Revealed: The secret behind Mercedes getting on top of tyre issues
Innovation
Posted By: James Allen  |  13 Sep 2013   |  11:31 am GMT  |  106 comments

One of the defining stories of this 2013 F1 season has been the rise of Mercedes and the way they not only grabbed pole position in eight of the first 12 qualifying sessions (by getting the most out of the Pirelli tyres), but also got on top of heavy tyre wear issues in races to allow Rosberg to win twice and Hamilton once.

Analysis by former Williams chief engineer and JA on F1 technical adviser Mark Gillan of photos of Mercedes wheels, taken by leading F1 photographer Russell Batchelor of XPB Images, shows the complex internal design which Mercedes has evolved to master thermal management of the tyre. It is F1 innovation in action.

Mercedes’ steady improvement in tyre management in races has not happened without controversy, as they took part in a 1,000km Pirelli test in May which landed them in the FIA International Tribunal, where they were found to have breached the Sporting Regulations, but the Tribunal found that the breach had been made in “good faith” based on communications with the FIA.

Here is Mark Gillan’s analysis:

Background

Take a look at what the regulations say about wheels (at the bottom of this post).

As the wheels are easy for other teams to look at one is always very careful to ensure that their legality is crystal clear and if there are any ‘grey areas’ then one will run the idea past Charlie Whiting at the FIA to ensure that there are no problems. Whilst wheels are relatively inexpensive to manufacture (per item) the manufacturing lead times are relatively long and one typically needs 30+ sets of wheels (i.e. 120+ wheels) to remain operationally efficient at races so wheel upgrades during a season are not too common.

The Mercedes wheels in detail
In my experience conjecture about what a team is actually doing with a particular design is often wide of the mark.

What one can say is that to modify a wheel a team needs a good reason to do so because of the lead-times and quantities involved. As tyre thermal management has been a major performance differentiator this season all teams have been working on mechanisms/process to get the tyres into their operating temperature window as soon as possible and then keeping them in this window for as long as possible. The thermal window is quoted by Pirelli as typically 20C to 25C, with running temperatures of between 90C to 135C, depending on compound.


Mercedes has been evolving what it does inside the wheels. Mercedes now has a new set of front and rear wheels which were captured very clearly in Monza by photographer Russell Batchelor. On the inner surface of the wheel there is a complex dimple pattern, which is actually fully integral to the wheel itself and almost certainly there solely for thermal management purposes in order to get and keep the tyres within their optimal temperature window.

This complex dimpled and scalloped pattern (see close up of the front tyre, below) is not straightforward to manufacture and therefore indicates a lot of research and development has gone into developing this component and proving its benefit before committing to its manufacture.

This type of pattern is quite common on modern heatsink designs, where dimples have been shown to give up to 25 to 30% thermal transfer improvements over the smooth surface variant. Only Mercedes will know whether the effort was worthwhile and how good the correlation was to their simulation and rig programme, but one has to applaud their ingenuity and effort.

What the F1 regulations say
Firstly, Article 12 of the 2013 Technical Regs determines what a team can/cannot do with the design of their wheels. The regulations are pretty prescriptive, but the main points can be summarised as:

i) Wheel must be made from a magnesium alloy (AZ 70 or 80);
ii) The width and diameter of the complete wheel (wheel and tyre) is specified within a range;
iii) The wheel minimum thickness is 3mm increasing to 4mm at the bead;
iv) The wheel must not be handed i.e. the left and right wheels on a given axle must be identical;
v) Surface treatments are only allowed for appearance and protection e.g. painted/clear coated to avoid corrosion and allow for livery schemes.
vi) One can then add to the wheel a limited number of items such as spacers, balance weights, tyre pressure and temperature monitoring systems, pegs etc

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1

Graining happens when the surface temperature of the wheel improves. This improves situation temperature, thus reducing graining.

2

That’s just a great piece of insight!

Thanks for your investigative efforts that you don’t get from other F1-related websites!

