Advanced Spring Rate Tuning

Hi All,

Suspension is a mysterious and eluding area in the tuning world, and being unable to physically experience proper car control in gt5 only furthers that metaphor. So in an attempt to relieve you of these troubles, I have developed a simple mathematical expression/formula to denote spring rate settings.

First of all, many people forget or simply fail to consider the car's engine/chassis layout, meaning their spring rates are off or outright wrong, meaning they'll find different (often wrong avenues) to compensate for their wrong set up; i.e. bad camber, toe or overly stiff anti roll bars. The immediate problem on gt5's tuning interface is its lack of relation of one component to another, meaning the spring rates literally give you no indication of its stiffness relative to the car or be it ride height.

As I have mentioned above, a car's layout is crucial in determining spring stiffness. Tuning guides will tell you that a softer front paired to a stiffer rear will result in oversteer or vice versa, but they never mention that *the front spring rate doesn't necessarily have to be softer than the rear*. To determine whether a spring rate is 'soft' of 'stiff' we must consider the following;

Weight distribution (front - rear) and;
curb weight

Take the following example;

Make: Honda NSX Type R '02
Curb Weight/Mass: 1051 KG
Weight Distribution: 40% / 60% (found this on some thread, I'm not entirely sure of its validity)
Axle Load: 420.4KG / 630.6KG
Wheel Load: 210.2KG / 315.3KG
Spring Rate: 8.8KGF/mm / 13.2 KGF/mm

Front Sprung Height:
210.2Kg / 8.8KgF/mm = -23.9mm

Rear Sprung Height:
315.3Kg / 13.2KgF/mm = -23.9mm

As demonstrated, the spring rates are quite distant, but the overall sprung height is exactly the same, meaning this is a BALANCED set up. though it may not feel balanced in practice it is very sound mathematically. by way of stiffness/softness, this is a considerably hard set up. to figure what constitutes soft and hard, one will have to take the minimum value of spring rate and subtract that to the ride height - I will try cover that in another post.

So please remember to ALWAYS consider the curb mass/weight and also the weight distribution.

A major flaw is that gt5 doesn't record the transfer of weight from axle to axle or wheel to wheel, meaning a lot of dynamic tuning will have to be done via estimates, but I'll write another thread concerning spring rates and bound rates another time!

I hope you guys enjoyed this thread and have a blast tuning your car!

Appreciate the effort, but please try to capitalize your sentences and "I's". (you can edit the post long after posting it) Otherwise, very well written 👍 , though I believe some may have a different opinion as to how to approach spring rate tuning.

What about this?

http://www.nsxprime.com/FAQ/Performance/suspension.htm

Shows that apparently NSX-R and S Zero had stiffer front springs than rear. Also, NSX racing suspension kits commonly have stiffer front springs than rear despite the weight balance being firmly towards the rear. Street kits on the other hand will have stiffer rear and softer front.

Some 32-34 GTR track suspension also has stiffer rear rates despite the front being heavier.

For most street cars, the rates reflect the weight distribution for comfort/balance reasons. For race, many other factors come into play!

Yes i understand the specifications of different uses, but I'm using this as a general expression to link stiffness to mass and weight distribution, so new tuners can actually understand how they are affecting the car's balance and weight transfer.

Thank you for your input though, much appreciated.

I shall mention other factors in another post.

Cheers

Fusion

What about this?

http://www.nsxprime.com/FAQ/Performance/suspension.htm

Shows that apparently NSX-R and S Zero had stiffer front springs than rear. Also, NSX racing suspension kits commonly have stiffer front springs than rear despite the weight balance being firmly towards the rear. Street kits on the other hand will have stiffer rear and softer front.

Some 32-34 GTR track suspension also has stiffer rear rates despite the front being heavier.

For most street cars, the rates reflect the weight distribution for comfort/balance reasons. For race, many other factors come into play!

Click to expand...

the OP isnt saying that this is what all spring rates should be and anything else is wrong. you can obviously tune stiffer or softer for X application. hes merely giving us a place to start, mathematically-wise. greatly appreciated.

konkong

Tuning guides will tell you that a softer front paired to a stiffer rear will result in oversteer or vice versa, but they never mention that *the front spring rate doesn't necessarily have to be softer than the rear*.

Click to expand...

Hate to disagree with you, but stating that no tuning guide ever tells you this is simply inaccurate.

Mine have been telling people this since GT4...

When setting spring rates one of the first considerations that needs to be made is the weight of the car itself, as what would be considered a ‘soft’ spring on a 2,000kilo car would feel very ‘hard’ when fitted to a 500kilo
car.

After this the front to rear weight distribution of the car should be accounted for, as the heaviest end of the car will require a stiffer setting than the lighter end of the car.

For example a car with 50% front and 50% rear weight distribution could run equal spring rates front and rear, but a car with 60% front and 40% rear may require a slightly stiffer front end setting.

Click to expand...

....and....

Once the initial setting for the car’s weight distribution and the track have been taken into account, the rates can then be used to trim under and oversteer. The guides below give an indication of the effect, however great care should be taken when changing spring rates.

To give an example of a potential problem, you may be tuning a front wheel driver car to reduce understeer. This can be done by making the front spring rate softer than it was; it does not mean that the front spring rate should be set softer than the rear.

