Review: Wokeby Trunk Extension for the i3 BEV

BMW i3 Forum

Help Support BMW i3 Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Staff member
Sep 9, 2019
I bought and installed a Wokeby Trunk Extension ("WTE") for my i3 BEV. I've been using it for three months and have some thoughts to share. For the record, I paid retail price for this product and have not been asked to write this review.

I've corresponded with Wolfgang Kern, the man behind Wokeby and this design. I didn't seek out any information specifically with this post in mind, but gather that he's a low-volume one-man operation who had a vision, the engineering chops to bring the WTE into the physical world, and the resourcefulness to evolve it into its current form and material choice.

The Trunk Extension is compatible with all BEV models of the i3 and i3s. It takes advantage of the space that would otherwise be occupied by the REX, over the rear axle. Although it features the original version, the video Wokeby produced demonstrates installation perfectly and doesn't need additional clarification.

The WTE adds 1.25 cubic feet of storage to the i3's 15.1 cu.ft. trunk, roughly an 8% increase in storage capacity. It is somewhat comparable in volume to the i3's frunk, which has a capacity of about 1.1 ft³, except that the Trunk Extension creates a dedicated space for the i3's flat tire kit. This results in the remaining space being less encumbered.

For me, this added space is quite useful. For starters, unlike the frunk, the WTE is weathertight. If break-ins or thefts are of concern, it provides a hiding space where a camera or laptop might be stashed. In my case, I use it for a handful of occasional use items that would otherwise be clutter in my main cargo area, and have a small amount of room left over. The photos below cover this.

The WTE is on its second design (the original version was constructed of stainless steel), and the Glass Reinforced Plastic version I received is the second iteration with this material. What is GRP? It's 3mm thick fiberglass, with a claimed weight of under 8 1/2 lbs. It is finished in a shiny piano black on the showy side. It falls right in line with BMW's CFRP material choice for this car.

I haven't seen a weight limit for the Trunk Extension, however I don't know what could be stuffed in this relatively compact space that might challenge the material's integrity. The bottom of the WTE rests on a chassis crossmember, so whatever the load, it's supported from below.

The "big picture" durability of the Trunk Extension deserves a more nuanced answer. But as a TL;DR -- treat it with respect. As you'll see in the photos below, the GRP is breakable. It's not designed to bear weight directly -- in other words, it's not intended to be used in lieu of the load floor; the load floor needs to be left on top of it. The i3's load floor is a good half-inch thick, but not entirely rigid, meaning heavy items being transported in the main cargo area will press down on the center of the WTE. I've loaded mounted car tires in the 50 pound range on top of it with no ill effects.  Planning to carry stacked sacks upon sacks of dry concrete mix? I'm not so sure that's prudent.

Additionally, there's no way I'd willingly turn this car in to BMW service with the WTE installed if I thought they'd need access to the motor bay. A heavy handed yank of the flat top while removing could lead to a break, right down the center, and an unprotected Trunk Extension sitting on the floor of the service bay, waiting to be tripped over, doesn't bode well with me. Thankfully, it lifts out easily with the removal of 9 screws, and the original motor cover can be swapped back in.

Lastly, with respect to durability, the beautiful glossy finish is prone to cosmetic damage, as you'll see in some of the photos below. I've chosen to line the compartment with useful items to keep scratches at bay. I'd like to see Wokeby use better protection during shipping, and I recommend replacing the stock BMW engine cover screws & washers with something more forgiving (I chose M5 x 16mm EPDM washers). 

One final aspect deserving mention is the acquisition of the WTE. Wokeby accepts bank transfers for payment -- no PayPal or credit cards. This sort of international purchase may cause pause for some. Although my banks and credit unions all offer international bank transfers and currency conversion, the best deal for me was using Xoom, a PayPal service, with a $5 transaction fee. Obviously, you'll need to factor in the current exchange rate to figure out your actual cost. 

