Tire Rack pits Integrity against Energy Saver, Ecopia and Fuel Max

FYI,
The EP20 is all season tires, while the EP100 is summer tires.
The Japanese 2010 Prius 15inch version comes with the EP25 OE summer tires.

Ken@Japan

 

I would rather have an AST...be nice if Bridgestone's site mentioned

 

it would be neat to see how long the tires last and take that in account some how. The michelin's get the best mpg but the also only have 9/32 tread depth.

 

Depends on the definition of "lasting." Their Michelin OEM tires that came on my Toyota Avalon "lasted" until I got so tired of taking them in to be plugged for leaks (fast and slow which often took two or three tries to find) that I dumped them at about 30,000 miles for Toyos. The Toyota sales manager (in Nampa, ID) recommended them (and that I go a size larger) and it was a big improvement. Not sure how long the tires would have lasted but never had another leak during the second 30,000 miles (when I sold the car because I wanted an AWD vehicle (current CRV).

 

by lasting i mean till they hit 2/32nds. I know a good amount tires dont get this far due many reasons but lets just say they do. so if u assume that the tire tread will last till they hit the warranty and your main concern is money saved, wouldn't you want to get a tire with the highest tread warranty.

I will put some numbers together and see what comes out, I think you would have to see a pretty big hit in mpg with the higher tread life tire or a big gain with the energy saver/fuel max tires.

This also probobly relates to how u drive as well, so this may be a wasted effort. If your a super hypermiller maybe the new tires are better for u.

 

OK call me stupid because I have been wondering about going to thinner tires to reduce rolling resistance, but as one person pointed out, the load capacity just isn't there with thinner tires.
According to Tire Rack and if remember correctly, my tire width is 195, but the tires tested were 185's?

 

Appearantly you have the Touring Pkg.?
If so, you won't find a 185 in a 16" tire. That (16") is a more performance oriented size, not economy. Touring Prius' have never gotten the gas mileage that Std Prius does, because of the tire type/size.

These new LRR tires are oriented toward economy sizes, not performance.

You could always replace your wheels with STD Prius wheels.

The Bridgestone EP100 comes in your size but it is a summer "performance' tire that toughts some LRR qualities. Not quite the ultra LRR of Michelin

 

Bringing this thread back to let everyone know that tirerack.com has an EXCELLENT price on the EP20. I hit a curb (avoiding an overzealous trick-or-treater) and had sidewall damage to one of my tires. The local Firestone TOLD me they had the tire I needed, but when I got there they tried to mount an EP100 on the rim (completely different tread pattern). They told me it would take several days to get an EP20 and it would cost $137. I went home and ordered an EP20 from tirerack.com for only $85 and it arrived two days later. Tire Rack FTW.

 

According to Tire Rack's test protocol
When Round and Black Becomes Lean and Green
all tyres were set to 35 psi front, 33 rear. I didn't check each tyre spec to see if recommended max psi are the same, but if not I am skeptical about the results.

 

Why? The same tire pressure is recommended regardless of the "max" tire pressure. The tire's maximum pressure does not affect the recommended pressure.

They did the right thing by using the recommended tire pressures.

 

The recommended pressure was by vehicle, not by tyre.

 

As they should be.

 

The right tyre pressure is a complex decision. The sidewalls of different tyres flex differently, so will provide greater or lesser amounts of spring and damping in the suspension with different pressures. (Formula 1 cars have absurd sidewall heights, being complete diameter of 660mm on a 13" rim - most of the suspension is actually through the tyre deflection rather than movement of springs and dampers!) Increasing pressure gives stiffer sidewalls, which tends to reduce rolling resistance but cause a firmer ride. It also improves handling.

In addition, the grip of the tyre varies with the pressure. It's possible to induce or correct under- or oversteer by varying the pressure. The grip level has a definite maximum - over- or under-inflating causes the tyre surface not to lock properly with the road surface. Indirectly, the pressure also affects the temperature of the tyre (greater flexing causes a greater increase in temperature), and temperature is also a factor in grip.

