“One bike to rule them all“

Discuss light weight issues concerning road bikes & parts.
Post Reply
FlatlandClimber
Posts: 665
Joined: Tue Mar 31, 2020 3:37 pm

by FlatlandClimber

Hey there,
With the ever growing offering of aero climbing bikes or lightweight aerobikes, I wanted to start a central thread to discuss what matters and what might be marketing bs. Especially with the launch of the Tarmac SL7, there has been a lot of chat about "now Aerobikes are obsolete", and how it may be faster than this and that bike.
For me, a competitive cyclist and a fan of bike tech in general, but not an expert on aerodynamics, physics or sports science, I was doing a bit of research, but would also love to learn things from you guys on this topic. Since we are comparing the lightest aerobikes, and the most aero light bikes, the results can only be very marginal, and they are. In the end, all of this is about saving a watt here and there, so if you think to yourself "why does anyone care about 3 Watts?", I highly advice against reading any further. :thumbup:

The conundrum that the whole industry is faced with is making a bike that is fastest based on the two variables of weight and aerodynamic drag. Obviously, the by far biggest factor will always be the rider. The rider propels the bike forward, the rider creates the biggest air friction (70 to 85% as I understand it), and the rider is by far the biggest part of the system weight (usually over 85%). I would refrain from discussing how the biggest gains are made north of the saddle, as that should be a given. Also, I am talking about the latest and greatest bikes here, that are clearly aimed at ambitious athletes, that already put in significant effort into becoming lighter, stronger and better at staying aero. Also, most of the lightweight aerobikes or full aerobikes nowadays are very similar in the terms of geometry, so the rider aerodynamics shouldn't really be affected by the choice of the bike. Feel free to disagree.

Weight:
This forum of course is a gold mine of knowledge about this topic. I'd say the weight difference on "aero bikes" is around 1kg on the top end, with the BMC Teammachine, Tarmac SW SL7, Emonda SLR9 being around 6.8kg, and the heavier aero bikes Cannondale SystemSix HM, Cervelo S5 Disc and TREK Madone SLR9 being between 7.5 and 8.0 kg.
So, how much does a kilo of system weight more or less matter?
In (male) road racing, system weights range from around 63kg (54kg rider + 6.8kg bike + 2.2kg clothing, shoes, water, helmet, spares) to just over 90kg (80kg rider + 8kg bike + 3.5kg of clothing, shoes, water etc.). That means a 1kg reduction will reduce the system weight by 1.6% at most, and 1.1% at least.

Flats:
On the flats, we know that the weight difference is making hardly any difference in speed. This will be the more relevant section when discussing aerodynamics. The two relevant topics here are increased rolling resistance and increased inertia (disadvantage when accelerating, advantage when free wheeling). According to this article on Training Peaks (https://www.trainingpeaks.com/blog/unde ... esistance/), a 5lbs (2.2kg) increase in system weight will increase rolling resistance at 20MPH by 0.8 Watts. Since the graph is fairly linear, we can assume it is probably around 0.3 or 0.4 Watts for the range of bikes we are talking about.
The effects of weight on acceleration are a bit more complex than that. What I, as a physics noob know is, that the power put into the system is not lost until you brake. So while a heavier bike is more difficult to get up to speed, it should stay at a higher speed at a lower effort. Acceleration being a linear function of weight (correct me if I am wrong), a 1.6% increase in system weight should mean that for the same level acceleration the rider on the heavier bike would need to overcome 1.6% more power. When accelerating at upwards of 500 Watts for a short sprint out of a corner, that would be 8 Watts more. I am not a good sprinter and can probably use any help I can get, but I am sure that 8 Watts more or less here, for such a short period, are just not noticeable for me. Considering the difference between 1100 Watts (my approx. max power output at 70kg bw) and 1083 Watts, I think the same holds true.
Also, unlike wind resistance or rolling resistance, these 8 or 10 or 20 watts you have put more into the heavier bike will help you roll along for a little longer at some point. The only real advantage here would be a very tight angled Crit, where you brake a lot, and the energy is actually "lost".

Climbs:
This is where the 6.8kg aero-climber should really outshine the "fat" 7.8kg aero bike.
Again, not an expert, so I am quoting (https://mccraw.co.uk/2012/06/19/bike-we ... rformance/)
The speed at which you climb is dominated by the power you put out versus the work needed to overcome gravity – rolling resistance and other frictional losses are minimal and unlike riding everywhere else, aerodynamics isn’t getting a look in.

