Aerodynamics - bike or rider??

I am the god of hell fire

My question is inspired by the Spesh/McL superbike threads and reviews

How important are aerodynamics to both a GTour rider and the keen amateur?

Im talking road riding and/or racing rather than full on time trialling with its extreme positioning

In racing Im sure every tiny saving counts but what difference does shaving a few mm from the headtube actually have over 200km with a muscle bound Manxman mashing the pedals?

And would a regular bloke really notice a difference over 100km riding a Canyon Aeroad over its conventional sibling let alone a Venge over a Roubaix besides a sore back and neck?

Cheers

twotyred

The bike causes about 20% of the aerodynamic drag the rider 80%. Of that 20% about 10% is caused by the wheels so riding an aero frame will knock a few % of that 10% figure which may be significant if you are racing and will be more significant the faster you are travelling such as in a sprint.

But why would you you get a sore back and neck riding an aero bike? The riding position isn't any different from any other road bike. If you have decent core strength then there's no need for a "sportive" bike with an upright riding position. That's just marketing BS to sell bikes to middle aged guys with bad backs and beer guts.

Buckled_Rims

Aero bikes are mostly marketing hype to sell a sexy carbon frame.

The reality of a GT rider is that they cruise for huge mileages. The average speed for a GT rider hasn't really changed in the last 20 years. I think the Paris–Roubaix average speed hasn't changed for the last 40 years (correct me if I'm wrong someone). An aero bike doesn't work effectively on steep hills as the air flow is far too low, and the high altitude negates the need for aerodynamics anyhow.

However, in TT, aero is essential as rider is almost permanently in the tucked in position.

If this Venge starts winning all the races I will, of course, eat my Assos!

cougie

Rider position is far more important than the aeroness of the bike.
Take a head on shot of you on the bike and trace it onto graph paper. Now look at how many squares is your body and how many the bike.

It will give you a rough idea anyway.

Bar Shaker

By far the biggest drag cause on the bike will be the spokes.

The spokes at the top of the wheel are travelling through the air at twice the speed of the bike and they will be creating a lot of drag.

A true foil section creates approx 20% of the drag from a round section, of the same cross sectional area.

pianoman

By far the biggest drag cause on the bike will be the spokes.

The spokes at the top of the wheel are travelling through the air at twice the speed of the bike and they will be creating a lot of drag.

So assuming we only use aero spokes, what is better; medium-depth rim with few spokes (e.g. Bontrager Race Lite Aero) or deep rim with maybe a few more spokes (e.g. Superleggera 50mm carbon wheels, or other generic ones such as Planet X or Token)?

Is it best to just have as "short" spokes as possible?

Monty Dog

Firstly, the Paris-Roubaix record in exceptional as it was a howling tailwind - any increase in race average speed is more attributed to training methods, PEDs than any equipment changes.
In terms of performance improvements, the biggest impacts are as follows:
1. Rider position
2. Wheels
3. Aero helmet and clothing
4 The rest i.e. bike
Consequently, the impact of an aero frame is going to be marginal at best and frankly some of the claims is marketing bollox.
Another factor is comfort - deep rims and frame tubes can make a bike extremely stiff and will induce fatigue more quickly - fine for short races, but a killer for long rides on rough roads.
Finally, a harsh frame can actually reduce power delivery on a rough road because the wheels are bouncing around so much.

Ber Nard

In racing Im sure every tiny saving counts but what difference does shaving a few mm from the headtube actually have over 200km with a muscle bound Manxman mashing the pedals?

And would a regular bloke really notice a difference over 100km riding a Canyon Aeroad over its conventional sibling let alone a Venge over a Roubaix besides a sore back and neck?

When you're at the top of your game like Mark Cavendish, then it becomes all about marginal gains. He (probably) can't get that much stronger, his bike can't get that much lighter (UCI rulings) so the obvious place to make gains is in aerodynamics.

For the keen amateur, more significant gains will be made by training harder to increase power or lose weight. And, unless you're very lucky, most people own a bike where saving height would be more beneficial than a fancy pair of aero wheels.

