When I first started cycling the LBS owner told me that the difference between a $5,000 aero road bike and a $2,500 endurance road bike is less than 10 watts. He races on a Giant Propel so I assumed he was just being nice and telling me not to spend a lot of money on something so marginal.
Fast forward a year and I’m wondering if what he told me was legitimate, or if it was a sales tactic to not scare me off by telling me to buy the most expensive bike. Assuming all things are equal, what exactly are the watt savings on an aero bike vs an endurance road bike?
I think it helps here to think of the gains in 3 main ways:
more aggressive positioning. The body represents about 75% of the overall aero drag, so a lower more aggressive positioning will reduce drag, even if the frame itself isn’t any faster. Aero frames typically have a more aggressive default positioning than endurance frames, but if you are flexible enough, you can probably achieve a similar body position by slamming the stem, etc. And if you are considering moving to an aero bike, it might be worth slamming the stem to see if you can comfortably hold that position over a longer distance, before outlaying money on an expensive new bike.
wheels. Wheels are a big part of the aero bike equation, and a big chunk of the aero price is often the fact that they come with aero (ish) wheels as default, rather than heavier bombproof shallow stock wheels on an endurance bike. But there is no reason you can’t fit deeper and more aero wheels to an endurance bike.
frame. After you strip out the above factors, yes, the benefit of the aero frame itself is pretty small.
Would just add that the difference between similarly specced aero and endurance bikes from the same brand is nowhere near $2500, more like $500 or less in most cases. For a $2500 difference you’re looking not just at a more aero frame but also better wheels, better components and/or a higher spec frame (e.g. high end carbon compared to entry level carbon or aluminium).
I don’t think Giant Propel is an endurance bike. In my understanding endurance bikes are of shape Giant Defy and similar - top tube pointing up, handlebars at saddle level and so on. They are not designed to be fast, so normally aero/race bike would outperform them hands down in every way other than comfort perhaps. The difference between aero and race frames are more subtle, they have their weaknesses and strengths - there is right job for both types. One can gain free 10W going aero on flats and equally loose time cornering, climbing, etc.
The differences between a aero and an endurance bike are very small, if you were to add aero handlebars, seatpost and wheels to a endurance bike almost no difference. nordic
Riding an “aero” bike in the drops with locked elbows and straight arms will incur a far bigger penalty to overall speed, than riding an “endurance” bike on the hoods with your elbows bent and your ulna/radius bones parallel to the ground (all other things being equal).
The above is not a matter of opinion, it is fact.
Remember, the “aero” bike (just like the “climbing” bike, the “gravel” bike, etc.) are just new ways of bike companies selling more bikes.
Buy a bike you can afford, that fits you well and has the features you need for the riding you’ll be doing.
Differences between endurance and aero are very subtle, we all agree. We are also talking about head tube angle, fork rake and offset, chainstay lenght and downtube angles, etc. It all translate to: a more stable and compliant bike for endurance, vs a slightly stiffer more nervous if you are talking about a full on aero race bike. The aero design, early on resulted in very stiff, quite un confortable rides. That now has been fixed and improved.
Now on the gains, all things being equal (position, components and wheel/tire, etc) yes an aero frame may be more efficient but that is a fraction of a fraction. Merckx in the 90 identified that body drag accounted for 75-80% of total drag leaving 20-25% for all things bike. Getting an aero frame won’t reduce this to 0, you will agree. The best of the best frames will cut 1-2% of total drag. At 300W we are talking 3-6W (not accounting for wheels).
This is like all things bike, a lot of marketing pinpointing your desire to have that n+1 beautiful sleek road machine with that “je ne sais quoi” which for sure will make you crush you Sunday ride buddies on that last sprint to the coffee shop. We have see that when everyone were weight weenie and were spending ludicrous amount of money to save grams on stems and seatposts.
Now, don’t dispair, we are all looking at those magnificent machines and drool. On the other hand, you can reap significant gains by training in that aero position @chad reminds us to get into, you will shave a significant amount of wasted watts with an investment of 0$.
I, happened to have all 3 types of bikes and they are all setup exactly same way, saddle over BB and bars height (via negative stem on the endurance one), etc. Even saddles and bars are the same, same groupsets. I’m not saying there is day and night difference, but there is some. I ride them all as aero as I can, often in praying mantis position with my back nearly flat. This is just my experience with them. The most relaxed frame is the slowest on straights, but it climbs ok, rather well actually. Aero is quite heavy, very fast on straight line, but is worst in climbing, the front end being narrow lacks compliance turning and putting power down. The non-aero race frame is a good all rounder, gets the job down well. I ride and competed on them all. However these bikes are of different price ranges, age, it could be just that, not sure. Go figure.
