Why don't you just ride to the wattage you are capable of instead of adding weight to the equation.

254 watts is the same power whether you are 77Kg or 87Kg

if you have a power meter, this is irrelevant

if you don't, and want to estimate from climbing data, then this issue should be looked into (along with CRR and wind direction)

If where you’re riding is flat, Watts/kg is irrelevant what matters is watts/cda.

You should not ride to watts/kg - you should ride to watts.

In other words if your workout says ride at 250 watts for X minutes - you ride at 250 watts regardless of what your bike weighs. The fact you have a heavy bike just means you will climb slower that you would if you had a light bike. There is no fudge factor here.

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He who understands the WHY, will understand the HOW.

Do you know how well watts/kg trends with watts/CdA? Seems like it should track well, but based on how bigger guys treat me on rollers it seems to not track as well as i thought. Then again i was riding on flat and my +60lb friend was putting out 20% more power than me so not sure what to think

I think watts/kg maybe flawed. How about watts/BMI... 6'0" rider vs 5'6" rider both 150lb doing 300w must be taxing 6'0" guy more

out of curiosity, why would this be?

i'd think the 6'0" rider would be able to manage heat better...

Hill climb challenge, KOM attempt on a local hill, hilly road race........sure.

Flattish stuff (under 50 feet per mile)......I wouldn't worry about it. You sound like you're in the watts/CdA territory as others have stated.

W/kg was romanticized from the glory days of the super doped TdF contenders and timing their climbing speeds and estimating w/kg of them and competitors to gauge strategy and attacks. If the w/kg on an attack was over a certain number, don't follow. If it was under or at a certain w/kg, respond to the attack.

Not something I have to worry about.

It's largely become a peen measuring tool among us bench racers.

I agree with you in principle, but just so you know, the bolded part is not how it played out.

Sometimes it amazes me how many people don't read the OP, but just begin responding to posts midway into a thread.

Your question doesn't really make sense to me. Exactly what are you trying to figure out? If you are just trying to figure out what your raceday WATT output should be, that's strictly a function of your FTP in watts, not watts/kg. I'm guessing (like all the rest of us) that you have a WATT-meter, not a WATT/KG-meter. So, you are going to be getting a power reading in WATTS. Bike weight doesn't have any impact on those WATTs.

254 watts on a 45 lbs bike = 254 watts on a 14 lbs bike. Both require exactly the same effort level from you---One will just go uphill faster.

Am I missing something about the intent of your question?

Don't compensate. Only use your body weight for watt/kilogram FTP calculation. Both for outdoors and also for Strava/Zwift. Race day watts will be the same regardless of weight. If you're trying to hit a certain speed, you'll need to figure out your watts/CdA.

http://www.slowtwitch.com needs a Glossary.

What is cDa?

The drag area (Cd - coefficient of drag, A - frontal area), which represents how streamline or aero an object (rider+bike in this case) is.

Thanks

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Kind regards,
DJ

Got it thank you.

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Kind regards,
DJ

Good point, thanks.

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Kind regards,
DJ

Thank you.

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Kind regards,
DJ

Ok thanks for your time here.

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Kind regards,
DJ

You guys are spot on, just started thinking further into the theory of needing more watts to push a heavier bike VS a lighter bike.

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Kind regards,
DJ

Perfect . Thanks

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Kind regards,
DJ

As above, bike weight only really comes into the equation on a hilly course or one with a lot of turnaround points where you're having to accelerate back up to speed a lot. Though if all that weight comes from having half a dozen bottles attached between the arms, on the frame and behind the seat then they're probably also reducing how aero you are!

W/kg is a useful yardstick both for measuring your own personal bike fitness, and also comparing to others if that's your thing (and assuming they're being honest and have accurate power). W/kg is a better measure than simply FTP, since FTP improvements that are accompanied by weight gain may not be beneficial (and will almost certainly hurt your run), whereas improving W/kg will nearly always improve real world performance. If you're doing a hilly/bendy course and worried about bike weight, then don't let me discourage you from buying a lighter bike as well ;-)

W/kg is used as a rule of thumb to predict performance because it's very important on hills, has an effect on rolling resistance and also gives some indication of potential air resistance losses. It is not useful as a training target. Where elevation changes or rolling resistance are concerned, it's your total weight that matters. The rider+bike+clothing+water+food+repair kit are all resting on the tyres and must all be lifted up the hill. However mass does not effect air resistance directly. A heavier bike does not create more drag than a lighter one and a full water bottle is not less aerodynamically optimised than an empty one. W/kg is only useful for aerodynamic purposes in so far as it can be used as a very approximate rule of thumb. It ignores position, equipment/clothing choice.... all of the specifics of any given rider.
Train on watts. Your performance will take care of itself and musing over W/kg values will not gain you anything unless you have a specific reason for wanting to optimise it (perhaps competing in hill climb events). This is especially true if you don't really understand exactly what the figure relates to and is useful for.

To answer your original question: when W/kg is discussed it almost always refers to rider weight and should be clear from the context and discussion if this is not the case. This value tells you about the rider's ability to produce power relative to their mass. it tells you nothing about their bike, or position, and cannot accurately predict a race performance without additional data.

All else being equal a heavier bike will require more power for equal performance, a little extra on a flat constant velocity route, and a more significant amount extra where there's lots of altitude gain or accelerations required. BUT, you'll surely use the maximum power at your disposal either way? So you can't compensate on the heavier bike because you don't have any extra power to compensate with. In fact the reverse is true. Since you'll be a little slower on the heavy bike you'll be riding a little longer and will need to reduce your intensity slightly to allow for this. Thus you will in fact go slightly slower still, but the effect will typically be fairly minor unless it's a VERY heavy bike, and you're gaining a LOT of altitude; or it's a draft legal race and the bike weight is the difference between holding a wheel or not.

A lower W/kg figure MIGHT mean it's worth digging a little deeper on hills at the expense of power on the downhills or flats, but that's not easily quantified without using something like BestBikeSplit software which will use your total weight and does not base your aerodynamics primarily on weight data.

Info, or recommendation for a good read? I'm always trying to catch up a bit on the history and background and like having new things to read.

FWIW, I got that bit from the recent documentaries in the past few years. I'm sure they embellished for entertainment.