11-50 SRAM Eagle cassette - trainer difficulty setting?

Hi all…

Newbie here - just bought a Wahoo Kickr to do some indoor training during the dark Scottish evenings!

I’m a mountain biker, and have hooked my old 2017 Stumpjumper onto the Kickr. The Stumpy has an Eagle X01 groupset, so I’ve bought the Eagle NX for the Kickr as it’s not got an XD driver. The indexing is slightly out, so I’ll have to tweak that before some real use. Bummer - I hoped it would just be a straight fit and go.

I had a brief blast round, and realised that I was pretty much in my top gear all the time on flats. The 11-50 cassette is generally designed for steep hills, and is quite easy to spin out on flats and downhills.

I wondered if there was a way of changing some settings to give me a bit more resistance, and see there is a ‘trainer difficulty’ setting. I’m led to believe this is an adjustment for different gear ranges - but doesn’t effect flat riding?

Is there a way of adding resistance so that I’m not spinning out on flats? What ‘trainer difficulty’ setting should I be using to help make my gearing more useful in Zwift?!

Thanks in advance…

Hi @Peter_Rattray

Welcome to the forum.

Trainer difficulty won’t change flat roads. Best option is a bigger front chainring.

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Well you could add 50 KG to your weight…that might slow you down a bit. If you have not done already, once into the ride, go to Menu/Settings and move slider all the way to right (100%). @Gerrie_Delport is correct, no help on flats but it will add a bit even at 1-2%. Do not ride flat routes.

Yet a third way to tweak your resistance is to manually set your Functional Threshold Power setting artificially too high. You’re tricking Zwift into thinking you’re stronger than you are, and because you have a smart trainer, the resistance will be increased.

Fudging weight and bumping FTP come with downsides that impact other people if you’re racing. Don’t do either if you’re going to race. If you’re sticking to free rides, workout, or non-race group rides, it’s probably fine.

Pair the kickr a power source in Zwift, but don’t pair the smart trainer / resistance control. Use the Wahoo mobile app on your phone to manually set a high resistance. Obviously you won’t get automatic resistance changes on hills. Or, always ride up mountains.

Thanks for the suggestions…

I was going to try one of the specific MTB training plans (Dirt Destroyer), so I’ll see how my bike copes with that first. Hopefully it’s got lots of tough climbs that’ll save me having to do any changes to setup or settings.

I’ve no intention of racing, so tweaking the FTP might be an option for road cycling.

If I move the trainer difficulty to 100%, it’ll make the climbs tougher, but I guess I’ll just be freewheeling downhill?
I wondered if moving the slider the other way would be better - giving me better gearing for downhill, and going up would still offer more resistance than flat?

A front chainring with more teeth could be an easy fix… although it kind of makes the bike unusable for real life use, as most of the riding I do on it is hilly!

A cheap road bike or ‘hybrid’ is probably an option too… however this is a last resort - more for storage / space reasons than cost!

If you are spinning out on the flats you will spin out going downhill.

Remember that when going downhill, Zwift halves the incline percentage…So if your slider is at 50%, 10% gradient will mimic 5% uphill but 2.5% downhill.

Also note that just because 0% is indicated on screen, fractions of a percent are lopped off. I do not know how much actual FLAT there really is. When the slider is set to 100% I can actually feel differences in 0% indicated grades (Saris H3); some easier and some harder. I now run 50% to save my trainer from overheating on uphills (big guy that grinds…not the best for DD trainers).

I think if you can add a bit bigger chainring without mucking up your chain (or stay off the 50) that is the easiest way to go.

Out of curiosity…how much time, IRL, are you actually using the 50?

I’ve now re-indexed the bike to run on the Kickr. Took considerably longer than expected, as it was so far out I had to adjust the cable tension and start again!

I now have smooth access to all the gears, so should be able to actually run in 12th for a bit and see how it is.

My 50T cog is used IRL probably a lot more than you’d expect. A lot of my rides have over 1000ft of ascent and are 15-20 miles. Last weekend I was tackling over 20% gradients in a climb that seemed to go on forever! Crawling up loose rocky Land Rover tracks in 1st gear was the only way to do it… whilst trying to keep the nose down!

The chainring I have is 32T, and I’m not sure how big I can fit? I can’t imagine 34T being a huge difference, so I’d have to see if a 36T fits.

I couldn’t get it to work with my Pivot with Sram xo1 Eagle. My front chainring just wasn’t big enough for good enough gearing on flat roads.

I bought a cheap road bike

Your best option is to ride in erg mode if you really insist on using the mountain bike

I didn’t want to put a bigger chain ring on and mess with my mtb but I also don’t think I could have gotten close to the gearing I use everyday on the road bike. I definitely couldn’t see enjoying races with mtb gearing.

