conversion to 4 wheels disc brakes

Possibly. But it would involve hacking into the computer(s) that control the regenerative braking system.

 

I have seen several cars in our area that have beaten that number by a long shot, typically something like 90-0 in 2 inches. All it takes is a really big oak tree by the edge of the road.

As long as a braking system has the power to stop the wheels and can be controlled to avoid lock-up, it doesn't matter how the energy is dissipated. Disk, drum, or electric, it's all the same in terms of the absolute limit in short distance braking. If your are talking about sustained braking, such as down a long hill, then the ability to dissipate the energy becomes important, in which case disk brakes are better than drums and electric is better than disks, as long as the electric has a big heater to dissipate the waste energy (the Prius does not). Diesel-electric locomotives use this sort of braking system; it's called dynamic braking. That's what the big fans are for on the top of a diesel engine.

Drum brakes can stop a car just as fast as disk brakes, only they can't dissipate heat as well. This leads to fade during extended braking. The reason that drum brakes are usually beaten by disk brakes in short braking tests is that high-end brake controllers are only put on high-end brakes that use disks. It's not that drums won't work, it's just that it doesn't make sense to put a lot of extra money into a system that is going to fade during extended use.

Tom

 

Whoever is talking about an 85foot stopping distance from 60-0 in a Prius must have accidentally removed the 1 from the hundreds place. I have $20,000 in suspension and brakes in my race car and it only comes close to an 85foot stop from 60. And it sits 2" off the ground and doesn't pitch down at all; it stops so hard the passenger seat folds over and, before I switched fuel methods, the carburetor choked out and the engine would kill.

Trust me, a 90-95 foot stop from 60 feels VERY VERY DIFFERENT from any kind of panic stop in a Prius.

I'd be elated with a 110 foot stop in a Prius; in fact, I doubt the car is capable of better without ridiculous modifications.

~ dan ~

I still want four-wheel discs, though.

 

Disc brakes associated with ABS is that you can stamp on the brake peddle and get maximum braking.
A good test would be if someone with drums on the back to get up to 60 mph and stamp on the brakes. If the rear brakes lock up then they do not pull the car up as fast as discs all round.

 

ABS stops lock-up regardless of whether you have disc or drum brakes in the rear.

 

Agreed, thankyou.

 

Well, -I- think disks in the rear would be a waste, as the usable braking forces back there are tiny in the Prius. Around 10% of the cars braking force. Unless you're backing up. I also think the current rear drum brakes are "cute". Like what you'd see in a display "this is what a drum brake looks like".
I doubt very much the rear disks would decrease the stopping distance of the car. The main reason they are on the European car is because Toyota wouldn't be able to sell the car in Europe without disk brakes all round. The people there think disk brakes all round are necessary.

The 3rd gen RX-7 I sold this past summer was rated at 100 ft from 60 MPH. It was scary fast at stopping (and turning, and accelerating), and I always worried about absorbing some PU truck or SUV if I had to stop fast.

 

Sorry about the last post, I must have had my mine in neutral.
It would be interesting for 2 Prius, one with discs and one with drums, to do a trial to see what the difference in stopping distance is. Perhaps one of the Prius clubs could arrange for a trial.

 

For those who have a online subscription to Consumer Reports, they can view the figures at http://www.consumerreports.org/cro/cars/types/performance-comparison.htm. Your assessment of the Prius being about 30th percentile about right, but I wouldn't say the braking is much worse than average (@ 143 ft).

I copied and pasted the table into Excel and found that the average for all the vehicles they tested was 139.059 feet and the median was 138. The range was from 112 (Porsche Boxster) to the 176 feet (Dodge Ram 2500). Virtually all the top performers were sports cars. Most of the poor performers were SUVs and pickups along w/some econoboxes.

Out of 267 vehicles, 184 vehicles had better stopping distances than the Prius, 6 others had the same, and 76 were worse.

Yeah, the small, relatively skinny tires of the Prius doesn't help much with respect to braking.

 

Neither does the comfortable, soft suspension. I don't think anyone would disagree with this fact, though, whether they think rear discs are worth it or not: when I need to stomp on the brakes, I want the car to stop in minimal time and distance. And that's why it's worth converting to rear discs for me at any cost; the safety is improved.

 

So are you going to hack into the ABS and VSC computers? Just putting on rear disc brakes could make things worse (less safe).

 

If necessary. But if they're built that way for other export markets, it means the car should already know how to do it. It would be way less cost-effective for Toyota to build two ABS and VSC units depending upon the markets and it would be much, much easier to teach one unified set of computers how to handle both brake types, which means there's a jumper somewhere, a firmware setting, a software option, or an expansion card to swap around.

It's pointlessly stupid to replicate work that's already been done correctly; the better option is just to buy the already-finished product.