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Yes I am being a little defensive here, but the OP made a rather bold statement without checking reference materials that available at the top of this very page.


The OP's work is a fine starting point, be be sure not to make sweeping statements like this without being sure.


Scaff

The OP is spot on about tuning springs based on weight distribution. Where's he wrong is in not understanding that GT seems to somehow take into account the motion ratio of the suspension links, which affects how spring stiffness translates into actual suspension stiffness. The MKIV Supra is evidence of this as the rear spring rate is way higher (roughly double, IIRC) than the front, just as in real life. Since GT doesn't share either the motion ratios or weight distribution with us we're basically flying blind when tuning spring rates. However, it does give us a little hint with the spring rate adjustment range. Take for instance a car with a spring rate range of 4.0 - 10.0 in front and 5.0 - 14.0 in rear. What is GT telling us? That the rear rate should be higher in the rear than in the front. So what I do is pick spring rates based on a percentage of the adjustment range. If I want a slightly soft spring to soak up bumps on the Nur, I may pick 1/3 of the adjustment range which would work like this:

Front:

10.0 - 4.0 = 6.0
6.0 * 1/3 = 2.0
2.0 + 4.0 = 6.0

Rear:

14.0 - 5.0 = 9.0
9.0 * 1/3 = 3.0.
3.0 + 5.0 = 8.0


So far I've been pretty happy with the results and it's eliminated a lot of trial-and-error.

I don't know too much about car springs, but I think I know enough about the physics of springs in general to know that the OP is dividing a Mass by a Force per unit length and getting a unit length. That does not compute to me...


Kgf/mm = 9.81 N/mm = 9.81 kg*m/(s^2*mm).

If you divide Kg by that you just get s^2/(m*mm).


You would also have to multiply by the force of gravity to get the number you actually want.
Even then, that number doesn't make much sense outside of telling you how much the spring compresses due to the weight of the car.

This is a great post! I'd really like to try this method on one of my cars. The Subaru 22B completely stock weighs 1270kg. In GT5 after weight reduction you can get the weight down to 1056kg while tuned to 550 hp.


More specs-
Wheelbase 2520 mm
Track front 1480 mm
rear 1500 mm
Length 4365 mm
Width 1770 mm
Height 1170 mm
Length:wheelbase ratio 1.73
Ground clearance 140 mm
curb weight 1270 kg

stock engine specs-

Maximum power 279.8 PS (276 bhp) (205.8 kW)
@ 6000 rpm
Specific output 124.8 bhp/litre
2.04 bhp/cu in
Maximum torque 363.0 Nm (268 ft·lb) (37 kgm)
@ 3200 rpm
bmep 2062.2 kPa (299.1 psi)
Specific torque 164.1 Nm/litre

I can not seem to find specific weight distribution.

Is it possible to for your calculation to work with the information above?


Thanks much.

The spring rate calculator I created in my iPhone app (link below) follows the general guidelines of this thread... that springs should be set in relation to the amount of weight over a specific axle, and then tweaked for fine tuning of under/oversteer...

Regarding the Subie's weight distribution, I couldn't find it on google but if I recall correctly Imprezas have been 50/50 in the past two generations. I might go with 55/45 (front/rear) assumption, but it really comes down to how the car handles for you. If it understeers, assume it's 50/50 and adjust your spring rates appropriately.

Cheers

konkong

First of all, many people forget or simply fail to consider the car's engine/chassis layout, meaning their spring rates are off or outright wrong, meaning they'll find different (often wrong avenues) to compensate for their wrong set up; i.e. bad camber, toe or overly stiff anti roll bars.

Click to expand...

I'd like to echo that sentiment.

I'm really hesitant to say that some setups are ideal while they're using severe camber and toe adjustments. I think proper weight shifting should make those sorts of dramatic settings irrelevant.

Right. The best cars in the world require the absolute minimum tuning to feel great. This is why proper engineering is so important (and rare). The Ferrari 458 Italia is one example.

konkong

Yes i understand the specifications of different uses, but I'm using this as a general expression to link stiffness to mass and weight distribution, so new tuners can actually understand how they are affecting the car's balance and weight transfer.

Thank you for your input though, much appreciated.

I shall mention other factors in another post.

Cheers

Click to expand...

Where is that other post? Need it because what you're saying makes sense.

FishHunters

Where is that other post? Need it because what you're saying makes sense.

Click to expand...

Given that the member you quoted has not been on the site since 2010 I would not hold your breath for a reply.

Scaff

Given that the member you quoted has not been on the site since 2010 I would not hold your breath for a reply.

Click to expand...

Funny!

I know the thread is ancient but there was something mentioned that piqued my interest and since its already been bumped up from 2010 I may as well ask in here now

My philosphy has always been to use weight distribution to set my spring stiffness (mainly because I use roll bars are for balance and a few other reasons). However there is now a spanner in the works in the form of motion ratio. I had no idea GT modelled different motions ratios from front to rear.

Has anyone got any experience to shine on what cars this is an issue for? I really hope the inclusion of a 7 post shaker that has been promised becomes a reality - one of GT's biggest weaknesses compared to other racers is it's subpar telemetry.