Home Mobile Forum News Cookbook FaceBook Us T-Shirts etc.: Europe/Worldwide. eBay Motorsport Links Advertising Live Chat  
Site Partners: SpotterGuides MotorsportAds  
Related Sites: Your Link Here  

Go Back   TenTenths Motorsport Forum > Racing Talk > Racing Technology


Reply
 
Thread Tools Display Modes
Old 1 Sep 2003, 12:27 (Ref:704762)   #1
ozracer
Rookie
 
Join Date: Apr 2003
Posts: 6
ozracer should be qualifying in the top 10 on the grid
tyre pressures vs tyre temps

Is there a correlation between temps and pressures. ie will starting with a low pressure result in a higher or lower tyre temperature? I would have thought a higher pressure would result in a higher temp, but then i was thinking that with a lower pressure there is increased sidewall flex which generates more heat.

Another question is for sedan circuit racing, do yuo pump the tyres up or let them down in the wet? I know the go-karters pump them up to make the tyres stand up, but some people have told me that you let them down in the wet as you get more grip and the sidewalls work harder allowing the tyre to get up to its operating temperature.
ozracer is offline  
Quote
Old 2 Sep 2003, 08:35 (Ref:705429)   #2
Mackmot
Veteran
 
Mackmot's Avatar
 
Join Date: Feb 2000
United Kingdom
Melbourne, Victoria, Australia
Posts: 2,188
Mackmot should be qualifying in the top 10 on the grid
You use the temperatures and camber to get a good temperature distribution. Ideally the tyre should be even temperatures accross which means that you are using the tyre evenly. if you find the middle temperature down a few degrees you increase the pressure if its too high you reduce it. If the inside is too cool then you increase the negative camber etc. By a engineer to win by carroll smith it'll explain it better
Mackmot is offline  
__________________
A Saudi saying, "My father rode a camel. I drive a car. My son flies a jet-plane. His son will ride a camel."
Quote
Old 2 Sep 2003, 21:19 (Ref:706127)   #3
Lemans B
Rookie
 
Join Date: Aug 2003
Location:
Near Namur, french part of Belgium
Posts: 2
Lemans B should be qualifying in the top 10 on the grid
Higher presure result in a higher tyre temperature .(stiffer springs to!) The temperature generated by sidewall flex is less importend and heats the tyres sidewalls, not the tyre patches on the road surface.
For your second question , yes and no.
If I have really soft wet tyres, I pump them up and gain heat at the normal way, at the tyre patches.Now it is possible to race in the wet with stiff springs.
If I have not soft wet tyres, I let them down to gain a little heat from the sidewalls . More importend is that with lower pressure in the tyres the stiff springs are no longer "un-driveble"
Lemans B is offline  
Quote
Old 3 Sep 2003, 11:02 (Ref:706723)   #4
ozracer
Rookie
 
Join Date: Apr 2003
Posts: 6
ozracer should be qualifying in the top 10 on the grid
We have to use to same tyres for both wet and dry, Bridgestone RE540S.
ozracer is offline  
Quote
Old 3 Sep 2003, 11:17 (Ref:706757)   #5
zefarelly
Veteran
 
zefarelly's Avatar
 
Join Date: Apr 2002
England
good old Sussex by the sea
Posts: 8,696
zefarelly should be qualifying in the top 5 on the gridzefarelly should be qualifying in the top 5 on the gridzefarelly should be qualifying in the top 5 on the grid
same for the CR65 Dunlops for historic saloons, I've overheard talk of upping pressures in the wet to open the tread . . . . .in short theyre **** tyres (by todays standards) wet or dry !
zefarelly is offline  
__________________
Joe Allenby-Byrne
trading as Zefarelly since 1985
Quote
Old 3 Sep 2003, 15:57 (Ref:707080)   #6
avsfan733
Veteran
 
avsfan733's Avatar
 
Join Date: Oct 2002
Location:
Rochester
Posts: 1,618
avsfan733 should be qualifying in the top 10 on the grid
you can use the tire pressure to effect the tire temperature by having it change the shape of the tire, but its not the best way to do it unless your out of time
avsfan733 is offline  
__________________
I refuse to let fact get in the way of my opinion
Quote
Old 9 Sep 2003, 08:40 (Ref:712792)   #7
laser2
Rookie
 