Thus, the best choice is to get the conversion parts from those export markets.

~ dan ~

 

It all depends on how strongly Toyota wants to keep each market segregated. All of your arguments are premised on Toyota being indifferent about market segregation. If they want to keep Euro disc brakes from 'migrating' to the N.A. market, you will have your work cut out for you.

I guess a first pass could be made with an inquiry by your dealer to the Toyota regional technical rep. If the response is negative, then expect tough going.

Keep us posted on your progress at getting a completely integrated set of rear disc brakes implemented on your car.

 

I don't believe this is a good argument. I'm not sure, though, as I can't provide specific documentation. I can tell you with old Mustangs (the other car about which I have any specific depth of knowledge), every locale-specific part was mechanically compatible with every locale-specific chassis.

However, I'd be willing to GUARANTEE you that at the high-volume production (and with the waiting lists they frequently have for these cars) of the Prius, it would dip so deeply into their profit margins for them to make the parts entirely interchangeable that they couldn't possibly have incentive to do so.

Seriously, what's Toyota's market advantage in making the car's parts non-interchangeable at some level (even if you need to replace ECU units)?

It doesn't make sense.

~ dan ~

I doubt it's even that hard to switch a car to RHD. At some level, you almost always only have to swap out parts.

 

I am not saying you are wrong in your interpretation; just that I don't share your optimism.

Let me share an experience with proprietary architectures: In addition to the Prius, I own a 2006 Volvo XC90. The XC90 has one of the most backward stereo systems (even the premium edition) in existence: the only way that an Apple iPod (or any mp3 player for that matter) can be played on the stereo is with an FM transmitter. I don't know how much you know about FM transmitters, but that is basically Volvo giving the XC90 owners the middle-fingered salute. Want to swap out the factory stereo for an aftermarket system? Think again. Remove the CD player and the car won't start. I was able to ultimately find and exploit a hole in the proprietary architecture of the XC90, but Volvo sure wanted to make it hard for me. By your logic, Volvo should not have made it so hard for me to upgrade the factory stereo system (they sell less XC90s than Toyota does Prius'). But they did (make it hard).

If you get a negative response from the Toyota regional technical rep regarding swapping out the drums for Euro market discs, expect a tough slog in getting to your objective.

It is not about logic (at least not your logic). I am not trying to be nasty or snippy; it is just one of the lessons I have learned along the way. If the manufacturer doesn't want you mucking about with their cars, they can (and will) make it very hard for you to muck about.

As long as there are no computers involved, it is as simple as swapping parts. That is what I did with my suspension, tire & wheels and brake pad upgrades. At the end, I have a real tight handling and stopping car that is easily better than the base or Touring edition versions that Toyota is selling. With no mpg penalty.

I guess at an extreme level, you could swap out all of the computers and parts in the U.S. spec car for the Euro-spec parts, and you would have a car with rear disc brakes that worked exactly like the Euro-spec cars.... Because it would then be a Euro-spec car.... But then what happens if there is a recall of U.S.-spec cars? Are you going to pass on the recall? If the recall is for an emissions-related component, you will not be able to register your car without proof the recall was performed on the car (at least in California).

 

I think apriusfan has it right -- at some point, it would literally be easier and cheaper to simply swap out the entire car for a European model rather than heavily mod the car with European parts.

Consider the lack of success people have had getting the MFD to switch from Fahrenheit to Celsius, and that's a much simpler change than messing with the braking system.

 

Be careful with -my- logic. Applying my logic to your Volvo story, the factory deck is part of the anti-theft system and therefore replacing it with an aftermarket system becomes impossible only as a by-product of their "sophisticated" anti-theft implementation.

Moreover, if Volvo offers an upgraded sound system, it makes perfect sense for them to make it impossible for you to save the money on a new XC90, upgrading later; if you want a high-quality stereo system you have to buy theirs.

It's logically disconnected from what I'm talking about as it has nothing to do with marginal profit and everything to do with keeping you to their own devices. If you said, "It's impossible to install Volvo's upgraded stereo system into the vehicles built with the standard stereo system," then my logic would apply. Sort of.

The proprietary architecture song and dance is played a thousand times a year; the best examples coming to mind are the Memory Stick and iPod.

I'm saying it SHOULD be a simple matter of replacement of parts (and ultimately, at some level or another it logically must be, considering Toyota does put together Prii with rear wheel disc brakes). The question we're essentially asking here is, "How much stuff do you have to swap out and at what expense? Am I going to be replacing every computerized component of my car?"

Yeah; boy can I agree with that :/ I don't want to have to pioneer something here. I want to buy something that's already matured.

Likewise, and understood. I don't mean to seem snippy. It's just kinda late and I'm anxious about a flight across the country tomorrow. Flying wastes a day.

