Tire scrubbing validation

[extyrebloke]

Many years ago, I wrote the following information for users of a particular brand of tyre:-
http://www.avonmotorsport.com/resour...re/user-advice

I no longer work for them because I didn't want the insane amount of travel; much as I loved it, it's not compatible with a young family if they are not also married to petrol.
I can't claim to be the world's greatest tyre expert, anyone who says that probably hasn't a clue about even the parameters of what such a person should actually know, but I've been around a fair bit and was a single seater tyre engineer for over ten years (working with several people here in the process).


There are several subjects involved here and I can't touch on them all, but bluntly, the fastest a tyre will ever be will be when it's new. But you have to have it at the right pressure and know that it's balanced, it must be fitted to a car that presents iteself at the optimum ride height and then when that tyre's done, it's done.
Most people want more mileage out of a set (here at least, I suspect Alonso for example, with whom I worked in F3000 can afford to fling tyres at a car should the regulations allow). They run cross-plies, crew for themselves, may even fit the tyres themselves and always want the most miles on a race weekend. All of these things point toward a scrubbing in procedure that reduces the risk of hitting the track and having something not quite what you want.

Scrubbing in lets you KNOW that the pressure is correct, assures you that the balance is correct, stabilises the volatiles in the compound and breaks the very weak links in the cross-chain matrix, leaving a more stable presentation to the road, the only part that means anything. Please bear in mind that when I say pressure, I care not for what you set them at cold, becuase if you're doing it right, the tyre won't be cold when it's near the circuit. Hot pressure is all that matters, and you need to research all the elements that come together to effect that hot pressure. Maybe your tyre brand absorbs water? Do you need to purge them? Veryify that all the water has come out? After all, they've been sitting in a warehouse / trailer / outhouse / garage for who knows how long. Water vapour screws your tyre pressure more than anything else you can think of. Are you certain that it's all gone?

Please note, not always, but largely, there is very rarely anything at all used to release slick tyres from moulds, mould release is a pain and best avoided. Race rubber is very rich in oils, it leaches from the second it's made and softer compounds are obviously worse.

Why do FSAE teams run for specific cycles? Usually, because they can repeat the process and that makes for a logical sequence.





Ah, I could go on for a lifetime and still not explain everything, not least becuase I don't know everything (hardly anything, some may say).

[Allen_W]

I know you knew that. But, I think it is a valid point. We often accept conventional wisdom. Brian does challenge conventional wisdom pretty often. There is often something to be learned in the challenge even if the conventional wisdom ultimately proves true.

Regards,
Barry

It would be different, and definitely more interesting, for the challenge to have some basis in contrary experience like, in this case, "Hey guys, I've been scrubbling my Hooiser 35s the way y'all say I should, but then I ran some stickered tires on a lark. I was surprised to find them slower by a second than scrubs for the first heat cycle but then, on the second heat cycle, my lap times were spot on - and by the 103rd heat cycle I was about a second and a half faster than I've ever been at Tinfoil Hat Raceway." With something like that we could at least get past the quaint notion that tire makers are deceiving us by advising that new tires be scrubbed in and withholding their test results to put one over on us.

[extyrebloke]

I spent a VERY long time watching people scrub and others not scrub tyres.
I can't posisbly divulge details (even I could remember them) as to how things went, but the eventual advice, based on 1,000s and 1,000s and 1,000s of laps was to scrub them in.

It should be fairly easy to disprove this argument over the space of a weekend. All you need to do is ensure that nothing else touches the circuit, that the atmospheric conditions remain utterly constant and that nothing at all (including fuel load and driver fatigue) changes in the car.

In the absence of such a test, I would at least consider the advice from a series of tyre manufacturers, who let's be honest here, have little to gain from leading you astray given your tyre budget is what it is, and if they don't work, you'll jump ship to A.N.Other brand of tyre. Noteably, all the tyre manufacturers appear to agree.



