RE: Prodrive Megane R.S. RX revealed
Thursday 5th April 2018
While many may now bemoan the lack of 'proper' homologation cars for competition, machines as dramatic as this new Megane World Rallycross car do make it hard to be too upset that it doesn't share much with the road car. Well, apart from the roof and driver's door. Look at it!
Look at the wheels. They're just 17-inch in diameter, with a new design possible because the brakes are no longer housed in them. The RX features what Prodrive calls 'inboard' brakes, where the front calipers are fixed to the gearbox and the rears are attached to the differential. Clever. It means that the upright assembly can be far lighter - as well as the wheels - which means that Prodrive claims an unsprung mass for each corner of less than 30kg.
"The design team have thought about every aspect and introduced ideas never before seen in motorsport. I truly believe this is a game-changer in RX", said Prodrive's Motorsport MD John Gaw. Finite Element Analysis (FEA) was used for designed "safety and performance critical items", with CFD (Computational Fluid Dynamics, in case you weren't sure) for aero and engine cooling development.
Prodrive Megane R.S. RX revealed
If you think it looks mad outside, wait until you hear about what's underneath...
You may remember that the Prodrive-built Megane R.S. RX was previewed last year, but here it is in full race spec, ready to go for the 2018 WRX season. The headline number is 600hp (there or thereabouts) from a 2.0-litre four-cylinder turbo, with power reaching all four wheels via an Xtrac five-speed sequential. However, there's way more to this Megane than just power...
That's not all. Prodrive has collaborated with Ohlins for the Megane's suspension, a bespoke four-way adjustable damper the result. Double wishbones at each corner further reduce unsprung mass. Both front and rear diffs come from Xtrac, and the carbon plate clutch is from Alcon. A serious spec for a very serious looking car.
The Megane R.S. RX will be driven by Guerlain Chicherit this year, who said he "can't help but be excited!" about the prospect. It's easy to see why. Should be one heck of a season. Will the new Megane give Chicherit an advantage? Not long before we find out, as the first race is next weekend...
Discussion
I know inboard brakes have been used in motorsport for years but not used for road cars. The twisting forces on the shafts between the wheels and the inboard brakes must be immense, even when say, braking a one tonne vehicle from 100mph.
Is this the main reason why they are not used on supercars - imaging the twisting forces on the shaft when braking a 1.5 ton car from 150mph+?! Then imagine doing that on a track day for 20 laps or so.
Brakes and tyres are the two areas that seem to be under developed compared to engines and suspension development in the last 20-30 years. Although I'm sure the construction and compounds used in tyres are advances, we still rely on small rubber contact patches to keep us on our poorly surfaced and potholed roads.
Still, I love older cars so more an observation than a moan.
Is this the main reason why they are not used on supercars - imaging the twisting forces on the shaft when braking a 1.5 ton car from 150mph+?! Then imagine doing that on a track day for 20 laps or so.
Brakes and tyres are the two areas that seem to be under developed compared to engines and suspension development in the last 20-30 years. Although I'm sure the construction and compounds used in tyres are advances, we still rely on small rubber contact patches to keep us on our poorly surfaced and potholed roads.
Still, I love older cars so more an observation than a moan.
I had to laugh at the line "what Prodrive calls 'inboard' brakes". A technology that was commonly used in F1 almost 50 years ago, and PH seem to think Prodrive invented it for their new rallycross car...
ETA: @DanG355 I suspect they're mostly not used in road cars because the packaging compromise is not worth the small performance improvement, particularly when taking into consideration the need to keep them cool.
ETA: @DanG355 I suspect they're mostly not used in road cars because the packaging compromise is not worth the small performance improvement, particularly when taking into consideration the need to keep them cool.
Edited by spikyone on Thursday 5th April 15:50
My old Alfasud had inboard discs as did the old Jag IRS and I believe brake cooling was one of the main reasons it never became mainstream. I don't ever remember half shaft failure being real problem but I could be wrong.
It's a great way to reduced unsprung weight if you can find a way to keep the brakes cool.
It's a great way to reduced unsprung weight if you can find a way to keep the brakes cool.
Agreed on the comments re: 'inboard' brakes. Even as a complete non-engineer I know firstly that inboard brakes have been variously used and not used on competition and road cars and secondly that the concept itself is hardly so arcane that it merits inverted commas.
As to the car itself, great. Glad it exists so that we can enjoy chatting about it on this 'website'.
As to the car itself, great. Glad it exists so that we can enjoy chatting about it on this 'website'.
