Yet Another Cycling Forum

General Category => The Knowledge => Topic started by: mrcharly-YHT on January 05, 2019, 09:30:34 am

Title: Flints and tyres
Post by: mrcharly-YHT on January 05, 2019, 09:30:34 am
Flints are something new to me. A cycle commuter in my office (15mile each way) has warned me that the local roads have many flints, worse in winter.
Best flattish tyres? I guess people will say M+
Title: Re: Flints and tyres
Post by: Andy64 on January 05, 2019, 10:03:56 am
I have used Vittoria Randonneur Pro 37mm, without getting any punctures on my CAADX, on glass strewn cycle paths, horrible roads and off road gravel paths. You also get a reflective strip on the tyre, which is handy in the winter months
Can't compare to M+ as I've never used them
Title: Re: Flints and tyres
Post by: Brucey on January 05, 2019, 10:08:08 am
there are only a few strategies against flints. Do bear in mind that they don't puncture tyres in one fell swoop; they usually lodge in the tyre and are driven through it by successive rotations of the wheel.

 In winter there are more flints (e.g. freshly washed out of the soil), the flints you have are sharper (they lose their sharpest edges if they lie in the road for long) and when it is wet they penetrate the tyre more easily (water is an effective cutting lubricant for rubber)  The main strategies against them are

a ) a tough layer that cannot easily be cut; eg a Kevlar layer.  This can be thin and light but it does usually adversely affect the Crr of the tyre. This approach isn't 100% effective because a flint that is lodged in the tyre can gradually nibble its way through almost anything.

b) a thick layer of some kind; if it is thick enough most flints won't make their way though it even if the layer is easily cut. M+ tyres work like this; the layer is so thick that even a drawing pin may not be long enough to penetrate the tyre. Extra weight is inevitable, Crr increases are mitigated by using an elastic(low hysteresis) layer

c) knocking the flints out of the tyre. This is how 'tyre savers' (flint catchers) work. They are never 100% effective and they only work well on smooth-ish tyre treads and then only if they are correctly fitted too.  One downside is that they throw crud outwards and sideways  and this can make a mess in its own right, even if the tyre saver is mounted under a mudguard. However this approach does stop flints from cutting the tyre carcass badly.

d) using a sealant of some kind (in a tube or tubeless).  This has the significant disadvantage that it does nothing to stop the carcass of the tyre from being cut to ribbons and this may cause the tyre to fail if it is built light.

Harder rubber compounds make a difference too but this is usually at the expense of grip.  When commuting things are different from most other 'training rides' in that a puncture may make you late; you either need to be almost 100% sure you are not going to get one or you need to allow enough time to fix one should it occur.  Most folk accept the slowness/lack of comfort and just fit M+ tyres (or similar ) because it is the most straightforward approach.  However these may be overkill for your roads; less strongly built tyres may work well enough for you.

cheers
Title: Re: Flints and tyres
Post by: Jurek on January 05, 2019, 10:27:14 am
After I've been riding in the wet, I make a point of deflating the tyres and going round them, pinching the carcass to expose and remove anything which has embedded itself in it.
This results in very few punctures.
Title: Re: Flints and tyres
Post by: Kim on January 05, 2019, 12:35:38 pm
After I've been riding in the wet, I make a point of deflating the tyres and going round them, pinching the carcass to expose and remove anything which has embedded itself in it.

+1 to this, especially when the tyres have a tread pattern that's good at accumulating nasties with little initial penetration.

Not ideal for commuting, mind.  I'd probably just bung Marathon Pluses on and consider it 'good training'.  Certainly in winter when fixing punctures is miserable, even if the tyres are reasonably cooperative.  Otherwise, tubeless might work reasonably well...
Title: Re: Flints and tyres
Post by: quixoticgeek on January 05, 2019, 12:42:29 pm
Flints are something new to me. A cycle commuter in my office (15mile each way) has warned me that the local roads have many flints, worse in winter.
Best flattish tyres? I guess people will say M+

I'm not sure M+ has enough benefits over normal Marathon greenguard to be worth the extra rolling resistance.

What i can say:

Gp4000s II are crap when it comes to flint.
GP 4 seasons aren't much better...

J
Title: Re: Flints and tyres
Post by: Kim on January 05, 2019, 12:51:12 pm
Flints are something new to me. A cycle commuter in my office (15mile each way) has warned me that the local roads have many flints, worse in winter.
Best flattish tyres? I guess people will say M+

I'm not sure M+ has enough benefits over normal Marathon greenguard to be worth the extra rolling resistance.

