Home / General / I-Track Suspension – Design thinking: An interview with Hugh McLeay

I-Track Suspension – Design thinking: An interview with Hugh McLeay

I first heard about Hugh when he started posting on Ridemonkey forums in one of the topics about bike suspension. It struck me how willing he was to help and educate people about bike suspension even in the middle of a forum flame war. His posts showed he has put a lot of thought and work in every post. He is one of the most knowledgeable people you can currently find publicly posting about bike suspension. When I heard that his suspension design is going to be implemented in a production bike I got very excited. His I-Track suspension is probably the first truly innovative ideas in our industry in a very long time. Stay tuned for another article explaining his suspension. If you are feeling impatient Hugh’s site (http://www.i-tracksuspension.com/) is an amazing source of knowledge both about his design and bike suspension overall and I truly believe everyone should read it. If you want to buy a bike using his design go to (http://craftworkscycles.com/index.php/enr). Read on to get to know more about Hugh and why he thinks his design.

*DISCLAIMER – For anyone who doesn’t understand the term anti-squat head to Hugh’s site under this link: http://www.i-tracksuspension.com/suspensiontheory2.html#antisquat

 

o   My name is Hugh McLeay, and I’m a mechanical engineer from Adelaide, South Australia. I’ve been riding mountain bikes in one form or another for about 20 years. I don’t really recall how I got into mountain biking; I think it was just through having friends with a common interest. Adelaide is great place for MTB; there are loads of trails throughout the hills, all within about 20 minutes from the city centre.IMG_4968-e1468766762440-744x558

o   I-track suspension is just me expressing my passion for suspension design. I established it as a brand to license my patented suspension design, and to assist partner companies with developing their ideas. It’s also a great avenue to publish what I know about MTB suspension, so that others who are interested can find lots of good information in one location.

Was designing bike suspension always the plan or did it start more spontaneously?

o   When I was studying engineering at university, I wanted to end up designing bikes. Looking back now, I realise that I knew absolutely nothing about suspension design at the time! That idea kind of faded into the background as I became interested in some other things. In my final year of university, I did a project called Formula SAE, where you design and build a race car. During this project I was introduced to vehicle dynamics, which really sparked my interest. After finishing university, I got a regular job in the construction industry, and continued on with my interest in vehicle dynamics on the sidelines – reading lots of books, and volunteering for several race teams. Around 2008 I got back into DH after several years of riding trials bikes (without suspension!). I was riding a Giant Glory, and I remember being completely blown away by how well my friend’s Ironhorse Sunday pedalled compared to my Glory, despite their very similar layouts. That moment inspired me to start analysing MTB suspension characteristics, which later on led to developing my own suspension system that could improve on what was currently available.

Why do you think rearward bikes are so popular among the more tech savy people in the bike industry

o   I think rearward axle paths are popular because it makes perfect sense, even to the layperson. We run our forks at an angle so that they can absorb frontal impacts better, why not do the same at the rear of the bike? The basic concept is very simple, and it has been tried many times before, but the challenges associated with the drivetrain and anti-squat have meant that it has often been poorly executed. Unfortunately, this has resulted in a bit of a stigma associated with rearward axle path designs.

o   To the layperson, it’s relatively intuitive that with a rearward axle path design, the rear wheel can react better to frontal impacts from large rocks. In more technical terms, it can be described that the wheel rate felt due to rider inputs when cornering/pumping/jumping (which are generally vertical in direction), is higher than the wheel rate observed by rough terrain impacts (which is more rearward in direction).

o   For a rearward axle path bike to pedal well, it needs an idler pulley. This necessary element is unfortunately what makes these designs look quite different, and is probably why only the more technically minded people are willing to explore the benefits further. More recent designs like Canfield Jedi, Zerode, Commencal Supreme V4, and of course the Craftworks ENR are really great looking, so I hope that it generates wider acceptance of rearward axle path designs.

Craftworks ENR 700w

Do you also consult geometry? How do you cope with reduced agility in turns due to chainstay lengthening

o   Yes. I designed all the kinematics, geometry, structure and aesthetics on the Craftworks ENR. On this bike, I was able to get the rear end quite a bit shorter than what I had previously been able to do on my home-made prototype (i-track P3). This made a large improvement in being able to un-weight the front wheel, and in cornering. But the rear end can only be shortened so far before you run into packaging and/or structural issues, so it’s definitely something that needs to be considered in parallel with the kinematics. I also make sure that there is a good amount of progression in the leverage ratio at sag. This helps provide good support, and a more lively feel, which alleviates the sensation of the ‘reduced agility’ that you mention due to chainstay lengthening when cornering.

o   I also think that the sensation of the chainstay lengthening is something that people can quickly adapt to. I like to think of it as being similar to the slackening of head angles that we’ve seen over the last few years. It wasn’t that long ago when DH bikes had 66deg head angles, and it would have been ‘unrideable’ to have that head angle on a trail/enduro bike. These days, DH bike head angles are closer to 64deg, and we’re quite comfortable riding trail/enduro bikes with 66deg head angles. We’ve accepted a slight compromise associated with the slacker head angle, but overall, we are better for it. How far will it go?… Time will tell!

