As Monday was a public holiday my wife suggested that this weeks article should be called ‘Tiny Tweaks Tuesday’ but we’ll stick with ‘Marginal Gains’ for the sake of consistency. However, this weeks topic is not really marginal – Tyre selection is one of your biggest opportunities to gain (or throw away) performance.

The three key characteristics for race tyres are:

  • Rolling Resistance
  • Aerodynamics
  • Weight
  • Durability

For this week I’ll cover Aerodynamics, Weight and Durability. Part Two will cover Rolling resistance and the overall picture.

Tyre Aerodynamics

Tend to be glossed over in most discussions of tyre selection. Especially with many wheel brands contending that they have designed their new wide wheels around 23mm or wider tyres. All this means is that 23mm tyres don’t ruin the aerodynamics of the wheel quite as much as they did with the old, narrower wheel designs. Narrow tyres are still proving to be fastest on wide rims.

Zipp Tyre AeroZipp have very helpfully tested several Continental tyres of different widths on their 303 Firecrest Clincher wheels. The 303FC is 45mm deep with a max width of 28.5mm – intended to be fast but tough enough to handle the pounding of the cobbles in the great classic cycling races. As part of the classic oriented design process Zipp worked towards having a wheel that suited tyres of up to 27mm in width (as classic riders use wide tyres at lower pressures for more comfort and grip on the unpleasant surfaces they face).

It is clear from the graph that the 22mm Continental Attack Tyre is fastest at low yaw, while the GP4000S 23mm is the best at higher yaw (this is a common theme of tyre testing – the GP4000S has a certain magic at high yaw). The 25mm Continental GP4000 is the worst all round.

I’m not going to delve into what this means as power or time differences as that information is meaningless if not considered alongside the effect of rolling resistance. Which comes next week when I combine the data to examine the tradeoffs that keep me awake at night.

Tyre Weight

Your tyres can weigh nearly as much as your rims (on race wheels) and they’re further from the hub – which means they have a significant impact on the Moment of Inertia (MoI) of the wheel/tyre system. Moment of Inertia, simply put, gives an indication of how easy the wheel/tyre will be to accelerate.

I modelled a rider accelerating from 44kph to 54kph (club level sprint) with two different tyre/tube scenarios (same wheel) with a 100g weight difference. The extra weight costs 0.4 Watts. This is not a lot, however it certainly qualifies as marginal gains so is worth considering.

In flat, steady riding the extra weight will have a negligible effect. On a sufficiently steep climb it will have the same effect as any other extra weight.

Tyre Durability

Often closely tied to weight. Though I’ve had heavy, soft tyres that struggled to resist the knife-like edges of a blade of grass – in general though – heavier means tougher.

A big consideration for Triathletes (especially Ironman) is that no tyre is as slow as the one you spend several minutes sitting on the side of the road fixing. Or 20mins if you haven’t practised before your event. So the speed elements of a tyre should be weighed against your risk appetite and ability to fix a flat. Serious road cycling races usually have wheel wagons so there is  less of a concern about being able to repair a flat, they’re still not a good thing though.

Conclusion

Each of the above elements can have an effect on rolling resistance, which is the biggest factor in tyre performance. So next week we’ll discuss why a super aero and light tyre, or a really durable tyre may not be the best option for your individual case.