The latest example is a Bridgestone (I think) ad where they are driving and explain that you can drive 50 miles on a flat.
This seems like a good idea. You get a flat because you hit something, then you can drive the remaining miles to a place and fix it. I am making a few assumptions, but I have a few general questions.
1.) If you hit something and are able to drive away, how do you know you have the flat?
2.) If it isn’t rather obvious to the driver, wouldn’t this just lead to you driving 50 miles further before you have to get out an change it – effectively making no difference?
3.) Is there a sensor? I know every vehicle we’ve owned with a TPMS has had a large number of false alarms of “low air” - one had a flat and the shop replaced the tire and the sensor - it’s always read low ever since. How reliable are the drive flat sensors?
I’m just curious. Seems like this is the best place to ask!
Getting a flat with a run-flat tire is pretty much the same as getting one with a conventional tire, the only difference being that with the run flat you can limp home a short distance at low speed without destroying the tire. You’ll definitely notice you’re driving around with a flat tire and won’t want to do it any longer than you have to.
The tire doesn’t stay fully inflated when you get a flat with run-flat tires. You can feel it if you get a flat and your tire pressure senor should light up as well.
The driver will notice the flat. Many vehicles today don’t have a spare at all so run-flat tires can help you get home or to the shop without much drama although you generally can’t drive at high speeds if they get a flat.
They have tire pressure sensors in each wheel. The sensors can develop faults just like anything else but they are generally fairly reliable these days.
For the record, my Toyota RAV4 Sport came with run-flat tires. I got two flats with them and they did work fine to get me home. However, I still didn’t like them and eventually got rid of them completely and just got a AAA membership in case I get another flat. Run-flat tires tend to generate a whole bunch of road noise because their sidewalls are so stiff, they affect driving performance negatively in my experience, they wear out faster than most other tires and they are very expensive. Unless you drive around a lot in some remote and dangerous places, I don’t think they are worth it
That was pretty quick. I’m going to have to think of harder questions to be curious about. Although I never trust our pressure monitors, I guess it makes perfect sense that you would be able to feel it.
I also understand that I probably drive more than the average vehicle owner - at least 40 miles in each direction per weekday, plus each weekday is basically a different direction. On top of that, we’re at least 20 miles from a real grocery store in any given direction, so evenings may include just as much driving as day time, which makes me think “only 50 miles? that might get me close…” any time I hear something like this.
I’m going to be a little contrary on this and say that you may not notice a flat when you have run-flat tires. I had a Mini Cooper S with very low profile run flats on it, and a very stiff (aftermarket) suspension Even when all 4 tires were inflated, it felt like riding on the rims.
So much so that the one time I did get a real honest to og flat tire, it was only the TPMS that alerted me. When the warning light suddenly popped on, my initial reaction was "Well, that’s a glitch, since I don’t feel a flat tire. Pulled over at the next exit (about 3 miles) to double-check, and yep, one of my rears was down. Used my tire-plug and inflator, back on the road in like 15 minutes.
I drive right at that much too. 50 miles is only a guideline, not a strict limit. You can probably make it a whole lot further than 50 miles if you are careful. The point is that the tire companies don’t want some idiot to think that it is perfectly normal to drive thousands of miles on punctured tires because even run-flats need proper inflation to perform correctly.
I had a bad run for punctured tires a couple of years ago. It was just bad luck as far as I can tell. The most notable puncture was a very large piece of a bike rack that impaled my left drivers side tire in a way that is hard to imagine at 80 mph. It destroyed most of the tire but it still worked OK. I still had someplace to be 60 miles away and still made it fine after slowing down to below 55 mph on the interstate. I drove all weekend like that for a total of about 150 miles. Performance and handling suffered but I never thought it was unsafe. The way that they work is to have a reinforced sidewall that can support part of the weight of the vehicle without letting the rim hit the pavement and destroy it. You can drive a very long way like that if you are careful or you can destroy the whole assembly if you do something dumb like drive fast over rough pavemen or start hitting curbs.
Run flats do work but, like I said, I am not a huge fan because they introduce lots of other financial costs, noise and performance penalties to mitigate a risk that most people don’t face that often these days. I have had exactly 4 flats in over 500,000 miles of driving. In two of those cases, run flats saved me a little time but I could have also made it without them as long as I was willing to wait for a AAA tow truck for a lot less money because you have to have to go to the tire shop anyway even if you get a flat on run-flat tires.
