I get asked many times about what the tyre pressure`s should be, now with many zeds running non standard wheels sizes, you need to calculate for each individual tyre/car (zed) combination, follow my guide below and you should be ok.

 

So we know tyre pressures can have a dramatic effect on how your zed steers, gets the power down and reaction to suspension movement, so its very important to get right.

 

1)So take the max. rated weight and pressure from the tyre wall. It will say something like ????lbs at 50 psi.

 

2)Then take your zed weight (users manual figure), assume equal weight on all four tyres.

 

3)With a bit of maths you can work out the % weight you have to the max. of the tyre and from that a % of the max. tyre pressure you should use.

 

Ok I have done a calculation here based on a tyre size 265 x 35 x 19 the max. load per tyre is 1433 lbs at a pressure setting of 50 psi both of these details are shown on the tyre wall.

 

1) Average zed weight is around 3637lbs.

 

2) Next the max. single weight of each individual tyre is now multiplied by 4

1433 lbs (max. single weight ) x 4 = 5732 lbs. max. load of all 4 tyres

 

3) Now the zed kerb weight needs to be shown as a percentage of the max. weight x 4 wheels

 

So the kerb weight of your zed is 3637 lbs. and represents a % of the max. 4 wheel load of 5732 lbs. so take 3637 and divide it by 5732 = 0.634 % so by taking the 63.4% from 100% (max pressure) the resultant figure is 36.6psi

 

That is how you can get an accurate tyre pressure from any tyre fitted on any car and weight of car, of course providing you have the same tyre size all round that's it, if your front tyres are smaller then calculate for them too, adding weight of passengers and big stereo equipment often gets forgotten so when your mates and their luggage is on board add an extra few lbs.

Jeff TT

I'll PM you later with my details and you can do the fancy maths for me :D

I tried this at my local bp garage and by the time i had worked it out the pressure req`d i was gonna get lynched by some unhappy motorists!!:rofl:

I've always set all my cars to 32psi all round... maybe I should actually do it correct from now on! :rofl:

so what bout tyre types ie soft/hard , side wall stiffness, hot and cold pressures and rear/front weight, more or less understeer. the more pressure the less surface area but you get less flex and more response the tyre also warms up quicker with more pressure, the other way round with less pressure you get more surface area more grip but more flex and less response and takes longer to warm up (unless of course using nitrogen instead of air.), there are loads more factors, i think it depends what you want from your tyres if it be fast road, high wear rates or even track use. you cant really put it down to a certain pressure setting, imo anyway.

On the track i had to set my pressure at 24psi which then when hot shot up to about 32psi.

so what bout tyre types ie soft/hard , side wall stiffness, hot and cold pressures and rear/front weight, more or less understeer. the more pressure the less surface area but you get less flex and more response the tyre also warms up quicker with more pressure, the other way round with less pressure you get more surface area more grip but more flex and less response and takes longer to warm up (unless of course using nitrogen instead of air.), there are loads more factors, i think it depends what you want from your tyres if it be fast road, high wear rates or even track use. you cant really put it down to a certain pressure setting, imo anyway.

On the track i had to set my pressure at 24psi which then when hot shot up to about 32psi.

 

Bloody hell mate Forza style lol. I think its more of a generic set up for road cars, but i know what your saying suppose thats why there is telemetry to get things spot on.

Bloody hell mate Forza style lol. I think its more of a generic set up for road cars, but i know what your saying suppose thats why there is telemetry to get things spot on.

 

lol forget forza i been testing it out for real :D

 

I had to much pressure at one point and the rear tyres over heated, the rear was all over the place almost hit the grass a few times, so pulled in and reduced pressures. had a temp probe and everything.

lol forget forza i been testing it out for real :D

 

I had to much pressure at one point and the rear tyres over heated, the rear was all over the place almost hit the grass a few times, so pulled in and reduced pressures. had a temp probe and everything.

