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Old 07-06-2023, 05:47 AM   #29
autoracer86
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Another drawback of excessive caster and thus more overworked power steering may overheat it on earlier twins (if paired with grippier tires) resulting it switching off sometimes.
What do people consider excessive caster on the gt86 ?
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Old 07-06-2023, 07:25 AM   #30
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What do people consider excessive caster on the gt86 ?
I won't call specific numbers, so probably would think how much more "relative to stock caster", just that remember reading few years ago in thread about powersteering switching off with slicks and also extra caster. Reverting caster increase fixed IIRC. My guess, that also other bits that make steering heavier (and thus "add work" for powersteering to do), may cause similar possibility, eg. increasing scrub radius by high offset difference vs stock.
EPS supposedly was among improved things.. not recalling when exactly though, for MY2015 or for restyle MY2017. As i limit my tire choice to UUHP 225 width class, i've yet to see such issue, even if having early twin. As free bonus, not going overboard with tire grip still leaves stock suspension & brakes semi usable on track, thus also no compromises for dual-use for daily driving compliance aswell.
You can skip overthinking on caster/EPS issue. Just keep in mind as ways to fix if you'll get it (i.e. reducing bits that "make steering heavier", like lessen caster/or way different from stock wheels offset (for eg. flush fitment sake)).
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Old 07-06-2023, 08:30 AM   #31
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I won't call specific numbers, so probably would think how much more "relative to stock caster", just that remember reading few years ago in thread about powersteering switching off with slicks and also extra caster. Reverting caster increase fixed IIRC. My guess, that also other bits that make steering heavier (and thus "add work" for powersteering to do), may cause similar possibility, eg. increasing scrub radius by high offset difference vs stock.
EPS supposedly was among improved things.. not recalling when exactly though, for MY2015 or for restyle MY2017. As i limit my tire choice to UUHP 225 width class, i've yet to see such issue, even if having early twin. As free bonus, not going overboard with tire grip still leaves stock suspension & brakes semi usable on track, thus also no compromises for dual-use for daily driving compliance aswell.
You can skip overthinking on caster/EPS issue. Just keep in mind as ways to fix if you'll get it (i.e. reducing bits that "make steering heavier", like lessen caster/or way different from stock wheels offset (for eg. flush fitment sake)).
You said so much but said nothing at the same time

If I keep with my current plans I should have around 8.9. Stock my car is 5.2
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Old 07-06-2023, 10:44 AM   #32
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What do people consider excessive caster on the gt86 ?
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If I keep with my current plans I should have around 8.9. Stock my car is 5.2
I would consider 8.9 degrees of caster *excessive*.

Don't worry about caster unless you know *exactly* what differences in handling demeanor you want and *exactly* how changing caster and in which direction will affect it.

FWIW on the '17 I had RaceSeng caster/camber plates which allowed for some caster adjustment, but also were configured to maximize caster at max end, and still gave more than stock caster at the min end of the adjustment range. I just kept it at the min end which IIRC was about 6.25 degrees. Honestly I woulda preferred to have an adjustment range more like 5.25 to 7.25, ish...

A buddy of mine took crew chief responsibilities for an SCCA team of BMW E36s, improved their overall race times by tens of seconds just by dialing out all the excessive caster that had been dialed in. ABsolute quickest lap times were similar, but laps were far more consistent and the cars more driveable and raceable with more reasonable caster.


Anecdotal, but still... In my experience, my 240Z with home-made mods had barely 3 degrees of caster, I *loved* its handling and steering feel characteristics!

Last edited by ZDan; 07-06-2023 at 12:41 PM.
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Old 07-06-2023, 11:22 AM   #33
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From a very good/talented motorsports engineer: "Caster is track and application dependent."

Good to consider how much steering input/angle you expect to use for a track or application (meaning street or auto-x or gravel stage rally).

In the old days, the "as much caster as possible" mantra was not a bad thing for the Subaru people because they didn't come with very much and very few were ending up with 8.9 degrees after all the caster mods lol.

If you're not changing your alignment each event and also driving home, you'll have to make a compromise. There's some driver preference as well.

- Andrew
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Old 07-06-2023, 12:56 PM   #34
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What do people consider excessive caster on the gt86 ?
OEM specs say 5.2 to 6.7 as a range. IMO you're safe till 7.5, I would not go over 8.
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