ideal spring rates for coil-overs on Yaris

[botchilah]

I'm ordering TEIN coil-overs for my Yaris and was wondering what spring rates to order them with.

The default springs included on TEIN's that I've tried (Flex, HA's, Monoflex, SS and Basic Damper) seem to be too stiff for our local roads (having test-driven Evo's 4-10, GC8 and GDB STI's, Z33, Silvias and a Supra) so you guys might know of the best spring rates to go for fast-road and some track driving.

Tires used most likely will be Advan Neovas, 205/55 tires on a 15X7 wheel or a 16X7 wheel.

Thanks.

[ddongbap]

It doesn't really matter what rates you use. Just don't get spring rates that'll over do the shocks dampening.

[IllusionX]

it does matter.

i still have not found the spring rates of the OEM springs. Finding that out, will help deciding what aftermarket springs to choose.

The thing is, you do not want to alter the front/rear spring rate ratio.

[AdeJong 03]

Originally Posted by IllusionX

The thing is, you do not want to alter the front/rear spring rate ratio.

very true

unless you are complementing the coilovers with a lot of other suspension mods and REALLY know what youre doing lol

im sure that the suspension companies have done some decent r&d on their products so whatever you buy will be good. If it might be too stiff, i guess you could get the spring rates of the coils that are too stiff for you and compare them to other companies (such as silk road) and see if you can find anything softer

good luck

[Loren]

For track driving, you most certainly DO want to change the front/rear ratio.

Most of the suspension companies leave some understeer on the table for liability purposes, they also typically avoid over-springing the rear because it makes for a less-comfortable ride. Remember that 95% of their market wants their product for "bling" and will never drive on a race track! They know that, and they design their products accordingly.

Botchilah, you've stated that typical Tein coilovers are too stiff for your liking. Understand that there is a lot of setup involved that can affect how harsh the ride is on a rough road. Set the suspension too low and you don't have enough travel to absorb a big bump without bottoming out hard on the bump stops. Set the shock damping too stiff and the suspension simply won't move over most bumps! You need to find an adequate ride height for the surfaces you drive on, and then tune the shocks so that they're soft enough to not beat you up, but firm enough to not wallow around.

Then, when you get to the track, if it's a smooth track, you can dial the shocks stiffer for better response.

As for spring rates, the stock rates are about 133 lb/in front and 117 rear. (I don't remember where I got those numbers, but I have them in a spring rate reference sheet)

To combat the understeer of the FWD platform, you want the rear rates to be close to the same as the front rates, sometimes even MORE. I'm running 4kg/mm front and rear on mine, and it could still use a touch more in the rear. I tried 7kg in the rear, and it felt REALLY good on a short test drive, but I was afraid that it might be too much on the track and lead to problems. So, maybe something like 4kg/5kg would be ideal for a "trackable street" setup. For a more track-biased suspension, you'd want to go a lot stiffer, maybe 6k/8k.

The problem with the Yaris suspension is the spring perches on the rear beam axle. I'm pretty sure this is why many of the aftermarket kits stick with a near stock rear spring rate. If you fit a stiff spring in the rear that's short enough to give the ride height that you want, it's too short to stay seated under suspension droop. The solution to that problem is a tender spring, a softer rate spring that stacks on top of the main spring to hold the spring stack in place at full droop. BUT, that doesn't work all that great on the Yaris, either, because the lower spring perch doesn't rise straight up and down, it rotates up and down as the axle swings on it's pivot point at the front. Makes for an awkward situation. I stuck with a tender spring stacked on a standard spring, but I think ideally, I should be using a heavier tender spring (more of a "helper" spring) and the springs should be welded together. That might work better.

Alternately, I think I've seen a Yaris coilover kit that uses a "true coilover" setup in the rear. The stock spring perches aren't used at all, instead, 2.25" ID race spring is used around the shock. Much better solution, I think.

Buuut... if all of this talk of the hassles of tuning the rear suspension with a proper spring rate is scary to you, just fit the Tein kit with its default rates, fit a big rear swaybar and be happy. It's close enough to goodness that you won't know the difference.

[CASTREX]

I have the Tein Basic's and I don't find them harsh at all. And the streets here are as rough as they can get.


Loren I have a question. ( Sorry for the threadjack )

My Teins come with 4K front 3K rear springs.
I'm lowered like 1.5"-1.75" That's as tall as the Teins would go.

