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  • Bike fitness gurus: answer me this…
  • vlad_the_invader
    Free Member

    I’m experimenting with different turbo trainer apps and noticed something odd with Tacx training app which doesn’t seem to use ERG mode with it’s videos

    I was following a climbing route which had multiple sections of over 11% (peaking at 15%) but most of the route was 6-8% range; some sections were less and it even descended slightly in one place.

    Apart from the brief descent, I was in my smallest gear most of the time and pushing out a pretty consistent wattage and cadence.

    Anyway, the resistance was pretty consistent (so maybe this is Tacx interpretation of ERG) but the relative speed up the climb was adjusted to “compensate” for the gradient (i.e faster for slight gradient, slower for steeper sections).

    So this got me thinking:

    I’m going on a biking holiday later this year where I’m hoping to bag multiple Cols over consecutive days. I’m not going to be troubling the pointy end of the Strava leader boards but I’m concerned about fatigue setting after a couple of days.

    Is there a way of calculating “effort” based on my metrics (my weight, bike weight, length of climb, vert climbed and gearing)?

    I’m curious whether a heavier bike (+ 2kg) with considerably lower gearing (30*40 versus 36*30) will result in less accumulated fatigue, even though climbing time is likely longer. Or is weight everything?

    (I’m not really interested whether I’ll get up the climb faster on a lighter bike – all things being equal, I would do but my knees might blow up before the end of day 2. I’m more interested whether maintaining a consistent power output means less accumulated fatigue even when I have to produce that power for longer)

    Someone’s bound to have thought this through and put a website with a suitable algorithm and someone on STW almost certainly knows!

    theotherjonv
    Full Member

    My understanding – ERG mode adjusts resistance so you have a constant power output. Certainly when I had a smart turbo and a subscription to Zwift that’s what it did; it would wind resistance on or off depending on the demands of the session (2 mins at 110% FTP etc.) and you just pedalled, it would adjust further for cadence so power remained the same. Didn’t matter where on the ‘course’ you were, gradient didn’t affect resistance because it was session not terrain led, although as noted you still went slower uphill because that’s what you do.

    To your other question. It depends. On whether you can climb in this terrain in 36*30 and remain in lower power zones for several days. Over a few days, or even long rides on a single day it’s usually accumulated fatigue that does me in. As per a thousand other similar discussions I almost certainly don’t eat enough as I’m going, hence deplete reserves that then cannot easily be rebuilt and then when the engine management light comes on…it’s limp mode home. I’m not you but in your case I’d be going with the low gear option, and if you don’t need it you’ve not lost. Walking up col after col because you’re knackered and are now finding you DID need it would soon wear thin.

    tjagain
    Full Member

    The way I see it with the slightly heavier bike with lower gearing you will use slightly more energy total to get to the top but that will be over significantly more time so the power output will be significantly lower to do the climb.  So it depends on your fitness and endurance

    For me I can output medium / low power outputs for hours and repeat this day after day but high power outputs for seconds and then take ages to recover . Others may be different but for me low gears and slow up hills is sustainable

    The biggest climb I did on my tour took me effing hours and it was a popular cycle route so loads of racing snakes came past me at much higher speeds – but I made it to the top and was able to do the same again the next day and the day after.  At some point tho a climb that a racing snake can do in a much higher gear / much higher speed means they are only making the effort for an hour whereas I was climbing for 3 hours which could lead to more cumulative fatigue.  It also depends on the cadence you like to use when climbing

    Long and short it depends but IMO you cannot have too low a gear for climbing.  You don’t have to use your lowest gear but its nice to have.

    didnthurt
    Full Member

    Volume is the key. Essentially try to climb as much as possible as part of your training, up the steepest climbs you can find. Always try to have at least one spare gear for when you’re knackered.

