Wheels & Tires

[Snick]

Snick, you obviously missed why I said I wanted certain tyres. You are quoting basic physics without giving a meaningful answer (you missed out the significance of 9 x root P, btw).

I do understand how tyres work! I compete in on and off road trials (read all surfaces including wet grass and mud) on 145 section crossply tyres in that car, which weighs considerably less than the design weight of the Elio and has just 40 bhp. I also drive another road car that weighs five times as much and has six and a half times as much power and is fitted with very wide run flats (BMW M Sport saloon). I have also been riding motorcycles since 1967. So I do have a good understanding of tyre requirements, especially traction.

Again I ask of you, what size and type of tyres do you expect to be fitted by Elio? Posted my best guesses earlier up in this thread.

Irrespective of the fact that the Elio is classed as an auto cycle it makes little sense to fit motorcycle tyres to any car. The vehicle doesn't roll into turns so during cornering the lateral forces on the tyre are far higher than on a bike. Never said anything about motorcycle tires, did I? That would be really silly.

Round profile motorcycle tyres wear out very quickly on a car, they run on the apex so another disadvantage is that the handling is skittish. You waste rubber because the middle of the tread reaches minimum thickness while almost full tread depth remains on the shoulders. Again, don't put words into my posts, please.

Been there, done that. The only way to improve the grip is to run low pressures, which causes tyre heating so you waste fuel and performance. I disagree that lowering tire pressure is the "only" way. Tire compound makes a massive difference to handling and FE. "Right-sizing" the tire to begin with and getting tire factors inside the correct parameter envelope also helps tremendously, especially in adverse weather conditions.

Expand the quote above for my specific responses in orange text.

goofyone may be right after all, we will see. Maybe EM will grab some excessively wide tires - I dunno. Only father time will tell. I posted my best guesses based on the 6 items of my post above, not on my "feelings".

 

[wheaters]

Here's myself and one of my sons in my home built getting the best out of our tyres. Note the previous tyre marks finish a little below where we got to. The section Marshall had got used to cars stopping some distance from the top of the section, so he had to run after us to mark our progress.

 

[wheaters]

Expand the quote above for my specific responses in orange text.

I did that. I wasn't putting any words in your mouth. My post #66 explains why I mentioned motorcycle tyres. If you go narrower than 145 there is limited tyre choice other than those designed for motorcycles, which would not be ideal for the Elio. I explained why.

 

[Snick]

I did that. I wasn't putting any words in your mouth. My post #66 explains why I mentioned motorcycle tyres. If you go narrower than 145 there is limited tyre choice other than those designed for motorcycles, which would not be ideal for the Elio. I explained why.

Okay, thank you for that clarification. I guess I am saying that Elio Motors will have a hard time indeed hitting the FE goals if they insist on sourcing an existing tire > approximately 90 mm section width.

 

[wheaters]

I'd agree. My point was that I'd rather lose a little of that very ambitious mpg target than lose out on handling and tyre life and have to buy special tyres at a silly price more often than ought to be necessary.

Btw, a couple of days ago I was contacted by another owner from our car club. He has many years of trialling experience and was asking advice about the tyres I use on my little car. His car has done far fewer miles than mine and still has the designer's supplied tyres and they finally need replacing after fifteen years or so (!). As part of our discussion, I measured the contact patch widths of the 145 / 5" cross ply tyres on my car. They actually measure only 97 mm!

 

[Snick]

I'd agree. My point was that I'd rather lose a little of that very ambitious mpg target than lose out on handling and tyre life and have to buy special tyres at a silly price more often than ought to be necessary.

Btw, a couple of days ago I was contacted by another owner from our car club. He has many years of trialling experience and was asking advice about the tyres I use on my little car. His car has done far fewer miles than mine and still has the designer's supplied tyres and they finally need replacing after fifteen years or so (!). As part of our discussion, I measured the contact patch widths of the 145 / 5" cross ply tyres on my car. They actually measure only 97 mm!

Are they over inflated? That is highly unusual for modern tire construction.

 

[wheaters]

These are not modern tyres, they are based on those fitted half a century ago, but with a more recent rubber compound. In UK they are known as cross plies, in USA you would call them bias belt construction.

I run them at just 18 psi, which is correct for the car. Reducing the pressure wouldn't make the tread any wider, this is moulded on at the factory.....

 

[Snick]

Okay, well that those tires aren't a good example for discussing the Elio's tires then, I'm afraid.

1. They're bias ply.
2. They're for hill climbing car.

I'm 99 percent certain the Elio will ride on steel belted radial tires, where the footprint width is usually within 85%-100% of the section width if the tire pressures are correct and meet manufacturer's recommendations for the vehicle load.


Your tire's footprint and pressure range is ...let's say...highly unusual, and not at all representative of what 99% of us drive with 99% of the time on roads.

I ran the math, and if your footprint section width is 97mm, your tire's footprint length for the quoted 1000 lb car must be 9.2cm. What diameter wheel, sidewall profile percent were they?

