Aerodynamic rear box? Speed up my commute with CFD type content

I have a longish commute to work, 35km each way and I am trying to reduce the journey time.
I took off my rear rack and pannier and put on a rear wheel cover and some frame bags and it appears to have knocked about 5mins off the commute, it is not just a case of increasing the average moving speed a bit but there are a few stretches where I have to do 45km/h to ride the green wave through the traffic signals, anything below that I get stuck on several reds.

Unfortunately, being pannierless is not very practical though as i need to carry laptop, clothes, shoes, etc. So I am wondering if if a streamlined box behind the saddle would work well aerodynamically and what kind of speed gain to expect? I’m thinking a motorcycle top box mounted on a beam rack would be fairly easy to implement but something more tapered like below would be best but most likely lots of fuss to implement.

Am I right in thinking that I best want to position a box where the hole is shown in in the flow to the rear of the bike in the image below, with as close to 7:1 taper as I can?

BTW electric bike is not really practical as limited to 25km/h
Strava indicates about 75min total journey without pannier moving @ 30km/h, 80min total journey with pannier moving @ 28.5km/h, at 215W av power.

That’s pretty niche, something like Rob English’s Trans Am bike?
http://www.ruckuscomp.com/news/2017/06/02/ruckus-composites-x-english-cycles-trans-am-aero-box

All pretty much bespoke though. What size laptop do you have to take to work?

Hi, good point yes the laptop is the most challenging thing to fit, it’s a 15″ workstation measuring 360x240x12mm (slightly rounded up).

I saw that Trans Am bike when I was doing a google search. He tried out the rear box by carving it out of polystyrene and sending it somewhere to then make the box out of carbon fibre. I think if I was making a box I’d definitely want something more rounded top profile and longer tapers.

I am a bit surprised there isn’t more out there in terms of aero commuting goods given the number of people commuting on fairly high end CF/Di2 bikes.

I am a bit surprised there isn’t more out there in terms of aero commuting goods given the number of people commuting on fairly high end CF/Di2 bikes.

I’m not.

Do you really have to carry your laptop?

I do try to reduce laptop haulage but sometimes I do have to carry it.

A full frame bag would carry your luggage and laptop (your most challenging item to carry IMO) if you get the right one. You could then mount a couple of bottles on cages from your saddle triathlon style.

I’ve no idea on the effect of the full frame bag on your aerodynamics but it must be better than a rack and pannier.

TT Extensions are surely the fist option

TT Extensions are surely the first option

Yep. Plus wear a skinsuit, aero helmet. You are more draggy than a bike.

Deep section front has way more benefit than a disc rear.

I wonder if a rucksack of the right shape, and a suitable rider position, can smooth out the airflow? Have the bulk of it lower down and keep it narrow.

Laptop on its side inside main triangle. Replicate TT position etc. What about a recumbent. Better aerodynamics and carrying space.

There’s not a cat in Hells chance I’d use a disc rear wheel for commuting.

Commuting isn’t/shouldn’t be a race, you’ll just end up in an accident.

I commute a similar distance and drop my stuff at the office on a Monday with panniers and racks and then try to ride Tue/friday on a bike without them. I also use small pannier bags (front rollers) on the rear. My latop is a 17″ mobile workstation, so whilst it is portable, the laptop and the PSU are almost 8kg. My office were kind enough to provide another laotop which I keep at home.

Get a cheap chrome book?

Can you get into the drops and maintain that position? I would hav thought that position and clothing would be the main benefit. Followed by deep section rims.

Getting rid of everything on the bars and TT May help with aero.

As someone has said. You are a much bigger lump than the bike so probably better to minimise your frontal area than the bike.

drop my stuff at the office on a Monday with panniers and racks

This

another laotop which I keep at home
And this……

When I used to commute by bike I took 5days clothes on a Monday and then take them home on a friday. Left the laptop at work over night during the week and only took it home at weekends if I had to.

Have a look at the Carradice SQR Slim saddlebag with the SQR bracket, you should be able to mount it quite high on the seatpost to get best aero position for it.
Prehaps you could bodge some kind of fairing to make it more aerodynamic?

Concentrate on the other end of the bike. A frame mounted fairing will smooth the airflow around your body and you could create luggage space behind it.

I wonder if a rucksack of the right shape, and a suitable rider position, can smooth out the airflow? Have the bulk of it lower down and keep it narrow.

Didn’t Fränck Schleck try that CamelBak base layer with integrated bladder to try and improve aerodynamics in a TT?

Don’t piss about.

