Run Flat limits
 

Has anyone had experience or heard of situations where someone has gone past the speed or distance limits of the run flat tire? I have searched and want to know what happens if I drive over the 50 speed and distance limits. Will my differential be reduced to a mess of molten metal? Will the tire disintegrate to the rims as I continue down the highway in a shower of sparks like on those cops shows? I hope these are precautionary limits and if needed I could for instance drive 80 mph or 100 miles distance without damaging my vehicle.

It's all related to heat in the tire. If you drive too fast for too long you will internally damage the tire then eventually it will come apart.

I know that. I was asking how fast and how far if anyone has tested those limits. The differential may also be damaged because of the disproportionate tire rotation speeds.

No experience driving on a 'de aired' RFT, but my guess is: the '50/50 limit' is the tire mfgers being overly cautious and figuring 'everyone' lives in the 'Burbs and can get to their local tire store for a new ~ $250+ tire, combined with barrister buzz words and liability limits...

Otoh, a cursory glance at RFTs on the net did not elicit much info or success in driving well past the '50/50' limit.

Fwiw, I have one car that came with RFTs, (our '02 VetteVert), but the OE tires were replaced by non-RFTs after the original tires wore out. 8 yrs and 35,000 miles later I have never had a prob with the non-RFTs, though I do pack a plug kit and compressor in the large trunk well, in that car.

All anecdotal, but I have had my share of tires going flat, but in the past decade and a half those low air situs have all come to my attention 'in the driveway/garage' and an easy patch/plug job has taken care of the situ. When was the last time one had a 'blow out' or flat on a trip? Happens, but so does getting a hole in one. :)

RFTs have some slight benefits, (mostly emotional), but are really designed for Buffy's piece of mind, imo. ;)
GL, mD

PS: My non tech opin is to not drive an AWD X on a de aired RFT for very far or very fast...

True enough MD. Though I've had my share of flats I have never been on the side of the road with one. I always look at my tires when I approach the car and if I see one getting soft I'll inspect it closely and usually find a nail or other slow leak. I once won a bet that I could see a 3 pound differential in air pressure in my tires.

The real object of my question is because on the freeways I travel on the actual speed limit is around 80 mph. Driving home at 50 would be unsafe with a 30 mph difference in speed. I wouldn't care about shredding a tire but would not want to sacrifice a differential.

As a final thought I believe that run flats will continue to become more popular and non run flat tires will go the way of tires with tubes. Buffy's everywhere rejoice.

On the car, I blew a front runflat tire 65 miles from home. I hit what looked to be a chunk of concrete that had popped up out of the roadway doing about 80 mph. With the speed limit being 70 mph for cars and 60 mph for trucks, I wasn't crazy going much below 55 mph. It was about 60 miles on the highway at 55 mph and then the last 5 miles is 40/35 mph through neighborhoods. It lasted me the drive home, but was definitely getting squirrely the last 10 miles or so and I definitely took it much slower off the exit ramp and turning in the neighborhoods.

Don't know what it would do to the X5, but that's why I have the spare tire kit and non-runflats now.

I have gone through 4 runflat tires in 2 years from the blowout, two sidewall punctures, and a pothole sidewall blowout. Prior to that, I think I have had 2 flat tires in probably 20 years. So far, just not impressed with the cost and frequency so I went with the spare tire kit and non-runflats which will all be put on next weekend.

Run flats are generally pretty terrible tires but they give housewives a nice false sense of security. I hope and expect they will continue to improve to a point where I'll consider using them.

I just switched out my 19" runflats for normal Michelin Latitude HPs. I was surprised that my ride on bumps is not significantly better. I live in FL with perfect roads so I was not exactly having road issues. The normal tires have taken the edge off the on center feel. It is now slightly mushy and not as laser sharp. I can't believe I am saying this, but I may switch back to run flats for my next set. The pricing is similar now although they won't last as long. The bottom line is the engineers tuned the suspension for runflats. I have Adaptive Drive so this may have made the switch more drastic for me.

No mater what, I always will have a spare and never drive on a run flat that is low.

I had the dash warning that my right rear was low, Stop or drive under 50 etc...

I slowly drove through curves and straights to have a feel for handling, ended up going about 25 miles at 75 mph. Tire shop found a screw dead center in the tread and was able to safely plug and boot the tire for $14.95. Reset TPMS and all is well. There was 0 damage to the tire other than the screw in the tread.

Echoing MD's comment,

PS: My non tech opin is to not drive an AWD X on a de aired RFT for very far or very fast...

Thanks. Thats exactly what I wanted to hear.

As an aside. Last year I brought my 2001 X5 with 19" Bridgestone's into my Goodyear tire shop because I had a nail in the rear tire and a slow leak. After a quick inspection they informed me that they couldn't repair the tire because it was ""too worn". I looked at the tire and the wear bars were not even close to showing. They said that on the inside of the tire it was worn so there was no tread left. I said that X5's always wear that way. They refused to repair the tire. I had used that shop for 10 years for all of me families cars. I found another shop that did repair the tire and that are my new go to tire shop. Is this another government rule to keep us safe from ourselves?

