Oval Chainrings – Are they any good?

Before anybody shouts, I know these rings are not necessarily ‘oval’ but you know what I mean, rings that change their diameter and so give different gear ratios at different crank arm positions.

Either way ‘Oval’ shaped chainrings have been growing in popularity again in recent years and the long lingering shots of Bradley Wiggins’ chain bobbing up and down on the Tour de France or Olympic coverage can only reinforce this.  I say ‘again’ because many of us are old enough to remember Shimano’s Biopace chainsets of the 80′s early 90′s which were of a similar shape. Osymmetric and Rotor sell rings in the UK, as do Highpath Engineering who have offered their ‘Eggrings’ for years.

Biopace rings were fitted to my first ‘proper’ Dawes road bike, bought when I started to take cycling more seriously. They seemed to fall out of favour though, and with STI shifters coming along a few years later, the upgrade bug got to me and new groupsets or bikes came along with round rings and barely a second thought for the old irregular ones.  I used to think that it was an urban myth that Biopace were fitted the ‘wrong way round’ but sure enough, the largest diameter is approx 90o away from the Osymmetric / Rotor Ring position. I know this because I hoard all the bits I ever take off my bikes and still have a set, having unsuccessfully tried to flog them on ebay a few years ago!

So, always keen to use technology to go faster rather than just train harder,  I began to wonder if I should invest in a set of oval rings. I also needed to form a professional opinion as many customers were either coming in with them, or asking me about them.  As a Bike Fitter I am well aware of how the ‘dead zone’ as the cranks go through the vertical can affect your performance and comfort on a bike and see how crank length and saddle height effect  this region every day.  From my earlier blog posts you may notice that I have a bugbear about manufacturers fitting cranks that are too long on their bikes, so I became very interested in not only the performance of oval rings per se, but also if they could ameliorate the effects of overly long cranks.  An event that sparked this interest was a recent customer who came in with two bikes,  a road bike with 170mm cranks and round rings, plus a TT bike with 172.5mm cranks and Rotor Rings.  This chap was quite small, with an inseam even shorter than mine (which is unusual), so I was fairly sure that both crank lengths were too long for him.  We fitted the roadbike first and it quickly became apparent that this was the case. Even after optimising his saddle height, he still struggled to hold a cadence much above 85rpm, but when trying him on 165mm, you could see the stress  flow out of his system as he became ‘free’, whizzing up to well over 100rpm. Expecting a similar conclusion on the TT bike, I was surprised to see that  he was spinning almost as easily on the 172.5s, something I could only attribute to the rings fitted to this bike.

Rotor UK are based just up the road in Stratford upon Avon so it did not take me long to get hold of a suitable set of rings. I did not want to leap to any conclusions without a proper assessment so decided on both a road and lab based test programme spread over a few weeks.  A weeks holiday in Dumfries and Galloway provided the ideal opportunity for the road assessments, especially given our proximity to the delightful Mennocks Pass.  The intention was to use a combination of both subjective impressions and performance data recorded on my Garmin and Strava.com.  I was also keen to get into the lab environment with the capability to measure HR,  Power and via my Computrainer the metrics of Pedalling Efficiency, Average Torque Angle and Left Right contribution.

 Road  Assessments

The equipment variables I had available to me were 34t, 36t and 50t round chainring, plus 36t and 50t Rotor Rings, all of which were compatible with a set of both 165mm and 167.5mm cranks.  I had been tinkering with the 167.5mm cranks previously, so knew my preferred saddle height for both crank lengths. I was also a little worried about ‘adaptation’ but as I had been tinkering  recently, I wasn’t sure I was strongly adapted to anything anyway!

Unfortunately, as anybody who has tried to do anything similar will know, the vagaries of our British weather far outweigh the differences between these components. If you were to believe my Strava data, the 36t round rings were far superior to anything else because I climbed so much faster on them. In fact, the tailwind was so strong that day that when I turned round to come back down the 5% hill, I had  to pedal quite hard to make any sort of progress at all! So although cycling in Scotland had been fun, it was inconclusive and I needed to get a few more miles in back home. Fortunately, we then ran into a more settled spell and I could get in three assessments under very similar conditions. I chose a 38mile local route incorporating a couple of tough climbs (Burton Dassett, Edge Hill). The specs and average speeds are as follows, with similar average and maximum heart rates.