Depends on whether you want to reliably get to work on time, surely?

The regular Marathon is my tyre of choice for touring-ish riding, where I'll happily trade a slightly higher puncture rate for a tyre that rolls better and isn't a bastard to get on and off the rim.  But they[1] do have a bit of a weakness for flints, in as much that when I have had a deflation that's usually the cause.


[1] Well, the HS368 did.  I've yet to have a visitation on the newer HS420.
Title: Re: Flints and tyres
Post by: mrcharly-YHT on January 05, 2019, 03:40:18 pm
For a 10mile commute, I think using slower tyres wins out over faster tyres and risking punctures.

As I have nearly new tyres on the bike, I'll give it a week and see (might regret that).

Looking at the bicycle rolling resistance site, schwalbe Almotion look like the holy grail here - fast and puncture resistant. But, my life, they are expensive!
Title: Re: Flints and tyres
Post by: Pickled Onion on January 05, 2019, 04:02:14 pm
M+ are massively better than anything, if your priority is avoiding punctures. I've used them on the brompton for about ten years of daily commuting and they have punctured once — that was when I wasn't looking and went over a half-bottle standing upright. Even that, something that would have normally destroyed both tyres, only punctured one and it was still in a fit state to ride after the inner tube repair. By comparison, when I changed brompton but hadn't got round to changing the tyres I had three punctures in a single wet morning.

They are not nice to ride, definitely slower, but not too bad if you pump them up to the rated limit which is somewhat higher than expected for the size.

I would add to Brucey's list: e) ride well away from the verge in the line of the left car tyre.
Title: Re: Flints and tyres
Post by: rogerzilla on January 05, 2019, 06:43:41 pm
They can rip a 2" gash in a sidewall!  Avoid gravel at the edge of the road or anywhere else that water has dumped it.  The flints tend to stay when the chalk or clay around them has washed away.

They aren't a massive problem if you keep.out of the gutter - I grew up somewhere that was infested with them.
Title: Re: Flints and tyres
Post by: Brucey on January 06, 2019, 01:07:49 am
FWIW by 'flints' I would normally assume that you meant small stone fragments that are typically about 3mm long.

  Bigger things that can gash sidewalls are always a threat on some off-road tracks but correct use of the Mk1 eyeball is the primary protection against those when riding on the road. If you don't keep your eyes well peeled enough to spot such then you will surely also smash your wheels to bits through potholes amongst other things.

Remember I mentioned that the hardness of rubber makes a difference?  Well, I try and use tyres that I have 'matured' for at least six months on my training/utility bikes, reckoning that I am better off trading away some grip in return for better puncture resistance.  Contis (4000 or 4S) in particular are often exceptionally soft when they are brand new and cut up rather easily as a consequence.  After about eighteen months they are often so hard they lack wet grip, but are somewhat more resistant to flints. Gatorskins have harder rubber from the start.

cheers
Title: Re: Flints and tyres
Post by: LittleWheelsandBig on January 06, 2019, 05:25:41 am
HK has Almotions on her Kinesis and they seem to have performed as advertised for the past 3 months or so of almost exclusive use for commuting and brevets (about 7,000km, another 500km or so on other bikes or trike). Run tubeless but with no evidence of sealant plugging holes. No cuts, no obvious wear, better comfort and traction and lower rolling resistance than her previous favourite Contis (which I've never rated). Few flints on her commute but lots of glass and hedge debris.
Title: Re: Flints and tyres
Post by: Kim on January 06, 2019, 12:49:13 pm
Bigger things that can gash sidewalls are always a threat on some off-road tracks but correct use of the Mk1 eyeball is the primary protection against those when riding on the road. If you don't keep your eyes well peeled enough to spot such then you will surely also smash your wheels to bits through potholes amongst other things.

I once had a nasty sidewall gash from a bit of bent wire that was almost invisible on a wet road.  Nothing short of a solid tyre would protect you from that sort of bad luck.  But that's going to be pretty rare.
Title: Re: Flints and tyres
Post by: Brucey on January 06, 2019, 01:46:50 pm
didn't someone recently post a picture of a nail that had gone through both the rear tyre and the rear rim?  I don't think anything will protect against that..... :o

BTW I mentioned that to the folks in my LBS and they confirmed that they had seen something similar, but only once. Between them they have a hundred-odd man-years of spannering/riding behind them.

