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F1 tyres, a what if?


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#1 rory57

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Posted 30 August 2013 - 16:54

F1 regulations define tyre and wheel sizes, not to mention tyre supplier(s). This has been the case for quite some time (don't know how long).

 

Assuming other aspects of F1 were broadly the same as we see today but tyres and wheels (sizes, construction, number of tyres per car per race meeting etc) were free and had been all along, what would we now see the cars rolling upon? Would tyres be lower profile? much wider? would six wheelers have got anywhere? 

 

My guess is tyres would still be black and there would be sticky specials for qualifying. Any thoughts?

 

 



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#2 munks

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Posted 30 August 2013 - 17:20

I think it was the Bridgestone spokesperson who said (perhaps during the Bridgestone/Michelin tyre war) that: "if rim size was free, we would prefer larger ones, but the drivers might not be able to handle it." I was never sure if the latter part was implying that the drivers couldn't handle the resulting g-forces, or if it just meant the limit would be more of a knife edge.

 

In either case, if all other rules stayed the same - standard ECUs, for example - they would (as always) have to find the balance between ultimate grip and what the driver can actually use. And it sounds like they might go a little bigger on rim size, but nothing extreme like the ugly ass rims we see nowadays on the street.



#3 Lightknight

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Posted 30 August 2013 - 17:40

Yes with the new regs they would love wider tires and greater diameter for an increased contact area - but lower profile - tires to cope with the turbo engine torque. This would mean teams might need to put much softer springs on with the resulting loss of compliance. The tires ought to be at least dual compound to deal with high speed straights and corners. Maybe some rear end steer should be built in and hell, if they reduce the size of the front wings even more then let go to 4 front wheels too....



#4 MatsNorway

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Posted 30 August 2013 - 17:42

Would a taller but narrower tire be beneficial?

 

you get more cooling time meaning you can run softer tires.

You get less speed difference left/right on the tire in corners meaning less wear. (negligible?)

You get more space for diffusers and wings.

You get more space for brakes

You get more rim less rubber without sacrifying profile

You get overall a lighter wheel.

 

Hit me!


Edited by MatsNorway, 30 August 2013 - 17:45.


#5 Lightknight

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Posted 30 August 2013 - 20:23

hard to see your logic here...more cooling time? What, why?

I could go on....but last and not least: a lighter wheel? Why?

As things stand next year they will struggle with the contact patch hey have now, let alone a lesser one.

 

Would a taller but narrower tire be beneficial?

 

you get more cooling time meaning you can run softer tires.

You get less speed difference left/right on the tire in corners meaning less wear. (negligible?)

You get more space for diffusers and wings.

You get more space for brakes

You get more rim less rubber without sacrifying profile

You get overall a lighter wheel.

 

Hit me!



#6 malbear

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Posted 30 August 2013 - 21:27

A small diameter wide tyre has a line contact patch ( knife edge) whereas a large diameter narrower tyre has a large oval contact patch (not so knife edge)

so from a traction  feel point of view it would be more friendly to the driver.

If you have done any dirt riding or tractor driving then it becomes apparent that a tall narrower wheel gives much better results. but a wide low wheel is much more impressive and fasionable.



#7 Greg Locock

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Posted 31 August 2013 - 09:13

That's a neat question. One tradeoff that hasn't been mentioned is that the drag from the tires is substantial, so bigger wider tires have a definite downside. 

 

There's actually not much evidence that a short wide contact patch is more difficult to steer than a long thin one, at the limit, the shape (ie rectangular or elliptical) is at least as important.

 

So, supposing we just do the easy thing and fit twice as many tires. Obviously the drag from the tires will roughly double, and the grip at max acceleration would increase, perhaps by 20%. Also the wear rates would drop.

 

That sounds to me like a faster setup. Note that you could then back off on the wing a bit, so regaining some straight line speed.



#8 KWSN - DSM

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Posted 31 August 2013 - 10:03

I have no idea about any of this, but I do remember Bennetton racing on tires which were not black. Maybe just a few races, maybe just the sidewalls.

