1

I found similar questions:

But I haven't found a structured analysis on the subject of tyres.

Stack exchange technicalities: It is the rear tyres on two bikes in my family that seem to be a concern, so I kept my question specific to rear tyres. But please feel free to edit the title and question if you feel that provides a better balance of things like keeping the question specific vs effort required to provide a clear answer. I just don't know if it's better to deal with just the rear by itself or both wheels together to make this question useful.

Logic: Ideally I would love a structured answer, perhaps based on this article about hazards vs risks. Naturally there may be other ways to approach this.

The hazards that come to my mind are:

  1. Loss of grip in a bend/obstruction avoidance
  2. Braking performance - this is probably fairly gradual until the tyre punctures?
  3. Puncturing - the resistance can probably be measured, with some graphs based on some standard puncturing object vs tread depth?

How the hazards translate to risks then probably depends on several factors, like the sort of riding you do, what mode of failure is developing on the tyre (cracks vs thinning) etc. You could probably write a books about this, right?

Clearly if I'm already pushing my tyres to their limits in bends/braking etc. then the tyres need to be it tip-top condition. I don't think I ever get anywhere near these limits, but I guess I am conscious about emergency braking in commuting on roads.

Do countries have government rules for bike tyre safety, like the MOT rules for cars in the UK? I'm not asking about the annual testing and certification, I'm on about the minimum standards of roadworthiness.

I really thought that this subject has been dealt with on this site or elsewhere, but I couldn't find anything complete/clear/structured.

It if matters, the reason I'm asking is I am a bit of a pessimist (perhaps a primary characteristic), and therefore both a cheapskate and safety-conscious, which I would argue are both secondary characteristics on one hand, but clearly conflicting on the other. Safety and frugal are valid tags on this site, pessimism isn't:-)

  • 4
    Movie plot - tire blows out, rider crashes and slides under a truck, truck swerves and runs into crowded bus stop squashing every one, rider stands and while lookoing on in horror walks in front of bus arriving at the bus stop. – mattnz May 13 at 6:55
  • 2
    What's the advantage of using a worn tyre? Saving money. That's it. Everything else would be the negatives. – Criggie May 13 at 7:22
  • It would be interesting to know why my question is currently -2. I linked two questions as an introduction, both seem similarly formed and both are above +15. No ambition here, just genuine curiosity about asking useful questions etc. – pateksan Jul 9 at 1:41
  • Seems like a perfectly valid question to me, and the OP has demonstrated that he or she has searched the site for existing answers: +1. – rclocher3 Jul 16 at 0:20
4

As others have said, the biggest risk comes from sidewall failures. Even with the tread worn out there's usually enough (reinforced) rubber to prevent splitting on the tread, but the sidewalls are weaker.

I would say the worst case is for it to blow out while cornering hard. You're likely to lose grip and not get it back again, so slide out and hit the ground. That hurts. Taking this to extremes it would happen while being overtaken very closely and you'd get run over, but that requires multiple simultaneous bad things to happen at the same time that you're doing something (cornering) that's a small proportion of your riding.

A rear tyre blowout in a straight line isn't a big deal in my experience (though I had some warning from the sound of the tube bulging through a damaged sidewall). I have had the rear wheel lock up when riding steadily a few times (derailleur sucked into wheel, broken spoke catching on chain, tyre coming off the bead and wedging against the seatstay)

What's more likely is that you'll get repeated punctures. These aren't inherently hazardous, but can easily leave you cold,wet and exposed to traffic in fading light for which you're not prepared, as you walk home, fix it, or wait for help.

| improve this answer | |
  • 1
    Are you sure about sidewall failure? One generally wears out the center tread first, and if you’re determined you can wear it completely down to the carcass. The sidewalls themselves are basically the sidewalls of the carcass, although there might be a puncture protection belt in there somewhere. I think that in the scenario given, the issue is more failure of the carcass itself, due to abrasion. – Weiwen Ng May 13 at 10:50
  • 1
    @WeiwenNg unless you're really putting the miles in, ageing is a bigger factor than wear. You and I may wear out tyres but very many bikes won't be ridden far enough. I've worn out marathon plus on one bike, but on another that did around 15km/week and was stored outside the tread was almost new when the sidewalls started cracking. Even cheap tyres generally have thicker rubber on the tread than the sidewalls, even excluding any knobbly bits. – Chris H May 13 at 13:02
  • 1
    I'd like to add that if a rider suddenly loses traction in the rear wheel during a turn to the point that the wheel slips, such as may happen in a blowout, then the result is generally a skid, which may or may not be recoverable. However, if a rider suddenly loses traction in the front wheel during a turn so that the wheel slips, then the rider will soon crash. – rclocher3 Jul 16 at 0:29
4

If it’s just the rubber tread which is worn down and thinner: Keep using it. With treadless tires you’ll only suffer from increased susceptibility to punctures. Of course with knobby/treaded tires your grip on soft surfaces will gradually decrease.