Rob

danowat

You can make big improvements with rider positioning, the more aerodynamic your position you can for faster for longer, I thought the figure was 90% drag is rider, 10% bike, however, saying that, I can definately tell the difference between a set of "normal" wheels with normal spokes compared to my TT wheels (which are deep section and bladed spokes)

Slack

If riding on the level, hands on hoods, and speed is 18-19mph, moving onto the drop bars increases my speed by 1-1.5mph for the same level of effort.

pianoman

I can definitely tell the difference between a set of "normal" wheels with normal spokes compared to my TT wheels (which are deep section and bladed spokes)

How deep is "deep" if you don't mind me asking? I'm not exactly bothered about comfort as I use traditional FSA wheels for everyday riding.

danowat

50mm carbon tubs with bladed spokes vs my Easton EA70

matt.rochfort

Agree with slack, riding on the drops without any extra effort seems to give you an extra 1 mph from around 20 mph so about 5% quicker. Much of the aero stuff is surely marketing hype or so marginal you may as well save you money and train harder or ride behind someone else! Aero bikes look pretty horrible anyway. Just bought a traditional geometry steel frame and building up so it will be interesting to see how different from my CAAD9 it will be on my 20 mile commuting time - not a lot i expect but much more comfortable, and better looking.

Buckled_Rims

Slack wrote:

If riding on the level, hands on hoods, and speed is 18-19mph, moving onto the drop bars increases my speed by 1-1.5mph for the same level of effort.

But do you want to be tucked in on the drops for 300km of the Milan San Remo?

The vast majority of the time, riders are totally un-aero...eating, drinking, talking to each other, stretching, next to team cars, fighting with Cadel, etc....Then for that small percent of the actual race a mad push, but then again a sprinter can be all over the place. Even Cav is not the tidiest rider to take advantage of a small aerodynamic bike.

Riding in the peloton is probably the most aero efficient way to cycle anyhow.

on-yer-bike

The way to really appreciate how much the aerodynamics of a rider effects speed is to go down a hill in the tuck position with your hands either side of the stem. In this position I always close on the rider in front and i am not heavy. Wheel bearings probably have a big effect on speed too.

flanners1

.....and aero spokes and rims

FransJacques

If you *want* a new bike and are interested in an Aero bike then by all means go for it - check out the Canyon, it's amazing.

If you already have, for example, an R3 and want an S3 only b/c it's aero, or if you have a Canyon Ultimate CF and want the Aeroroad *just* b/c it's aero, then don't expect to see any huge improvements in performance unless also you get some 404s or 808s.

If you TT then get a specific TT bike with 808s. The Shiv is mega sexy! So is the Rabo Giant.

Dodger747

Does anyone know how riding in an aero-tuck on the hoods compares to riding in the drops?

Such as this...



I ride a lot in this position and really like it but is is more efficient in the drops?

warrior4life

I always thought flat for arms where better, I used to practice by putting my arm out the window while doing 70mph down the motorway, Flat arm just cuts through the air but tilt it down a little and its a huge difference.
I think this position is very aero but you cant hold as long as you can on the drops as your triceps take a lot of weight.

FransJacques

It's 6 of one. in that pic his upper arms are at their worst aero angle - i.e. 90 degrees - but his lower arms are very aero. Note that TT bars put you basically in this position.

In the drops, your whole arm is at a, I dunno, 30 degree angle to the breeze, but it's your whole arm, and they're necessarily at a slightly wider stance so more in the breeze.

I guess to get really aero if you're pedalling into a big breeze, would be to put your hands on the tops near the stem, bring your elbows in, but without changing your back angle. Imagine if Fabian did this in the pic above - he took his hands of the hoods and put them near his stem. That would get his arm narrower, maybe out of the wind more, but it might present problems of his elbows hitting his knees.

i think narrow hands & elbows is fast b/c it's close to the original Obree position.

cougie

It's a balancing act - if you go too low - you may not be able to generate the power.
Aero bikes are nice but the average Sunday rider wouldn't see any measurable benefit.