Pete, the notatyreengineeranymorebutstillequippedwithsomeoft heknowledege chap.

[RobLav]

What more could one want from a thread???!! This is informative and amusing!

[mblanc]

It is trolling for me to doubt the tire break-in myth?
Brian

I say no,

All the above is very interesting, even though I'm not from the 'show me' state.

It reminds me of advanced math classes,
Your answer is not right, unless you can show your work, and how you got there.
Some credit given even if the answer ends up wrong, its more about the process.

So many other things in vehicle dynamics are measurable, calculable, and if you care to learn, excess information is available. Math and formulas abound.

Shocks used to be 'black art' (I read it inSportsCar) but now we've got sensors, histograms, velocity traces, shock dynos, and force curves with and without knees.

Aerodynamics has gone from "it looks fast" to pictures of strings taped to a car, to full CFD modeling on the club level.

I still think Brian is just saying 'show me'
me too.

Been around long enough to get my butt continually kicked by another Coello dude, pretty much saw nothing but stickers there, while he was running away from our car on long race runs with our 'properly' scrubbed tires.

Anecdotal evidence aside,......
When teams do 'tire modeling', (or is it mapping?) what is really going on there, and what is involved?
Could some of that modeling/mapping help provide an answer?

[extyrebloke]

But while I've got my "Just do it, dammit" head on...


Please use metal valve caps. You've spent far too much £/$ to rely on the tiniest spring the world ever saw keeping the ever precious air in your tyres. They cost nothing (from an Factory Avon chap at least) and they remove just one of the many, many variables that affect your tyre pressure.

P

[BLS]

With something like that we could at least get past the quaint notion that tire makers are deceiving us...

Alan, maybe I missed it but I don't think the tire companies are being accused of deception. Or anyone else for that matter. Brian has just asked for something other than seat of the pants evidence, in his artful way.

As I said, I have no idea and would defer to those with the experience. I've watched as really good drivers manage their tires by scrubbing so I am not doubting the benefits.

[Allen_W]

Alan, maybe I missed it but I don't think the tire companies are being accused of deception. Or anyone else for that matter. Brian has just asked for something other than seat of the pants evidence, in his artful way.

As I said, I have no idea and would defer to those with the experience. I've watched as really good drivers manage their tires by scrubbing so I am not doubting the benefits.

Was thinking of this "Why are the tire manufactures not providing a more detailed individualized procedure?" (which raises some suspicion regarding tire cos. that I don't grasp other than as a suspicion) and then sracing's comment on tire makers, which I think made more comments in the same vein. But who the heck am I, I don't even race any more.

[DaveW]

Was thinking of this "Why are the tire manufactures not providing a more detailed individualized procedure?" (which raises some suspicion regarding tire cos. that I don't grasp other than as a suspicion) and then sracing's comment on tire makers, which I think made more comments in the same vein. But who the heck am I, I don't even race any more.

The main factors limiting concrete information on scrubbing, etc., and I've seen them personally, are:
1. Rubber and other tire components' characteristics vary from batch to batch, no matter how tightly they are controlled, resulting in tire characteristics also varying from batch to batch
2. All race cars are different, resulting in vast differences in how the tires react to being used on them. Some will heat tires quickly, and destroy them easily if run hard. Some will have trouble getting heat in the tire, but once at operating temperature, tires will last a long time.
3. All race tracks are different. Some are abrasive and heat tires quickly, but also destroy them quickly. Some are polished, and treat tires very gently, requiring softer compounds.
4. As above, no two drivers drive exactly the same, causing similar variations.
5. And then, we have all of the factors of weather conditions, other cars depositing different tread rubbers on the track, whether the track is "green" or "rubbered-in," etc.

So given all of these variations, any blanket conclusions drawn from one or even a series of tests, are bound to be incorrect a majority of the time, no matter how carefully they are obtained. And responsible manufacturers, etc., try not to give out misleading data.

So, IMO, accurate information on things like this will always be in short supply.