One of my mad ideas is that if you have a skinnier front tyre then the number of rear wheel punctures might decrease; there may be fewer FOs flicked up at a jaunty angle by the narrower front tyre.  In a similar vein it is unclear if the typically higher rate of rear wheel punctures is due to the difference in the loading on that wheel or if it is flicking up of FOs by the front wheel.   Miles Kingsbury seemed to get more rear wheel punctures on his USA trip in his Quattrovelo thingy than his companions who rode similar width trikes, so maybe there is something in the flicking hypothesis; the loading on his rear wheels would have been about half that of a three-wheeled velomobile rear wheel but his rear wheels were in line with the fronts.

cheers
Title: Re: Flints and tyres
Post by: Kim on January 06, 2019, 01:48:59 pm
A velomobile doesn't wobble like a bicycle, so the rear wheel spends more time in the track of the front wheel, too.
Title: Re: Flints and tyres
Post by: rogerzilla on January 06, 2019, 04:16:20 pm
Jobst Brandt refused to believe that flints are a thing.  They must exist in California, surely?  The South Downs (Hants/Berks) are the place for them in the UK - they occur with chalk landscapes.
Title: Re: Flints and tyres
Post by: mrcharly-YHT on January 06, 2019, 04:40:57 pm
Jobst Brandt refused to believe that flints are a thing. 
Seriously? Jobst can be very clever and then counteract that with extreme ignorance.
Title: Re: Flints and tyres
Post by: Brucey on January 06, 2019, 04:45:23 pm
flints exist anywhere there is chalk nearby and anywhere there are glacial moraine deposits of the right sort (eg from the last ice age).  The latter includes a lot of places you wouldn't at first expect in southern England especially.

 IIRC what we call flint is a subset of a wider category called 'chert' by geologists; this refers to any microcrystalline quartz. Chert fragments are almost identical to flakes of flint both in appearance and their ability to work their way into bicycle tyres.

If you have never lived/ridden in a cherty/flinty area it is hard to comprehend just how troublesome these little blighters can be.

In some places I have seen a high grip surface locally applied to roadways made of otherwise slippy materials eg concrete.  This appears to comprise almost exclusively of the things we call flints and every single one could give you a puncture. Since about half the material applied soon comes unstuck, such surfaces represent a major risk to bicycle tyres.

cheers
Title: Re: Flints and tyres
Post by: LittleWheelsandBig on January 06, 2019, 05:18:03 pm
There are plenty of concrete roads around the world, including motorways in heavy rainfall regions. Highways England has a wealth of applicable standards and specifications for them, accessible to the public. Bituminous overlays are usually to reduce traffic noise and spray. Traction usually isn't an issue.
Title: Re: Flints and tyres
Post by: LittleWheelsandBig on January 06, 2019, 05:53:35 pm
A velomobile doesn't wobble like a bicycle, so the rear wheel spends more time in the track of the front wheel, too.

The vast majority of velomobiles are trikes, so the rear wheel is rarely in the track of a front wheel.
Title: Re: Flints and tyres
Post by: Cudzoziemiec on January 06, 2019, 05:55:07 pm
Someone on the ACB* Whatsapp posted a photo of a nail or screw through their rim this summer. I don't think that was posted here though. I'm not sure if it was flicked up or simply run over.

I've had a large bolt flicked up by the front tyre and straight into the back. But not through the rim, thankfully! That was at a fail lick (downhill) and with knobbly tyres. I wonder if knobbles increase the likelihood of items being flicked up? They could get caught and 'channeled' between the knobbles.

*A group of admirable cycling nutters in Bristol.
Title: Re: Flints and tyres
Post by: Kim on January 06, 2019, 10:09:09 pm
A velomobile doesn't wobble like a bicycle, so the rear wheel spends more time in the track of the front wheel, too.

The vast majority of velomobiles are trikes, so the rear wheel is rarely in the track of a front wheel.
Well yes, but we were talking about quads.
Title: Re: Flints and tyres
Post by: Brucey on January 06, 2019, 10:20:50 pm
There are plenty of concrete roads around the world, including motorways in heavy rainfall regions. Highways England has a wealth of applicable standards and specifications for them, accessible to the public. Bituminous overlays are usually to reduce traffic noise and spray. Traction usually isn't an issue.

yes but as I said I have seen this stuff overlaid on smooth concrete and it has caused considerable puncture  problems for cyclists.

cheers
Title: Re: Flints and tyres
Post by: LittleWheelsandBig on January 06, 2019, 10:55:29 pm
Smooth concrete provides a good friction coefficient provided the coarse aggregate doesn't polish easily or is iced over/ gunged up. Concrete roads are always coarsely brushed or raked to provide drainage.

