Tyre directionalness

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Chris Jeggo
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Re: Tyre directionalness

Post by Chris Jeggo »

MikeF wrote: 16 Aug 2022, 7:54pm Any motor vehicle tyre with an asymmetric tread either around the circumference or laterally is unidirectional.
A motor vehicle tyre that is asymmetric laterally must be symmetric circumferentially (i.e. bidirectional) unless it is made in both right hand side and left hand side versions.
borisface
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Joined: 19 Feb 2010, 3:48pm

Re: Tyre directionalness

Post by borisface »

If you rode fixed wheel it wouldn't make any difference. You could easily cycle backwards.
MikeF
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Re: Tyre directionalness

Post by MikeF »

Chris Jeggo wrote: 18 Aug 2022, 11:35am
MikeF wrote: 16 Aug 2022, 7:54pm Any motor vehicle tyre with an asymmetric tread either around the circumference or laterally is unidirectional.
A motor vehicle tyre that is asymmetric laterally must be symmetric circumferentially (i.e. bidirectional) unless it is made in both right hand side and left hand side versions.
Indeed. I don't disagree.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
MikeF
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Re: Tyre directionalness

Post by MikeF »

borisface wrote: 18 Aug 2022, 12:05pm If you rode fixed wheel it wouldn't make any difference. You could easily cycle backwards.
Have you tried cycling backwards??
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
cycle tramp
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Re: Tyre directionalness

Post by cycle tramp »

Hey wait.... a couple of years ago I cycled through some floods. They were so deep that when I cycled the pedals splashed into the water.. my tires had no grooves in them, but strangely I could still steer the bike even though the contact patch between the tarmac and the tyre were completely underwater....

..does this mean I have some sort of super power?
Motorhead: god was never on your sidehttps://www.google.com/search?ie=UTF-8&client=m ... +your+side
borisface
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Re: Tyre directionalness

Post by borisface »

MikeF wrote: 18 Aug 2022, 7:53pm
borisface wrote: 18 Aug 2022, 12:05pm If you rode fixed wheel it wouldn't make any difference. You could easily cycle backwards.
Have you tried cycling backwards??
Yes, it was easy. I think I got about 6 feet.
MikeF
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Re: Tyre directionalness

Post by MikeF »

borisface wrote: 19 Aug 2022, 7:39pm
MikeF wrote: 18 Aug 2022, 7:53pm
borisface wrote: 18 Aug 2022, 12:05pm If you rode fixed wheel it wouldn't make any difference. You could easily cycle backwards.
Have you tried cycling backwards??
Yes, it was easy. I think I got about 6 feet.
A short cycle ride then. As you note it shouldn't make any diffence for riding 6 feet either forwards or backwards.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
gxaustin
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Re: Tyre directionalness

Post by gxaustin »

The tread of road tyres is so vestigial and shallow as to make little or no difference to the way they roll. My Contis have no tread on the central part of the tyre anyway. I wouldn't worry
cycle tramp
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Re: Tyre directionalness

Post by cycle tramp »

gxaustin wrote: 19 Aug 2022, 11:19pm The tread of road tyres is so vestigial and shallow as to make little or no difference to the way they roll. My Contis have no tread on the central part of the tyre anyway. I wouldn't worry
The whole idea of grooves in tyres came from car tyres, and the grooves were originally placed in car tyres as an attempt to stop them from aquaplaning.
The reason why car tyres aquaplaning is because the car wheel from 1960s 1970s onwards had a reduction in its diameter but in order to maintain the same amount of contact with the road, made wider. Had the wheel been kept of a larger diameter and a thinner tyre width (think seiers 1 landrover of even tge citreon 2cv) there would be less chance of aquaplaning...
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axel_knutt
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Re: Tyre directionalness

Post by axel_knutt »

cycle tramp wrote: 19 Aug 2022, 5:09pm Hey wait.... a couple of years ago I cycled through some floods. They were so deep that when I cycled the pedals splashed into the water.. my tires had no grooves in them, but strangely I could still steer the bike even though the contact patch between the tarmac and the tyre were completely underwater....

