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Steve T Fleet
#1 Posted : 23 October 2018 12:41:59(UTC)
Steve T Fleet

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Simple question I have booked onto track day in November at Castle Combe through Boundless Motor Group. The MX-5 is completely standard road car but should I let the tyre pressures down for a track day? I have done a few track days before but never in my own car. Anyone else going to Castle Combe on 13th November?

Gerryn
#2 Posted : 23 October 2018 14:22:00(UTC)
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Don't decrease tyre pressure - big mistake. Tendency was to increase it, though I found doing so meant a harder ride . I'm led to understand the main reason was a fear of tyres coming off the rim, due to side forces, but never experienced that at any trackday. I went from normal 26 psi to 30 psi, but stopped doing that later on. - Settled for 28 psi, which seemed to give me the best of both road and track settings. These days, no track events, so gone back to normal 26 psi. If you decide to increase tyre pressure, don't check them after arriving at a track, give them time to cool down before checking, or you'll get a higher reading when the tyres are still hot, rather than cold.

Note - you don't say which model you have, so I'm quoting tyre pressures for a Mk1 or Mk2, later cars may have higher normal pressure?

Nick D seems to be the expert, so I'll give way to anything he says.
Five is Alive 2002 Mk2.5 Sport, with added Mazda body kit, 15 inch Rota Circuit 8 with Toyos, rescued wood rim steering wheel from a crashed Arizona. Air intake mods to come (one day!) Hard Dog Deuce rollbar. and HT (permanent fixture!) - It's still a sportscar.
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Steve T Fleet on 24/10/2018(UTC)
martin
#3 Posted : 23 October 2018 14:27:21(UTC)
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whats the car and tyre size etc?

Advice would be to put up not down. Tyres are subject to a huge amount of stress on a track day, not least when cornering hard, an under inflated tyre will roll over on itself when going hard into a bend, which is not a good thing, you need the tyres and tyre side walls to be stiffer, not softer.

at least, that's what I understand, and have always done... on a MK1 pressures of about 30 psi, rather than 26. 

martin

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Mad Malc
#4 Posted : 23 October 2018 14:29:51(UTC)
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  My advice would be no. Set them to your normal pressures. the ones you drive on normally. This is you reference point, try a session on these as there will be much to get used to without having an unknown variable in the mix. Once you are comfortable with yourself and the car on track try putting an extra 2/3psi in on top of what ever they are at when you check them. If 28psi is a normal COLD value, they will not be 28 when the car has been used. Do a few careful laps, assess and move on from there. You can add 2psi more or play with front to rear adjustments. 

If you are new to 'track' driving then see if some tuition is available as this will be invaluable and enhance the experience.

Have fun.

Mad Malc by the sea in Filey with a Mk4 SE-L Nav 2.0 in Artic White
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Steve T Fleet on 24/10/2018(UTC)
John M
#5 Posted : 23 October 2018 15:53:35(UTC)
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I did a track day at Castle Combe with my NB a couple of years ago.  Pressures were carefully set to 26psi (per manual) cold, and left there.  It was a cool April day but completely dry.

The car did over 40 laps without incident and seemingly even balance (on a little-worn set of Vredestein Sportrac 3s).

Some people seem to think more pressure is better, others that 2-3psi lower to start with will allow for heating up the tyres.  I didn't feel like dropping the pressures and loading up under-inflated tyres, or running round on over-inflated ones with probably less grip, so not being any sort of expert (take note) I left them standard.

If you have track tyres, seek advice from someone with experience of using them would be my instinct.

Just take care at CC -  no gravel traps as I recall, if you leave the black stuff you'll be on grass, and possibly quite close to some solid banking:)

I'd be interested to hear what NickD says too, but he hasn't been on for a while.

 

Edited by user 23 October 2018 19:59:46(UTC)  | Reason: Not specified

2017 Arctic #320
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Steve T Fleet on 24/10/2018(UTC), Paul G on 25/10/2018(UTC)
Paul W
#6 Posted : 23 October 2018 18:37:23(UTC)
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I don't think there's a "one size fits all" answer to this simply because different tyres will react differently to pressure changes, depending on their design and other factors such as temperature and track conditions.

