I’m using a single speed bike for the turbo trainer - 1x with a modded cassette on the back using a broken derailleur as a tensioner.
I’ve been using 39 x 18 so far but the front chainring is getting noisy (it was worn anyway as I built the ‘bike’ using spare parts)
I’m wondering if there is any benefit in changing the gearing as I now need to buy a new chainring anyway.
I haven’t found the bottom or the top of the range on trainer in the past year (it’s an Elite Drive II)
I know that a bigger front ring means less transmission power loss but in ERG that doesn’t matter. It might also make the chain last longer but it’s always clean anyway so that’s probably marginal too.
I have found that I prefer the trainer feel, even in erg mode, with a ring in the 44-50 range. Too small and my Kickr trainer just feels like pedaling through mud at all times.
I use my 34 ring and a middle cog of an 11-28 cassette. I find ERG mode changes Watts quicker for intervals and responds quicker to cadence changes than when using a higher gear (larger ring / smaller cog) because the flywheel isn’t spinning so fast. There are rare times I will shift to facilitate big cadence changes, and those associated with going between sitting and standing, but I could get by fine without shifting if running single speed.
Interesting question, and I wondered about this recently. My default erg is big front ring (52) and probably the 14T or 15T in the rear… because that’s the quietest.
A couple weeks ago I did a virtual iTT that was about 7minutes and mostly flat. I stand up indoors for better power over that duration, and I was in the biggest gear (11T) a good portion of the time, and otherwise in the 12T. Over those 7min, my pedals recorded the effort as being 6W higher than my trainer. After 10min of easy pedaling, I did another 4min erg mode at the same power, and my pedals recorded the effort as being 1W less than my trainer. I don’t know if the difference was from different chainline & gearing efficiency, or simply an erg-mode difference. The 52/11 combo was slightly noisy, but not bad. At some point I intend to test if it’s erg vs. normal, or due to different gearing.
If you are running singlespeed you can literally run it up until the point the teeth on the chainring no longer hook into the chain. When you do need to replace the drivetrain you might as well go for a big chainring 50+ with an equivalently large sprocket on the back to give a similar ratio to what you are running now, if you find that ratio suits you and your trainer in erg mode.
Rings and sprockets with prime numbers of teeth will wear the most evenly eg. 51, 53, 17, 19, 23, 29. If you wax the chain as well it could easily last 25,000km plus.
Thanks all for your contributions. It sounds like I’m not missing out on anything experience wise, but ‘you don’t know what you don’t know’, and as my setup doesn’t have the ability to change gear, on the fly testing is limited.
Just took another look, it’s actually 39-20. @JonGreengrass your comment about prime numbers is a very good point, I ride a 47T chainring on my fixed gear (outside) for this very reason.
I guess another consideration is ‘flywheel speed’ and its effect on how quickly TR and the hardware can change on intervals. I’m finding a bit of a lag at the start of intervals.
My front chainring is a too-worn-for-the-road dura ace 11 speed chainring, but flipped the other way around as the teeth aren’t as worn that way, and using 1x conversion bolts to secure it. Oh, and an 8 speed chain, as I figured why not have a wider chain for this application.
So, I’ve kept the 39T on the front for now, but swapped the rear for a 23T. I didn’t say that my rear sprocket setup is a single sprocket removed from a cassette that I separated, and I’m using a load of the Shimano plastic spacers either side of it. The RD has a very short length of cable with the barrel in the adjuster that sets it in the right position.
Anyway, drivetrain is a little quieter now, and as its now a prime number setup, I’m going to let it run until (if) it all wears out.
Interestingly the interval starts are a little smoother than they were, so I guess it was slightly overgeared before.
To bring this to a better conclusion, I decided to see if TR support had any wisdom. They did. (Pasted below).
I’ve now fitted a brand new 36T chainring and it works just fine. I’ll be back here in about 5 years time to tell you all how long the chain lasted.
There isn’t one optimal gear ratio, but the current setup you have should work well. Typically, we recommend using the middle or small ring in the front (which would be a 39t on a standard road setup) and a cog in the top half of the cassette block (which would typically be 19t-36t), so your current setup matches this recommendation.
As long as you are able to pedal at a comfortable cadence in Z1, avoiding the ‘wattage floor’, this gearing setup should work well. Since ERG mode will take care of the resistance, the only thing you need to account for is being able to pedal at the minimum resistance.
Unfortunately I tend to spend a lot more time on the trainer than I’d like and my experience has been that which gearing you use makes a pretty big difference because of the flywheel speed. Using gears 1-4 in ERG mode have much more of a climbing feel where you really have tension through the full pedal stroke like you do when climbing because the flywheel is spinning much slower. Gears 8-12 in ERG mode have much more of a flat land feel where the top and bottom of the stroke don’t require much because you’re essentially coasting on the speed of the flywheel. That said, I’d say it depends on what you want to target.
Sorry I can see how that’s misleading. I was referring to 1st gear as the easiest and 12th as the hardest. Either way I’m sure you get the concept that even though ERG is creating the level of resistance you’re feeling, what gearing you choose makes a big difference with how fast the flywheel is spinning and really dictates what the feel of the pedal stroke is. IRL doing 300w @ 100rpm on a flat feels different than it does on a climb. That’s what this is doing as well.
