Friday, May 5, 2017

Efficiency (2)



Efficiency (2)
Velomobile efficiency is one of the best reasons to own a velomobile.  The subject is fairly complex and I will try to cover the subject in a few posts here.   In my last post I reviewed how aerodynamics played a role in making velomobiles efficient. 

I received many comments and some pointed to items I did not mention.  There are radical ways that could potentially further improving aerodynamics but the potential gain would come at a cost like difficulty to manufacture, complexity, weight, etc.  What I tried to identify were practical and safer ways for improvements. 

Something I forgot to mention however is the potentially positive impact of velomobile shells while riding in the wind.  Not only does the shell reduce the effort when riding up wind but when the wind comes from the side or the back, the shell can act as a sail further improving performance.  On a regular bicycle, the effect is only felt when riding with the wind is coming more or less directly from behind.

In this post I will discuss rolling resistance; again, this is a high-level view at the issue, not a comprehensive thesis.  If readers want to explore this subject, there are many sources that can be accessed on-line but there is still much to be discovered.  Riders may want to perform rolling resistance tests to contribute to the discussion.

Following aerodynamics, rolling resistance has probably the second largest impact on performance.  In my opinion, paying attention to rolling resistance may be even more beneficial for a velomobile compared to a bike.  There are several things that affect rolling resistance that velomobile owners need to take into consideration.

Since the tires are effectively the points of contact with the road, therefore they are the point we measure for rolling resistance.  Several factors affect rolling resistance including weather, temperature, rolling surface but also tire construction, tire size, weight, inflation and type of inner tube/tubeless.  I will try to address most of these factors, more specifically their influence on velomobile performance.

Compared to a bike, a velomobile has three or four wheels increasing the points of contact with the road by 50 to 100%.  Furthermore velomobile wheels have a significantly smaller diameter that make the same tire brand/model potentially less efficient compared to a road bicycle with 700 wheels (size 622).  Most velomobile use significantly smaller wheels such as size 406 (20in) all around or a combination of 406 (20in) tires at the front and 559 (26in) at the rear.  More recently some velomobiles that can accept wide 406 tires have been able to replace those with narrow tires size 451 to provide more tire choices.  Australian Pedal Prix velomobiles use 349 (16in) all around or 349 (16in) at the front and 406 (20in) at the rear. There are exceptions for example the LeMans but these configurations cover most velomobiles and some riders have experimented with other sizes like 650B (size 584) and 24in (size 540).

The heavier weight of the velomobile may also increase the impact of an increase in rolling resistance.  While the weight is distributed over 3 or 4 wheels vs two, think of a heavy cart that you have to push empty vs fully loaded.

One has to recognize that most; maybe all tires are not developed for velomobiles, since the market is too small.  Tires are developed mostly for BMX, MTB, e-bikes and to a lesser extent trikes.  As a result, it is difficult to find the perfect tires for velomobiles.  Tires are adapted to velomobiles, to find the best tires for velomobiles involves research and experimentation.

A smaller diameter tire will be more affected by road surface than a large one.  To illustrate this, imagine you are driving a truck with large tires where you can drive over a pothole while the driver of a Smart car can fit the entire wheel in the same pothole.  The energy of the rolling wheel is almost completely lost when the small wheel gets in the hole while the larger wheel skims over with only part of the tire entering the pothole resulting in a minimal energy loss.

To a smaller extent, tires encounter bumps, holes and cracks even on regular road surface.  While it can be hardly noticeable, it will affect how much power is required to move the velomobile.  One advantage of the velomobile is that the wheels and tires are mostly hidden behind the shell while unfaired bikes wheel and tires are subject to aerodynamic loss.  That loss prompts unfaired bike riders to use narrower tires to reduce the aerodynamic effect while velomobile riders can use wider tires with negligible aerodynamic penalty.  Using slightly wider tires will help minimize the impact of road surface and compensate for the use of small tires.   Unfortunately some velomobiles may not be fit on all velomobiles that have narrower wheel wells.  A wider tire gives more contact surface and provides better weight distribution putting less pressure on the road.