Im sure it was.

25 miles at 75mph?? IMO...that is a tire that was almost surely over heated.

One of the reasons mfgs tend to recommend replacement is most rire shops cannot/do not understand tire damage. It is hard to ascertain when the carcass has been damaged due to overheating.... safer to say 'we wont repair a runflat that has been driven on'

why would you drive on a runflat and ruin the tire, when a spare and a tire repair can save the tire?

BMWs wear tires like that because BMW dealers put too much toe on them. Owners are clueless, thinking 'oh its for handling' or 'its the camber' or 'all BMWs do it'

I have no issues with tire shops not repairing tires that are abnormally worn- not a government thing

Ruining a tire is a small price to pay for returning home or a safe harbor safely. Being on the side of the road changing a tire exposing me and my vehicles occupants to danger is not a vision i embrace. I am glad to be running on run flats that can deliver me to safety without having to pull off the side of the road. BMW is known for great engineering and leading edge vehicles. BMW's endorsement of run flats is good enough for me.

I believe the rear tires on X5's wear the inner edges because of too much negative camber. This is designed in at the factory for better handling limits. I had my tuner dial out as much negative camber as possible and I was still at 1.5 degree negative.

Here two interesting videos taking run flats to the limit;

https://www.youtube.com/watch?v=mxHwrMh76tE

https://www.youtube.com/watch?v=FumXPC8MQAI

Whatever dude. Someone is drinking the BMW koolaid...

"small price to pay"? Why not pay body guards to follow you and your family around from safe harbor to safe harbor? Out in the wilds of Los Gatos....

I will usually engage with folks and let them know where they might be mistaken. I know a bit about alignments.

But you seem so wrong, and comfortably smug about it.

Enjoy

Funny you should mention overheating as that was my first concern. Being an old truck driver with over a million miles crossing Donner Pass most days I take my tires and safety very seriously. One of my OCD habits during and after any trip is to actually feel the tires with the back of my hand and "taste" the temperature. While not an entirely scientific process it does allow me to know if one tire is significantly hotter than another. Running duals on truck and trailers it's not always visually apparent that one of your tires is low. The hand trick has saved me from adding to the tire carcasses along the road by discovering a hot tire and taking appropriate action.

I did the same with my X5 after arriving and found no discernible difference between the low RFT and the other 3 tires. I guess the proof will be to see if it survives as long as the other tires over time.

And why run on a RFT? Isn't that exactly the point of having RFTs? Having 3rd row seating there is no place to stow a spare. I was originally thinking about replacing the RFTs with non RFTs when they wore out but now I'm rethinking those thoughts.

Not trying to be adversarial at all Ard. I highly value your opinions on this and other BMW forums. Just sharing my personal perspective.

I was trying to have an intelligent conversation about run flats. I welcome your comments if you can tell me "a bit about alignments". If you want to insult me and other "clueless" X5 owners about where I live or being smug I am glad to continue this off line...

surely, if safety is any concern at all, you wouldn't exceed the safe operating limits of a blown RFT by as much as 50%, irrespective of your in-depth knowledge of the vehicle. i wouldn't.

https://i.imgflip.com/nybrr.jpg

coincidentally, i don't actually see a problem with changing a wheel by the roadside. i did it before RFTs became a thing without incurring loss of limb or life.

[QUOTE=the_ulf; i don't actually see a problem with changing a wheel by the roadside. i did it before RFTs became a thing without incurring loss of limb or life.[/QUOTE]

I don't have a problem with changing a flat on the side of the road either. But my wife takes the car sometimes and I would rather she just drove home or to safety. In my area most of the travel is on superhighways so moving along with traffic is important and getting off an off ramp at night in some neighborhoods has its own risk. I would easily sacrifice a tire, a rim, or a major repair to get her home safely.

without wanting to turn this into an argument, i wasn't debating your or your wife's capabilities of changing a wheel, or the rationale behind preferring to drive home on a flat RFT. the thread is about the operating limits of RFTs and i'd most certainly question the wisdom in finding out just why exactly there's indeed a 50 mile/50mph limit while travelling at 75mph. you *might* get to your destination maybe 5 minutes sooner or maybe not at all. and is that really worth risking your vehicle?

Good input.

While the point of having a RFT is to be able to drive on them, the question of "once driven on will this retain a safety rating" drives repair shops (and BMW) to declare 'no'. This protects them against the idiot that damages a tire, goes to a shop and an untrained tech pops a plug in a tire with a damaged carcass.


Personally havent seen enough internally damaged tires to know when they are toast- once I saw a tire with fine rubber 'shreads' coming off the interior. But in terms of looking at a puncture, feeling for delams, how to inspect the inner surface of the tire- I dunno.

I carry a spare, Id pull off the next exit or safe spot. My wife would do the same and call AAA. And Id have no qualms about repair of the tire in that scenario.

