Question to the aero gurus - "non aero" frame vs Cervelo S5 frame / fork / seatpost

Back by popular demand, the general all-things Road forum!

Moderator: robbosmans

Post Reply
mbrider
Posts: 34
Joined: Fri Mar 12, 2010 10:49 pm

by mbrider

I have a 2008 Trek Madone 5.5 with an Easton EC90 SL carbon fork - this fork has a different rake / trail than the stock one. I mention this because it not only makes the handling a little sharper, but also brings the front wheel closer to the down tube on this bike. Am I crazy to think this helps with the aero of this bike too?

So my question is, all other things being equal (wheels, SRAM Etap, brakes, aero bars, position) what would be your guess as to the wattage savings - a new Cervelo S5 frame / fork / seatpost vs 2008 Trek Madone 5.5 frame / Easton EC90 SL fork / Trek seatmast?

This model of the Madone has an aero seatmast, mine is the H1 / pro fit (140mm headtube / 56 size) and I have a "slam that stem" bearing cover, so the position is quite low. I can achieve the same position with the Cervelo S5, but might have a very small spacer. The Madone has some other design ques that leads me to believe it is not too bad with regard to aero. The model after this one (I think 2010?) switched to more traditional tubing shapes - round downtube, round seatmast etc.

The Madone model I have has a triangular shape at the top of the downtube and is a bit like a boat hull at the bottom of the downtube. The shape of the underside of the top tube has a very subtle curve and similar boat hull shape too (something fairly similar looking to the underside of the latest super aero Madone). The seatube / seatstay / top tube junction is a bit unique as well, and fairly narrow (though certainly not as narrow or aero as the S5). And lastly, the "yoke" above the seatstays is a closed design - my guess is that this has some aero properties as well. Anyone know what happens with the air that comes off of the rear wheel when spinning, inside that small triangle behind the seatube?

My guess is that there is about a 10 - 15 watt advantage for the Cervelo S5.

What do you guys think?

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



DamonRinard
in the industry
Posts: 396
Joined: Fri Apr 29, 2011 8:32 pm
Location: Connecticut, USA

by DamonRinard

mbrider wrote:So my question is, all other things being equal ... what would be your guess as to the wattage savings - a new Cervelo S5 frame / fork / seatpost vs 2008 Trek Madone 5.5 frame / Easton EC90 SL fork / Trek seatmast?


If I remember correctly, maybe 25 Watts at 40 km/h.
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

User avatar
cyclespeed
Posts: 1112
Joined: Mon Jun 06, 2016 8:45 am

by cyclespeed

25 watts sounds like a hell of a lot to me, assuming the body position is equal.

User avatar
BRM
Posts: 817
Joined: Sun Mar 16, 2014 3:43 pm

by BRM

I think he forgot the comma . . . . :D

youngs_modulus
Posts: 668
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

Without a wind tunnel or CFD program, there's no way to answer your question with any certainty. The fork swap you mention will make no detectable difference, however.

That said, you could get pretty close by comparing Cervelo's numbers for its R3 to those for its S5. Those will get you in the right ballpark, and you won't do any better than the right ballpark without CFD, a wind tunnel, or possibly the Chung method.

mbrider wrote:I have a 2008 Trek Madone 5.5 with an Easton EC90 SL carbon fork - this fork has a different rake / trail than the stock one. I mention this because it not only makes the handling a little sharper, but also brings the front wheel closer to the down tube on this bike.


Minor nitpick: If by "sharper," you mean "faster-handling," then you're imagining things. A fork that brings the front wheel closer to the down tube than the stock fork has less rake than the stock fork. It would result in a slower-handling bike than the stock fork would.

To make the handling "faster," you want more rake. That's because increasing take decreases trail. This is counterintuitive to many people, but it's true. Have a look at a geometry chart that explains rake and trail and you'll see what I mean.

mbrider
Posts: 34
Joined: Fri Mar 12, 2010 10:49 pm

by mbrider

Good to know, regarding the fork rake / trail. Still, for some reason the bike is noticeably more responsive and easier to crossover / switch direction. could be due to the wheelbase being shorter or that this set up is significantly lower, therefore placing more body weight over the front wheel.

I think you are pretty close that the Madone is similar to the same aero as a Cervelo R3, though with an aero seatpost.

Regarding the aero question - let me ask in another way. Lets baseline on a Specialized Tarmac SL4 with standard handbuilt clinchers 28/32 spokes / regular round bar / cables in the wind / standard brakes sticking out / regular pedals.

What would be the aero advantage of a Cervelo S5 with all the aero do dads (zipp 404s ~ 10 watt / Cervelo aero bar ~ 6 watt / SRAM Etap ~ 6 watt / TriRig front brake / EE rear brake ~ 2- 3 watt combined / aero pedals ~ 2 watt)

Would the aero advantage be 45 watts over the Specialized? 50 watts?

