A Spare Tire That Fits Under the Load Floor

[bandit81]

Could you take the wheel to a machine shop and have them first open the holes then re-machine a 60 degree shank for the factory lug nuts? This would obviously cost some $ but then you would not have to worry about using the flat flange nuts.

The use of the hub centric ring in this particular case is 100% required (someone else mentioned this but want to re-remind folks). Conical seat lug nuts center the wheel so the hub is technically extra insurance that everything is centered. In this case you are no longer centering the wheel via the lug nuts (when using a flat nut/washer). YOU MUST USE THE HUB CENTRIC RINGS OR ASSUME THIS WHEEL IS ONLY INTENDED HOLD THE CAR UP - NOT INTENDED FOR ROAD USE.

If you truly want to have a failsafe spare (idiot proof that any road side assistant will not screw it up), you should use a spare tire size that works on all 4 corners made of the same wheel material. This way the spare can be installed in the front or rear without question using an aluminum spare wheel for aluminum wheels or steel spare wheel for steel wheels so bolt torque is the same. In other words, get an 18" aluminum wheeled spare tire to be 100% confident nothing bad will happen. I think I am going to go this BMW wheel route myself, but I am going to put a big label taped to the wheel for anyone else who may come across it "NOT INTENDED FOR THIS VEHICLE UNLESS YOU FOLLOW SPECIFIC INSTRUCTIONS".

Last, in 2-5 years you may forget how to use this spare. Plan on writing down a procedure (move front wheel to back, use these nuts, use this hub centric ring, torque to X, etc..) and stash a copy with the tire as well as in the glove box.

Thanks for an awesome solution!

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[kjechel]

Could you take the wheel to a machine shop and have them first open the holes then re-machine a 60 degree shank for the factory lug nuts? This would obviously cost some $ but then you would not have to worry about using the flat flange nuts.

Yes, I considered that however I wanted a solution that could be implemented without special tools or services. Some machine shops might be hesitant due to liability concerns. Furthermore, the original lug nut seats are formed to shape, so there is a raised lip around the circumference of each hole. Some of that lip would get removed if the seats were opened up to accept standard 60 degree M14 lug nuts - Not a major concern, but something to be aware of.

The use of the hub centric ring in this particular case is 100% required (someone else mentioned this but want to re-remind folks). Conical seat lug nuts center the wheel so the hub is technically extra insurance that everything is centered. In this case you are no longer centering the wheel via the lug nuts (when using a flat nut/washer). YOU MUST USE THE HUB CENTRIC RINGS OR ASSUME THIS WHEEL IS ONLY INTENDED HOLD THE CAR UP - NOT INTENDED FOR ROAD USE.

Yes, agreed 100%

If you truly want to have a failsafe spare (idiot proof that any road side assistant will not screw it up), you should use a spare tire size that works on all 4 corners ....

Good point about road side assistants, or any time someone besides you drives the car without you.

I am going to put a big label taped to the wheel for anyone else who may come across it "NOT INTENDED FOR THIS VEHICLE UNLESS YOU FOLLOW SPECIFIC INSTRUCTIONS".

... Plan on writing down a procedure (move front wheel to back, use these nuts, use this hub centric ring, torque to X, etc..) and stash a copy with the tire as well as in the glove box.

Not a bad idea! If you go the BMW wheel route, let us all know how it works out.

 

[Compromise]

Thanks for your report - I'm glad to hear everything went well. Is your load cover raised up at the front or the back? Initially mine was at the back until I put a 1.5" spacer (scrap of 2x2) under the tire at the front (see last photo in Post #1). That made the plane of the wheel and tire parallel to the load floor, and then the load floor fit perfectly flat.

I was able to get the load floor flat after centering the wheel. I used some microfiber cloth instead of a 2x2 and it worked fine. Thanks again

 

[thui001]

All the information is very helpful; just want to drop off a note to Thank you to everyone.
just curious, if the cargo floor box might work part#84545-3S5-A10 with this spare tire setup.

 

[kjechel]

All the information is very helpful; just want to drop off a note to Thank you to everyone.
just curious, if the cargo floor box might work part#84545-3S5-A10 with this spare tire setup.

No, because the concave side of the wheel will be facing down. But all this stuff fits UNDER the wheel

And I have refined it a bit further by sliding a piece of rubber tubing over the Coupler Nut (that's sticking up) and then I close the jack so it's squeezing down on the rubber tube. That way it does not move around or rattle one bit. There's still more room around the outside of the tire for a small bag of tools, roll of paper towels, window cleaner, Lithium-Ion jumper battery, first aid kit etc., and even the Air Compressor that came with your car, as shown here.

 

[thui001]

No, because the concave side of the wheel will be facing down. But all this stuff fits UNDER the wheel

And I have refined it a bit further by sliding a piece of rubber tubing over the Coupler Nut (that's sticking up) and then I close the jack so it's squeezing down on the rubber tube. That way it does not move around or rattle one bit. There's still more room around the outside of the tire for a small bag of tools, roll of paper towels, window cleaner, Lithium-Ion jumper battery, first aid kit etc., and even the Air Compressor that came with your car, as shown here.

Understood i totally forgot, and that is a great idea on the location of the for the air compressor, So smart. I was concern since there is some area is hollow out and I am concern the board can be very easily bent if a heavier item is laying on top of it. . Thank you again.

 

[bandit81]

I suspect the Modern Spare could just fit under the floor if the spokes could come through the floor. I am thinking I may cut a perfect circle in the center of the floor to allow the spokes to come though. Anyone with a Modern Spare care to confirm if it would fit if the spokes were allowed to protrude? I also suspect it may fit with letting some air out of the tire, I can live with the spare being low on air as I will always have a pump in the car.

