# Question about aero bars



## jfd986 (Jul 17, 2011)

Aero-bars, or tri-bars, as they are otherwise called, are supposed to allow the rider to get into an aero position.

Oh yeah?

I'm a super-novice rider who currently averages 13 mph after 100 miles of city riding, and I have no idea how to verify my elevation gain/loss per ride. My top speed on my bike is 42 mph made on a giant decline on the way to the mma gym.

1) Scientifically speaking, what is the average speed that a rider must be able to attain before gaining significant advantage from aero-bars? 

2) When this advantage is gained, how large is it? How many mph faster, how many fewer minutes in a 20 mile ride ?


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## spade2you (May 12, 2009)

Entirely too many variables to give you exact numbers, but they're faster from an aerodynamic profile, especially when a TT helmet is used. 

When descending, you can often get in a better tuck on a road bike than a TT bike. 

Benefit and gain depends on how much of the slow speed is due to poor aerodynamics vs. a lack of motor.


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## AndrwSwitch (May 28, 2009)

I think around 15mph (instantaneous, not average) on a flat road is fast enough to be effected by good or bad aerodynamics.

How much benefit a rider gains is pretty subjective. My city averages are influenced more by my luck with traffic signals and getting stuck behind slow cars and other cyclists than by how I'm feeling that day. Which can be frustrating, especially now that I have some software that can track times and spot PRs for me - it would be fun if being strong and feeling good on a day meant I could do some of my usual routes faster, but that's just not true in a city. I try to get out onto less interrupted roads when I'm on a "real" ride. I still chose a road bike for my commuter, but that's partly because it was available for the price I wanted and partly because I'm more comfortable on them, when I'm not actually mountain biking. If I'd run into a mountain bike in my size and at the right price first, I'd probably have bought it instead, and it would probably have a minimal effect on my averages.

Of course, nobody will give me a prize for completing my commutes or training rides faster, and if I compete on the road, the vast majority of those events won't allow aero bars. So as I see it, no benefit, unless I get a lot more serious about road racing and want to practice the position for better TT results.

Cycle tourists like them because it's another option on a long ride, and may save them a little energy. Which is nice if you're riding to get from A to B and see some country and don't care if it's a good workout.


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## spade2you (May 12, 2009)

I believe the initial appeal of touring bars was to change to a different position for comfort, but the slight aerodynamic benefits didn't go unnoticed. Just because touring isn't a race, saving a little effort on long rides is never a bad thing.


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## Jerry-rigged (Jul 24, 2009)

> 1) Scientifically speaking, what is the average speed that a rider must be able to attain before gaining significant advantage from aero-bars?
> 
> 2) When this advantage is gained, how large is it? How many mph faster, how many fewer minutes in a 20 mile ride ?


1) - if you are riding into big good headwind, Aerobars make a difference even at single digit speeds.

2)no idea, I never TT'ed.

I did ride a lot with aero bars, I liked them. I ride solo a lot at about 15mph, and if there is any wind, the bars make a noticeable difference in the effort level...

Also- other than the aero position, there were two other things I liked about the bars - one - gives you a way to get all your weight off your hands (really nice on a long ride) and two, riding on the bars works a different set of muscles - more gluts and upper hams. Again, on long rides, this is nice...

Last - I would never ride the bars on downhills or other high-speed stunts - you really don't have a lot of control over the bike when you are on the bars, and you can't get to the brakes...


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## spade2you (May 12, 2009)

Jerry-rigged said:


> Last - I would never ride the bars on downhills or other high-speed stunts - you really don't have a lot of control over the bike when you are on the bars, and you can't get to the brakes...


You can, but I wouldn't do it unless I knew the road was safe enough and conditions were dry. In my last ITT, I had a short and steep descent with a gradual left bend. I had ridden that descent many times before, but took me a few attempts to feel comfortable on my TT bike. I briefly hit 45mph and I'm usually in the 30-35mph range on my regular road bike on that same descent, although I'm usually a little preocupied to be watching my computer while going that fast.


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## minutemaidman (Jun 14, 2010)

I see way too many guys and gals on aero bars on a bike with comfort geometery (really tall head tube) and stems angled way up. They dont look smooth or comfy. Dont these people know better? They would be much lower and more aero just getting in the drops.


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## jfd986 (Jul 17, 2011)

minutemaidman said:


> I see way too many guys and gals on aero bars on a bike with comfort geometery (really tall head tube) and stems angled way up. They dont look smooth or comfy. Dont these people know better? They would be much lower and more aero just getting in the drops.



In what book is the geometry of different bicycles explained ?


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## AndrwSwitch (May 28, 2009)

Are you being sarcastic, or is this an honest question?


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## minutemaidman (Jun 14, 2010)

AndrwSwitch said:


> Are you being sarcastic, or is this an honest question?


I was wondering too. I dont know of a "book"


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## AZPOWERHOUSE (Dec 16, 2008)

I have seen this in books. I have two triathlon books sitting next to me that mention it: _Triathlon Made Easy_ and _Going Long._


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## jfd986 (Jul 17, 2011)

AndrwSwitch said:


> Are you being sarcastic, or is this an honest question?


Honest question. I've never been in a race, never maintained a bike myself, never been taught or learned anything about bikes. I heard the word "Geometry" being thrown around when I read some articles about fitting, but I have no idea what the geometry of a TT bike vs. a cruiser actually entails.