:cool:

#9 malbear

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Posted 31 August 2013 - 11:03

That's a neat question. One tradeoff that hasn't been mentioned is that the drag from the tires is substantial, so bigger wider tires have a definite downside. 

 

There's actually not much evidence that a short wide contact patch is more difficult to steer than a long thin one, at the limit, the shape (ie rectangular or elliptical) is at least as important.

 

So, supposing we just do the easy thing and fit twice as many tires. Obviously the drag from the tires will roughly double, and the grip at max acceleration would increase, perhaps by 20%. Also the wear rates would drop.

 

That sounds to me like a faster setup. Note that you could then back off on the wing a bit, so regaining some straight line speed.

didnt some modelss of mercedes have two skinny rims and two tyres on each axle making 8 tyres on 4 wheel arches of the car

also http://en.wikipedia....iki/Tyrrell_P34



#10 MatsNorway

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Posted 31 August 2013 - 18:48

One issue with having a higher dia tire is that it makes it neccesary to mount the suspension mounts higher due to roll center? So there is a limit to it there.



#11 Wuzak

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Posted 01 September 2013 - 01:08

Michelin are said to be interested in tyre supply for F1, from as early as 2014.

 

But they have provisos - they don't want to make tyres that degrade quickly (as Pirelli have done) and they want to move to 18" rims, sooner rather than later.



#12 Kalmake

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Posted 01 September 2013 - 07:51

Open wheels also produce lift. One of the advantages of the P34 was reduced lift at front.

 

8 (or more) smaller wheels would definitely be the way to go. You get half the wheels almost free as far as aero is concerned.

 

 

For a perioid in the early to mid 70's they used lower profile at front. Then they moved (back to) to using fronts as tall as rears, but not as wide as regs would have allowed. This went on until the grooves I believe. Since lower profile is supposed to be better, why didn't they go lower and wider with the fronts? Did taller profile give better braking performance?



#13 Lee Nicolle

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Posted 01 September 2013 - 09:21

A taller tyre the same width will give more stability and probably be more stable too. BUT the cars will then all be wrong. Though if the same for everyone not quite the same problem. Drag and aero though would be a major factor.
For us mere mortals though a tyre an inch taller can be a real advantage. Though often the manufacturers don't want to continue making them as low profile is more trendy. Even when the dealers tell them the demand is there.

#14 indigoid

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Posted 01 September 2013 - 11:08

Michelin are said to be interested in tyre supply for F1, from as early as 2014.

 

But they have provisos - they don't want to make tyres that degrade quickly (as Pirelli have done) and they want to move to 18" rims, sooner rather than later.

 

Hm. Picking the midpoint widths in the current tech regs and assuming the total wheel+tyre package diameter would not change, that would yield roughly a 30/27 F/R profiles, vs. 50/44 with the current wheel sizes. I think it would look "wrong", but it's a matter of what you're used to I suppose. I like the fat tyres look. Especially now that we're back with slicks.

 

 

Save the big wheels for LMP!


Edited by indigoid, 01 September 2013 - 11:11.


#15 RDV

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Posted 02 September 2013 - 13:39

Contact patch is all...you can increase it by running a wider tyre or lower pressures so more tyre deflection. Softer pressures reduce vertical spring rate, but also reduce lateral, increasing carcass deflection and slower response. The concept of open-wheeled racing cars is archaic also, but we are stuck with it, drag from exposed wheels is ridiculous. Given all cars run same mandated tyres, at least it is an equal factor for all the grid.

 

 

One issue with having a higher dia tire is that it makes it neccesary to mount the suspension mounts higher due to roll center? So there is a limit to it there.

 

If you look at suspension travel on current F1s, roll center position is immaterial, as most of the suspension movement is in the tyre. A lower profile tyre would change this of course, but layout is mainly determined by aero efficiency, geometry is a second order factor.

A taller tyre the same width will give more stability and probably be more stable too.

