Effects of spacers/ET on suspensions? - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

gpvecchi · 08-14-2021, 09:08 AM

I know the effect of spacers on handling, but I'm interested in understanding what are the effects of spacers or different ET on spring and dampers stiffness.
My behavior (but I'm not an engineer) is that dampers will be softer, because they are more sensitive to unsprung mass movement, and the lever with spacer will be longer, while the body roll will be less. Is this correct?

marco_mc22 · 08-14-2021, 10:52 AM

I don’t think so, motion ratio variations (different length arms or different knuckles which could change both the knuckle pivot point and or the spring centerline) and spring inclination (more or less SAI with camber plates for example) should be the only factors which could change the final wheel rate on two identical struts with the same spring rate.

The biggest variation of high positive ratios is the dynamic toe change Imo, very noticeable during hard braking, I’m currently using et35 rims (17x7.5 with 215 tyres) plus 20mm spacers on the front only to test wider front track and the difference is high, for reference alignment is always the same, just added spacers.

Icecreamtruk · 08-18-2021, 12:29 PM

Quote:

Originally Posted by marco_mc22

The biggest variation of high positive ratios is the dynamic toe change Imo, very noticeable during hard braking, I’m currently using et35 rims (17x7.5 with 215 tyres) plus 20mm spacers on the front only to test wider front track and the difference is high, for reference alignment is always the same, just added spacers.

What did you find specifically with the spacers up front? It toes-out more during compression? I've driven with spacers in the back and without (20mm) and without them the car wanders a lot more on hard braking (not enough toe-in, or maybe its even toeing-out during braking)

marco_mc22 · 08-18-2021, 02:51 PM

Quote:

Originally Posted by Icecreamtruk

What did you find specifically with the spacers up front? It toes-out more during compression? I've driven with spacers in the back and without (20mm) and without them the car wanders a lot more on hard braking (not enough toe-in, or maybe its even toeing-out during braking)

Yep, I’m also using static toe out which doesn’t help. Probably using spherical joints for the steering arms would reduce the wandering.

08-14-2021, 09:08 AM	#1
gpvecchi Senior Member Join Date: Mar 2018 Drives: Toyota 86 GT Limited PP (Model G) Location: Italy Posts: 1,052 Thanks: 414 Thanked 359 Times in 202 Posts Mentioned: 14 Post(s)	Effects of spacers/ET on suspensions? I know the effect of spacers on handling, but I'm interested in understanding what are the effects of spacers or different ET on spring and dampers stiffness. My behavior (but I'm not an engineer) is that dampers will be softer, because they are more sensitive to unsprung mass movement, and the lever with spacer will be longer, while the body roll will be less. Is this correct?

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08-14-2021, 10:52 AM	#2
marco_mc22 Senior Member Join Date: Jun 2017 Drives: Toyota 86 Location: Italy Posts: 139 Thanks: 42 Thanked 74 Times in 57 Posts Mentioned: 2 Post(s)	I don’t think so, motion ratio variations (different length arms or different knuckles which could change both the knuckle pivot point and or the spring centerline) and spring inclination (more or less SAI with camber plates for example) should be the only factors which could change the final wheel rate on two identical struts with the same spring rate. The biggest variation of high positive ratios is the dynamic toe change Imo, very noticeable during hard braking, I’m currently using et35 rims (17x7.5 with 215 tyres) plus 20mm spacers on the front only to test wider front track and the difference is high, for reference alignment is always the same, just added spacers.

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