Is our suspension setup correctly by aftermarket strut MFR's? Is the bias correct?

[wingnut]

Hmmmm...mitsu evo?

[Nihil]

Hey, Jeremy, you ever figure this out? Or anyone else? This was an interesting read, been subscribed, never posted until now, since it's been awhile with no updates, and I've been researching this stuff since coilovers are on my list of next buys when I have the money

[J. Fast]

I measured the motion ratio for all 3 of my vehicles. The race car, sandstone, and my street car. The motion ratio at the rear is identical for all of them. I confirmed it to be 1.00. For every one inch of wheel travel each corner articulates one inch.

These are my confirmed calculations.

REAR SUSPENSION:

1.5" rideheight = 8" perch to perch gap
2.5" rideheight = 9" perch to perch gap
3.5" rideheight = 10" perch to perch gap
4.5" rideheight = 11" perch to perch gap.

I disconnected the sway bar and removed the strut springs and fully unloaded the suspension. I then reinstalled the shocks by themselves and the wheels and measured. The above are my results. I have pictures, I will post them if I have time (hopefully this afternoon).

[J. Fast]

I determined the spring rates for the front and rear of the vehicle should be the same if you are running an oem rear wing or larger. If the front springs are heavier than the rears then the suspension is likely set up incorrectly and you're doing it wrong. Also, if you're lifting a tire on roadcoarse you have too much spring and your scrubbing speed. I spoke with Rhys Millen about his lifting a tire at pikes peak because his suspension was setup for drifting and was too stiff. His crew chief determined they scrubbed about 0.20 per corner from loss in wheel contact.

Its manageable to have the suspension setup to stiff, but you have to wait for the suspension to settle. While you're waiting you're losing time.

[J. Fast]

Here's the photodocumented real world results of the Motion Ratio for the rear end... it is a true 1:1

1/2" Ride Height





1.5" Ride height





2.5" Ride Height





3.5" Ride Height

[J. Fast]

According to the wind tunnel testing that was conducted by the Russians there's a hundred twenty pounds of lift on each corner in the front and approximately 150 pounds down force at each corner at the rear when Active Aero is engaged.
I'm seeing corner weighed setups with 950 lbs at the fronts and 700 lbs at the rears. When you add aerodynamics into the equation the wheel rates for all the corners are equal therefore it would appear that all the aftermarket suspension options available for VR4's are set up incorrectly unless the spring rates in the front and rear are equal. It's looking like 10k front and rear its a good starting point. If you have a GTC 300 wing or bigger add a couple hundred pounds to the rear Springs. That's just my. 02

[Nihil]

Awesome! Great solid, confirmed information! Looks like the Ksport Version RR #CMT191-RR are setup even at 14k/14k and that's the only one out of the box I could find with a proper starting point.

Having this information now, it'll be interesting to see some testing done from those who have coilovers installed, to play with different spring rate setups.

It's looking like 10k front and rear its a good starting point.

When you say good starting point, what is this a good usage starting point for? Road course? Auto cross? or?

Thanks for the research on this Jeremy!

[sergechronos]

	Spring Rate
kg/mm	3	4	5	6	7	8	9	10	12	14	16	18	20	22	24	26	28
lb/in	168	225	281	337	393	450	506	564	674	787	899	1012	1124	1232	1344	1456	1568

Let's see here, assuming proper corner balancing and a speed of 70mph, Known Front Motion Ratio of 1:0.98, Rear Motion ratio of 1:0.84 @ 2" drop and MR of 1:0.86 at stock ride height. Estimated 600 lbs rake/frontal downforce and 500lb downforce in rear.

1. Stock 3/S Ride Freq of 1.60Hz corners weights of 1270lb fronts, 720lb rears
2. Stock 3/S Ride Freq of 1.75Hz w/1.25" drop, corner weights of 1270 fronts, 720lb rears
3. Modified 3/S Ride Freq of 2.05Hz w/1.5" drop, corner weights of 1000lb fronts, 650lb rears
4. Because Spec Racecar 3/S w/ Ride Freq of 2.2Hz w/2" drop, corner weights of 965lb fronts, 585 rears

Wheel Rate = ((60(Hz))/(187.8))^2 x (corner weight)

1. Wheel Rate:

• FRONT ((60(1.6))/(187.8))^2 x 1270= 332lb
• REAR ((60(1.87))/(187.8))^2 x 720= 257lb