3

I could bet my last penny that those are not dimples, but holes into a space in the wheel hub. Before this, Merc spotted wheels that had a slot in them. Some argued that the slot was an illusion and really just a piece of tape, but those that argued it was a slot seem to have been proven right.

You can check some of the arguments (F1 technical) that raged as far back as July about Mercs wheels starting from this page: http://www.f1technical.net/forum/viewtopic.php?f=12&t=14607&start=2775

4

franed

I have argued somewhere above that:

“The reason for the colour is most likely because Merc is creating a heat pump between the brakes and the inflation gases in the rear wheel. So, the heat from the brakes would actually be cooling the rear tyres.”

I really think that’s whats going on. Merc have used the rear heat from brakes and exhaust to create a tuneable fridge for the rear wheels. Holes and a sophisticated set of chambers would suit such a purpose better.

5

They do look more like holes than dimples. Holes have all the advantages of dimples (they would increase surface area and thus promote better cooling) and others as well.

6

No it’s just a conductive, or non reflective coating. (since there will be radiated heat as well as convected.)

Enlarge the top photo in yr link as far as poss then look far left, you can just see the coating on the rim where the balance weights go. The lower pic shows a weight in place (near the red arrow) on top of the coating. I had said tape initially but I doubt you would stick a weight on top of PTFE, tape

7

There are a few more pages of interesting arguments (and pics) at that link. The holes in the current rear wheel convince that we are looking at an evolution of the slot in the previous incarnation of the cooling concept. Perhaps, holes are suitable for some circuits, while a slot is preferable at others.

8

Slight miss-quote of the regs there James.

12.8.1 Actually says:-

The only parts which may be physically attached to the wheel in addition to the tyre are surface treatments for appearance and protection, valves for filling and discharging the tyre, wheel fasteners, balance weights, drive pegs, tyre pressure and temperature monitoring devices and spacers on the inboard mounting face of identical specification on all wheels for the same axle.

The magic word there is of course “attached”, while the patterning seems to be part of the wheel casting itself.

It is an interesting problem, moulding or casting on a concave surface, since the male part of the mould has to collapse in on itself. Of course if one machines the pattern on instead it looks like two or more cutting operations (lathe plus linear shaper) and a lot of time, still I suppose a decent sized CNC machine tool could handle it.

One thing to consider is that not only is the surface area increased, possibly doubled but the mass is also increased.

(It must be a surface addition since to cut into the wheel would take it below required minimum thickness of 3mm. Which is pretty dramatically thin anyway. On a CAD course (ProE) some 14 years ago one of the exercises was using a prt file of an F1 wheel and at the time we could not believe how thin it was.)

It is all obviously to increase the heat transfer rate from the brakes into the wheel, but Lewis is still having problems with the brake characteristics.

9

James is it safe to assume the dimpled pattern actually sits on the drum, this cause a space between the dimples and sustaining a constant temperature and allowing excess heat to ease out.or does the wheel sit more on the smooth inner edger of the wheel just ahead of the dimples ?? Thanks

10

Sergio Perez said that McLaren are bringing new parts to Singapore with an eye to next year’s car. Does this mean that the parts will work on both cars? I had assumed that there would be drastic changes to the chassis that would prohibit this. Any chance you could do an article on how the engine affects car design James? Cheers.

11

Innovation is not dead in Formula One! This kind of insight is the reason your site is a must-read, James.

Now we just need to figure out whether they have had this design all season or if it was only introduced after the tyre test.

12

Scarbs discussed this about a week ago, maybe more.

13

Wow, looks as if they could throw these wheels on without wheelnuts in a sub 2s stop and they’d stick on!

Amazing that the friction heat on the outer contact patch could still be influenced by the inner heatsink, I guess every little helps.

DC did always say it was the brakes that heated the tyres more than the weaving on warm-up laps. You’d think it could affect the drivers getting the tyres up to temp on a cool day say after a pitstop or safetycar.

They surely also have air blowing on the heatsink area somehow through the wheel hub?

