## Does tyre wear affect top speed?

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Not being educated in the laws and math of this, I would guess there are only 2 ways tyre wear would influence a cars top speed.

On a final corner approach onto a straight, if the tyres are shot, there is no way you will achieve the same top speed as if the tyres were giving up more grip allowing greater exit speeds, and therefore more momentum to allow a higher top speed.

2. I wonder what the resistance of a worn tyre would be to that of a brand new tyre.
I doubt they would be the same, and would the aerodynamic profile of the tyre itself nullify any rubber/road resistance?

Hmmmm
More could have been done.
David Purley
JohnsonsEvilTwin
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Joined: 29 Jan 2010
Location: SU 419113

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JohnsonsEvilTwin wrote:Not being educated in the laws and math of this, I would guess there are only 2 ways tyre wear would influence a cars top speed.

On a final corner approach onto a straight, if the tyres are shot, there is no way you will achieve the same top speed as if the tyres were giving up more grip allowing greater exit speeds, and therefore more momentum to allow a higher top speed.

2. I wonder what the resistance of a worn tyre would be to that of a brand new tyre.
I doubt they would be the same, and would the aerodynamic profile of the tyre itself nullify any rubber/road resistance?

Hmmmm

Let's cut this crap once and for all, it your final gear is perfectly optimize to terminal speed against air-resistanse, obviously wearing the tyres down will offset said optomization, but by a very small margin. JT?
"Bernoulli is a nine-letter name"
xpensive
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Joined: 22 Nov 2008

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xpensive wrote:
JohnsonsEvilTwin wrote:Not being educated in the laws and math of this, I would guess there are only 2 ways tyre wear would influence a cars top speed.

On a final corner approach onto a straight, if the tyres are shot, there is no way you will achieve the same top speed as if the tyres were giving up more grip allowing greater exit speeds, and therefore more momentum to allow a higher top speed.

2. I wonder what the resistance of a worn tyre would be to that of a brand new tyre.
I doubt they would be the same, and would the aerodynamic profile of the tyre itself nullify any rubber/road resistance?

Hmmmm

Let's cut this crap once and for all, it your final gear is perfectly optimize to terminal speed against air-resistanse, obviously wearing the tyres down will offset said optomization, but by a very small margin. JT?

Sorry xpensive but I cannot resist.
Two questions.
First does this offset mean an increase or decrease in speed and two what is the result when top speed is not optimized to air resistance, as it will be on most circuits?
autogyro
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Joined: 4 Oct 2009

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xpensive wrote:Perhaps something like this then, Dave?

Wheel power (Watt) = Aerodynamic resistance (Newton) plus accelleration (meters per second squared) times mass (kg) * Speed (meters per second)

Something like that X - (e)xcept that drag is more than just aero resistance (it includes friction from various sources & tyre forces usually bundled as "rolling resistance") & both drag & inertia force should be multiplied by speed. Aero resistance would be expected to dominate at maximum speed, however (hopefully). Some energy will also be absorbed by the dampers, bump rubbers, tyres, fuel, & vehicle structure (including the engine) when disturbances are encountered. Again, the majority of these should, in a good car, be negligible.
DaveW
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Joined: 14 Apr 2009

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Good lord, have I found a detailist worthy my attention?
"Bernoulli is a nine-letter name"
xpensive
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Joined: 22 Nov 2008

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IMO this is really all intellectual masturbation not worthy of analysis.

On the one hand yes, small changes are important in pro racing. A lot of small things add up to a large difference.

On the other hand you DO have to be a realist and understand that there's a point where you're never going to be able to confidently sort one thing versus another.

"Worn" (used) tire at end of stint versus new tire at beginning...

-Tread rubber will be inherently different as it goes through more cure or reversion
-Tread temperature will change, affecting grip and response levels
-Tread thickness changes, affecting running temperature and response levels
-Change in radius and profile affecting gearing and aero to the smallest degree
-Construction may be different as cords stretch and are affected by heat and strain
-Rubber laid down or picked up from race track affecting all sorts of things
-Etc etc etc

Believe me.. you don't even wanna get into all the subtle, and not-so-subtle changes a tire goes through when it's been used. You will never be able to sort it all out and determine what is affecting what. Waste of time.
Grip is a four letter word.

2 is the new #1.
Jersey Tom
127

Joined: 29 May 2006
Location: Huntersville, NC

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xpensive wrote:Good lord, have I found a detailist worthy my attention?

Interestingly, the devil is sometimes in the detail. For example, it is a commonly held view that a significant performance "edge" in IRL is to be found by reducing transmission friction. Again, the engine of one F1 vehicle dissipated over 30 percent of input energy during a rig test (around 6 times the energy absorbed by the front dampers, contextually). Whilst the magnitude of the energy "lost" might not have been overly significant in the grand scheme of things, it did suggest that engine reliability might be an issue. It was.
DaveW
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Joined: 14 Apr 2009

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@Dave W; Intersting, wanna discuss potential energy-harvest with KERS? Btw, God is also there somewhere, in the details.