Buy a cervelo px5 and buy a laptop to fit in the BB “glove box”. Sorted.

Nothing wrong with a disc on the back. Add a 60 mm front for more aero gains, and get down not some aerobars. Position is the biggest factor. Skinsuit is also very efficient, but I only commute in mine if racing after work!

You could also consider http://www.ogio.co.uk/ogio-no-drag-mach-1-backpack-stealth.html an aero rucksack.

I use an sqr slim as mentioned above, I have it mounted quite high and look like I’ve got a spoiler….

As the others have said, you are the most draggy thing on the bikes.assume you are on the drops the majority of the time and not wearing club fit clothing?

I am a bit surprised there isn’t more out there in terms of aero commuting goods given the number of people commuting on fairly high end CF/Di2 bikes.

Because people that commute aren’t that bothered about shaving seconds off their time. Mu commute is about a mile less than yours and I’ve never ever though of getting that much more aero to save time.

I occasionally see Graeme Obree on my commute, he rides an old tourer with panniers but rides in his ‘superman’ position in the long 12 mile traffic free stretch.

It might be the IT Consultant in me, first I was going to say – get another device and share data between work and home (if your in-house nerds will let you).

But then I took a step back from the problem – either you’re working from home when you shouldn’t be (I.E. In your own time) or you’re commuting pointlessly – if you can work from home, work from home and use Skype.

Then get up every morning, ride 17.5km away from your house without carrying anything, then stop, smile at the absurdity of it all and ride 17.5km back.

I’ve made it my goal in life to do whatever I can, however small an impact it makes to save the world’s energy problems by trying to help people stop getting up in the morning and traveling from one place, to another to communicate electronically, it’s just daft. I know OP is a cycle commuter, but most people aren’t.

http://www.chainreactioncycles.com/topeak-mtx-trunk-bag-ex/rp-prod28664?gs=1&utm_source=google&utm_term=&utm_campaign=Chain+Reaction-UK-PLA-PLA-All-DT-SE-Shopping+QLB+Manufacturer+Desktop&utm_medium=base&utm_content=mkwid|s3W84OJ0L_dc|pcrid|161845658788|pkw||pmt||prd|89411UK

and

http://www.chainreactioncycles.com/topeak-beam-rack-ex-mtx/rp-prod28819

Also this bit

Strava indicates about 75min total journey without pannier moving @ 30km/h, 80min total journey with pannier moving @ 28.5km/h, at 215W av power.

How did you manage to remove all other factors that affect your commuting time so you know the panniers are the only thing that made the difference?

I’m trying to commute ~25 miles each way at the moment (building upto doing it every day).

Leave shoes and trousers at work, shirt, underwear, sports towel and cloth in a 5l drybag bungeed to the bars. I have to change the towel and cloth daily as there’s no shower so it’s just a wipe down at the sink. I don’t carry anything else other than the usual jersey pockets full of crap.

If you want to gain 5 minutes, get up 5 minutes earlier. Although at 1h40 I’ve a lot of time to contemplate whether disks and deep section rims would be faster. I considered a TT position, but even though there’s only 1000ft of climbing it’s in short undulations which aren’t conducive to fast TT’ing, and the flatter bits are around town or on horrible road surfaces.

For everybody saying that or something similar – the OP’s proposal of a tail fairing would decrease the drag of his body more than any of the standard aero measures. Bit of a nightmare in a side wind though.

If you want to be a lot quicker with all that crap then drive!

Otherwise do what everyone else has said and leave it all in work and then cycle in free of all that weight.

I’d be building some sort of pointy nose cone with a windscreen shield to stick stuff in. I think the shiv used to have something similar for water.

Fit the laptop inside the frame of the bike, where the triangle bag is. I imagine you could bodge a laptop sleeve and some Velcro / zip ties fairly easily

Or of course, listen to all the sensible suggestions about taking a weeks worth of kit in etc…

Or…………

Obtain a 2nd identical laptop for home use, and an external SSD, flash an image of the current internal drive on the laptop onto the SSD, then remove the internal drive. Set both laptops up to boot from an external drive and voila, the laptop is now a ~200g SSD drive.

May be MAC address issues though as those stay with the laptop.

John Nobile won the Great Divide Race using exactly what you are after – an aero rear beam rack box (oh, and a front fairing). Both carbon/kevlar but homemade unfortunately, as is I think the rack – they are all pretty niche, though similar fairings are available by i.e. Zzipper.

