Measured Bump Steer on my stock ap1
09-20-2010, 04:45 PM
#1
Measured Bump Steer on my stock ap1
From stock height to 3" of compression, I got 0.42 inches toe in. Seems like A LOT, anyone else have numbers for comparison?
Didn't measure rebound. Oddly, even with the sway bar disconnected and the shock/spring removed, it only sagged 0.75". Has anyone else observed this?
Didn't measure rebound. Oddly, even with the sway bar disconnected and the shock/spring removed, it only sagged 0.75". Has anyone else observed this?
09-20-2010, 05:50 PM
#2
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Wow, that is a lot! That's per side I assume? Measured at the edge of the tread or the edge of the rim?
The suspension bushings are quite stiff. If you don't tighten them at ride height after they've been loosened they'll alter the ride height of the car. I always wondered if you could corner-weight a Stock-class car by exploiting this but was too lazy to do it.
The suspension bushings are quite stiff. If you don't tighten them at ride height after they've been loosened they'll alter the ride height of the car. I always wondered if you could corner-weight a Stock-class car by exploiting this but was too lazy to do it.
09-20-2010, 06:57 PM
#4
Measured using the longacre plate, which should roughly correspond to the edge of the rim.
This was measured at the rear.
Correct, per side.
I can't believe how stiff the stock bushings seem to be. Makes my M3's stock bushings look like butter.
This was measured at the rear.
Correct, per side.
I can't believe how stiff the stock bushings seem to be. Makes my M3's stock bushings look like butter.
09-21-2010, 06:25 PM
#6
sorry still confused................. i really thought the rear of ap1's toe OUT under compression in stock configuration. that's what causes "snap oversteer" as I understand it--when the car corners hard the suspension moves up, toes out, and your rear end becomes loose. do I have this completely wrong?
did you check the toe at different amounts of compression (1" vs 2" vs 3")?--is it possible it toe's out through the range, then toe's back in?
thanks for sharing this. i am having some issues with my own car oversteering on corner entry, but seems more neutral when settled into the corner. trying to figure out if i should mess with my j's racing rear bsk.
did you check the toe at different amounts of compression (1" vs 2" vs 3")?--is it possible it toe's out through the range, then toe's back in?
thanks for sharing this. i am having some issues with my own car oversteering on corner entry, but seems more neutral when settled into the corner. trying to figure out if i should mess with my j's racing rear bsk.
09-21-2010, 06:53 PM
#7
I checked at 0.5" increments of compression form 0-3". I didn't check rebound because the rigidity of the stock bushings made it a PITA.
The numbers I reported above are at 3" compression.
I observed toe in with compression with the stock suspension and toe out with the BSK installed. Note that I didn't test multiple spacer configurations with the BSK. I don't know how different spacer arrangements may alter my observations.
At a glance, the stock curve appears fairly linear.
The curve with the BSK installed is a bit different, in that the was no change in toe from 0-1" compression, and then appeared to become linear with additional compression. This is my impression from glancing at the numbers, haven't actually graphed them out.
My understanding of the "twitchiness" of the stock setup is that it's not a product of the absolute direction of toe i.e. in or out, but the magnitude.
The numbers I reported above are at 3" compression.
I observed toe in with compression with the stock suspension and toe out with the BSK installed. Note that I didn't test multiple spacer configurations with the BSK. I don't know how different spacer arrangements may alter my observations.
At a glance, the stock curve appears fairly linear.
The curve with the BSK installed is a bit different, in that the was no change in toe from 0-1" compression, and then appeared to become linear with additional compression. This is my impression from glancing at the numbers, haven't actually graphed them out.
My understanding of the "twitchiness" of the stock setup is that it's not a product of the absolute direction of toe i.e. in or out, but the magnitude.
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09-21-2010, 08:03 PM
#8
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A quick search reveals two posters in this thread that agree with the toe in under jounce seen by the OP.
The only time I've seen snap oversteer in my AP1 is off throttle situations, which would cause toe out as the rear rebounds.
Also to consider is the negative caster of the rear suspension and the subsequent toe-in compliance under cornering loads. So sudden loss of lateral grip would also cause toe out from steady state cornering. Though, that bushing is quite stiff so I wouldn't expect too much compliance.
The only time I've seen snap oversteer in my AP1 is off throttle situations, which would cause toe out as the rear rebounds.
Also to consider is the negative caster of the rear suspension and the subsequent toe-in compliance under cornering loads. So sudden loss of lateral grip would also cause toe out from steady state cornering. Though, that bushing is quite stiff so I wouldn't expect too much compliance.
09-21-2010, 08:13 PM
#9
Originally Posted by Suspension,Sep 21 2010, 09:03 PM
A quick search reveals two posters in this thread that agree with the toe in under jounce seen by the OP.
The only time I've seen snap oversteer in my AP1 is off throttle situations, which would cause toe out as the rear rebounds.
Also to consider is the negative caster of the rear suspension and the subsequent toe-in compliance under cornering loads. So sudden loss of lateral grip would also cause toe out from steady state cornering. Though, that bushing is quite stiff so I wouldn't expect too much compliance.
The only time I've seen snap oversteer in my AP1 is off throttle situations, which would cause toe out as the rear rebounds.
Also to consider is the negative caster of the rear suspension and the subsequent toe-in compliance under cornering loads. So sudden loss of lateral grip would also cause toe out from steady state cornering. Though, that bushing is quite stiff so I wouldn't expect too much compliance.
i think next time i get the car aligned i'm going to do the same test--remove shocks and sway bar and go through the whole movement up and down, and then set my front and rear bsk's accordingly.thanks for the info guys, and that link.
09-22-2010, 02:44 AM
#10
This really should be done anytime a bsk is installed.
I should probably experiment with different spacer configurations, but I dont know that I'll do much better than my first configuration. The amount of change in toe with the bsk is small when compared to stock, but I do wish it also toe'd in with the bsk.
Anyone have experience that may indicate that I could achieve toe in with a different spacer arrangement on the bsk? I don't believe this is possible.
I should probably experiment with different spacer configurations, but I dont know that I'll do much better than my first configuration. The amount of change in toe with the bsk is small when compared to stock, but I do wish it also toe'd in with the bsk.
Anyone have experience that may indicate that I could achieve toe in with a different spacer arrangement on the bsk? I don't believe this is possible.