Screw in the tire

"...On a couple of our previous cars, boosted pressures very significantly improved the tread wear patterns. Though those cars were of the same era and had the same 26 psi recommendation label...."
A few years back the manufacturers started putting on placards for tire inflation pressure that was realistic. The old 26 psi was for comfort and not the best all around. Current tire pressure recommendations are likely the best in most circumstances. It's always a compromise. Higher pressures do decrease traction.

 

Yes, I'm aware. Unfortunately winter in Colorado has a very wide range of temperatures in the winter. The temperature can literally change 60 degrees F or more in 24 hours. (Storm Recap: Potent storm delivers promised first snow and frigid temperatures – BoulderCAST) Not much I can do about it. If I had my own pit crew maybe I'd change out my tires for the most appropriate type everyday.

My post about tread wear is here. GET YOUR DEDICATED SNOW TIRES NOW !!! | Page 10 | PriusChat

This season the front tires don't seem to be wearing excessively, and the weather isn't much different. The only difference I can think of is pressure.

 

I know of the snow tire rubber, because a friend used to live in Colorado.
Pressure is a factor for traction, but could simply that you have adjusted to the Prime better in that time. Tire age might be another factor. rolling resistance is worse with new tires in part because of the effect the mold release agent could change the top layer of rubber. Perhaps it has a negative effect on the rubber's grip.

"The Prime in EV mode seems to be a tire shredding machine."

It's that instant torque. Tire manufacturers are starting to make EV tires that hold up to it better.

 

Blizzak recently (this year?) came out with the WS90 that's supposed to be much longer lasting than the WS80 (which I have). They probably developed it partly because new cars have more power and torque than ever before. The WS90 isn't specifically designed for EVs from what I can see, but it sounds like it would help.

I have the same torque this year, and I still floor it all the time, but this year I'm not accidentally doing front wheel burnouts if I try to start to quickly.

Mold release could be a factor, but that should be worn off in the first few hundred miles. I wonder if maybe I slightly rounded over the edges of the tread blocks, which then made the tire more slippery? I rotated the tires that were on the back last year to the front this year, so they had a more gentle start to their lives.

I've it said before; I still think the traction control is poorly programmed and allows too much wheel spin. Assuming they have tight feedback control of MG2 speed (which they probably need to power the motor with the inverter), they should be able to keep the motor speed from increasing unreasonably quickly, as it does when one or more wheels lose grip.

 

They might be using ABS to watch for wheel spin.

It can take thousands of miles before fuel economy on new tires reach what it was previously. Remember, the rubber is being heated and is under some pressure, so the compound could be diffusing in further than the surface.

 

They are, but it could be better. It sounds like older generations were criticized for cutting engine power when a wheel started to slip, making it hard to accelerate. To some extent ABS is part of the problem because it can only relatively coarsely brake a slipping wheel to send power to the wheel with traction. But if that braking wheel hits a patch of pavement with more traction, it will slow you down when you're trying to accelerate.

The 4th gen apparently allows more wheel spin, but wheel spin doesn't accomplish much. I think if they controlled the speed of the motor, the slipping wheel would never get going too fast, and a lighter amount of ABS could be used without shock loading the drivetrain or making it hard to accelerate.

With a non-hybrid, the engine has more momentum than an EV motor, so it spins up a little slower. I think they could electronically simulate very high momentum in the motor by not letting the speed increase much faster than the car can reasonably accelerate.

 

Which year was that? All my household's cars are older than just a few years.

Yes, it is a compromise between numerous conflicting goals. And comfort is still heavily weighted into that compromise. But numerous drivers don't place the same relative weighting on those various goals, so naturally their personal preferences lead to different results.

The cars we have rented in Europe had multiple choice tire pressure labels, depending on the use. I looked for those labels because a number of PC members had previously mentioned them. But the U.S.-market labels are simplified, as if American drivers are less able to make such judgements.

Do you have some good references for that?

A previous poster who referenced a technical study to back up this assertion, turned out to be misreading the study's nomenclature, as discovered by a quick skim of the glossary section

 

I'll be the reference on this.

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As a long time SCCA racer, higher tire pressure can & is used to decrease traction on one end of the chassis.


Rob43

 

Can you link your technical publications on this? So that I can review the studies and figure out how they apply to ordinary non-racers?

 

Sorry no.

It was something taught to me a million years ago at the track, then I used it successfully going forward in racing & street use.

I will tell you this is the exact reason I always run my Prime with "roughly" ~3 psi more in the rear. Currently I'm at 38F & 41R, it simply helps to get rid of some of the built in understeer.


Rob43

 

I've seen technical reports from studies that actually measured rolling resistance, and hydroplaning onset speed, vs inflation pressure. They gave me a better technical understanding about what is happening, and the magnitude of the changes.

There are at least two camps on the traction issue, hypermilers claiming improved traction at higher pressure, and another group (e.g. racers and 'conventional wisdom') claiming a reduction. But I've seen no studies measuring it, so don't know which group is correct, or if both may be partially right within their particular domains of interest. Thus I also have no clue about the relative magnitude of any traction changes vs pressure, whether or not it significant enough to be concerned about.

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Personally, I don't care about dry traction, because that is the best case. I live in a wet climate, so hydroplaning and wet traction are the important factors in my environment. And snow and ice in winter. If one takes care of them, the worse and worst cases, and drive as if they are always present or just around the corner, then the dry traction case takes care of itself.

 

Another myth.
It depends on:
What tires and what vehicle AND higher than WHAT.

 

You should try selling that statement to Auto-X'ers... OR better yet someone like me.

Tuning the chassis "on the fly" with tire pressure works.

All of these simple rules trickle down to our FWD Prime.


Rob43

 

SIGH.
You can't state "rules" without also stating the context.
"higher" is not better......unless you know "higher than WHAT"........and applied to WHAT.

And as is often the case, you can't apply racing information/design/parts/rules to a street car without a careful explanation of how and why.

 

Off-topic?

 

Lol, yep.

But sams on a flyer.


Rob43

 

Go ahead. Throw a few more insults.
It was not ME who took the thread on a side road.

 

Wow...

I'm glad you got it all sorted out, but hearing stories like this makes me glad that I plug my own tires in 5 minutes for less than $5 dollars.



Rob43