Shipping -- or shall I say patience - is another matter. My experience may have been atypical, as it was shipped leading into the holiday rush. It initiated with DHL, who handed it off to USPS. The fist shipment took 25 days. The second, 53 days. There appears to be a hang up upon reaching the US, where it passes through customs. The box is so large you may not be able to fit it in your i3 if you're picking it up from the Post Office.

Considering that the Wokeby Trunk Extension represents the equivalent of an additional car payment (give or take), it's difficult to make a blanket case for installing it without knowing that the modest amount of added space is going to be put to good use. But I can say with certainly that this part is thoughtfully designed, well made, pleasing to look at, and matches the overall design ideals of the i3. And it's portable -- either to your next i3, or to eBay, should you be finished with it.
It's not easy to grasp that this is only 8% of the cargo volume of the hatch. It's also not the simplest shape to express dimensionally, but if it's looked at in layers:

Top Layer: 13.75 x 13.75 x 2.5
Middle Layer: 13.25w x 9.5d x 8.75h
Bottom Layer (tire kit storage): 11.5w x 5.75d x 9.0h
Total Height to Rim: mid to top: 11.25; bottom to top: 20.5

The area on the right side of the motor bay is where the WTE sits, taking advantage of the space left vacant by the missing REX.

The bottom of the WTE is supported by the chassis crossmember. The kit includes a vibration-isolated mounting point, circled.
A sample of what I'm currently transporting in my WTE: BMW EVSE, tire repair kit, tool / bike rack pouch, bike locks, miscellaneous straps, sweat shirt & plastic bags (also used as scratch-prevention liners).

Here's all of that same clutter, nicely stashed.

The WTE is roughly similar total capacity to the i3 frunk, where I keep my daily use EVSE and a 50' cord.

The BMW tire repair kit gets a dedicated, custom-shaped space at the very bottom of the WTE to get it out of the way. (11.5w x 5.75d x 9h)

The rest of the items fill the remaining space in the tire kit layer, plus the middle layer, which combines with the top layer, where the two orange wedges are sitting. (mid: 13.25w x 9.5d | top 13.75 x 13.75 x 2.5h) In fact, the "tray" where the two orange wedges are sitting can be partitioned off with Velcro and a plastic divider to separate it from the abyss of the main compartment; Wokeby intended it to hold roadside safety triangles. The dimensions of this "tray" are 15 5/8 x 4 1/8.

An oblique look at how the three layers are organized.
GRP, or glass reinforced plastic, aka fiberglass.

The GRP is 3mm thick around the perimeter flange.

The i3's cargo area load floor is 1/2" thick and has some flex to it, but has been adequately supportive of 50-pound loads I've carried, with no ill effects to the WTE. I wouldn't hesitate to sit or kneel right in the middle of all this, but would still recommend caution carrying something super-heavy.

The underside of the i3's cargo floor has a 3/8" (~10mm) layer of foam -- similar to carpet padding -- that doesn't provide any additional strength, but should help to spread point loads out a little.

The glossy finish is prone to scratching. Just a few days installed using BMW's hardware and I found this marring under the washers. I ordered up some M5x16mm EPDM washers (eBay, from a German seller) to soften the contact. These should be installed with new M5x25 screws, because the washers are difficult to remove from the stock BMW screws. Save the BMW screws with the engine cover.

As a point of comparison, here's the damage the BMW washers do to the stock stainless steel motor cover panel.

The 16mm EPDM washers are just a millimeter larger than the stock BMW washers.

Each fixing point on the i3 is fitted with a rubber pad which the WTE sits upon.

Because of the taller stack height of the EPDM washers (4mm) vs. flat washers (<1mm), I ordered thin head M5x25 stainless steel wafer head screws (eBay, from China) to keep dimensions close to stock. These screws have a 3mm hex head (Allen head screw) rather than the star-shaped Torx head found on the stock BMW fasteners. That's fine; they call for a very low installation torque.

Side-by-side stack height comparison of the stock BMW cap-head screw and flat washer, 5mm (left), uncommon wafer-head screw and EPDM washer, 5mm (center), and a common button head screw + EPDM, 7mm.

