16" Wheels

I'm sure you can find them... Google is your friend.

And if the big switch was from 14" to 15", why do the euro spec models offer 16" wheels? Why do the UK car reviews of the prius almost always say that the UK version, with it's 16" wheels, is much more responsive and handles better than the 15" US version.

For that matter, why are we stuck with disc/drums?

 

YOU are proposing that people consider spending around $700 for new rims & tires. So it would be most appropriate that YOU explain why.

My theory about 16" being available in Europe is just like the reason hybrid SUVs will be available here. It's because that is what the market wants. Regardless of trade-off (there is no such thing as a perfect solution), they provide what sells... even if it isn't the best choice.

Even though Toyota sets a very high priority on reducing emissions & consumption, making profit is still their ultimate goal.

 

:roll: Excellent argument, John. Change your wheels to 14'' and your numer plate to "PriusCult". :lol:

 

Ok, there are a number of factors here and everyone has part of it right.

The major factors:

Diameter
Sidewall Height
Tread Width
Unsprung Weight

Let's ignore the Unsprung Weight, because it's effects are going to be relatively minimal for our purposes and because I don't know the real values

Taking the stock US tires

185 = Tread Width
65 = Sidewall Height
15" Rim

Stock Euro Tires

195 = Tread Width
55 = Sidewall Height
16" Rim

For both, the Overall Diameter is almost identical.

Let's take Overall Diameter first, and get it out of the way. Diameter is what affects the Speedometer, Odometer, and Transmission. It's why you worry about "Revolutions per Mile".

If you change the diameter, two things happen. Your measurements of speed and mileage get screwed up, and you change your effective Gear Ratio, because you've changed the diameter of the final gear between your engine and the ground, the tires.

Neither of those is really a good thing.

John is right when he says that changing diameter will screw with acceleration, mileage, and readouts. It can also possibly put un-anticipated stresses on the Transmission.

But, worse than that, it changes the calculations for things like Stability Control. The computers think they know that variable, if you change it, who knows what will result.

I think most folks will be happiest if their speedometer, odometer, and safety equipment continue to work, so let's not change overall diameter too much.

Though in fairness, once you get up to speed, larger diameter tires will give you better fuel mileage at the same engine RPMs. If we were only driving long distances at constant speed on flat surfaces, we should probably go with 10 foot diameter tires for really good mileage.

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Now, we are left with two variables, we can change either together or independently. To be clear, lets take them separately.

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Tread Width.

Putting Fatter tires on without changing anything else will do the following for sure:

1) Increase Braking Performance on Dry Pavement
2) Increase Skid Pad numbers on Dry Pavement
3) Increase Rolling Resistance and thus Decrease Mileage
4) Make it more difficult to turn the wheels when stopped or at extremely low speed (parallel parking)

They MAY Increase acceleration on dry pavement, because you can apply more power before the tires break loose and traction control limits you. That depends on whether you have enough horsepower available to break the stock tires loose, which is a questionable situation on something as low powered as a Prius.

Performance on Wet or Icy pavement is more problematic. There's no way to say for certain what will happen.

Wide Tires provide a larger contact patch, but that in turn decreases the force/area you're putting down. That means you are MORE likely to hydroplane with wide tires. Same with snow. Narrow tires can cut through slush to reach traction better in some cases than wide tires because they have more force/area pushing down. They don't get lifted up as easily.

Generally, narrow tires will do better in rain and slush. Wide tires will do better in deep snow and mud.

If you don't hit the point of hydroplaning, wide tires will still brake and corner better in wet/slush conditions, but once you do hit that point, the narrow tires win.

-------

Sidewall Height

Another tradeoff.

High Sidewalls act like an addition to the car's shock/spring system. They 'give' when going over bumps, ruts, and pot-holes. This means a smoother ride.

John is absolutely correct in saying that high sidewalls, in general, will give a better around town ride, with less rattles and tooth knocking.

But, when you are cornering, high sidewalls tend to 'roll over' and can result in the contact patch decreasing. This limits cornering force. That's really only an issue at higher speeds/G-forces, so it's irrelevant in town, but it is an issue on highways and back roads.