 

Why? Vertical stiffness vs. lateral stiffness is a function of pressure and carcass structure. It is very difficult to increase lateral stiffness with same vertical. On several classes going from 19" to 18" or even 17" dia (I.E. changing aspect ratio, as O.D. stayed the same) improved traction, but on rears only, low aspect ratio kept in front as steering response was better, but even on these rims still a low aspect ratio compared to F1. The only cars who still run high aspect are F1 and Oz V8s. All others are modern.

For a perioid in the early to mid 70's they used lower profile at front. Then they moved (back to) to using fronts as tall as rears, but not as wide as regs would have allowed. This went on until the grooves I believe. Since lower profile is supposed to be better, why didn't they go lower and wider with the fronts? Did taller profile give better braking performance

Was mainly a function of weight distribution. When aero came in generated by undershape the CP was forced forwards by the increase of area in sidepods, between the wheels. Keeping CG and CP close forced CG to car center, increased front tyre load, so tyre size increased. Relative tyre sizes before was a fuction of load.  

 

The high aspect ratio on current F1 needs ridiculous camber angles to maintain contact patch as very floppy in lateral.

Though often the manufacturers don't want to continue making them as low profile is more trendy. Even when the dealers tell them the demand is there. 

 

 


On production cars low aspect tyres have a function, it is not only for looks. The future introduction of in-hub electrical motors on series-hybrids and electrical cars also need more space, plus the tyre is the bigger part of weight in tyre/wheel unit.

 

All tyre manufacturers would prefer to go to low aspect ratio as it fits in with the tyres they produce for road cars, and make more sense. The high aspect ratios in F1 are an archaic structure, due to regs. introduced to restrict the size of brakes and thus braking distances. This concept has been obsolete for over two decades now.

 

..on the other hand more tyres has its attractions...



#16 MatsNorway

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Posted 02 September 2013 - 19:16

I don`t think In hub is going to be a thing. Not with direct drive to the hub.

 

Sounds more costly as you need stronger bearings etc, better capsuling (including heat shielding for disc brakes) And a odly shaped motor compared to a close to over the counter industrial motor.

 

If it was so viable the current electric cars would have had it me thinks. ^^



#17 gruntguru

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Posted 03 September 2013 - 02:27

I think low profile is a no-brainer for the increased vertical stiffness. Tighter control of ground clearance is a benefit to aero and aero is everything!



#18 Kalmake

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Posted 03 September 2013 - 05:23

Was mainly a function of weight distribution. When aero came in generated by undershape the CP was forced forwards by the increase of area in sidepods, between the wheels. Keeping CG and CP close forced CG to car center, increased front tyre load, so tyre size increased. Relative tyre sizes before was a fuction of load.  

 

Yes, I know why the fronts had to get bigger. I was wondering why they grew taller instead of wider.



#19 MatsNorway

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Posted 03 September 2013 - 17:54

Guessing bigger brakes was needed.



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#20 Lee Nicolle

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Posted 04 September 2013 - 03:33

A bigger dia steer tyre steers better. The initial turn in may not be quite a responsive but it stays turned in instead of 'pushing' from mid corner. A bigger rim ofcourse helps. And can package bigger brakes too.Though a really low tyre seldom ever steers as well.
Current F1 cars do look rather silly with skinny tall tyres.
As for only F1 and V8 Thupercars having tall tyres lets get real. Many classes run bigger dia tyres. Bigger cars will never work on small tyres. Then look at Nascar, tall skinny tyres with 900hp. They are ofcourse way overpowered for the tyres but on ovals do a decent job. Until recently Indy Cars too had fairly tall tyres though these days they are open sports cars!
For road cars low tyres is 50% wank. And the low tyres kill the ride, increase the road noise and even the places where you can actually drive the car. And only increase the handling a little.That on smooth roads!
For a common or garden passenger car a 60% aspect as is low as is ever needed. And you do not bend the rims driving through every second pothole. Though most new cars defy logic with tyres as low as 30%. Dumb dumb and dumber.