This means it’s possible to express the effect of weight on climbing, with a fair degree of accuracy, by dividing one weight with another using the following formula:
(System weight heavy)/(system weight light) * speed heavy = speed light
For my example the maximum gain should be:
(64kg/63kg)*15kph = 15.24kph (0.24kph advantage). Well of course the 1.6% weight loss results in a 1.6% speed gain in this example, where rolling resistance and aerodynamics are disregarded...
Since we are talking climbs that are steep enough, that wind effects are minor, speed is based on W/kg mainly.
I would like to go with 3 examples show the effects the 1.6% decrease in weight has in different scenarios.

Short climb at 64 v 63kg system weight, effort at 400 Watts: 400/63 = 6.35 W/kg. With 1kg more: 6.35W/kg*64 = 406 Watts for the same speed uphill. So this is 6W saved.

Longer sustained effort at 78kg vs 77kg system weight, effort at 310 Watts (around 4.5 W/kg of BW). 310/77kg = 4.03 W/kg. With one kg more, that's 314 Watts for the same speed uphill. So this is 4 Watts saved

Even longer sustained effort at 91kg system weight vs 90kg, effort at 250 Watts. 250/91kg = 2.78 W/kg. With one more kg more, that's
252.8 Watts and 2.8W saved

Mixed: Of course a mixed course is what is most likely what people are looking at, and it is very difficult to analyze, since every course is different and there are several variables to consider. What I found quite interesting, was the estimate from this article, that states during the Transcontinental race 2016 (3900km, 45km of climbing), that 1kg in saving would result in a saving of 1 minute per 1kg. Mind that this a "slow" ultra endurance race, so the effects of weight per distance are greater than in a shorter, faster race). This is around 1minute per 4 to 5 hours or 12 to 15 seconds over an hour.

Conclusion on Weight saving: the weight saving of the lightest aero climbing/ light weight aero bikes over top end aero bikes is around 1kg, which is between 1 and 1.6% of total system weight, This results in a saving of just under half a watt everywhere, and at best 6.5 Watts on steep short climbs (including rolling resistance).

Aerodynamics:
So then, what is the aerodynamic gap between the bikes like the SL7, Emonda SLR, Wilier SLR Zero and bikes like the Venge, Madone or S5.
I have exhausted all my resources here and purchased TWO issues of the Tour Magazine, to get some Aero-Data :lol:
They are pretty much the only mag to have aero-tested the SL7 yet, and have measured it to create a drag of 210 Watts (with a pedaling rider on it). I don't really think this is a realistic figure for that speed, since it will easily take north of 300 Watts to maintain 45 kph, even on a TT bike with a disc rear wheel. I once read an article saying that "wind tunnel speeds" only simulate around 85% of the speed outdoors. Don't know if that is true, looking forward to your input here.
What I find relevant here, is that the difference, since it's a measurement of the entire system, not the bike alone, therefore can be applied to various speeds.
The 210 Watts of the SL7 are a fantastic value, with the Madone SLR in this very magazine even testing two Watts slower (probably this shows the limitations of wind tunnel testing). The fastest bikes they have ever tested are the S5 Disc (205 Watts), the Factor One (206 Watts) and the Cannondale SytsemSix (204 Watts). They are on average 800g heavier than the SL7 or Emonda SLR9, and test on average 2.4% faster aerodynamically.
According to testing of Germany Cycling Magazine "Roadbike", the fastest bike they have tested (Cannondale SystemSix), and a Bike that Tour Magazine has tested to be just a little faster than the SL7 (the Canyon Aeroad was tested at 209W vs the 210W of the SL7), is 7 Watts in the frame alone (at 45kph, again, I doubt this is comparable to 45kph outdoors.) 69 Watts for the Cannondale, 76 Watts for the Canyon. That seems to be in line with the results of Tour.

