1 inch drop/ bumpsteer

[VinnAY]

This is my observation: 15GTPP w/Steeda IRS Subframe, Differential bushings, and SubFrame Braces. No mods to the front suspension, running the OE PZero 255s @32psi cold.
On a back road cruve, either left or right, it's hard to hold the wheel, each bump or dip pushes the wheel OPPOSITE and requires constant correction. It won't take or hold the road.

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[Anthony@HTM]

What springs were you using?

Steeda sport springs and now coilovers.

However it did it at stock height

My last track event was amazing

I could hit Burms and not have the wheel rip out of my hands

 

[moarhorsepower]

I'll have to keep the bumpsteer kit in mind. I'm getting my lowering springs (Steeda Ultralite progressive) installed tomorrow. If it's bad, i'll order the kit and get them installed as well.

 

[allgripnoslip]

Before I do that, perhaps people reading this thread could tell me if they think they've noticed it, and what it was that they noticed. Including a clear description of the pavement conditions.


Norm

I am about 1in lower than stock and I have not noticed any bump steer on my '15 GT PP.

I've never noticed it on the street and I've never noticed it on notoriously bumpy tracks like streets of willow springs.

I'm running a 305 wide tires, with cortex coilovers, steeda sway bars and steeda K brace.

I'm curious about this thread because I'm dropped about an inch, however I'm wondering if my wide grippy front tires or my JRi dampers have somehow insulated me from bumpsteer, but I've not felt any hit of bump steer yet.

My front steeda sway bar is on full stiff (and rear is on full soft) and I've heard others claim the stiffer front sway bar helps with bump steer, but due to ballance I've been seeking out either an even stiffer front bar or a softer rear bar.

I'm curious about this thread, but I'm not noticing any bump steer on my car.

 

[Norm Peterson]

I am about 1in lower than stock and I have not noticed any bump steer on my '15 GT PP.

I've never noticed it on the street and I've never noticed it on notoriously bumpy tracks like streets of willow springs.

I'm running a 305 wide tires, with cortex coilovers, steeda sway bars and steeda K brace.

I'm curious about this thread because I'm dropped about an inch, however I'm wondering if my wide grippy front tires or my JRi dampers have somehow insulated me from bumpsteer, but I've not felt any hit of bump steer yet.

My front steeda sway bar is on full stiff (and rear is on full soft) and I've heard others claim the stiffer front sway bar helps with bump steer, but due to ballance I've been seeking out either an even stiffer front bar or a softer rear bar.

I'm curious about this thread, but I'm not noticing any bump steer on my car.

I'd fully expect wide, stiff tires to exaggerate any bumpsteer, especially if they're mounted on wheels out toward max-recommended for the tire size.

Greater suspension stiffness should also mitigate it, since smaller amounts of suspension bump travel produce smaller amounts of steering.

FWIW, I've never noticed bumpsteer in my Mustang, and that includes running over apex curbings and occasionally out a bit more than I'd like to be on exit curbings. And that car is still on its OE springs. But it was a monster of a problem in the 1979 Malibu I'd owned previously. As in having to consciously saw away at the steering wheel in order to hold a line while driving through a turn that has always had frost heaves as the outside wheel and its suspension rose and fell to follow it.

Mine is ridiculous bump steer (at least to my very critical tastes) and without having done a single thing to my suspension yet, I would put this on if I wasn't in the middle of trying to find a place to live and packing my shyte after selling my house! I get bumpsteer especially when my front wheel falls into a divit in the road (like a dip in the road caused by years of trucks driving over that area, for example) and either my tire is running on the edge of that or the divit is not wide enough to accomodate the whole tire, so that tire "bump steers" the car in some unpredictable direction. Usually happens at 30-ish range speed or when I'm accelerating fairly quickly and just catch the wrong part of the road. It's not every day, but when it happens it's a surprising amount of influence the bumpsteer has. Could be poor toe alignment, too, I guess.

I always thought that was called tramlining, and was a side affect of wide front tires.

I'm with Chad on this one. There's also a "camber thrust" effect at play.