Lets keep this as a discussion about the bikes and not about position. Assume the same position can be achieved on either bike.

wingguy
Posts: 4318
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

mbrider wrote:Regarding the aero question - let me ask in another way.

Dude, that's not asking the question in a different way, it's asking the same question just with different references. The answer is just the same - no-one knows. Seriously, unless you test them properly (and even that's a big bag of worms), not the foggiest.

Well, actually one thing is certain - you can't take the theoretical savings of each component and just add them up. It absolutely, 100%, does not work like that. So 50 watts? I'm afraid you need to scale your expectations way back. Sorry.

youngs_modulus
Posts: 668
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

mbrider wrote:Good to know, regarding the fork rake / trail. Still, for some reason the bike is noticeably more responsive [...]

Would the aero advantage be 45 watts over the Specialized? 50 watts?



mbrider, I can see from your thoughtful responses that you are a man unburdened by reflection. You're no slave to science or analysis; rather, you plow forward with all of the reflexive determination of a newly-gelded ox.

Here's the scoop: the S5 will save 51.7 watts over the Specialized, no matter what speed you're going. You'd be a fool to think about it a moment longer.

I can't believe Wingguy tried to confuse you with the facts. You demanded a simple answer and now you have one. If the world had more people like you, people who insisted on easy answers to hard questions, we'd have a lot more easy answers. And who wouldn't want that?

mbrider
Posts: 34
Joined: Fri Mar 12, 2010 10:49 pm

by mbrider

Heaven forbid I would ask a question. And even worse if I try and clarify something.

You know, this is a forum, you can choose not to answer. Hell you could choose not to even read my topic. But I guess you both have to be a couple of snarky A##holes. Way to live up to the "why are roadies such a**holes?" stereotype.

But I guess aero is more difficult to quantify than weight. Oh no actually it isnt. Or at least it isnt if you actually want to ride your bike.

So go back to oogling over a 10lb bike that no one can actually ride, unless they happen to weight as much as a 8th grade school girl.

*f##k* this forum - Im out

Fiery
Posts: 420
Joined: Sat Mar 16, 2013 9:21 am

by Fiery

youngs modulus wrote:Minor nitpick: If by "sharper," you mean "faster-handling," then you're imagining things. A fork that brings the front wheel closer to the down tube than the stock fork has less rake than the stock fork. It would result in a slower-handling bike than the stock fork would.

To make the handling "faster," you want more rake. That's because increasing take decreases trail. This is counterintuitive to many people, but it's true. Have a look at a geometry chart that explains rake and trail and you'll see what I mean.

It's not really that simple. When fork rake is decreased on a bike, without changing anything else, this results in two things: the trail increases, but the wheelbase (and in particular, the front-centre) decreases. While the increased trail will make steering with the handlebar feel slower, the shorter wheelbase will make the whole bike more eager to change direction, and especially more sensitive to changes in weight distribution - steering from the hips. To a point, the overall handling of the bike will feel sharper without feeling less secure. Depending on what it was like to begin with, it can also become less sure-footed over rougher roads, and quite hard to ride no-handed. Go too far, and the bike will start oversteering, the rear wheel will start losing traction in corners and it will become downright dangerous to remove hands from the handlebar at any time.

Obviously, the opposite happens if the rake is increased: while the steering will feel quicker in hand, but the bike as a whole will keep direction better and feel slower to turn-in. You may have noticed that Paris-Roubaix special bikes typically have more rake with the explanation that it makes them more stable over cobbles - this is what it is about. Go too far in this direction and the front end will start feeling vague with not enough weight on the front wheel and a tendency to sort of drift in direction at higher speed, and hard to pick and adjust the line through corners.

Now, if you were designing a bike from scratch, you would be able to choose the trail regardless of the wheelbase. In this case, more trail would simply mean slower steering and less trail would mean quicker steering, everything else unchanged.
Last edited by Fiery on Wed Sep 21, 2016 3:01 pm, edited 1 time in total.

wingguy
Posts: 4318
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

mbrider wrote:You know, this is a forum, you can choose not to answer. Hell you could choose not to even read my topic. But I guess you both have to be a couple of snarky A##holes. Way to live up to the "why are roadies such a**holes?" stereotype.

Dude. Calm the *f##k* down. I told you the truth, I was polite about it, I even apologised for the answer not being what you wanted to hear. If you're unable to handle even that without feeling slighted in someway, then I'm afraid the internet is not for you.

