Run-flat tires gives better FE?

Discussion in 'General' started by duke 5, Oct 3, 2007.

  1. duke 5

    duke 5 Member

    Just out of plain curiosity…

    Will run-flat tires give you better FE without the added weight of a spare tire, or will it give you less FE due to the extra weight from the stiffer rubber side-walls of the tire?
     
  2. tbaleno

    tbaleno Well-Known Member

    I don't know how much extra they way, but I'd say, getting rid of the spare would save a tiny amount of fuel (but it all adds up). Altneratively you could probably keep a can of fix-a-flat in your trunk for emergencies ;)
     
  3. cillakat

    cillakat Member

    they weigh a ton, much more than a spare. on the odyclub.com forum I frequent, the consistent reports are significant hits in mpg. on the ody, iirc it adds about 200#

    Katherine
     
  4. brick

    brick Answers to "that guy."

    I don't know if it's literally 200#, but adding weight to the wheels is far worse than adding it to the suspended part of the vehicle. They could easily be equivalent to 200# of dead weight.
     
  5. cillakat

    cillakat Member

    200 lbs for the runflats on the ody is the estimate I hear......that is 200 lbs added to a similarly equiped non runflat/pax ody. sounds like it includes the weight of the spare too for the nonpax equipped car. it's perhaps different for smaller/other vehicles.

    but i've only skimmed those posts (since i don't have pax) and you could very well be right....200 lbs dead weight. how much does a typical ody tire/wheel weigh I wonder? The 'official' honda statement for the pax is 75 # each but those that have weighed them have found just over 80 lbs....wonder what the weight diff really is...

    :)
    k
     
  6. Shiba3420

    Shiba3420 Well-Known Member

    Wont the run flats tend to be stiffer, like an overinflated tire? Might that in combination with loosing the spare increase mileage? 200lbs sound about right for 4 tires, what do 4 regular tires weigh?
     
  7. nash

    nash Well-Known Member

    Prius Chat has an interesting discussion on run flat tires (RFT) The key items brought up are RFT are heavier, tend to have a rougher ride and poor rolling resistance, have to be replaced if driven more than a couple miles when flat.

    BMW has been using RFT on many of it's cars. Here is a discussion of a RFT having to be replaced after only driving 9 miles at speeds under 45mph. Another BMW owner had her RFT shred and was told the other 3 needed replacing after only a year.

    Toyota's Sienna minivan comes with RFT. Toyota and Goodyear were sued due to many owners finding their tires worn out after only 10K miles. The problem caused Toyota to offer a supplemental tire warranty coverage to cover uneven or premature tire wear.
     
    Last edited: Oct 4, 2007
  8. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Nash:

    ___I was in the process of pulling data over at TireRack to find out the specifics. I think your post gave everyone all they needed to know. Nice job!

    ___The Sienna’s OEM Bridgestone B380’s had terrible end user comments about treadwear.

    OEM Bridgestone B380 Run Flat’s - 225/60TR17: Tire weight = 37 lbs.

    Pirelli P6 All-season non-RFT’s - 225/60TR17: Tire weight = 25 lbs.
    Continental Touring Contact AS non-RFT’s - 225/60TR17: Tire weight = 24 lbs.

    ___Good Luck

    ___Wayne
     
  9. Takashi

    Takashi FUD

    I have RFT installed. I hope my comments can help remove the myths about RFT.

    Weight differences- The car came with Continental proContact SSR RFT (205/55 R 16, H rated) which weights 27 lbs per tire. It's non-RFT variant Continental proContact (205/55 R 16, H rated) weights 20 lbs (7 lbs less). In essence the RFT added an extra 28 lbs to the car. The absence of a spare tire (~ 20 - 30 lbs including tire, rim, air), car jack, and the wrench might make up for the weight savings. Note I cannot comment on FE since I have never driven my car with non-RFT installed.

    Appearance- RFT looks exactly the same regardless whether they are flat or inflated due to its thicker side walls. It will take a trainned eye with a tire gauge to find out which tire is flat.

    Requirements - A TPMS or FTM is needed in order to safely operate a vehicle with RFT. In an event of a flat tire, you are not going to know unless you physically measure the tire pressure of each tire or the computer gives you a warning. Since RFT can only be travelled a certain distance with 0 pressure, to ensure safety the driver must be made aware of a pressure loss in a tire so the driver can take immediate action.