1)  36t round, 50t round,  165mm cranks                                                               16.6mph 

2)  36t Rotor, 50t Rotor, 165mm cranks                                                                 16.8mph

3) 36t Rotor, 50t Rotor,  167.5mm cranks                                                              16.2mph

This is by no means a statistical sample, but the average speeds tended to support the subjective impressions. I had decided recently that I preferred 165mm to 167.5mm cranks and the Rotor RIngs had not changed this conclusion. This is a shame as I really wanted them to work, but, as with round rings,  the longer cranks just made my legs feel heavy and everything seemed much harder work. When on the 165mm cranks, if anything the subjective impression  with Rotor Rings was better than the average speed increase suggests. It is not easy to describe the sensation, but it feels like you are getting the lower gearing benefit of a 34t chainring coupled with the performance of a 36t. More significantly, two out of three of my fastest climbs on Edge Hill since my Strava records began have been on Rotor Rings! The one downside is when climbing out of the saddle, as your foot seems to accelerate quickly around the bottom of the stroke in a slightly jerky fashion.  I imagine this needs a few rides to get used to. 

Objective Data

As a Bike Fitter, I am quite keen on making very quick changes to the bike for people to subjectively assess. The quicker you can make a change, the easier it is for people to notice the difference. This philosophy is also applicable to objective measurements as stopping to change components, even for only 10 minutes can cool people down with no guarantee they will stabilise at the same condition on restarting.  So what better way to affect a quick change than to fit both the same size rotor and round ring side by side and use the front derailleur to flick between them. This only works with the small ring, can be a bit tricky to set up, but is possible. The two big rings can also be fitted alongside each other, but you have to take the front mech off completely and move the chain across manually.  

50t round and Rotor ring

Although the weather was no longer an issue, I then worried if the inertia properties of the turbo trainer would compromise the result. As there is no translational inertia of the bike and rider, but only rotational inertia of the wheel, trainer and cyclists legs, how would this effect the changing gear ratio and by implication wheel or foot speeds? If you worry about things too much though you can end up not doing anything. So I thought I’d crack on and see what happens.

Results

The simplest way to assess the different rings was to measure heart rate and power, correlate to perceived effort and keep switching back and forth between round and rotor rings every few minutes or so at a range of different intensities. Somewhat disappointingly, there was very little difference seen on either the 36t or 50t rings when just considering HR and power, but the Rotor Rings always felt a little easier.  I am also able to look at other metrics provided by the Computrainer Turbo and Spinscan software.  The brake unit in this turbo has a fine enough resolution to measure torque every 15 degrees of crank rotation and plot this against crank angle. This ‘Polar Plot’ can be very informative, showing any significant asymmetries and highlighting the extent of the torque drop off as the cranks go through the vertical.

An idealised polar plot is something like that shown here. 

 

The definitions of the relevant metrics are as follows. 

Spinscan, also known as pedalling efficiency. This takes the average torque and divides it by the maximum torque.  If you were to pedal in perfect circles with a consistent torque, this number would be 100% but as a rule, I think anything over 70% is fine.

Average Torque Angle. (L.ATA) The angle of the crank where the torque measured at the brake unit is at its highest. Ideally this would be the same each side and between 90o and 110o.

%Watts – Contribution to total power from either the right or left down-stroke. This is sometimes misread as a right  / left leg contribution, but as the upstroke leg may also be pulling round the bottom, pulling up, or pushing forwards, it will also be making a contribution to the down-stroke.

Thinking about how Rotor Rings are supposed to work, with a smaller diameter as the cranks go through the vertical, larger on the down-stroke, you could predict that the Spinscan numbers could appear to be worse.  As the diameter reduces, the foot will need to speed up, but as the feet, legs, shoes, cranks and pedals have their own inertia, there will be less of the applied muscle force available to turn the cranks as it is being used to accelerate the feet. Likewise, as the diameter increases. the foot will slow, with the change in inertia creating a positive impulse to the pedals.