And isn't this the truth: Volvo especially is renowned for ball-and-chaining you to their dealerships...

Whole-vehicle recalls are sorted by VIN whenever possible. My family have a long history of dealing with different parts in different cars ('55 Karmann-Ghia with a Chrysler Hemi, 1957 thunderbird with 1966 427ci shelby cobra lemans), and as long as you know where vehicle model A stops and model B begins, it's not so tough to sort.

~ dan ~

 

A stock new Mini has a typical braking distance professionally measured as anywhere from 122-130ft, depending on conditions.

I will grant you that the rotational inertia of lighter wheels helps braking to a point, but mostly for more drastic changes like going from clunky 25lb wheels to 13-15lb racing wheels. A stock Prius 15" wheel weighs ~14.5lbs. The stock 16" wheel weighs ~17lbs. Even changing to racing wheels of the same diameter won't make much difference given the Prius' excellent starting point.

Changing to brake pads with higher ceramic contact *might* offer a modest improvement at best, but likely worse under most conditions. For example, 100% ceramic pads have terrible stopping distance until they are warmed up from repeated hard braking (like at a race track). The reasons for modern brakes pads with a higher ceramic content are (1) to reduce or eliminate brake squeal, (2) for less dusting to reduce damage to alloy and/or painted wheels. Unless a driver brakes *very* aggressively (think dangerously so), generic "ceramic" pads are more likely than not to make braking distance slightly worse in normal driving.

The ultimate enemy for braking distance is that a Prius weighs ~3,000lb and comes from the factory with "pedestrian" brakes and tires (I'm being generous). By comparison:

1) A Lotus Elise weighs ~2,000lb and comes from the factory with track-ready brakes and racing slicks. The best stopping distance professionally measured for a stock Elise from 60-0 at a race track is 105ft. And, for those who wonder, stopping that quickly is brutal, much more so than panic stops in a typical sedan. I say this about the Elise from personal driving experience, not based on mag/internet reviews or claims in internet forums.

2) A stock Mitsubishi EVO VIII MR is professionally measured from 60-0 as 110-115ft typical, which is no small feat and extremely impressive for a sedan (albeit track-ready) weighing ~3,250lbs. Then again, the EVO has super-grippy racing slicks, 17-in Brembo racing discs and 4-piston calipers fore, and 16-in Brembo racing discs and 2-piston calipers aft.

Given the two examples I cited, the notion that a 3,000lb Toyota Prius with basic DIY upgrades equals an EVO VIII and nearly so a Lotus Elise for braking capability is not believable.

 

You have stated your decision to not believe that the Prius' braking can be improved. I certainly won't try to change your mind. It is for others to decide whether they want to realize the benefits I have been able to achieve.

 

I tend to doubt that the CD player is part of Volvo's anti-theft system. The ultimate hole in the proprietary architecture that I was able to exploit is in retrospect, quite simple. The Volvo anti-theft system for the car is much more robust. It is on a par with the best from BMW and Mercedes. In fact, I would argue that it is superior - swap ECUs on a new Volvo and the car won't start. The old ECU must be sent to the factory (by Federal Express no less) for re-programming the replacement ECU to enable the car to start. But I digress.

Actually, I think it is indeed not possible to upgrade a base stereo with even a Volvo Premium stereo. I have not personally checked this little detail because I started with the upgraded factory stereo (which is still obsolete). But the accessory catalog from Volvo does not have a stereo upgrade for sale, which would reinforce my belief that the stereo can not be upgraded.

And, by extension, if one must replace every part on the car, what happens when there is a recall campaign for the original car (N.A.-spec) that must be performed or the car can not be registered? Are you going to revert the car back to N.A.-spec so that the campaign can be performed and then re-convert to Euro-spec? How are you going to keep current with Euro-spec service campaigns? At some point, it seems more of a hassle than it is worth.

I am not referring to whole vehicle recalls. I am referring to what might better be referred to as a service campaign, where some subsystem must be replaced. I have another experience to share that is relevant: In 1997, I purchased a Land Rover Defender 90. Approx. 2000, Land Rover announced a 'recall' (service campaign might be more accurate) of the evaporative emission control system for the D90. I didn't want to be bothered until I was told that I could not register the D90 absent the emission service being performed. At first, I did not believe the dealer, but no registration renewal packet arrived. After a trip to the local DMV office confirmed they were not going to issue a registration sticker until I provided proof that the evaporative emission campaign had been performed, the D90 was dropped off at the dealer for the service.

Fast forward to the present, and I am sharing my experience as an example of how one could get tripped up by converting their Prius to a Euro-spec car to be able to have the rear disc brake feature. One tiny little service campaign that involves the emission control system, and you could be in rather hot water.