The things Merc have to do to stop oversteering Lewis chewing up his tyres eh!

(joke, it’s a joke, fanatical fanboys please sit back down…)

I expect to see the Mercs back fighting for pole as we move back to the slower tracks. They just need to watch the driver tracker screens for Sutil… 😉

14

the mercedes public relations efforts has no bounds.

15

Brilliant stuff James. Thanks for that really interesting info. It explains why Mercedes suddenly became competitive in the races.

Just need Lewiws to believe in himself now, and get his head right !!!

16

People, this isn’t to decrease the tire temp, it’s to increase the temp of the tire case. By using the brake as a heater.

Graining occurs when the surface temperature of the tire increases significantly more than the case temp does. This increases case temp, thus reducing graining.

See also: http://scarbsf1.com/blog1/2013/09/06/mercedes-cross-cut-wheel-rims/

17

Well, dimples increase the surface area to volume ratio, so when the brakes are loaded their heat will transfer faster into the wheels and when the brakes are not loaded, the heat will transfer faster from the wheels into the air. So I’d gues that the wheel heat up faster in the braking zones (after getting cold on the straight) and when during and accelleration they are not overheating so fast.

18

That was meant to be: “when cornering and durung accelleration”. My bad.

19

It is a lot of unknown about this finish. But according to paragraph V it is not legal. The link that you are referring to contain one incorrect statement that black pain absorbs the heat. Mat black dissipates the heat and matt white is absorbing the heat. There are some other exotic finishes involving ceramic particles which are used in thermal control of various components.

20

Black absorbs heat and white reflects it.

21

Thanks for the link.

But, lighter colours are only used where convection (or conduction) matters more than radiation (eg home radiators – which are really convectors).

In the Ferrari case, they wanted to minimise heat transfer to the surrounding air, if they’d wanted to maximise it, then the colour would have been matt black like the inside of the Mercs rear wheel.

@ThrowFarFarAwy

The reason for the colour is most likely because Merc is creating a heat pump between the brakes and the inflation gases in the rear wheel. So, the heat from the brakes would actually be cooling the rear tyres.

22

Right you are, but we are here not observing reflectiveness. If you have the heat that is inside some physical body radiator, exhaust system or wheel which contains gas then it’s different all together. To allow heat dissipation one would use matt black paint and in order to contain it one would use white. We are not here discussing if the black absorbs or white reflects the sunlight or any other light source fir that matter. Heat dissipation(conductivity)and reflection are two different physical phenomenons. In order to improve the gas flow in the exhaust system by reducing heat dissipation Ferrari use to finish their pipes in white. They didn’t do that just to make their cars prettier. Kindly refer to the link. http://www.tumblr.com/tagged/ferrari-312

23

It’s basically a heat sink which dissipates heat very effectively… Clever

24

James, is this so idiosyncratic to Mercedes’ tyre issues or will other teams be likely to take a similar approach to either get the heat in or out of the tyre better?

25

Working on that info

26

The profile of those ribs, seems to be far too shallow for any significant thermal effect. Unless there is an enormous airflow, or they extend in to the air space between the wheel and the tyre. Of course that could also provide a means to help with a partially deflated tyre, if the top of the ‘spikes’ was covered with a solid layer. Maybe a deflation compensating device. Remember how Lewis had a slow puncture for a few laps, and no real problems with it, as I recall. I think what we are seeing, is a surface effect for aerodynamic reasons. Similar to a golf ball.

27

I can’t help thinking the wheel looks like a washing machine drum… Maybe smaller holes?

28

Thank you – I knew that it reminded me of something – lol 🙂

29

The reality of technical regs in F1 is that they are whatever Charlie Whiting (or in some cases, the tribunal) says they are.

The Renault mass damper of 2006 was ruled illegal for being a “movable aerodynamic device”, for instance. Rotating dimples (or are they actually small holes?) are far more obviously a moving aerodynamic device than the mass damper was. And if they ARE holes, which they appear to be from the photos, than this could also run afoul of the “Air Ducts” section of the regs.

