Bump steer or something else?

chung_chang · 09-18-2006, 06:35 PM

Ok, this subject was posted before in the General section but didn't really pan out. I wanted to post some new observations about high speed handling of our trucks.

Today, I purposely wanted to test this out. So, on the way back from work on an open stretch of highway, I took her up to 90 mph. Everything tracked straight and smooth. Then, I proceeded to do a very controlled slow lane change. First lane change went ok. On the second lane change, a whiff of crosswind (not much I mind you, it's not a windy day) blew my truck to the next lane as if I was doing a very fast lane change.

Granted, I was going excessively fast purposely to get a feel of how bad it can get. But even at normal crusing speeds of 60-70 mph, I get these little sideway jerks that often requires steering corrections from me.

Before someone dismisses this as "all trucks do this", I wanted to add that my previous vehicles, namely Ford suvs, did not feel nearly this bad. Especially back in my younger days when crusing 85 mph was the norm and going 95+ mph was for fun, I don't remember those vehicles behaved this way. Even my wife's current suv doesn't feel this bad when we took it out of town going mostly 80 mph on the highway for hours.

Whatever it is, bad bump steer design or not, this is a bit frustrating. I thought going with 20's and 305-50-20 grippy street tires would solve this but I'm afraid they just amplify the issue. I wouldn't call this dangerous but more of a nervous drive at high speeds. Any words of wisdom is appreciated. All my mods are in my sig.

kartman · 09-18-2006, 06:54 PM

Bumpsteer requires bumps, you made no mention of a large bump on the 2nd lane change.

Do you have any kind of lift of lever kit? Sounds like the toe is off, and that typically makes handling very twitchy.

chung_chang · 09-18-2006, 07:05 PM

Do lane markers count as bumps?

Down here in southeast Texas, roads are pretty bad. I don't believe there is a single smooth highway in town. But this road condition has existed for the last couple of decades I've been living and driving here.

I do have a PRG mini-lift. I've had the truck aligned twice in the last 6 months. How can I easily check for toe myself just in case the shop has bad alignment machine?

kartman · 09-18-2006, 07:11 PM

road turtles dont count, you need something big enough to make the suspension cycle to get bump steer. But these trucks dont really have bumpsteer. My old blazer would change lanes going over train tracks before I fixed the steering. Thats real bumpsteer in a big way.

I would suggest calling Greg, he can fill you in how to measure toe and anything that might need to be checked.

**Carbeaux** · 09-18-2006, 08:47 PM

Quote:

Originally Posted by chung_chang

Any words of wisdom is appreciated.

By "didn't pan out" do you mean that no one else thought it was bump steer? Quit looking for "bump steer" to be the demon you're chasing. Enjoy your truck. It just drives differently than others you might have had. Call Greg like Kartman suggests. You tried to pull Greg in with you on the other post, and that didn't "pan out" either IIRC.

SOCALTITANKC4X4LE · 09-18-2006, 09:06 PM

Hey Chung, I had that same problem, until Greg installed PRG Street traction bars. Greg is the reason you all should move to So Cal !

chung_chang · 09-19-2006, 04:25 AM

I wish I was there in SoCal so I can just take my truck to Greg and let him drive it to see. That's interesting about traction bars fixing your issue. To me, that hints possibly a thrust angle issue?

I'll try Greg agin (tried before but couldn't get a hold of him). He did reply to my PM and that's when I referred him to the other thread but he never posted there.

PrerunnerGreg · 09-19-2006, 06:23 AM

there could be a few things. first is toe, check it with a tape measure, the tires shoudl be aobut 1/16-1/8inch closer together at the front (almost parralel). Next is the tires, sticky tires can do weird stuff on the road. On my stang it was a pretty light car with sticky 245's and it would follow the grain of the pavement on the freeway. too much traction? Bumpsteer is when you hit a bump and the tire steers (not the steering wheel, that is just feedback). but it as bad as the titan can be, no regular road undilations would be noticed as bumpsteer. If you have your stock wheels/tires laying around, i would slap those back on for a test drive to see if its the tires, im guessing that it is.

chung_chang · 09-19-2006, 06:47 AM

Thanks Greg! I'll tape measure my toes tonight. Glad to know that bumpsteer would not cause this behaviour even on our bad highways as I was pondering on buying the 4" spindle just to address this specific issue. I'm hoping it is the toes out of align so I can take it back to the shop. If it is my sticky street tires, then it's a compromise I'm willing to live with as the handling gains from these tires out weighs the issue. I'll post back later.