I'd firstly try the standard pressures on the day and experiment - that's half the fun.
Mk2 1.8i, built Jan 1998.
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Steve T Fleet on 24/10/2018(UTC)
Dipstick
#7 Posted : 23 October 2018 22:33:24(UTC)
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I did my first track day at Rockingham earlier in the year and left the pressures at 26 psi as recommended for my Mk2.5.

On my second stint on track I noticed that the car was tending to drift out more on the corners.

Had a word with the men that know and was told to increase the pressures by 2 psi per wheel for better handling.

The theory being that as the sidewalls get warmer they flex more and traction is lost.

I increased the pressures and the car behaved much better.

Hope this helps.

2005 MX5 2.5 1800i ICON / Manual / Brilliant Black / UN05 AJW / South Central Member
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Steve T Fleet on 24/10/2018(UTC)
Dipstick
#8 Posted : 24 October 2018 22:08:40(UTC)
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Hi Steve

Just fishing...........does the Fleet refer to your place of residence?

If so, pop along to one of our South Central meetings with your wife and meet the rest of the crew.

We have quite a few members local to Guildford and Aldershot, with as many ladies as men attending.

See the attached pages for details:

https://www.mx5oc.co.uk/areas/south-central/

https://www.facebook.com/groups/253800145183630/

2005 MX5 2.5 1800i ICON / Manual / Brilliant Black / UN05 AJW / South Central Member
Hilux
#9 Posted : 10 November 2018 08:24:50(UTC)
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Originally Posted by: Dipstick Go to Quoted Post

I did my first track day at Rockingham earlier in the year and left the pressures at 26 psi as recommended for my Mk2.5.

On my second stint on track I noticed that the car was tending to drift out more on the corners.

Had a word with the men that know and was told to increase the pressures by 2 psi per wheel for better handling.

The theory being that as the sidewalls get warmer they flex more and traction is lost.

I increased the pressures and the car behaved much better.

Hope this helps.

 

I have a few thousand miles under my belt on tracks in the UK and abroad.

Modern cars with multilink suspension use low profile flat tyres as the suspension allows the 'flex'.

You will note that the original/older MX5's had higher profile tyres as the side wall flex is part of the suspension design and keeps as much of the tread on the surface as possible.

Going to big wheels and very low profile tyres on an older car doesn't work as the suspension isn't designed for it.[Which is why an older MX5 will feel harsh with bigger wheels and low profile tyres and be edgy in corners on bumpy roads]

Side wall flex is useful in keeping the tyres in contact with the road/track but less important with multi link suspension.

The newness of the tyres also factors in as the tread blocks squirm and heat up - hence track day tyres have little or minimum tread blocks.

A heavy block tread tyre's grip will improve as it wears out and the block squirm lessens.

I have found that hot pressures are about 3-4 PSI above the normal pressure.

I have found that on older cars 45/50 profile tyres are best for reasons given above in that they do flex as this helps keep the tread flat on the tarmac.

I have found that running tyres about 2-3 PSI above the norm is optimal.

I have found that very light cars don't need much wider tyres - you can over tyre a car and lose grip.

Increasing camber helps keep tyres flatter to the tarmac when cornering but it is a case of experimenting to get the best results.

I would suggest that in stripped out MX5's the Colin Chapman rule of softer springs and heavy damping would work and would help tyre contact but bow to others as I am not minded to track mine as it doesn't have a full cage [based on experience having rolled a Ginetta G27 V8 with a cage]

Do a few laps and check the pressures when hot and reduce as necessary.

 



Red 1992 1.6 Eunos Roadster




NickD
#10 Posted : 14 November 2018 22:16:52(UTC)
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Tyre pressures are a huge can of worms and depend on so many things including tyre, vehicle weight, suspension set up, driving style and circuit, as well as length of driving. 

However, if you are worried about this, it is the hot pressure you are looking for. Over that, using a tyre probe to measure tyre core temperatures across the tyre will tell you all sorts of things about your set up. Temperatures need to be taken immediately you come off track. 

For a normal MX-5 around 30 hot is in the right area. Driving style will influence this more than anything. If you are "on it" then you will find that the starting pressures are around 24 or 25 to achieve this although it is the hot pressures that mater, not the cold. 

