Under a classic Camaro, big rear meats are as American as apple pie and superchargers. It’s also more than just an aesthetic deal done to look cool. Larger tire width equates to more grip. With engines getting more and more potent, it’s challenging to get that power mated to the asphalt, especially when the road becomes curvy.
Detroit Speed and Engineering (DSE) is in the business of making old iron handle like modern sports cars. Long ago, they saw the need for wider back tires and came up with a straightforward solution: Mini-tubs. Think of them as factory inner wheelhouses on steroids. We’ve covered the install of these sheetmetal marvels before, but this time we wanted to see how they would drop into a convertible . After all, why should coupes have all the fun?
Here’s the key players in our little sheetmetal ballet. Designed to replicate the look of factory inner wheelhouses, these mini-tubs from Detroit Speed and Engineering (DSE) have one big difference: they’re deep. How deep? How about enough room to stuff in a set of 335 tires?
The limiting factor on fitting big meats under a first-gen is the shock mount placement. If you are going with an aftermarket rear suspension like DSE’s Quadra-Link, then you can just ditch these mounts. If you want to stay with leaf springs, then DSE has you covered with all the parts necessary to relocate the shock mounts inboard of the framerails. This ride is going four-link, so all we have to do is widen the tubs.
The first thing we came to grips with is that a convertible is not a coupe. Without the roof support, GM beefed up the support structure behind the rear seat, so there’s a lot more metal tied into the stock inner wheelhouses. There’s also the matter of the brackets for the convertible top which are also attached to the inner wheelhouses.
Even with these extra structures, the process for installing the mini-tubs is pretty close to how DSE instructs for the coupe. First, a line is scribed about 2 1/2-inches from the stock wheeltub. Remember, it’s better to cut too small than too big.
Once this project is done, the seat back will be a few inches shorter due to the wider wheeltubs. Rather than take this out of the ends where we have nice flanges to work with, we decided to take it from the inside sections. This should give us a more factory look when we’re finished.
With the cut made, we drilled out the spot-welds from the front and rear of the section we wanted to remove. We then cut it free from the stock wheeltub and removed it from the car. Once out, we cleaned up the flanges and put the seat braces aside until later.
Here’s the biggest challenge compared to doing this surgery on a coupe. The bracket for the top mechanism can’t be allowed to move up, down, or out. If it’s off, then the top won’t function properly. We tack welded a couple of braces in place to keep it positioned while we removed the stock wheeltub below it.
We then quickly removed the majority of the stock wheeltubs with a 3M cutoff wheel. With the big pieces out of the way we could concentrate on cleaning up the edges. First, we separated the inner and outer wheelhouse flanges by grinding down the spot welds. Then, using a small pry bar, we separated the stuff we wanted to keep from junk destined for the scrap pile.
Here’s the driver’s side with most of the stock wheeltub removed and the flange cleaned and straightened. On convertibles, the flange is bent over to protect the top, which folds down over of it.
It was time to start cutting into the floor using a cutoff wheel. Towards the front you can see where we marked “flange.” This will be bent down and later used to further secure the new DSE wheeltubs. Remember what we said earlier about how it’s better to cut too small than too big? That statement applies here too.
We continued to clean up the edges and remove all the leftover bits of the stock wheeltubs. Here we drilled out a couple of spot welds and pulled out the last of the front section of the old tub. The tab left behind is needed to help secure the new tub, so resist the urge to just cut it away.
At this point we were just about ready to cut into the frame. Since this can weaken the car, we took a few precautions: the first was to weld a steel bar across the car that will help keep the Camaro from twisting. We also supported the body on its frame rather than the rotisserie it was mounted to.
Here you can see how much of the frame was occupying the space needed for our passenger’s side DSE mini-tub. Nothing a sharp cutoff wheel can’t fix.
Behold the new hole in our frame. Since the rear factory frames angle inward, clearance is critical to stuff the most tire under our drop-top Camaro. When finished, the frame will be as strong as it was before we started.
The procedure for the driver-side is just like the passenger's except the floor has a slightly different topography. The cutoff wheel was our best friend during the sheetmetal surgery.
We were hoping we could slide in the new tub without removing the convertible top bracket, but no luck. After drilling out the five spot welds, we used a small chisel to separate the pieces. With that done we cut the two spot-welded-in supports about a 1/2-inch from the car body. These will be crucial later when we put this bracket back in the car correctly.
Next, we test-fit the new mini-tub. We were a bit tight in several places, so we trimmed and re-tested it until we were happy. The mini-tub was then removed so we could finish up the frame modifications.
Patch panels were made for the driver- and passenger-side frame areas from 3-inch wide, 1/8-inch thick steel, then welded in place. Once stitched in, the welds were ground smooth.
We also made patch panels for the forward seat support area. This will add strength and minimize any rattles or squeaks. Once done, these panels were then ground smooth like the rear ones.
With the frame finished, we could then re-install the DSE tubs and begin welding them in place. We used our Miller MIG welder to place 1-inch welds about an inch apart around the bottom of the mini-tubs.
For the flange, we brought out the big gun: our spot-welder. If you don’t have a spot-welder, then you can just punch, or drill holes through the flange of the DSE tubs every couple of inches, then weld away.
With the new tubs secured, we could begin re-attaching all of the various brackets. First up, we welded the trunk hinge supports as shown.
Next, we tackled the seat back. As stated earlier, we felt it would be better to take out the distance from the center area rather than the ends. It might take a bit longer, but it yields a better finished product. This is also where we practiced the “measure twice, cut once” principle.
With the section removed we could re-install the end piece. After welding it to the middle section, we stitched it to the floor and DSE mini-tubs. Once done, all the welds will be ground down and everything will be painted.
Time to re-install the top mechanism brackets. By using the rods we tack welded in place, and the holes we drilled as reference points, we were able to precisely place the bracket in the same exact spot it was located before we started.
We had to slightly modify the lower flange for the bracket in order to get it lined up with the new tub. Once in place it was welded to the bracket and the tub. With the bracket secured, we could remove the rods we welded in earlier.
Here you can see the driver-side completely welded back together. Once seam-sealed and painted, we will be sure to bend the flange back over to protect the convertible top that will eventually reside there.
Here’s what the interior of our ’69 Dynacorn drop-top looks like with the DSE tubs installed and all the brackets re-attached. Once sealed and painted you would be hard-pressed to know this wasn’t a factory option. Keep in mind that some modifications will need to be made to the rear seat, but it’s nothing major.
Here is the outside view of the installed left and right DSE tubs. Before starting, we measured the available distance and came up with around 11 1/2 inches of room for a tire. With the DSE tubs installed we now had a whopping 14 1/4 inches of clearance. Even more if we rolled the wheel lip. At this point, all we needed to do was to seam-seal and paint, or undercoat.
And lastly, here’s the view from the bottom. It’s easy to see how the increased width of the tubs, combined with the frame notches, will allow for super-sized rear tires. Total install time for a coupe is around 35 hours, but since our ’vert was a bit tougher, it took us a few hours longer.