How does i-track address pedalling performance, and how does it differ from other rearward axle path designs?

o   Firstly, in terms of pedalling performance, all rearward axle path designs have a common advantage over  ‘conventional drivetrain’ designs. Having a rearward axle path means that the same amount of anti-squat can be achieved with less chain growth. This means that there is significantly less pedal feedback when pedalling over rough terrain. For example, consider a high-pivot single pivot, with idler on the pivot. If you put it in a gear so that the rear cog size is the same as the idler size, then it has zero chain growth, but it still has a reasonable amount of anti-squat. If the main pivot was lower, and the idler pulley was also lower, then chain growth would still be zero, but the anti-squat would be significantly less. So having a high pivot allows you to get a good amount of ‘free’ anti-squat (without having to pay for it in chain growth). Most high-pivot designs still use some chain growth to get a bit more anti-squat, or to create a more ‘interesting’ anti-squat curve, but a high-pivot design will always require less chain growth than a ‘conventional axle path’ design to achieve similar anti-squat values.

 

o   Secondly, i-track has a distinct advantage over other rearward axle path designs. Having the idler mounted on a link that moves relative to the BB and relative to the rear axle, means that I can carefully tune the rate of chain growth, which has a significant effect on the anti-squat curve. Specifically, I can tune it so that the anti-squat increases with suspension travel, which creates what I call a ‘dynamically stable’ pedalling platform. What this means is that when you accelerate, the overall wheel rate increases, so that it can properly support the additional mass on the rear suspension that occurs due to weight transfer.

An animation showing the idler moving as the suspension compresses based on an early I-Track prototype.

While I understand how your design copes with pedaling induced problems how did you solve the issue of brake jack?

o   My priorities for optimising kinematics are as follows: First is Leverage Ratio, second is Anti-Squat, and the braking performance (Anti-Rise) is the lowest priority. The reason for this is that the majority of braking is done by the front wheel. Braking force generated by the rear tyre is relatively small, and therefore the Anti-Rise characteristics have a relatively small impact on suspension behaviour. In contrast, 100% of forward acceleration forces are transmitted by the rear wheel, so Anti-Squat characteristics have a greater impact on suspension behaviour.

o   My first prototype (i-track P1), has a single-pivot swingarm, which resulted in very high Anti-Rise numbers. When riding it, sometimes if you needed to grab the brake in a corner, it would pull the bike down (lengthening the wheelbase), and upset the balance a bit. All my bikes since have featured a 4-bar linkage, which allows me to position the IC further forward, and reduce the Anti-Rise somewhat.

Why do you think the big bike companies seem to avoid the rearward axle path bike despite its obvious benefits?

o   Big bike companies need to cater to the average bike buyer, and unfortunately the average bike buyer isn’t particularly interested in rearward axle path designs. It would be huge risk for a big bike company to produce a bike that is unlikely to appeal to the average bike buyer. I hope that I can play a role in changing the way that ‘average Joe’ sees these types of bikes, and maybe one day the big bike companies will start producing some rearward axle path designs.

o   On the other hand, there is enough of a market out there looking for more interesting designs, that a smaller bike company can target this market and be quite successful. For example, Canfield and Zerode have a very loyal following as a result of their use of rearward axle path designs.

 

P3 Middle logo 700w

An earlier proto of I-track. A closeup of the moving idler pulley mechanism

For those of us that are worried about durability. How do you make the idler mechanism durable, especially when it’s moving?

o   The chain load on the idler pulley is quite large, however it’s different from the type of loading seen on chainrings and cassettes. The idler pulley doesn’t actually transmit any torque, so you don’t get uneven wear on the front of the tooth like you would see on an aluminium chainring. The type of wear we do see, is wear at the base of the ‘saddle’ between two teeth, and on the sides of the teeth from when the chain engages at extreme angles. On the Craftworks ENR, the idler pulley is mounted on a stainless steel axle, which is attached to the rocker link. We undertook extensive stress analysis in this area to design the assembly so that it could withstand the large forces.

Is it possible to run the bike without a chain guide and with just a narrow wide ring?

o   Because of the rearward axle path, the derailleur arm would have to move further than it does on a ‘conventional drivetrain’, which would cause the chain to either be too tight at bottom-out in the largest cog, or too loose at top-out in the smallest cog. By running the chain over the lower pulley on the chain guide (and setting it as high as possible), it reduces the amount of chain growth on the lower run, so that the derailleur arm doesn’t have to move as far as the suspension compresses.

It really depends on the range of the cassette and derailleur you are using. If you were to use a long cage derailleur (designed for a double or triple chainring), then it might be possible for the chain to work at both extremes without having to use the lower pulley in the chain guide.

Anything else you want us to know about the suspension, the craftworks bike or any future projects?

o   There’s so much about suspension that I want the world to know, and I’ve tried to publish a lot of it on the i-track website. I often receive complimentary emails from people who have found my website through trying to learn more about suspension design; it’s really rewarding when I get these emails.

o   As far as Craftworks goes, I think the ENR will be very well received. We’ve also got plans to do a DH bike, but the market for DH bikes is significantly smaller than Enduro bikes, so it’s difficult to justify financially. We’ve got a great partnership going, and I’m looking forward to continuing to develop bikes together.

 

 

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