Grand Prix Commission Approves Use Of Larger Brake Discs At All Circuits

MotoGP riders are to get some help with braking. From Mugello, all riders will be able to choose once again between running 320mm and 340mm brake discs on the front wheel. Use of the 340mm discs had been made compulsory at Motegi for safety reasons, but now, they will be available at all circuits.

The 320mm brake discs had been made compulsory at the end of the 2011 season, in an effort to cut costs. At that point, teams were free to choose from multiple sizes and masses of brake disc, meaning they were forced to purchase and transport sizeable numbers of discs to each race, while only using one or two sizes. Limiting choice was meant to rationalize the process, and cut costs for the teams.

Unfortunately, the compulsory brake disc size was imposed at the same time as bike capacity and weight were increased. In 2012, the first year of the restrictions, capacity of MotoGP machines was increased to 1000cc, and weights were increased to 157kg, and a year later to 160kg. With more power and nearly 7% more weight, braking forces were growing very large once again. A series of braking problems, most notably for Cal Crutchlow, appear to be related to the size of the brake discs. It was becoming more and more difficult for the teams to manage braking safely, especially at the faster circuits. With Mugello and Barcelona up next, two of the fastest tracks on the calendar, this was a good time to allow the larger brake discs.

The news will be especially welcome for the Yamaha riders, who have struggled with braking for the last two years. Larger discs will help the bike stop more easily, though it will also require changes to set up to handle the greater braking forces and absorb some of the load. Riders are already complaining about the front Bridgestone squirming under braking, and bigger discs will make this problem bigger. 

Allowing larger brake discs is a prelude to more changes to the technical rules. At some point in the near future, minimum weights will also be reduced again, probably from 160kg to 155kg. With the new Open class bikes based far less on production bikes and much closer to the factory prototype machines, the allowance of extra weight is simply not needed. Talks on weights have been going on in the background for the last few weeks. More on the reduced weights will appear here soon.

Below is the press release from the FIM on allowing larger brake discs:

FIM Road Racing World Championship Grand Prix

Decision of the Grand Prix Commission

The Grand Prix Commission, composed of Messrs. Carmelo Ezpeleta (Dorna, Chairman), Ignacio Verneda (FIM Executive Director, Sport), Herve Poncharal (IRTA) and Takanao Tsubouchi (MSMA) in the presence of Javier Alonso (Dorna) and Mike Trimby (IRTA, Secretary of the meeting), in an electronic meeting held on 22 May 2014, made the following decision:

Technical Regulations

Effective Immediately

The Commission unanimously decided, in the interests of safety, to modify the regulation concerning the front carbon disc brake sizes in the MotoGP class.

Currently the regulations permit two sizes of front carbon discs; 320 mm discs must be used at all circuits except at Motegi where the use of 340 mm discs is mandatory and at Montmelo and Sepang where use of 340 mm discs is optional.

Following a recommendation from the Safety Commission and with the support of the brake manufacturers it has been decided that the use of 340 mm disc brakes will be optional for all circuits with the exception of Motegi where such use remains mandatory.

A regularly updated version of the FIM Grand Prix Regulations which contains the detailed text of the regulation changes may be viewed shortly on:

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I'm surprised Dorna didn't decree that riders' leathers be made thinner. Cheaper leather = lower costs, right?

No matter... they've come to their senses. I don't see why they should stop at 340. 360, 380 should be options too. Max braking force isn't dictated by rotor size; it's dictated by front tire grip (which itself is dictated obviously by the tire compound, but also bike setup, rider weight, weight distribution etc etc). Bigger rotors = higher braking torque enabled by the same caliper force, which also means lower level effort, which could mean less arm pump. And also, obviously, bigger rotors = more fade resistance. This seems like an easy place to keep riders safe for next to no money.... how much more does a 340mm rotor cost than a 320mm one?

My guess is you can't go too large on brake disc size. Carbon disks have to be heated up (like tires) to reach their peak performance.

Too big of a rotor might not get the discs hot enough.

The larger the brake rotor diameter, the more resistance there is to steering input, due to the gyro effect of the wheel/rotor. So going bigger than 340 might bring undesirable side effects.

Bigger disks don't increase braking power. More power is the result of the master cylinder ultimately.

Having said that, the brakes are already more than powerful enough. I can't see any situation where a rider would use full braking power (he'd be over the handlebars)

The fade resistance of the larger disks via larger surface area to get rid of heat is the primary benefit

It seems to me that the bigger discs won't generate greater forces, since the maximum braking force is determined by the rear wheel lifting due to the bike's geometry. I would say the larger discs simply have more thermal capacity and are used to prevent brake fade and give better, more consistent feel.

Anyway, good to see that common sense seems to be gaining ground in the Grand Prix Commission. I don't really see how carrying around less ultra-light and compact brake discs was saving the teams substantial money. Having less sizes available does not mean you are using less discs in the end.

Apart from that, it still means that an alternative concept like the rim-attached discs like Erik Buell uses on his EBR bikes are still not allowed. Not saying they would be better, just a pity you can't think out of the box on this point either.

"Riders are already complaining about the front Bridgestone squirming under braking, and bigger discs will make this problem bigger."

Surely a rider can easily do an endo most of the time with the existing disk diameter. Larger brakes will just mean better braking for longer. Lever pressure will still be regulated by the rider won't it?

Carbon brake discs shed carbon as they are used so there is actually less disc as the carbon is used up. Besides thermal capacity and a larger swept area the larger disc offers more life because there is more carbon to be used during a race.

I'd favor going to a combined bike + rider weight limit, with a generous allowance for rider weight, like 75 kg. These guys have to be powerful with great endurance, and I hate seeing them forced (by competition) to be so skinny. This would require lighter riders to carry some ballast, but I feel that is the better alternative. Get those boys something to eat!


Although you'd still see smaller guys favored in the Moto3 feeder class just because the HP isn't there and frontal area is smaller.

Redding stated once that he was at a slight disadvantage in Moto2 because of his size. Whether it was true or not... ?

I suppose they could do the same limits in all classes.

It'd be interesting to see a write-up by someone like Kevin Cameron on carbon discs/calipers. What the trade-offs are of bigger/smaller discs are, why bigger/smaller size/mass is better at some tracks vs. others (before the rules in 2011). What the operational temperatures of carb discs are.

Maybe he already has a write-up like that you could publish David?

I could be wrong but I would have swear that a larger diameter would provide more stopping power because of the greater leverage of those extra 20mm would have over the 220's, the fact that there will be more heat dissipation capabilities is an added bonus but aside from that, diameter is a greater factor. Also count in the mass of the rotors to create a larger momentum so not everything is positive in the equation.

When the bike is upright, weight transfer (lifting the rear wheel) is the limiting factor. When the bike is leaned over, tire contact patch grip available for braking is lower so it becomes the limiting factor. While a 340 mm disc does provide more braking force (greater swept area and greater leverage), that is not the limiting factor. The reason to use a 340 would be heat management and wear resistance.

I must disagree with a part of your analysis. When the bike is leaned over, tyre patch is meaningless, the limiting factor is whether you are 93, or someone else.