Spring rates please educate me

Springs are not springs .. in that manufacturers measure different ways, they are wound differently, different materials, some are progressive, some straight rate, compression and rebound rates are different, so comparing different manufactures springs is not always .....well... comparable ....

Then there is the black art voodoo of actually picking spring rates ... which for proper performance goes well beyond vehicle weight and its relative relation to wheel position which gets real confusing when dealing with an odd number of contact points ....

Which is why it is best to use a company who has done actual field testing on the vehicle the shock/spring combination will be used on in the environment (track, street, etc) it is intended to be used ..... the combinations that work from manufacturer to manufacturer can be very different if only raw rate numbers are used ....

How is that for an answer .....

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Okay, "spring rate" really comes down to two things: spring constant, and resonance rate.

Spring constant is commonly referred to as spring "strength". How much force does it take to compress (or stretch) a spring a certain distance. The metric unit is Newtons per meter (N/m), the imperial equivalent is pounds per foot (Lb/ft).

The stronger the spring, the stiffer it is. Road contact improves, ride gets harsher. The time it takes to rebound from any given shock is shorter, spring travel for any given shock will be less.

Resonance rate is a spring's "period" - the amount of time it takes to compress fully, bounce out to full extension, and return to the original position. Think of a pendulum: shove to the right; it goes a distance rightward, swings back left as far as it will go, then returns to center. The time for one full cycle like this is a spring's period.

Spring period is affected by two things: spring constant, and load (the weight attached to the spring.) Strengthen the spring (higher spring constant) and the period gets shorter. Increase load and period gets longer. You can't change load easily in a vehicle... well, I suppose you could get a really beefy copilot!

To change the period, we select stronger or weaker Springs. Weaker springs give us a softer ride. The longer period means you need less force to soak up bumps... oooh! Cushy! But the long periods mean tires out of road contact for many milliseconds, less responsive rides.

Stiffer springs go the other way. Shorter periods, higher forces, harsher rides, better road contact, more spirited driving is possible.

It's all a tradeoff. Adjustable shocks try to offer the best of both worlds, but there are compromises here, too. Even so, Ima going to save up for the adjustable shocks.

PS: no "voodoo", just physics & good engineering. 🤠

Dave@DDMWorks has several posts about springs. Here's one - What was today's Sling project-Mods , goodies.....?, Post #23,151.

Try searching here or on TDS for "spring" or "springs" or "spring rate" and enter Dave@DDMWorks as the poster (here) or Dave@ddmworks if on TDS.

Quote from Doc&Ruby

PS: no "voodoo", just physics & good engineering.

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Good engineering makes straight roads, but the crooked roads are roads of genius .....

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The Hahn QA-1s are 250 front and 350 rear. I started out with 250/350 and it was hands down better than stock, but after a couple years I dropped to 300 on the rear. It rides even smoother and still stays flat in the curves.

I don't have an after market sway bar, and don't know if it would make much difference with the 250s on the front, but I can see it improving the cornering with the JRI GTs. Dave@DDMWorks would have more knowledge on that.

Sorry, just getting back in and taking care of a lot of catch up after all the events the past couple weeks.

In general, the front of the Slingshot controls your roll and the rear controls your comfort. That being said, just the spring rates by themselves are not a complete picture of how the handling of the Slingshot is going to be since the compression and rebound control of the shocks is going to also have a big impact also. The springs support the chassis on the suspension and the shocks control the motion, both of those work together to keep the tire in contact with the road, so you have to take a look at all those parts together to get a more accurate picture of how the suspension is going to behave. Also you have to figure in the sway bar on the front since that is acting essentially as a spring in roll.

So far we have tried all the way up to 500# springs in the front of the Slingshot and if on a perfectly smooth level surface, that would work really well. Unfortunately, when going around corners and hitting bumps it was pretty easy to get the Slingshot up on 2 wheels with that combination on the front, which causes a loss in stability and definitely not something most drivers would want. Since most of us do not drive on a perfectly level smooth surface, you want the suspension to be able to move and travel independently and be able to compress and rebound to soak up the bumps and irregularities in the road. This is where the compromises of suspension start to come into play, the softer springs give you more body roll and weight transfer, but in general also allow the suspension to absorb irregularities easier (unless compression and rebound of the shock is very high). If you add in a sway bar that adds a little more roll stiffness without essentially turning the front end into a solid axle, you can run a spring rate in the front that is responsive and yet can still allow the suspension to move and do its job.