This is my observation: 15GTPP w/Steeda IRS Subframe, Differential bushings, and SubFrame Braces. No mods to the front suspension, running the OE PZero 255s @32psi cold.
On a back road curve, either left or right, it's hard to hold the wheel, each bump or dip pushes the wheel OPPOSITE and requires constant correction. It won't take or hold the road.

You'd understand that old Malibu of mine.


Bumpsteer isn't the bumps directly kicking the front end of the car sideways but the fact that bumps cause suspension motion, and when the tierod geometry doesn't agree with the suspension front view geometry it's that the suspension motion includes a small amount of steering. It can't be avoided entirely, but it can be minimized. You could consider bumpsteer to be a suspension "error function" created by the arcs followed by the various components all being different from each other and not always constant-radius.

Technical tidbit: bumpsteer is also affected by the amount of caster that you're running, and might intentionally be some small value even when your caster is precisely set to "factory preferred".


Norm

 

[NightmareMoon]

At the track I dropped the front left wheel off a 2" lip and suddenly I was all 4 off. It felt like the car suddenly steered left. Took me completely by surprise. Is that an example of bump steer?

 

[Norm Peterson]

I don't think so - when a wheel drops, the suspension goes into 'droop', which you'd normally expect to toe the drooping wheel 'in', or back toward the track. When the suspension and the car "catch up" with the surface, the toe on the wheel that dropped would move back to more or less where it was rather than way off in the 'out' direction, and all this is happening at the lower friction surface.

Going off over a 'step' at a very shallow angle can result in some directional weirdness, though I'm only guessing that's what the situation was.


Norm

 

[Push13]

I want to get in on this so I understand my situation better. My issue is at higher speeds (100+), even in a straight line, I hit bumps and need constant correction. I never know which direction it's going to shoot to. It is far from stable and needs to be fixed because I want to go faster. I have steeda ultralight linears and 25mm spacers all around on stock PP wheels and tires.
I also have noticable understeer whenever any weight is taken off the front, even at low speeds with moderate or mild acceleration. I let off the gas without a steering wheel change and the card turns in, back on the gas and it pushes.

Any thoughts on this?

Front brace and bump steer kit?

Shane

 

[wildcatgoal]

Remove the spacers, which are changing your suspension geometry, before you spend any more money. That's what I'd do.

 

[GreenGuardian]

Yall are making me really nervous about lowering my mustang. I have a 2015 GT bought used with 14,000 miles on it already. I put new 20x10 Niche M133's and 275/35/20 on it with the ford racing catback reso delete kit. I purchased the BMR performance springs, SP081 & SP082 (same as the SP080 kit) and am installing them next with with a buddy of mine. No other suspension mods made yet either. I did buy the Steeda alignment kit and Steeda IRS subframe support braces. I was thinking about buying the new BMR front subframe brace as well and possibly the Steeda extreme G-trac K member brace. Should I forget about these two braces and buy the steeda bump steer kit and the irs subframe bushing kit instead?

I'm looking for some advice on what other parts I should buy and install along with the lowering springs.This is my daily driver, i'm looking for a stiffer ride than stock (not by to much though, that's why i got the bmr performance springs) and think I should add some braces.

 

[wildcatgoal]

I would go as you have planned and get the bump steer kit if you have an issue when you save up enough money. The BMR springs are not aggressive.

 

[dubster99]

Anybody installed one of these on their own? Trying to come up with ways to compress the suspension in the garage and adjusting without a lift....

 

[timd38]

If you plan to set the bump steer, don't forget to do the rear. I took a solid day to set the bump steer on my Corvette. you have to remove the spring, keep moving the tie rod washers up and down while you use the dial indicator to measure the change.

I used the Longacre bump steer fixture when I did it.

 

[Norm Peterson]

Trying to come up with ways to compress the suspension in the garage and adjusting without a lift....

I think it usually involves removing the springs and disconnecting the sta-bar.


Norm

 

[timd38]

Anybody installed one of these on their own? Trying to come up with ways to compress the suspension in the garage and adjusting without a lift....

First, you have to remove the spring and shock, then you need the equipment to do it with. You have to articulate the suspension to see the rate of change as it goes through the cycle and then move the tie rod center point up and down.

Please don't take this personal, but it sounds like you have no clue what you are getting yourself into.

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