Where to save aero drag?
The general rule goes, over 80% of aerodynamic drag is created by the rider, so a better position, a skin suit and such will likely yield the best results. Also, savings made at the front of the bike will be to much greater effect, than those on the rear. Aero front wheel with slim enough tire, an aero cockpit, a slim head tube etc. are likely the greatest aero of savings.
On this forum, I once so numbers posted that are allegedly from Cervelo. They quantify the potential savings that can be made in certain areas of a road bike. I can't varify their legitimacy. But here they are anyway:
Handlebar: 30% Frontwheel: 16% Frame: 16% Fork: 9% Bottles: 9% Drivetrain: 9%, Rear wheel: 5% Brakes 5% Seatpost: 1%
Regardless of how accurate these numbers are, I believe them in that regard, that they take into account, that a pedaling rider obstructs the air flow, so that things like the seatpost offer minimal saving potential. Also, bottles are taken into account, which I think is often neglected in the design of aero frames (my eyes say it's neglected on the SL7 for example).

Conclusion of Weight v Aero.
There will be an incredible amount of inaccuracy and lack of understanding of physics in all this. That's why I don't want this to be:" here are the facts, take them as they are!" But much rather: "this is my understanding and what I found, let's have a chat if you like."
From the data I have gathered, the advantage that the fastest all out aero bike (Cannondale SytsemSix/Cervelo S5, Factor One) has in terms of aero drag over the lightest aero bikes (SW SL7), is slightly larger (2.4%), than the weight/ rolling resistance advantage (under 2% in a best case scenario of the entire system) the lighter bike has. So even at speeds slow enough, that aerodynamics only make up 50% of total resistance (usually quoted as "over 6% gradient", under 18kph), the aero advantage will outweigh the weight advantage. Even at these small margins.

Does any of this matter?
Not really. The differences in Watts between aero climbing bikes and aero non-climbing bikes should be around 1% of total power output. Not really anything to get crazy about. I mean, we aren't comparing ultra-WW climbing bikes with zero focus on aero vs the most aero built with no focus on weight, but we are comparing super-light very aero with very-light super aero.
The real conclusion probably should be, you can't really go wrong with either of the bikes. Buy what feels best for you, what you get along with, what is most fun, and what gets you out riding the most.
However, what I have also learnt for myself is, that a light-weight aero bike is NOT the fastest everywhere, as companies like to claim, but the all out aerobike is likely still the fastest option pretty much everywhere. In the case of Specialized, the "one bike to rule them all" is likely called S-Works Venge. :beerchug:

Edit: The reason this is so focused on the SL7 is NOT to talk bad about that bike. Quite the opposite, actually. The SL7 is probably the "most aero 6.8kg bike" there is, and there is quite a lot of data that exists on it already. Could be applied to any other lightweight aero bike (or however you want to call it), with slight alterations on data.
Last edited by FlatlandClimber on Sat Aug 01, 2020 6:46 pm, edited 6 times in total.
Cervélo S5 Disc (2019) - 7.8kg
Open Cycles WI.DE (2019) - 8.5kg
Specialized Shiv TT Disc (2020) - 7.9kg
Specialized SW Roubaix Team (2020) - 7.3kg
—Soon— TREK Émonda SLR 9 (2021) - 6.XXkg

*all weights include pedals, computer mounts, and bottle cages.

Stueys
Posts: 470
Joined: Sat Nov 22, 2014 1:12 pm

by Stueys

I think the SL7 tells us that Spesh can't improve on the Venge other than adding a threaded bottom bracket....

by Weenie


Skeeleye
Posts: 47
Joined: Mon Apr 27, 2020 8:52 am

by Skeeleye

Just seeing this post and hope to contribute, but Strade Bianche is on. But I wanted to say thanks for all the effort you put into this post, interesting read and makes me happy as I just bought a Venge before the SL7 launch

uraqt
Posts: 1008
Joined: Mon Apr 03, 2006 8:53 am

by uraqt

As my hate for UCI is well know : ) and they should be disbanded immediately. The UCI are the real limiting factor for bike design and the sport of cycling as a whole.

The racing/bike rules should be a 50/50 committee of riders and bike manufacturers.

And for one bike, it's never going to happen, I have to guess that Cervelo will go below the weight rule with the next gen R5 or the next one. They already make non-UCI approved bikes, what is the big deal with one more? While the average rider can't afford 2 or 3 super bike there will allways be a few that will. Why not a own a PX, SCR - 058, U.P.P.E.R. and whatever the lightest mountain bike is?

I have read that Trek makes less than 10,000 totaly top of the line frames in Waterloo, and that includes the frames for the trek sponsored teams/riders so that implies that none of the manufacturers are selling significant numbers of top of the line bikes/frames and that they all are just halo products.