 

Ha Ha yer seen your vids mate. :bow:

The manufacture of the tyres have no idea what car their product is going to be used and hence give a max load figure on the side wall this is at a set pressure often 50psi or 65 psi the calculation is to simply match the optimim normal road use pressureto the weight of the car the tyres are fitted to.

 

Jimmy the reason why your tyre pressure made had a heating effect they did on the track is a clear indicator they are NOT track tyres hence the manufactures max loading is based on normal road use.

 

Jeff TT

very interesting Jeff.

 

My skyline is having two new front tyres fitted today 235/40/ ZR18. I bet the tyre shop set the pressure to stock nissan settings.

The manufacture of the tyres have no idea what car their product is going to be used and hence give a max load figure on the side wall this is at a set pressure often 50psi or 65 psi the calculation is to simply match the optimim normal road use pressureto the weight of the car the tyres are fitted to.

 

Jimmy the reason why your tyre pressure made had a heating effect they did on the track is a clear indicator they are NOT track tyres hence the manufactures max loading is based on normal road use.

 

Jeff TT

 

They were r888's tho?!?!?! they heat up very quickly, pressure went up to 45psi lol

On my zed there 27psi all round :rofl:

They were r888's tho?!?!?! they heat up very quickly, pressure went up to 45psi lol

 

Try filling them with nitrogen rather than coMpressed air will give more uniform results and less leakage.

 

Jeff TT

34 psi front and 36 psi rear for 235/40 - 18 front and 265/35 -18 rear seems about right. Anyone running less than 30psi runs higher risk of a bent rim from a pot hole and when less than 27psi also risks blow outs from overheated sidewalls at high speed. This is especially true of low profile types

so what bout tyre types ie soft/hard , side wall stiffness, hot and cold pressures and rear/front weight, more or less understeer. the more pressure the less surface area but you get less flex and more response the tyre also warms up quicker with more pressure, the other way round with less pressure you get more surface area more grip but more flex and less response and takes longer to warm up (unless of course using nitrogen instead of air.), there are loads more factors, i think it depends what you want from your tyres if it be fast road, high wear rates or even track use. you cant really put it down to a certain pressure setting, imo anyway.

On the track i had to set my pressure at 24psi which then when hot shot up to about 32psi.

 

Try filling them with nitrogen rather than coMpressed air will give more uniform results and less leakage.

 

Jeff TT

 

I will be trying this one day :D

34 psi front and 36 psi rear for 235/40 - 18 front and 265/35 -18 rear seems about right. Anyone running less than 30psi runs higher risk of a bent rim from a pot hole and when less than 27psi also risks blow outs from overheated sidewalls at high speed. This is especially true of low profile types

 

 

Yes fully agree, especially the last comment.

 

Jeff TT

ive run 27psi all of the time in the zed without any problems and also been on a track

 

anything over 30psi the ride is way to harsh :(

Re

ive run 27psi all of the time in the zed without any problems and also been on a track

 

anything over 30psi the ride is way to harsh

 

The reason for that is you're on lowered springs and you have less compliance in the suspension. You are way too low at 27psi and risking other problems. You will probably also get a shoulders wear pattern.

Jeff

 

I followed this until the last bit:

 

"So the kerb weight of your zed is 3637 lbs. and represents a % of the max. 4 wheel load of 5732 lbs. so take 3637 and divide it by 5732 = 0.634 % so by taking the 63.4% from 100% (max pressure) the resultant figure is 36.6psi"

 

At the risk of being shouted at and proved wrong should it not be 62.4% of the max pressure which is 31.7psi ((50x63.4)/100) ?

 

 

Fire away ! :nelson:

Also for going on a trackday are you not best to increase the pressures by 3 - 5 psi from the normal road settings, not lower them?

 

I know the issue is the shape and size of the contact patch on the road but everything is a compromise. The lower the profile in general the higher the running pressure for higher speeds and loadings.

