ideal spring rates for coil-overs on Yaris - Toyota Yaris Forums

Loren · 01-21-2009, 03:40 PM

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 · 01-21-2009, 04:08 PM

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?

largeorangefont · 01-23-2009, 03:27 PM

Quote:

Originally Posted by Loren

...

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....

That scares and intrigues me at the same time. That is a small single shear bolt at the bottom of that shock.

Undoubtedly a conventional coilover would work better at the limit, but it is just a beam axle in the back so I'm sure you could get 95% there with a good shock/spring setup.

Loren, do your rear K sport shocks have less droop travel than the factory units?

Loren · 01-23-2009, 04:26 PM

Quote:

Originally Posted by largeorangefont

Loren, do your rear K sport shocks have less droop travel than the factory units?

I didn't do a lot of checking with the stock suspension, but I'm pretty sure they do have less. I've got them set to droop as far as possible (maximum suspension travel) and they still don't seem to droop very far. Lots and lots of "impressive" rear wheel lift when cornering.

rob323 · 01-26-2009, 06:04 PM

Quote:

Originally Posted by Loren

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.

I was contemplating the same thing on my echo yesterday while installing the new shocks on the rear. I still haven't decided what I am going to do spring-wise yet and was thinking about those kits that put the rear springs on the shocks (which would be easy to do on my shocks). It worries me though that if using a spring on the shockie mounts, it could stress the mounts more than they are designed for.
Although, the standard shocks have the bump stops on the shock so any bottoming out would be transmitted to these points anyway.
I might have a bit of a closer look at this method tonight to see if it has any merit, and check for any clearance issues.

rob323 · 01-27-2009, 04:24 PM

Had a good squiz at my echo last night with tape measure in hand. Maybe a Yaris has more clearance than an echo, but it would a very tight squeeze to fit 2.5" ID springs in there. They would fit with the standard 175 wide tyres and 5.5" rims (about 10mm clearance to tyre) but any other offset or width could cause problems and may require spacers. There is also the rear brake line to the drums that would possibly get in the way. Not really worth it for my application but might be worth investigating further for smooth tarmac type work where limited suspension travel is needed (and therefore shorter springs can be used).

01-21-2009, 03:40 PM	#1
Loren What? Drives: 2007 Yaris LB Join Date: Nov 2008 Location: Safety Harbor, FL Posts: 1,006	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. __________________ ----------------------- Loren@InvisibleSun.org -----------------------

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01-21-2009, 04:08 PM	#2
CASTREX Who said Yaris was slow? View User's Garage Drives: Yaris T-Sport 2008 Join Date: Nov 2006 Location: Costa Rica Posts: 1,287	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?

01-27-2009, 04:24 PM	#6
rob323 Don't drive it, RALLY it! Drives: 1999 echo PRC rally car Join Date: Oct 2008 Location: Joyner, Brisbane Posts: 321	Had a good squiz at my echo last night with tape measure in hand. Maybe a Yaris has more clearance than an echo, but it would a very tight squeeze to fit 2.5" ID springs in there. They would fit with the standard 175 wide tyres and 5.5" rims (about 10mm clearance to tyre) but any other offset or width could cause problems and may require spacers. There is also the rear brake line to the drums that would possibly get in the way. Not really worth it for my application but might be worth investigating further for smooth tarmac type work where limited suspension travel is needed (and therefore shorter springs can be used).