The only rule of thumb I learned is that a headwind slows you by ~1/2 of its velocity (ex. you'll go 5mpg slower into a 10mph headwind).

The relationships are obviously not this linear. Given tools like best bike split, etc. I think folks tend to do more exact calcs these days given their particular power and routes.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

What's the purpose of this? For example, if you're trying to measure training effect/effort level, a power meter is what you want. Or at least a heart rate monitor.

I happened to watch this just this past week: https://www.youtube.com/watch?v=ACnCIhJJupc

Maybe that will help some

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Not a coach. Not a FOP Tri/swimmer/biker/runner. Barely a MOP AGer.
But I'm learning and making progress.

How about figuring out a route when I know I have to be back by a certain time?

But even that is a bad measurement... same with running. Pace may vary (and should) day to day.

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USAT Level II- Ironman U Certified Coach

I don’t see how that follows. I have a workout for a specified duration and intensity, but at the end of that time I must be back home. I need to know my average speed accounting for wind to know where I should go.

1) I'd like to be able to understand how the difficulty of different courses or wind conditions compares. I get that you can do that with best bike split, but that feels like a black box to me.

2) I'd like to track my improvement in training by using average speed with some cursory accounting for wind + grade effects. I know that power measurement is the gold standard but it's not super cheap and I'm curious how far simple corrections can go.

3) I'd like to have a quantitative grasp of how wind and elevation affect average speeds of different riders differently. I think we have sensible intuition about this, but it would be nice to have a better sense of the dependencies.

I don't think you're going to get what you are looking for because there are too many variables. What about the air pressure on the day. What about the number of cars/trucks that overtake you. What about the fact that it isn't a headwind, it's at 5 degrees. It's at 10 degrees. It's gusting. Etc...

If you're looking to measure fitness improvements, then consistently tracking your time around a set course compared with heart rate will help show improvements - not in a single ride, but the average time over a number of rides should slowly drop.

Who says hills and wind will slow down average cycling speed?

These are 3 separate cycling skillsets:

- slipping through the wind (good aero form) and maximizing tailwind speeds

- charging up the hill and down it

- flats expertise

A person may be good at climbing or an expert on the flats, it just depends. Lots of variables here.

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https://www.strava.com/...tes/zachary_mckinney

..
You are making life more complicated than it needs to be. You are riding in the real world so allow for real world issues that might delay you and leave for your ride earlier.

This type of thinking has mystified me over the last fifteen years or so ( since coaching became more popular).People seem to train for the perfect conditions or take their scheduled sessions as set in stone and fail to apply any variables at all.That habit is then exposed on race day when the perfect conditions fail to appear and athletes don't know what the hell to do about it.

I'll say it.

There are very specific instances where small rises and falls may not impact you since you can carry speed from downhills onto uphills and maintain velocity, but once you are steady state on a hill, you are losing time. What strategies to you suggest to avoid a drop in average speed with wind? Sure, you can use an aerodynamic position to reduce loses into a headwind, but you can use that position with no wind for savings too. Are you talking about using a wing or sail?
The simple reality is that the headwinds and uphills will lose you more time than the tailwinds and downhills will gain you; simply because they effect you for longer. The exceptions being if you don't start and finish in the same place, the windspeed/direction changes, or perhaps some special cases of a wind that offsets a climb but that last one is dubious.

My comments added in red. One of the reasons power meters are popular is because it's not feasible to make accurate comparisons in different circumstances without them.
There are a myriad of variables. It's not feasible to adequately measure the variables themselves. If you could, then a tool like a more advanced Best bike Split would still be required to calculate their impact and provide you with simple insights. Measuring power is simpler and cheaper than measuring all the other variables so that you can calculate power. There isn't an easy rule of thumb that does the same thing.

Play with this

http://www.kreuzotter.de/english/espeed.htm

Everyone else seems to be on the attack, I've no idea why.

My n+1

For elevation..

In my local area, I have three loops I like to do, all are near to 65km long.

1 - 300m (1000ft) Elevation, I usually average around 29kph
2 - 1100m (3500ft) Elevation, average normally 27kph
3 - 1800m (6000ft) Elevation, average normally 25kph

Over the years (since 2008 anyway) these have remained remarkably consistent.

For wind..

I have a point to point route to my mother-in-law that is all in a north-north-west direction and quite flat. If the wind is light, I stay near 29kmh average. Two weeks ago the wind was strong, between 16 - 35kmh (10 - 20mph) form the north and my speed was 27kph average.

Again, over the years, I've seen consistency here.

Like you, especially with the mother in law visit, I need to know how long it will take (dare I be late), so my rules of thumb per 70km ride are:

> 1500m elevation lose ca 4kmh
> 1000m elevation lose ca. 2kmh

Headwind over 16kmh lose 2kmh


There you have it, hth

wind fucking sucks. hills are fun. source: now live in the flattest fucking place on earth after living in a mountainous region.

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"The person on top of the mountain didn't fall there." - unkown

also rule 5

This is true. Your average speed is the harmonic mean, not the arithmetic mean, of your speeds over the sections, which applies to things in series. The min/km average will also get you there. The slow sections slow you down more than the fast sections speed you up.

I know about how fast I tend to go in the hilly terrain I live it. If it's windy, it's a little slower. Not sure it's worth trying to get more precise than "about x mph" and "a little slower". I couldn't really estimate my avg speed for big mountains.

