[Physics Update] Group 5 - 20/05/2020

Discussion in 'Car Information and physics updates' started by Alex Hodgkinson, May 21, 2020.

  1. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Before anything, the #1 rule here is that old setups will not work with any updated cars. Trying to use these setups will result in a very poor handling car. They must be deleted!

    For the 1976 season the FIA introduced a new Group 5 Special Production Car category, allowing extensive modifications to production based vehicles which were homologated in FIA Groups 1 to 4. These cars would contest the World Championship for Makes series from 1976 to 1980 and then the World Endurance Championship in 1981 & 1982. The FIA rules restricted the width of the car, therefore cars were built with standard body widths but wide mudguard extensions. The regulation required only the bonnet, roof, doors and rail panel were left unmodified. The rules however did not mention headlight heights, therefore when Porsche originally were to enter the 935 with the production headlight, they read the rules and discovered the loophole, therefore they raced the 935 with the hallmark flat nose. The category was also mostly associated with the wide boxy wheel arches and extravagant body style. The category would be banished after 1982 in favour of the Group B regulation, but continued to compete in JSPC, IMSA GTX category and other national sports car racing championships for a few more years.


    In Japan, the wide arch boxy with extended front spoiler body style is still favoured amongst kaido racer/silhouette car drivers, impersonators of the former and fans of the body style, who usually build a more exaggerated body style.

    Tyres

    Back in the late 70s/early 80s crossply tyres were the norm, with radials only starting to appear in high end motorsport from around 1983. A crossply tyre uses a stiff sidewall to support the car's weight, with a relatively flexible tread section in the middle. This gives them a distinctive difference in feel to a modern radial. They typically operate at much wider slip angles and are more forgiving at the limit without the dreaded snap-back a radial can give you. As they flex when loaded laterally, they do not respond quickly on turn-in, so the front of the car needs to be "lead" into the corner. Also due to the stiff sidewalls they do not respond well to camber, and much prefer to sit perpendicular to the road surface. Big camber angles with a crossply tyre will only serve to overheat the sidewall and reduce grip.


    A further development of these tyres (which is are shared with the Group 4s) has been in the heating and wear behaviour. These older tyres took longer to get up to temperature and pressure than modern rubber, so you won't feel the tyres getting close their optimum grip levels until you've completed at least 3 laps at an average length circuit. Rears will usually come up to temperature quicker as you've got all that power putting heat into them!

    Brakes

    Ever so often we review certain systems we have in place, whether it's one which generates a set of values or it's looking at how those values are implemented. The brake heating and cooling aspect hadn't had a whole lot of attention for some time, if we're honest. Then a conversation about brake behaviour sparked up in a WTCR WhatsApp group we're part of which includes a lot of the real drivers from that series. What that lead to was several days of pawing through real world data and comparing it to how our brakes were behaving differently across the board. The conclusion is what our brake temperatures were showing too much range, so some new systems were built to rectify that, the result being more consistent brakes with better initial bite. These updates are already on several series in game such as Group 4, the RaceRoom Junior, and now these babies too.

    The brakes are generally very good, as you'd expect from a big-spending race series. Just as with the tyres, you will need to wait for them to come up to temperature to feel their full effect. That'll take 3-4 braking zones usually. The limiting factor in deceleration is how much braking force the tyres can cope with.

    Suspension

    [​IMG]

    Despite what some people like to think, suspension layouts of top-line race cars haven't really changed much in 50 years. Sure, some trends have come and gone, such as third springs and the carbon fibre anti-roll bars TWR Jags used in the 80s. Most of our Group 5s use independent double A-arms, which first appeared in the 1930 on Citroens and is even commonplace in a lot of road cars nowadays. There are some exceptions within the Group 5 cars, such as the Zakspeed Capri which runs an ancient live-axle setup with a Watts Linkage, something which was actually invented in 1784 for steam engines...!

    The biggest difference to contemporary race cars is in the damper department where they're a much simpler affair than a modern unit. Separate high speed damping has not been invented yet, so all you get it a low speed adjuster. This means you have to consider behaviour over bumps as much as general handling needs when adjusting them as you can't separate the two elements out.

