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i3 makes local news

7K views 25 replies 8 participants last post by  A_Camera 
#1 ·
#2 ·
Apart from the headline, what makes you think that i3 was aquaplaning? I would have thought that with its skinny tyres it would have been safe.
 
#4 ·
9 times the square of the tyre pressure: 2.5 bars = 36 psi = 9 x 6 = 54 mph. Not many cars travel in the outside lane at less than 54MPH - and there is only so much that narrow tyres can do! It looks like the driver might have been a passenger for a while. I bet it gave the guy behind quite a shock as well.
 
#5 ·
9 times the square of the tyre pressure: 2.5 bars = 36 psi = 9 x 6 = 54 mph.
I have no knowledge here...but intuitively that looks like a random number generator...(even assuming square root ;))
What has tyre pressure got to do with aquaplaning that means contact patch area, size/shape/volume/direction of cuts, weight of car, and no doubt other stuff makes no impact on?
 
#8 ·
Total width of the tyre is pretty much irrelevant for aquaplaning resistance compared to the tread pattern design.

This is why aquaplaning resistance is one of the metrics measured when testing different tyres - of the same size against each other. Sure, if the tread pattern is identical a narrower tyre will do slighty better but not much, and the difference is smaller than staying with the same size tyre with a different tread block design more optimised for removing water.

Tyres with tall tread blocks with sipes and wide gaps between blocks tend to be best for aquaplaning reistance as they give the water a lot of room to displace within the tread of the tyre before aquaplaning can initiate.

So winter/all season tyres can do quite well here as they tend to have tall tread blocks with sipes and have a lot more water channels and less rubber than a summer tyre. Most summer tyres have large flat areas of tread with no sipes that can't displace large amounts of standing water.
 
#11 ·
All that doesn’t change the fact that the i3 with narrow front tyres has better aquaplaning characteristics than many other vehicles I have driven/tested over the years.

And to be accurate the tread pattern on the front tyres of the i3/i3S are effectively the same being the same tread design and construction, so there should be a difference.
 
#13 ·
I fail to see how a simple equation like Vp = 10.35*sqrt(pressure in psi) can give any meaningful insight into the aquaplaning characteristics of a car/tyre when it takes nothing about the tyre into account except the pressure. Where does the 10.35 come from ? I also notice this equation is lifted directly from the Wikipedia article and the section of the article says "This section does not site any sources". So I call BS on this dinky formula. It might as well say that red cars aquaplane more easily than blue ones. Tyre pressure is a minor factor relative to tread depth and pattern.
 
#14 ·
Fair enough: I will put my hand up to one basic school boy error. For 54 mph read Knots, so the speed for an i3 is just over 60mph.

Might I respectfully suggest that you search for Horne's Formula. I chose Wik as it a source that many people are familiar with. Here are other sources that you might not have seen before (there are many others with lots of scientific references):


The original research into aquaplaning tyres was carried out by NASA in the 1960s. I suggest that you look at page 5:


Of course, it is entirely up to you whether you think what I have posted is BS. All I am saying is that when I am driving on very wet roads, it is at the back of my mind that at high speeds on wet roads there is the possibility of aquaplaning. Sadly, from experience, many drivers on wet Motorways have a different opinion.
 
#20 ·
Might I respectfully suggest that you search for Horne's Formula. I chose Wik as it a source that many people are familiar with. Here are other sources that you might not have seen before (there are many others with lots of scientific references):


The original research into aquaplaning tyres was carried out by NASA in the 1960s. I suggest that you look at page 5:


Of course, it is entirely up to you whether you think what I have posted is BS. All I am saying is that when I am driving on very wet roads, it is at the back of my mind that at high speeds on wet roads there is the possibility of aquaplaning. Sadly, from experience, many drivers on wet Motorways have a different opinion.
Driving faster increases aquaplaning risk, I have no argument with that. If it's wet, slow down.

What is BS is taking an over simplified formula that is used as a rule of thumb on aircraft tyres and only takes one input variable - tyre pressure, and extrapolating it to car tyres. Totally different scenario and totally different kind of tyre.

From the very article you just posted above:

V = 9 x √P

This formula is based upon the validation of hydrodynamic lift theory by experimental evidence. For many modern tires the constant maybe closer to 6 or 7 rather than 9.
In other words the fudge factor at the front depends on the type of tyre and isn't just some magic number. What a surprise, this is exactly what I already said...tyre design is the most important factor.

Another thing to keep firmly in mind is that car tyres are not balloons. It's a common fallacy to think that if you halve the tyre pressure in a car tyre that the contact patch area must automatically double or vica versa. Nope, doesn't happen. This is because most of the strength of the tyre in supporting the weight of the car comes from the relatively rigid tyre carcass not the air in the tyre. Pressurising the tyre serves mainly to convert compression loads into tension loads, and a reinforced rubber wall is of course weak under compression but strong under tension. But ultimately the majority of the load carrying ability of a car tyre comes from the tyre carcass under tension loads not the air inside. As a result tyre contact patch size changes much, much less with pressure than the balloon model proposes.

About the only thing useful from that formula above in relation to car tyres is that the faster you go the more risk of hydroplaning you have. Trying to calculate a specific speed from a tyre pressure though is non-nonsensical when the "fudge factor" at the beginning is specific to a class of air-plane tyres and not car tyres, and would have to be redetermined (empirically) for every different tyre.
 
#26 ·
Wh

Who said that EVs are immune from aquaplaning? Certainly nobody I have seen in this thread, and not even in that post. The simple truth is, you can't admit that your arguments (mainly your calculation) is totally wrong and not even applicable as an approximate value on cars. Nobody of sane mind would ever claim such an idiotic claim the "EVs are immune from aquaplaning", everyone who has ever been a child skimming stones across the water knows that not even stones are immune from aquaplaning, but how well that can be done and how far they go, or how many times they jump on the water depends on many things. Same is true for cars, ICE, PHEV or EV, planes... all are in the risk, but all behave differently depending on many factors, not depending on if they are EV or not, and this is what you refuse to realize or admit.
 
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