 

[Snick]

Okay guys, this is why I've been harping on tires -- I have been inputting the Elio's parameters into one of the most rigorous mpg estimation engines I could find. It is the one in my signature link called Road Load Calculator. Here is the copy/paste for the urban UDDP driving cycle:

Input Parameters

Curb Weight:1275 lb
Payload:250 kg
Drag Coefficient:.28
Frontal Area:9 ft2
Rolling Resistance Coefficient:0.008
Wheel Diameter:15 in
Rotation Factor:1.0
Grade0 percent
Air Density:1.2 kg/m3
Ave. engine efficiency:27 percent
Ave. drivetrain efficiency:93 percent
Ave. regen efficiency:0 percent
Fuel heating value:114132 btu/gal
Driving Cycle:UDDS


Energy Breakdown - UDDS Cycle

Total energy demanded at wheels:2483237.49 J (0.6898 kWh)
Consumed by Aerodynamic Drag:369121.46 J (14.86 %)
Consumed by Rolling Resistance:779137.50 J (31.37 %)
Consumed by Braking:1334978.54 J (53.75 %)
Distance traveled:7.45 miles
Gross efficiency:333.30 kJ/mile (0.0926 kWh/mile)
Gross thermal fuel economy (at wheels):361.04 mi/gal
Net fuel economy (engine 27%, drivetrain 93%):90.66 mi/gal
With regenerative braking at 0 percent:90.66 mi/gal
Time in Idle:241 sec
Time in Acceleration:544 sec
Time in Powered Deceleration:91 sec
Time in Cruise:109 sec
Time in Braking:384 sec
This accounts for 1369 of 1369 seconds in the cycle.


Plot
Key:
Velocities (bold green)
aero power (thin red)
rolling resistance power (thin black)
braking power (thin blue)
total power (thin gray)
inertia power (thin orange)
cumulative aero energy (bold red)
cumulative rolling resistance energy (bold black)
cumulative braking energy (bold blue)

Scale: 1 vertical square = 2 kW (power) or 0.2 MJ (energy) or 10 mi/hr. Time: 1 horizontal square = 20 seconds. Each square is 20x20 pixels.
Any values beyond the vertical extent of the chart are cut off.

Potential mi/gal on UDDS Cycle
The cells in the matrix indicate the potential fuel economy of this vehicle (mi/gal) as a function of average regenerative braking efficiency (horizontal) and average fuel-to-wheels efficiency (vertical). The fuel-to-wheels efficiency is the average efficiency with which fuel energy is converted to work and transmitted to the wheels. It includes the engine and drivetrain efficiencies. For anything powered by an internal combustion engine, only values well under 40% could be considered realistic.

Average efficiencies necessary for 84 mi/gal on UDDS Cycle
The cells in the matrix indicate the average engine efficiency necessary to achieve 84 mi/gal, as a function of average regenerative braking efficiency (horizontal) and average drivetrain efficiency (vertical). The drivetrain is the portion of the powertrain downstream of the engine output. For a conventional vehicle, the engine efficiency is the average efficiency achieved in meeting the highly variable road load. Reasonable values would be significantly lower than the engine's peak efficiency. For series hybrid vehicles, an efficiency closer to the peak efficiency may be reasonable to consider, and the average drivetrain efficiency represents the efficiency with which energy from the engine is successfully delivered to the wheels - including, of course, the roundtrip efficiencies for any portion of that energy that passes through a storage medium on the way, such as a battery.

And here is the copy/paste for the highway driving cycle (HFET):

Input Parameters

Curb Weight:1275 lb
Payload:250 kg
Drag Coefficient:.28
Frontal Area:9 ft2
Rolling Resistance Coefficient:0.008
Wheel Diameter:15 in
Rotation Factor:1.0
Grade0 percent
Air Density:1.2 kg/m3
Ave. engine efficiency:27 percent
Ave. drivetrain efficiency:93 percent
Ave. regen efficiency:0 percent
Fuel heating value:114132 btu/gal
Driving Cycle:HFET


Energy Breakdown - HFET Cycle

Total energy demanded at wheels:2714933.67 J (0.7541 kWh)
Consumed by Aerodynamic Drag:1199533.75 J (44.18 %)
Consumed by Rolling Resistance:1072611.83 J (39.5 %)
Consumed by Braking:442788.09 J (16.3 %)
Distance traveled:10.26 miles
Gross efficiency:264.70 kJ/mile (0.0735 kWh/mile)
Gross thermal fuel economy (at wheels):454.61 mi/gal
Net fuel economy (engine 27%, drivetrain 93%):114.15 mi/gal
With regenerative braking at 0 percent:114.15 mi/gal
Time in Idle:4 sec
Time in Acceleration:338 sec
Time in Powered Deceleration:193 sec
Time in Cruise:126 sec
Time in Braking:104 sec
This accounts for 765 of 765 seconds in the cycle.