Well they are new on any 'new' application, novel as such and new kids on the block would not have heard of it. Like twenty somethings that don't know who Elvis or even Michael Jackson is...
I thinks it cool... And hope they are cool, wondering in such case, how...
As for twisting force, tyres have limited grip and given that 600bhp will break traction at almost any time, the driveshafts will take the braking no problemo...
I thinks it cool... And hope they are cool, wondering in such case, how...
As for twisting force, tyres have limited grip and given that 600bhp will break traction at almost any time, the driveshafts will take the braking no problemo...
You are all correct that inboard brakes are not new, but are not found on any other current race/rally/rx vehicles. Prodrive has considered using them before. on the the MINI WRC for example, because of the benefits it brings in significantly reducing the unsprung mass - ie the weight of the wheel, hub, brakes and suspension components. In the case of the Megane RX it is less than 30 kg per corner; the MINI WRC was more than 50% heavier. The issue with inboard brakes is heat dissipation, which is why it was not put on the MINI WRC, but short WRX races mean it is not such an issue.
Prodrive PR said:
You are all correct that inboard brakes are not new, but are not found on any other current race/rally/rx vehicles. Prodrive has considered using them before. on the the MINI WRC for example, because of the benefits it brings in significantly reducing the unsprung mass - ie the weight of the wheel, hub, brakes and suspension components. In the case of the Megane RX it is less than 30 kg per corner; the MINI WRC was more than 50% heavier. The issue with inboard brakes is heat dissipation, which is why it was not put on the MINI WRC, but short WRX races mean it is not such an issue.
Are the brakes carbon/ceramic or again do the short races mean this is not necessary? Must have some advantages in removing the torque reaction from the suspension too?Prodrive PR said:
You are all correct that inboard brakes are not new, but are not found on any other current race/rally/rx vehicles. Prodrive has considered using them before. on the the MINI WRC for example, because of the benefits it brings in significantly reducing the unsprung mass - ie the weight of the wheel, hub, brakes and suspension components. In the case of the Megane RX it is less than 30 kg per corner; the MINI WRC was more than 50% heavier. The issue with inboard brakes is heat dissipation, which is why it was not put on the MINI WRC, but short WRX races mean it is not such an issue.
it's also actually quite hard to package a large disc brake inboard! The "hole" in the middle of a wheel is a handy space for them!It'd be interesting to see the under bonnet package to get the engine, trans, diff and brakes in?
Max_Torque said:
Prodrive PR said:
You are all correct that inboard brakes are not new, but are not found on any other current race/rally/rx vehicles. Prodrive has considered using them before. on the the MINI WRC for example, because of the benefits it brings in significantly reducing the unsprung mass - ie the weight of the wheel, hub, brakes and suspension components. In the case of the Megane RX it is less than 30 kg per corner; the MINI WRC was more than 50% heavier. The issue with inboard brakes is heat dissipation, which is why it was not put on the MINI WRC, but short WRX races mean it is not such an issue.
it's also actually quite hard to package a large disc brake inboard! The "hole" in the middle of a wheel is a handy space for them!It'd be interesting to see the under bonnet package to get the engine, trans, diff and brakes in?
There is of course more than one way to skin a cat...
wait?
You take the penalty of running the engine well forwards in the engine bay? Is this because the start is all important? (get ahead off the lights and the race is yours too loose) A front weight bias gives you a good launch because you can use the front tyres more? ie you are biasing towards "Traction" from "Handling")
(The WRC Subaru's were always hampered by the fwds / high engine compared to the other cars that pretty much could bury the engine under the bulkhead....)
Way back in the day, a certain pretty successful RallyCrosser got very creative and "split" the front diff in two, and placed each half (2 crownwheels and pinions) on each side of the longitudinal engine block, placing the actual "diff" in the gearbox, and feeding a shaft forwards down each side of the engine. In that way the engine could be back and low, without having to get the drive to the front wheels "though" the crank.......
You take the penalty of running the engine well forwards in the engine bay? Is this because the start is all important? (get ahead off the lights and the race is yours too loose) A front weight bias gives you a good launch because you can use the front tyres more? ie you are biasing towards "Traction" from "Handling")
(The WRC Subaru's were always hampered by the fwds / high engine compared to the other cars that pretty much could bury the engine under the bulkhead....)
Way back in the day, a certain pretty successful RallyCrosser got very creative and "split" the front diff in two, and placed each half (2 crownwheels and pinions) on each side of the longitudinal engine block, placing the actual "diff" in the gearbox, and feeding a shaft forwards down each side of the engine. In that way the engine could be back and low, without having to get the drive to the front wheels "though" the crank.......
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