I wondered if Computrainer had any view on this but a brief peruse on their forum revealed this  response to a previous similar enquiry.  

“We’ve never done any research with them, nor do we have any plans on doing so.”

I found this a bit surprising from a company whose product is advertised as helping to reduce the dead-spots in the pedalling action and suspect they may have  predicted and are possibly  perturbed by the likely outcome.

Sure enough, as shown below, the Spinscan numbers and shape of the plot do deteriorate  when fitting Rotor Rings.  But as stated previously, the power and heart rate did not change and the perceived effort was lower.

Round Rings

 

Rotor Rings 

You may not be able to read the Spinscan numbers, but they both drop about 7% when the Rotor Rings are fitted. In the cold light of day, if your ‘pedalling efficiency’ reduces when fitting Rotor Rings, then why on earth would you do so.  Either Rotor Rings don’t work or ‘Pedalling Efficiency’ is an inappropriate metric.  I’m fairly sure that Rotor Rings do work and the only thing wrong with the metric is its name and targets. So don’t worry Computrainer blokes, Spinscan is still a fantastic tool to develop a good pedal stroke, but you need to acknowledge that high numbers will be harder to achieve with Rotor Rings. Calling the metric ‘Spinscan number’  is fine, but ‘pedalling efficiency’ could be misleading.

Thinking again about how ring shape and position affects foot speed. If you really wanted to pedal in perfect circles (and I’m not suggesting you should),  you would place the large diameter in line with the crank to take advantage of the foot deceleration and fill in the dead zone as the cranks go through the vertical. The acceleration 90o later would be coincident with high pedal forces, so less of a problem.  This would position the high points of the rings around 90o from the Rotor recommendation- Blimey!  I’ve just reinvented Biopace!

Summary

Objective measurements taken on a turbo trainer, which I appreciate do not include oxygen uptake or blood lactate are inconclusive, showing no significant benefits to fitting Rotor Rings.

Objective measurements on the road, particularly on specific climbs suggest Rotor Rings are better.

The subjective impression of Rotor Rings in most riding conditions  is positive.

I have no hesitation in recommending Rotor Rings to my customers, but not as a means to cope with cranks that are too long for them.

 Where Next

I shall keep the Rotor Rings on my bike and continue to assess over the usual range of distances and efforts that consitutes my typical riding.

But why do some people not like them? I can’t help feeling that the issue of crank length is still relevant, so will try to gather more data on the subject.

ps

 So what shall I do with my Biopace rings now. That’s easy, I’ve put them as close as possible to the right position (i.e. rotated round 1 spider arm = 72°) and reunited them with an old steel frame I use as a turbo trainer bike.

pps

Since posting the blog I’ve been alerted to this fascinating report

http://www.trainsharpcyclecoaching.co.uk/images/osymetric-study.pdf

Not only does this describe the shape of the far more numerous alternative chainrings that I thought existed (Rasmussen oval, Ogival oval, Ovum ellipse, Polchlopek oval anybody?) and uses some complex mathematics to try to define the advantages of each one. I’m pleased to see the report agrees with my conclusion that Biopace was designed to utilise the  inertial properties of the system, and that essentially it does not work. As a rule though, most other designs do seem to offer some benefit.

 

 

Saddle Height – Do formulas work?

When setting up the BikeDynamics business a few years ago, I was keen to establish in my own mind how to set the absolutely critical dimension of saddle height. The established formulas of 0.885 x inseam length to bottom bracket, or 1.09 x to pedal platform had not worked particularly well for me, nor did I think I could justify asking people for large sums of money just to shove a tape measure into their crotch. More on my precise technique later, but I’m pretty happy that dynamic knee angles, combined with direct observation and subjective impressions give a robust methodology.

Whilst reading some journals and articles recently it became apparent that some of the ‘big names’ in Bike Fitting were very keen on the 0.885 x inseam rule, so I became very curious to see how well it works. Fortunately, the information required is part of my every day data gathering, so it was quite easy to plot the last couple of months worth of customers inseam and final saddle heights. Note these were all roadbikes as TT or Tri saddle heights would introduce a whole new level of variability.

