, and that the trainer is calibrated as instructed.

I understand the text book answer is, 'if you calibrate it regularly you’ll be good", but trust me there’s a lot of evidence that disputes that.

A calibration will help but the unit can still be way off.

I jumped from a Kickr Snap to a tacx Neo 2 a year ago only to discover my ftp was about 60 watts lower than I had been led to believe.

Ok, of course there can be differences between units.

As I switched from Kickr Snap to Kickr as a handcyclist this year, I got only 2W drop on my FTP using the Kickr. This with significantly lower FTP compared to the regular cyclists (130W-ish for me).