Also, keep in mind that a very highly inflated tire of any kind is going to act like it has lower sidewalls and will 'perform' better on corners, but ride harsher.

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The Euro Tires changed BOTH sidewall and tread width, in the direction of performance.

They gave up ride comfort and mileage for better dry performance. That's cool. They also got the Rear Disc Brakes, so it's clear to me that the Toyota folks think that there is a differance between what Americans and Europeans value in terms of performance.

I don't think they made major changes in the rest of the systems/programming. I could be wrong, but I'm willing to assume that we can safely swap around wheels/tires within the limits Toyota has used as Standard Equipment.

That leaves us with 4 choices:

185/65/15 - Good Ride and Mileage - Less Cornering and Braking

195/65/15 - Good Ride, Lower Mileage, Better Braking, Marginally better cornering

185/55/16 - Worse Ride, Good Mileage, No Braking Change, Better Cornering

195/55/16 - Worse Ride, Worse Mileage, Better Braking, Better Cornering

If you change Diameter or Width outside those parameters though, I think you're in uncharted territory. Will wider tires fit in the wheel well and give problems when you turn the wheel? Will taller tires bottom out in the wheel well when going over bumps? I don't think either is worth the risk myself.

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Of course, some people also think the 16" Rims look better

When considering changing tires/rims, you need to be careful with another couple of things unless you are swapping straight between US and Euro OEM rims.

Weight - You will be fine if you go with a lighter rim, but if you go to a significantly heavier rim there can be bad things happen. It's hard on the suspension, and acceleration and braking will suffer. As long as the total Tire+Rim weight is roughly the same or a little lighter though, it's not a worry.

"Offset" - This is a toughie. This is how far the Plate on the Rim that holds the Lugs is from the Center of the Rim.

If you change it, the tire will move in or out in the wheel well.

You've all seen custom cars with the tires sticking way out. You want to avoid this. If the wheels are too far inside, they can limit turning because they hit the inside of the wheel well, you also want to avoid this extreme.

You can't just pick up any Rim that happens to be 15X6 and assume it will work. You HAVE to pay attention to offset.

Most reputable places, like tire rack, will list rims that match closely to the factory offset, and may not list ones that don't when you look up options for your car. Just be careful.

Anyway, sorry for rambling, hopefully though we can recognize the tradeoffs, and agree that within the parameters Toyota has tuned for, choice is good

 

By far the best post regarding tire size I have ever, ever seen.

I'd just like to add one little thing.. Wider tires *generally* tend to have lower sidewalls, which aren't good if you're going to be dealing with a lot of potholes. My current car has 225/45 on 17" rims (factory standard) and this year I've blown one tire on a pothole and bent a rim.

Personally I think the 16"s would be the best compromise of handling and milage. And I think you're probably right when you said that Toyota must view American drivers a little differently than European drivers. Perhaps we're less aggressive thru the corners? Shows how little they know.... :lol:

 

Toyota's practice of equipping the same car 2 different ways for different markets isn't uncommon at all. Cars that are sold in Europe tend to be more oriented towards the "driving experience" and things like ride comfort are sacrificed for handling. Over here in the states, it's assumed that we like the "highway cruiser" approach, where ride is emphasized over handling.

Personally, I wouldn't care so much if Toyota at least made the better suspension/disc brakes available over here, and I seem to recall that was one rumoured upgrade for the '05 line, so maybe we'll get it after all.

 

The experience of most car manufacturers is Americans prefer a soft, cushy ride and few care about performance driving characteristics. This results in base and midlevel cars being equipped with less than ideal tires and very often less costly drum brakes. Europeans, on the other hand, are more demanding with respect to how a car rides and handles from a precision point of view, and consider road feel an important input. Americans call it a crappy ride. The speeds are generally higher in Europe, resulting in the use of higher performance tires, brakes and linings, again things few here can appreciate but many want. Think for a moment of the Big 3. How many "performance" sedans do they offer? The ones they do offer compete with European vehicles such as BMW. Keep in mind this is the country that still thinks NTSC TV picture quality is fine while the rest of the world is often astonished at the poor picture quality we will tolerate.