    I’d not worry about any other metrics that metres of ascent achieved.

    didnthurt
    Full Member

    I’d not be happy unless I was achieving at least 1000m of ascent in each training ride. I’d even try to get at least 1 2000m ascent ride per week.

    jameso
    Full Member

    I’m curious whether a heavier bike (+ 2kg) with considerably lower gearing (30*40 versus 36*30) will result in less accumulated fatigue, even though climbing time is likely longer. Or is weight everything?

    36×30, as in 36 front 30 rear? That’s a fairly high gear for consecutive Alpine days. Whereas 30×40 is really low, a good value gain for +2kgs. But possibly lower than an averagely fit rider would need if unloaded.
    Less weight helps equally but it’s just a fine tune if you’re talking 2kgs. Like having a 36T rear vs a 34T when the 34T was OK anyway. ime, gearing first then worry about small amounts of weight.

    I’m more interested whether maintaining a consistent power output means less accumulated fatigue even when I have to produce that power for longer

    I don’t know if this answers the Q because it’s over a wider range of effort than you’re describing but time:effort level is not linear, if you can work at an aerobic level you can ride for far longer and feel better the next day. The higher the % of time riding anaerobically the less time you can ride for in total and it drops off fast as your average HR / power rises. You’ll know how your fitness handles a number of ‘digs’ on a ride and you’d need to make a call on average pace and number of efforts. Remember how altitude will have your heart rate well up on normal too.

    DrP
    Full Member

    Is there a way of calculating “effort” based on my metrics (my weight, bike weight, length of climb, vert climbed and gearing)?

    Yes…
    In reality, what you want (in order to answer your question) is power data!
    This would mean power meter on crank or pedals…

    I guess you COULD backward calculate this buy saying “me and bike weigh X kg, and the climb height is Ym, and we want to do it in Z time…..”, but really, the only awy of managing this on teh fly is with power data.

    For example… I know i can climb Alp du Zwift in 58 minutes if i average 210 watts….
    I’m planning (kinda..maybe) a IRL everest attempt, and owuld want to stick to 210 watts…
    Of course, 250 watts would climb quicker, but i’d fatigue earlier

    DrP

    n0b0dy0ftheg0at
    Free Member

    Is this oldie but goodie http://bikecalculator.com/ any use?

    theotherjonv
    Full Member

    The higher the % of time riding anaerobically the less time you can ride for in total and it drops off fast as your average HR / power rises. You’ll know how your fitness handles a number of ‘digs’ on a ride and you’d need to make a call on average pace and number of efforts. Remember how altitude will have your heart rate well up on normal too.

    This – particularly for riders that shop at the far end of the clothing rack to your proper mountain climbing cyclist, just keeping going on steep climbs in a higher gear can cause me to redline, where a superlow gear would enable aerobic spinning (albeit at a speed where you can time me with a calendar). It’s then no more a matter of choice as necessity to go into the red, if you don’t have the spinny gear.

    For example… I know i can climb Alp du Zwift in 58 minutes if i average 210 watts….
    I’m planning (kinda..maybe) a IRL everest attempt, and owuld want to stick to 210 watts…
    Of course, 250 watts would climb quicker, but i’d fatigue earlier

    and if your threshold is between 210 and 250, at 210 you’re comfortable for hours on end, at 250 you’ve blown in virtually no-time. Even though it’s only nominally 20% harder, we don’t have linear engines in that way.

    ampthill
    Full Member

    and if your threshold is between 210 and 250, at 210 you’re comfortable for hours on end, at 250 you’ve blown in virtually no-time. Even though it’s only nominally 20% harder, we don’t have linear engines in that way.

    This is what I came in on to say

    2kg more mass is 4% more power at the same speed if you and the light bike weigh 50kg

    So for me it’s 2% more power 😳

    Low gears gears doesn’t have to increase the bikes weight

    vlad_the_invader
    Free Member

    Hmmmm, took a look at the bike calculator and it’s not giving me the info I want.