I know it sounds funny but it would look something like this picture I mocked up. I am not a graphic designer, this is as good as it gets sorry!

 

[Frenzal]

I suspect the Modern Spare could just fit under the floor if the spokes could come through the floor. I am thinking I may cut a perfect circle in the center of the floor to allow the spokes to come though. Anyone with a Modern Spare care to confirm if it would fit if the spokes were allowed to protrude? I also suspect it may fit with letting some air out of the tire, I can live with the spare being low on air as I will always have a pump in the car.

I know it sounds funny but it would look something like this picture I mocked up. I am not a graphic designer, this is as good as it gets sorry!

Deflating the tire won't reduce it's size very much.

Also, you need to secure the tire in place if you don't want it to fly around and kill occupants in case of a crash.

 

[bandit81]

UPDATED: THESE ARE NOT THE CORRECT SIZE LUG NUTS

@kjechel on post #37, you said you machined 12mm nuts to 14mm? Where those aluminum lug nuts? Did you try conical seat 14mm steel nuts? Steel on Steel should fair better than steel on aluminum.

I have hardened steel lug nuts from my trans am, same M14 x 1.5 NOT THE SAME thread, looking at them then the conical portion gets quite close to the threads, but they are steel not aluminum. My thinking is a good set of hardened steel lug nuts should not squeeze onto the threads and still provide a conical seat on the rim without modification, at least based on what I see from your picture. Do you mind using a caliper and measuring the diameter where the lug nut scored/compressed (before you bored open the wheel holes)? I am digging out my Trans Am lug nuts to compare.

THANKS!!!

 

[bandit81]

@Frenzal Thanks! I am going the BMW wheel route, and thanks for the heads up on anchoring it. I am designing a simpler approach that should only require 1 drill hole in the floor for the 8mm buttonhead bolt, though the bolt may need to be 35 or 45mm long. My plan for anchoring is to drill the hole smack dab where I want to screw down the wheel, add two 3" square or 4" round plates, one for under the car and one inside the car to "sandwich" the bolt down to, then tighten down a locknut over that followed by a jam nut and then ending with the Coupling Nut. The jam nut is for the coupling nut, should allow for some adjustment upward if needed this way.

I thought about using the Dorman 41064 (https://www.amazon.com/Dorman-41064-Spare-Tire-Hold-Down/dp/B000DEMJOS/) for mounting to the floor (using it as the mounting point, not what it was originally intended) and then drilling two holes at the ends to rivet or bolt to the floor. I may still go that route, but I think this 1 hole only approach will cause less distortion to the floor, in case someone really goes to town tightening down the spare tire. I know better, the tire just needs to be anchored down enough that it's not moving in case of a roll over.

 

[kjechel]

@kjechel on post #37, you said you machined 12mm nuts to 14mm? Where those aluminum lug nuts? Did you try conical seat 14mm steel nuts? Steel on Steel should fair better than steel on aluminum.

I have hardened steel lug nuts from my trans am, same M14 x 1.5 thread, looking at them then the conical portion gets quite close to the threads, but they are steel not aluminum. My thinking is a good set of hardened steel lug nuts should not squeeze onto the threads and still provide a conical seat on the rim without modification, at least based on what I see from your picture. Do you mind using a caliper and measuring the diameter where the lug nut scored/compressed (before you bored open the wheel holes)? I am digging out my Trans Am lug nuts to compare.

THANKS!!!

They were steel lug nuts, these exactly: https://www.ebay.com/itm/124689867495. The diameter at the base of the scored/compressed area of the machined-down conical lug nuts is a very consistent .680 inch (17.3 mm) for all five. That's the ID at the top of the "virgin" conical lug nut seats on the wheel. I saved one lug nut in virgin condition and measured the OD at the pointy end - it was also ~.680" (slightly radiused at the top). So if used in the virgin state, there would be no engagement into the conical portion of the lug nut seats on the wheel. If your Trans Am lug nuts have a smaller OD at the pointy end then you may get some engagement into the conical portion of the seat, and if they are harder than the wheel material maybe they will "form" the seat even larger when torqued. Let us all know if you try that and it's successful, as it would be a good solution if we can get those same lug nuts.

 

[bandit81]

On it, will have some time to caliper the lug nuts tonight, I got a good feeling. Those old factory nuts have the grade 8 steel feel and weight to them, you would need a cobalt or better drill bit to tap them.

 

[bandit81]

YES! Will post pictures shortly. The conical edge starts at 0.625" and ends at 0.89". Quick math, at 0.68, that is about 20% down from the start of the conical edge. If you look at the tip GM rounded them from the inside thread to the tip, which would give you a little more breathing room if the lugs did start to implode into the threads.

The semi bad news, I did damage one of these lug nuts once using to pull in wheel studs into new rear axle shafts with my impact wrench. In that scenario it was direct force on the tip. If I can find it I will take a picture of that so you can determine if you think the strength is there or not. It did zip right back off the studs I was pulling into the axle shaft ends, it just flattened the tip if I recall. I didn't want to stop and run to the store to get a flat nut so I sacrificed that lug nut and a handful of washers to get the job done. It pulled in 10 wheel studs total.

 

[bandit81]

I set the caliper to 0.68" to show where it falls in the conical area.

Here is a photo of 5 in random positions. The black plastic fake nut would then screw onto the lug nut for a cleaner finish, that is what the outer threads between the nut and actual conical end is for, we would have no use for it obviously.

I don't have the Trans Am here otherwise I would be looking at the spare in that car to measure what diameter those holes are.

 

[bandit81]

The nut would use a 19mm or 3/4" socket BTW.

Dorman part number: 611-150, GM part numbers: 9594683 and 10194314

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