Plot
Key:
Velocities (bold green)
aero power (thin red)
rolling resistance power (thin black)
braking power (thin blue)
total power (thin gray)
inertia power (thin orange)
cumulative aero energy (bold red)
cumulative rolling resistance energy (bold black)
cumulative braking energy (bold blue)

Scale: 1 vertical square = 2 kW (power) or 0.2 MJ (energy) or 10 mi/hr. Time: 1 horizontal square = 20 seconds. Each square is 20x20 pixels.
Any values beyond the vertical extent of the chart are cut off.

[Broken External Image]


Potential mi/gal on HFET Cycle
The cells in the matrix indicate the potential fuel economy of this vehicle (mi/gal) as a function of average regenerative braking efficiency (horizontal) and average fuel-to-wheels efficiency (vertical). The fuel-to-wheels efficiency is the average efficiency with which fuel energy is converted to work and transmitted to the wheels. It includes the engine and drivetrain efficiencies. For anything powered by an internal combustion engine, only values well under 40% could be considered realistic.

Average efficiencies necessary for 84 mi/gal on HFET Cycle
The cells in the matrix indicate the average engine efficiency necessary to achieve 84 mi/gal, as a function of average regenerative braking efficiency (horizontal) and average drivetrain efficiency (vertical). The drivetrain is the portion of the powertrain downstream of the engine output. For a conventional vehicle, the engine efficiency is the average efficiency achieved in meeting the highly variable road load. Reasonable values would be significantly lower than the engine's peak efficiency. For series hybrid vehicles, an efficiency closer to the peak efficiency may be reasonable to consider, and the average drivetrain efficiency represents the efficiency with which energy from the engine is successfully delivered to the wheels - including, of course, the roundtrip efficiencies for any portion of that energy that passes through a storage medium on the way, such as a battery.

As you can clearly see, tire rolling resistance drag is the 2nd most drag on the Elio! Tire rolling resistance will be THE "alpha factor" for your mpg (because there are almost no gains to be had on aerodynamic and braking. It will NOT be subtle, it will be significant.

Also, with the bottom 1/3 of the tire unfaired every gain in width is an increase in aerodynamic drag, much more so that raising the roof because of the high turbulence and crummy form factor.

I do see your point about the overall cost. I just wonder how they will hit anything near the mpg goals with wide tires. As we all know, gasoline cars fair far worse in the "real world" than these models suggest. Gasoline cars almost never live up to their mpg claims becuase of throttling losses at partial loads and most drivers habits of jack-rabbit driving style.

 

[wheaters]

Okay, well that those tires aren't a good example for discussing the Elio's tires then, I'm afraid.

1. They're bias ply.
2. They're for hill climbing car.

I'm 99 percent certain the Elio will ride on steel belted radial tires, where the footprint width is usually within 85%-100% of the section width if the tire pressures are correct and meet manufacturer's recommendations for the vehicle load.


Your tire's footprint and pressure range is ...let's say...highly unusual, and not at all representative of what 99% of us drive with 99% of the time on roads.

I ran the math, and if your footprint section width is 97mm, your tire's footprint length for the quoted 1000 lb car must be 9.2cm. What diameter wheel, sidewall profile percent were they?

Sorry, but I think you haven't understood my original posts. These tyres are definitely not hill climbing tyres, they are Avon Tourist road tyres, as I have already explained they are 5" x 16". They were chosen as a compromise, from a very limited catalogue, to replace the unsatisfactory motorcycle type recommended and supplied when I bought my car.

As I keep trying to get across, I'm obliged to use cross plies only because there are very few car radials available in a suitably narrow section. The ones that are available are highly expensive racing tyres for classic/vintage cars and they cost upwards of 300 dollars each and are not necessarily road legal.

The only other option is to use round profile motorcycle tyres, which, as I have already said, aren't suitable for a car for a number of reasons. To put this in perspective, the original original m/c tyres I had on the car lasted just 6,000 miles! On my other cars I can get four or five times this mileage and replacements cost far less.

Irrespective of what the theory books say, if the tyres you need aren't manufactured you have to use something else or pay a high price. Make no mistake, I'd much prefer to use modern radials because in general they perform better, especially off-road, and these days they generally cost far less than cross plies. Unfortunately, very few radials are manufactured in narrow sections (i.e. 145 or less) because for many years the trend has been to use increasingly wide tyres. If you don't believe me, simply try searching online and look at the prices charged.

It will be interesting to see how Elio overcome this issue. They might well have to get a one-off tyre manufactured and from personal experience, that is likely to come at an unreasonably high price for the car owner.

Again, back to my original point, which was merely:

I'd prefer, for economic and practical reasons, to fit a wider, more widely available size of tyre than the theory books might suggest would be needed to achieve Paul Elio's very optimistic mpg figure, and sacrifice a few mpg rather than sacrifice handling and tyre wear rate and pay through the nose every time I visit the tyre shop.