as i understood it, is that ideally the tires would be as on bicycle, but it is impossible to make tire so high pressurized and compound so good that it would handle the load of modern cars. Also wider tire helps side roll and better keeps with broken road so the car would handle worse and ride would be harsher. Or am i all wrong.

But i think it is same as what you write that it is all down to physical possibilities and each tire is designed to work best at condition X, weight Y and you can hardly change it. If condition is different, each tire/weight/condition can have different effect.
All i remember from my LR Experience course is, that all tires, even offroad tires should be always thin and tall, that fat wide tires are only for look :-). We even tested that by deflating tire you get more surface contact then having a fat tire, so even for sand and mud (where you want large surface contact) are those thin land rover tires the best. But ice and snow and that LR Experience slide test track, all was done on fully inflated tires. On fat tires car would not even try to climb up and they were both winter tires.

 

but weaker. If you have three skates biting on one foot, they bite weaker then one skate on one foot.
So ideally the tire should be front facing as thin as possible but bite as strong as possible in rotation direction. So we are back at thin tires with as little as possible ground contact (to be as skates when they bite). Rotation then does the biting in sideways direction (something skates does not have or need because they want to slide forward while rotating tires not). Winter tires should act as wheel with many glued skates where always only one is on road in driving direction and one 90° angled (but that would be very harsh ride). Something like driving on metal HHHHHHHH. Practically also all theory behind the best snow/ice traction for cars - studs and chains. Take it to the extreme. Thinnest tire on the world inflated at infinity, would have ground profile as a stud. Realistically wide tire, inflated as max as possible would have profile as skate 90° turned against the driving direction.

 

I am beginning to think that you have a better understanding of it than me.... Are you in engineering by any chance?

I think it is also a compromise - consider a farm field tractor which has very tall and wide tyres on the rear and very narrow tyres on the front. The rear tyres are optimised for traction in bad (muddy/wet) conditions, however the front tyres are optimised for direction control (they are narrow which means they can turn easily).

If all the tyres were the same size on the tractor it would be a compromise between traction and direction control - unfortunately on a car it is impractical to have wheels/tyres of such a contrast at the front and rear of a car (especially one with such elegant lines as ours?)

 

A couple of years ago in the UK we had a really bad winter with very cold temps for the UK. It was so cold that the usual dangers of underinflated tyres overheating at speed would never arise-you can't go fast enough in the snow to overheat the tyres as you'd crash anyway due to driving stupidly fast in the snow.

When you're doing 20-30mph in snow at daytime temps of -10C, you really aren't going to overheat an underinflated tyre. With a standard tyre under these circumstances, dropping the pressure at least allows the tyre to flex & distribute more tread over the snow.

Whilst the rubber may well be harder at that temp than on a true winter tyre, the lower pressures do actually increase grip on standard tyres as the softer pressures allow the tyre to flop & mould it's tread on the snow more easily.

I would carry an electric tyre inflator anyway if the road conditions suddenly changed & the normal higher tyre pressures were needed.

The climate in the UK is notoriously variable on a day-by-day basis & also depending on which part of the country you live in. I live in the North-West coastal part of England & due to the coastal climate here there is considerably less snowfall than in the North-East of England or up in the Scottish Highlands.

So from my point of view winter tyres are not essential as the snow doesn't last long enough to be a serious problem where I live-they would hardly get used & would spend most of their time locked up in the shed anyway...

So when the snow comes, I just drop the tyre pressures by around 30% & the car handles acceptably-let's face it, you can't really drive around normally & quickly in the snow anyway...

Thrashing the Big Cat is always more fun on a dry day anyway-in the snow the biggest problem is other vehicles losing control & colliding with you, so the last thing on your mind is exploiting the power & handling capabilities of your own car when other vehicles around you may not respond the same way.

I normally reverse into my driveway, which involves a small short sharp slope. With the tyres at normal pressures in the 30 psi range, the rear tyres would not give enough grip in the snow to reverse the vehicle into the driveway-but with tyre pressures in the low 20 psi range, I was able to reverse up the driveway acceptably.

Yes, the car handling was more 'mushy', but the road conditions were so grim that there would have been nothing gained with sharper handling at higher tyre pressures if you would then just slide around all over the road...

On standard tyres, lower pressures do indeed give you more grip-but you do need to carry the means to inflate the tyres to normal pressures again if the road conditions changed quickly, hence the electric tyre inflator in my boot

 

I think when considering skates as tread, we have to take the angle into account. For instance, when you want a skate to slide you point it in the direction you want to travel. However when you want to stop very quickly, you angle it at 90 degrees to the direction of travel to gain the maximum braking effect.

Tyre tread is a compromise as the tread is in the region of 45 degrees to direction of forward travel, giving 'best of both worlds'?

Of course, dependent on how agressive the tyre is for the conditions the tyre tread would be angled more towards 90 degrees to direction of travel?

Theoretically the 3 skates on one foot vs 1 skate on one foot is correct - however if you consider a modern razor blade that has up to 5 blades and is more efficient than the old traditional razor with one blade then the theory becomes very complicated - technically a razor with 5 blades should perform worse that a razor with 1 blade given constant applied pressure?

 

tractors have not wide tires, they have same as land rovers as tall and thin as possible to handle the load. Nobody can make a tire as strong and even thinner. Size the agricultural tire down to be as tall as jaguar tire and you will find that it is like bicycle thin. Not engineering. And i dont know if i am telling the truth, i am discussing! Front tire looks thinner because is smaller and can be even thinner because the forward grip is not needed.