Basically though, what we have found is 225-275 for the front and around 300-325 for the back seems to give a pretty good ride and also decent turn-in response. Those spring rates could definitely be customized depending on tires and vehicle weight, but those numbers work well. With adjustable shocks the rebound and compression is also going to be able to have a big effect on the roll and comfort also though and is something to also consider.

Hope that helps,

Dave

Quote from edwardaneal

having the stiffer sway bar does add to the spring rate from a body roll perspective but when hitting things like ruts in the road or going over train tracks where both tires are hitting the bump it does not. Like I said above the way all of these things work together fascinates me.

Also I must say that it seems odd to me that Alpha / JRI went with a 350 lbs spring on the rear of the GT's - - I would love to know how they went about making this decision

The reason why it is a 350lbs/in spring in the back is because the GT has a internal valve that allows more fluid to pass through which is that gives it the "cadillac" feel.

Originally when he(Henry) was doing the testing he lent me a tester unit which had 250 rear and it just bottomed out all the time, heck even the 350 that I currently have rubs on the welter dual from time to time.

Quote from Neosolidus

The reason why it is a 350lbs/in spring in the back is because the GT has a internal valve that allows more fluid to pass through which is that gives it the "cadillac" feel.

Originally when he(Henry) was doing the testing he lent me a tester unit which had 250 rear and it just bottomed out all the time, heck even the 350 that I currently have rubs on the welter dual from time to time.

On the shocks there are basically internal bleeds and a shim stack that control the fluid flow through the piston. Most likely they are running a light shim stack which allows a big movement of fluid at lighter pressures, making their compression damping relatively lighter than some of the other setups out there. The bleeds are used more for the low speed motion like traveling down the road and the shim stacks are used more for high speed movement like bumps and some of the handling characteristics. The tuning of the shock with the shim stacks and internal bleeds though is where the magic really happens and why some shocks are $600 for a set and some are $3000 for a set.

Quote from Dave@DDMWorks

The tuning of the shock with the shim stacks and internal bleeds though is where the magic really happens and why some shocks are $600 for a set and some are $3000 for a set.

Now lets really confuse Edward Neal and start talking position sensitive electronically variable spool valve dampers .....

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So I'm going to dig this up again, not so much for the springs, but where to set the Rebound/Compression on the adjustable shocks.

I had the dealer add the TD 3-way adjustables. (I dunno if they are better/worse than any others, but this particular dealer has an agreement with TD.) PIcked it up yesterday and felt that it was way too harsh - I felt like I was hitting every pebble. To be fair, they also added TD Sway bar and TD Recluse 20" front/22" rear wheels with Nitto 555 G2 tires. So a lot of variables got changed.

Came home today and counted where they set them at the dealer. All shocks had 18 clicks available and everything was set at 10. I set them all to 8 and the ride seemed a little better.

Now, reading above, front and rear can be set differently. Front for roll and rear for comfort. (I also googled some other sites and I don't even want to get into over/under steer, etc.)

So anyone got suggestions? Mine is a daily driver and I would only be running hard when I go to one of the GTGs (ie Eureka Springs in Sept).

I have the DDM 3 way which have 19 clicks, and here is their page on settings:

I have my DDM's set on the Handling/ Mountain Road suggestion which was item #3. Have tried them on several different settings and found this to be the best of both world's for me. Between handling and comfort.

Sent from my SM-N950U using Polaris Slingshot Forum mobile app

Quote from wokka

I have the DDM 3 way which have 19 clicks, and here is their page on settings:

You are AWESOME! That's exactly what I was looking for. Thank you.

Yes, these might have 19 clicks too. They went past 18 (hard!) but I never felt that last "click". I'm surprised how low some of the numbers are considering the dealer set everything at 10 to begin with. And I wished the dealer would have left me some of the paperwork that came with anything.