If the tire’s structural integrity could be compromised: Don’t use it. It could fail catastrophically at any time. Things like bulges, abrasions of the sidewalls, cuts or large cracks are all bad signs.

| improve this answer | |
  • Thanks, I suppose this answers it to some extent, but I'm trying to get a picture of what exactly could happen if a tyre does "fail catastrophically", perhaps how much of a sideways push/force/throw it could generate etc. I edited my question by adding the paragraph about whether/how much the the tyres are pushed to their limits. – pateksan May 13 at 5:58
  • 1
    When the fabric under the rubber starts to show then it's time to get rid of the tire, regardless. – Daniel R Hicks May 13 at 12:28
2

Worst case from a worn tyre would be it splitting, and popping off the rim causing the wheel to lock up, and you to probably fall off, or at least damage the wheel.

I managed to get an innertube pinched between the front rim and the tyre on a racing bike, got a few hundred metres down the road and it popped with enough force to completely blow the tyre off the rim, but I managed to coast across the junction I was in and nothing really came of it.

To deal with your hazards:

  1. This is possible if you have worn through the grippy layer of rubber entirely on a slick, or are riding a bald rear tyre offroad, however you're far more likely to slip, particularly in an uncontrollable manner due to road conditions. This is more likely to be caused by an old tyre which has hardened than wear.

  2. Braking performance is as above really, its probably more likely to lock up, but until you're at the point of locking your wheel there won't be any change. You should be putting most of your braking force through the front anyway.

  3. This has too many variables. Is the object glass, flint, thorns, a thumbtack, or have you gotten a pinch flat? Tyres come in many different compounds and tread patterns, and different types of punctures are more or less likely at different levels of inflation, and depends on your inner tubes, whether they are thick or thin butyl rubber, or latex, or even tubeless! Extremely simplified, you'd have a yes/no scenario, with a 2mm object causing a puncture as soon as the tube is less than 2mm from the outside of the tyre.

I cannot think of any country which has a 'bike MOT' as bikes don't have licence plates etc, so it'd be impossible to monitor. Many countries don't even have a car MOT equivalent!

If you aren't sure about a tyre, change it. Decent ones can be found on sale for £10 or less.

| improve this answer | |
  • Thanks. I edited the MOT bit of my question to add "I'm not asking about the annual testing and certification, I'm on about the minimum standards of roadworthiness." – pateksan Jul 16 at 3:27
1

This answer is from the OP, I don't like the fact stack exchange doesn't seem to show it clearly. Also, for now it's just a stub for an answer, written on a mobile, I hope to extend it when time permits.

The question has become a lot less important to me since I started working from home due to covid, but I have been looking into this occasionally.

There doesn't seem to be anything like an MOT for bikes or any detailed rules for roadworthiness. However, case law is a good indication, and I have come across two cases which have some relevance.

https://www.bbc.co.uk/news/uk-england-hereford-worcester-33236920

http://thecyclingsilk.blogspot.com/2017/08/the-alliston-mis-trial.html?m=1

More reading here: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/685600/cycle-safety-review-report.PDF

| improve this answer | |
  • Some countries (among which the Netherlands) have annual checks with a 'checked' sticker for kids bikes: "deze fiets is OK", and the tradition to have an annual bike check-up with prices given for that. (I think Denmark, Belgium and Germany might have similar checks.) – Willeke Jul 16 at 11:01
1

The biggest risk is some sort of sudden tire failure, either a "blowout" or the tire actually coming apart.

On a smooth, level roadway with no traffic a simple blowout is usually not too hazardous, but if it happens on a tight turn you could be sent into a nasty slide, if it happens on a fast downhill you could lose control and crash, and if it happens in traffic no telling what could happen.

And if the tire comes apart it's apt to lock the wheel, further compounding things.

(And you don't even want to think about these scenarios on a front tire.)

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.