As I mentioned above, all tires are not created equal.  Tire construction incorporates several components that will affect how the tire performs under different conditions.  Tire construction is a set of compromise to meet a perceived market demand.  In order to explain, I will re-purpose some information related to tires I previously posted on BROL.

Tire/tube/sealant weight also has an impact on rolling resistance; as a rule of thumb, if you compare tires of similar construction, the lighter the faster.  Changing the inner tube to a lighter and subtler tube will lower rolling resistance in the same tire and the improvement can be significant.

Tire characteristics
Engineers determine the physical characteristics that will be used in the construction of a tire, this will in turn determination the tire’s different qualities. It is important to note that two tires by the same manufacturer using the same name may have a different construction depending on size or manufacturing plant.  You have to examine tire specs carefully to spot this.

Some of the physical characteristics including:
• number of threads per inch (TPI) - the higher number of threads normally the better;
• foldable bead - faster tires normally fold;
• subtleness of the tire is a factor in rolling resistance;
• Protection rolling band to make the tire more durable and puncture resistant;
• Compound is the rubber mixture used to make the tire;
• Thread is the pattern of groves in the tire - a tire with more groves will evacuate water better but may also increase rolling resistance;
• Weight of the tire will impact the performance a heavier tire will take more power to move it;
• Most tires require tubes but some of the better tires are tubeless.

Some of the tire characteristics to consider include durability, puncture protection, handling, rolling resistance, noise. You also have to take into consideration that these characteristics may be significantly different under hot vs cold and wet vs dry or even on snowy and icy conditions. Unfortunately when it comes time for shopping you may fall victim to marketing hype. Many website will provide an assessment of the characteristics but for the most part the information is biased.

The tube inside the tire will affect the characteristics of the tire.  There are two main type of tubes used in bicycle tires Latex and Butyl What are the advantages/disadvantages of the latex tubes vs butyl.

Butyl Tubes
  • Butyl are inexpensive
  • Available everywhere
  • Available in all sizes
  • Available with Schreader and Presta valves
  • Have a slightly higher rolling resistance compared to latex tubes
  • Pressure remains for longer periods
Latex tubes
  • Much more expensive
  • Not available everywhere
  • Not available readily in velomobile wheel size
  • Available mainly with Presta valves
  • Have lower rolling resistance compared to butyl tubes
  • Requires frequent pumping to maintain desired pressure

Weather conditions and temperature also have an impact on rolling resistance.  As a rule of thumb, rolling resistance increase as the temperature gets.  Wet conditions also increase rolling resistance.  Some tires have provide better rolling resistance in low temperature or in wet conditions so it is important that you consider this when choosing a tire for your velomobile.

Tire pressure is critical to rolling resistance, the higher the pressure the lower the rolling resistance.  For best rolling resistance tires should be inflated to the maximum pressure for the type of tire used.  Some riders in order to further reduce rolling resistance, exceed the maximum recommended pressure but one has to be careful as blowout could occur.  While appears to be true in tests, tests performed by the BHPC found from roll-down tests that a wider tire at lower pressure e.g.: 50-60 psi actually gave lower rolling resistance on a broken road surface than higher pressures, presumably this is due to the suspension effect.  It is not clear if this is also true for fully suspended velomobiles.

Rolling resistance tests:
Several people and organizations perform rolling resistance tests of velomobile and bike tires.  Here are a few places where you will find this information.  There are generally 2 main methods where the rolling resistance of tires is tested.  The most common is to measure the rolling resistance of tire by spinning the tire against a friction wheel/roller.  Rolling resistance is calculated in Watt.  The second is to use a pendulum on a rig where two tires are mounted with the arm of the pendulum at the top.  The arm of the pendulum is pushed to the maximum and released.  The time that the pendulum takes to stop provides a relative measure of the rolling resistance.  The longer the pendulum swings the lower the resistance of that tire.

Some of the tests have compared rolling resistance at different temperature even in snow/ice conditions but I don’t think that the same tests were performed on different rolling surface.

For more information on measuring rolling resistance of tires, you can check Carboro (www.velomobil.ch/ch/en/rollenpruefstand) – The site in German and provides very good information on measurements and tire rolling resistance in general as well as some measurements.
 