Portrait-John Nobile by Adventure Cycling Association[/url], on Flickr

Integrated lights in the fairing, and the fairing means you can keep a normal position with aero benefits. A few discussions around the web as to whether they actually make much of a difference or not on an upright vs recumbent bike…

Otherwise for your setup, TT bars will likely make the most difference, then aero clothing or skin suit plus shoe covers, mid section front wheel, road aero helmet… (to keep it relatively practical for commuting vs a TT machine). And small things like figuring more aero places for lights, reducing the number of bags in random places etc. And I guess an aero frame/seatpost/bars if you have the money!

I was hoping that the aero benefit for a rear fairing can be very significant as a majority of drag is created by trailing area wakes and not leading area pressure zones but I am far from being expert in this area so would really appreciate some expert advice, I while ago I did try to set up an analysis in openFoam but it got a bit too tricky/time consuming to do as a little project. Surely a rear fairing would make an order of magnitude more difference than switching from normal lycra stuff to full race gear and aero helmet though?

I saw the MTX, looks better than a pannier perhaps, not sure if laptop will fit.
Rucksack looks nice, albeit expensive, but very hot here so best not to wear anything on back, I still want to consider aero gains of rear fairing too.
Laptop does not fit in frame triangle.

Based on what a lot of people are saying it looks like you want some more background: When I got this job I started out commuting 4-5 times a week, but after a few weeks I realised it was too tiring for me to do it that often and was becoming too much of a chore, so I dropped back to 2-3 times a week. I’ve now improved a bit, but not enough to go back to cycling more often, I am on a precipice where if I can make things a bit easier/quicker I can do more cycling trips vs paying out for Taxis or cramming myself on buses and trains. Ideally, I’d stop eating so much crap and drop some weight, but realistically this is not going to happen so I’m looking for technical solutions, besides playing with technical stuff and eating ice cream is far more fun than eating lettuce.

As mentioned previously, if I am more aero then I think I’ll be able to catch more signal green waves without having to push really hard. I’m generally cycling in 30C heat with 80%+ humidity so which makes stopping not fun at all, immediately start sweating buckets etc. Plus any time saved is a bonus an extra 5 mins in bed in the morning is very welcome, plus the closer I travel to motor traffic speeds the safer it is on these roads, plus going fast is fun.

I do have a spare base/aero bar which I’ve contemplated putting on the bike at some point, but I don’t think I’ll be comfortable spending much time on the aero bars, I really need my hands on the brakes most of the time incase a car cuts me up. Plus it’d leave me without a UCI road race legal bike and I occasionally like to do races which need a compliant bike.

P5X a bit on the expensive side and I’d rather keep my commuter cheap and cheerful. I do have a P3 which is nice and fast but would rather keep that for more special occasions.

I rarely use drops, when I am going at pace I usually grab the top of my hoods with my forearms flat which does result in a pretty flat back and I understand is more aero than riding in the drops, otherwise I do not have a flat back and could be more aero but I am not good enough to ride with a flat back all the time, my bars are about 160mm below my saddle height though.

Sometimes needing to carry laptop is simply a design constraint, sometimes I’ve gone to a meeting on the way home the previous day, or need to go to a meeting on the way into work the next day, etc.

How did you manage to remove all other factors that affect your commuting time so you know the panniers are the only thing that made the difference?

Well I have a powertap hub giving some power data but other than that to be honest the answer is that I didn’t, it’s highly subjective conclusion but it’s the best I can do with available data.

But then I took a step back from the problem – either you’re working from home when you shouldn’t be (I.E. In your own time) or you’re commuting pointlessly – if you can work from home, work from home and use Skype.

Then get up every morning, ride 17.5km away from your house without carrying anything, then stop, smile at the absurdity of it all and ride 17.5km back.

I’ve made it my goal in life to do whatever I can, however small an impact it makes to save the world’s energy problems by trying to help people stop getting up in the morning and traveling from one place, to another to communicate electronically, it’s just daft. I know OP is a cycle commuter, but most people aren’t.

It’s 35km each way, not 17.5km, if I work from home I’d either be very uncomfortable or turning the air-con on all day which is not great for the environment, plus the working culture here is different, they expect face to face meetings.

The other option for true speed increases is of course a recumbent, but they aren’t for everyone.

Or a speed pedelec type ebike, not sure what regulations for that are where you are though (presumably not UK if it’s 30 degrees! Licence, insurance, proper helmet and possibly licence plates needed in the UK as 15-28mph capable bikes are classified as mopeds in UK law I think).

What about an e-bike? De-restricted it would give the performance you’re looking for and with normal racks and panniers and would also save you some effort, perhaps even allowing you to ride 4-5 times per week.

