Motion Ratio?
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heel2toe (May 10, 2019)
May 28, 2019, 07:59 AM
#39
I know of at least one member here that had MCS doubles with their suggested spec that had less than an inch droop (it was way less IIRC) with the rear at about 25.5" ground/fender. MCS did change the body after we figured out that was a big source of his on throttle hopping (fixing helped a bunch), but I dont know if they charged him plus he had the downtime.
Feb 3, 2020, 05:33 AM
#40
i bring this topic up again because i might have not understand something correctly. The motion ratio is different from front to rear and we try to bring an equilibrium. However the weight differences are huge between front and rear. And Isn't this the reason why we put "stiffest" springs in front?
Feb 3, 2020, 06:59 AM
#41
Basically, yes.
The key numbers are:
Sprung mass: The weight of the vehicle on each corner, minus the weight of the wheels, brakes, and other parts that follow the road. Evo has more sprung mass in the front than the rear.
Wheel rate: The effective spring rate at the wheel, which is not equivalent to the rate of the spring itself. The wheel rate is determined by the spring rate and the motion ratio.
Natural frequency: A function of the sprung mass at a corner and the wheel rate at the corner. This is the number you should be targeting as a guideline. You'll see recommendations in the range of 2.0Hz to 2.5Hz for most types of racing, at least until you get into high-aero situations.
The typical suggestion is to start with a target natural frequency, then use the sprung mass at each corner to work backwards to a wheel rate, then use the motion ratio to work backward to a raw spring rate.
And don't forget that it's all a guideline. Some people find non-traditional springs rates to work for their situation. If you're starting from zero, it's best to target a natural frequency of 2.2Hz or less though.
The key numbers are:
Sprung mass: The weight of the vehicle on each corner, minus the weight of the wheels, brakes, and other parts that follow the road. Evo has more sprung mass in the front than the rear.
Wheel rate: The effective spring rate at the wheel, which is not equivalent to the rate of the spring itself. The wheel rate is determined by the spring rate and the motion ratio.
Natural frequency: A function of the sprung mass at a corner and the wheel rate at the corner. This is the number you should be targeting as a guideline. You'll see recommendations in the range of 2.0Hz to 2.5Hz for most types of racing, at least until you get into high-aero situations.
The typical suggestion is to start with a target natural frequency, then use the sprung mass at each corner to work backwards to a wheel rate, then use the motion ratio to work backward to a raw spring rate.
And don't forget that it's all a guideline. Some people find non-traditional springs rates to work for their situation. If you're starting from zero, it's best to target a natural frequency of 2.2Hz or less though.
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Nicolas (Feb 3, 2020)
Feb 3, 2020, 07:11 AM
#42
Yep, on any new car I would look at starting figuring out rates for would start with mid 2s hz front and about 10% higher rear. On things like the Evo or anything else with significant weight different on one end but equal tire size, that light end can tolerate more stiffness which adds grip to the other end (Effects of total weight transfer distribution). On cars with heavy aero, spring rates are less important for balance as it is for keeping the nose flast and there you'll see cars with opposite spring rates. If you're into hill climbs or rally, you may also see reversed rates where the car is stable and safe to push on throttle but can be "flicked" into transition/rotation or throttle rotated.
I prefer to work from what setup gets the maximum mechanical grip first, then work to fix stability via other methods (shock valving, aero balance, alignment, etc.)
I prefer to work from what setup gets the maximum mechanical grip first, then work to fix stability via other methods (shock valving, aero balance, alignment, etc.)
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kikiturbo (Feb 5, 2020)
Feb 5, 2020, 11:36 AM
#43
Evolved Member
i bring this topic up again because i might have not understand something correctly. The motion ratio is different from front to rear and we try to bring an equilibrium. However the weight differences are huge between front and rear. And Isn't this the reason why we put "stiffest" springs in front?
Feb 6, 2020, 02:27 PM
#45
EvoM Guru
iTrader: (1)
Originally Posted by Nicolas
Ok about the motion ratio. But what happens with the huge difference in the weight? Isn't it logical that stiffer holds more weight?