After all that, you need not stress too much about the stack height of the screws. The 10mm foam padding on the bottom of the load floor has cutouts for each fixing location, so I don't believe there's truly a clearance issue. But if new screws are being installed, may as well do it right.
The GRP is not impervious to damage. This spiderweb crack is damage sustained during shipping, and occurred in two corners. It's only "skin deep" and is not easy to see (or to photograph) unless at the right angle with the right light. Wolfgang Kern has assured me this does not affect the structural integrity of the WTE. But it does show that the Trunk Extension must be handled with respect.

This is the first WTE I received. Somewhere in the USPS system (I'm presuming US Customs), it was smashed into three pieces, and completely re-boxed. Wokeby shipped out a replacement ASAP. After seeing this, I'm not eager to let an auto mechanic touch my Trunk Extension.

The Post Office "owned up" to the damage and left this note inside the box, but jumping through their claims process was an ordeal.

I wasn't exaggerating, the box the WTE ships in is huge. This isn't even the original box -- this is the smaller-sized reboxed-box that the Post Office shuffled the smashed pieces of my first Trunk Extension in to. I seriously don't believe the original box would fit in the car.
eNate said:
As a point of comparison, here's the damage the BMW washers do to the stock stainless steel motor cover panel.
Our 2014 U.S. BEV has a CFRP motor cover panel. It's probably a bit thicker than the stainless steel cover. Wonder why BMW made this change.

Thanks for the very detailed review! Unfortunately, the shipping cost to Honolulu would be prohibitive for such a large box.
alohart said:
...Unfortunately, the shipping cost to Honolulu would be prohibitive for such a large box.

What surprised me is the relatively reasonable shipping cost -- it was the first question I asked, assuming it would be prohibitive for such a bulky international package! A: "The price for shipping to the US no matter where is €54." Now, I should know better than to put a number there because prices go up and exchange rates fluctuate, but that's not such a bad price.
Since about a week, I've installed the 'trunk extension'. I did notice the piano finish is quite scratch sensitive, but then again, this is a storage compartment under the floor of the boot. The past week I've noticed how nice it is; no more loose cables flying about in the boot or getting wet/dirty in the 'frunk'.

I'm happy with it, it's not cheap, but the car isn't either.
tliet said:
... the piano finish is quite scratch sensitive, but then again, this is a storage compartment under the floor of the boot. ...

True, true. But it's also easy to line it with a trash bag for a little protection, and trash bags come in handy from time to time to contain grimy items or... hold trash?

I noticed a selection of inexpensive lightweight cotton laundry bags that might act as a nice liner. I get your point about this bin being out of sight, but it's not too much hassle to try to keep it looking nice.
I came across a spare random dry cleaners laundry bag stashed in a desk drawer at work. It's 22 inches wide and 28 inches in height, and made of a medium-weight nylon. So not necessarily soft to the touch like cotton, but potentially heavy enough to prevent any pointy edges from scratching the Trunk Extension.

Good news is that this size seems fairly on-target as being ideal, placed over the tire repair kit. Bonus is that it's really easy to lift all the random items out in one heave and keep them contained, and for the most part they go back in in the same manner.

So if you have or are planning on getting a Trunk Extension for your BEV, add a laundry bag to your shopping list -- not just for the scratch protection, but for added utility!

eNate –

Great writeup, thank you for the extensive pictures! (and hoping they're hosted somewhere that won't go offline in a year or two)

Love the design, but a piano black finish? An odd choice for a vehicle's storage compartment.
Mine has been holding up just fine and I use it daily. Very valuable space to have available. I emptied it a few weeks ago and didn't spot any structural or finish issues.

BTW I noticed my photos are not displaying on most browsers due to recent changes in how photos hosted on websites without security certificates are handled. The pics are still there if you have an old copy of Explorer, or if you click on the individual broken photo icons are open in a new tab. I'll have to work on getting a security certificate and editing my photo links.