Brake performance wrong in GT4 prologue!?

Discussion in 'Gran Turismo 4: Prologue' started by Buggy Boy, Jun 5, 2004.

  1. Buggy Boy

    Buggy Boy

    Messages:
    660
    After being surprised of the braking performance of the Elise (incredibly bad) and the SL 500 (incredibly good), I did some testing :

    The brake tests were done on Fuji, I drove to the first corner, returned, and accelerated to a constant speed of 150km/hr.
    At the start/finish line, I did a full stop with several cars. After the finish line are the starting positions, which allowed me to "measure" the brake distance from 150km/hr to a full stop. Every test was repeated at least once.

    1. Lotus Elise
    - weight : +/- 700 kg
    - distance : 5 lines and 2 car lenght

    2. Mercedes SL55 AMG
    - weight : +/- 1800 kg
    - distance : 4 lines and 2 car lengths

    3. Impreza 2003
    - weight : +/- 1300 kg
    - distance : 4 lines

    4. Impreza 99
    - weight : +/- 1200 kg (in any case lighter then the '03 version)
    - distance : 4 lines and 1 car length

    5. Integra 98
    - weight : +/- 1100 kg ??
    - distance : less then 4 lines

    6. NSX 97
    - weight : +/- 1200 kg ??
    - distance : 4 lines and 2 car lengths

    Conclusions
    ---
    1. The lightest car needs the longest brake distance?? :confused:

    2. The SL55 stops as fast as the impreza, which is 2/3 of its weight?? and faster then the Elise, which is +/- 1/3 of its weight??

    Is Polyphony Digital joking with Newtons Law here??

    3. The newer Impreza stops faster then the older, allthough 100 kg heavier : Result of the improvement in technolgy the last years? I'd like to see this confirmed in a R/W test report

    4. The Integra 98, however one of the "older" cars, stops very well. Was the braking technology then not so bad by all a few years ago?

    5. The NSX is also braking bad. Should the mid-engined cars get an artificial penalty here by PD? The weight distribution in these cars is better then in most other cars, so the brake forces should be better transferred to the ground. Mid engined cars are supposed to stop better, not worse!!

    Another physics law screwed by PD?

    6. The Xanavi GT-R and Takata Dome NSX were tested at 150 and 200 km/hr : both with the same braking performance
    - 150 km/hr : 3 lines
    - 200 km/hr : 5 lines

    Any comments, or real life data to compare this?

    Btw : the weights are approximative, but the relations won't be to far wrong.
     
  2. Arwin

    Arwin

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    2,093
    How do you brake (full probably) and what tyres do you use? Certainly the price of the car determines in part how expensive breaks will be applied, and a lighter car can also have less downforce for instance. A type R car like the Integra will very likely have sports brakes. In some countries however you're not allowed to drive on the roads with certain performance parts. There are so many issues here far beyond that of just weight and braking distance ...
     
  3. Buggy Boy

    Buggy Boy

    Messages:
    660
    The braking was full, assisted by PD-ABS on all cars :)
    Tyres are "normal", except on both race cars.

    The increase in weight on a tyre is not linear with the increase in horizontally transmittable force, that's THE reason why a lighter car should stop faster then a heavy car.

    Regarding "sport equipment" : I think we can suggest that an Elise, and certainly an Elise 190 is conceived as a high performance car with dito parts.

    But thanks for the comments Arwin, I'm not convinced however. :)
     
  4. AndreasN

    AndreasN

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    46
    the sl55amg has pretty big brakes, so its possible right!.

    that the lightest car needs most distance, could be that the
    tires doesnt get enough grip?.. too light car, and you easily
    lock up the tires maybe?

    or that the brakes arent that good on elise.
     
  5. AndreasN

    AndreasN

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    46
    btw. honda has pretty good brakes :))

    i was driving my brothers civic vtec from 98, and i almost put
    my head thru the window (i had seatbelt, but it felt like it)
    when i was gonan brake for the first time.
    incredible good brakes!.. feels like my kart to drive aswell :)
     
  6. PjotrStroganov

    PjotrStroganov

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    283
    This is the same reaction as in another topic:

    Why wouldn't it be possible for an m5 to brake better than an elise. It could be that an m5 has a bigger surface of braking disks per kg than an elise. Also the elise has no electronic braking help where the m5 does.

