I was driving down a rural road today at about 65 mph. As I came up to a traffic light it changed unexpectedly so I got on the brakes pretty hard, but in a straight line. The road was pretty bumpy and rough and as I started slowing down the car veered hard to the right despite the fact that I was holding the wheels straight. I had to turn pretty hard keep the car from going off the road. Is this bumpsteer? This also happened one other time where the car veered hard while braking after hitting a small bump.

I've only lowered the front 1.0" from stock and did not think this would put the suspension into bumpsteer territory. I've not noticed any bumpsteer in cornering. Only other thing I can think of that would cause this would maybe be brake fade, but my brakes are bedded in...

 

How wide are your front tires? I'm wondering if it could also be "tramlining".

 

I'm running 255/40/19 front tires. Haven't really had a tramlining problem with them on the highways. This really wasn't a gentle, wandering type of direction change. It was very sudden and sharp. It gave me a pretty good scare actually.

 

From what I've read on tramlining it doesn't sound like that happened to you. tramlining seems to be a wandering due either to grooves in the road or poor tires. Bumpsteer normally occurs when you radically increase unsprung weight. In the 4x4 world this meant putting 35" or larger tires on the truck. When you would hit bumps the mass of the front tires and wheels would jerk the steering to one side or the other. Correcting the direction of steering isn't difficult but it can get tiresome. To correct bumpsteer a standard shock absorber is used and that would not have helped with what you described.

You said you had to turn the wheel pretty hard to keep from going off road, this sounds more like a caliper piston sticking. If one piston grabs and the other sticks just short of grabbing then you will experience a rapid pull towards the working piston. Once you release the brakes in this condition the steering will act normally. If one works normal and the other sticks at full expansion then you will pull towards the sticking piston. In this scenario the vehicle will continue to pull when the brakes are released and I've had to pump the brakes several time to unstick the piston. I've experienced Ford's phenolic pistons sticking on my '88 Ford Bronco quite a few times. The fix was getting calipers with metal pistons though I have heard of metal pistons sticking as well. It's a heat problem when experiencing hard braking.

I've not heard of too many new cars experiencing caliper sticking but I see you have aftermarket brakes and I'm not familiar with that brand.

BB
Semper Fi

 

I doubt that it was bumpsteer. Bumpsteer is a geometry effect that does not depend on whether or not you're braking, and virtually all cars have at least a little of this. Call it an "error function" between the arc that the knuckle (aka "spindle") follows and the arc of the outer tie rod pivot, as they do not pivot about anywhere near the same point (think front view here).

Best way I can think of to tell bumpsteer by driving the car is to drive through a longish corner that has gentle heaves in the pavement. Drive through it hard enough to get the suspension to rise and fall as you go over the unevennesses. If you then find yourself gently sawing back and forth with the steering wheel in order to maintain your arc without wandering side to side in your lane (or perhaps out of it) then you do have a noticeable amount of bumpsteer. A 1" difference from stock is unlikely to result in huge bumpsteer changes from stock.

Struts that are in really poor condition would exaggerate bumpsteer, since the lack of damping would allow the suspension to rise/fall through a greater distance (larger "error") and do so more rapidly. This is more of a general comment, as I'd hope that the struts of a 2010-anything would still be in decent condition. Then again, it wouldn't be a big deal to check them.


Two other possibilities:

Was the car into the ABS?

Is the offset for your wheels a lot different from OE?


Norm

 

I was braking at about 60% to 70% in a straight line. The nose dived and the weight was shifted forward. The ABS did not kick in. It then felt like, as I was braking and hitting a few bumps, the car just suddenly veered hard right maybe 2-3 feet before I corrected with the steering and moved it back to straight ahead in the center of the lane.

The struts are Roush and have about 500 miles on them. They aren't leaking and don't have any other handling problems. The wheels are 19"x8.5" 45mm offset.

I'm stumped... Would the brakes grabbing or sticking cause a violent pull like that?

 

Not bumpsteer....

Confused suspension. The road wasn't flat, you have what's probably a lot of weight on a low-profile tire. The tire most likely just hooked a rut.

 

I think I figured out what happened. Driving on the highway to work this morning I noticed that my front end was vibrating a little like a wheel was out of balance. Also, when braking I was getting some pulsing in the pedal and that woob woob woob sound from the brakes whens slowing. I think one of the calipers must have stuck or grabbed and caused the veer. It also left a high spot on the rotor causing the noise and vibes i had today.