[Allen_W]

This makes perfect sense to me. Thanks for your comments DaveW. I sure as heck wish I were still driving those funny little cars around race tracks trying to use all this kind of information to, say, catch up with Marc Blanc.

[racerdad2]

Geez ! I coulda had a V-8 !!! This is a perfect test question for the Myth Buster guys Or, for more fun, Top Gear ! British version. All others need not apply. Better still.... lets get together with our cars & have the tire makers provide each of us with a few sets of their tires, in each compound, at COTA, at their expense, for a week or two of non-stop tire testing. They also supply spares, including engines... & catering.... & 5 Star accommodations...

[sracing]

...(which raises some suspicion regarding tire cos. that I don't grasp other than as a suspicion) and then sracing's comment on tire makers, which I think made more comments in the same vein...

I think some people are reading more into this than (I certainly) asked.

If someone told me that if you should use white mirrors instead of black mirrors and it appeared that the winning drivers WERE using white mirrors, I would likely take their advice.

But, No matter how well that seemed to work on track I would like to see a white paper on WHY? It has nothing to do with suspicion or trusting the vendors.

[mblanc]

I sure as heck wish I were still driving those FUN cars around race tracks

/\
FIXED THAT FOR YOU

If someone told me that if you should use white mirrors instead of black mirrors and it appeared that the winning drivers WERE using white mirrors, I would likely take their advice.

Isn't that the 'dog turd' analogy?

"If the leader had a dog turd on his hood, pretty soon the whole damn field would too.."

Was that a smokey saying? or who?

[Allen_W]

I think some people are reading more into this than (I certainly) asked.

If someone told me that if you should use white mirrors instead of black mirrors and it appeared that the winning drivers WERE using white mirrors, I would likely take their advice.

But, No matter how well that seemed to work on track I would like to see a white paper on WHY? It has nothing to do with suspicion or trusting the vendors.

In that vein, however, Hoosier at least was always extremely informative with my team. Sans white paper but with benefit of their own internal work and on-track support. That said, white mirrors are so much faster - and that can be proven simply by looking at 1000s of lap times in all conditions except ice and snow.

[Allen_W]

[QUOTE=mblanc;404024]/\
FIXED THAT FOR YOU

Thank you Marc. I have not, however, forgotten that part!

[Beartrax]

Hang on Pete, Brian was discussing tires and you're talking about tyres.
Try to keep it on topic.

(A little more levity, sorry)

No offense - Grandpa was from England. I occasionally write/type "colour" myself.

[TimH]

Scientific certainties...

There's no such thing. Popper has pointed out that the scientific method can at best disprove something to some level of probability. It can never prove anything at all.

As for tire technology, though, "When the green flag drops the BS stops." The racing arena is in some ways more rigorously confirmatory or denying than most science.

[Neil_Roberts]

Having written several myself, I can tell you that the only reason that anyone writes a technical paper is to fill a major gap in workload. Apparently, there is no such thing for racing tire engineers.

[DaveW]

Having written several myself, I can tell you that the only reason that anyone writes a technical paper is to fill a major gap in workload. Apparently, there is no such thing for racing tire engineers.

And, as the closely involved will say, the closer you get to a non-trivial problem, the more complex it gets. Unless the system is very basic, there seldom are simple conclusions. So the most knowledgeable refrain from overstating their knowledge. That is left to those who only think they understand.

[racerdad2]

Anecdotally speaking... our local kart track was repaved last fall. The old track was abrasive & fast times were with stickers. This year, new surface is very smooth. Sticker tires are slower. Scrubbed / heat cycled tires are faster.... go figure....

[TimH]

And, as the closely involved will say, the closer you get to a non-trivial problem, the more complex it gets. Unless the system is very basic, there seldom are simple conclusions. So the most knowledgeable refrain from overstating their knowledge. That is left to those who only think they understand.

I think I'll save that as a generally useful observation..