    Now, a quick introduction to the cars one by one;

    BMW 320 Turbo
    600hp at the flywheel
    960kg with driver

    Built on the E21 320 saloon, this project actually started life with a NA F2 powerplant, the BMW M12. If you've ever heard one in person you'll recall the howling sound making the hairs on the back of the neck stand up! It was then developed in conjunction with McLaren North America into a turbocharged powerplant, which almost doubled the power output. Schnitzer also got involved and developed a turbocharged engine which was used to dominate the DRM series in 1978. Interestingly, this very same engine was downsized and further developed into the M12/13/1 of F1 fame with a claimed 1400hp in 1986.

    Corvette Greenwood
    [​IMG]

    850hp at the flywheel
    1309kg with driver

    Presumably the motto "There is no replacement for displacement" was on the wall of the workshop at Greenwood. This car is built around a 7-litre V8 capable of nearly 1000nm of torque. Suspension-wise it's actually quite advanced, with double wishbones all round. Tyres are massive especially at the rear, to give them some sort of chance of surviving the absolute beating the V8 gives them. Unfortunately that big engine is very heavy, so despite a really trick tubeframe chassis it's by far the heftiest car in this class. That really harms cornering ability and brakes can really take a pounding with this beast too.
    Gearbox is a Muncie M21, designed and built for trucks and gear ratio choice is therefore limited.

    Dekon Monza
    600hp at the flywheel
    1088kg with driver

    Designed by a certain Lee Dykstra who was also responsible for designing the Group 44 Jaguars and Mazda RX-792P GTPs. Double wishbones all round, lots of torque and plenty of downforce.

    Fabcar 935/84
    [​IMG]
    620hp at the flywheel
    1026kg with driver

    It really is fairer to call this a Fabcar and not a Porsche. Fabcar are a racecar manufacturer which was founded in the 70s, building a reputation throughout the 80s for producing better-than-factory Porsche 962 chassis as well as their own GTP. More recently they built a Daytona Prototype.

    This car, made in California, was a one-off chassis built right at the end of the 935's racing life. So naturally it incorporates many of the developments ever seen on a 935. It runs a spool axle, meaning there is no differential (you'll notice you won't be able to find it in the setup menus) and a syncromesh 4-speed Porsche G50 gearbox. Ratios are all as-per the period Porsche parts list I have in my possession. Weight distribution is improved over the 934 with a 40/60 split.

    Interestingly it never actually ever raced at a Group 5 or in the GTX class, instead always competing as a GTP.





    Nissan Skyline 2000RS
    [​IMG]

    600hp at the flywheel
    1005kg with driver

    Both this and the Silvia are the original 'mother chassis' produced in Japan. As a lot of the circuits in Japan are tight and twisty, the focus was on producing downforce, which they do but at the expense of drag.

    Nissan Silvia Turbo
    620hp at the flywheel
    1050kg with driver

    A later version of the car above, developments have added downforce and some more power but also drag and weight. A lot of the underpinnings are interchangeable with the Skyline 2000, but a wider track and slightly shorter wheelbase means the suspension setups are different.

    Zakspeed Capri Turbo
    545hp at the flywheel
    895kg with driver

    Thanks to the only diffuser in it's class, this is the highest producer of downforce by quite some margin. The numbers are comparable to the previous generation GT3s, however there are drawbacks. Drag is high, so top speed suffers and a lot is yet to be learned about producing consistent downforce from underbody venturi. Run the car too low, the downforce drops off dramatically, run too high it'll do the same. Take it to a bumpy track and the downforce will be switching on and off like a flickering lamp. Interesting to say the least.
    An unusual feature, as I touched on way up there somewhere is the suspension layout. The front end is a strut-type, which is a bit behind the times, while the rear end uses a live-axle which is even more so. A live axle links both the back wheels together, so bumps on one wheel will affect the other. There is also a matter of torque reaction across the axle, which when accelerating pushes one wheel into the ground while lifting the other. This gives you a slight yaw to the right when hard on the power.
     
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    Last edited: May 22, 2020
  2. Manuel Staedel

    Manuel Staedel Active Member Beta tester

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    It's an another world now with that beasts. Very nice. I am not fast, but have much fun with it.