Also for going on a trackday are you not best to increase the pressures by 3 - 5 psi from the normal road settings, not lower them?

 

I know the issue is the shape and size of the contact patch on the road but everything is a compromise. The lower the profile in general the higher the running pressure for higher speeds and loadings.

 

on the track the temp of the tyres are way beyond normal running temps unless using nitrogen the pressures can raise from 3-8psi meaning instead of being 30psi they are now 35 or so. You cant just put pressures down to a bog standard pressure you have to try and test them too see what works best for you, read my first post.

J1mmytt - Re your first post

 

I did read it. I just don't entirely agree with it. Especially...

 

On the track i had to set my pressure at 24psi which then when hot shot up to about 32psi.

 

I am not suprised they got so hot and the pressure then rose up. 24psi is a very low pressure for a low profile sports car tyre to start with. If you had set them to 32psi or more to start with they would have worked more like they are supposed to and the pressure increase would have been more limited since the sidewall flex would have been more normal. I think your car would have handled much better also. Of course you want some heat in the tread but not an overheated sidewall that is folding over on the bends and tearing off the tyre shoulder to create the heat.

 

I know that nitrogen doesnt expand as much as air when hot so you dont have such big pressure variations with it and I also understand that maybe in hot places where track temperatures get really high you will need to then drop the pressure during time on track if pressures get towards the fifties but it should never be into the twenties even to start with.

 

I admit to never having tracked mine so what do I know but I am sure there's others here that have and they will tell you that low pressures to start with on a track are just not right.

 

Of course you need to let them down a bit to normal levels for normal road driving afterwards.

J1mmytt - Re your first post

 

I did read it. I just don't entirely agree with it. Especially...

 

On the track i had to set my pressure at 24psi which then when hot shot up to about 32psi.

 

I am not surprised they got so hot and the pressure then rose up. 24psi is a very low pressure for a low profile sports car tyre to start with. If you had set them to 32psi or more to start with they would have worked more like they are supposed to and the pressure increase would have been more limited since the sidewall flex would have been more normal. I think your car would have handled much better also. Of course you want some heat in the tread but not an overheated sidewall that is folding over on the bends and tearing off the tyre shoulder to create the heat. the stiffer suspension also eliminates any roll so the tyres have more contact patch not to mention better predictability and control.

 

I know that nitrogen doesnt expand as much as air when hot so you dont have such big pressure variations with it and I also understand that maybe in hot places where track temperatures get really high you will need to then drop the pressure during time on track if pressures get towards the fifties but it should never be into the twenties even to start with.

 

I admit to never having tracked mine so what do I know but I am sure there's others here that have and they will tell you that low pressures to start with on a track are just not right.

 

Of course you need to let them down a bit to normal levels for normal road driving afterwards.

 

 

Ok now i can say i completely disagree, to begin with you propably dont realise a track tyre has very hard sidewalls very different to a road tyre they are also a fatter profile than what im using on the road, and also the higher the pressure the quicker it heats up forget about sidewall temperature for a minute and think about the centre of the tyre and what its doing, also the negative camber i am running which is 2.5degrees which means when leaning into the corner the tyre remains more flat than leaning onto the outside wall of the tyre so im using more of the tyre and not wasting the insides like a road setup.

 

Now i did start of with about 35psi but they got too hot and i had to reduce pressure, if i show you the wear pattern you will see that they are wearing evenly across the tread which is what you want, i probed the tyres and they were also pretty even temp from outside in, i bet if you used your car how it is now you would notice excessive wear on the outsides of the tyres while the insides remained pretty new.

 

ok now read this taken from toyo tyres.

 

The pressures you use will initially depend on the weight of the car, too little pressure on a heavy car can lead to over deflection of the tyre and subsequent failure.

