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conversion to 4 wheels disc brakes

Discussion in 'Gen 2 Prius Technical Discussion' started by bsj44, Dec 22, 2007.

  1. bsj44

    bsj44 New Member

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    I read that Prius sold in UK got F/R disc brakes. Has anybody tried converting USA version into the all wheels system?
     
  2. bestmapman

    bestmapman 04, 07 ,08, 09, 10, 16, 21 Prime

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    My question is, why would you want to have 4 wheel disc brakes? Because of the regenerative braking, the brakes get very little wear. It just doesn't seem that there is a need for the 4 wheel disk brakes on the Prius.
     
  3. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    i have to agree... taxi cabs in Vancouver, BC are the acid test from brakes... one taxi went over 300,000 km, only had like 6-7 brake jobs. that is pretty low brake wear especially in a town that like every other town on the west coast, hilly, hilly and HILLY!!

    i worked for car parts delivery in San Francisco when i was a kid, had Chevy Sprints and S-10 pickups, the hills there are a killer. new brakes every 15 miles or so. S-10's needed new clutches every year...
     
  4. Boo

    Boo Boola Boola Member

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    The Prius' braking is below average. Consumer Reports measured its 60-0 stopping distance at 143 feet (the best braking cars generally have distances in the 120s (although the very best ones -- all sports cars -- have distances in the 110s)), which puts it at approximately the 30th percentile of all cars Consumer Reports has tested.

    Assuming the 4 wheel disc Prius has a shorter braking distance, then that's a big plus. But I think it will be cost prohibitive to try to convert the American Prius to 4 wheel discs. I believe no one here has done it (we've had several threads on this topic).

    Among the cheaper ways to reduce braking distance is to install performance ceramic compound brake pads in the front (around $80 for Hawk Performance Ceramic Pads), and to get wider and better performing tires (around $400-$500) although wider, stickier tires will result in a mpg hit.
     
  5. apriusfan

    apriusfan New Member

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    It is more than just swapping out the drum brakes for disc brakes...

    Even if one were to purchase the euro spec parts (for the rear discs), you might have problems with the calibration of the ABS computer. Drum brakes have a different stopping profile than disk, and the ABS computer needs different programming to compensate for the difference. I doubt you could just swap out the euro computer as part of the upgrade. See how things can start to get expensive?
     
  6. brick

    brick Active Member

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    I would invest in better tires long before replacing the rear drums with discs. If you make a hard stop with the stock tires its clear that they scrub on just about any surface, which means they're the limiting factor. More clamping power wouldn't do much for you.
     
  7. MattFL

    MattFL Member

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    This is exactly what I was thinking. With these tiny low resistance tires, I would bet lack of traction is the limiting factor; not lack of brake power. We need someone to suit up their prius with some wide really sticky tires and perform a brake test on dry pavement for us. :D
     
  8. apriusfan

    apriusfan New Member

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    With 205/60-15 Michelin Pilot Sport A/S tires on Motegi Traklite 15x6.5 wheels (~1 lb less than the OEM tire & wheel combination) and ceramic brake pads, my 60-0 distance is between 110 - 115 feet.
     
  9. Boo

    Boo Boola Boola Member

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    Did you get a chance to measure 60-0 braking distance with the OEM Touring wheels and tires?
     
  10. statultra

    statultra uber-Senior Member

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    brake balance between front and rear is controlled by computer, and you would probably require the european brake ECU in order to take advantage of the 4 wheel disc brakes, when my front caliper messed up on my 05 prius the computer shut off front brakes and just used rear.

    i want to upgrade my braking system on my 05, but i dont like the fact you need a stupid scantool to do everything.
     
  11. apriusfan

    apriusfan New Member

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  12. hobbit

    hobbit Senior Member

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    Y'know, the Camrys we used in this course were only allowed 85
    feet for 60-0, and they did it handily within that. Is the real-life
    braking performance of the Prius that much longer to stop? I
    haven't gone out to ream the crap out of my own tires...
    .
    _H*
     
  13. apriusfan

    apriusfan New Member

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    85 feet for 60-0 is incredible. P-cars don't get that short of a stopping distance. Are you sure it was 85 feet and not some other number?
     