I’ll try working with the MTB for now and see how I get on… as I really don’t have the space for another bike!!
At the moment, I have no intention of racing. The Kickr / Zwift are just a means of me keeping my legs moving when it’s too dark / miserable to get to the trails in the evenings.

I’ve read a few people saying to use ERG mode - but what does it actually do? I enabled it in the Kickr settings app, but it didn’t seem to make any obvious difference?

What you are experiencing now is basically how I got in to road cycling. I converted an old hardtail to use as a commuter to try to improve my fitness for mtb’ing. The gearing was terrible for the roads, running out of gears way to early. So I bought my first road bike… I now have four.

same here. started off on mtb and rode in the woods a lot. tore my acl and was stuck on the road for a while, and eventually realized that 30 miles fighting knobby tires and low gearing sucks! now i mostly ride on the road, and zwift does a pretty solid job replicating riding on the road.

ride your mtb on the trainer as long as it stays fun!

In erg mode you set the power you want to ride at and the trainer adds resistance until you get to that power or removes resistance if you are above that power. So you don’t use any gears. But you also don’t have the resistance change with the road.

I also had no intention of racing. But it’s one of the best workouts on Zwift.

Yeah - ride it as long as it’s fun. It wasn’t fun at all on my mtb.

I went out on my other MTB yesterday… which has the same 11-50 cassette, but a 30T chainring.

I struggled to spin out, even on some downhill (fire road) sections. I could pedal up to about 30mph. Above that was a struggle. I could quite happily ride that on the road for most sections - obviously big downhills would be freewheeling.

Why is my 32T bike spinning out so easily? If anything, it should be harder than my 30T bike. Is it down to the weight of the flywheel on the Kickr?

I still haven’t really had a chance to spend any real time on the Kickr, and am away for a school holidays break tomorrow. Interested to try the Dirt Destroyer training plan when I get back and see how that is.

My mtb with a 32 front works fine on the road but horribly in Zwift.

Dirt Destroyer was ok.

If you hit 30mph on that setup your cadence would have been 130, and as you say you can happily ride that on the road, then were always going to spinout in Zwift (which is about 125 rpm on 32t chainring) which doesnt have air resistance.

I’m primarily a MTB’er and bought a 2nd hand cross bike for a 3rd of the price of an xx1 cassette, primarily because I kept spinning out. Zwift is based around road bike gearing and the only place MTB gearing is going to be useful is a couple of the 15% plus inclines. You’ll be able to go to at least a 42t chainring if you know enough about chainlines, chainring offsets and your mtb bikespec’s but you will likely still spinout depending on how much power you have.

And whilst you say you wont race, if you enter a group ride, its a race. If you are just cruising click off the routes and come across other riders, you’ll have a race. If your ride has a start and finish, its a race. Not many people I know can resist the urge :wink:

MTB’s are not made to go fast.

Look at the calculated wheel speed with different gear ratios at 100 RPM

With a 52 chainring you can get 42Mph
With a 30 chainring you get only 24Mph

I’m probably happier to step up to a 42T or bigger chainring on the front than buy another bike. This one will probably be unused for most of the winter anyway, so I’m as well using it for something.

Problem is I don’t know how to change a chain ring! Assume I’d have to put more links in the chain too - but I do have about 6 spare links from the one on my other bike.

I guess the next site I visit will be YouTube, with the search ‘how to change a chainring’!

The one that’s on it was part of the SRAM Eagle X01 groupset. I’m sure a quick google will tell me the offset of that - does it need to be replaced with the same offset?

It may be that eventually I have to bite the bullet and buy an ‘indoor racing’ bike… but I’d rather explore the avenues of using my spare MTB first to see if I can work with that.

If its X01 Eagle crank, then you need an 8mm hex/allen key to undo the crank bolt. That will allow the crank to be removed. The chainring will be using direct mount so 3 torx screws to undo.

Offset is likely either 3mm or 6mm. If you bike is boost (148mm rear axle), then its boast and 3mm. But note that the purpose of the offset is to get a proper chainline (straight line from chainring to middle cog on cassette). You could easily go 6mm offset giving you more leeway to go bigger with chainring , it just means that in 50t your chainline is a bit nasty and wont like back pedaling (you would be very unlikely to use 50t even with 42t chainring in Zwift so no problem).

Yeah you would likely need new chain but not necessarily - plenty of YT vids to show how to get this right.

I would really hesitate to spend too much money trying to get it to work given that you’re probably going to get a new bike anyway in the future. It’s just so much more pleasant on a road bike. And frankly Zwift should tell you that. It’s a little false to advertise that you can use it with a mtb.