 

Below are some basic settings:

 

VEHICLE WEIGHT COLD PRESSURE HOT PRESSURE

Very Light

Light 800kg - 1000kg 20 - 26 psi 24 - 32 psi

Heavy 1000kg - 1400kg 23 - 27 psi 28 - 40 psi

Very Heavy > 1400kg 27 - 35 psi 37 - 40 psi

 

 

As a tyre gets hotter the pressure increases, this is due to the moisture in the air. The cold pressure you set to achieve a desired hot pressure will depend on the conditions on the day i.e. ambient and track temperature, wet or dry. If the day/track is cold you will need to start with a higher cold pressure as the tyre will not get as hot therefore the pressure increase will not be so great.

Hot pressures must be balanced side to side. Once the tyres have cooled you will find that you will have a difference in pressure side to side, if you have been racing on a right hand track you will find the offside pressures will usually be higher than the nearside.

 

 

Changing hot inflation pressures by small amounts can be used to fine tune handling.

 

Reduce Oversteer Reduce rear pressures or increase front pressures

Increase Oversteer Increase rear pressures or reduce front pressures

Reduce Understeer Reduce front pressures or increase rear pressures

Increase Understeer Increase front pressures or reduce rear pressures

 

 

Achieving the required tread temperatures will depend again on the conditions on the day i.e. ambient and track temperature, wet or dry.

 

You often here competitors saying “My tyres started to go off towards the end of the race”, this is usually due to the tread getting to hot.

 

 

 

Basically williyo your getting mixed up, the less pressure the less the surface tyre patch heats up vise versus.

Edited November 19, 200916 yr by j1mmytt

just for proof, does this look like the tyre walls are folding over on the edge? I think not, and this is at full lean as you can see the sideskirts are almost touching the ground lol

I bow to your greater experience here J1mmytt!

 

Think I must have missed the bit where you said you were using special track tyres rather than normal road ones! Or the fact that you have 2.5 degrees of negative camber on the front. That must be fun on the public road!

 

My point was based on the assumption you were using road tyres in a track day application on a "normal" car.

 

Even the Toyo thing you quote gives a range of 27 - 35psi cold for a very heavy car which lets face it the 300zx is. You setting at 24 is even below that range but I see that you didnt start with that but reduced it to that when they were hot after starting with 35psi cold. I guess that on cool down they would have then been well soft. Toyo seems to be saying 37 - 40 psi hot is the right range

 

I still disagree with:

 

" the less pressure the less the surface tyre patch heats up vise versus. "

 

I think its the other way round.

 

Anyway your points are interesting and your car looks great at full tilt!

I bow to your greater experience here J1mmytt!

 

Think I must have missed the bit where you said you were using special track tyres rather than normal road ones! Or the fact that you have 2.5 degrees of negative camber on the front. That must be fun on the public road!

 

My point was based on the assumption you were using road tyres in a track day application on a "normal" car.

 

Even the Toyo thing you quote gives a range of 27 - 35psi cold for a very heavy car which lets face it the 300zx is. You setting at 24 is even below that range but I see that you didnt start with that but reduced it to that when they were hot after starting with 35psi cold. I guess that on cool down they would have then been well soft. Toyo seems to be saying 37 - 40 psi hot is the right range

 

I still disagree with:

 

" the less pressure the less the surface tyre patch heats up vise versus. "

 

I think its the other way round.

 

Anyway your points are interesting and your car looks great at full tilt!

 

 

 

Honestly the tyre heats up quicker with more pressure i too thought it was the other way around till i came across endless threads and write ups on tyre pressures etc. If the tyres were seriosuly low pressure then the tyre "walls" would heat up and probably blister duw to excess friction but its a different matter in the centre of the surface patch.

 

stock Zeds heavy yes especially when adding weight ie ICE systems, heavy 19inch cheap wheels, bolt on mods etc!?!

mine isnt so much anymore, it weights 1470kg ;) compared to some 1700kg zeds. im still to fit lightweight glass and lots more :D

The pressures i used seemed to work well so i stuck to them , dont forget it was in august and it was VERY VERY hot sun was blazing engine was overheating etc.