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Thread: The Physics of Renault Sport Car Pack

  1. #1
    Vehicle Technical Lead Casey Ringley's Avatar
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    The Physics of Renault Sport Car Pack

    Personally, this pack was a fantastic surprise. I had high hopes for the Alpine A442B but didn't expect the others to all turn out as such unique and enjoyable drives.

    Renault Mégane Trophy V6

    This car is so much fun; what a surprise!!! Bear in mind that it is Mégane in name only. Suspension geometry was mostly present in the CAD files we used for modeling reference and provided a good start. It uses your standard double wishbones front and rear with nothing too strange or clever in the design; it makes for very predictable setup and handling. The engine is a Cosworth-tuned 3.5L Nissan V6 good for 425hp unrestricted and will run up to 8250rpm. You have air restrictor options to run it down to 330hp as they did early in its Megane Trophy life. Idle is strangely high at 2150rpm, but it doesn't matter much. Gearbox is a Sadev SL90 sequential with a ton of ratio options and flat shifting. Aero package is not amazing, but pretty good for a car with this body style that only weighs 1000kg.

    Calling it a touring car is quite a stretch when it's a mid-engine silhouette built around a spaceframe chassis with very-much-race-spec double wishbone suspension front and rear. Not even remotely like the road car; more like a cousin of DTM. It has a slight better power to weight ratio than a GT3, perfectly balanced chassis and good brakes, yet tires that are much narrower than comparable GT cars. (only 21cm wide fronts!) You get to do a lot of steering on throttle with this and top speed is low enough that drafting is important on most long straights. Runs mid 2:20s at Spa, so a fast driver in this could compete with an average driver in a GT3. Great racing against the AI.

    Motion Ratio:
    Front= 0.87
    Rear= 0.75

    Damper Transitions: 50mm/s bump, 80mm/s rebound (front and rear)


    Renault Mégane RS275 Trophy-R

    Now this is more like what we think of when we think Mégane. I was a bit skeptical at first that this car would really be a major, or even noticeable, change from the RS265 we already have in game. There’s nothing too fancy here. It's the 265 with a bit more power, a bit less weight and different suspension tuning ranges. Dampers are matched to some Ohlins DFV shocks that should be the same as what's used on this car. Default setup for them is as recommended by the RenaultSport engineers. Numbers seem to make sense and it works pretty well.

    All those small changes come together to make something really great. Definitely a lot faster than the RS265 Mégane! Seeing close to 8:05 at The Ring here while taking silly risks or honing the lap too much. Plenty more speed on the table. Still, that will put it on par with the new Mustang and some other cars which are much more powerful. Fun little thing.

    Motion Ratio:
    Front= 0.94
    Rear= 0.86

    Damper Transitions: 51mm/s bump, 75mm/s rebound (front and rear)


    Formula Renault 3.5

    This was a very cool little project as we ramp up to Indycar stuff. The FR3.5 chassis is made by Dallara and has an underbody with full tunnels which aren’t all that different from the DW12. We got some very good data for what this kind of underbody does over a wide range of ride heights and matched the game model to it all *very* closely. The changes in downforce level and center of pressure balance are much larger than you might expect. Getting your ride height wrong by 10mm can mean a loss of 10% of total downforce and a shift in balance that is enough to push it from understeer to oversteer. Fascinating stuff to work with real data like this. In general, it wants to be low - very low - and you tend to run it very very stiff to get that aero working.

    The aero package also includes DRS, but it works in a very different way to what most of you are probably used to. Rather than reduce the angle of the second wing element, it flips UP a small flap at the trailing edge of the main element. This closes the slot gap and causes flow separation on the suction surfaces of the wing, stalling it out and reducing both downforce and drag. Similar in theory to how the old F-duct worked on certain F1 cars back before they added the DRS systems we now know.

    Suspension geometry is from CAD. We did have to make one compromise in that the real car uses a monoshock front end: essentially one spring to hold the car up plus an anti-roll bar for lateral movements. Our current chassis solver doesn’t handle this elegantly. It works perfectly right up until it doesn’t and the car explodes off into space. As a compromise we’ve matched a traditional configuration of four ride springs + anti-roll bars to the standard setup on the real FR3.5 as closely as possible.

    Engine is yet another 4.0L flat-plane V8 based on a Nissan block good for 530hp @ 9200rpm; this one being the Gibson ZRS03. Gearbox is the typical 6-speed sequential with flat shifting. In this case the same Ricardo unit as used in Indy Lights...somewhat interesting. Overall it's like driving the Indycar with 60% of the power and downforce, which is actually a lot of fun and a good challenge. Takes a good three laps to get the tires up to full temperature from cold as it doesn't work them very hard by being so light.