#21 gruntguru

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Posted 04 September 2013 - 05:10

And you do not bend the rims driving through every second pothole.

Not to mention damage to the tyres themselves - which often cost more than the rim to replace.



#22 Lee Nicolle

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Posted 04 September 2013 - 06:03

Not to mention damage to the tyres themselves - which often cost more than the rim to replace.

Surprisingly the tyres seem to live better than the rims. Though when run for a long while on a square, oval, hexagonal etc rims do seem to wear all funny!

#23 Kalmake

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Posted 04 September 2013 - 09:07

Guessing bigger brakes was needed.

No, the rims were always maximum size. Example Lotus 72D:lotus_72d_late_type-22367.jpg
Inboard brakes - like in this Lotus - were allowed, so the sport could have moved to smaller front rims if there was a benefit.



#24 RDV

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Posted 04 September 2013 - 11:57

I don`t think In hub is going to be a thing. Not with direct drive to the hub.

 

On city  road cars has a lot of pluses, not so much in racing cars...and currently involved in in-hub installation for a racing car, looks like going back to inboard motor with driveshaft as easier, more efficient and more reliable.

As for only F1 and V8 Thupercars having tall tyres lets get real. Many classes run bigger dia tyres. Bigger cars will never work on small tyres. Then look at Nascar, tall skinny tyres with 900hp. They are ofcourse way overpowered for the tyres but on ovals do a decent job. 
Read post, not small tyres in dia, low aspect ratio- and bloody new format on forum, quoting is a nightmare...arghhh
A bigger dia steer tyre steers better. The initial turn in may not be quite a responsive but it stays turned in instead of 'pushing' from mid corner.
Why? It is really a matter of weight distribution and contact patch, roll couple distribution plus control of same contact patch.
Inboard brakes - like in this Lotus - were allowed, so the sport could have moved to smaller front rims if there was a benefit.
One worked on the 72, the problem was that tyres were supplied by Goodyear and they were going for wider tyres as a way of increasing contact patch. It solved the traction problem and killed the 4wd cars that were being developed for that, then aero came in and reduced the need for big width.Once also ran a Porsche 917-30 with 22" wide tyres, it did a good job of passing 1300bhp plus to ground...but it was on the ragged edge structure-wise, the cords structure and direction in the carcass was very trick to maintain shape, plus very wide tyres are very roll camber sensitive (there was a de Dion version of the 72 to try to sort that one out...not very sucessfull, difficult to keep the de Dion rigid, as was a spaceframe version), remember they were still cross-plies at the time and very difficult to keep tread flat (er...cylindrical?).


#25 MatsNorway

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Posted 04 September 2013 - 19:26

No, the rims were always maximum size. Example Lotus 72D:lotus_72d_late_type-22367.jpg
Inboard brakes - like in this Lotus - were allowed, so the sport could have moved to smaller front rims if there was a benefit.

Drive shafts adds weight. At the time weight was more of a treasure than now perhaps. I know some cars had it at the time but it might not give the desirable brake feel with the shafts flexing and such. For modern car implementation i argumented and calculated against it a year or two ago. Not likely ever going to happen in modern form just so you know. :) Direct hub mounted electic motors is more likely then.

Driveshafts also reduces steeing lock and binds in corners affecting balance.


Edited by MatsNorway, 04 September 2013 - 19:27.


#26 Kalmake

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Posted 05 September 2013 - 17:00

Yeah that's all true. And they are effectively banned by current rules. But it is what they did use, and it meant they didn't have to fit brake discs inside the rim. Still they chose to use the 13".

 

Quite probable that they wouldn't have had a supplier for smaller option anyway. As RDV describes, tyre manufacturer dictated the path.



#27 BaLa

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Posted 06 September 2013 - 00:19

F1 regulations define tyre and wheel sizes, not to mention tyre supplier(s). This has been the case for quite some time (don't know how long).

 

Assuming other aspects of F1 were broadly the same as we see today but tyres and wheels (sizes, construction, number of tyres per car per race meeting etc) were free and had been all along, what would we now see the cars rolling upon? Would tyres be lower profile? much wider? would six wheelers have got anywhere? 