    What to do when you have a flat tire - RFT can be driven up to 50km at speeds of 80 km / h and the distance can be increased by decreasing the speed(double check on your user manual, don't quote me on this). Your TPMS or FTM should give you an alert. There is no need to stop and change your tire. You can continue on your journey but monitor your speed. This is very convinent since you no longer have to stop on the side of the road to fix a tire; instead, you can drive to your nearest tire repair center, or drive to your destination.

    Can RFT be patched - YES, they can be repaired professionally with the descression of the tire technician. Usually the RFT will be removed from the rim and inpected by trainned technicians. If the RFT have been driven for certain amount of time with 0 pressure, the tire must be replaced because of unrepairable sidewall damage. Note: Once RFT have been driven under decreased pressure, their distance of travel drops significantly when they are flat again. (i.e. you loose distance every time you run on your flat tire)

    Why RFT is replaced, not patched - It is recomended that RFT be replaced, not repaired. (Liability issue)

    Are RFT expensive? They cost a little bit more compared to regular tire (Continental proContact SSR RFT (205/55 R 16, H rated) - $ 125.00 each. It's non-RFT variant Continental proContact (205/55 R 16, H rated) - $ 96.00 each). Some shops, however, might charge you extra to mount RFT since they have thicker sidewall and thicker tire rim thus it can be more diffuclt to fit them on the rim. Most tire shops will not charge any more to repair a RFT.

    What is 'tire (or road hazard) warranty'? - Since RFT are more $$ to replace (some place charge $400 CAD to replace a tire), some manufacture offer a 'road hazard warranty'. During the purchase of your new car, you pay an extra fee of $800.00 CAD to cover for tire damage caused by road hazards (e.g. nails, pot holes...etc) for 3 - 4 years. The warranty does not cover curb rash or damage caused by driver error. Whether you get this warranty or not is up to the purchaser; nevertheless, it does pay off since I got a puncture in one of my winter tires when I went into a car wash and it's $$ to replace.

    Handling and ride quality - The suspension in my car is specifically tuned for RFT. Some other drivers say the ride is stiff; however, I prefer stiff suspension instead of soft suspension. I cannot provide any comments on the non-RFT tires since I only driven with RFT installed in my car. If the suspension of your car is tuned for regular tires, you might find RFT give you a harsher ride (driven with tires at recomended pressure).

    Durability - I have about 14K on the snows (Bridgestone Blizzak LM-22 RFT) and 10K on the all seasons (Continental proContact) . I don't plan to replace them and I have no problems with treadwear.
     
  10. wdb

    wdb semi-hyper

    The weight difference is all rotating weight and also unsprung weight. Both are much much more significant in terms of efficiency, ride, and handling than, say, the same amount of weight in books on the back seat.
     
  11. voodoo22

    voodoo22 Cheaper than the bus

    I had RFT's on my 330i. They were heavy and handled poorly compared to non-RFTs. Many people; myself included; got rid of their RFTs and went to conventional tires even-though the e90's have no room for a spare.

    Maybe when the technology improves RFTs will be better, but right now they offer no improvement worth sacrificing for in my opinion.
     
  12. Takashi

    Takashi FUD

    What make/model is your RFT? Since yours is a 330i, can I assume it's a 2006 model (tire)?

    Different make/model of the tire affects on ride quality. i.e. you can't test 1 brand and then make the assumption that all RFT tires are bad. I actually quite like them and glad I have them. I drove different BMWs with different makes of RFT installed. (loner cars) and strangely to say they all ride different (car is the same)
     
  13. koreberg

    koreberg Junior Member

    Those RFT sound different than PAX. Regular RFT have stiffer side walls and ride on the side wall when tires lose pressure. When PAX loses pressure it rides on an interior support insert separate from the tire. Also the Rims have a ridge in the middle to also help support the car the insert and the car. So they probably weigh a lot more. PAX has a range of 125 miles at 50mph.

    I'm going to get an ody soon, that is the only thing that I am dreading, is having to find somewhere to change these PAX tires at.
     
  14. Takashi

    Takashi FUD

    Yea. The PAX system is very different than RFT. I heard both good and bad things about the PAX system. I am sorry I haven't have much first hand experience with them; nevertheless, based on the information I read from the website it sounds like PAX is more $$ to repair.
     

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