Directional Tyres

[Deleted member 221031]

I had that problem many years ago, first time I tried to get a wheel off a Mondeo (on alloys). it was such a good fit on the raised part of the hub it wouldn't come off. I had to get behind it with a chisel and give it a right pounding. But it wasn’t due to adhesion between the wheel and the face of the hub. Lucky not a flat tyre in the middle of the night in the rain.

I had a go at the hole in the wheel with wire brush and emery paper, but it wasn't enough, the wheel studs were pulling it on to the hub. So I attacked it (and the others, naturally) with a half-round file, and was OK after. And gave it a smear of grease, naturally.

The wheel was rusted on. That happens all the time without correct servicing

 

[fixitflav]

The wheel was rusted on. That happens all the time without correct servicing

It wasn't particularly rusty, the car was nearly new. Problem was too good a fit between the hub raised section and the wheel. Enlarging the hole a little cured it.

 

[Ivor Windybottom]

Only in the GD could it be said wheels aren’t held on by wheel nuts!!

Only if you selectively paraphrase to try and make a strawman point that wasn't actually made.

 

[Deleted member 221031]

Only if you selectively paraphrase to try and make a strawman point that wasn't actually made.

Like I said I don’t want to argue. I just tried to state a wheel nut is the key to keeping a wheel on.

It applies the pressure needed for the coefficient of friction.

 

[fixitflav]

Another no wheel Nutter. Ffs lol

What are you talking about? I haven't joined the discussion about whether it's friction between wheel and hub, or bolt shear, which takes the load.

 

[Mottie]

So do you want grip accelaring or stopping? The same tyre went one way around on diggers, the other on tractors.

Yep. Have a look at pictures of most motorcycles with directional tread tyres. The front tyre is always fitted looking like it’s the ‘wrong' way round.

Yam R1 front and rear.

Rear wheels have to deal with acceleration force but the front wheel has to deal with braking force. They are usually labelled 'Front' and have an arrow marking the direction of rotation when going forward.

 

[Brigadier]

Off-topic but,

despite the fact that bike is built for function, isn't it a thing of beauty

 

[Mottie]

Off-topic but,

despite the fact that bike is built for function, isn't it a thing of beauty

Beauty is in the eye of the beholder. Mind you, half an hour on that and I’d need to see a chiropractor!

 

[fixitflav]

Absolutely. If you loosen the bolts then you reduce the friction between the wheel and hub.

It's a weird concept, but the bolts do not hold the weight of the car, and are probably not strong enough to do this, they just squeeze two surfaces hard enough together that they can't move. If you could insert a zero friction layer between the hub and wheel then the bolts would snap, even if tightened.

So greasing the surface is probably not a good idea.

Assuming wheel studs are 7/16 UNF (maybe Asian cars are M12 these days) and grade 8.8 (might be higher grade, perhaps somebody on here knows), when tightened to the recommended torque, bolt load is 85% proof stress, and total load for typical 5 bolts is just under 20 tonne. I can post details if anybody’s interested. So even with a dynamic load of say 2 tonne/wheel and low coefficient of friction due to some grease, it’s OK.

On the other hand, if the nuts were slackened just enough so there’s zero compression between wheel and hub, the bolts loaded in shear can take the force, even taking account of allowable shear stress something like 60% of tensile.

So it’s OK whichever way you look at it.

 

[carmanmemoranda]

Assuming wheel studs are 7/16 UNF (maybe Asian cars are M12 these days) and grade 8.8 (might be higher grade, perhaps somebody on here knows), when tightened to the recommended torque, bolt load is 85% proof stress, and total load for typical 5 bolts is just under 20 tonne. I can post details if anybody’s interested. So even with a dynamic load of say 2 tonne/wheel and low coefficient of friction due to some grease, it’s OK.

On the other hand, if the nuts were slackened just enough so there’s zero compression between wheel and hub, the bolts loaded in shear can take the force, even taking account of allowable shear stress something like 60% of tensile.

So it’s OK whichever way you look at it.

Until or unless the bolts have been overtightened and stretched at all of course

 

[fixitflav]

Until or unless the bolts have been overtightened and stretched at all of course

Anything can happen if they're abused enough. But even with substantial overtightening as discussed on here, the only problem is to the guy trying to remove the nuts.

 

[Ivor Windybottom]

Yep. Have a look at pictures of most motorcycles with directional tread tyres. The front tyre is always fitted looking like it’s the ‘wrong' way round.

Yam R1 front and rear.

View attachment 310057

View attachment 310056

Rear wheels have to deal with acceleration force but the front wheel has to deal with braking force. They are usually labelled 'Front' and have an arrow marking the direction of rotation when going forward.

I don't understand that. I get that the front will be applying resistance under braking rather than acceleration. But it will still be rolling forwards, so that directional tread will be squeezing water inwards instead of shedding it outwards which, to my mind, increases the risk of aquaplaning.

I think that front tyre is on backwards. Is there an official guide on this, or is this one of those things that people just do?

 

[Mottie]

I don't understand that. I get that the front will be applying resistance under braking rather than acceleration. But it will still be rolling forwards, so that directional tread will be squeezing water inwards instead of shedding it outwards which, to my mind, increases the risk of aquaplaning.

I think that front tyre is on backwards. Is there an official guide on this, or is this one of those things that people just do?

No, definitely not on backwards. That was my initial thought and I had never considered it until I bought and fitted a set of tyres on a bike I owned. I thought the front tyre had been marked up wrongly so I looked into it. Look at any pictures of a bike with directional tyre on the front. I think the fact that there is a radius on a m/c tyre instead of a flat contact area helps with water dispersal more than the read pattern.

 

[Ivor Windybottom]

The explanation I found suggests that the water within the treads has its own forward momentum. While the bike is slowing the water wants to carry on going ahead of the bike. So it shoots forwards within the treads, to the outer edges of the tyre.

That does actually make sense. But it still doesn't make sense when you're cruising and ride through a puddle. Then the water will be pumped into the centre of the tyre.

My suspicion is that it's largely all nonsense anyway. My non-directional car tyres have lines in each direction, and some dead ends. It doesn't jump in the air and fly off the road. It's just about having some grooves somewhere, the rest is largely marketing.

 

[Deleted member 294929]

I had a mate fit me 4 new tyres the wrong way round. I only noticed when I backed into the garage