 

My guess is tyres would still be black and there would be sticky specials for qualifying. Any thoughts?

I would like to see F1s with big diameter tyres, like the ones from the 80s and early 90s. The comparision: with lower-diameter tyres, F1s used to border and -sometimes- reach 370 Km/h between 2004 and 2005. Imagine how fast they would have been with bigger tyres...

 

And yeah, the sticky ones for qualifying would have been better too! 


Edited by BaLa, 06 September 2013 - 00:20.


#28 BaLa

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Posted 06 September 2013 - 00:23

Would a taller but narrower tire be beneficial?

 

you get more cooling time meaning you can run softer tires.

You get less speed difference left/right on the tire in corners meaning less wear. (negligible?)

You get more space for diffusers and wings.

You get more space for brakes

You get more rim less rubber without sacrifying profile

You get overall a lighter wheel.

 

Hit me!

I agree. 

 

I would like to see something like that, specially because a taller tyre with thinner profile would allow the car to go faster on straights of circuits like Monza. 



#29 gruntguru

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Posted 06 September 2013 - 00:45

Thinner perhaps but "taller" is irrelevant to top speed - except to say that an increase in tyre height will increase drag and reduce top speed.



#30 MatsNorway

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Posted 06 September 2013 - 19:52

Are you saying dia is irrelevant to roll resistance?



#31 gruntguru

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Posted 07 September 2013 - 04:05

Are you saying dia is irrelevant to roll resistance?

No. Only that rolling resistance at any normal levels has negligible effect on top speed. Especially on a high power, high drag racecar.



#32 JimboJones

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Posted 09 September 2013 - 20:56

Wow, there is so much wrong with this thread, in fact pretty much everything! For a technical forum surprising not a single person knows anything about tyres. Let me correct some ridiculous assumptions in order of lunacy...

Lower profile tyres suck. A 'taller' tyre will always generate more grip than a low profile one, simply because the contact patch is bigger/more evenly distributed. As for ride height you just make stiffer sidewalls.

Wider tyres are better, again because the patch is in better contact with the ground. The only limit to this would be physically being able to steer them at the front!

That leaves diameter, where again bigger is better. Longer contact patch plus more rubber means more grip and durability (or softer compound). The obvious limit here though is aero, and probably rotating mass/driveshaft height.

Yes you can package bigger brakes and nicer suspension in a big rim, but this is nothing compared to the performance you would gain from more grip, and when exactly is an f1 car ever limited by brake size?! Make the rims as small as you dare, and wide as you can steer, job done!

#33 desmo

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Posted 09 September 2013 - 21:09

 A 'taller' tyre will always generate more grip than a low profile one, simply because the contact patch is bigger/more evenly distributed.
 

Can you expand on this? 



#34 JimboJones

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Posted 09 September 2013 - 22:13

Well consider a low profile tyre... To extract more grip, you will generally lower the tyre pressure to increase grip, as the contact patch gets larger, up to the point that it starts being supported by the sidewalls rather than the tread. There is obviously an optimum, but go too low and the patch wont support the vertical load, and can damage/fail the tyre at the edges.

Take the same tyre, and now make the rim smaller, so taller sidewalls. This allows you to run a lower pressure, increasing the contact patch size further, without compromising the stress in the sidewall, or the safety of the tyre. This is what I meant by evenly loaded - more contact area, without running on the sidewalls.

The reason Michelin would want to run with 18"wheels rather than 13" is an image thing, not performance. They look more like road tyres, and they may get technology transfer to road or other racing series, which virtually all run 18" rims.

#35 Greg Locock

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Posted 09 September 2013 - 22:44

"Wow, there is so much wrong with this thread"

 

And now there's even more. If you have two tires with the same contact patch area, one long and narrow, the other short and wide, and hold as many other things the same as possible, then the level of grip available from each tire will be almost the same. The 'brush' model of contact patch physics probably provides the best intuitive explanation of why this is so.