I don't think anyone's attacking, they're simply pointing out that they think the question can't be usefully answered in the way the OP would like.

I too have routes I've ridden multiple times and could provide ballpark times for, but there is little point. It's not just about the total elevation it's also about what that elevation is composed of (a few big climbs or lots of small ones, short and steep, or long and shallow). And of course how you pace yourself on hills and generally. It's not usefully transferable.
You've provided data for 3 routes and claimed consistency within each route. Fine. But that's for one specific rider on 3 specific 3 routes. I see no reason to be confident this will be accurate for another rider on a different setup and different terrain. This is the argument everyone is making.

Your data is useful for you, but I doubt it's transferrability. I think the OP will need to generate his own experience after which he too will likely be able to make a decent educated guess for a given route. Otherwise, if you can't be late back, allow a little extra time and add some extra distance along the way or at the end if you're ahead of schedule and want to use all the time you've got available. This is a good idea anyway, if time is really important as it'll also come in handy should you get a puncture or any other unexpected issue.

Sorry to be blunt, but that's about the silliest response possible to the original question asked.

It not only doesn't answer the question, but it's a bunch of cotton in the mouth that means a lot of nothing.

"Maximizing tailwind speeds": what is this? Why wouldn't you hold a good position at all speeds? You should be skilled at being fastest at all speeds and situations.

"charging up and down hills": this suggests utilizing more effort on hills as a time split strategy......not a bad idea, but the reality is often a lot closer in watts/% than "charging up" hills. If you wanted to say something here, I would say ride the bike in aero often enough at high speed that you don't chicken out and sit up going down hills.

"flats expertise": what's this? everything else? I'd say being able to control yourself in a cross wind and near hedge rows or trucks passing would be what we need here. And the mental and physical posture to stay aero the entire time and not uncomfortable sitting up.




To answer the actual question:
I'd use aeroweenie calc plus or minus a speed entered accounting for the wind and average grade if you want quick and dirty.

Also, don't take "weather station" wind speed as being what you'll actually ride slower or faster. There's the yaw angle and the fact that even in a straight on 10mph headwind the wind is not non-stop perfectly 10mph. It'll go 0, 0, 2, 2, 2, 12, 10, 9, 8, 1, 2, 3, 10,10. It's an average, and stronger winds will affect more than light ones.

The OP asked for anyone with ballpark figures, I gave what I use, nothing more, nothing less.

As far as I can see, most of the answers don't do this, they just point out problems - like your post is also doing.

There's also wind gradient ;) - The earth has a boundary layer too and so windspeed varies with height off the ground.

Bingo -- Ai_1 and you have hit the nail on the head, but it was not obvious to me from a lot of other reading that this was the primary reason for slower average speed under variable-speed conditions (e.g., winds or hills). Lots of other resources cite the nonlinearity of aerodynamic drag as the primary factor, but I don't think it is essential at all. (Nonlinear aerodynamic drag does contribute to it being difficult to maintain speed under variable conditions by modulating power output, because it rapidly becomes physiologically impossible to maintain speed in any appreciable headwind if you are near threshold effort.)

Thanks all for comments -- happy to have this be an active discussion!

I think a common thread among some of the more skeptical responses is maybe a misinterpretation of the spirit of my question. I'm really asking a physics question and not an engineering one -- I don't care about all the myriad factors that might matter, I care about the ones that are most important and what their rough magnitude of effect is. If it's off by +/- 50% I'd still be happy to have a ballpark answer because I would have a better understanding of the problem. I think power meter makers want you to believe that it's impossibly hard to do any sort of correction of speed to account for hills or wind but I think (for solo riding on loop or out-and-back courses) that rough corrections should not be impossible to understand.

To Ai_1 regarding your point -- "wouldn't a rule of thumb also be a black box" -- my answer would be no if it's grounded in physics or math that are easy to understand. For example, there is a rule of thumb that each pound of weight loss in running will make you faster by about 2"/mile. This "rule of thumb" can be derived fairly easily -- it it summed up by an assumption that your % increase in speed is equal to your % decrease in weight if losing weight does not diminish your total aerobic capacity. Apply this to a 150 lb runner who runs a fastest aerobic pace of 5:00/mile (or 300"/mile) and you get that 1 lb weight loss is 0.667% weight loss, which should increase top-end aerobic speed (or drop pace) by 0.667%, and 0.667% of 300"/mile is 2"/mile faster.

That isn't a derivation, though--it is, as you say in the next sentence, an assumption. Nowhere in your example do you show how to relate percent decrease in weight to percent increase in speed aside from a guess that they are the same. Coming up with a similar "rule of thumb" for wind and hills in cycling will, I suspect, require even more assumptions and not be very useful as a result.

Eesh, I guess I tried to simplify things too much for quick posting here.

Running is about repeatedly accelerating your body weight against gravity and and against momentum loss from tangential ground contact forces. Metrics of (inverse) running economy (call it RE) are thus typically normalized by body mass, e.g., have units of ml/kg/km or oxygen consumption per unit body mass per unit distance traversed -- this varies across runners and is affected by training but does not change much if you change your body mass by removing or adding dead weight. VO2max is measured in ml/kg/min, and if you lose X% of dead weight body mass but maintain total aerobic capacity, then your VO2max would go up by X%. Your maximum aerobic speed in km/min is then VO2max/RE, where X% weight loss has increased VO2max by X% but left RE unchanged -- so your speed would be X% higher. Remainder of argument follows.