One thing I have been wondering about since I first saw them was why are the bolts on the first wheels of trucks different from all the others? The ones in the trailers look like normal wheels, but the first ones stick out with giant evil bolts. All the other tires look like in-ies while the other one is a terrible out-ie.
I know there is a good reason for it, there has to be. But all my mind can think of is torture devices and trucks using them to have violent wars on the road. That might just be from watching too much ‘Robot Wars’ years ago.
So, anyone wish to inform me so I no longer fear for my life when on the road?
There is only one wheel on the steer axle, mounted convex side out, just like on a car. On the rear, dual wheels are mounted back to back, so your seeing the concave side of the wheel.
To expand on A.R. Cane’s post - On most cars the surface the bolts pass through is close to the centerline of the wheel. Normally the mounting surface is closer to the outside of the wheel but still recessed in far enough so the lug nuts do not stick out past the outer edge of the tire. If the car has steel wheels and hubcaps typically the hubcap will cover the lug nuts and be nearly flush with the outside of the tire. A car with alloy rims typically has recessed holes for the lug nuts.
On a truck the mounting surface actually sticks out several inches beyond the outside of the tire. When proportionally larger lug nuts are added they look like ‘giant evil bolts’. When a set of Dual wheels is mounted back to back the protruding surface creates a couple inches of space between the tires and you are looking at the ‘inside’ of the rim.
BTW, next to the front passenger side wheel of a big truck is terrible place to be, it is very difficult for the driver to see you.
The wheels in the front and rear have different ‘offsets’, so when you look at the front wheels’ offset, it it setup differently because of the handling characteristics of trucks with dual wheels (dualies) on one rear axle.
The large negative offset of the front wheels means that when you look at a wheel, it appears very convex, whereas we are tuned in to normal offsets, which are concave (a more natural/typcial wheel). Because the front wheel you are looking at is convex, the bolts/lugs are sticking out proud (and big…'cause it is a truck wheel after all).
But the cause of all this fuss is that to provide proper ride balance and handling, the front wheels in such setups have a big, negative off set. This affects how the truck tracks, rolls, turns and responds.
You guys are bouncing all around it, but nobody has hit the target yet.
On a large truck (even pickups with dual rear tires) there is only one part number for a rim. IOW the same rim that fits the back of the truck also fits the front of the truck.
In the rear of the truck, the duals are mounted convex side to convex side which spaces the tires apart. In the front, the single wheel is mounted convex side out (same as the inner wheel in the rear).
Could you mount the front wheel concave side out for a greater track? Well except for the fact that the suspension was designed for the wheel to be mounted the other way, and it would probably hit the bodywork sure.
It is an ease of design and service issue. It is a lot easier and cheaper in the long run to only need one part number wheel for any position on the truck then it would be to have a separate part number for the front, and rear. Using two different part numbers would allow Murphy’s law to rear it ugly head, you need a front rim, the parts house will only have rears in stock. :smack:
Even though this thread is over 5 years old, I don’t think anyone mentioned that the single rim design also allows you to rotate the LF tire with the outside RR and the inside LR, and the RF tire with the inside RR and the outside LR.