Saddle Height vs Inseam

If you can’t see the formula on the plot, it is

Saddle Height = 0.8766 (inseam) + 9.8

 with an R2 of 0.9162. To those that know their stats this is an OK correlation but not perfect. There was a very slightly better correlation with a polynomial expression, but the improvement did not warrant the added complexity of the equation.

I’m actually quite pleased with this formula because it recognises that the origin is not at zero. We all use similar shoes and pedals with an offset between foot and pedal axis. This formula suggest that offset is 9.8mm, which is probably not that far off the mark!

So what of the actual numbers. Taking a selection of inseam lengths, we can compare the saddle heights.

Inseam                              0.885x                   0.876x + 9.8

  1. 750                            663.7                     666.6
  2. 800                            708.0                     710.2
  3. 850                            752.3                     754.4

So I’m tending to set people up on average about 2mm higher than the established formula suggests. This could be explained by the fact that about 10% of my client base are women, whose more flexible hamstrings tend to allow slightly higher saddles for the same inseam. I’m guessing the 0.885 rule came about when less women cycled?

Initially I was not sure If I should be pleased or disappointed with this outcome. On one hand it suggests I should not have been so quick to dismiss simple formulae in the first place, but on the other, closer inspection of the data reveals how individuals could be very wrong if just doing simple sums. Looking at the data points, approx. 25% are close to the line but the majority are up to 15mm away from it! This includes myself as doing the sums suggests my saddle should be 8mm higher than I like it, but even going up 2mm starts to give me problems.

As mentioned earlier, I use dynamic knee angles, direct observation and subjective impressions to establish saddle height, and once ‘tuned in’ many customers are amazed at how even small height changes can make huge differences. Once in the right place, the power seems to flow so much easier, the upper body steadies and the turbo trainer emits a more consistent ‘hum’. I’m not going to give away all my trade secrets but observing a rapid decelleration of the knee joint at the bottom of the stroke is a strong visual indicator that the saddle is too high.  

 

Mike Veal

BikeDynamics Ltd

 

The Long and Short of it – Arms

Two chaps came to see me recently for Bike Sizing exercises. The first chap was considering buying two bikes, an MTB and a touring bike. He was about 175cm tall, with slightly longish arms and legs but still fell very squarely into the 54cm size category of the touring bike he was after.

The second chap came in a few hours later and was confused. He was keen on a Canyon road bike, but being an internet retailer, had no opportunity to go and sit on one somewhere. He was 178cm tall (5’10″) and had been putting his dimensions into the Canyon website size calculator. The reason he was confused was that the calculator kept telling him he was a 53, whereas his instincts (and mine) said 56.

He thought he may have been doing the measurements incorrectly, so I did them for him, and sure enough, the website suggested 53. But I could now see why,  he had extremely short arms for his height and simulating the 53 geometry with my jig confirmed he needed that size.

Comparing the two chap’s dimensions afterwards, the arms of the shorter 1st customer were a full 6″ (15cm) longer than  the 2nd!

Old vs New Geometry

A chap came in for a fitting last week with a lovely 1990′s steel framed ‘ten speed racer’. It was spotless and had obviously been very well looked after. The non indexed 5 speed shifters were on the downtube and it had a quill stem. I had been thinking about how bike design had changed over recent years and to see this bike ‘close up’ confirmed the conclusions I had come to.

You may think that the single biggest influence affecting bike geometry was the increased use of carbon fibre, but in my opinion, road bike design in the last 20 years has been changed the most by the movement of the shifters from downtube to hoods, coupled with the increasing number of gears.

When the shifters were on the downtubes, we had our hands on the bars tops and drops, moving to the ‘hooks’ when braking or climbing. With the shifters in the hoods, and more frequent gears changes, we prefer our hands to be on the hoods for a much larger proportion of the time.