 

You are telling the truth, I have just remembered that when I worked in Germany the tractors I saw did indeed have tall thin tyres on the rear - I think this is down to the type of ground earth that they work in?

However in the UK in muddy or wet conditions the rear tyres tend to be very wide with aggressive tyre tread. This to maximize forward grip - but as you say, the front tyres do not need this - they are thin to optimise turning performance?

 

Personally I use an electric shaver-much quicker & gives me more free time in the day to spend with my Jag

 

I have indeed seen winter tyres with HHHH pattern....Colway used to manufacture them in this way, and they were very good even though they were remoulds!!

Regards the razors, I think maybe that the more blades on the razor, the less pressure needs applying - and the more blood is given when it goes wrong!!!

 

I am a bit of a softy, still looking for an electric razor that cuts rather than 'pulls' the whiskers out!

 

the fat wide tires on tractors are used when you do not want to damage ground. Think of the tank, biggest tire you can get, closer you get to tracked car. It is about purpose. If you have flat land (no risk of sideway sliding) and you are not allowed to bite, you have to go really big and use the other extreme (taking little traction from as much as possible surface). You can drive with tracked car over grass and not damage it even if you are pulling 10 ton water tank behind you. But it is always ineffective for driving and can be used only for specific cases. You also need way more power and the tractors with big tires can never be as flexible as those with thin tires.
I know, i have grown up on farm.

 

Does it depend on the ground?

If your field was very wet and muddy, you would need wider tyres in any case otherwise the vehicle would sink?

This I think is similar to car tyre theory in reverse - on hard good contact ground wide tyres are better, however in wet and slippery narrow tyres are better - but in the case of a car the weight of the vehicle is very different...? tractors are extremely heavy and the ground they travel on is usually much softer....?

 

[QUOTE=sandy85;630733] (taking little traction from as much as possible surface). QUOTE]

I think in essence this is what we are talking about, but in reverse - with winter tyres we are 'taking maximum traction from as little possible available surface'? - the surface being unsuitable for tyres?

 

it is for special purpose only. You have to think about what weight you are designing your car for. If you are talking about those monster tractors, they need to have wide tires because the better option is not realistic (to be as tall as the ground would handle - 20meters tall tire?). But those tractors are very bad in most situations. They are worse at everything then tractors with thin tires, but they can handle huge pulling load, while thin tired tractor would need. To understand the problematic, always think in extremes. - Best for forward traction would be
a) 10mm thin tooth wheel
b) something as flat and wide as carpet (so it would not even move stones it would grapping on).

we both agree that a) is more universal (because it have loads of side traction needed for working on fields in hills, but you can never make it as tall as it would not cut it self 10m deep. So you find some compromise.

 

[QUOTE=richard thomas;630744][QUOTE=sandy85;630733] (taking little traction from as much as possible surface). it is same, traction is traction. You either get perfect traction from a track because it have so huge contact with the ground that it grasps even on free laying stones or something as thin that it bites so strong it gets the power to weight needed to overcome resistance. Art is to find the balance. For tires it is always better to be thin because you get less forward resistance, less weight, and on normal condition you can never dig so deep to get stuck up to the car floor. If you would go to syberia, where snow is 1m deep, you would want to have fat wide tires or tracks because even though you would slide sideways, you could push more ground under you as opposed to sit with car bottom on the snow. If you could reach the firm enough floor to move you forward, thinner is better.

 

I think you have it - it is all about compromise. That is why tyre manufacturers spend a lot of money on research and development?

However, in order to keep our very interesting discussion alive (I think you are an engineer in secret, by the way) - the tyre must be designed to enable at least one thing - to overcome the weight of the vehicle with grip to start forward motion - a 10mm tyre would not be able to do this as it would (as you say) saw itself into the ground if the weight of the vehicle was enough and the engine was powerful enough?

 

The Russian used wide-tracks on the T34 tank, so it could go pretty much anywhere...

There's probably an ideal tyre width for each surface condition-if the tyres were razor thin then the vehicle weight would just 'cut' the surface due to the immense pressure loading at the point of contact.

So car tyres in particular have to be designed as a compromise between several different requirements in road conditions. If you look in the Jaguar handbook, it quotes different tyre pressures depending on whether you want a soft, comfortable ride-or whether you are doing sustained high speed driving.

To be really accurate, you'd need to adjust your tyre pressures every day for each particular set of road conditions-but, as human nature means we won't do that, then the manufacturers specify a compromise set of pressures that don't need checking or changing very often.

 

[QUOTE=sandy85;630749][QUOTE=richard thomas;630744]I agree nearly, but for traction you need friction?

I think that the forward resistance is created by the vehicle, not the tyre itself?

For a thinner tyre, you effectively create more weight per area due to the available contact surface over the weight of the vehicle?

 

Correct - in a perfect world you would be able to adjust pressure, size, compound and tread pattern to make the best solution for weight of vehicle, driving surface conditions and use of vehicle every hour of every day - but it is all about reasonable compromise?

 

Not really. They can only move forward or backward up and down the hill. You will not see a tank on muddy slide driving along the slide direction. You lose the little grasp needed to move forward and start sliding. Cars dig deep so can drive also along the slide.