Tuesday, August 04, 2009

Trucks That Can't Drive Straight

One of my father's everlasting complaints about "new" pickups was that the front and rear wheel tracks weren't the same. When Ford went to the Twin I Beam suspension in the early sixties, they also made the front track wider than the rear. Chevy and Dodge were the same.

So what, you say. Welp, that's what I'm here for, to enlighten y'all with minor trivia. Differences in wheel tracks don't manifest in any problems under ideal conditions - such as on dry pavement. When things get sloppy, then the fun begins.

We'll look at my Chevy - it's a 2000 Silverado Z-71 extended cab, so it is a 4x4. Front track is 68.1" and the rear is 67 even. Seemingly insignificant - only 1.1 inches narrower at the rear. But, this means the rear wheels do not follow exactly in the front wheel tracks. This makes a difference on muddy or snowy roads - the rear wheels must cut out a half inch on the insides of the tires. But it's an equal amount - how is that gonna make any difference?

Lets imagine we make a very gradual arc to the right - until the right rear falls perfectly into the front track cut. But, now the left rear is out of whack over an inch. So, the forces aren't in balance - the rear of the truck now wants to pull to the left, while you are steering to the right. This will induce oversteer - where the rear of the vehicle steers more sharply than what you, the driver, had in mind with your inputs at the front. Combine this with the normal severe understeer that occurs when the road gets messy - well, you might just be in for a ride into the ditch if yer not careful.

Roads aren't perfectly flat and with perfectly composed snow and mud, so just keeping the damn thing straight becomes a challenge. I like to drive fast and look serious in those kinds of conditions - I'm usually a day late and a dollar short and don't have time to mess with a muddy road. So, I find my truck drifting and sliding like I'm some sort of rally driver. Not that wheel track differences are completely responsible for that phenonemon of course, but it definitely bears some responsibility. I can feel how "nervous" the rear is while cruising up and down that road (Mercury not included).

Dodge trucks aren't any better - the 4x2 front track is 68", 4x4 is 68.1", and both rears are 67.5" - which is closer, but in your scribe's humble opinion - sorry, no cigar. Since Fords have abandoned the Twin I-Beam, they've managed to get it right (something I did not know until I did the prerequisite Googling for this post). 67" front, rear, 4x2 and 4x4 - all the same.

You'll notice that most of the stats are pretty similar - so this results in another muddy farm road characteristic. Since most farmers drive full size trucks, the ruts that are formed are best suited for similar wheel tracks. I say this as a former Nissan Pathfinder owner with a far narrower track. When driving through a rutted, sloppy mess, one side falls into a track while the other is actively trying to fall into the other side. But, that pulls the first side out. Worse yet is when the opposing corners fall into the tracks, making the mini truckster's forward progress a decidedly "sideways" proposition.

The full size trucks with odd tracks feel nervous, but the smaller, narrower vehicles seem to have a death wish under those conditions. I loved that Pathfinder - I drove it for thirteen years. Until it rained or snowed. Then, it was a Pain In The Ass. Which is why I decided since I wasn't planning on moving, I'd better fall in line and get what everyone else out here on the prairie had, just so I could relax a little when things got sloppy.

I've always been a Chevy guy - particularly a fan of the small block V-8. I've had a version of that motor in four vehicles and enjoyed listening to the music of each one. Were I in the market for a new truck, I can tell you I'd be looking at Fords very hard. Dad always drove Fords. I admire the company for not going the "bailout" route GM and Chrysler went - that's enough right there to make me want to support them. I've always believed that rewarding a company for the best product at the best price was the best way to go, rather than worry about politics or how well they recycle beer cans. So finding out Fords have matching wheel tracks is a plus.

Note: The Titan and Tundra both have matching wheel track figures in the 67 to 68" range as well. I'm not against imports - having owned several. Plus, these trucks have about as much imported content as the supposed domestics. When it comes to full size pickups, they kinda leave me cold. Perhaps I'll learn better in the future. Heh.


Cedar View Paint Horses said...

My grocery-getter is a 94 Merc Tracer. Those wheels must track perfectly straight. I've got a 3.3 mile stretch of hwy on the way to work where I can take both hands off the wheel and that little car rides the lane like those old cars at Six Flags. It's a crazy weird feeling having that thing drift one way or the other until the opposite side tires grab the hump in the middle of the road and pull me back in the right direction. It's the most exciting 6.6 miles of my commute.

Jeffro said...

Our "cheap thrills" department leaves something to be desired as we get older, eh?

CGHill said...

Gwendolyn runs 0.8 inches wider in front than in back. Then again, she's a front-driver, so she understeers anyway unless you really lay into the pedal. (And, I need hardly point out, she's not a truck.)