DT Swiss has partnered with aero upstart SwissSide for a new line of aero endurance wheels, the first of which is called ERC1100 Dicut from its new Endurance range. Combining DT Swiss hub technology and manufacturing capabilities with the 50 years of Formula 1 aerodynamic experience held by Swiss Side’s engineers could be a recipe for potentially great things, and we went to DT Swiss’ headquarters in Biel, Switzerland to learn more.
Wheel manufacturers don’t usually cooperate in this way, and DT approached Swiss Side with a list of targets the company wanted the new wheel to hit.
The targets included an endurance disc brake wheelset with a 19mm internal width, optimum aerodynamic performance with 25mm and 28mm tyres, a strong focus on aero stability and predictability for real world performance, an aerodynamically optimised hub shape, and to find the best spokes for strength, comfort and aerodynamics.
Siding with Swiss Side
Swiss Side’s JP Ballard spent 14 years working on aerodynamics for the Sauber F1 team. The carry-over technologies from F1 to cycling are principally CFD (Computational Fluid Dynamics)and wind tunnel testing, Ballard said, plus real world testing with bespoke aerodynamic sensing rigs fitted to bikes that can be ridden on the road. These instrumented bikes (of which there are several) are used to see if perceived improvements actually transfer from the wind tunnel to the road.
The quest for aerodynamic stability is important because if a rider feels stable on their bike, they’ll be more able to push harder, remain in an aero position for longer, and ultimately maintain greater speed, Ballard said. Wheels that are less stable in challenging conditions, such as narrower, sharper-profiled rims, can react suddenly to gusts, usually leading to the rider sitting up to regain control and therefore hugely increasing drag while often soft pedalling too, he said.
ERC stands for Endurance Race Carbon. Its blunt-nosed, slab-sided rim shape is 47mm deep, 19mm wide internally, and 26.93mm wide at its widest point externally.
Ballard claims that the new wheels’ fine handling comes from its very smooth stall characteristics. The instability mentioned above is an example of a rim with sudden stalling, where the passing airflow detaches from the rim, upsetting its balance, possibly violently. Ballard claimed that the new ERC1100 to be very aerodynamically stable and predictable, with a balanced sideforce response, meaning no nasty surprises when steering.
Taking Zipp’s 303 Firecrest wheelset to be a benchmark, and one with very similar dimensions, Ballard said that the ERC1100 shows a later aerodynamic stall, meaning it’ll remain stable for longer, and almost identical drag figures for both wheels, despite the ERC1100 having a wider tyre fitted. As well as excellent drag performance, the Swiss wheel also demonstrated a useful sailing effect, which is a drag reduction caused by increasing yaw angle, meaning that a stable wheel could help a rider to gain speed in generally downwind directions.
But the aim was to design a complete package for racing, not just a fast rim only. To maximise wheel efficiency, rolling resistance was examined. Lower tyre pressures obviously increase comfort, as the tyre can more easily compress, and wider rubber has a larger contact patch than something narrower. Wider tyres work best on suitably wide rims to avoid a floppy light bulb-shaped tyre, and give better pinch flat protection.
Wide tyres can also have low rolling resistance. The DT Swiss/Swiss Side test results showed that 28mm tyres reduced rolling resistance compared to 25mm tires, and those on a wider rim reduce it further. But the tests also showed that the big tyres' rolling resistance gains outweigh their aero detriment until 35kmh, at which point the aero gains become dominant, so a 28mm tyre makes more sense at the lower speeds, and 25mm tyres above 35kmh. (This aero/rolling resistance balance is just for the tyres; aero resistance more quickly becomes a major factor for the overall rider/bike equation at lower speeds.)
To help decide on a rim shape, Swiss Side first scanned the shapes of inflated Schwalbe and Continental 25mm and 28mm tyres to apply to their aero modeling. This helped them to optimise the rim’s 19mm internal width, which exceeds Zipp’s Firecrest’s 17.6mm. The new wheelset is designed for tubeless use, so the relationship between tyre and rim is crucial. One interesting fact that arose from wind tunnel testing is that Continental’s GP4000s clincher tyre is the most aerodynamic tyre on the market, Swiss Side claimed. This is made more interesting because it wasn’t designed with any aero considerations, and the moulded impressions on its shoulders that make it so aerodynamic (in conjunction with an appropriate wheel) aren’t there for that reason.
