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Rank: A-Class Racing License
#26 Posted : Tuesday, July 22, 2014 11:52:03 AM(UTC)
Originally Posted by: JimB3 Go to Quoted Post

For a car weighing 2500 lbs. with a weight distribution of 60% front and 40% rear and using t = 1.25, I get the following values
Front spring = 592.2
Rear spring = 394.8


Personally I find these numbers VERY HIGH which will require use of VERY LOW bump. The car will be responsive and tight but lose grip at bumpy surfaces and stay airborne longer at Nordschleife (I'm guessing). The effect of stiff springs and low bump is that the dampers are basically simulating the FAST bumps only (riding curbs) then using stiff springs (with virtually no damping) for cornering. High rebound would be essential to off-set/stabilize the low bumps. I believe this set-up is a popular hot lapping set-up; good for flat tracks.

My personal preference is softer springs (which allows fast compliance to bumps) combined with mid range bump and rebound (instead of low/high ends of the scale). This produces all purpose car that can be driven on any track but not necessarily the fastest.

My Miata is about 2500 lbs and I use 330 & 300 lb/in. In fact, FatCat Motorsports with extensive real life track experience uses spring rates in this range. Stock springs in real life, I recall, was about half that and corners on bump rubbers (what I remember reading, NOT my first hand experiences).

If wings are used, then high spring rates may give enough grip. If wings are NOT used, 600/400 lb/in for a 2500 lb RWD WILL result in a slippery ride.

Edited by user Tuesday, July 22, 2014 11:59:16 AM(UTC)  | Reason: Not specified

"Racing is life. Anything before or after . . . is just waiting." Steve McQueen, LeMans '71
Rank: B-Class Racing License
#27 Posted : Tuesday, July 22, 2014 6:44:19 PM(UTC)
GRD 4 3L,

You may be right and they may be high. I'm just beginning to figure out the spring adjustments. I was comparing the numbers to what the default settings are.

I adjusted the springs using the method GRD 4 3L mentioned earlier on a Mazda Miata on the Indy oval that I'm trying to learning tuning with. I ended up with the following settings.

Front spring: 466.5
Read spring: 448.5

I then used the equation provided and got the following settings

Front spring: 468.1
Rear spring: 449.8

These values are much lower than the default settings of 548.0 and 543.4 but are very near each other. I will go back later and try lowering the values again. I have been so used to the stiff springs that when it was under 400 the car didn't feel right. I may need to get used to the softer springs.
Rank: Racing Legend
#28 Posted : Tuesday, July 22, 2014 7:22:19 PM(UTC)
Originally Posted by: GRD 4 3L Go to Quoted Post
Originally Posted by: JimB3 Go to Quoted Post

For a car weighing 2500 lbs. with a weight distribution of 60% front and 40% rear and using t = 1.25, I get the following values
Front spring = 592.2
Rear spring = 394.8


Personally I find these numbers VERY HIGH which will require use of VERY LOW bump. The car will be responsive and tight but lose grip at bumpy surfaces and stay airborne longer at Nordschleife (I'm guessing). The effect of stiff springs and low bump is that the dampers are basically simulating the FAST bumps only (riding curbs) then using stiff springs (with virtually no damping) for cornering. High rebound would be essential to off-set/stabilize the low bumps. I believe this set-up is a popular hot lapping set-up; good for flat tracks.

My personal preference is softer springs (which allows fast compliance to bumps) combined with mid range bump and rebound (instead of low/high ends of the scale). This produces all purpose car that can be driven on any track but not necessarily the fastest.

My Miata is about 2500 lbs and I use 330 & 300 lb/in. In fact, FatCat Motorsports with extensive real life track experience uses spring rates in this range. Stock springs in real life, I recall, was about half that and corners on bump rubbers (what I remember reading, NOT my first hand experiences).

If wings are used, then high spring rates may give enough grip. If wings are NOT used, 600/400 lb/in for a 2500 lb RWD WILL result in a slippery ride.