Wim Schermer  (wimschermer.blogspot.ca/search/label/bandentest) – Wim Schermer has a blog (in Dutch) where he regularly tests only velomobile appropriate tires size 406 and 559 uses a pendulum to test relative tire resistance.
 
The Bicycle Rolling Resistance website  www.bicyclerollingresistance.com - the site has few tires test for tires in the sizes used by velomobiles. If the same brand/model is tested, check with manufacturer’s site to see if they the velomobile size has the same construction/compound. Use a friction wheel.

On the German velomobile forum, there is a 20in (406) tire testing thread (www.velomobilforum.de/forum/i...t.41020/) where Daniel Fenn and other velonauts discuss tires and post results. Daniel uses a friction wheel.

There is a thread on BentRiderOnline where velomobile tires are also discussed but there are no objective tire tests performed. (www.bentrideronline.com/messageboard/showthread.php?t=133279)

For the more technically astute, it is also possible to measure a specific velomobile overall rolling resistance through roll down tests or with velomobile equipped with a power meter.  These tests help you calculate not only the rolling resistance (Crr) but also the aerodynamic resistance (CdA).  Robert Chung developed a methodology that can be used to perform these calculations.

One important aspect of rolling resistance not mentioned above is to ensure that your velomobile alignment is correct.  When the alignment is not correct the rolling resistance will increase.  Remember that for the lowest rolling resistance, all (3/4) wheels should be properly aligned not only the front wheels.  After your alignment you can test your alignment using a roll down test.  To perform this test you need a road with small hill followed by a long flat section.  On a day when the wind is very calm, take your velomobile to the top of the hill, identify a spot where you can get the velomobile to coast down when you release the brakes and mark that spot.  Perform your first coast down and mark the spot where your velomobile came to a stop.  Climb back to the top of the hill and adjust the alignment of both front wheels very slightly about ½ turn.  Perform the same coast down if you go further, adjust another ½ turn and try again if you go further continue the same if you don’t go back to previous setting.  This should be the optimal setting for the lowest rolling resistance.

Velomobile tire and tube price/availability
On a related note, I searched for tires and latex tubes recently and was very surprised that latex tubes in sizes other than 700 (622) and 26 (559) were basically not available in North America and velomobile tires were significantly more expensive in North America.  Several tire models are only available several months after they are available in Europe and often not even offered by North American distributors. It certainly is unfortunate that manufacturers and distributors policies put North American velonauts at a significant price/availability disadvantage.

IntercityBike

The 4-wheel DF prototype DF-4 made its first public appearance at SPEZI alongside the DF and DF-XL.  The DF-4 had a wheel pants a tail extension.

Sitko-velo

The sitko-velo was another new velomobile making its first public appearance at SPEZI 2017.  The new velomobile made of plywood comes with electric assist.  In my opinion the Sitko-velo will compete with similar velomobiles like the new Cab-Bike and the Orca.

Sunday, April 23, 2017

Efficiency


Efficiency
Velomobile efficiency is one of the best reasons to own a velomobile.  The subject is fairly complex and I will try to cover the subject in a few posts here.  Today I will an overview of what characteristics of makes a velomobile efficient and address aerodynamics.

Out of the box, velomobiles are fairly efficient when you compare to an unfaired bike but there are still many things that will give you an even better performance including several options available from the manufacturers. 

How efficient are production velomobiles?  Again this depends on the velomobile you compare with but if you have a Milan SL or a DF, you have one of the most efficient velomobiles out of the box.  As a rule of thumb I say that since 80% of the effort on a road bicycle is pushing the air, a velomobile should improve this by halving this effort.  This gives a 40% advantage (50% X 80%) to the velomobile.  As a result to maintain a certain speed a bike requires 300W while the velomobile requires 240W X50% +60W = 180W.  I tried to see if my rule of thumb was close so I looked at segments that I rode and compared them to the next rider assuming he/she was riding a road bike.    In one example a rider is pushing 255W for 12.5km on a somewhat flat segment, no wind and a speed of 39.5km.  For the same segment, I rode the same segment with a 10km/h headwind.  I needed 155W to travel at a speed of 47.5km/h.  Leaving the speed difference and wind, my rule of thumb would give me an effort of 204W X 50% + 51W = 153W.  While it appears to somewhat confirms the rule of thumb, the difference in speed and the extra work due to the wind has not been accounted for so the efficiency appears to be even greater on flat ground.  Of course the difference on a hillier course would be somewhat different, as the power to climb the hills needs to be much greater for a velomobile.

