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Mazda RX-7 FD

Mazda RX-7  FDMazda RX-7  FD

Производитель - Mazda
Модель - RX-7
Тип кузова - Купе
Длина - 4280 мм
Ширина - 1760 мм
Высота - 1230 мм
Передняя подвеска - сдвоенные поперечные рычаги, поперечный стабилизатор
Задняя подвеска - продольные и поперечные рычаги, поперечный стабилизатор, винтовые пружины,амортизаторы
Передние тормоза - дисковые вентилируемые
Задние тормоза - дисковые вентилируемые
Тип привода - задний
Мощность двигателя - 265 л/с
Максимальная скорость - 250 км/ч
Разгон до 100 км/ч - 5 с
Масса(снаряженная) - 1250 кг
Масса(с полной нагрузкой) - 1490 кг
Колея задняя - 1460 мм
Колея передняя - 1460 мм
Колесная база - 2425 мм
Объем бака - 76 л
Год начала выпуска - 1991
Год окончания выпуска - 1991
Количество дверей - 2
Количество мест - 2

Ok so brake efficiency is 100% when a delteclraeion of 1g is achived.That means that your brake and tyre combiation are expected to apply a braking force equal to the weight of your car. Or put another way, your car shoud stick to a vertical wall. if it is also pulled towards the wall by the same force. Does that seem reasonable?At that point the total force applied by the road surface to your tyres is 1.4 times the car weight, directed at an angle of 45 degrees backwards (braking reaction force) and upwards (weight reaction). This force however is not evenly distrubuted as the point of balance shifts by an amount depending on it's height above the road. (Draw a line from the GG alonf the force vector, that's the 45 degree line for 1g. Where it hits the road that's your point of blance. If that get's in front of the front wheels the car will somersault.)In any case it affects the stability of the vehicle. The car will lose accurare steering long before is somersaults. Low slung sports cars ar more stable, and can remain stable for much higher braking forces. A vehicle with a much higher CG will not. An SUV for example will be much less controllable under heavy braking.The maximum braking force your vehicle can apply is limited by that stability factor.In formula 1, where speeds in excess of 100mph are normal, there is considerable aerodymamic downforce which increases the stability enourmoulsy. The angle of the braking vector is much steeper. Closer to the vertical. So stability is maintained at high speeds.However, reduce the speed and the downforce is also reduced. So a F1 car is less stable under braking at lower speeds.Also the downforce increases the maximum horizontal force a tyre can cope with before it loses hold. Tyres are not resisted by simple friction, as that is a dynamic force. Ie one resulting from the movement of one surface against another. Tyre grip is static friction, that's different. That's a maximum limit.Static friction is the result of the surfaces interlocking by their bumps and irregularities. Both surfaces ust be rough and at about the same scale to maximize this. For an ideal think of meshed gears! In practice, if one surface is rough and the other is not (and is hard) then it will be close to a minimum.Rubber is a good material to use when you cannot predict actual surface roughness, and cannot arrange a perfectly syncronised mesh. It conforms to the surface under pressure. The more pressure the better the conformance. Hence soft compounds use in F1 stick better, but are less mechanically strong. When they really lose grip the rubber becomes a lubricant!Some things to note.First understeer/oversteer/drift are not caused by the tyres sliding. It is cused by creep'. Tyres are flexible. They deform. Apply a side force, and the part of the tyre just about to hit the road is a little off to one side. Also the more forward force is applied (ie from a driveshaft) then the tyre deforms circumferantially. Effectively the back of the tyre is stretched compared with the front. (This is why steel belts are necesary to help distribute the force reducing the effect.) The net effect increases creep, which is why rear wheel drive tends to oversteer. Both driving forces and steering forces combine to increase creep compares with the front wheels.Second, rubber bounces. Or at least most do. At room temperature. It changes with temperature. When the front of your tyre hits the road surface you do not want it to bounce. That would reduce the tread area and grip. Rubbers are availblae which hardly bounce at all, but they also waste energy, which means more petrol, and absorb power. Not good for racing, and not really good for fuel economy in domestic cars either. Other rubbers bounce a lot. So it's possible to make a compromise.But this changes considerably with temperature.The non bouncy rubber is very bouncy at 100 centigrade, and the bouncy rubber loses it's bounce at higher temeratures. So you would think it's possible to make a perfect balance, but not so. Firts the bounce curves don't match, but more importantly they have other properties which are different, two important ones are tack, and tear strength. Tack is a measure of how sticky' the