I would be interested in other peoples views on what is high and low in relation to springs. On the one hand it is all relative to what we usually use I guess but GRD is using springs that add up to around half of the cars total weight (total of the 4 springs).

To me that sounds low scientifically and low based on what I have seen. My guess is that GRD likes soft springs but to him they are normal. I am not saying that as any way of criticism or right and wrong - just curious where everyone's ballpark is.

And yes I now that soft springs work on some cars and harder springs work better on other cars etc.

I blame the ants.
Rank: A-Class Racing License
#29 Posted : Wednesday, July 23, 2014 6:58:08 AM(UTC)
Originally Posted by: SatNiteEduardo Go to Quoted Post

I would be interested in other peoples views on what is high and low in relation to springs. On the one hand it is all relative to what we usually use I guess but GRD is using springs that add up to around half of the cars total weight (total of the 4 springs).

To me that sounds low scientifically and low based on what I have seen. My guess is that GRD likes soft springs but to him they are normal. I am not saying that as any way of criticism or right and wrong - just curious where everyone's ballpark is.


I appreciate all criticisms/feedbacks.

Scientifically speaking (or using napkin science), the transferred weight needs to be supported during braking, acceleration, and cornering. When the car is at rest, the spring compression can be considered at zero. During braking, front compresses and rear extends. During acceleration, front extends and rear compresses.

If any non-aero car has >50% weight transfer, one end of the car MUST lift. Therefore one can assume that the weight transfer is between 20~50%.

So during braking 50% (worst case) weight transfer for 2500 lb car is 1250 lbs or 625 lbs per wheel. Given wheel to spring motion ratio of 0.7 then the spring needs to support 625/0.7= approx 900 lbs of force. Assuming 2~3 inches of spring travel, the spring rate becomes 300~450 lb/in range.

My no-aero '94 Miata with 320/290 has Nordschleife time of 8:22.679, #104 on LB. I tried 430/300 last night and got 8:22.689 or virtually the same. The difference was that 430/330 did not have high speed understeer of 320/290.

This set-up suits my driving perfectly. To others it may not.

"Racing is life. Anything before or after . . . is just waiting." Steve McQueen, LeMans '71
Rank: B-Class Racing License
#30 Posted : Saturday, July 20, 2019 10:21:02 PM(UTC)
Originally Posted by: GRD 4 3L Go to Quoted Post
Originally Posted by: JimB3 Go to Quoted Post

For a car weighing 2500 lbs. with a weight distribution of 60% front and 40% rear and using t = 1.25, I get the following values
Front spring = 592.2
Rear spring = 394.8


Personally I find these numbers VERY HIGH which will require use of VERY LOW bump. The car will be responsive and tight but lose grip at bumpy surfaces and stay airborne longer at Nordschleife (I'm guessing). The effect of stiff springs and low bump is that the dampers are basically simulating the FAST bumps only (riding curbs) then using stiff springs (with virtually no damping) for cornering. High rebound would be essential to off-set/stabilize the low bumps. I believe this set-up is a popular hot lapping set-up; good for flat tracks.

My personal preference is softer springs (which allows fast compliance to bumps) combined with mid range bump and rebound (instead of low/high ends of the scale). This produces all purpose car that can be driven on any track but not necessarily the fastest.

My Miata is about 2500 lbs and I use 330 & 300 lb/in. In fact, FatCat Motorsports with extensive real life track experience uses spring rates in this range. Stock springs in real life, I recall, was about half that and corners on bump rubbers (what I remember reading, NOT my first hand experiences).

If wings are used, then high spring rates may give enough grip. If wings are NOT used, 600/400 lb/in for a 2500 lb RWD WILL result in a slippery ride.

Absolutely. 592/394 is 2.78hz, F/R. Slicks and moderate down-force territory.

It's been 8 months since you were last on the Forza forums. If you see this, try my ride frequency calculator(s).
https://docs.google.com/...MozkhJk/edit?usp=sharing
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