Tesla Semi

[jerry33]

It looks like single wide rear tires on the semi,
View attachment 265530
Tesla Semi prototype spotted driving in broad daylight
With dual mount tires you have to check daily for stuck rocks or object between them, the single could be an advantage.

That's correct, but it's very uncommon on highway trucks. Gravel and logging trucks are more likely to have a stone between the duals. Also some jurisdictions believe that single tires are harder on roads so they derate the gross axle weight by 1000 kg or so. As far as I know, the only time duals do less damage than singles is if the tire pressure on the duals is 100% perfect all the time. Drivers often don't like singles because they have to stop and have the tire changed right then. Of course, driving on only one of the dual tires causes massive amounts of road damage--far more than would ever be caused by the difference between perfectly inflated duals vs. singles.

In my opinion, the reason "duals do less damage than singles" is suspect stems from the way the force from the load is transferred to the substrate. Roads are constructed in layers. Typically pavement, coarse gravel, fine gravel, sand, native soil (varies depending upon available materials and the local native soil--it might be rock or it could be something that's just one step up from mud). Each layer has a different angle of repose (the angle that the material would naturally stack at without collapsing), so a properly designed and constructed road has no more force at the native soil level then the native soil can support (ideally less). With duals the cone of force transfer from the two tire contact patches overlaps very quickly doubling the force from the overlapping parts. Of course a road could be designed so that it would not be damaged by one of the duals failing, but that would increase costs by a non-trivial amount.

 

[mongo]

With duals the cone of force transfer from the two tire contact patches overlaps very quickly doubling the force from the overlapping parts.

Not sure I follow. Each dual tire is only about half the load a single would be, so the force is not double (overall) at the convergence. If all tread contact is a uniform force, the points between tires would be a little less total force (spread force from tires) than the points directly below the tire (force spread from both tire edges, plus vertical load). At least at a certain depth.

 

[LCR1]

I think the New Mexico one solved the issue there, the stockton one isn't happening. Tesla Pulled the permits over a year ago and the project was killed last week.<===Moderator: Please do not use this forum to make definitive and provocative statements like that one without being able to cite chapter and verse. As far as this forum goes - cf the Ft Stockton SpC thread - no one has reported what you write here.

Then you need to moderate your own forum where the original information was posted and cited from some Tesla representative. If the info in the Fort Stockton thread is so horribly wrong go moderate that so people quit quoting it.

 

[neroden]

It looks like single wide rear tires on the semi,
View attachment 265530
Tesla Semi prototype spotted driving in broad daylight
With dual mount tires you have to check daily for stuck rocks or object between them, the single could be an advantage.

I think they're going to have to do some design changes to make it possible to change the tires.... I don't see how you remove the wheel skirts to get at the lugnuts!

 

[AudubonB]

Not a problem - just provide the reference.

 

[dhanson865]

It looks like single wide rear tires on the semi,
View attachment 265530

With dual mount tires you have to check daily for stuck rocks or object between them, the single could be an advantage.

They had both style tires at the reveal, one semi with each showing how it would look with either. I'm sure it'll be a configuration option that each buyer can choose to have it either way as they prefer.

 

[dhanson865]

Not a problem - just provide the reference.

If that is a response to LCR1 you might want to use the quote feature, it's not clear who you are speaking to.

 

[dhanson865]

I think the New Mexico one solved the issue there, the stockton one isn't happening. Tesla Pulled the permits over a year ago and the project was killed last week.<===Moderator: Please do not use this forum to make definitive and provocative statements like that one without being able to cite chapter and verse. As far as this forum goes - cf the Ft Stockton SpC thread - no one has reported what you write here.

I wondered what the deal was so I went and looked. It appears you are referring to messages #294 to #298 on Supercharger - Fort Stockton, Texas

which culminates with this quote

As many of us had surmised, the original location for the Fort Stockton Supercharger fell through and Tesla has been actively searching for a new site in Fort Stockton (or immediate area).

If anyone knows of a landowner in the Fort Stockton area "who would be interested in hosting and have a property that would be a suitable location for a Supercharger station," Paul Luna at Tesla would like to get in touch with them. Please send their contact information to Paul. He is pluna on the tesla.com domain.

I have no idea if that quote is valid but quoting it in your post or linking back to the post in question might have helped to smooth things.

 

[AZ Desert Driver]

It looks like single wide rear tires on the semi,
View attachment 265530
Tesla Semi prototype spotted driving in broad daylight
With dual mount tires you have to check daily for stuck rocks or object between them, the single could be an advantage.

I don't recall ever seeing a truck with skirts that dragged the ground like I see in this photo. It is common and I just never noticed?

 

[SwTslaGrl]

I don't recall ever seeing a truck with skirts that dragged the ground like I see in this photo. It is common and I just never noticed?

I haven't seen it, but it could be tests collecting data for a future customer option. For example the skirts could reduce road noise by a few db from a passing semi.