[extyrebloke]

There was recently a bishop in Scotland who was accused of some bad behaviour (which, incidentally, was correctly levelled at him, and he's now enjoying a pension somewhere) and for a while, he denied it. During his denial, his supporters pointed to the fact that there was no proof, which I thought was rather odd when for a chap in his career, faith was supposed to be enough.....



Even at the very highest level, rock hard solid proof of the kind that stands up to peer scrutiny is challenging to come by in motorsport. Yes, round wheels are usually better than square ones, but if it really were so simple, why aren't all F1 cars within 0.01s of each other?
There are some truisms, but the black art of the rubber tyre (sorry, tire is something I do after this morning's cycle into work) is very hard to come to terms with.
I had a specific incident where new stickers were slower on a brand new chassis, the first off of a one make series. I was being proper beaten up about it, as no-one could understand why that would be, least of all me. Turned out to be a weak engine mount (new designs eh? When will we ever learn to not change it if we don't have to?) and the assembly was no longer as stiff as it should be. The extra grip of the new tyres bent everything and confidence went away.

Your local friendly tyre engineer, such as he is worth, will always try to get you the best from your outfit. If you can conduct a more thorough test, please do so, but you are unlikely to clock up as many laps as he has seen, given this is what he does, day in, day out, weekend and weekday after weekend and weekday, with no other outside tedious career to distract him.
But when you do conduct that test, think about how much you will share with him or indeed anyone else. After all, you've paid for it, you've learnt lots, why would you ever want to give that to the guy in the field next to you who hasn't spent a penny learning anything? Your local friendly tyre engineer needs to respect that privacy before he goes off spouting figures and setups just to convince you that his simple advice is worth listening to.

Obviously I was very proud of the service I was able to offer our customers, but only because I was in a challenging field full of very capable, knowledgeable and personable people. The other tyre brands set the bar very high when it came to the customer service of their local friendly engineers so I had my work cut out to even get an audience.

Do those that require 'white paper' levels of proof approach everything in life with the same vigour? Coz if so, I reckon it might be fun to watch them faced with a vast range of beers in a bar, or better still, a Peppermint Rhino expedition......


Pete, the ever light-hearted, ex-local friendly tyre engineer.
(ex as in no longer a tyre engineer. I'm still really friendly.)

[DaveW]

...Pete, the ever light-hearted, ex-local friendly tyre engineer.
(ex as in no longer a tyre engineer. I'm still really friendly.)

Thank you for your hard-earned thoughts on this subject. They are, IMO, quite enlightening.

[Bob Posner]

I spent a weekend with Pete at the Seattle double national 10 or 12 years ago testing what was to be Avon's new fv tire back to back against a set of Goodyears and Hoosiers. He's even more fun in person. I recall that the Avon was as if it were velcroed to the track,but alas never appeared in production.

[racerdad2]

All kidding aside... I want to thank Brian for asking the question. Apparently, there is as much art as there is science in our tires. The seemingly infinite number of variables involved with the maunfacture & the proper care & feeding of our tires / tyres is nearly incomprehensible. No wonder the guys I race against who have 30+ years of experience can beat up on me with minor changes in air pressure & chassis tuning. Kudos to all you race gurus !

[bobmelvin]

I wrote to the Hoosier engineer and got the following answer in 18 hours.

From: Bob Melvin [RGM@coloradopen.com]
Sent: Tuesday, September 03, 2013 8:02 PM
To: Tim Gilvin
Subject: Runoffs advice
Tim:

Thanks in advance for taking the time. FF R35s Front mono shock VanDiemen RF93.

Scuff or not to scuff?
First Runoffs. Have three fresh sets ready to go. Plus your rains which we won’t use…..

Assuming all dry sessions, I am seeking your knowledge with regard to scrubbing, how should my qualifying set(s) and race set be scrubbed/preconditioned?

We are scheduled for a Test Day (three sessions), one practice session, three qualifying and the race. Sessions are 20-30 minutes 7-9 laps.

