Words by Dex Fulton
If you were to ask a mechanical engineer to design you the ‘perfect’ driver’s car, they’d most likely come up with something closely resembling a Formula 1 racer. Low, wide, aerodynamic, and a wheel at each corner. While the others are only passingly important to a 4x4, the real kicker is the last point. Having a wheel at each corner means maximum stability through corners and, more importantly, all of the weight is contained between the front and rear axles.
Basic physics, right? Think of a table. The four legs are usually placed at each corner to effectively distribute the weight of the items on the table evenly. Now if you moved the legs towards the centre, anything placed on the edge could unbalance it, yeah? The same goes for your four-wheel drive.
Think of most utes and wagons. There’s usually close to a metre of overhang front and rear, and while this can put strain on the chassis, it can also have some serious effects on your vehicle’s handling. The solution? Stretch the frame so the wheelbase is larger, and the weight is more evenly distributed. What will this do exactly? Let’s find out.
"The weight balance is so much better and you will notice an improvement in handling."
1. BUT FIRST, WHAT’S INVOLVED IN A CHASSIS STRETCH?
Get an engineer involved; they will guide you through the process and tell you what’s
needed. The general rules of thumb are: cut the frame on a forty-five degree angle so there are no vertical welds on the frame which can create a stress-locating point. Weld in a section of steel that has the same width and height dimension of your frame to stretch it by the required amount and burn it in. Then run strengthening plates on the inside and outside walls of the frame at least 150mm past the initial cut, and use the same thickness metal as the frame is constructed from (so no welding 5mm sheet to a 3mm frame). Boom. Done.
2. YEAH, BUT WHY?
The advantages are numerous. As mentioned above, the weight balance is so much better and you will notice an improvement in handling. Many folks choose to trim the rearmost section of the frame too for a better departure angle, or, you can now run a longer tray without too many adverse side effects.
3. PUT THE POWER DOWN
When climbing hills, your new, longer wheelbase will be much more capable of effectively transferring the power from the engine to the ground. I could go into the trigonometry and physics of it but come on, unless you’re having trouble getting to sleep you don’t really want to hear that do you? Just trust me, it works.
4. CORRUGATION COMFORT
Yep, it’ll give a better ride over corrugations too. Don’t get me wrong, you still need good shocks and the correct tyre pressures, but the longer distance between the front and back wheels will smooth things out a surprising amount.
5. IT LOOKS BETTER
Looks are subjective, I get it. But have a look at most modern dual-cabs, or better still, have a look at the majority of wagon-to-ute conversions. The rear axle is right up behind the cab, and let’s be honest, it looks magoo.
A frame extension moves those back wheels back, the proportions of the vehicle start looking less heinous, and there’s less stress on the suspension mounting points on the frame. Can I get an Amen?
6. LOAD BEARING – IT’S NOT JUST FOR NERDS
Our final point uses a term that is more often associated with bridge-builders and engineering types. You know, the people who did really well in school and make the lives of people who actually build things lives hell. Load bearing. It’s a fancy way of saying ‘how well something holds up something else’. In our case, we’re talking moving the rear axle back via a chassis stretch, and what it means for your ute’s tray. Long story short, it makes its ability to carry the payload much easier. With the axle moved back and centralised under the tray, the majority of the weight is now over the diff housing, right where it should be.
What do you reckon? Is stretching a 4x4’s frame a waste of time and money, or is it right near the top of your must-do mods?