    Figure this: A Scania truck has a shorter stopping distance than an Opel Astra. It is heavier but it brakes better. How can this be? Well, because of the same reasons as I mentioned above.

    As said before in this topic. there are more factors at work here. It's not about the power to weight ratio, but about the brake disk surface to weight ratio. This combined with much more factors.
     
  7. GTXLR

    GTXLR

    Messages:
    1,391
    the SL55AMG is a tuned Merc much upgraded, it has massive 4 pot calipers & Huge drilled sports/racing Discs.
    The Lotus is a bits and pieces car at standard level.
    It has a Rover engine, and borrows numerous other bits from road cars.
    Pretty sure the Elise has quite small non drilled, road car discs.
    Although quite adequate for the job of Road driving, pretty sure the wouldnt be much cop on a race track, however if they were upgraded to some kind of Racing set, pretty sure the Elise is gonna stop as fast as the MERC.
     
  8. Buggy Boy

    Buggy Boy

    Messages:
    660
    I agree with you there - power has surely nothing to do here :)

    The formula by Newton : Force = mass x acceleration says it all here, with :

    Force : the decelerating force, that the tyres can make with maximal friction to the surface
    Mass : weight of the car
    Acceleration : here deceleration off-course

    So the deceleration will be linearly greater with a lower weight.
    The force that the tyres can apply, depends of their coëfficiënt of friction (= composition of the rubber, tyre pression), the surface area and the vertical weight upon the tyre.

    Maybe you will think now : aha, so a heavier car has more braking force. That's correct, but the gain in braking force due the weight, is less then the increase in force that's needed to stop the higher mass ... Still with me? :)

    So a reason why a Scania could stop quicker then a car, could be its tyre surface, since it has 3 axles.
     
  9. Buggy Boy

    Buggy Boy

    Messages:
    660
    I did a search on the web and found a test comparing an Elise to a Mustang Cobra. The Elise was definitely better in all area's due to it's low weight :)

    http://www.sportcompactcarweb.com/features/0205scc_coblot/

    So read on, and learn once and for all if size matters.

    Both of these cars offer performance worthy of their high-dollar price tags; still, it's the little Lotus that out-accelerates, out-brakes and out-slaloms the Cobra.

    The braking test again showed the difference in weight. Even the huge Brembos wouldn't allow the Mustang within striking distance of the featherweight Elise. The score in 60 to zero braking: Cobra, 122 ft.; Elise, 119 ft.

    That says something ... now still find a test comparing a Mustang Cobra with a SL55AMG :)
     
  10. AndreasN

    AndreasN

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    46
    i would be really surprised if it wasnt any faster then the mustang.
    its like comparing a Ferrari F2004 to a Minibus for gods sake :)
     
  11. PjotrStroganov

    PjotrStroganov

    Messages:
    283
    I meant the Scania with two axels.:D

    I have noticed that when I fully press the brakes with the elise, they still don't lock up. With the merc and beamer this does happen. This indeed is an indication of less braking power of the elise. Combine the great breaking power of the merc with fat tyres and it may be possible that it has a shorter braking distance.
     
  12. GTXLR

    GTXLR

    Messages:
    1,391
    I was wromg in my previous post it has eight pot electronic braking system.

    All in all the SL55AMG is in the supercar league, youd expect it to have decent brakes.

    The boffins at Affalterbach have also had a hand in the SL55’s braking system, the AMG technology incorporating perforated, internally ventilated brake discs with eight-piston fixed callipers at the front and four-piston affairs at the back, all painted silver with a natty AMG logo. Sensotronic Brake Control is a world first for the Sl, featuring a true ‘brake by wire’ system.The brake pedal is connected to the master cylinder electrically, rendering the traditional vacuum-powered brake booster redundant. The braking feel is replicated by a simulator that using spring pressure and hydraulics. At 70mph, SBC reduces braking distances by 3% in the dry, whilst in the wet it will imperceptibly allow the brakes to skim the discs, drying the rotors and improving the wet weather performance
     
  13. Buggy Boy

    Buggy Boy

    Messages:
    660
    I've been searching for data on the braking distance of the cars I measured above : most of the time nothing is given, but I found for the Elise :

    60 to 0 mph : 133 ft, which is in fact not that good :odd: and in contradiction to their other article I referred to above, but that was about an Elise with oversized rubbers I see now :eek:

    http://www.sportcompactcarweb.com/features/0106scc_lotus/

    If someone would find more, please post, perhaps GT4-P is really realistic :) I hope so!
     