2. Wheel Rate:

• FRONT ((60(1.75))/(187.8))^2 x 1270= 397lb
• REAR ((60(2.02))/(187.8))^2 x 720= 300lb

3. Wheel Rate:

• FRONT ((60(2.05))/(187.8))^2 x 1000= 429lb
• REAR ((60(2.32))/(187.8))^2 x 660= 363lb

4. Wheel Rate:

• FRONT ((60(2.2))/(187.8))^2 x 965= 475lb With Aero: FRONT ((60(2.2))/(187.8))^2 x 1265= 625lb
• REAR ((60(2.47))/(187.8))^2 x 585= 364lb With Aero: REAR ((60(2.47))/(187.8))^2 x 835= 519lb

Spring Rate = (Wheel Rate) / (Motion Ratio)^2

1. Spring Rate:

• FRONT (332)/(.98)^2= 346lb
• REAR (257)/(.86)^2= 347lb

2. Spring Rate:

• FRONT (397)/(.98)^2= 413lb
• REAR (300)/(.86)^2= 405lb

3. Spring Rate:

• FRONT (429)/(.98)^2= 437lb
• REAR (363)/(.84)^2= 514lb

4. Spring Rate:

• FRONT (475)/(.98)^2= 494lb With Aero: FRONT (625)/(.98)^2= 651lb
• REAR (364)/(.84)^2= 515lb With Aero: REAR (519)/(.82)^2= 735lb

According to the ref table above it's looking like beacuse racecar wants... 11K fronts and 13K rears.

I'd say GT Worx and Meullerized are about spot on with the bias.

That's enough for today.

Forgive me if I'm wrong (especially in light of doing this during a bout of insomnia), but it would seem then that this entire table would now be wrong then since we have a known rear MR of 1:1 wouldn't it? Different MR modifies at the very least the spring rate, giving very different rates than previously obtained. Possibly wheel rate as well. Quick and dirty math following #2 in the table, assuming AA as well, would give ~519 front and ~404 rear with a 1:1 rear MR. That would give spring rates of approx 9k front and around 7k rear, which we determined at the very beginning of this would be very wrong. Again, just based on following the table and plugging in updated rear MR info, and adjusting weights for AA.

If this is right (which I doubt), perhaps just edit the post to indicate that the information will need to be altered and get back to it later. Has me thinking further than without proper corner weighting, what the typical street 3/S should see would probably be around 8k all around, maybe 9k driver side front since we don't have the balance of being RHD. Hard to brainificate right now, but I think 10k is probably on the higher side for a full weight car.

Lot of variables for folks to consider though. Would be nice to get a stock (or mostly stock) car on a K&C machine, then take it back with these coil over set ups and see what the difference is. Information wouldn't be too useful for most of your hardcore racers out there, but would apply to a much larger percentage of the community.

[Erron Spalsbury]

I determined the spring rates for the front and rear of the vehicle should be the same if you are running an oem rear wing or larger. If the front springs are heavier than the rears then the suspension is likely set up incorrectly and you're doing it wrong. Also, if you're lifting a tire on roadcoarse you have too much spring and your scrubbing speed. I spoke with Rhys Millen about his lifting a tire at pikes peak because his suspension was setup for drifting and was too stiff. His crew chief determined they scrubbed about 0.20 per corner from loss in wheel contact.

Its manageable to have the suspension setup to stiff, but you have to wait for the suspension to settle. While you're waiting you're losing time.

Too little of a spring and you'll lift a tire. I think Rhys was messing with you as it's clearly the other way around.

[J. Fast]

Too little of a spring and you'll lift a tire. I think Rhys was messing with you as it's clearly the other way around.

Kinda, but not really seeing the need for 20k springs on a 3S... if springs are properly selected and we're lifting tires? That's a sway bar issue and possibly a weight transfer issue. In the event of weight transfer we can adjust the weight distribution by changing the corner weight bias. IE change the rideheight on the corners till they cancel another out. Additionally, we use sway bars and geometry adjustments to keep all the tires planted. I seriously doubt we have a roll stiffness issue that warrants 20k springs on the corners and a 1/2" of suspension travel. More sway and less spring combined with proper bump steer keeps the tires down while maintaining ideal compliance.