Rule of thumb for how much wind or hills slow down average cycling speed?

Triathlon Forum
1

I’m wondering if anyone knows of a simple rule of thumb for how much wind or hills will slow you down on the bike. I’m looking for something simple, e.g., if you ride a flat out-and-back course with no wind at speed V, then with a wind speed U (assume headwind one way and tailwind the other) and the same average power output, your average speed will be X% slower. Similarly for hills, if you ride a flat course with speed V, then riding a rolling course with no net elevation gain but average slope S and the same average power output, your average speed will be Y% slower.

Obviously, the answer to this can get way bogged down in details – but I’m not interested in exactness, I’m interested in the general picture (and how the average speed reduction scales with the wind or the slope) and any rules of thumb. For instance, with running, there is a rule of thumb that every 10 feet of climbing (on route with no net gain) slows you down by about 2".

If nobody has simple answers for this, I will give a rough sketch of a solution in the next few days!

2

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.

3

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.

4

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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5

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

6

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.
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.

7

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

8

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.

  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.

9

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.

10

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.

11

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

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.

…
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.

12

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

13

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.

  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. Any rule of thumb will also be a black box surely?

  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. It’s not realistic to expect to compare rides on different routes in different conditions by applying simple adjustments. Modelling on Best bike split after the fact is your best bet but that’s going to be fairly approximate too. However, you can usefully compare rides on the same route in very calm conditions. Over the long term you’ll get to know if you’re generally completing a known route faster, but this is not a precise method and it depends a lot on consistent pacing. If you ride the same route very regularly and therefore have lots of rides to compare, you’ll have much better info, but your rides may get a little boring. I would suggest identifying a local out and back route with minimal junctions and preferably on sheltered roads that you can use for benchmarking your ability (when the weather is suitable, i.e. calm).

  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. You could use BestBikeSplit for this too. Set up a route and run multiple simulations with different wind directions and speeds, then do the same with other routes with more or less hilly profiles. You should get some feel for the impact of wind and gradient on optimum pacing strategies and average speed.
    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.

14

Play with this

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

15

I’m wondering if anyone knows of a simple rule of thumb for how much wind or hills will slow you down on the bike. I’m looking for something simple, e.g., if you ride a flat out-and-back course with no wind at speed V, then with a wind speed U (assume headwind one way and tailwind the other) and the same average power output, your average speed will be X% slower. Similarly for hills, if you ride a flat course with speed V, then riding a rolling course with no net elevation gain but average slope S and the same average power output, your average speed will be Y% slower.

Obviously, the answer to this can get way bogged down in details – but I’m not interested in exactness, I’m interested in the general picture (and how the average speed reduction scales with the wind or the slope) and any rules of thumb. For instance, with running, there is a rule of thumb that every 10 feet of climbing (on route with no net gain) slows you down by about 2".

If nobody has simple answers for this, I will give a rough sketch of a solution in the next few days!

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

16

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

17

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.

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.

18

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

19

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.

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.

20

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

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.