When riding on the ‘hooks’ this customer’s hands were very uncomfortable, not surprising really given the wrist posture and white knuckles

 

The trouble with just putting the shifters into the hoods was that for a lot of people they were too far away, especially as the ‘reach’ of the bars was typically at least 100mm if not more. This is why we have seen the increased use of ‘compact’ bars with both shorter reach and drop as well as better designed shifters that attempt to spread loads over the whole palms. The position of the shifter has also altered, when they first came out, they tended to reflect the old ‘hooks’ position with sharp angles between bar top and hood skirt. Unfortunately, some people still set them up this way and their hands hurt. Fortunately, most manufacturers now ensure a smooth transition from bar to hood, optimising hand comfort. We have also seen an increase in ‘Sportive’ geometry with shorter top tubes and longer head tubes, but again this is just allowing us to ride on the hoods whereas we used to be on the bar tops.

Mike

BikeDynamics.co.uk

 

Bike Sizing Error – Oh dear!

Many people buy their bikes on the internet, which may save a few pounds, but  means you can’t always at least sit on the bike before buying it. This can still be reasonably safe though if the manufacturer uses ‘conventional’ sizing practices and the customer has a good idea what size he is.

A customer came in last week with his new Ribble ‘Stealth’. As soon as he came through the door I thought ‘this bike looks big’. When asking him what size it was, he said its a 52, which would normally be appropriate given he is about 5’6″ (168cm). I thought maybe the bike just looked bigger than it was really and we started the fitting. It soon became apparent though that it was far too big for him.

Looking at the Ribble website, the 52 Stealth was the second biggest in the range and more equivalent to conventional 56 / 58. The 52 referred to the size of the seat tube on the sloping frame. Funny sizing like this is just about ok if it follows through your entire range of bikes, but Ribble seems to have different sizing conventions depending upon the model. My Ribble Sportive Racing is classed by them as a 52 and fits my 5′”7 frame just fine. So, a big ‘Thankyou’ to Ribble for their ambiguous sizing. Ths customer was left with the only sensible choice of sending it back or selling it. I couldn’t charge him for the full fitting so lost out too.

Knee Pain Case study 2

This is a more traditional knee pain case study.

Jill W came to see me with anterior knee pain. She is about 5’4″ and was on a women specific Specialized Dolce. My first instinct was to check the crank lengths, but was pleased to find they were 165mm. From my earlier post you may imagine that I was fully expecting to see 170mm’s. Jill has an approx. 5mm leg length difference and it was the longer left leg that was giving her the most trouble.

Measuring the fully extended  right knee angle gave a result of 140 degrees, which is towards the bottom end of the expected range for a bloke. I would expect Jill’s much looser hamstrings to be able to stretch much further than this and sure enough, we were able to put her saddle up 26mm before introducing any negative effects at all. The cleats were also placed asymmetrically a couple of mm each side of the nominal to help minimise the leg length difference. Front knee pain is due to the tightness of the knee angle over the top of the stroke, so I am always keen to see this angle in excess of 70 degrees. The left was still below 69 degrees though, and as the saddle could not go any higher, questioned whether even shorter cranks were more suitable. As 160mm cranks are quite rare, we though it worth trying the new set up as is. As you will see from the quote below – she was fine.

“I  have returned from 3 days cycling around Cheshire, originally chosen for lack of hills due to concerns about my knees. I need not have worried. I sailed through with almost no discomfort so much so that I decided to climb The Cloud, near Congleton, just to celebrate the fact that I knew it would not be a strain on my knees.”

Saddles

You may well have noted that I have numerous pages on my site talking about the interaction between cyclist and bike, but very little on the key contact point which is the saddle. I hope to improve on this later this year and have formed some thoughts on the subject. The main conclusion is that saddles are very very personal and once you have found one that works for you – keep it and fit it on all your bikes. Some of my customers talk about garages and sheds full of discarded saddles they have tried over the years.

Here are a few considerations for now.

If ever swapping a saddle, don’t assume the new one will put you into the same place. I measure hip position before swapping a saddle and often find that the effective height and fore-aft location can change by +/- 10mm.

You will sit further forwards on a wide saddle and further back on a narrow one. Assessing sit bone width on foam pads is a good start, but I get a better idea of how suitable a saddle width is for a customer by seeing where they sit on it and how far back or forward on its rails it needs to be to get them in the right place.