So just for the sake of your delicate feeings lets try the answer you wanted to hear - yes, the S5 and 404s will save 50 watts at 40kph. Yes, you'll only have to push 250 watts to hold 25mph instead of 300 watts. Just because you changed your bike. Yes, that's totally a real thing that will actually happen. Buy the S5, win races. The world really is that simple. Happy?

But I guess aero is more difficult to quantify than weight. Oh no actually it isnt.

Oh no, it actually is. But if you really do think quantifying aero is as easy as putting a bike on a scale, why are you pissed at us for not having done it for you? Go and do it yourself.

mrlobber
Posts: 1928
Joined: Sat Oct 23, 2010 9:36 am
Location: Where the permanent autumn is

by mrlobber

mbrider wrote:But I guess aero is more difficult to quantify than weight. Oh no actually it isnt. Or at least it isnt if you actually want to ride your bike.



... well, it actually is. Your weight doesn't change substantially depending at which point you're on Earth, whereas aero (if you're so focused on watts) does change significantly depending on speed you're travelling (30 kph vs 45 kph is a huge difference). Now your CdA doesn't change, but is that what you really asked? ;)

There are several threads on this forum where external data (for instance, Tour Magazin) has been discussed, also including S5 vs Specialized, with pictures of test data if you don't want to spend a couple of euros to buy the appropriate issue.

P.S. Completely unscientific n=1 fact: when I started mostly riding aero bikes (including S5) in my training for the past 2 years, my average speed on the road throughout the season has increased by almost 2 kph. But not 50 watts saved, definitely not.
Minimum bike categories required in the stable:
Aero bike | GC bike | GC rim bike | Climbing bike | Climbing rim bike | Classics bike | Gravel bike | TT bike | Indoors bike

sawyer
Posts: 4485
Joined: Fri Dec 15, 2006 7:45 pm
Location: Natovi Landing

by sawyer

As others have suggested, look at the closest comparators and make a guess based on that. Why does it matter more than that anyway?

You will notice the difference of a full aero vs non-aero road set-up ... particularly if you ride with the same people frequently. You'll notice some relative improvement in your performance, and if it's close between you, it might be enough to edge you ahead. Say it is (roughly) 10-15 watts less effort to maintain 45km/h in the bunch ... you are going to notice that.

I'd liken it to having been away from a week's training camp, slept well, ate and rested well.

Anyway, isn't winning the arms race good for confidence?
----------------------------------------
Stiff, Light, Aero - Pick Three!! :thumbup:

User avatar
ergott
Posts: 2870
Joined: Tue Apr 18, 2006 3:03 am
Location: Islip, NY
Contact:

by ergott

Fiery wrote:
youngs modulus wrote:Minor nitpick: If by "sharper," you mean "faster-handling," then you're imagining things. A fork that brings the front wheel closer to the down tube than the stock fork has less rake than the stock fork. It would result in a slower-handling bike than the stock fork would.

To make the handling "faster," you want more rake. That's because increasing take decreases trail. This is counterintuitive to many people, but it's true. Have a look at a geometry chart that explains rake and trail and you'll see what I mean.

It's not really that simple. When fork rake is decreased on a bike, without changing anything else, this results in two things: the trail increases, but the wheelbase (and in particular, the front-centre) decreases. While the increased trail will make steering with the handlebar feel slower, the shorter wheelbase will make the whole bike more eager to change direction, and especially more sensitive to changes in weight distribution - steering from the hips. To a point, the overall handling of the bike will feel sharper without feeling less secure. Depending on what it was like to begin with, it can also become less sure-footed over rougher roads, and quite hard to ride no-handed. Go too far, and the bike will start oversteering, the rear wheel will start losing traction in corners and it will become downright dangerous to remove hands from the handlebar at any time.

Obviously, the opposite happens if the rake is increased: while the steering will feel quicker in hand, but the bike as a whole will keep direction better and feel slower to turn-in. You may have noticed that Paris-Roubaix special bikes typically have more rake with the explanation that it makes them more stable over cobbles - this is what it is about. Go too far in this direction and the front end will start feeling vague with not enough weight on the front wheel and a tendency to sort of drift in direction at higher speed, and hard pick and adjust the line through corners.

Now, if you were designing a bike from scratch, you would be able to choose the tail regardless of the wheelbase. In this case, more trail would simply mean slower steering and less trail would mean quicker steering, everything else unchanged.


Nice, well thought out response amidst the bickering. Thanks.
:beerchug:

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



User avatar
kgt
Posts: 8749
Joined: Sun Jun 18, 2006 10:29 am
Location: Athens, Greece

by kgt

mbrider have you checked RyanH's test?

viewtopic.php?f=3&t=139992&hilit=ryanH

You 'll realize that what you 're looking for is practically non existent in real conditions.

Post Reply