New UCI tech rules leaked: Is bike design about to get a shake-up?

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It came via email from a secret industry insider. A brief amendment to the UCI technical regulations, apparently approved by the sport’s governing body, and applicable from the start of 2021. In it is a bunch of interesting additions, changes and removals, all in red.

The new rulings are applicable to road, track, time trial and cyclocross bikes, and look to greatly open up design possibilities in relation to allowed tubing dimensions, shapes, and even the position of the “seat tube extension” (the seat post).

Such rulings have long been rumoured in the bike industry as the next frontier for (or existing barrier to) aero road bike design. And now, it seems we’re on the cusp of seeing a whole new wave of wind-cutting machines that create a new divide between lightweight and fast.

Meanwhile, it seems such updated rulings could offer a benefit that goes well beyond improved airflow. This new rule change is potentially big news.

A new rule relating to minimum thickness?

The new rules are a re-write to a small part of article 1.3.020 within the existing UCI technical regulations handbook. The UCI has long controlled the tube dimensions of bikes, notably that a tube has to remain between 2.5 to 8 cm in any direction. Recent years have seen the UCI relax this ruling in relation to forks, seatstays and chainstays, which are allowed down to a 1 cm minimum thickness.

The leaked document suggests big changes are ahead with that 2.5 cm minimum thickness set to change to just 1 cm, meanwhile the 1 cm thickness restrictions to seatstays and chainstays appear to have been removed altogether.

I reached out to Factor Bike’s director of engineering Graham Shrive (and former head of engineering at Cervelo) for his insight on what such a rule change could mean for future bike design.

“It’s caused a lot of challenges over time,” said Shrive, speaking of the existing 2.5 cm minimum tube thickness rule. “Especially if you’re working on a comfort-oriented bike, that you maybe intended for Paris Roubaix or something like that, where you might want to thin down a section of the seat tube. I believe the Focus Paralane had some challenges like that where they wanted to slim down the seat tube but couldn’t get it UCI approved.

The Paralane’s seat tube is designed to aid in flex, but imagine what’s possible with a greatly reduced thickness requirement.

“So that’s something where different rules could have an immediate effect on all different frame [designs], not just aero bikes or TT bikes. It could change all bikes.”

And that comment of Shrive’s sent my mind spiralling. When I first read over the rule changes my thought process was solely on aerodynamic gains, but these changes could spell real changes to how bikes are manufactured, how they ride, and much more. Looking to the mountain bike world, recent bike releases such as the Mondraker Podium and Canyon Exceed each feature impressively flattened top tube shapes that could now be used in other disciplines.

So what about aerodynamics? Shrive suggested the current rules already allow for reduced dimensions to be used at the fork legs and that there are advantages to be had. “Seatstays are another really interesting spot as well because they’re [currently] allowed to be down to 1 cm,” he said. “If you look at what was done with the Hope Lotus bike it shows you can do something really cool with them. On the main tubes the struggle will be to make a narrower tube that’s still really stiff.”

Could things get as radical as British Cycling’s new Olympic track bike? Maybe, but road bikes need to be far more practical for everyday use.

“If you look at our Factor Slick, it’s a good example of where things might go if we ever get past the 2.5 cm rule. Because if you have twin members [ed: Shrive is referring to the Slick’s Twin Vane down tube] you can probably gain back that stiffness.”

However, Shrive believes that, at least from an aerodynamic perspective, things won’t get too wild if the rules ever change. “I think that those base shapes would stay pretty similar. Most of the tube shapes are derived from NACA profiles that came out in the 1930s. From an absolute perspective, it probably won’t move the needle a whole lot.”

Timetrial and road bike shape rules amalgamate

Currently, the UCI technical regulations offer a section that applies to road, track and cyclocross bikes, and a seperate section for time trial and certain track bikes. According to the leaked document, it appears the UCI is soon to amalgamate a part of these two sections together.

Notably, this means that compensation triangles at key tube junctions – currently only legal on time trial and track bikes – could be used for all bikes in future. Such compensation triangles are already a common sight on many time trial machines, with Trek’s Speed Concept coming to mind.

A graphic from the existing UCI technical regulations for compensation triangles related to time trial bike design. The compensation triangles are indicated in blue, with the “80” measurements (80 mm) designating the max size.

“In time trial bikes they allow you to put an 8 cm compensation triangle behind most of the main tubes,” Shrive explained. “A good example of that is the junction of the top tube and seat tube — you get an opportunity there to create more surface area and generate a little more lift and better flow attachment over that part of the bike. It’s not a huge gain in performance, but there is some gain there.

“Compensation triangles are something everyone would like to see, if we can get that depth of a TT bike on a road bike than you can do some unique things with a bayonet-style fork. Currently, that design is still limited to having a maximum depth of 8 cm, but [if the rules allowed] you could do something really neat there.”

Such a rule change would effectively allow engineers to double the depth of the current head tube junction.

Speaking of changes to the head tube, the leaked document states “Additional frame components can be added between the head tube and the handlebar stem. These must be inside the dimension of the head tube box.” Certainly, some bike designers somewhere have intentions for this new rule, and it’ll be interesting to see whether it’s cable routing solutions or something more.

A seat post on the top tube?

The current rules call for bikes to look like, well, bikes. The tubes are required to join in ways that make obvious triangles — the top tube needs to connect to the head tube and to the seat tube. Meanwhile, the seat post must extend from the seat tube. In surprising news, it seems that latter element won’t be required anymore. Instead, the new rules merely require that the seat post (while complying with the “dimensional restrictions that apply to the seat tube”) is attached to the frame anywhere on the seat tube and/or top tube.

Yes, that’s, right. Bikes will be able to have the seat post extending from the top tube. So how would such a thing look? Well, BMC’s tri-focussed Timemachine perhaps offers a good example.

BMC’s tri-focussed Timemachine is an example of a semi-normal bike that doesn’t pass the UCI’s rules. Perhaps that could change?

Still, there are clear rules stopping our sport’s bikes from going the way of triathlon bikes. These are related to tubes needing to retain some resemblance of a straight path, and connect to each other in a typical triangle form. Or more simply, the bike has to have all the tubes.

“The interesting thing is that you look at the UCI, it’s a relatively conservative body and they’ve maintained that for some time it still needs to look like a bike,” Shrive said. “I don’t think they’ll back away from that anytime soon.”

What’s next?

All of this assumes our source is correct and that the new rules do come into effect for 2021. Assuming the info is good, then these new rules would certainly spell renewed investment in the aero bike world, and just generally open up wholly new possibilities for road, track and cyclocross bike design.

“As a bike designer what you really want is the freedom to do as you please,” said Shrive. “And that kind of freedom gives you the variety of really cool bikes out there. And that’s what everyone is after, and maybe everyone comes back to a similar design to what they have now, but hopefully, they’ll be able to explore that more fully. I think that variety and complexity are good for the industry and good for everybody.”

We contacted a representative from the UCI for comment and confirmation on these rules changes. We’re yet to hear back.

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