MTB on trainer gearing issue

So i have been using a old bike with a triple chainring on my K.kinetic road machine (dumb) trainer. I just put my mountain bike on the trainer as I am soley a mountain biker and wanted to train with what i use outside.

The problem is that my MTB has a 30T 11x46. and while this is perfect for the trails, i am about spinning out in the hardest gear just to hit my FTP on the trainer.

I reset the wheel circ. setting in TR when i switched, am i forgetting something else, or is this just how it is? Should I crank down the resistence setting on the trainer, re-ramp test, and move forward with an altered lower FTP #?

Since you are using Virtual Power, the reported power in TR is simply coming from the wheel speed as registered from you speed sensor, and the wheel size you set in TR. That is all the control you have for getting “reported power”.

You might be able play with roller pressure on the tire and/or tire pressure, but it is not likely to have a the desired impact on the overall speed and top end power that you seek.

  • If you drop tire pressure and increase roller pressure, the force on you will increase, but the wheel speed with decrease, which directly decreases the Virtual Power data.

All that said, the first thing you should do is setup the bike and trainer as recommended (max pressure for the tire/wheel combo, and then proper roller pressure via the trainer mfgr.) Then perform a new FTP test (your choice of method) and use that new FTP.

If you are trying to ride to the FTP you had with the other bike, and have different tire size, etc., you will be getting incompatible data.

The rule is: If you change any part of your power measurement method, you should retest.


Thanks. I figured thats what i needed to do. Just didn’t really want to, because it will lead to a FTP dip… and well ego


  • (picture that scene in Fight Club where Brad Pitt does the “YOU ARE NOT YOUR…” monologue)


  • Take if for what is it… a data point used to set training zones.
  • It does not define you as a cyclist.
  • There is so much more to your identity and abilities on a bike.
  • Ignore the tendency to measure yourself against others with a such narrow metric.

Like Chad said, definitely do another FTP test. Once you’ve “recalibrated” your virtual power, it’s possible that your gearing may be such that you really can’t spin the trainer fast enough to reach higher target wattages. In that case, I would suggest getting a larger chain ring (34 or 36) just for trainer duty.


Dont get frazzeled bro!! Recalibrate and take Chad’s advice. I made the change from a roadie to my MTB on the trainer and it has made a lot of difference. I’m running a Sram setup 32t / 10-50 and I’m a little guy 5-7 and 150lbs and can hit 650 watts when I’m sprinting setting down. What are your cadence numbers??

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i’m 150lbs as well. I hit my FTP number spinning like low 90sRPM in my hardest gear, pretty fast for me and I would hardly ever pedal that fast out on the trails.

Seems like i’ll be spinning like crazy to do any intervals. My natural cadence is low-mid 80s. I’m sure some higher cadence work will benefit me but I could hit higher watt #s pushing a harder gear.

maybe a 34T chainring for the trainer as Notso suggested may be a good idea. I don’t want gearing to be my limiter.

If you are running a 30T front right now I would jump to a 32T…in my opinion moving to a 34T front would be a HUGE jump and your cadence will crash to the 70’s …

I wanted to do the same as you, train on my XC bike as thats all I ride. I set it up on my (dumb) Road Machine and there just wasn’t enough gearing for it to work I guess?? (11-42, 32T). I was in the smallest cog already doing Sweet Spot…nowhere else to shift if the prescribed wattage increased. I ditched that idea and went back to my old 3x7 hardtail on the trainer.