A recent customer could not work out why a more ‘comfortable’ saddle he had bought made his hands hurt. The saddle was heavily padded and wide, so he sat further forwards on it, shifting weight onto his hands. We needed to use a seat-post wiith  more set-back, but got him into a position where both the saddle and his hands were good.

 

Knee Pain – case study 1

As a Bike Fitter, I quite like people presenting themselves with knee pain because as a rule, it is usually straightforward enough to track down the root cause and resolve it. Cleats holding the foot in an unnatural angle and  a low saddle are the usual culprits, but high saddles are also reasonable frequent.  A recent customer John W, came along complaining of posterior knee pain which is normally due to tendonitis of the hamstring attachment points and often due to the saddle being too high. If anything though, his saddle was too low and I wanted to put him up 2-3mm. His cleats were also well located with plenty of float either side of the nominal foot posture. There was an additional clue in that the pain was towards the outer rear of the knee which can indicate Popliteal tendonitis. The popliteal muscle is involved in unlocking the knee when running or walking and also rotates the femur relative to the tibia. Essentially, if the cleats allow too much rotatation of the tibia, the popliteal tendon is having to work too hard and becomes inflamed. The solution here was to swap his floating cleat for a fixed one, something I am normally loathe to do, but fortunately in this case it worked fine and John is now cycling pain free.

Crank Lengths

I’m fairly sure this will be the first of many blogs on the subject of crank lengths.

There is a perceived wisdom amongst many cyclists that there is no difference between 170mm and 175mm, so ride whatever comes on their bike. This may be true if you are 6 foot tall but for many shorter people (such as myself) this is a dangerous misconception. Researching crank lengths when I first set the business up a few years ago, I came to the conclusion that even 170mm cranks may be too long for my stumpy little legs (79cm inseam) swapped them for 165mm and loved them. I spin more easily and climb better because my legs are not too squashed up over the top of the stroke. The problem is that many manufacturer’s now fit 172.5mm as standard across a large proportion of their range, even as small as 53′s, 54′s  and S/M’s. They state that people are a lot taller these days, but I know that I’ve not grown at all in the last 20 years!

It only takes for a realtively short person to be sold a bike 1/2 to 1 size too big for them to get a big mismatch between leg length and crank size. On a purely selfish basis, this is good business for me as I see a lot of customers in this situation struggling with knee, hip and back problems. They are not always impressed though when I tell them their cranks are too long. This then creates tension with their local bike shop when they go in asking for a swap. The shops are not at fault because they are selling what the manufacturer’s specify, so either stomach the cost or tell the customer I’m talking rubbish and there is no difference anyway.

I’m generating evidence at the moment to see which manufacturer’s are the biggest culprits. Anything American seem to be the worst so far but I’ve also seen a shocking case of a 5’4″ girl riding a UK brand bike with  175mm cranks!

Mike

Job Satisfaction No 1

The job satisfaction with getting people set up properly on their bikes is normally quite high, but it went through the roof when I saw a chap called Chris Hartley. He is in his mid 50′s and time trialled all his life. Going under an hour for a 25 mile had always eluded him though and he suspected it was never going to happen now. Chris came to see me because he was struggling with hip position, never comfortable and suffering from hip pain. To cut a long story short, his saddle was too low and his 172.5mm cranks far too long for his 5’7″ stature.  His hip angle was very tight and no doubt contributing to his discomfort in this area. The key changes were to get his saddle up and forwards and swap him onto to 165mm cranks. Other changes to the front end were relatively minor.

The signs were looking good when he reported a 10 mile pb a couple of weeks later. Then this e-mail came through

“Mike, For the second time I am able to report another Life time personnel best! After 32 years of trying, I have done it. E2/25 59 min 30 sec (2 min 28 sec off my all time PB) Despite a gusty tail wind to the turn there were several sheltered stretches on the way back. It was at about 17 miles I suddenly realised that my dream was about to come true. I was on my best bike with a disc wheel this time but I had copied the other bikes setup as closely as possible. And yes before you ask I used 165mm cranks.”

Chris credits the positional changes, medical treatment on his hip and the support of people around him for the improvement. I’m delighted to have have been part of that team.