#36 Kalmake

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Posted 10 September 2013 - 10:34

Why would they run 18" rims in LMP1/2 if it's not better? There is no tyre manufacturer monopoly and rules state only maximum size.



#37 RDV

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Posted 10 September 2013 - 18:08

Wow, there is so much wrong with this thread, in fact pretty much everything! For a technical forum surprising not a single person knows anything about tyres.

 

 

...that's what I've been telling myself all these years...in fact nobody knows anything about tyres, including the tyre manufacturers, that's what they said at Calspan, last time I was testing tyres there...it is definitely a black art... :lol:  :cool: 



#38 JimboJones

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Posted 10 September 2013 - 22:57

Im afraid you're quite wrong. Ask any racing driver or engineer if they'd take wider tyres if they could have them, and they'd bite your hand off!

Even with identical contact patch area, the wider shorter one will be capable of more grip, because a smaller proportion of the patch is sliding as you approach the limit. It was correctly mentioned that this gives a more peaky, knife edge like behavior at the limit, but peak grip increases. Go ask BMW why they put wider tyres on the rear of their road cars, it's very simple really...

#39 Greg Locock

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Posted 10 September 2013 - 23:05

They fit wider tires to get bigger contact patches. So you are not comparing like with like.

 

Put it this way, compare the lateral and longitudinal maximum grip at a reasonable load for a tire. The contact patch is a compeltely different shape, yet the max grip is almost identical. That is to say, the length and breadth of the friction circle are almost identical.This even applies for really wide tires like f1. For instance p191 in Wright's Ferrari book. Max long 8400 N, max lat 8800 N. This is not a coincidence, the reason is that at max grip the rubber is just a blob of rubber, it doesn't care which direction it is being pushed in.


Edited by Greg Locock, 10 September 2013 - 23:19.


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#40 JimboJones

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Posted 11 September 2013 - 19:35

rubber is just a blob of rubber, it doesn't care which direction it is being pushed in.

we'll agree to disagree then...
This is the grossest simplification of a tyre I have ever heard, and certainly not one of an engineer who has worked with real racing tyres. First off, a contact patch is not a static blob of rubber, the tyre rotates through it. It creates a large proportion its grip from sliding, a very dynamic event that depends entirely on the way the patch is being presented to the ground. As a result, a tyre can be designed to completely different longitudinal and lateral qualities, the mechanisms involved in the two pure scenarios are very different. The fact you refer to a friction circle indicates how short sighted this 'brush' model is. you cant swear by some massively simplified model when talking about real tyres...

PS: a wider tyre can give exactly the same contact patch area, you simply adjust the pressure if neccessary. Oh, and it would still generate more grip!

#41 Greg Locock

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Posted 11 September 2013 - 21:00

Well, i guess you better discuss with ferrari why their published data is wrong. And why my tire suppliers have been giving me duff test data for all these years.


Edited by Greg Locock, 11 September 2013 - 21:02.


#42 gruntguru

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Posted 11 September 2013 - 22:52

This is the grossest simplification of a tyre I have ever heard . . . .

. . . . .

. . . . . .

Oh, and it would still generate more grip!

 

Simplification is good and should be performed wherever possible.

 

"Wider/bigger = more grip" is not universally true IMO.

 

Bigger contact patch = more grip may be true IF there is a softer combound available. If tread compound is fixed there will be an optimum width beyond which there is no gain in grip. (IMHO only)



#43 Canuck

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Posted 12 September 2013 - 03:02

It is engaging to read a discussion between known quantities and an unknown. I feel like getting some popcorn.



#44 gruntguru

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Posted 12 September 2013 - 03:32

I for one won't be rushing in to contradict Greg on this subject.



#45 rory57

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Posted 12 September 2013 - 08:27

Accepting that tyres do produce grip and that different tyres behave differently...........

What then of the cars?

Could we have a situation where one team went for grip with larger tyres and another with aero tweaks, both remaining compettative across a season?? 