I will concur the suggested European package with 16" wheels and lower profile with increased width tires would greatly improve handling, braking, and road feel. However the important point made earlier is what affect will this have on the ABS, TCS, and VSE systems? What someone needs to do is compare the brake controller part number in Europe with the NA one. It is possible the calibrations are robust enough for each. It is also possible that there are multiple calibrations and the selection is based on a calibration (NA build vs European build). Short of having someone make the change and taking data to compare performance with the European version, this might be more trouble than it is worth. On the other hand, the changes are not that big and might not be that significant. I've got to ponder this a bit more.

 

Since the diameter of the Euro and US wheel/tire combos is the same I really do believe the programming is fine for either. If you went far beyond that you would have cause for concern I think.

Remember, some dealers in the US are putting on alternate tire packages all the way up to 17/45 combos right off the showroom floor.

I know none of them are reprogramming anything, and Toyota apparently hasn't told them to cut it out.

 

The issue is not diameter, rather the mu slip curve of the tire. Significant changes can result in performance degradation of the slip control systems.

As for Toyota not stopping someone, all OEM's clearly state that changing tires from those recommended on the tire placard is done at your own risk. I have seen a few instances where dealers were warned of potential adverse performance affects and liability when they changed OEM tires and wheels prior to selling a vehicle (special dealer package). However these were not Toyota dealers.

 

Indeed, the ABS, TCS, and VSE systems programming differs between US, European and Japanese models. *Think global, act local*

From Toyota UK 2004 Prius press release:
===============================================
WHEELS AND TYRES (p.35)

• Sporty wheel design
• Optimum balance between grip and low friction

The rim size was also specially chosen and tuned to European demands. The seven-spoke lightweight aluminium wheels (16-inch) use wheel caps to reduce the weight of each rim and to protect the alloy wheel from damage. The 195/55 R 16 Michelin tyres deliver good all-weather
grip together with a lower than average friction coefficient.

------------ more about European customization

Vehicle dynamics tuned for European demands (p.31)

-------------more

European drivers demand very different vehicle dynamics from those in the USA and Japan, the two other principal Prius markets.
To ensure the new Prius satisfied European demands, a team from Toyota Europe travelled to Japan in 2002 to assess early development models and make recommendations to their Japanese colleagues. A year later they were putting development cars through their paces on roads ranging from smooth German autobahns to Belgian pave cobbles and the rough surfaces of British country lanes.
“Tuning the chassis to suit European tastes was a priority,†says Jos de Boes, general manager of the Vehicle Engineering Division at Toyota Europe. “For Prius the biggest priority was achieving stability in all driving conditions. Because this car can reach higher speeds we had to ensure it was safe at those speeds, even during an emergency lane change.
"Our second priority was control of the roll motion. We wanted to avoid excessive roll during cornering. What we ended up with was adopting rebound springs at the front and rear of the Prius for Europe – which are not fitted to Japan and USA versions, where driving conditions are very different.†(p.34)

===============================================

However, there are same 16'' wheels (and rear brakes) in Japan as in Europe.

Make up your mind guys...

 

All that tells me is some suspension components are different. My Jetta GLS has different springs, tires, etc than a Jetta GL, but there are no changes in the traction control or anti skid system.

 

Finally got my Prius yesterday.

Wheels here in Europe are with plastic cap too. Actually I didn't notice it when took Prius for a test drive in January.

Nice, practical and light. (And cheaper for Toyota, which is fine with me.)

Bigger pictures downloaded at
PriusChat.com Forum Index -> Album -> International Pictures

 

Evan, labels are correct. It's indeed the same rear left wheel (you can see disk brake as well) and it's ON THE CAR. I made pics in my garage one hour ago...

Again, you can see more details @
PriusChat.com Forum Index -> Album -> International Pictures

I'm going to leave these caps. Unlike in US, it's quite ugly without it.
We have sharp granite curbs here in Switzerland, therefore it's very practical too...

 

I'll have more time for that over the weekend...