I run with the cars back stripped and also have the TRD sway bar.

Even if the rear spring rates seem soft I find them stiff enough for my needs.

However I think I would like the front a little stiffer as I get a lot of rubbing on the inner plastic fenders over mild speed bumps. I have even hit the rubber stoppers over high speed bumps. I'm on OEM wheels 45mm offset and 205/45 tires.

I have tried to raise a little bit the front as I have some thread left but looks like all it does is load the spring instead of raising the car.

For normal driving the car behaves amazing! But when I go to the twisties for some spirited driving I have to be watching for every small bump on the road.

My car feels quite neutral now. Maybe a little ovesteer but nothing to compare to the factory handling.

I have tought about getting some 5K springs for the front instead of the 4K I have now.
But this kind of against your advice.

What would you say is my best call?

[Loren]

Tein Basics don't have adjustable damping. The spring rates and the damping of that kit are chosen to work together. Being a kit that's intended for a more casual street ride vs. all-out handling, the spring rates are on the soft side, as is the damping. I've not driven on Basics on a Yaris, but I think they're GREAT on a Miata. Excellent balance of handling and comfort. I was impressed.

Anyway... because the damping is fixed, is designed for the spring rate, and is already a little on the soft side, stiffer springs won't fix your problem. Or, if they do fix your problem (rubbing), they're going to introduce new problems that won't be any better. You'll be under-damped, which means the shocks can't control the springs. Transitions will be sloppy, bumps will be bouncy, etc.

The real solution to your problem is a little more shock damping to suit your driving style, but that means paying to have your Tein's revalved, or upgrading to adjustable shocks.

Well, no... the real solution is tires that fit. :) I get the same rubbing on my car with 195's and 41mm offset... got even more with 195's and 38 offset! 205's are a bit much for a Yaris, unfortunately.

I'd just live with a little rubbing until those tires are done, then go with 195's and see if they rub less. (there are some kick ass 195's available these days, btw)

Here's a tidbit I learned from my Miata days: If you always buy quality components, when you decide to upgrade, you can sell them for 2/3-3/4 what you paid for them to finance most of the upgrade! So, if you wanted to upgrade to a coilover kit with adjustable shocks (even if the "upgrade" was to a lesser brand, like K-Sport or something), you could do it for probably around $300 once it was all said and done. Pretty cool, eh?

[CASTREX]

Thanks! Your advise is much appreciated!!

Don't think that revalving is an option since I don't have a local Tein shop...

I don't want to go down to 195's The car came from factory with 205/45/17

If anything I would go to 215/40/17

My Yaris is a bit more privileged than the US yaris...

The 1.8L TS Yaris puts down around 120whp 118lbs/ft TQ So it has a little extra power to move some bigger rubber...
I'm running some RT-615's now and I just love the feeling of been glued to the street.... You know what I mean!

I've looked into the BC adjustable kit.. I will have to start looking for some one interested on my Basics...

[ddongbap]

Originally Posted by IllusionX

it does matter.

i still have not found the spring rates of the OEM springs. Finding that out, will help deciding what aftermarket springs to choose.

The thing is, you do not want to alter the front/rear spring rate ratio.

So, I'll retort. No it doesn't.

[botchilah]

Thanks Loren,

I have a pretty good idea of what I'm doing, but thanks for your long post nonetheless as it does help validate a lot of my theories. I did some hill-climb racing and and do a lot of trackdays and driver's ed days here in the Philippines with my old Evo IV. I spent 8 years finding the best spring rate, ride-height and corner-weighting and alignment settings. Too long simply because I didn't bother asking people who have had experience with the Evo in the first place. I'm trying to leapfrog that by asking people WHO KNOW their sh*t on the Yaris.

Going back to the topic, I was thinking 5kg/m fronts and 4kg/m rears but it seems you've recommended it the other way around so I'll try that! I hope my (over)weight doesn't become an issue!

[Loren]

Yeah, FWD cars like stiff rear springs for track use.

One good thing about going the route you did with your Evo... you probably learned more than you would have if you'd have just done what someone else told you. Well-considered experimentation is a good thing.

[cali yaris]

I have Silk Roads 7k front 5k rear and they are quite stiff but streetable, and they pass the Wife Test. I don't have them adjusted tightly or hard for street use, either. Very tweakable for the track.