Could suspension be dispensed with if tyres were free? (Like karts, after all F1 seems to be pretty close to that already).

Ultimately,would the tyre performance exceed the drivers ability either to control close to the limit or cope with the forces possible due to extreme grip?



#46 RDV

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Posted 12 September 2013 - 15:29

JimboJones- Im afraid you're quite wrong. Ask any racing driver or engineer if they'd take wider tyres if they could have them, and they'd bite your hand off!

 

 

...er, I am a racing engineer, and whilst one will not be oracular on street tyres, one has some rather strong views on racing tyres. Last year Michelin was only supplying wider front tyres for the LMP1 at Le Mans, as requested by Audi and Toyota, whereas the rest of the privateer LMPs wanted to stay in the smaller size. There was an option of having 11 spec (front tyre sizes), but only in the old compounds. Audi had changed their weight distribution, plus had the electric motors on the front for the eTron, needing more capacity, so logical. Everybody else wanted to keep the sizes previously used as a good balance for aero loads and needs. 

 

Changing the car to run these tyres involved a huge amount of work, new front bodywork, re-working aero for a different balance, more drag due to limited flow between the front wings, changing disk and pad sizes on the rear suspension due to brake balance issues, given that a bigger diameter and width of front tyres diminished disc tangential speed, thus changing rubbing speed and pad bite, which involved making new rear uprights and coping with an increased rolling resistance from the wider wheels. Front spring rate, damping and anti-roll bars had to be changed, as vertical stiffness rate of the bigger tyre was softer, which then brought in problems controlling ride height and increased issues with splitter touching ground under braking, not to mention CP change with pitch, as tyre spring rate ratio was changed.(Incidentally, tests with the windtunnel model using the new bodywork but with the original whee size showed that aero drag was mainly due to the tyre size despite being in the wheel well and not exposed to the air, as a single seater.) Ackerman, roll camber geometry and offset had to be changed, plus caster and kingpin angle, plus brake master cylinders just to cope with brake balance bias issue , consequence of the different disc radius and size. 

One would be very happy to keep the original smaller size never mind bitting any hand. There is a huge amount of consequences on any tyre choice, not only size.

 

This year, on another championship, with another tyre manufacturer am obliged to run same tyres front and rear, giving me huge headaches to make the front end work, as lateral stiffness is less than the opposition, who run the smaller front tyres (and lower aspect ratio).

Why do we run bigger fronts? Because our weight distribution is biased to the front, as they are run in GT-3 and based on a production car, so what you get is what comes from the original car. With a high front weight, the smaller tyres are not rated to carry that much weight, and as they are spec tyres for the championship one has no choice in having either a smaller tyre with a higher rating, or a big tyre(same size as the rear) but with a different carcass so as to have a higher lateral stiffness for the same vertical.

 

The bodge solution is to run higher tyre pressures and ridiculous camber angles to ensure the contact patch in cornering (the bigger tyre and different aspect ratio with this construction means that side deflection is higher under a given load, so tyre wear is happening on outside shoulder and can be critical if you are trying to double stint the tyre set... and running the risk of blowing tyres on hot and fast circuits by cycling the inner walls (which at this point are carrying most of the load and consequently softer in vertical stiffness. Arghh...it's circular, and we will probably have to go back to first principles to explain adequately...sooo, deep breath....a tyre spring rate is consequence of the sidewall construction, and for a tyre rolling at zero camber both sidewall share the load. Increasing camber shifts the load to a single sidewall making for a softer tyre, and increasing the deflection cycling, making for a carcass that gives up earlier as the cords detach themselves from the embedded matrix of rubber and carcass, which then also generates a higher running temperature, which increases the pressure, which entails a different thread patch giving more crowning even with a belted tyre. More crowning then reduces the contact patch which in turn increases the area unit load vertically, longitudinally and laterally, which then increases the temperature and surface wear. The inner wheel in turn suffers by running an adverse camber, and drags the inner shoulder increasing the risk of blistering due to overheating, not to mention the problems of pickup...the bane of my life....)