  14. PjotrStroganov

    PjotrStroganov

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    283
    It is indeed strange that braking distances are very hard to find. As if manufacturers don't want the public to know.
     
  15. Buggy Boy

    Buggy Boy

    Messages:
    660
    Yes, it seems almost so ...

    It's like the weight of a car, you really have to search for it ... constructors are allways talking about lighter materials and their cars become heavier all the time ...
     
  16. TooN

    TooN

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    9
    Hi ...
    Im new in here but I have been reading GTP forums since I play GT4:p ...
    I would like to add something about SL55 AMG ...
    The McLaren Mercedes is the upgraded version of SL55 AMG it is also around 2000kg but I think it has the same ( or very simillar ) brakes ( it uses 12 callipers brake system ) ... It brakes from 120 mph ( 200 km/h ) in less than 240 ft ( which i think is good for a 2ton car ). I saw it in Top Gear ( episode 2004.05.16 ) and it really looks unbelivealbe ...
    ps. sorry for my english though its not my main language
     
  17. vat_man

    vat_man Staff Emeritus

    Messages:
    9,428
    Braking's a difficult thing to measure - I mean, look at the disparity in performance figures you get from road test to road test.

    I don't think full-on braking is the best way to test here, either, since I've found that much like real braking (sans ABS) you can't just hammer the pedal, you need to brake just short of lock up to extract maximum braking performance.

    Interesting exercise, though. Might try it myself later.
     
  18. AndreasN

    AndreasN

    Messages:
    46
    we could use a standstall camera on a track.. (not sure which
    track would be best)

    accelerate the car up to a certain point where we know the camera are pointing, and brake.

    get the replay.. grab it.. and then do so with the cars.. and
    overlay them etc. :)
     
  19. dble07

    dble07

    Messages:
    11
    BB...

    I think you are over-simplifying the braking with just weight and tyre contact patch.... speaking of the laws of pyhsics..
    matter cannot be created or destroyed... the discs glow red because the energy of the moving vehicle is transformed into tremondous heat under heavy braking... the point being the discs glow not the tyres.. the friction between road and tyre is low..
    thats why stopping distances are greatly increased when you lock the wheels... there is no more friction between pad and disc (coz it has stopped!) and you are relying on the friction between
    road and tyre.

    The AMG MB has HUGE disc/pad area ratio and thats what counts... combined with VEEERY clever electronics to ensure max braking!!

    BTW the GT40 (whoops.. GT!) has great brakes... try racing at FUJI
    .. 5 laps (pro) against the GT1 cars... great fun.

    regards
     
  20. Buggy Boy

    Buggy Boy

    Messages:
    660
    Hi vat-man, I hope you do the exercise yourself and give your comments.

    However, as far as I know, it still is impossible (and that's a shame) to lock your brakes in GT4-P. So there's no need to brake short of locking.
     
  21. Buggy Boy

    Buggy Boy

    Messages:
    660
    Hi dble07,

    You're making it too difficult :) Stopping distances are higher when you lock the wheels, I guess that's what you meant and it's correct. This is a typical property of a tyre, the most of the braking force can be transferred to the road just before locking. It's hard to explain, if you want I can try to scan and attach a graph that shows this.

    (This is similar as the sidewards force, where a max side force can be transferred just before sliding)

    The quality of a good braking system is in allowing a max friction on all 4 wheels, without locking. Because if the disc is locked, the wheel will be locked too, and in that condition it provides less braking power.
     
  22. PjotrStroganov

    PjotrStroganov

    Messages:
    283
    Braking has a more sophistocated feel too it, but indeed, locking up your tires is very hard indeed. The sound of the tires suggest you can lock up, and there is an amount of understeer, but you still can control the car when "locking up" your brakes.

    I guess we must conclude that this must be seen as an improvement to gt3, but to keep everyone happy some consessions have to be made to realistic controls. I think yamauchi wants gamers to feel like they really can control the car as a racing driver. This wouldn't be possible when gt4p had real simcontrols. Then, this game would only attrackt sim enthousiasts. He wants to make it accesible for everyone.
     
