Why Three Wheels?Posted by dave-hoder on October 12, 2022 at 3:59 pm
Maybe a dumb questions but the only answer I could find was rolling resistance. Wouldn’t putting 2 narrower tires together (same rolling resistance) make it 4 wheel and eliminate any helmet or tax credit issues? What are the rules that would change it from an autocycle (or whatever it’s called) into a car if it follows automotive safety regulations?
Sorry if this has been asked before but I couldn’t find the answer.
- 22 Replies
- MemberOctober 12, 2022 at 4:23 pm
My guess is that its a combination of efficiency and using hub motors. If they were to use two rear wheels, they might need to have some sort of shared motor and drivetrain for the rear wheels. This would add complexity and weight to the vehicle. Even if it was just a front wheel drive unit, the extra rear wheel would add resistance and weight.
- MemberOctober 12, 2022 at 4:36 pm
Efficiency is one aspect, but there is another rather LARGE issue. When you have four wheels, you legally have a car and have TONS of rules and regulations that you MUST comply with. All of those regulations cost lots of time and hundreds of millions of dollars to design, test and certify before you can sell the vehicle. This greater cost is a huge barrier for startups like Aptera. Yes, there are four-wheel startups like Rivian, but those vehicles also cost 3x to 4x what Aptera plans to sell for.
Once Aptera is established and has the cash flow, they intend to enter the 4 wheel market too, but that is sure to be years down the road. Meanwhile, we have a really cool and ultra-efficient vehicle to drive around.
- MemberOctober 12, 2022 at 4:56 pm
Yes it was discussed before. No conclusion was drawn whether making the rear wheel a dually will make it a “car” and subject to car regulation for NHTSA, or will make it satisfy the “four wheels” requirement for IRS. To make the effort worthwhile, a dually rear-wheel aptera would ideally be still seen as autocycle in the eyes of NHTSA, but would be counted as having “four wheels” in the eyes of IRS.
- MemberOctober 13, 2022 at 7:06 am
Hmmm <Checks TireRack and finds 125/70-SR16 with same overall diameter and wonders if can find a slender rim and a dually of that fits inside the rear pants, then removes after getting tax break>
- MemberOctober 13, 2022 at 7:28 am
The only advantage of being considered an autocycle by NHTSA is to eliminate the need for crash safety tests but it causes licensing problems at the state level and it also adds regulatory problems in the EU. Aptera has promised to meet the crash safety requirements for a car, that eliminates the one reason to have NHTSA treat it as an autocycle. I for one won’t buy one until they’ve passed the crash safety tests, I want a safe vehicle. At the state level many states and provinces lack autocycle laws which means that you need a motorcycle license to drive one. My state, Massachusetts, is in that group. I can’t buy an Aptera until either the state passes an autocycle law or Aptera adds a fourth wheel. In the EU there is a width regulation for motorcycles that the Aptera violates, if it had a fourth wheel it wouldn’t have a problem. Legislatures move very very slowly, engineers move much faster, they could add a fourth wheel in less time then it will take the various legislatures to pass autocycle laws.
- MemberOctober 13, 2022 at 10:03 am
Biggest issue I see with adding a 4th wheel is the requirement for front and rear bumpers. They would totally ruin the aerodynamics.
- MemberOctober 14, 2022 at 4:24 am
Three wheels to avoid safety tests? How can I explain this to my loving wife?
- MemberOctober 14, 2022 at 5:49 am
Avoids decades of big auto lobbying that makes it harder for new companies to come into the market.
- MemberOctober 14, 2022 at 6:20 am
From the beginning of APTERA’s development it was to make the most efficient manufacturable vehicle ever made. Along with aerodynamics removing the 4th wheel was key, aside from added weight, a 4th wheel is also added friction.
As far as safety goes, APTERA has a thick roundish composite body (egg shape), this allows for a natural benefit of being in a roll cage. APTERA will also subject the vehicle to US standards of crash testing, many will be waiting for these test results before completing their purchase. APTERA has already claimed through computer simulations that safety of this vehicle will not be a compromise.
- MemberOctober 14, 2022 at 9:51 am
Dave, besides the 25% less rolling resistance, the shape with only a center rear wheel allows much less air drag, it also evens out the weight distribution per wheel for better handling and traction. This makes the all wheel drive version perform very well in all weather conditions.
- MemberOctober 14, 2022 at 2:50 pm
Rolling resistance, weight, and aerodynamic difference would be negligible with two narrow (dual) tires taking the same space as the wider single I would think. The laws seem pretty gray and outdated from what I could tell but making it a car would solve a lot of issues it seems.