    Some more background: I weight 90kg and my FTP is around 300w. I have a couple of local sustained climbs between 8-11%. My lighter bike has 36f 30r lowest gearing and a power meter. To get up those climbs, I’m usually in that lowest gear and cadence is around 70rpm (I’d normally spin around 85rpm on the flats) and I’m putting out around 275-300w.
    That’s not sustainable for me.

    The heavier bike is a gravel bike which is why it’s so much lower geared but I don’t have a power meter on it and I haven’t taken it up the same climbs (yet).

    Ideally, that bike calculator needs input parameters for gearing and cadence so it could calculate likely time and power for a given climb…anyone know of such a tool?

    (Btw: I can’t swap the gearing of the lighter bike without a big outlay of cost as it’s got a short cage Di2 mech…and it’s a Giant so warranty would be void 😉)

    theotherjonv
    Full Member

    My lighter bike has 36f 30r lowest gearing and a power meter. To get up those climbs, I’m usually in that lowest gear and cadence is around 70rpm (I’d normally spin around 85rpm on the flats) and I’m putting out around 275-300w.
    That’s not sustainable for me.

    Like we said. You’re having to put out close to your FTP to be managing a 70 cadence on those hills. To go easier, – well the obvious answer is to pedal slower but that’s the next issue, most of us are built to pedal at somewhere around 80-100rpm ish (very ish) and go much lower or higher and you aren’t efficient either, unless you specifically train to do it.

    So you need a gear where you can pedal at an optimal rpm but in doing so only need to exert at say 230W. ie; a lower gear than you have.

    ampthill
    Full Member

    Ideally, that bike calculator needs input parameters for gearing and cadence so it could calculate likely time and power for a given climb…anyone know of such a tool?

    I think if you add in the sheldon brown gear calculator it will tell you everything you need to know

    Tell Shelton brown about your gears. It’ll give you speed in that gear at an rpm you choose. Then put that speed into bike calculator

    anagallis_arvensis
    Full Member

    I’d not be happy unless I was achieving at least 1000m of ascent in each training ride.

    Kind of depends doesn’t it, round here I’d need to do at least 10 climbs over say a 2.5hr training ride, it would become like interval training which will help the top end but not the lower (as much). For this sort of effort he has talked about (no idea of which cols or how big) you are looking at prioritising 20 or 30min efforts in training I would think, somewhere just under sweet spot. I am off to Majorca at Easter so 30-40 min efforts will be needed with the ability to climb up to 10% in zone 2ish when I want to.

    As for the op’s bike if you weigh 90kg, I wouldn’t worry about 2kgs on bike and take the easier gears.

    vlad_the_invader
    Free Member

    @ampthill

    I think if you add in the sheldon brown gear calculator it will tell you everything you need to know

    Tell Shelton brown about your gears. It’ll give you speed in that gear at an rpm you choose. Then put that speed into bike calculator

    Yeah, that’s what I needed, thanks:

    Using Sheldon Brown Gear Calculator to predict speed based on different lowest gearing and different cadence’s:

    Giant (56/36, 11-30 11 spd + 700c x 25mm tyres @8kg)
    90 rpm = 13.6 kph
    80 rpm = 12.1 kph

    Diverge (46/30, 11-40 10 spd + 700 x 47mm tyres @ 10.4kg)
    90 rpm = 10.6 kph
    80 rpm = 9.4 kph

    Using bikecalculator.com with Col du Tourmalet as sample climb (18.4km, 1324m climbing, averaging 7.1% and 90kg bodyweight)

    To average:

    13.6 kph (with 8kg bike) needs 301w for 82 minutes and would consume 5961 kJ

    12.1 kph (with 8kg bike) needs 266w for 92 minutes and would consume 5917 kJ

    10.6 kph (with 10.4kg bike) needs 237w for 105 minutes and would consume 6018 kJ

    9.4 kph (with 10.4kg bike) needs 209w for 119 minutes and would consume 5990 kJ

    So, the time difference between fastest and slowest theoretical speeds is 37 minutes but only a 100 kJ difference between the most and least “efficient” efforts….

    andrewh
    Free Member

    Can you put the lower gears onto the lighter bike?