I have been running your tires with great satisfaction. I would deeply appreciate your advice on above.


Bob Melvin

ANSWER:
Scuffing them in - takes about 4 laps at Road America. First, easy lap, increasing speed for the next two until at full speed, them one easy cool down lap.

Tim
________________________________________

[Matt King]

I think Brian needs to refine his original question. He has demanded scientific proof to dispel the myth that tire scrubbing provides "any benefit." But how can that question be answered without first defining what constitutes a "benefit?"

[extyrebloke]

(Thank you Bob, I recall the time very fondly. Can't recall why bratts and burgers just keep popping into my head.....)


I used to give lectures to motorsport groups, teams, clubs, universities etc. on racing tyres, and on one of them I got visit the local Monoposto group. I talked for way over my allotted time because there were many questions and bluntly, there was a lot to say. After my over-run, a respected team owner sood up and said (and I quote):-

"I've known Pete for a number of years, and be assured, if you follow the advice he's given you today, without doubt, your lap times will improve. Indeed, I have learnt something today, and I thought I was a little long in the tooth to gain too much from such a young lad (t'was a while ago now). However, if there are 13 corners on a circuit and you only get two of them right, who gives a f**k what your tyre pressures are?"

Fact is, he was utterly correct; don't be distracted by the voodoo when by far and away the best thing you can do to improve a laptime is to turn the wheel at the right time.

(The metal valve caps won't make you any faster, but they may keep your car out of the barriers!)


Pete the-father-of-the-sadly-still-born-velcro-FV-tyre
(it was a commercial thing and out of my hands :-( )

[extyrebloke]

Also, many thanks for your observation Dave W...
The aim is to illuminate a difficult area to shine lights into.

[gcoffin]

Absolutely true.....the fast guys are the guys who get every turn right, every lap. I have watched drivers search for that extra mechanical advantage for 25 years. Not to say it is not important to arrive with the machine in optimum condition, but having shared the track with drivers in as near equal machines as it gets it is the driving talent that shines thru. On the rare occasions I have still had some of these guys in sight at the end of a race I have been very happy with my performance.

That said I will be scrubbing my Avons next year as I missed an overall win this year by 0.225 seconds.

[DaveW]

I have used them for at least 30 years now. I just don't trust plastic, and I sure don't trust the little check valve to not leak - all it takes is microscopic piece of dirt, and you're done for.

Also, about the same time, because of a wheel-to-wheel-rubbing incident where a metal stem got broken off, I stopped using metal valve stems. I now use only rubber valve stems. In all the races since, they have never caused a problem, or been knocked off in wheel-rubbing incidents.

[Jon Jeffords]

A FF competitor at Road America recently "lost" the rubber valve stem on his right rear after less than two seasons of use. Tire went flat near the end of the race, with no sign of any of the valve remaining; just an empty hole in the wheel where the valve used to be.

We all stood around scratching our heads trying to figure out the failure mode on that one. Best we could figure the rubber simply split in half were it went through the wheel, with one half falling into the wheel and the other half bouncing off into the weeds.

[DaveW]

A FF competitor at Road America recently "lost" the rubber valve stem on his right rear after less than two seasons of use. Tire went flat near the end of the race, with no sign of any of the valve remaining; just an empty hole in the wheel where the valve used to be.

We all stood around scratching our heads trying to figure out the failure mode on that one. Best we could figure the rubber simply split in half were it went through the wheel, with one half falling into the wheel and the other half bouncing off into the weeds.

I wonder if the valve stem departed due to the trauma of running with the flat tire, rather than causing it. That makes more sense to me. It would be easy for the deflated tire to scrape off or catch the part of the stem that was inside the wheel.

Either that, or maybe it was damaged in tire mounting/dismounting and finally failed on the track.

[Purple Frog]

Just saying...

Some cast/forged wheels are too thick in the stem area for standard rubber stems to work.

