Picture an F1 car standing still in the pit lane. The sidewalls of the tyre are nice and straight and the contact patch of the tyre is touching the ground. But imagine what that tyre looks like when loaded up in a high speed corner – it flexes and the shape is no longer that ideal vertical line, so easy to model in a wind tunnel.
In modern F1 there is a real premium on understanding this phenomenon and being able to work with the changing shape of the tyre so that the car’s aerodynamics are the best they can be at all times.
In simple terms there is lap time to be gained from doing better in this area; so there’s a lot of work going on there at the moment.
For F1 fans looking to get insights into some of the more fascinating reaches of the sport, we’ve presented this special insight into a key innovation of today from one of our team who has an intimate knowledge of the problem, to find solutions for the F1 teams.
JA on F1 technical adviser Prof Mark Gillan was formerly chief operations engineer at Williams, Toyota and Jaguar and he recently gave a lecture on this subject as principal R&D engineer of MTS Systems, which makes testing equipment.
Tyre Testing and Impact of Deformation on Aerodynamics
Background to the problem:
In F1 and motorsports in general the tyres are the most important performance item on car. The tyres tend to have a relatively narrow optimal operating window, so loads and running pressures and temperatures must be controlled and monitored as well as possible. Wear, graining, blistering, degradation, durability, surface roughness, pick-up, inter/wet impact, are terms you hear all the time in commentary of F1 races and are all issues to be considered. With this in mind accurate modeling of this complex transient system is fundamental to ultimate performance, but all Teams are missing key elements to the puzzle (and so is the tyre manufacturer).
In F1 the tyre shape can have a significant impact on the car’s aerodynamic performance. Knowledge of the profile and contact patch shape is therefore vital to ensure that the key flow structures are in their correct places. In order to ensure good correlation in the development process the Computational Fluid Dynamics (CFD) virtual tyre and the wind-tunnel 50 or 60% scale model tyres must be accurate representations of the full-scale tyres, with the correct shape profile and contact patch throughout the entire operating envelope.
The image below (of a Michelin F1 tyre circa 2004) gives one a good indication of the complex shape the side wall deflects to under load. The Pirelli shape will be very similar.
The Teams have a number of tools at their disposal to ensure good correlation and they tend to use a mixture of virtual modelling, model scale testing, whole/part car multi-post rig testing and on track testing to improve their understanding of the car’s performance.
The motorsports tyre manufacturers will use, amongst other equipment, a tyre test-rig similar to the MTS Flat-Trac™ system. To control costs the F1 teams are restricted in the Technical Regulations (see below) from using these machines to extract certain force and moment data but the tyre manufacturer Pirelli can use them.
The most advanced system is currently the electric motor driven MTS Flat-Trac™ LTRe which is installed at SoVA Motion in the USA http://sovamotion.com This machine can simulate speeds of up to 200 mph (320kph) and simulate forces of up to 30,000N.
This video gives an indication of the amount of tyre deflection possible during extreme manoeuvres. If you stop the video at about 20 seconds you can see a good correlation between the side wall deflection on the Michelin F1 tyre in the image above and the motorsports tyre under investigation.
The key to it then, is to learn from this and to match the tyres’ full scale true loaded shapes to the virtual CFD tyre and wind-tunnel tyre shapes, otherwise a significant amount of CFD and wind-tunnel development runs will be wasted as they will not correlate to the real life conditions. And as F1 teams are now limited to only 30 hours a week for both, that’s a big problem.
This is the work that is going on behind the scenes today; the push to match the tyre shape and improve correlation is one part of the technology innovation that is taking place in motorsports and within F1 in particular. With the recent reductions in both wind-tunnel and CFD usage F1 teams need to continue to ensure that any testing is both efficient and correlates well to the track.
Tyres and in particular tyre shape and optimal aerodynamics are inextricably linked.
* FIA F1 2014 Sporting Regulations
25.5 Testing of tyres :
a) Tyres supplied to any competitor at any time may not be used on any rig or vehicle (other than an F1 car on an F1 approved track, at the exclusion of any kind of road simulator), either Team owned or rented, providing measurements of forces and/or moments produced by a rotating full size F1 tyre, other than uniquely vertical forces, tyre rolling resistance and aerodynamic drag.