    Top speed at Monza approaches 298-300km/h with another 10-15 added via DRS. Lap times are close to real: 1:34 Monza, 1:41 Nurburgring GP, 1:59 Spa. Pretty quick car for the specs!

    Motion Ratio:
    Front= 1.0
    Rear= 1.0

    Damper Transitions: 50mm/s bump, 80mm/s rebound (front and rear)


    Renault R.S.01

    Engine is a Nissan VR38DETT almost straight out of the Nissan GT-R GT3. Good for 550hp @ 6800rpm. Occasionally they run slightly lower boost for 500hp; not sure exactly how they decide. Power to the rear through a 7-speed Sadev sequential with flat shifting. Smart design using the 7 gears. It means there is no need to ever think about changing ratios for a given track; there is always one that will have you in the power band for each turn and an appropriate top speed. Suspension geometry is all from CAD points. Nothing to fancy there, but it is kinda nice how they've designed the rocker arms to give a near perfectly linear 1:1 motion ratio at front and rear. There was also enough detail in the CAD to estimate wheel rates for the anti-roll bars, which is cool. We almost never get that kind of data as pure wheel rate numbers. No official aero numbers yet, but vague PR-type numbers are floating around the web. Official website claims 1.7 metric tons of DF @ 186mph. This is very hard to believe as it would mean a lift:drag efficiency over 4.0 - better than some LMP cars. Other reviews are stating 1200kgf @ 190mph. This makes much more sense. It's essentially a GT3 car with LMP2 underbody venturi tunnels. If I put an LMP2-style underbody/diffuser on one of our GT3 models, it matches up to that number very closely and performance looks about correct. Tires are Michelin's standard GT3 set. No mention of what type of rubber compound, but I'd have to guess it's one of the harder versions. The WSR series seems to stress tire management with teams only getting 2 or 3 sets per weekend. Making them last takes some effort, too, because with more power, no driver aids, and much more downforce than a GT3 car, this thing really stresses the tires. It is very easy to overheat and cook them. It is very very fast; just off DTM pace, really. Fast drivers will be in the 2:11s at Spa, which could conceivably match up with an average driver in LMP2. Impressive race machine here.

    Note that we did deviate from the standard RS01 suspension setup slightly for defaults. Numbers from RS indicate 900lb/in front springs and 1200lb/in rears with very low ride heights of 42mm front / 55mm rear. That works quite well at a fast, smooth track like Spa, but is a bit harsh for a lot of others like Oulton Park. Our default raises and softens it a bit to work better all around, but you will find some more pace at the fast tracks with the numbers above.

    Motion Ratio:
    Front= 1.0
    Rear= 1.0

    Damper Transitions: 50mm/s bump, 80mm/s rebound (front and rear)


    Renault Alpine A442B

    Interesting car to drive! This was right at the start of the turbo era and it comes across in the engine response and how many things are compromised for the sake of getting the power numbers. Engine is a precursor to the Renault V6 from our Lotus 98T but in 2L form and with a single, larger turbo. There is a good bit of lag and it takes about 100m out of slow corners before it builds up to the target 0.9bar boost. A N/A version of the engine was good for peak power around 12000rpm, but that rpm came well down with the changes to turbocharge it. Peak is around 540hp at 10,500 but it was geared to hit top speed around 10,200 and in 1978 they would only run it to 9,200 or 9,500 during the race to try and save the pistons. The gearing used meant that 9500 was still good for over 340kmh. Not too shabby. Has a very nice power band despite the lag issues; it will pull nicely from 6800 to 10200 without any unpleasant spikes or dead spots in the power curve. There is a ton of rubber at the rear too - 80cm total tread width on a car that is only 180cm wide! - so power oversteer isn't really a worry. Handling, in general, was something of a tertiary concern behind top speed and stability at top speed.

    Weight distribution was somewhere north of 70% rear and what downforce it did make was very heavily biased to the back with the rear wing slung 1.3m behind the rear axle. No firm aero numbers available for the Alpine, but the Porsche 936 is similar enough and used it's 500lb downforce / 375lb drag numbers were used as a baseline. The car is so rear-biased that it will even pick up the front wheels for an instant on hard launches. Makes it very much a straight line car. No bad in corners, but being fastest in the tight portions of a track were never the intention.