    Video are uploading now...
     
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  3. Badgerous

    Badgerous Well-Known Member

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    A great little write-up. These blurbs really should be a part of the game/UI somehow (a little info tab), and expanded upon for all cars. :). They really help understand why a particular car feels/handles the way it does

    I'm looking forward to trying the update later.
     
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  4. OldFart

    OldFart Active Member

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    now that is what I call a great post, thank you that must have taken quite some time
     
  5. fischhaltefolie

    fischhaltefolie Well-Known Member

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    That's a very interesting reading. Impressive, what you're bearing in mind, when you model the cars.
     
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  6. ducman888

    ducman888 Well-Known Member

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    Last edited: May 22, 2020
  7. FeltHλt

    FeltHλt Well-Known Member

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    no premium no cry :p
     
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  8. CheerfullyInsane

    CheerfullyInsane Well-Known Member

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    And nobody stopped to think whether this was actually a good idea? :D
     
  9. Cheeseman

    Cheeseman Well-Known Member

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    They are hard to drive as before. Fun, nevertheless.
     
  10. Beastux

    Beastux Well-Known Member

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    I think they are harder to drive than before. I used the Zakspeed at Brands Hatch yesterday, with the default setup, it's hard to keep it in a straight line in the pit straight, even in 5th gear. I hope I'll find a good setup because, for the moment, it's not really fun to drive this car compared with the previous version.
     
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  11. Jukka Karppinen

    Jukka Karppinen Well-Known Member

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    Yes of course they are harder to drive now, because with old physics/tyres there were way too much grip for example. I don't know why people often assume Gr5 cars should be easy to drive. Just look at the power/weight ratios, 70's tyre technology, no tc/abs or other driving aids etc. They were certainly handful to drive fast but still very controllable, just like they are in game now with current physics. Having to be extra careful with gas pedal IS the part of the fun with these beasts.
     
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  12. memoNo1

    memoNo1 Well-Known Member

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    I've been out for 3 weeks because of moving and renovating. How are the G5 compared to the RSR 934? Is the Porsche a lamb against it?
     
  13. Beastux

    Beastux Well-Known Member

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    I don't think they should be easy to drive. The previous versions were not easy, even with more grip. I just feel that the behaviour of the Capri (I haven't yet tested the other Gr. 5) with the default setup seems strange.

    You should have a try with it at Brands Hatch and tell me if the slides in 4th or 5th gear in the pit straight are not exagerated. I lapped in 47:994 yesterday and it was exhausting!
     
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  14. Jukka Karppinen

    Jukka Karppinen Well-Known Member

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    Will try tomorrow, i'm not a fan of that track so i haven't driven gr5 cars there. But i just did few laps at nurburgring with Capri and it felt absolutely great to drive, so much fun :)
     
  15. Jukka Karppinen

    Jukka Karppinen Well-Known Member

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    934 is slower than gr5 cars, as expected. So is gr4 M1, with procar version i can stay at least few laps with slower gr5 cars (ai at 107). Need to do some more testing.
     
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  16. memoNo1

    memoNo1 Well-Known Member

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    And from pure driving? Are the G5 even more brutal and demanding?
     
  17. OldFart

    OldFart Active Member

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    Thought I would try as I like the Capri, and to be honest if you can not drive it I am in big trouble, So conclusion, 1st to second less than a third throttle, spun, several trys later 2nd to 3rd spun, then I remembered Alex said at least three laps to warm the tyres; so very slow three laps, tyres now showing nice and warm; so 2nd to 3rd about third throttle not bad into 4th spun, gave in put TC on revs against the limiter almost all the time again less than a third throttle, for me this is no longer derivable, regardless of the model being more accurate it is not a good step for me, the group 5 are now of my list of cars to drive
     
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    Last edited: May 22, 2020
  18. Beastux

    Beastux Well-Known Member

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    Yes they are!
     
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  19. memoNo1

    memoNo1 Well-Known Member

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    Dear Lord...:eek:
     
  20. FeltHλt

    FeltHλt Well-Known Member

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    its brutal all right :D im scared of going full throttle on straights
     
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