Join Date: Jul 2003
Location:
australia
Posts: 14
laser2 should be qualifying in the top 10 on the grid
Quote:
Originally posted by Mackmot
You use the temperatures and camber to get a good temperature distribution. Ideally the tyre should be even temperatures accross which means that you are using the tyre evenly. if you find the middle temperature down a few degrees you increase the pressure if its too high you reduce it. If the inside is too cool then you increase the negative camber etc. By a engineer to win by carroll smith it'll explain it better
what page does carrol smith say this in Engineer to win??????
laser2 is offline  
Quote
Old 10 Sep 2003, 20:49 (Ref:714506)   #8
graham bahr
Veteran
 
graham bahr's Avatar
 
Join Date: Jan 2003
England
cambs
Posts: 2,071
graham bahr should be qualifying in the top 10 on the gridgraham bahr should be qualifying in the top 10 on the grid
currently you are juggling with 3 variables, tyre temp, tyre pressure, and the change in pressure caused by the change temperature of the air inside the tyre, if you inflate the tyres with nitrogen you will find the pressure wont vary with temp, therefore you only have 2 variables to consider and life gets a bit easier.
graham bahr is offline  
__________________
AKA Guru

its not speed thats dangerous, just the sudden lack of it!
Quote
Old 11 Sep 2003, 12:37 (Ref:715001)   #9
Revracing
Racer
 
Join Date: Jul 2003
Location:
Kent
Posts: 142
Revracing should be qualifying in the top 10 on the grid
Sorry graham I beg to differ, pressure, temp and volume of the gas within the tyre are all connected, since the pressure and volume can be considered fixed once set then the only variable is temperature (this directly affects pressure etc etc). The pressure within the tyre will rise a given amount for a quantity of heat input, which means if you can limit the quantity of heat that the gas within the tyre can absorb then you can limit the pressure increase and hence gain greater control over tyre performance and consistancy.

Since air is approx. 73% nitrogen the heat absorbtion rate will be no different with pure nitrogen, Right idea but wrong gas. I beleive Helium has the lowest heat absorbtion rate.
Revracing is offline  
__________________
"Racing is life, anything before or after is just waiting"

Steve McQueen
Quote
Old 11 Sep 2003, 15:28 (Ref:715217)   #10
Adam43
Race Official
20KPINAL
 
Adam43's Avatar
 
Join Date: Jul 2001
European Union
The Road to Rouen
Posts: 30,798
Adam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of FameAdam43 will be entering the Motorsport Hall of Fame
I thought the main reason for using N was to reduce the other gases in the tyre, especially water and CO2. However it doesn't eliminate the fact that the temperature and the pressure are always proportional.

There are separate and related problems here. Al of which have been mentioned above.

Firstly as the temperature of the tyre increases so will the temperature. PV=nRT (this is the ideal gas equation, but apart from a small deviation it works).

The temperature of the tyre is effected how it is used. It increases as it is driven. How it increases is effected by the shape of the tyre. However the pressure of the tyre effects the shape and the contact area! Complex? Yes.

Therefore a general knowledge of what is going on is needed, however in practice the fundamental theory is not that helpful.

One way of checking is seeing if your tyres are working well is checking the temperature difference across them. Making sure that the inner, centre and outer parts are working as much as each other. Having the same across the whole tyre is what a lot of people think is best, but some like a slight difference toward on edge. The pressure and camber required to achieve this will change for each circuit depending on how much straight there is to corner!

There is no wonder that tyres are described as a black art.

For all this talk we run the same pressure everywhere (we don't get a lot of practice to try anything! We have settled on something that is thereabouts). We run slightly lower pressures if it is hot! We might change if we feel the tyres going 'off' towards the end of practice, but track conditions change through the day too!

Experience is the key and it is hard to get quickly!

Last edited by Adam43; 11 Sep 2003 at 15:29.
Adam43 is offline  
__________________
News just in. Every manufacturer to pull out of every race series ever.
Quote
Old 12 Sep 2003, 08:31 (Ref:716014)   #11
Revracing
Racer
 
Join Date: Jul 2003
Location:
Kent
Posts: 142
Revracing should be qualifying in the top 10 on the grid
I agree with what your saying Adam, That is exactly what we used to do when I raced Karts, However we never managed to correlate an even tyre temp accross the tread to better tyre performance. I suspect that was due to not having any suspension and hence not having the entire contact patch in contact during cornering.

My point was that in limiting the pressure increase of the gas you can produce a more stable tyre condition that is less likely to go "off".

The principle i am discussing is that the pressure within the tyre will only increase if the gas within the tyre becomes hot, not the rubber. It is possible to have a comparatively hot tyre surface with a much cooler gas and hence limit the pressure change and avoid the more heat = more pressure = more heat problem.
Revracing is offline  
__________________
"Racing is life, anything before or after is just waiting"

Steve McQueen
Quote
Old 12 Sep 2003, 08:44 (Ref:716027)   #12
Revracing
Racer
 
Join Date: Jul 2003
Location:
Kent
Posts: 142
Revracing should be qualifying in the top 10 on the grid
Made some corrections but was out of time, went on to disscuss specific heat of gasses and such but can't be bothered to write it all out again.....
Revracing is offline  
__________________
"Racing is life, anything before or after is just waiting"

Steve McQueen
Quote
Old 12 Sep 2003, 18:37 (Ref:716792)   #13
Mackmot
Veteran
 
Mackmot's Avatar
 
Join Date: Feb 2000
United Kingdom
Melbourne, Victoria, Australia
Posts: 2,188
Mackmot should be qualifying in the top 10 on the grid
Carroll Smith books in general will give people with no idea how their car is working a better idea of how to get the most from it.