C

User avatar
wheelsONfire
Posts: 3691
Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

Ofcourse Specialized could design a better aero bike than SL7.
But it would carry more weight. I don't care a sec for Specialized, but i'm sure there will be something coming after Venge (2022-2023?).
Probably when most fan-boys have been fooled and bought SL7.
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

spdntrxi
Posts: 3912
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

the faster you are the more an aero bike makes sense.. if you can do sustained 15+mph up 10% gradiants by all means I think an aero bike makes alot of sense. The slower you are the slope/speed/weight tipping point is lower.

whatever makes you feel good on the road and get out the door works for me
2019 BMC TM01 Road UCI config 7.36kg

FlatlandClimber
Posts: 665
Joined: Tue Mar 31, 2020 3:37 pm

by FlatlandClimber

spdntrxi wrote:
Sat Aug 01, 2020 6:43 pm
the faster you are the more an aero bike makes sense.. if you can do sustained 15+mph up 10% gradiants by all means I think an aero bike makes alot of sense. The slower you are the slope/speed/weight tipping point is lower.

whatever makes you feel good on the road and get out the door works for me
No one maintains 15mph up a long 10% climb. Then again, how much of your riding is made up of 10% gradients? How much of your riding is made up of going faster than 15mph? Also, the point at which a 7.7kg SystemSix is faster than a 6.8kg SL7 is likely much closer to 10mph. I don't know where that point lies for a 7.1kg Venge in comparisson to a 6.8kg SL7.
I don't know about you, but there are very few climbs that I can't maintain 10mph on (long >8% climbs).
Last edited by FlatlandClimber on Sat Aug 01, 2020 7:16 pm, edited 1 time in total.
Cervélo S5 Disc (2019) - 7.8kg
Open Cycles WI.DE (2019) - 8.5kg
Specialized Shiv TT Disc (2020) - 7.9kg
Specialized SW Roubaix Team (2020) - 7.3kg
—Soon— TREK Émonda SLR 9 (2021) - 6.XXkg

*all weights include pedals, computer mounts, and bottle cages.

spdntrxi
Posts: 3912
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

not me man.. I was throwing numbers out there, I'm sure someone here is capable.
2019 BMC TM01 Road UCI config 7.36kg

Nickldn
Posts: 381
Joined: Mon Mar 25, 2019 12:35 am

by Nickldn

spdntrxi wrote:
Sat Aug 01, 2020 6:43 pm
the faster you are the more an aero bike makes sense.. if you can do sustained 15+mph up 10% gradiants by all means I think an aero bike makes alot of sense. The slower you are the slope/speed/weight tipping point is lower.

whatever makes you feel good on the road and get out the door works for me
If I remember correctly a lot of SL6 fans love the bike for its supple ride, responsive handling and the riding enjoyment it brings.

Usually these are not strong aero bike traits, as the bigger frame tubes kill the suppleness and responsiveness. What I really want to know is does the SL7 'feel' as good to ride as the SL6, does it handle as well, is it as much fun?

Certainly some reviews of the TCR Advanced SL suggest that it is quite harsh and unforgiving, so not like its predecessor at all. Has the SL6 fallen into the same trap and if so is the SL6 still the one to have?
Giant Propel Advanced SL Red Etap 11s Easton EC90 wheels 6.5kg

spdntrxi
Posts: 3912
Joined: Sat Jul 20, 2013 6:11 pm

by spdntrxi

no argument there.. If I'm doing a mostly climbing ride I prefer my moots over my BMC aero
2019 BMC TM01 Road UCI config 7.36kg

FlatlandClimber
Posts: 665
Joined: Tue Mar 31, 2020 3:37 pm

by FlatlandClimber

Skeeleye wrote:
Sat Aug 01, 2020 5:04 pm
Just seeing this post and hope to contribute, but Strade Bianche is on. But I wanted to say thanks for all the effort you put into this post, interesting read and makes me happy as I just bought a Venge before the SL7 launch
Cheers. Looking forward to what you have to say.
Cervélo S5 Disc (2019) - 7.8kg
Open Cycles WI.DE (2019) - 8.5kg
Specialized Shiv TT Disc (2020) - 7.9kg
Specialized SW Roubaix Team (2020) - 7.3kg
—Soon— TREK Émonda SLR 9 (2021) - 6.XXkg

*all weights include pedals, computer mounts, and bottle cages.