With the previous incarnation of the DT Swiss 240s hub comprising 15% of the front wheel’s total drag, it needed to be slimmer. Tests showed the new slim-bodied front hub to save half a watt over the whole wheelset, which equates to 2.5% less drag. The new front hub weighs 90g, with the redesigned star ratchet 24-hole rear hub a further 190g. The rear hub has 36-degree engagement and SINC ceramic bearings as standard, which have an ultra-low friction seal on the outside only, and the hub can be serviced with no tools. The RWS 12mm thru-axles have a removable lever that produces more clamping force, and can be removed and carried elsewhere to save 0.9 watts, or 5.5% drag.
The final part of the ERC1100 wheelset to receive attention was the spokes. DT Swiss designed a new Aerolite 2/3 spoke, which has a straight pull head and regular thread for the nipple, but the outer two-thirds have an aero-bladed profile, changing to a round, butted spoke for the central third, which DT says maximises comfort without negatively affecting aerodynamics.
One area of the new wheel’s development drew some interesting parallels with Zipp’s recently released 454 NSW wheelset. Swiss Side also looked at whale Tubercles as an aerodynamic stability aid in the development process for the ERC1100, and showed a similar-looking development wheel, although with a little less vertical height difference between the highest and lowest points on its rim, plus slightly different spoke placement. From his time with Sauber F1, Ballard knew that the concept had been trialled as part of a car’s rear wing, but it was never used, as F1 wings are static in the airflow, whereas a wheel rim is clearly rotating through the air.
His conclusion was that tubercles work well in a more dense material such as water, but not as effectively in air. The tubercles concept is intended to create vortices in the air ahead of spokes, but in practice, Swiss Side found that working the airflow in this way creates drag, so they didn’t use it. Ballard said that he likes the idea, and thinks it’s pretty cool, but it wasn’t the preferred solution for these wheels.
One other factor to note is that although these wheels are designed for racing use, and this particular wheelset won’t be cheap, it’s wrong for slower riders to believe that aerodynamics matters less to them. The opposite is true, as the percentage drag reduction is more relevant to a slower rider for the simple fact that they’ll be riding for longer.
The ERC1100 wheelset is currently top of a (yet to be seen) range of five wheelsets, although we know that the entry-level wheels will be the E1800 with sleeved aluminium rims. Unlike DT Swiss wheels of old, the numerical part of the name doesn’t denote a rough weight, merely their position within the range.
Claimed weights for the ERC1100 are 710g front and 820g rear, totalling 1530g. The ERC1100 wheels are priced per pair at £1999.98 / €2,418 / $3,117 and there’s a maximum system weight of 120kg. Availability is expected for complete bikes in January 2017, and for purchase in late February 2017.
First ride impressions
I got to try out the new wheelset on a circuit of Seeland, a lake close to Biel. Riding BMC Roadmachine 01 bikes from their near neighbours, we covered the tarmac opening half with 25mm tyres fitted, following the rolling resistance examples outlined earlier. A fairly brief stop around half way allowed us to observe just how fast the tool-free rear hubs permit freehub bodies with cassettes in place to be swapped, as every bike slipped on another pair of wheels shod with 28mm rubber.
It seemed an unusual length to go to, but soon we left the tarmac and began our gravel odyssey, as the ride took on a hint of Paris-Roubaix. Rough gravel and grassy, potholed tracks were no problem, and slippery mud interspersed with some epic puddles dampened many things, but not the spirited riding. Rather than maximising our rolling resistance, the ride’s average speed actually increased on the sketchy surfaces, with over 18km of gravel in all, it became a fight for position on the rough stuff, either for fleeting glory, or just to avoid the mud flying from wheels in front.
It’s safe to say that the new wheels had a good pasting, as no one held back. Despite universal lowering of tyre pressures to around 70psi or less, and general hooliganism, there were no flats or mechanicals of any kind.
With the earlier, hillier tarmac section, plus an extra ride the next day, I can certainly say the ERC1100 wheelset has great potential, climbing and descending with composure, and doing all I asked of it. As ever, trying to gauge the true performance of wheels on an unfamiliar bike over unknown roads, within the throng of a group ride is next to impossible, so I’ll reserve final judgement for a later date when I’ve had time with them on home roads. Until then, there are no negatives to report, and plenty to pique my interest, so I can’t wait to get my hands on a pair.