@JT, thanks, most educting. Btw, is it obvious that Max power of today's F1 engine will come at 18k?
"Bernoulli is a nine-letter name"
xpensive
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Joined: 22 Nov 2008

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xpensive wrote:@JT, thanks, most educting. Btw, is it obvious that Max power of today's F1 engine will come at 18k?

No not really 17500rpm would be more accurate....

Getting the driver to change at exaclty 18000 rpm is asking a bit too much really Bouncing off the limiter wouldnt be conducive to a fast lap no?
More could have been done.
David Purley
JohnsonsEvilTwin
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Joined: 29 Jan 2010
Location: SU 419113

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In that case, optimizing 7th gear for a terminal speed at 17500 would seem logical, no?

Anyone knows the potential increments of today's F1 gearing anyway?
"Bernoulli is a nine-letter name"
xpensive
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Joined: 22 Nov 2008

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xpensive wrote:In that case, optimizing 7th gear for a terminal speed at 17500 would seem logical, no?

Anyone knows the potential increments of today's F1 gearing anyway?

Check Hamilton's rev counter down the straights at Monza. 17-5 17-6 17-7 Brake for the silly monza s-chicane.

Dont really know the second one.
More could have been done.
David Purley
JohnsonsEvilTwin
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Joined: 29 Jan 2010
Location: SU 419113

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Anywhichway to find a power-curve for an F1 engne of today's, if you don't gear for 18k, it makes you wonder a bit?

Q was however how much a gear-difference would change things, in percentages, cog for cog so to speak?
"Bernoulli is a nine-letter name"
xpensive
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Joined: 22 Nov 2008

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I think its peak power would be spread over the area its most likely to be used.

I chatted to an engineer over at pro drive on a karting day about 3 weeks ago and he intrigued me by saying that maybe Renault or Ferrari have a more pwerful engine than Mercedes. BUT the Mercedes can use its peak power for longer and has better driveability.

More could have been done.
David Purley
JohnsonsEvilTwin
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Joined: 29 Jan 2010
Location: SU 419113

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Wow! My innocent question has attracted a lot of of posts. Funny considering that I found it answered to my satisfaction after about 8 or 9 posts...
In the interest of peace I'll summarize a little bit:
My original question was aimed at the effect of the tire circumference. We established that it will have a very small effect, in the range of 1Km/h. It turns out that there are many more effects at play than just the amount of rubber, but the effect on rolling radius will remain small.
Then, we agree that if the car is geared "right" or "for it", the terminal speed of the car is really a function of power and drag. This has little to do with tyres. That speed would of course only be achieved in a very large straight, and real strights in F1 circuits tend to be smaller, so the car could potentially be still accerelating at the end of it. In that scenario the tyres become a dominant factor by influencing the exit speed from the last corner. But this has little to do with rolling radius.
And we also established that if the gears are too marginal, or a circuit demands an unusual compromise, and the car really hits 18000RPM in 7th gear in the track, then the rolling radius will be determinant, but this scenario is rare or never happens at all.

Guys, we all agree and I think we all see the complexity in this. There are 3 right answers to the question, they are all right depending of the circumstances and that is how it should be. Whether your favourite answer is A, B or C, it doesn't make the other two wrong. It is really A except in this cirmstances where it is B and in those, where it is C.

Let's be friends, this type of complex and detailed answer is what makes this site great.
Wind turbines are cool, elegant and magnificent. TANSTAAFL!
hollus
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Joined: 29 Mar 2009
Location: Copenhagen, Denmark

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hollus wrote:OK, I am risking looking a bit ridiculous here, but I'll ask anyways, one learns from errors.
With the current cars having an RPM limit, the car can only go as fast as the longest gear will allow, and we see current F1 cars hitting this rev limiter all the time, and I think then hitting top speed. Many slipstreams seem to be aborted simply for this reason.
So, for so many engine RPMs, the gear makes sure that the wheel makes so many revolutions (per minute, per second, per hour, whatever), and this many revolutions times the circumference of the tyre translates into so many meters (meters per second of kilometers per hour, same same).
Logically it would follow that a worn out tire, with less rubber, also has less circumference, and the the top speed would be reduced accordingly.
This sounds weird, though...
Am I right? Am I completely wrong? Why?

To answer the quest yes the rollout would affect the top speed in racing top speed on the straight isn't what necessary required on on a non oval racetrack. You would usally aim to gear the gear for straight so that car is accelarating till the braking point this is dependant on the corner exit speed and length of the straight. As running the running a max rev with a high aeroload will overstess the engine that why hockemhiem had it straight shortenend as they were bouncing on the rev limiter for too long and the aero loads stopping the car going any faster.
Smokes
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Joined: 30 Mar 2010

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