Changing shock absorbers: KYB, B4 or Sachs?

[Vins213]

Hi there, I have a 2017 Yaris hybrid with +100k km. I would like to change shock absorbers and springs with something more comfortably (the OEM are like a kick on the teeth on my bad roads). I know that the hybrid GR sport has a Sachs with a -11mm (that I love).

Do you have any opinions on Bilstein B4, Sachs or KYB? 
thanks! 

[APS]

KYB is usually OEM for Toyota. I can't imagine the others would deviate too much from OEM specifications. Lowering springs will be stiffer and make the ride harder.

From what you describe, if anything, you'd need softer springs and damping that will soak up undulations in the road. See if you can find adjustable dampers, then you can experiment with softer or stiffer damping.

[flash22]

shock and spring should be ok tire size is a big factor 16" have a firmer ride 15" have a taller sidewall and are more compliant

softer springs will may less stable at speed

lowering springs will make the ride more firm

FWD cars tend to wear out the rear shocks first

[Vins213]

I have 175/65 15 wheels at 2.2atm, and I have noticed that when I'm braking, I feel the car a bit 'noosing'

and I feel potholes like hell when I'm going slowly, I listen carefully a 'toc' noise

[TonyHSD]

Shocks are big factor in vehicles comfort and stability. They not only work in one way to stop bouncing of the springs but two ways to absorb sharp shocks and car body movements. The work in combination with the springs as a specific set ups, therefore if you change one of these you need to change the other too. Sport shocks should go with sport springs. You can deviate from different brands as long as the specs are matched. 
Toyota oem shocks KYB has very interesting behaviour, in certain condition and weather temperatures can become very hard, almost like rally cars suspension. , add the fact that these cars are small and lightweight with simple suspension and the results are harsh drive and horrible bumps absorbing. Tyres presented come into play here too. You need to have exact pressure set and regular checks. Any low pressure or higher by much will make the ride and shock absorbing worse. 
On the positive side, Toyota KYB shocks can lasts very long time. My one for example are still good after 13 years and over 255k miles. 
I hear that Sachs shocks exact specs are slightly more comfortable than oem KYB. Bought a rear set last year when I changed my springs but after I tested my original shocks off the car and they showed no signs of wear I decided to put them back on and return the Sachs. The later were made in china, I don’t know if this put me off too.
My suggestion to you is to test your shocks and if they are good , don’t replace them.  👍
 

[Vins213]

thanks @TonyHSD, your info are valuable

I'm feeling the car absorbing potholes very badly at low speeds, as if I were arriving at the end of the shock with a metallic 'toc' (and also silent block/rubber support are squeaky)

What 'test' can I do to see if shocks are good?

[Vins213]

for the replacement, I wanna try a gas technology, like the B4, but with the OEM springs

[TonyHSD]

9 minutes ago, Vins213 said:

thanks @TonyHSD, your info are valuable

I'm feeling the car absorbing potholes very badly at low speeds, as if I were arriving at the end of the shock with a metallic 'toc' (and also silent block/rubber support are squeaky)

What 'test' can I do to see if shocks are good?

Hi, 

there are various tests you can perform yourself. 
First thoroughly inspect the shocks for leaks, lift up the car with wheels off the ground and look for any oil leaks and then grab the wheel 12 and 6 a clock, shake and look for any knocks or movement. 
Ehen release the car to the ground do that slightly sharper and watch if the car bounces, it should go down then up and stop. 
Then on level ground you can try to press each corner again the car should be hard to press but go down a bit and up and stop, any excess bouncing is a sign of bad shocks. 
And final test is to watch wheels moving up and down while driving. You can do that from another car and give yours someone else to drive on a motorway and you watch for a side, change sides and watch behind, all tyres should move slightly up and down as car goes over road imperfections but no jumping and no tyre should lift off the ground. 
Lastly when going slowly 0-15mph over speed bumps, lower side windows and you should be able to hear hissing noises when shocks get compressed.

These are most common and very accurate tests. 
If the shocks are off the car the compress the piston rod should go slowly in with moderate to hard resistance and then slowly pops out . If any of these two in and out movement are not smooth and with a rear of no resistance at all means shocks aren’t good. 

[Vins213]

7 minutes ago, TonyHSD said:

If the shocks are off the car the compress the piston rod should go slowly in with moderate to hard resistance and then slowly pops out . If any of these two in and out movement are not smooth and with a rear of no resistance at all means shocks aren’t good. 

like this test...the B4 has the best movement (I think)

 

[TonyHSD]

2 hours ago, Vins213 said:

like this test...the B4 has the best movement (I think)

 

Exactly like that. 👍

But shocks can fail one way and be good the other. For example they can be good to cancel bouncing after been compressed but not good at accepting, for example don’t let tyre goes up or let it go too quickly and compress the spring excessively. 
Proper tests are your first steps.