  14. Mawcawfee

    Mawcawfee Prius-less (for now)

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    That stopping distance is highly unlikely. 110ft 60-0 handily beats nearly every supercar with $10K+ high-end brakes. It also beats the flyweight 1,975lb Lotus Elise. No way will a 3,000lb Prius beat the Elise. 120-125ft is more like it, since that's about what Prii have achieved in many performance tests.
     
  15. Mawcawfee

    Mawcawfee Prius-less (for now)

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    85ft 60-0 is a physical impossibility unless that Camry is hitting a wall or another vehicle. If it really could stop that fast, the owners of the driving school must be incredibly stupid, since they could be making tens of millions of dollars tomorrow licensing that braking technology to automobile manufacturers. ;)
     
  16. patsparks

    patsparks An Aussie perspective

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    I vote get stickier tyres if you want to stop quicker. Maybe use the Euro/Aussie spec tyres, Michelin Energy XM1 195-60h 15

    I have serious doubts that rear disc brakes will help at all really. Most cars have something like an 80%F 20%R brake bias due to weight transfer under brakes. Disc brakes aren't so much better than drums in a single stop event and with regen to share the load of slowing the car there isn't a big heat buildup anyway. The big advantage with discs isn't more stopping power, drum brakes are more powerful which is why old cars that had 4 wheel drum brakes often didn't need power boosters, the advantage is discs dump heat better.

    The front rotors could be bigger and 2 piston callipers would help, but that would require a larger rear wheel cylinder bore to maintain balance. Also better disc pads may help, however be aware that a lot of high performance pads perform poorly until they are hot. I had metal pads in my Mazda RX2 front and rear and the first stop in the morning was always very interesting.

    This is all easy for me to say, I have 4 wheel disc brakes. :D
     
  17. Boo

    Boo Boola Boola Member

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    I don't doubt apriusfan's reported stopping distance of his modified Prius. The thing is that road testing protocols/conditions differ and are rarely known. Different protocols/conditions lead to different results. If I remember correctly, I've seen the standard Prius' dry braking distance reported as being as low as ~120 feet and as high as ~150 feet.

    But I understand your general point. In Consumer Reports' road tests of some 270 current cars (I assume that they have the same protocol for all their road tests), they report a 60-0 mph stopping distance of 143 feet for the standard Prius, and 117 feet for the Lotus Elise (and the other 6 cars with braking distances in the 112 to 117 feet range were also sports/performance cars).

    Agreed. Consumer Reports reported the Camry's 60-0 mph stopping distance as being 139 feet.
     
  18. apriusfan

    apriusfan New Member

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    110 ft 60-0 is a number that has been met by at least 3 cars that I am aware of with stock brakes: BMW E46 M3 (109 ft if memory serves), 1995 Volvo 850 Turbo (110 ft if memory serves) and 2000 Volvo C70 (110 feet). For an expenditure of ~$2,000, my 2005 MINI will stop 60-0 in 105 - 110 feet. The stopping distance number that you quote of 120 - 125 ft for the Prius is for the base version. I have added wider and more sticky tires and ceramic compound pads to my car along with slightly lighter wheels & tires (less rotational mass).
     
  19. hyo silver

    hyo silver Awaaaaay

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    Would there be a way to improve the braking electrically? AFAIK, friction brakes work by converting kinetic energy into heat. More swept surface and higher-friction pads equal better stopping times, which is part of the thought behind rear discs instead of drums. But what about the regenerative system, which converts kinetic energy into electricity? Subject to the limits of traction, maybe there's a way to increase the current draw from the wheels through the motors/generators.
     
  20. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    i would imagine with regen brakes, Toyota engineers have already looked at getting maximum charge back to the batteries. but have to look at the super high current values in a very short period of time. the 04's did have much improved regen over previous models so that does show they are looking at that or have looked at that issue