 

[jerry33]

Not sure I follow. Each dual tire is only about half the load a single would be, so the force is not double (overall) at the convergence. If all tread contact is a uniform force, the points between tires would be a little less total force (spread force from tires) than the points directly below the tire (force spread from both tire edges, plus vertical load). At least at a certain depth.

The contact patch area equals the load on the tire divided by the inflation pressure. However, the load on each square area of the contact patch is not equal. A large single has a more uniform loading over the contact patch than does each of the dual tires. This is mainly due to the extra stiffness of the belts in the large single and the reduction in stiffness of two sidewalls compared to four. The loading that really counts is the loading on the native soil where dual tires have a considerable overlap, so not only is there more loading there, but it's less even because there are more overlap/non-overlap areas. It's the overlap area that has a double loading. A large single tire avoids this.

 

[jerry33]

I don't recall ever seeing a truck with skirts that dragged the ground like I see in this photo. It is common and I just never noticed?

Not common. It's presumably for wind resistance. This isn't practical in trucks today because brake cooling will be very bad, however, when the braking is mainly done by the motors, it's shouldn't be much of an issue.

 

[mongo]

The loading that really counts is the loading on the native soil where dual tires have a considerable overlap, so not only is there more loading there, but it's less even because there are more overlap/non-overlap areas. It's the overlap area that has a double loading. A large single tire avoids this.

Agree on the lateral variation.

For clarification, are you saying the load is highest in the center of the tire/ gap, or that the gap causes the load to be double?

I agree that, when deep enough, the loading is maximized in the center of the wheel set due to having the most load points within the angle of dispersion. Above that level, there is less loading in the gap region than the tire region (less points to impose loading). Similar to starting with a single wide tire and removing the middle, it unloads the area below the removed section.

Ran a low quality simulation on a spreadsheet program. Starting with 4 points value 1, 4 points 0, 4 points 1. Next column, each cell value is sum of the three closest previous cells/ 3. Repeat for a while. Starts with all load under the tires in two regions. The deeper it goes, the less the average loading and the less peaky the tire loads become (tire loads blend into the gap).

 

[jerry33]

Agree on the lateral variation.

For clarification, are you saying the load is highest in the center of the tire/ gap, or that the gap causes the load to be double?

I agree that, when deep enough, the loading is maximized in the center of the wheel set due to having the most load points within the angle of dispersion. Above that level, there is less loading in the gap region than the tire region (less points to impose loading). Similar to starting with a single wide tire and removing the middle, it unloads the area below the removed section.

Ran a low quality simulation on a spreadsheet program. Starting with 4 points value 1, 4 points 0, 4 points 1. Next column, each cell value is sum of the three closest previous cells/ 3. Repeat for a while. Starts with all load under the tires in two regions. The deeper it goes, the less the average loading and the less peaky the tire loads become (tire loads blend into the gap).

That's correct. Let's see if I can run this through one more time. A perfect contact area would have the load identical at every point in the contact area. This would match up exactly with your simulation. The beetles in the pudding are that the contact area is not evenly loaded (of course, far more even in a radial tire than in a bias-ply tire). In dual tires, each contact area is less even than in a large single. At the intersection of the native soil and the pavement bed the load needs to be less than the bearing capability of the soil and as even as possible.

Getting the load to be less than the bearing ability of the soil is very difficult to achieve with dual tires because each tire is not evenly loaded, and the contact area on each tire is less evenly loaded than the contact area of a large single tire. (Note that the drainage slope of the road means that dual tires which are evenly inflated and have the same tread depth still don't have equal loads. Trucks could be built with each tire independently sprung which would solve this issue but it would be very expensive and very complex. An alternative would be to have a system that measures the load on each tire and adjusts the pressure accordingly. This would also be very complex and would have to take into account thermal equalibrium.) The distance between the centre of each dual tire means there are two cones transferring load with the resulting overlap.

Given a deep enough road bed the unevenness can be eliminated to the point where it no longer matters as your calculations indicate. However, that would add cost to road construction, so roads tend to be made "just good enough less whatever the contractor can get away with". There is some justification to the "just good enough" philosophy because floods, earthquakes, etc. can destroy any road regardless of how well it's built but the outcome is that trucks with duals in practice damage the road more than trucks with singles and the roads need constant maintenance.

Interestingly, the basics of road construction haven't changed since Roman times, but the Romans had it much easier because the loads were much lighter which is why there are some Roman roads in good condition today.

 

[mongo]

That's correct. Let's see if I can run this through one more time. A perfect contact area would have the load identical at every point in the contact area. This would match up exactly with your simulation. The beetles in the pudding are that the contact area is not evenly loaded (of course, far more even in a radial tire than in a bias-ply tire). In dual tires, each contact area is less even than in a large single. At the intersection of the native soil and the pavement bed the load needs to be less than the bearing capability of the soil and as even as possible.