    Performance ends up strangely close to a modern GT3 car; somewhat faster than GT3 at tracks where top speed is important and just a bit slower at tracks where it isn't. Don't expect to hustle it through turns and it's a lot of fun. Runs around a 7:15 at Nurburging, 1:27s at Brands Hatch, and 3:55 at modern Le Mans.

    There is a series of books out there which I highly recommend documenting the path of Renault & Alpine from the A110 through the A442B Le Mans win and on to the F1 cars. Such a fascinating era as turbos started making waves in the racing scene and the books have amazing detail of the testing and design, trials and successes and failures that made it all happen. Well worth space on the shelf.

    Motion Ratio:
    Front= 0.78
    Rear= 0.87

    Damper Transitions: 30mm/s bump, 60mm/s rebound (front and rear)


    Radical RXC Turbo

    Sweet little car.

    Engine is a tuned 3.5L V6 Ford Ecoboost. Really good engine to drive with a fat torque curve peaking at 500lb-ft @ 3600rpm and then a very smooth drop to the power peak for 454hp @ 6100rpm. They have a new version - RXC Turbo 500 - boosted up for 537hp but tuned so it loses all that mid-range torque. Tried that boost curve on our model; Don't like it. The fatter power band is so much nicer to drive around a track. Power is to the rear through a Quaife QBE81G 7-speed sequential. It has three optional gear ratio sets and three optional final drive ratios; all available to mix & match in setup.

    Downforce is claimed at 900kgf at the max speed of 185mph. That works out to a lift:drag efficiency of 2.0, which is perfectly plausible for a car like this. Experimenting a bit on this car with a much more aggressive model w.r.t. sensitivity to ride height and rake. It's a flat-bottom car with no front diffuser, and things like this tend to be very sensitive with a large penalty for getting either end too low to the ground. Airflow becomes choked and downforce vanishes in an instant. I think it is working well. Setup is quite important and there is a definite sweet spot where it likes to run. Slamming it down all the way to minimum ride height puts you outside of that window unless the springs are run so stiff as to be very unpleasant over bumps.

    There were enough points our the scanned model and good CAD views on the web to draw up suspension geometry and work out motion ratios. Super-basic double wishbones; nothing special at all. The standard RXC I looked at had 50N/mm springs all around. Probably nice on the street but too soft on track. Ours defaults to 80N/mm instead.

    Thing is fast! Don't have a ton of laps on it yet, but it's just about equal with the McLaren P1 with a much nicer balance between handling and power.

    Motion Ratio:
    Front= 0.90
    Rear= 0.88

    Damper Transitions: 30mm/s bump, 60mm/s rebound (front and rear)
    Haste Is Slow

  2. #2
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    Great. This is what I wanted

    Now time to read
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  3. #3
    WMD Member dodge33cymru's Avatar
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    The cars in this pack don't interest me (more standalone classes), but I thoroughly enjoy reading these threads and they're arguably more persuasive than anything in video or photo form with regards to influencing my desire to purchase.

    The Alpine and Formula Renault in particular are very well described, thanks for the information and descriptions.

  4. #4
    WMD Member Sankyo's Avatar
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    Only drove the Alpine and the Trophy V6 so far. Both great cars, handling very nicely (the Alpine was much more oversteery than I thought I would be!) and the sound is awesome. Driving the Alpine around Hockenheim Classic is just sim racing heaven
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  5. #5
    WMD Member hotak's Avatar
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    i really love the alpine and the radical, didn't really expect to enjoy this DLC so much, but i'd say it's second only to the racing icons one (and japan one, but that's just because i love japanese cars)
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    GT4 Pilot Pink_650S's Avatar
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    Okay, 5 cars for 3,49€ is great, bought.
    Especially the Megane Trophy could turn out to be a great car for close multiplayer races.
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    I'd like to know a little bit more (everything) about the diffusor and the changes in downforce and centre of pressure over different ride heights of the 3.5
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  8. #8
    Superkart Pilot Scuderia Paul's Avatar
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    I love reading these physics write-ups by Casey almost as much as driving the cars.

    Casey, do you get to drive many of the cars first and if so which ones? That is for all cars in the game not just the Renault Sport Pack.

    Happy Christmas.

  9. #9
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    Really enjoy reading these. Also I very much like the comparisons to other cars/classes in the game to give people a direction to mix it up a little. Keep up the great work.

  10. #10
    WMD Member RomKnight's Avatar
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    Another one here thar enoys reading this kind of stuff. Thanks Casey
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