TheRich
Posts: 734
Joined: Tue Jan 01, 2019 1:36 am

by TheRich

Stueys wrote:
Sat Aug 01, 2020 4:34 pm
I think the SL7 tells us that Spesh can't improve on the Venge other than adding a threaded bottom bracket....
I wonder if part of the reasoning is cutting costs.

If you optimize all the leading surfaces (wheels, bars, headtube) and get half way to the numbers of an aero bike, why make both? If they could do the same with weight with an aero bike, the opposite might have happened.

Plus, despite it being generally overhyped by consumers, weight is a big marketing/selling point.

Stueys
Posts: 470
Joined: Sat Nov 22, 2014 1:12 pm

by Stueys

Taken the time to read through properly now, thanks for pulling together, interesting reading.

Think your summary is what Cervelo and Spesh have both been saying for a while, aero is always faster (or everything). What Spesh now seem to be saying (with both the Venge and more so the SL7) is that we can make a few compromises to aero (3-5w) but give you a bike that handles better, is better to live with and more comfortable. So erking out the final few watts of aero performance doesn't make sense, suspect in the real world where riders are moving, positions aren't consistently perfect, the airflow is dynamic, etc, etc, that logic is compounded even more.

Stueys
Posts: 470
Joined: Sat Nov 22, 2014 1:12 pm

by Stueys

TheRich wrote:
Sat Aug 01, 2020 9:18 pm
Stueys wrote:
Sat Aug 01, 2020 4:34 pm
I think the SL7 tells us that Spesh can't improve on the Venge other than adding a threaded bottom bracket....
I wonder if part of the reasoning is cutting costs.

If you optimize all the leading surfaces (wheels, bars, headtube) and get half way to the numbers of an aero bike, why make both? If they could do the same with weight with an aero bike, the opposite might have happened.

Plus, despite it being generally overhyped by consumers, weight is a big marketing/selling point.
It's interesting, I would have thought that both Tarmac and Venge sell more than enough to justify their costs. And rationalising the range options would have reduced costs if needed. The Venge has a strong brand resonance so killing it seems odd to me, think most of us have realised for a while that an aero bar on an SL6 closed the gap to the point of not worth worrying about so I get the logic, but marketing and logic don't often go hand in hand.

I'm hoping the re-venge theories are true. Either way Spesh hit it out the park 3 years ago with the Venge, think the Tarmac moving effectively to being the Venge proves that.

by Weenie


FlatlandClimber
Posts: 665
Joined: Tue Mar 31, 2020 3:37 pm

by FlatlandClimber

Stueys wrote:
Sat Aug 01, 2020 10:25 pm
Taken the time to read through properly now, thanks for pulling together, interesting reading.

Think your summary is what Cervelo and Spesh have both been saying for a while, aero is always faster (or everything). What Spesh now seem to be saying (with both the Venge and more so the SL7) is that we can make a few compromises to aero (3-5w) but give you a bike that handles better, is better to live with and more comfortable. So erking out the final few watts of aero performance doesn't make sense, suspect in the real world where riders are moving, positions aren't consistently perfect, the airflow is dynamic, etc, etc, that logic is compounded even more.
I believe what Specialized has done is given the "aero skeptics" and the "aero-extremists" what they want. A bike needs to be light, otherwise people are upset. I read all the time "I would never pay XYZ for a bike that weighs X/Y/Z kgs." What handles best, feels best, and looks best really is so personal, that we shouldn't get into "because a Tarmac is more comfortable than a Venge". I have Roubaix and an S5, exactly the same geometry, and besides the my hands (the Roubaix has a front shock, a rounder bar and thicker bar tape), I wouldn't choose one over the other in comfort, when ridden with 25c tires. The difference is minimal to me.

The whole point of what I am saying is exactly what I said: "aero is ALWAYS the better choice" (bar hill climbs) if speed is your top priority, and the more aero, the better. It's probably the only thing that is "non-negotiable", while what feels comfortable to one person, may not be comfortable to another, and some people will need the sharpest handling there is, while others will want a more "forgiving" feeling.
Cervélo S5 Disc (2019) - 7.8kg
Open Cycles WI.DE (2019) - 8.5kg
Specialized Shiv TT Disc (2020) - 7.9kg
Specialized SW Roubaix Team (2020) - 7.3kg
—Soon— TREK Émonda SLR 9 (2021) - 6.XXkg

*all weights include pedals, computer mounts, and bottle cages.

Post Reply