rubber is, tear strength relates to wear. YOu want both to be high. Unfortunately they rubber with both these properties in aces is the one which is not bouncy at room temperature.In F1 to get grip they use a lot more of the bouncy rubber wich is not so bouncy at high temeratures. These run at much higher temepratures than ordinary car tyres. This is what they want as it maximises grip, by minimising traead bounce. They can afford to lose a little power, which is no god if the tyre is not gripping anyway. On the downside this is the rubber which wears a lot more. One reason why F1 tyres wear so quickly. It's not just the sheer hammering they get.This leaves you with the tyres on your car which have to grip at lower temperatures, and operate efficiently without the benefit of a ton of added downforce, last a long time, and not waste too much petrol. Depending on how you set your priorities.The setting of stopping disctances is based on an economy tyre running on a cheap domestic car without ABS or other shenannigins. On the basis of this the actual stopping distances are barely adequate. Especially under less than ideal conditions.It is true that a car fitted with ABS, with a low CG, and a competent driver will under test conditions pull up in less than this distance, but that is not a typical situation. The Ford Anglia will only just pull-up safely under ideal conditions with an expert driver behind the wheel who is expecting the emergency stop. Most people could not manage that after a week of tutoring, certainly not anyone used to a modern sports-car.The imprtant factor is control. The distances set are mimimum safe stopping distances, not just the stopping distance. They take into account the ability and reactions of real drivers, in real cars. That includes granny in her old Ford Anglia.If you find you can comfortably stop your car using your tyres in much less than that distance on an ordinarly road surface than great. You have a good margin for safety, but the bloke behind you may not be simialrly equiped, and it's no good arguing about tailgating after the event, the insurance claim will still leave you out of pocket!So it's not a matter of whether your car will do it, or if your reaction times are better. (In fact studies have shown that racing drivers reaction times are at best marginally better than the average. The big difference is anticipation. They read the road better, and besides have had plenty of practice laps!) It's to do with a safe minumum so that granny has plenty of time to stop, in controll of the car, and not for instance stuff it into the traffic lights.In any case, consider this.Traffic lights are set for a 3 second amber phase for 40mph but could be as short as 2 seconds. At 40mph with 100% brake efficiency and allowing 0.65 seconds reaction time, you can stop in 2.5 seconds. This gives a stopping distance of 36m which is just shy of the official figure. So half a second margin right.With the minumum brake efficiency allowed by law of 50% stopping time is 3.8 seconds, and you've jumped the light despite braking as hard as is safe in that car. Tell that to the judge!That's of course assuming that you are not momentarily distracted. I for one prefer to monitor the traffic, and look out for pedestriand when approaching lights. On more than one occassion I have had people step out in front without warning. Haven't hit one yet.Given that at 40mph it will take 2 seconds to reach the light if you are the official safe' stopping distance from the light should you carry on to avoid the possibilty of a fine? I would say not, but then I would not like to have to make an unnecesary and possibly unsafe emergency stop either (Which can also be an offence!) in order to slavishly pull up behind a light that might just flick red just before I cross the line!Sooner or later it seems we will all get caught on a red-light camera unless we all make sure that we have brakes of at least 100% efficiency (and who knows without having the brakes tested?) watch the lights to the exclusion of all else as we approach the braking limit, and are prepared of course to risk a possible shunt in order to stop behind the line. (I know that you are allowed to cross the line in order to avoid an accident, but if you are watching the light, not the daft git behind you )Stopping distances, fine the less I have to break hard the happier I am, I'm ok with that. The bloke in front may not agree but then I'm not sitting on his tailpipe so what do I care. It's those darn traffic lights that assume that I can and will mak an emergeny stop every time I see amber that bother me. I would rather a longer amber phase to allow for the minumm allowable braking efficiency, and time to scan the road properly on approach than the current timings which may not be possibe.In fact I would like to see much fewer traffic lights in the first place. Many don't do the job they are supposed to, but that's another story for another day.

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