Getting the load to be less than the bearing ability of the soil is very difficult to achieve with dual tires because each tire is not evenly loaded, and the contact area on each tire is less evenly loaded than the contact area of a large single tire. (Note that the drainage slope of the road means that dual tires which are evenly inflated and have the same tread depth still don't have equal loads. Trucks could be built with each tire independently sprung which would solve this issue but it would be very expensive and very complex. An alternative would be to have a system that measures the load on each tire and adjusts the pressure accordingly. This would also be very complex and would have to take into account thermal equalibrium.) The distance between the centre of each dual tire means there are two cones transferring load with the resulting overlap.

Given a deep enough road bed the unevenness can be eliminated to the point where it no longer matters as your calculations indicate. However, that would add cost to road construction, so roads tend to be made "just good enough less whatever the contractor can get away with". There is some justification to the "just good enough" philosophy because floods, earthquakes, etc. can destroy any road regardless of how well it's built but the outcome is that trucks with duals in practice damage the road more than trucks with singles and the roads need constant maintenance.

Interestingly, the basics of road construction haven't changed since Roman times, but the Romans had it much easier because the loads were much lighter which is why there are some Roman roads in good condition today.

I agree with all that, perhaps I am just misinterpreting what you meant by doubling.

With duals the cone of force transfer from the two tire contact patches overlaps very quickly doubling the force from the overlapping parts.

The cones of force merge in an additive way for twice the loading, but that force is only the dispersed force, it is not double of the peak load located directly under the tires.
In other words, at the depth where the cones intersect, the load is higher than at shallower levels, but at any depth, the region under the gap has a lesser load than the region under the tires.

Interesting point regarding the interplay of tire pressure vs total load per tire. Doesn't impact road surface so much, but does alter ground loading.

 

[jerry33]

I agree with all that, perhaps I am just misinterpreting what you meant by doubling.

The cones of force merge in an additive way for twice the loading, but that force is only the dispersed force, it is not double of the peak load located directly under the tires.
In other words, at the depth where the cones intersect, the load is higher than at shallower levels, but at any depth, the region under the gap has a lesser load than the region under the tires.

Interesting point regarding the interplay of tire pressure vs total load per tire. Doesn't impact road surface so much, but does alter ground loading.

That's it.

 

[RobStark]

 

[BioSehnsucht]

Watching that Toyota fuel cell semi video, the time lapse of them building it, feels like they were pretty much just winging it without doing their homework, they spent so much time wiggling things around slightly to make them fit, and the cables going just all over the place ...

Did they not lay this out in CAD before hand? It may be just a prototype, but if I'm building a fuel cell vehicle of any kind, I'd like to have already figured out exactly where all my wiring and so on is going before I even start laying it out in real life ...

The speed comparison gave me a chuckle. I'm sure someone can figure out the math on the acceleration from the video, based on measuring pixels or whatnot, clearly they are trying to reference the animation from the Tesla Semi reveal, but also, clearly, that was not a quarter mile or 0-60, not nearly a long enough distance covered.

 

[SwTslaGrl]

^So.. Toyota put fuel cells in the sleeper cab

 

[AZ Desert Driver]

That's correct. Let's see if I can run this through one more time. A perfect contact area would have the load identical at every point in the contact area. This would match up exactly with your simulation. The beetles in the pudding are that the contact area is not evenly loaded (of course, far more even in a radial tire than in a bias-ply tire). In dual tires, each contact area is less even than in a large single. At the intersection of the native soil and the pavement bed the load needs to be less than the bearing capability of the soil and as even as possible.

Getting the load to be less than the bearing ability of the soil is very difficult to achieve with dual tires because each tire is not evenly loaded, and the contact area on each tire is less evenly loaded than the contact area of a large single tire. (Note that the drainage slope of the road means that dual tires which are evenly inflated and have the same tread depth still don't have equal loads. Trucks could be built with each tire independently sprung which would solve this issue but it would be very expensive and very complex. An alternative would be to have a system that measures the load on each tire and adjusts the pressure accordingly. This would also be very complex and would have to take into account thermal equalibrium.) The distance between the centre of each dual tire means there are two cones transferring load with the resulting overlap.

Given a deep enough road bed the unevenness can be eliminated to the point where it no longer matters as your calculations indicate. However, that would add cost to road construction, so roads tend to be made "just good enough less whatever the contractor can get away with". There is some justification to the "just good enough" philosophy because floods, earthquakes, etc. can destroy any road regardless of how well it's built but the outcome is that trucks with duals in practice damage the road more than trucks with singles and the roads need constant maintenance.

Interestingly, the basics of road construction haven't changed since Roman times, but the Romans had it much easier because the loads were much lighter which is why there are some Roman roads in good condition today.

In a perfect world, every user of public resources pays exactly what he consumes. So a truck uses up the road resources faster than a car, and should pay more (per mile, per ton, per day, per some equilibrium denominator). Drilling deeper - if a dual wheel does more damage than a single wheel - it should pay more to the public bucket. Does any of this happen? Do dual wheels pay more than single wheels? Is the system anywhere close to fair?