If the authorities *wanted* to ban what Mercedes are doing here, they could plausibly do so. But such decisions always have as much to do with politics as with the strict letter of the law. A modicum of success for Mercedes is necessary to keep them in F1, so Charlie isn’t going to rock the boat.

30

They are not holes, device works by transferring heat therefore not aero device

31

Nobody outside of Mercedes knows whether they are holes or dimples.,

Holes increase the surface area, just as dimples do, and also allow for air flow. So it would be smart for Merc to have used holes rather than dimples.

32

True, the dimples work for creating more surface area but there has also been speculation that the dimples might have a secondary benefit of reducing airflow resistance in the small space between the brake duct and the rim.

33

I meant the 11.4 air ducts section, discussing air ducts around brakes.

34

Some very clever boffins at Mercedes 🙂

36

Yeah, a week ago. With pics from SomersF1 blog. It’s great to see all these fan tech blogs getting started and even getting the scoop on some of the new ideas cropping up during the season.

37

Well the Merc is much slower now, with this tech.

So neither here nor there really.

38

Nah! Not much point going by their performance in Monza, where the track characteristics would mean the team coming with the lowest downforce setup would perform the best. I’d actually take heart from Hamilton’s race pace which was quite good. Singapore will provide a much better test. I think the Merc is still the best in generating heat and getting the most out of their Pirelli’s over one lap, so it should be interesting.

39

Please explain this comment it does not make sense?

40

Hamilton had the fastest lap of the race in Monza, and I think Rosberg had the second fastest. So no, they have not gotten “much slower”.

41

No one designs, develops, produces components or assembly with the idea to make them slower. The intent was to make them, faster, more consistent, more reliable. So when one judge those components he/she isn’t worried how successful it is, but the intention.

42

Was this tested and perfected during Mercs private in season test? We will never know…

43

Why were they then out-qualified?

44

Looking at the two photographs, the upper picture seems to show the dimples included in the construction as part of the rim. However the bottom picture appears to show an “insert” rather than a completely new design of wheel as suggested in the article?

45

The upper photo is the rear wheel, while the lower is the front.

The front and rear wheels have different heat characteristics, that’s why they are constructed slightly differently.

Both the front and rear wheels get heated by braking and the energy of the tyres from repeated flexing.

In addition, the rear wheels get heated by exhaust gases and sliding around corners, while the fronts are the focal points of the cornering forces.

46

Front and rear wheels ? I believe the front brakes work harder , hence more heat produced , different design required to dissipate the heat ?? Not sure, just a guess .

47

Get to work Martin! (Whitmarsh)

48

…but not on this design. They need work in other areas!

49

You do realise that the only car capable of looking after it’s tyres as well as the McLaren is the Lotus?

50

Christos Pallis

Its a mixture of things. Stiff springing makes the tyre take the place of the springs and buckle under load. That would help to heat the tyres up, but wouldn’t do much good for their longevity. However, the loading (and life) of the tyre greatly depends on how it is set up for cornering and braking, and these are affected by how tightly sprung the car is.

51

Well, yes, but that’s because the MP4-28 is slow in the corners, and can’t load up the tires the way the other cars can. 😉

52

I wonder weather the stiffly sprung McLaren suspension lends its self to being kind on its tyres. Stiff suspension would mean less deforming over surfaces hence less energy going through the tyres!

It’s not strictly related to corner speed as the comment about other teams makes clear. That would suggest that Marussia would have the least tyre wear of all teams!

53

You mean like the Sauber, Torro Rosso, Caterham, Marussia and Williams; all slower cars that can’t generate the loads of the top teams, or McLaren, yet still have higher tyre ware.

54

Concept can work in two directions – it could transfer heat _out_ of the tire in marginal conditions.

55

Would have assumed the modelling done pre-manufacture would allow them to tweak the design for different typical conditions, obviously you cant cover all basis and there must be an eliment of tuning

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