I don't spring rates strictly translate into ride feel, I never would have thought the rates I have would be street-friendly at all - but they are.

[IllusionX]

to keep a certain comfort level. yes


Sure you do want to change the spring rate ratio depending what you want to achieve. BUT....

let me give an example. If your OEM spring rate are of 2:1. So you really want to use 4:1 spring rates ratio? I've had the chance to test the eibach pro kit for the echo. They are such horrible springs. The fronts are much stiffer than OEM, but the rear is about the same as OEM (by feeling, because nobody was able to give definitive numbers on the OEM spring rates)

result? a very harsh ride, and under steer like no tomorrow.... Not to mention the echo is an under steering car from factory..


loren: thanks for the spring rates, now i know where to start to shop for springs.

[Loren]

Cali, you're right. Shock damping has more to do with ride quality than spring rate. You can get pretty darned stiff with the springs, and as long as you use mild damping, the street ride will be okay. But, as you go stiffer, you'll find that it takes a certain amount of damping to keep the springs from oscillating (bouncing) over a bump... and when you have them set stiff enough to do that, they'll ride harsh. So, there is a point where you have to stop with the spring rate to avoid having to underdamp them for street use.

IllusionX, as someone mentioned (first post, I think), you need to "know what you're doing" when you start monkeying with the spring rate bias. You don't just want to go and make extreme changes like changing from 2:1 to 4:1 without knowing exactly what you're doing.

But, a subtle change in the right direction never hurts. It is well known that the Yaris understeers because it's FWD. The stock 133/117 rates give a ratio of 1.14:1. Changing that ratio to 1:1 is not too far of a stretch, and that gives us even rates front and rear.

Don't get too confident in the simple "front/rear ratio" thing, though. There's a lot more to it than that. The motion ratio of the suspension comes into play, too. In the front, the MR is 1:1, the motion of the wheel is the same as the motion of the spring because it's a MacStrut. The rear beam axle is not 1:1. The wheel moves a greater amount than the spring does because the spring is closer to the fulcrum point of the beam axle assembly. That motion ratio could be .6 or .7, which means that the effective spring rate, or the "wheel rate" (which is what really matters) is actually less than the actual spring rate.

Is your head spinning yet?

[cali yaris]

^ Yes, but thank you

[botchilah]

Ooh I hate that bobbing / thumping / bouncing sensation!!!

[Loren]

Originally Posted by botchilah

Ooh I hate that bobbing / thumping / bouncing sensation!!!

Not necessarily all the same problem, though.

Bobbing = underdamped
Thumping = bottoming due to insufficient suspension travel OR really stiff damping
Bouncing = underdamped

Typical "lowering springs" on stock shocks will often cause all of the above. The spring rate is enough that they're underdamped on stock shocks, and they typically reduce ride height too much for the spring rate allowing the suspension to bottom out.

[ddongbap]

Originally Posted by Loren

Cali, you're right. Shock damping has more to do with ride quality than spring rate. You can get pretty darned stiff with the springs, and as long as you use mild damping, the street ride will be okay. But, as you go stiffer, you'll find that it takes a certain amount of damping to keep the springs from oscillating (bouncing) over a bump... and when you have them set stiff enough to do that, they'll ride harsh. So, there is a point where you have to stop with the spring rate to avoid having to underdamp them for street use.

IllusionX, as someone mentioned (first post, I think), you need to "know what you're doing" when you start monkeying with the spring rate bias. You don't just want to go and make extreme changes like changing from 2:1 to 4:1 without knowing exactly what you're doing.

But, a subtle change in the right direction never hurts. It is well known that the Yaris understeers because it's FWD. The stock 133/117 rates give a ratio of 1.14:1. Changing that ratio to 1:1 is not too far of a stretch, and that gives us even rates front and rear.

Don't get too confident in the simple "front/rear ratio" thing, though. There's a lot more to it than that. The motion ratio of the suspension comes into play, too. In the front, the MR is 1:1, the motion of the wheel is the same as the motion of the spring because it's a MacStrut. The rear beam axle is not 1:1. The wheel moves a greater amount than the spring does because the spring is closer to the fulcrum point of the beam axle assembly. That motion ratio could be .6 or .7, which means that the effective spring rate, or the "wheel rate" (which is what really matters) is actually less than the actual spring rate.

Is your head spinning yet?

Never thought about the fulcrum point. Damn you're smart.