[problemchild]

I wonder if the valve stem departed due to the trauma of running with the flat tire, rather than causing it. That makes more sense to me. It would be easy for the deflated tire to scrape off or catch the part of the stem that was inside the wheel.

Either that, or maybe it was damaged in tire mounting/dismounting and finally failed on the track.

I've lost several tire valves recently, including one sliced as described, from trailer transport. I just have too many for racks and proper tie-downs. It just takes one stacked tire to bounce and sit crooked ..... now sitting on a tire valve for 1000 miles of travel. Cannot blame the part in this case, just the people

[extyrebloke]

Valves:- Ah, now there's a whole new box of chickens to unwrap....

If there is any chance of wheel rubbing, then the sensible thing to do is use as short a rubber valve as you can get away with. However, if the wheel size is big, (and hence the centripital load is large) then you may find a rubber valve bends away and weakens the inside portion. After many heat cycles, this can fail, so change them regularly.
When removing a tyre from a wheel, ALWAYS insert the tyre level under the tyre just next to the valve. Then the bead of the tyre never befouls the valve.
When fitting a tyre, the back bead goes on without effort, but the front bead should be more-or-less opposite the valve so that the very last bit to pop in is by the valve. If the tyre slips because of soap, then stop and re-position, do not persist with a wheel sliding inside a tyre. Ripped beads and torn valves are the inevitable result of not doing so.....

Pending on wheel design, you might get away with a short stumpy alloy valve and these are the most preferable as they won't deflect but they are obvious candidates for a carrotting if the paintwork polish is getting a testing.

If you get bored, play with mr (omega)^2 calculations and work out the load on a long bendy valve and all of a sudden you'll see why shorter is better.

Ditto balance weights. 50g of lead flinging off of a wheel at 90 mph is not so far off a bullet. Clean wheels are obviously the order of the day, one of the few times that the prettier it is, the more effective it really is.




Pete and-his-box-of-rubber-knowledge.

[DaveW]

Just saying...

Some cast/forged wheels are too thick in the stem area for standard rubber stems to work.

True. Hadn't thought of that - I use Jongbloeds with thin spun rims.

[DaveW]

Valves:- Ah, now there's a whole new box of chickens to unwrap....

If there is any chance of wheel rubbing, then the sensible thing to do is use as short a rubber valve as you can get away with....

I use "golf-cart" valve stems, which are ~3/4" long from the rim surface. Thanks for reminding me about that...

[CGDerian]

From a retired performance tire development engineer friend:

"Scrubbing tires does two things, 1) heat and temperature increases the [polymer] cross-links if there is sufficient sulfur in the mix. 2) heat and shear energy breaks down the molecules and makes them more visco and less elastic, which is stickier."

link:
http://invsee.asu.edu/nmodules/engmod/manipulation.html


And, more colorfully...

"Cured rubber is like a pile of centipedes holding hands. Green rubber is like a pile of earthworms, no hands so they slide around."

-Craig

[DaveW]

From a retired performance tire development engineer friend:

"Scrubbing tires does two things, 1) heat and temperature increases the [polymer] cross-links if there is sufficient sulfur in the mix. 2) heat and shear energy breaks down the molecules and makes them more visco and less elastic, which is stickier."

link:
http://invsee.asu.edu/nmodules/engmod/manipulation.html


And, more colorfully...

"Cured rubber is like a pile of centipedes holding hands. Green rubber is like a pile of earthworms, no hands so they slide around."

-Craig

From my relatively limited experience with tire tread-rubber compounds, there is a fine line between having uncured, unstable rubber, and having it over-cured to the degree that it behaves somewhat like a hard plastic, with too little hysteresis, too little compliance and too low Coefficient of Friction. Part of the black art is to get it to just the right place where it is stable, but still has its hysteresis, compliance, and high CF. And, then there are all the complications of oils and resins that enhance grip and CF, but get depleted with extended time at racing temperature. So the whole thing is a balancing act which makes scrubbing and tire life such a complex subject.