On the principles of gases discussion Adam is right about why we use nitrogen. Id like to add that water vapour that you get from ordinary compressors expands 19 times when it turns to steam.
Mackmot is offline  
__________________
A Saudi saying, "My father rode a camel. I drive a car. My son flies a jet-plane. His son will ride a camel."
Quote
Old 14 Sep 2003, 10:10 (Ref:718291)   #14
laser2
Rookie
 
Join Date: Jul 2003
Location:
australia
Posts: 14
laser2 should be qualifying in the top 10 on the grid
ok...but carol smith doesn't advocate the use of a pyro at all. From what I remember, he prefers to "read" the tyre and let the stop watch tell the story, thats why I was asking. He doesn't like pyros and I don't agree with this reading the tyre temp across the tread because you have one other factor which affects the reading, which is carcass construction. Tread foot prints can distort under load and give a really poor reading across the tread. Changing the tyre pressures doesn't fix a construction problem.

I also have found that the pressure increase for 'air' is about twice that for 'nitrogen' filled tyres i.e. air filled will increase by say 12 psi while the nitrogen filled tyre will increase by 6 psi.
laser2 is offline  
Quote
Old 11 Nov 2003, 10:15 (Ref:779693)   #15
PeterMorley
Veteran
 
Join Date: Sep 2003
United Kingdom
Belgium
Posts: 714
PeterMorley should be qualifying in the top 5 on the gridPeterMorley should be qualifying in the top 5 on the grid
Quote:
Originally posted by zefarelly
same for the CR65 Dunlops for historic saloons, I've overheard talk of upping pressures in the wet to open the tread . . . . .in short theyre **** tyres (by todays standards) wet or dry !
I've heard the same - seems that it depends where you are from:

American practice is to up the pressure, in the wet, to open out the tread.

European practice is to lower the pressure, in the wet, to get the temperature up.

Having noticed that Americans tend to avoid racing in the wet whenever possible, I would think twice about taking their advice on wet racing.

Lowering the pressure ups the temperature due to side wall flexing. But you are losing the temperature increase you would gain from increasing the pressure (as governed by PV/T = constant gas equation).

The Temperature in question is absolute (e.g. Centigrade plus 273) so you need a fairly large change in pressure to make a large change in temperature, assuming the volume is constant. Which suggests that flexure is more significant than pressure.

Back to the point:

We've found that the simplest solution is to adopt the mid point of both theories - e.g. run with the same pressure in wet & dry.

Just set the pressure so that you get an even contact patch (e.g. maximum contact/grip) across the tyre (where possible, some things like Bugatti suspension geometry makes that difficult!), and keep to that pressure wet or dry.

The advanced version of that is to check the pressures when the tyres are hot and to stick to that one - there will be a tiny variation due to ambient temperature!

In the end with historic racing it doesn't make a lot of difference - changing driver will have a far greater affect on speed than the tyre pressure!

Quote:
I thought the main reason for using N was to reduce the other gases in the tyre, especially water and CO2. However it doesn't eliminate the fact that the temperature and the pressure are always proportional.
I was told that Nitrogen had less water (none hopefully) and it is in fact the expansion/contraction of the water (moisture) in air that causes tyre pressure to vary with temperature (e.g. the volume increases but since that is fixed the pressure goes up).

The expansion of air or Nitrogen themselves is relatively insignificant in the temperature range we are talking about.

My local tyre place have started offering Nitrogen for road car tyres, should avoid the need to adjust the pressure of your tyres between winter & summer.
PeterMorley is offline  
Quote
Reply

Bookmarks




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Tyre Pressures Ilikeearlgrey Racing Technology 18 27 May 2005 18:29
Tyre Pressures at Pitstops Rennen Formula One 21 4 Mar 2005 16:57
Tyre Pressures Pug620 Racing Technology 14 8 Feb 2005 18:47
tyre pressures laser2 Racing Technology 9 20 Aug 2003 12:29


Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 18:40.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Original Website Copyright © 1998-2003 Craig Antil. All Rights Reserved.
Ten-Tenths Motorsport Forums Copyright © 2004-2016 Royalridge Computing. All Rights Reserved.