Goodness don’t people read all of my huge and rambling OPs 😉
Here [in Singapore] ebikes must cut out power at 25km/h. [Also must be under 20kg, must have an official registration/tag, soon will require licence plate, unlike bicycle are not allowed on footways] Anything else with two wheels is a motorbike and subject to high tax etc.

Oh and recumbent I wouldn’t have space for it plus I would end up under the wheels of a lorry.

What about an e-bike? De-restricted it would give the performance you’re looking for and with normal racks and panniers and would also save you some effort, perhaps even allowing you to ride 4-5 times per week.

Derestricted it would be an unlicensed moped with a flat battery before the end of the round trip.

Others have said it but I’ll say it again – get your body in the right position, it’s bigger than anything else. I reckon if you got a rack top bag it’d be pretty much in your slipstream so any drag would be minimal. Wheels make very little difference, maybe the effect is psychological allowing you to hit the green wave, or maybe you had more favourable wind?

I’ve started to occasionally rest my forearms on the tops on the commuter – it’s quite a high front end so this is comfy, not sure I’d have the confidence on the road bike – and it gives me about an extra gear for the same effort (so 5-10% speed increase). Most of the time it’s not safe to ride like that on my commute though, so it makes no difference to overall time.

The road bike saves a couple of minutes (over a 10-11 mile commute), and it saves this even when I don’t take a pannier on the normal commuter. I suspect the significant weight difference (small difference) plus lower bars on the road bike (much more significant difference) are behind this.

Oh and recumbent I wouldn’t have space for it plus I would end up under the wheels of a lorry.

This is a pity as I would like feedback on one I’ve seen that’s fully faired with ample luggage space (but it’s a bit spendy). It’d be great on days with a big headwind I reckon. But not great for cutting through traffic or for storage.

Topeak made an MTX laptop case, but these are rare and, I believe, discontinued. I have such a rack (V-type) and like it very much. It will take a change of clothes but not a laptop. Won’t clamp an aero seatpost either 😉 .

You’d want the A-type to raise the bag to behind your derriere. You could fashion a cover to go around the bag to a tail quite easily with corraplex. I would avoid the bags with drop down pannier sides, if you don’t use them, they fill the side pockets and make this unusable space. Mine carries spares and a coat all the time, and lives between the beam rack and my recumbent trike’s Topeak touring MTX rack. The rack is very secure against rotations and I have ridden with it off-road regularly.

I think something like this: https://www.alpkit.com/products/koala will make a big difference over panniers. I know its not aerodynamically shaped but reduces the frontal area of the bike compared to panniers and hides behind the rider.

Goodness don’t people read all of my huge and rambling OPs
Here [in Singapore] ebikes must cut out power at 25km/h. [Also must be under 20kg, must have an official registration/tag, soon will require licence plate, unlike bicycle are not allowed on footways] Anything else with two wheels is a motorbike and subject to high tax etc.

In my defence, your only objection to an ebike in the OP was a comment related to assist cutting out at 25KPH which I addressed with the “de-restricted” aspect of my post.

If the bike had a 600w/h battery, you’d get 40-50 miles out of it at full power.

Yep you likely have to pay tax anywhere on a speed-elec ebike e.g. anything over the local cutoff limit. It would get you to the office faster and without sweating as much, and if you can afford a Cervelo P3 frame I doubt the tax would come into the equation much! (And why not use that, it would be faster than the posted bike I’m sure, I’d forgotten it was a TT frame).

Toppeak Office MTX laptop bag plus some corraplex or similar as TiRed suggested? Looks like it is still available in the states…

FWIW i use a backpack and I don’t notice any difference in my average speed compared to not using a backpack (i did notice panniers slowed me down though, especially if there’s a headwind).

You are definitely vastly overthinking this.

I really can’t see a tapered back box making anything other than a minimal difference to your commute time compared to a standard backpacking style seatpack or even just a bag lashed to the top of a pannier rack out of the airflow.

However, you are dead set on this plan, and given no off-the-shelf aero-laptop-back-box’s exist.. what about getting some benchmark times in to determine maximum possible speed gains?

Can you ride your commute on a borrowed aero/TT bike or even just your own bike carrying nothing to see how much faster it is. Or just fashion up some kind of non-structural back box out of cardboard and sellotape or something?

I’m guessing you’ve looked at sites like this?
https://cyclingtips.com/2010/04/biggest-bang-for-your-buck-in-time-trial-equipment/

What about sticking a paramotor on your back??

Or… crazy suggestion, get a training/diet plan and try and get fitter?