I get it, many people are happy with the weather protection and carrying capacity of velomobiles.  Others do not see a need for improvements or are unable to fully extract the performance of a stock velomobile or they opted for e-assist that gives them the boost they need.  Still there is a large segment of riders who want to get as much speed as possible for the power they can generate. Getting the most performance out of your velomobile requires paying attention to the details.

There are four areas where improvements can normally be made: aerodynamics; rolling resistance; weight and mechanical efficiency.

Aerodynamics
There are many ways to improve the aerodynamic efficiency of a production velomobile but it depends on the velomobile you ride.  It may be the low hanging fruit for improving velomobile efficiency.  Every thing that sticks out like mirrors or holes in the shell like the hatch for the cockpit creates drag.  I will provide some ideas on how drag can be reduced but these recommendations have to take into account your own velomobile and circumstances.  Beyond these tips there could be many more improvements that may be possible.

I was reminded of this recently as I started my season riding without any significant modifications on my DF, it was essentially a stock DF.  The only small improvement was a mini visor.  I rode a few weeks until I decided to put on the hood.  That single improvement provided me a 3 to 5km/h average speed improvement on the same courses; this is very significant in the order of 10 to 12% for the same power output.  Going down hills where I had a maximum speed of 62 to 65km/h, I was now maxing out at 72 to 74km/h, a 10 to 14% increase.

Open hatch velomobile and the rider’s head/torso have a major impact on aerodynamic efficiency.  Even a rider’s helmet increases the drag.  First let’s look at the obvious.  Many open hatch velomobile usually have a neoprene skirt that covers the hatch leaving only room for the head to stick out.  This provides a significant improvement but it can be uncomfortable to ride with the skirt regularly.  Another small improvement is the mini visor that is attached to the front of the hatch with a Velcro.  The visor deflects some of the air around the rider.  There is a small aerodynamic impact.  A hood that covers the open hatch of the velomobile is probably the best way to minimize the drag of the velomobile.  Some velomobiles like the Quest have several different hood designs and manufacturers to choose from.  Each has its own advantage and disadvantage and have differing level of efficiency while others have a more restricted choice.  The hood has the added advantage of weather protection in cold and wet conditions.  On the other hand, visibility can be somewhat more restricted, it may be difficult if not impossible to wear a helmet, the cockpit can become too hot for some or it can fog-up.   For racers, commercial hoods have also been modified to make them even more efficient for example by reducing the frontal area.  While hoods are not created equal, as I mentioned above the gain from a hood can be significant, it is probably the single biggest aerodynamic improvement that can be made. 

Open wheel velomobiles like the Strada, Mango, DF, Evo-K suffer to different degree from the turbulence created by the front wheels and wheel wells.  There are several ways this can be addressed with different levels of performance improvements. First wheel cover help for open wheel velomobiles by covering the turbulence from the spokes.  Some wheel covers are made of Lycra while others are made of fiberglass or carbon fiber discs glued to the rim. 

The wheel wells are a source of air turbulence.  Some velomobiles have tighter space between the wheel well and the tire to reduce this turbulence.  Small plastic deflectors that essentially cover the gap in the wheel well between the shell and the wheel leaving just enough room for the tire to pass when turning can be added to minimize turbulence. Deflectors are normally taped to the shell just around the wheel wells. This provides a small but noticeable improvement in efficiency. 
If you would like to further, increase efficiency wheel pants are the solution.  Wheel pants essentially cover the whole wheel well making the airflow past the wheel well following the shape of the velomobile.  This minimizes the turbulence significantly.  Only the bottom of the wheel is visible.  Unfortunately, there is a small price to pay because the wheel pants are restricting tire size and increasing turning radius.  Some racing wheel pants or wheel pant extensions can be installed on racing velomobiles to further reduce drag as the wheel pant/extension are made to cover the whole wheel leaving less than a centimeter of air space between the ground.  Even velomobiles where the wheels are covered like the Quest could see performance improvement with extensions of the wheel covers effectively hiding the bottom of the wheel and closing the bottom of the wheel well.