..does this mean I have some sort of super power?
No, it means that the weight on the tyre was sufficient to push the water out* from under the points where the tyre contacts the road. The faster you ride, the faster the water has to be pushed out, and the more weight it would take to do that. The greater the distance the water has to travel the longer it takes for the water to escape from under the contact points too, that's why tread grooves are more important on wide car tyres than narrow bike tyres.

Eventually, if you go fast enough, or the space for the water to escape is insufficient, the tyre aquaplanes. High speed and wide tyres are more of a problem for cars than bikes though.

*Even when "all" the water has been driven from under the tyre, there remains a very thin film, which is why wet weather grip derives from a completely different mechanism to dry weather grip:

In the dry, grip is simply the result of friction, but in the wet, the residual film of water lubricates the interface and removes almost all the friction. When the tyre is pressed onto the road, the rubber conforms to the texture of the road surface creating an interlocking pattern like meshed gear teeth, and for the tyre to slip in the wet, this pattern has to move across the tyre surface. This means that each point on the tyre is alternately compressed and decompressed, and in doing so, the hysteresis loss of the rubber absorbs energy. It is this energy absorption that provides the wet weather grip.#

Since energy loss is undesirable from the point of view of rolling resistance, the compromise between these conflicting requirements can be improved by laminating a tread made from high loss rubber onto a carcass made from lower loss rubber.

(#Ref: Ashby & Jones, Engineering Materials, Part 1)
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jb
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Re: Tyre directionalness

Post by jb »

The tread on bicycle tyres as far as I understand is to grip onto irregularities in the road surface to prevent slipping and has nothing to do with aquaplaning as the tyre is far to narrow for that to matter.
A slick tyre on a perfect surface gives the best grip but in real life with moss frost and slime lurking round every corner a small amount of tread increases the chance of staying upright.
Direction is for motor vehicles with wide enough tyres for aquaplaning to matter and also remoulds may be effected by direction due to the set of the inserted moulded pieces - but that may be incorrect.
Cheers
J Bro
Tompsk
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Joined: 6 Nov 2014, 9:35am

Re: Tyre directionalness

Post by Tompsk »

Apart from some heavily treaded off road tyres I don't think it will make any material difference. For those on flip flop hubs you'd have to change the tyre round every time you flipped the wheel!

AFAIK early TdF racers had different cogs on each side of the rear hub to 'change' gear, no tyre changing back then - however perhaps less tyre technology (or is that hype) back then too.
hamster
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Re: Tyre directionalness

Post by hamster »

MikeF wrote: 15 Aug 2022, 7:17pm The purpose of the chevron(s) and, more importantly the grooves alongside them, is to shed water etc to the outside, so that the centre rubber is in contact with the surface underneath, thereby providing maximum grip. If you put them on the other way round then water etc is trapped under the centre of the tyre, which is what you don't want for maximum grip.
Water is squeezed out by the weight on the tyre.
Aquaplaning occurs when the tyre rises and floats on its bow-wave like a waterski. Lots of studies have been done on its mechanism, mainly for aircraft landing. Tyre width is the main factor. Hence car tyres will aquaplane from around 50mph up.

However a bike tyre is so narrow that it only could occur over 100mph.
MikeF
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Re: Tyre directionalness

Post by MikeF »

hamster wrote: 22 Aug 2022, 10:20am
MikeF wrote: 15 Aug 2022, 7:17pm The purpose of the chevron(s) and, more importantly the grooves alongside them, is to shed water etc to the outside, so that the centre rubber is in contact with the surface underneath, thereby providing maximum grip. If you put them on the other way round then water etc is trapped under the centre of the tyre, which is what you don't want for maximum grip.
Water is squeezed out by the weight on the tyre.
Aquaplaning occurs when the tyre rises and floats on its bow-wave like a waterski. Lots of studies have been done on its mechanism, mainly for aircraft landing. Tyre width is the main factor. Hence car tyres will aquaplane from around 50mph up.

However a bike tyre is so narrow that it only could occur over 100mph.
Tractor type tyres have directional treads to allow water or a water mix to be squeezed to the outside. It's not related to aquaplaning. Most bicycle tyres are at slightly higher pressure though so there is more sqeezing effect.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
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