    Garry_Lager
    Full Member

    30 cassette would be miserable in the mountains for a big man, vlad, it’s that simple. For a one-off pb effort, no prob. But sustained riding over multiple cols it is not the way.

    Shimano rear der capacity is very conservative and can comfortably be exceeded on 1x drivetrains. Not sure with 2x – I guess you could get a 32 in there but ideally you’d want a 34.

    theotherjonv
    Full Member

    So, the time difference between fastest and slowest theoretical speeds is 37 minutes but only a 100 kJ difference between the most and least “efficient” efforts….

    Not sure why that’s a surprise. You need to look at the definitions of work and power.

    The work in all cases is the same (actually not exactly because one set up is 2kg heavier – which is why the Diverge numbers are a bit higher. IDK why the two sets aren’t the same between the two – rounding errors or maybe they add some wind resistance or….. the diff is too small to really consider a difference)

    So work = force x distance moved. There is no time element to it. In all cases you’re moving you and a bike to the top of the Tourmalet. Whether you do it slow, or fast, you’ve done the same amount of work in the end.

    Power = work done / time taken. So, as is obvious, to do it in a faster time takes more power. But doesn’t change the work done.

    Your calcs are therefore all basically circular, because the answer is the same if you are trying to calculate which expends least energy. If you put in a higher (pro gear say – try 39-25). Speed and power will go up, work will be pretty much the same.

    What the calc doesn’t do, you have to interpret your efficiency in producing the power (or indeed, capability). Which as before – means pedalling with a cadence of 80-100ish, typically. And because we don’t have linear energy systems, in fact we have this dual aspect aerobic and then anaerobic system, you need to also stay within the limitations of your system capability.

    The work done / kJ expended is only a factor if the efficiency is the same. Back to the pro gear…. same energy output in the end, just going a lot faster and more power. Why don’t you do that? – because you can’t.

    [other example – drive a car 100 miles at a constant 50 miles an hour on the same road. Same weight moved the same distance = same work done. Do it in 3rd gear, then repeat in 6th. What happens to fuel consumption? Yet you did the same work??]

    Helpful suggestion – if you can’t move the gears over, can you move lighter wheels and tyres over? Do you need 47mm tyres, might sabe a few hundred g, not that that’s the major issue here. Which is that you’re fat and weak 😉

    BadlyWiredDog
    Full Member

    Just a thought, but you could always look at a sub compact crankset as a way of lowering the gearing without having to fit a mahoosive cassette. I thought about this when I was contemplating a post long covid Whitton last year and was hampered by ye olde Campognolo groupset on my road bike.

    I’d agree that you need to avoid going anywhere at or over threshold if you want to recover for mulitple days’ riding and the only way you’re going to do that is by running a bottom ratio low enough that you can climb at a relatively low level of effort.

    I think maybe you’re overthinking this a little. Whenever I go to the Alps / Pyrenees I simply take my normal bike and ride it. If I get obviously tired, I have a day off or an easy one. Your body can cope with it for a short period of time like a week, more problematic if you’re looking at three weeks plus.

    vlad_the_invader
    Free Member

    Hmmm, some food for thought. Thanks for the input.
    “Unfortunately”, the lighter bike is 11spd Di2 and the heavier bike is 10spd GRX so it’s not realistic to swap components around. And I’ve also been told by my lbs that the rear derailleur does not have the capacity for a bigger cassette (otherwise I’d try and put a 34t cassette in there).
    I haven’t tried this yet, but I’m assuming I could put the light weight wheels from the Giant onto the Diverge (and swap cassettes) which may save a little weight.

    Anyway, it’s early planning stages and I’m not sure what type of riding I’ll be doing other than the Tourmalet.

    tjagain
    Full Member

    Get some proper low gears man!   According to Sheldon at 80 rpm i would be doing 3.5 mph in first 🙂

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