- MemberJanuary 22, 2023 at 9:12 pm
I really admire a lot of the design and engineering decisions Aptera made. Instead of simulating a box with a combustion engine in front of it (like most electric cars out there and being developed presently) to redesign a car to optimize aerodynamics also considering the lower half of the car. I was a fan of in wheel electric motors after I read about PML’s Mini QED more than 15 years ago. Using solar to supply the daily range is great especially if one can not park one’s car next to an outlet as is true in many urban situations. Also using light weight construction based on composite materials is very admirable.
The main issue I have with Aptera is its width (and there is an entire discussion devoted to it but mostly ignored by the company). It is basically a consequence of the decision to design a three wheel vehicle and to produce a vehicle with sufficient stability against centrifugal force. This weeks presentation of gamma stated that Aptera will stick with the three wheel design also in the future. That width will make that vehicle completely impractical in urban spaces (not only in Europe) but also in many tighter off road situations. I see Aptera presentations showing suburban neighborhoods and driving up Torrey Pines Road (I lived there once) where width is not an issue.
So what are the technical reasons to insist on the three wheel design? Of course one saves the weight of one wheel (and motor). The rolling resistance will be less. I was reading that rolling resistance in a standard car is 20% of the energy usage without giving any specifics. Is Aptera optimized for rolling resistance by using standard tire width but having significantly lower body weight? I would be very interested to understand more how much rolling resistance plays a role.
Is a three wheel design more aerodynamic? Aptera has a very good drag coefficient with 0.15 (or 0.13). Most cars are not very good but remember EV1 which had 0.195 better than anything one can buy today. The drag coefficient is equally a factor of aerodynamic resistance as the front surface area. So having the front wheels distant from the main body is an increase in area compared to being integrated to the main body. I assume one of the main reasons for that low drag coefficient is that the underside is not flat like in most other cars but sweeping up. Why could one not design a car with 2 back wheels similar to the present back fin but keeping the basic underbody design? That reminds me of an aerodynamic design model I saw form ETH Zürich.
- MemberJanuary 23, 2023 at 11:07 am
Most US non-cities are designed around the average American vehicle; most popular vehicle by product volume is a Ford F150. Aptera width would be widely supported due to the large number of large trucks on US roads.
I listened to Engineering Explained today regarding the Mercedes EQXX (https://www.youtube.com/watch?v=8kY7BGGtDeY); his or maybe Mercedes conclusion was that once you approach a CD ratio of 0.16 or less you no longer look like a typical car. Aptera needs to hit a niche of people who either: dont want a car looking car or care only about efficiency. So, it seems they are doing that first; then once they are known for their “spaceship” or “mako” three wheeled car they will then design and produce additional form factors. I do love the lightyear 2 for its reasonable aero with higher seating capacity; but they are going after a different audience than Aptera. That said, if Aptera makes a 4 door sedan I may swap my reservation over to Aptera if its more efficient.
- MemberJuly 2, 2023 at 10:54 am
Why not put an additional wheel on the back?
It might not be the ultimate in efficiency, but it might win us some government funding!
- MemberJuly 2, 2023 at 12:08 pm
My understanding is that aside from the physics reason for choosing three wheels vs four there was the cost of regulatory compliance. I vaguely recall a Sandy Munro video from a couple of years ago where he claimed that the cost of compliance for a car is vastly higher than the cost of compliance for a motorcycle. As it turns out there are serious costs for not being a car as well. The biggest is not being eligible for credits and rebates, but there are other costs such as the vehicle requiring a motorcycle license in states that don’t have autocycle laws. While the US has very few motorcycle regulations that’s not true everywhere. In Europe the Aptera is too wide for a motorcycle, they have regulations which are aimed at sidecars which were never a thing in the US but were in Europe. Width is a good thing for a vehicle like an Aptera because it makes it more stable, it’s a bad thing for a side car where it increases the stress on the connection between the sidecar and the motorcycle. BTW I’m guessing about the sidecar reasoning because the only ones I’ve ever seen are in WWII movies where the Nazi’s on motorcycles always end up in a ditch.
- MemberJuly 2, 2023 at 12:50 pm
Joshua, it is interesting that you mention motorcycles with sidecars since here in Prescott, there is a used vehicle dealer that seems to specialize in them. It is called “Scooter and Auto Source”.
- MemberJuly 3, 2023 at 12:47 am
Why 3 wheels?
Aerodynamics, aerodynamics and aerodynamics.
- ModeratorJuly 3, 2023 at 7:17 pm
In 1886, the first car had three wheels (Karl Benz’s “Patent-Motorwagen” ) because that was enough.
Adding equipment for regulations, without adding a technical feature that forms some sort of the basis of that regulation, is bad engineering (imho). The federal tax rebates were made to help employ Americans (voters), or at least North Americans, and Aptera would not score high by that measure … not yet, anyway.
- MemberJuly 4, 2023 at 1:16 am
Partly I think it is also to protect the big domestic manufacturers from competition (both international and from startups). In the days when the WTO had teeth, these rebates would not have been possible.
- MemberJuly 4, 2023 at 5:58 am