  23. Buggy Boy

    Buggy Boy

    Messages:
    660
    I see you're also firmly addicted to this forum? ;) Imo a good solution was to make this :irked: brake assistance unselectable.
     
  24. dble07

    dble07

    Messages:
    11
    yes... stopping distance IS increased when locking ( I have corrected that) and yes... max grip between road and tyre in any direction (lateral or otherwise) is at the point just before slippage,
    hence the pad and disc are doing most of the work.... so size of disc and pad area (actually swept area) is more important....
     
  25. Buggy Boy

    Buggy Boy

    Messages:
    660
    The pad and the disc are most effective if they lock, but then the tyre isn't effective any more. So the art is not the make a disc-pad combination that is powerfull (in that case an old brake drum would be a good solution), but a combination that can transfer max force without locking and during a long period.

    All the stopping force however to reduce the speed of the car, has to be generated between the tyre and the road.

    That's why stopping distance is longer on a wet road and even more on ice ...
     
  26. dble07

    dble07

    Messages:
    11
    I am not disagreeing with what you are saying about the tyres.... just that you are still over simplifying things...

    .. on a heavy car.. we have 13inch and not 6 inch discs and 6 piston calipers and not one piston to help the car slow down... then you have the whole suspension system and chassis dynamics to transfer all this stopping to the tyres...

    ... to say that it is all between tyre and road is just to simple
    for any kind of analysis....

    BTW... nothing wrong with a drum brake... they work just as well, except they retain heat..
     
  27. AndreasN

    AndreasN

    Messages:
    46
    I dont think the numbers of callipers have so much todo with it.

    There are sportscars with 1-2callipers. but its how good they
    work that counts.

    and you dont really want wheight transfer under braking?
    cause then the frontwheels have to take all braking by itself,
    where on the MB SLR, you get a rearwing up, to get the
    rearend down, and it brakes amazingly good (as stated earlier)
     
  28. Rapidone

    Rapidone

    Messages:
    75
    http://uk.cars.yahoo.com/newcars/lotus/elise/323087a.html

    http://autos.yahoo.com/newcars/merc...amgroadster_2005/15566/style_specs.html?p=all

    Elise tyre width 185/205

    SL55 tyre width 255

    The SL55 has wider tyres that are roughly 30% wider than the elise.

    http://www.suninternational-usa.com/pr_els04.html

    http://www.engine-power.com/mercedes-benz/sl55_amg.html

    Elise weight distribution 38% on the front.
    SL55 near 50% on front.

    SL55 has more weight on the front wheel which is beter for stopping.

    This may explain some of the difference, but still the mercedes is more than twice the weight. It still doesn't make much sence.
     
  29. Rapidone

    Rapidone

    Messages:
    75
    No, I'm not still with you. Why is that the case?

    Having thought about this problem a little more, it seems obvious that the mass of a vehicle has little effect on the braking distances. Assuming that the breaks are able to apply enough stopping power to make the wheels almost lock, and cars are designed for this proviso to be true.

    The only reason a heavier vehicle will have a slightly longer stopping distance is because wind resistance slows a lighter car more than a heavier one. For the same reason two objects of equal shape and size but different weights will have different terminal velocities.

    It's the size of tyres that has the biggest effect on stopping distances and the ability of the chassy and suspension to keep the tyres on the ground.
     
  30. Buggy Boy

    Buggy Boy

    Messages:
    660
    Hi Rapidone,


    You sound like an engineer :) are you?



    You're right, this explains some, perhaps even much of the difference.



    I agree with this too, probably the SL55AMG is better in this domain too, what could explain the rest of the difference.
    ... however, the Elise really brakes badly compared to all other cars, and I don't think all other cars beat the Elise's tyre width, frame and suspension ...



    You probably want to say that if two cars have the same aerodynamic drag, the heavier one will be slowed down less due to its inertia (= mass x speed) ;)



    I must admit that I'm not for 100% sure any more that this principle is valid for longitudinal forces, but :
    you can draw a graph for a tyre, that gives, at a given speed, the Max sideward force in function of the weight on the tyre. The value of that Max sideward force increases as the weight of the car increases, but not as fast as the weight.
    In other words : the increase in sideward force that can be exercised by the tyre, is not linear with the weight of the car.

    It sounds logical that this is valid for longitudinal (braking and accelerating) force too, but I find no graphs that prove it.