Again, if you are on it, then a full tread tyre will suffer far more than a "scrubbed" tyre in the dry as the tread blocks will move far more, create more heat and the rubber will over heat and wear quickly as well as the tyre going greasy. Over heating tyres is not a good thing. 

It is common to put more air in a tyre in the wet. The amount depends on driving style. Firstly the water cools the tyre so it never achieves the dry pressure unless you help it. However some drivers will go considerably higher and some very competent MX-5 racers will run as high as 45psi,  as the very much stiffer sidewall means the car load energy goes into the tread block rather than the side wall, which heats the tread rather than the carcass and heat in the rubber is everything for wet grip. 

Whoever said putting more air in as the sidewall flexes more when the rubber is hot is wide of the mark. You may well add pressure, or allow it to build to reduce sidewall flex because if you over flex it it will just over heat, which is the reason you blow tyres up for load or fast driving and the second pressure shown on most car door panels, the heat does not make more flex. 

You can play with the pressures as you like to suit your driving style. What I normally tell people on circuit, without trying to get too technical is if it feels stodgy and floppy, put more air in and if it feels bouncy take some out. If you are experiencing wear down the sidewall, definitely put more air in. 

For C1 racing we use around 50psi in the front tyres and 70 in the rears. The front is to keep the tyre from rolling onto the shoulder and the rear is to keep the back loose to stop terminal understeer, so don't be afraid to play with your tyre pressures, but don't run then under about 22psi cold or you run the risk of sidewall damage.

Keep an eye on your tyres as they can tell you a lot. 

Paul G
#11 Posted : 15 November 2018 12:32:05(UTC)
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If I can just add to Hilux's and MOT's posts:-

 

If you do take readings, both hot and cold, then you must use an accurate gauge.

I have one with a 60mm face that reads to 2.5 bar (35psi). A blind man could read it. Wink 

 

I borrowed a 12v plug in type pump once and it read 6psi high. Yell

 

Paul G

Steve T Fleet
#12 Posted : 18 November 2018 18:03:37(UTC)
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Thanks Nick, very good advice. The day was wet when we started but dried out. In the end I left tyre pressures at 29psi as they didn't get too hot. Next time I will have to try harder!

 

 

Tyre pressures are a huge can of worms and depend on so many things including tyre, vehicle weight, suspension set up, driving style and circuit, as well as length of driving. 

However, if you are worried about this, it is the hot pressure you are looking for. Over that, using a tyre probe to measure tyre core temperatures across the tyre will tell you all sorts of things about your set up. Temperatures need to be taken immediately you come off track. 

For a normal MX-5 around 30 hot is in the right area. Driving style will influence this more than anything. If you are "on it" then you will find that the starting pressures are around 24 or 25 to achieve this although it is the hot pressures that mater, not the cold. 

Again, if you are on it, then a full tread tyre will suffer far more than a "scrubbed" tyre in the dry as the tread blocks will move far more, create more heat and the rubber will over heat and wear quickly as well as the tyre going greasy. Over heating tyres is not a good thing. 

It is common to put more air in a tyre in the wet. The amount depends on driving style. Firstly the water cools the tyre so it never achieves the dry pressure unless you help it. However some drivers will go considerably higher and some very competent MX-5 racers will run as high as 45psi,  as the very much stiffer sidewall means the car load energy goes into the tread block rather than the side wall, which heats the tread rather than the carcass and heat in the rubber is everything for wet grip. 

Whoever said putting more air in as the sidewall flexes more when the rubber is hot is wide of the mark. You may well add pressure, or allow it to build to reduce sidewall flex because if you over flex it it will just over heat, which is the reason you blow tyres up for load or fast driving and the second pressure shown on most car door panels, the heat does not make more flex. 

You can play with the pressures as you like to suit your driving style. What I normally tell people on circuit, without trying to get too technical is if it feels stodgy and floppy, put more air in and if it feels bouncy take some out. If you are experiencing wear down the sidewall, definitely put more air in. 

For C1 racing we use around 50psi in the front tyres and 70 in the rears. The front is to keep the tyre from rolling onto the shoulder and the rear is to keep the back loose to stop terminal understeer, so don't be afraid to play with your tyre pressures, but don't run then under about 22psi cold or you run the risk of sidewall damage.

Keep an eye on your tyres as they can tell you a lot. 

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