 

And we are talking only of one part of it, as the softer carcass then entails problems in controlling rake under braking and acceleration, which in turn brings in aero load distribution issues. Getting tyres up to temperature for qualifying runs runs into huge problems in making front and rear tyres coming in at the same time and keeping car balanced36.

 

The same car run in another championship has bespoke tyres, with a correct carcass and is a lot easier to run.

 

 

Another prime example of practicalities comes from the start of 76 in F1, when front tyre carcass changed by going from 4 to 6 plies, consequence of safety concerns by the manufacturer, after Donohue's accident at Zeltweg, said tyres brought in after the Spanish grand prix, which instantly killed some leading contenders, amongst them Shadow and Lotus, which had optimised their weight distribution on the 75 tyres, and compounded by having most of the winter testing done by McLaren and Ferrari, more front biased cars. Note this not involve tyre size or aspect ratio, just carcass.

 

Hope this opens a bit the number of factors and issues given by tyre size and aspect ratio, one would be very careful about blanket statements. Bigger diameter or higher/lower aspect ratio is not all, neither is tyre width. Tyre material is a multi-layered, non-uniform, anisotropic cord-rubber composite and even trying to model it has severe problems, be it the elastic foundation model, the string model, the beam model or the brush model, thus the road and rig testing ends up being essential. Rubber is the ultimate non-linear material, plus temperature and load dependent. 

 

Suggest reading Dixons'  "Tyres, suspension and handling" (ISBN 0-340-67796-1), Haneys' "The Racing and High -performance Tire" (ISBN 0-7680-1241-4), Millikens' "Race Car Vehicle Dynamics" (ISBN 1-56091-526-9), Sakais' "Study on Cornering Proprieties of Tyre and Vehicule" TCTA -18(3) 1990, , Nordeen "Force and moment Characteristics of Rolling Tires " (SAE paper 713A), in fact there are a slew of SAE papers on it, just google SAE and tyres for a good coverage, and , of course the seminal "Tyre and Vehicle Dynamics" (ISBN 0-7506-5141-5) by Pacejka, although it is very heavy going, has been my bed-side book for a couple of decades and still trying to wrap my head around it.

 

(..er, one suspects this post a bit of an overkill...  :p )



#47 RDV

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Posted 12 September 2013 - 15:43

gruntguru-Bigger contact patch = more grip may be true IF there is a softer combound available. If tread compound is fixed there will be an optimum width beyond which there is no gain in grip. (IMHO only)

 

 

...forgot to note this, Yes indeedy, bingo gg...



#48 rory57

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Posted 12 September 2013 - 16:28

RDV - Thank you for your post, not overkill at all. I now know more than I did. (Which is why I hang around in here)



#49 Rasputin

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Posted 12 September 2013 - 17:54

Drive shafts adds weight. At the time weight was more of a treasure than now perhaps. I know some cars had it at the time but it might not give the desirable brake feel with the shafts flexing and such. For modern car implementation i argumented and calculated against it a year or two ago. Not likely ever going to happen in modern form just so you know. :) Direct hub mounted electic motors is more likely then.

Driveshafts also reduces steeing lock and binds in corners affecting balance.

 

Naah, the argument of the inboard brakes was saving precious unsprung weight with the at the time heavy steel discs. Not an issue today.

 

With a Formula libre on tires, something like this perhaps?

 

http://www.google.co...2F70834;907;605



#50 JimboJones

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Posted 12 September 2013 - 17:56

Hmmmm, definitely an interesting post RDV, many thanks for sharing. As it was in response to mine though, I just wanted to point out that my statements were in light of tytes being completely free (front and rear), and in Formula 1 the entire car would be designed around them, hence not considering concerns over adapting to a change.

And Greg, personally, your suppliers don't concern me. I am merely trying to make the point that you are talking about a tyre MODEL. Reputable companies often release simplified models for customers, and support them with data sets, so this does not surprise me. However, one must understand the limitations of said models, especially when discussing real tyres.