Finally I applaud the 'we will see how it fares' attitude. I cannot tell you how annoying the 'gotta pay to play' and 'are you willing to risk your FAMILY to save a few bucks" responses are. :cool:

PS Put that tire on the rear, just in case....

Just FYI: My flat was right rear, and there it stays. Had it been one of the front tires we would not be having this discussion.

I'm not a tire guy but I trust the place I go to and know the guys well. I watched as they spent a few minutes going over the entire tire in and out very carefully. They plugged then booted on a spreader machine. After booting they attached some sort of electrical tool to the booted area inside the tire and left it sit for about ten minutes. I don't know what this thing was but I'm guessing some sort of curing or annealing device. I don't know rubber compounds so I may not be using the right terms, but just saying it looked like they did a thorough job rather than a plug n run.

I'll be the first to return and report if that tire fails prematurely because I firmly believe we all learn from the shared experiences.

Finally, I want to be clear that I was neither condoning nor encouraging anyone to do as I did, I was merely sharing my own experience. I'm old, kind of onery, drive alone, and have driven through more rear blowouts and tire shreds than I want to remember over the years. If you've got a family in the car do the safe thing and follow the rules.

I completely agree :thumbup: By the way, what was the size and manufacturer of the tire?

My tires are the BMW standard for that year, Bridgestone Dueler, 18 inch, about 12 k miles so far.

really interesting this..
recently had a rear run flat go on my 4.6is with 20" standard wheels, i was in slow moving motorway traffic(30-40mph) and i only noticed when i could smell the burning rubber as the tyre was rubbing the inner wheel arch. i pulled over as soon as was safe and found a screw dead center of the tread. my car has LPG fitted so no spare !! i put 2 cans of aerosol emergency snot in and drove the last 6 miles home at around 25mph (side roads) stopping every 5 mins to check how hot the tyre had got, very. finally made it home and pulled the wheel off to find the inner wall of the tyre was almost completely worn away.
went to see my local tyre shop and asked him what he recommended as a replacement.. cheap Malaysian non run flat or bridgestone run flat. he explained the differences, and prices, and i decided to go with the cheap Malaysian as an experiment. these tyres are rated for the same speed as the expensive options and the fitter said he had fit loads of them with no come backs.
i am not a fast or sporty driver and here in the uk there are too many cameras to be anyway so why not. i will keep an eye on the wear and report back on here in a few thousand miles regarding wear/comfort/handling, if anyone is interested, but so far all is good.

ps, 2 cheap Malaysian tyres fitted and balanced were less than half the price of 1 Bridgestone !!!!!

Pat

Only warning I can add is that you want to be sure the 'rolling diameter' is the same on the Malaysian tires as those on the other axle. Not just the numbers 3xx/xx-20, but the actual spec'd number.

ps, 2 cheap Malaysian tyres fitted and balanced were less than half the price of 1 Bridgestone !!!!!

Pat

What was the brand of those Malaysian tyres? Your tyres link didn't reveal. Just wondering. I am going to stick with Bridgstone when its time for a change.

Hi Tomaz,

The tyres are made by a company called Jinyu.

Eu ratings, wet economy noise (db) price each £/$

Jinyu C C 73 62/81
Bridgstone B E 73 250/328

A obviously the best, E the worst.

Like I said, a bit of an experiment

Pat

Hi ard,

Thanks for the warning

Do you mean rolling circumference?

The static diameter of the new rear tyres is <1 cm greater than the fronts, which considering the fronts are part worn I think is quite close. That said, this gives a difference of 18mm (3/4") in the static circumference front to rear.

Do you know if there is an allowable difference/tolerance and if so what it Is?

Thanks Pat

Technically it is 'rolling diameter' or 'rolling radius' (since the tire deflects when rolling it really isnt a perfect circle so there isnt a circumference per se, or the circumference just gets distorted and doesnt change.)

0.75 is WAY TOO MUCH.

The stock BMW tires allows up to a 1% variance. We actually dont know the actual specification, but certain BMW wheels from the factory come with (I think) 712 rev/mile on one axle and 720 on another 8/720=1%. Hence one might infer that if BMW ships cars with that mismatch, that the engineering allows at least 1% tolerance

Stock size is roughly 29.0"... 29.0 versus 29.75 is way more than 1% You are probably running 3 times the tolerance.

You are likely stressing, perhaps wearing and maybe overheating the diff.

Thanks. Good luck and keep us informed.

Great prices... you can probably get 25 tires per transfer case.

Hi ard,

Once again thanks for the info.

I think I may have confused the issue a bit, I quoted the circumference of the tires, not the diameter......

I work best in metric so will try to give best info possible, even though they are metric size tires on imperial rims ???!!!!

Fronts, 50.8cm (20") rim, 11cm tire height (×2) = 72.8cm diameter (new) - 0.8cm (wear) = 72cm.
Rears, 50.8cm (20") rim, 11.025 tire height (×2) = 72.85cm diameter

Total difference 0.85cm. Which I think works out around 1.1% so only just outside the BMW 1% spec.

If my maths or understanding of your info is incorrect, please correct me. It's been a long time since I left school and college :rofl:

Pat