While it may be “fact” (and I am not certain it is), the above is certainly misleading. You are not comparing the same position between the bikes, but drawing conclusions are the aero differences of the bikes as a result.
The implication is that the only option for an aero road bike is to ride with locked elbows and straight arms, while with an endurance bike you can ride with forearms parallel to the ground.
If you have the same position on both bikes (very achievable) the aero road bike is faster…and that is 100%, without a doubt, fact.
As for the question of drafting, riding in groups, etc., yes, the aero benefit of a road bike is muted…but it is still present. Even drafting, you are reaping the benefits of improved aerodynamics. The draft is not a apace where the laws of physics stop. An argument can be made that the energy saved with an aero bike while drafting can make the difference between making a split at a crucial point later in the ride / race. I will admit it is a somewhat tenuous argument, but there is some truth to it.
Position and body equipment (helmet, kit) will make the biggest difference in aerodynamics. Start there. But the benefits of an aero road frame are real and tangible. For data, I think it is worth looking at what companies like Specialized and Trek have published on their aero road bikes vs. their traditional road bikes. I would ignore their comparisons vs. other brands, but their data against their own models should be fairly straightforward.
Aero bikes ARE faster, but they are so expensive and have their flaws too. Sure if I was buying a new bike right now I’d highly consider a Madone, but having made huge improvements to my speed and fitness through TR, I don’t really see a need for an aero bike. They are faster in some scenarios, but slower in others. Like to climb? No aero benefit. Ride on windy days? A deep aero frame can turn into a detriment/danger, much like very deep wheels.
Combine this with the fact that almost every brand is now adding aero features to the rest of their frames (even the new TREK Domane sports some pretty fly aero profiles), I can see aero bikes as a whole fading from the market as the years go on, they will be there, but not with such popularity. I’m waiting for the 2021 Emonda since it’s essentially going to be a lighter, more versatile, and baby Madone, and consdiering I’ve been going for the hills more and more lately, a Madone just doesn’t make sense, as badass as it is
That is not really accurate…a light climbing bike does not out perform an aero bike on the climbs until you reach ~6% (and for us everyday joes it is closer to ~8%). Cervelo proved that almost 10 years ago in their studies.
Bike handling re: wind is primarily impacted by the aero design in front of the steering axis. Aero frames have very little impact (positive or negative) on handling. This is a corollary to the myth that a disc wheel is dangerous in windy conditions…it is not.
The reality is that aero road bikes are faster in nearly every situation. The one notable exception is if your ride / race ends on a climb over 6-8%. (key word is “ends”)
I think you may have that backwards. I’ve always seen the tipping point for higher W/kg riders to be at higher gradients. This being due to pros going faster on the same gradient than you or me so there is more of an aero benefit.
Yes and no to the “ahead of steering axis”, if frame shapes did not affect crosswind performance, everyone would be riding a SHIV or some other super aero bike, with a 20mm shallow front wheel. Yes, the front wheel has the primary impact, but its not all there is to it. Even if we compare a thin rider to a larger rider, the larger rider is going to pick up more crosswind, as will a larger (deeper) frame. I agree that the rear wheel has the smaller effect on crosswinds.
there are other aspects to on bike performance than just aerodynamics…in the case of the Shiv, it is outside of the UCI regulations re: frame shape, etc. Tradition, adherence to the weight dogma, aesthtics and others are also factors. But yes, you are correct…if we relied solely on the data to make our choice, we would (almost) all be using aero frames.
Right…as you note, it is the primary impact. I did not say that frame design would have zero impact on handling. But the idea that an aero frame would be “dangerous” or “difficult to handle” in crosswinds is not borne out in the data. In fact, a properly designed aero frame can (and should) handle better and faster in a cross wind. For an example, see how the development of wider rims led to increased handling characteristics in a crosswind vs. v-shaped and toroidal shaped rims.
Age groupers regularly ride very aero frames in Kona in arguably the most challenging wind conditions of any competitive event.
Great post…I would just add that the data is becoming clearer that yaw angles over 10* are fairly rare. I believe the average yaw rate tends to be between 5-10* (could be wrong on the exact numbers, but it is less than 10*).