If you are talking about chipseal over concrete slabs, it is usually applied for waterproofing of excessively cracked concrete and the subgrade below. It doesn't last very long, even on farm tracks as the chips can't mechanically interlock with underlying layers and in its absence the bitumen emulsion doesn't provide enough adhesion to resist braking and turning wheel loads. Anybody who is taking that approach is probably a shyster and of course they are going to use cheap and nasty materials.

There are thin overlays specifically for use over concrete highways (that are pre-cracked to change them from a rigid pavement to a flexible or semi-rigid pavement) but the technology and intent is quite different and they don't lose aggregate to any great extent.
Title: Re: Flints and tyres
Post by: Brucey on January 06, 2019, 11:02:15 pm
this was used on precast roadway sections, only in places where there was (seemingly) a skid risk.  Being precast the surface of the concrete is smooth.  I have never seen the coating (which is exactly as described earlier, and accordingly has no resemblance whatsoever to chipseal) used on anything else, thank goodness; in causing bicycle tyre punctures it would come a close second to just strewing drawing pins all over the place.

cheers
Title: Re: Flints and tyres
Post by: LittleWheelsandBig on January 06, 2019, 11:18:00 pm
A velomobile doesn't wobble like a bicycle, so the rear wheel spends more time in the track of the front wheel, too.

The vast majority of velomobiles are trikes, so the rear wheel is rarely in the track of a front wheel.
Well yes, but we were talking about quads.

Quattrovelos have different track widths front and back.
http://en.velomobiel.nl/quattrovelo/maatschets.php
Title: Re: Flints and tyres
Post by: LittleWheelsandBig on January 06, 2019, 11:27:29 pm
this was used on precast roadway sections, only in places where there was (seemingly) a skid risk.  Being precast the surface of the concrete is smooth.  I have never seen the coating (which is exactly as described earlier, and accordingly has no resemblance whatsoever to chipseal) used on anything else, thank goodness; in causing bicycle tyre punctures it would come a close second to just strewing drawing pins all over the place.

cheers

A smooth concrete surface has a good friction coefficient.
https://www.gomaco.com/Resources/worldstories/world36_1/bristol.html

I have no idea what type of surfacing you are talking about as usually the aggregates used in normal bituminous pavements (asphalt or whatever) have shape and durability requirements that rule out using a high percentage of anything that behaves/ looks like flints.
Title: Re: Flints and tyres
Post by: Brucey on January 07, 2019, 07:29:37 am
having unexpectedly skidded on smooth concrete myself I think there are conditions under which the measured coefficients of friction do not apply. Clearly those responsible for this roadway thought likewise else they wouldn't have added the surfacing to it.

  As I said in the first instance this is an unusual surfacing which I have not seen more widely used (thank goodness).  If I had to describe the aggregate used in two words, I'd say it was 'shattered flints', any one of which might, once loose, be sharp enough to cut/puncture a bicycle tyre.

cheers
Title: Re: Flints and tyres
Post by: LittleWheelsandBig on January 07, 2019, 07:46:23 am
That sounds more like the grit used on bituminous roofing or to prevent an emulsion seal coat from being lifted up by construction traffic tyres.

Precast concrete panels are an extremely unusual way to construct a road surface (quite rare even on bridges), so probably best considered an experiment or aberration.
Title: Re: Flints and tyres
Post by: Brucey on January 07, 2019, 08:43:04 am
not that I have any great knowledge in this field but I have never seen an aggregate like this before; it might well be meant for some other purpose, but I don't think it is the same stuff as appears on roofing felts.

 The added surfacing has only been applied in a few key areas but as for describing the roadway as 'an experiment or aberration' I think that is about right.

cheers
Title: Re: Flints and tyres
Post by: Tigerbiten on January 07, 2019, 01:38:08 pm
At a guess it sound like some form of blast furnace slag as it a glassy aggregate that can be used in tarmac and concrete.
Title: Re: Flints and tyres
Post by: LittleWheelsandBig on January 07, 2019, 01:56:23 pm
I don't know of anybody using blastfurnace slag as aggregate in recent times; it is pretty valuable for other things. Ground Granulated Blastfurnace Slag (GGBS), fly ash (electrically precipitated from coal-fired power station smoke) and silica fume (from making ferro-silicon alloys) are all used as cement replacements when making concrete (replacing 25-85% of the cement content) with some quite handy performance enhancement, apart from the green benefits. The continuing reduction in blast furnaces, coal-fired power stations and steelmaking in the UK must significantly reduce the availability of these materials at some point.