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## wim (Feb 28, 2005)

jfd986 said:


> When this advantage is gained, how large is it? How many mph faster, how many fewer minutes in a 20 mile ride ?


In wind tunnel tests, clip-on aero bars fairly consistently increase speed about 1 mile per hour at 25 mph with everything else being the same. This at 0 yaw angle (resisting air directly onto the front of the bike). That 1-mph increase would give you a 2-minute savings over a 20-mile course ridden at around 25 mph. Keep in mind that these are lab figures—on the road, it would be more difficult to achieve that 1-mph increase.


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## AndrwSwitch (May 28, 2009)

jfd986 said:


> Honest question. I've never been in a race, never maintained a bike myself, never been taught or learned anything about bikes. I heard the word "Geometry" being thrown around when I read some articles about fitting, but I have no idea what the geometry of a TT bike vs. a cruiser actually entails.


If you're looking at all safety bicycles - the group of all bikes with wheels that are the same size and the rider in a position in which he sits well above the pedals and his hands are forward of his feet, basically almost all contemporary bikes, there's a pretty wild variety of different geometries. It can really refer to almost all aspects of the way the frame is put together.

If you're only looking at the group of XC mountain bikes, hybrids, and massed start (as in, drop handlebars) road bikes, it gets a little easier. They mostly have a 70-72 degree head tube angle and a 73-75 degree seat tube angle. This is the angle above the horizontal of the axis of the tube. For a rider who pedals continuously, the seat tube angle puts the clamp of a setback seatpost in the right place for the saddle to be close enough to right for most riders to fine tune with the adjustment available on the saddle rails, and the handling is a fairly well-accepted compromise between stability on flats and descents, and ability to initiate turns and climb. There's some variability here, and it influences a bike's personality. That's why test riding is important.

Race vs. comfort vs. touring geometry is really more about facilitating a riding position than anything else - sometimes comfort/endurance bikes have a slightly slacker (smaller angle) head tube, but it's rarely a big difference. The biggest differences are that they tend to have a shorter top tube and taller head tube. That means a rider can sit more upright and have the handlebars in a good place.

The introduction to this article covers the difference in riding style and bar position pretty well.

http://sheldonbrown.com/handsup.html

Something Sheldon is too charitable to say here is that it's not just power output but power to weight ratio that influences a person's riding position. I'm not a big guy, at 150 lb. I don't know my power output, but I think in absolute terms it's fairly mediocre. However, climbs are my "office" - the part of a race where I'm most competitive with my peers. That's because while my power output's merely medium, I'm pretty small, so my power to weight ratio's pretty good. If I was a much bigger guy, I'd probably have a slightly bigger power output, but I'd be pretty bad on climbs and I'd have to sit more upright on my bikes in order not to put a lot of weight on my hands.

Time trial bikes screw everything up. The assumption is not that the rider should be comfortable, but that he should be aerodynamic and have an acceptable pedaling position for good power output. Also, the little elbow support thingies on the aero bars are made to support weight, and that's supposed to be much less uncomfortable than supporting weight on the hands.

This article talks about the fit of a triathlon bike. Time trial bikes legal in UCI events are almost the same - they just have to meet a couple more restrictions.

http://www.slowtwitch.com/Bike_Fit/..._Reach/Stack_Reach_Primer_Chapter_One_95.html

Both Sheldon and Slowtwitch are great resources for the different kinds of fit their authors preferred.


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## Jerry-rigged (Jul 24, 2009)

wim said:


> In wind tunnel tests, clip-on aero bars fairly consistently increase speed about 1 mile per hour at 25 mph with everything else being the same. This at 0 yaw angle (resisting air directly onto the front of the bike). That 1-mph increase would give you a 2-minute savings over a 20-mile course ridden at around 25 mph. Keep in mind that these are lab figures—on the road, it would be more difficult to achieve that 1-mph increase.


At first glance, that sounds "won't matter to me" fast. But while I never ride 25mph except downhill/downwind, I often ride 10-15 mph into a 15-20mph headwind. And yes, the difference is noticeable, Aero bars vs drop vs hoods (order of increasing effort).



> I see way too many guys and gals on aero bars on a bike with comfort geometery (really tall head tube) and stems angled way up. They dont look smooth or comfy. Dont these people know better? They would be much lower and more aero just getting in the drops.


Even if the HT is tall, and the stem has a rise, the aero bars should help. Now if you are talking tall HT + big stem rise + aero bars, vs big saddle to bar drop + riding the hoods, then yea, the race bike (big drop) will be more aero. But if you only have one bike, the bars will help. Plus they give you an extra "rest your hands" position, which is nice on long rides... Even if they aren't more aero.


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## jfd986 (Jul 17, 2011)

Thanks for the figures, confirms what I saw the other users say, that it's not for someone who's fruit to run errands or get groceries in a city. Even for training rides if and when I start them there's no point i feel, unless I'm training for a race that has a time trial component.


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## spade2you (May 12, 2009)

jfd986 said:


> Thanks for the figures, confirms what I saw the other users say, that it's not for someone who's fruit to run errands or get groceries in a city. Even for training rides if and when I start them there's no point i feel, unless I'm training for a race that has a time trial component.


It _seems_ excessive for someone just running errands, but I've had many road rides heading home in a 30mph head wind where aero bars would have helped get home just a little quicker.


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