What we do know is that the Prius pressures given for the 2G's OE Integrity tyres are too low. The wear pattern is affected by the pressure, because different areas of the tyre contact the road. If underinflated, the centre of the tyre buckles slightly and doesn't make good contact with the road. As a result the shoulders wear more quickly.

My suspicion is that the torsion beam rear suspension has to be quite stiff so it doesn't pick up a wheel when the other traverses a dip, so the rear tyres have to be deflated to compensate. The front tyres then have to be deflated as well to prevent oversteer (the rears would be, relatively, providing less grip than the fronts and therefore tend to step out). The correct fix is to provide a near-£20,000 car with independent rear suspension - the Ford Focus's handling was massively improved over the Escort largely due to a switch to 'control blade' independent rear suspension.

I think the 'max cold pressure' rating on the sidewall is based on the tyre manufacturer's measurement of grip levels at different pressures, and allowing for the fact that the pressure will increase as the car is driven, due to the heating effect as the tyre is worked. Inflating the tyre above this level may well cause decreased grip (though not necessarily less grip than if the tyre were under-inflated). Part of the heating comes from the car's suspension geometry: toe-in and camber - the further away from true horizontal and vertical, the more heat is produced but the more rolling resistance. Greater toe-in tends to keep the car straighter. The 2G Prius has quite low toe-in and camber to reduce rolling resistance, at the cost of lower heating (less grip) and less straight-line stability. I believe the 3G has more toe-in to keep the car more stable - the drivetrain improvements mean that although more energy is lost to rolling resistance, overall the car generally uses less fuel.

Tyres will actually withstand quite a lot of pressure before bursting or, more likely, the bead coming off the rim - generally 100s of psi. Failures tend to be caused by the sidewall flexing too much on underinflated tyres.

Basically, take both the manufacturer's pressure and the tyre's sidewall max pressure as guidelines, and note you'll probably need to find a different value as and when you change tyres. (US-made Goodyear Integrity are reportedly different from the Japanese-made ones fitted as OE in cars imported to the US - they're actually Toyo-made, branded as Goodyear). I personally run 40psi front, 38psi rear although that tends to understeer a bit, so I may reduce the front a bit. The Bridgestone Turanza ER30 tyres fitted as Original Equipment over here were really designed for Mercedes and BMW as summer tyres, and I think they run too cool as the Prius doesn't work them very hard.

It would be nice if tyre reviewers would find the combination of pressures that gave the best ride, grip, wear and rolling resistance on a specific car, and evaluate the tyres after doing that, but frankly that's a long research project and they really have to go with something fairly simple to test.

 

ok, Mike. Thanks for the lecture (really), but now give an opinion: what would be the fairer test of mpg given need for simplicity --

As they did it, setting each tyre's pressure to vehicle recommended, or
set each tyre to max cold rated, or
something else ?

 

Depends on your definition of fair:

Aiming for max fuel economy - use the max cold pressure on the sidewall, front and air.
Aiming for max grip - adjust tire pressures while testing on the skidpad/slalom until fastest times are found.
Aiming for max comfort - use the lowest pressures possible.

Or some arbitrary combination of the above to suit your preferences.

The average person will always use the recommended pressures by the auto manufacturer as stamped on the door-plate. As such, the only way to "fairly" test the tires is to use those pressures.

I would expect each tire to improve proportionally given higher pressures, anyway - I would put money on the Michelin beating all the others in rolling resistance with all inflated to the maximum cold pressure printed on the sidewall.

 

Unless something better comes along I've decided to get the Yokohama db Super E-Spec once my Nokian i3s wear out (2 are still on tread bar #7 and 2 are on tread bar #5, out of 8 new). They'll cost me about $96 more than the Bridgestone EP-100 (purchasing from Tire Rack and installing them myself) including possible MPG differences over 50,000 miles. I like the idea of the alternative materials used instead of petroleum and they rank really well for steering response and overall feel. I tend to corner pretty hard and prefer a tire that is predictable.