Le futur de l’automobile
With the Symbioz concept car, Renault presented its vision of the future of cars in 2030. An autonomous, electric and smart future, where the line between car and living space is blurred. A concept car Michelin has been involved with from the very beginning. The Group is the only partner whose name appears, along with the Renault diamond, on the sides of the vehicle’s tires.
A slimline tire
MICHELIN and Renault: historic partners
With Symbioz, MICHELINand Renault are pursuing their work together on energy efficiency. A collaboration which started in 2014 on the Renault EOLAB prototype fitted with MICHELIN 145/70 R17 tires and which continued in 2016 with the new Renault Scenic, equipped with MICHELIN PRIMACY 3 tires in a slimline format (195/55 R20).
Improved energy efficiency
One of the challenges Renault gave the Michelin engineers was to enhance the vehicle’s aesthetics. But most importantly, the slimline tire helps reduce energy consumption. At equal width, the higher the tire, the lower its rolling resistance; a larger perimeter is subject to less deformation and therefore dissipates less energy. Inversely, the increase in a tire’s width, which generally goes with its height, reduces energy efficiency. The slimline tire does not have this disadvantage; its narrower tread further improves its aerodynamic performance.
5 QUESTIONS FOR PATRICK SÉGUR ET SYLVAIN LEYNAERT, RESPONSIBLE FOR THE DEVELOPMENT OF THE SLIMLINE TIRE FOR THE RENAULT SYMBIOZ CONCEPT CAR
What difficulties do you encounter with this type of concept tire?
On this kind of project, our biggest challenge is time. Generally, when my manufacturers contact us, their project is already well-advanced. To be able to provide an initial estimate, we must quickly understand their size constraints, their schedule and the specific characteristics they want (colors, profiles, treads, etc.) and also what they want to do with their concept car: exhibit it, make a film of it actually driving, loan it to journalists, etc. Finally, we need to know the number of tires required. The greatest issue is defining the protocol for manufacturing the tires on time. We have two or three projects like this a year.
What were the specific challenges for Symbioz?
Renault got in touch six months before the presentation of its concept car at the IAA show in Frankfurt in 2017. Considering the tight deadline, we couldn’t respond with a standard tire protocol, so we used a heavy truck workshop. Also, we had to design a special curing mold. We then got in touch with the CPV teams (curing molds). We ordered the mold at the end of January and received it early May. The 8 Symbioz tires were delivered to Renault early July. Heavy truck workshops, CPV, treads, uncured and cured development, calculations... In total around twenty people worked on this project at Michelin. The dimensions of the tire presented no particular technical difficulties. The technical challenge was above all their profile, in particular for molding then grinding.
Can you explain that in more detail?
Symbioz asked us for two things. Initially, Renault wanted a sort of rubber wheel cover, to create a continuous effect from the tire sidewall over the rim and wheel. This created big molding problems... Finally, the idea was abandoned. We nevertheless carried out many tests and trials with a lot of hand-finished work, in particular complete grinding of the shoulders and sidewalls to give the impression of an uninterrupted surface from the edge of the rim to the top of the tire. Very delicate work which needed a great deal of expertise! Initially, Renault weren’t entirely satisfied by the results. But through discussions and hard work, we managed to create what they wanted.
What is your work process with manufacturers for this kind of project?
For the Symbioz project, as an example, their intentions were confidential. So it’s not easy for us to know what the vehicle will look like. We knew that it was a vehicle that would actually have to be driven, that it would be electric, that the outside tire profile needed to be smooth with special rims, and that it had to generate the least heat possible. With this information, we gave Renault sketches, a design, a tread... We were inspired by work already done on tires for electric vehicles, with small sipes to make the structure mobile in the center of the tread, generating more flexibility and grip. We also kept the center of the MICHELIN Primacy 4 tire, and changed its shoulders and sidewalls. We also did a lot of work on the material, with a rubber that has a satin look with a more matte finish. There were many discussions about the Michelin markings, to optimize their position.
Symbioz has been announced for 2030 at the earliest. Is the time-frame the same for the tires?
These are concept tires for a show. Just like the car, these tires are not for the road. With this type of project, we are not looking for performance or aerodynamics, rather suggesting these elements through the design. In the case of Symbioz, we illustrate performance through very smooth shoulders and lots of rubber on the sidewalls, which would make no sense in terms of performance and aerodynamics for real tires! If this tire was one day designed for retail, it would not be made with the same materials at all. The inside, for example, would be completely overhauled. And then it would be a completely different project, where notions of performance, rolling resistance and aerodynamics would take priority over design. Such a project would require 2 or 3 years in development.