Velomobile with foot holes can see improvements by closing the foot holes with special covers that have bumps under the shell to give room for the feet to move freely on the pedals.   While I don’t have a number to give, the improvement can be significant.

The perfect tail for a velomobile is shaped like a wedge.  Unfortunately in order to provide a surface for rear lights and reflectors to increase visibility, most velomobile tails are somewhat truncated.  Many riders have found a solution and added a tail extension transforming the blunt tail into a wedge using transparent plastics.  The reflectors and lights are still visible but the airflow is better reducing turbulence. The improvement is small but noticeable for racers.

The nose is something that has attracted attention lately.  The DF, for example is a velomobile that has an air intake at the front.  While it is designed to minimize the aerodynamic drag but it still has an impact.  Closing the hole will result in a warmer cockpit but that may not be an issue for a race or when the temperature is cold but may lead to an increase in fogging up inside the hood.  To get the improvements, the cover has to follow the shape of the current nose and using clear plastics would not impede the headlights hidden inside.  While this small modification provides improvements, you can go further.

Recently I was made aware of one rider who modified the nose of his Milan SL by extending it making it pointier and saw speed increase.  This modification is not without drawbacks.  The modification makes the velomobile more susceptible to side winds and this could make the velomobile difficult to control at high speed under windy conditions.

Beyond these modifications, those racing may also try to use tape to close seams and other holes and cracks in the shell.  Anything protruding from the shell like lights, cameras and mirrors especially large ones are also creating drag.  While I would not recommend removing any items used for safety, riders may choose to reduce their impact or removing them for special events like races.

IntercityBike

Daniel Fenn is hard at work on the DF-4, the 4-wheel DF prototype.  He recently went on a 170km ride with the prototype.  Daniel even took his dog in the velomobile on this journey, the dog can fit in the luggage compartment just behind the seat is much larger than the DF.  ICB has posted several pictures and video on their blog.  The prototype will see more refinement before a decision is made to go to production. 


There are a number of interesting innovations in the design.  The pedals will drive the left wheel of the velomobile while an optional motor providing assistance will drive the right wheel.  The DF-4 prototype has a mid-drive Rolhoff  and a 10 speed cassette at the back.  The wheel wells are larger than the DF/DF-XL and would enable the use of popular larger tires like the Shredda and the F-Lite.

Busy as usual, Daniel is also in the process of producing a new racing hood for the DF with no side windows.  This is the type of hood that Milan riders have used in record attempts.  The hood is apparently 33% lighter and hopefully more efficient than the original DF hood.

Spezi

The annual Special Bike Show SPEZI 2017 will take place April 29 and 30 2017, in Germersheim Germany.  This is the 22nd edition of this annual event that started in 1996.  The show provides attendees the chance to view and test products. Several velomobile manufacturers from Europe will attend but some will not. 

Saturday, April 15, 2017

I’m back!



I’m back!
Last June I posted my last column and I did not even post an update since.  No contrary to what some of you may have thought, I did not fall off from the face of the earth.  I did reply to a few enquiries in the comment section but maybe it should have been a post explaining that I had to take a break.  I apologized to those who came to visit my blog and did not see new posts.

Since the spring of last year, I’ve been doing major home renovations that are still ongoing.  Doing most of the work by ourselves has meant that I did not have much free time available for riding, participating in forums, gathering information and post this information here.  In addition, last year I had major “hotfoot” problems when I rode.  After riding a 300km brevet in August where the pain forced me to stop frequently to give my feet a rest, I decided that I should stop riding until the situation improved I had lost sensations in most of my feet except for tingling.