Once they invent run-flats that are quiet, don’t introduce a huge cost premium and have performance similar to regular tires, I will look at them again. Otherwise no. I don’t live in Afghanistan and can get a tow truck if the worst case happens.
I’ve had nails in my BMW run flat tires several times. I know because my tire pressure monitor warned me that a tire was low. I actually pumped it up once a day for a few days until I had a chance to get a new tire. It drove perfectly normally.
Saves you from having to change a left side flat on an interstate, or any flat on either a curvy, rolling-hill, two-lane, shoulderless country road on a cloudy night (pitch dark & no safe place to pull over) or the worst drug-infested, gang-turf war intercity block you were driving thru which is one of the three places Murphy’s Law says you’ll get your flat.
But the OP appears to have been answered, so; if you get a puncture in a run flat and drive it 50 or so miles to the repair shop, is that tyre still repairable? (assuming it’s a smallish hole in the tread of the tyre)
If the tyre is repaired, is it then as structurally sound as it was in the first place? What if Murphy’s law strikes and I get another (repairable) puncture in the same tyre? Can I keep driving 'til I reach the next repair shop or have I used my 50 miles up?
Note that 50 miles is being used as an example, not a definitive figure. What I’m asking is, where is the limit? I’ve had tyres come in for repair with half a dozen plugs in them already and seen them do thousands of further miles, because they were swapped for the spare before serious damage occurred. Would anything approaching this be possible with run flats that have run flat multiple times?
A run flat tire should be just as repairable as a normal tire.
With the space-saver spares, the 50 mile range isn’t because the spare tire wears out but because it isn’t safe handling-wise to drive around with the spare on. 50 miles is just sort of the arbitrary number meant to communicate that you shouldn’t be driving around with the thing on any more than necessary. I don’t know for sure but I suspect the same is true with run flats-- the run flat components probably won’t be worn out at 51 miles and the tire will still be repairable, but driving around with a flat tire in general isn’t a good idea.
The Tire Pressure Monitoring System (TPMS) would alert the driver that the tire has lost air pressure. Most cars just have one TPMS warning light on the instrument panel and don’t indicate which specific tire(s) have low pressure. But all cars that come from the factory with run-flat tires standard indicate which specific tire has lost pressure.
Most run-flat tires have VERY rigid sidewalls which is what allows them to continue to function without air pressure. The ability to drive XX miles on a ‘flat’ is intended to allow the driver to reach assistance (dealer/tire store/service station) for help. You also aren’t forced to stop immediately when the flat occurs, regardless of how unsafe and/or inconvenient it may be.
As for changing the tire 50 miles later, new cars that come with run-flat tires VERY rarely have a spare tire! The ability to drive on the ‘flat’ is considered a substitute for a traditional spare tire. Another nasty truth is that while the tires may allow you travel 50 or even 100 miles with no air pressure, the tire is usually not repairable after just a few of miles of driving flat! On the plus side, the run-flat will protect the expensive alloy wheel that the tire is mounted on. A new run-flat tire may cost $250+, but a new wheel can cost $1000 or more in some cases!
Even the 20" wheels on my Mazda CX-9 cost $828/each and I don’t have run-flats. I picked up a screw last month and had my first flat since I bought the CX-9 in 2012. The instant that that TPMS light came on, I hit the emergency lane and stopped as quickly as possible. The thought of ruining an $800+ wheel freaked me out. The wheel was fine, but the screw punctured the sidewall of the tire, so it was trashed. I was only about 5k miles away from buying new tires anyway, so I went ahead and got a whole new set for what one ruined wheel would have cost.
All new BMWs come with run-flat tires from the factory. BMW claims that it saves space and weight and that it provides a safety benefit. While the safety benefit claim may have some merit, the space/weight argument seems pretty absurd. A ‘doughnut’ temporary spare, jack and lug wrench don’t take up much space and weight 30-40lbs (at most)!?
Run-flats also share a trait that you hear tire manufacturers or car companies talking about- those rigid sidewalls translate into noticeably harsher ride quality. Not a tradeoff that I’d be willing to make.
As mentioned earlier, cars that come with run-flats from the factory also have a more advanced version of TPMS. But I’m sure that false warnings are still possible. I’ve had issues in the past with TPMS alerts if the car sat outdoors in cold weather for more than an hour or two. As soon as I drove a few miles, (after getting out and double checking the damn tires first, just to be sure) the TPMS light went as the tires warmed up and air expanded!
I would suspect that installing run-flat tires on a vehicle that came with conventional tires would be more susceptible to TPMS issues.