Over the winter the foot situation improved and I slowly started to get normal sensations in my feet.  I was waiting for a particularly snowy and cold winter to finish in order to start riding.  In March, when the winter was dragging-on and I was unable to suffer it any longer, I drove south to start my riding season.  Even after many sessions on the indoor trainer, I needed to regain my riding shape and frankly enjoy riding outside.

While I was waiting for the weather to improve I made some improvements to the velomobile.  First, in order to try to prevent the reoccurrence of the hotfoot problems, I decided to switch the cleat and pedal system from the standard SPD to the SPD-SL road bike pedals.  The SPD-SL uses a larger pedal and cleat that hopefully will distribute the pressure more evenly on the sole of my shoes.  I did not upgrade my shoes, they have a hard nylon sole and they do not appear to flex but I may upgrade to shoes with a carbon fibre sole if the problem persists.

After years of lusting over power meters, I finally took the plunge and purchased a Power2Max crank based power meter.  It took a bit of time to install it but the process was straightforward and I’m very happy with the results so far.

I have more upgrades coming.  Soon I will convert my front wheels to tubeless and install Schwalbe Pro-One 28-406 at the front to replace the Kojak 35 and a Schwalbe One 28-559 at the rear to replace the Continental Grand Prix 28-559.  I hope this change will save me a few watt of power and propel me faster down the road.

Last year I received my wheel pants but I was unable to ride with them first because the Schwalbe One 23-406 significantly lowed the DF as they have a much smaller diameter than the 35 or 28=406.  As a result, the DF was too close to the ground to ride on not so nice pavement.  I did not address the issue last year for lack of time and the choice of tire was not very good.  I hope that the 28-406 will fit nicely in the wheel pants. This would help save a few watt too.

In the last few weeks I also had a few mishaps.  Once again I broke a brackets holding the crank in the velomobile.  I spoke about these last year and Alligt produced brackets with a new design.  They are somewhat similar to the old ones but instead of a square corner, they have a V grove at the top and bottom of both half that should better distribute the torque.  The brackets have been available for a few months so if anyone has experienced any issues please post a comment.  Even more recently, I broke the stem of the DT Swiss rear shock valve when I tried to disconnect the pump.  The pump was screwed to the threaded stem just enough to ensure there were no leaks.  When I tried to unscrew the pump, the stem broke off the shock.  The stem made of aluminum is apparently very brittle.  I cannot see how much less force I could have used to ensure proper seal.  I have ordered a replacement valve/stem from ICB as well as the new DF shock made with regular springs.  I will use the opportunity to compare the two shocks.  In the mean time, I locked the shock and continue riding.

It will still take me a while to be on top of what is happening in the world of velomobiles.  I will do my best to gather information and make it available here.  I do not know if I will be able to provide weekly posts as I have done in the past but I will do my best.

Here are a few industry news items to report.

Bluevelo

It is sad that Bluevelo has been selling the inventory and fixtures.  Most recently the molds for the Quest were put for sale.

Eretic

The Italian company has unveiled a new velomobile, the Carbon Snail, designed for very short riders (below 160cm).  The velomobile also appears to be designed for the track with very close to the ground with very tight wheel wells.  Unfortunately there is no information on the Carbon Snail available on Eretic’s website. (www.eretic.it)

Eurocircruits

Eurocircuit started selling a new version of the E-Cvelo Challenger shell for the Azub Tricon 20 trike.  The fiberglass shells are built and assembled in Hungary.  One important thing to know: Eurocircuit only sells to European customers.

Katanga

Katanga recently posted a notice on their website site to inform users that suspension arms for WAW152 to WAW323 should be replaced and owners should get in touch with Katanga to request their new front suspension arm. The arms will be shipping at no charge do to a issue with the old ones snapping.

Trisled

On March 10/11, Australian riders Tim Marquardt and Jeffrey Nielsen's were successful in breaking the Tandem 24hr distance record of 909km set by Jason Miles and Guy Martin using a tandem four-wheel velomobile.  While the official distance needs to be confirmed, they traveled more than 1015km in 24 hours at a track in Edithvale, a suburb in Melbourne, Victoria, Australia.