The easiest way to get your head round corner weighting is to imagine the car is a toy, balancing on a pencil. If you raise one corner the diagonal corner will effectivley have more weight on it.
James, I've got some old Yoko A520's but they're past their best now. I didnt think they were still available. Where do you get yours from? Sorry to post off topic! Sean
Sean, Yes - they are OOD, I have six that I bought some time ago. Rarely used now as regs here in Scotland allow 32R`s etc...
Blimey! 40psi cold? I used to run 032R's and the like 32psi hot on the same Yokohama advised pressures.. Confused..
... me too but it works The old Rover 216 challenge used to run up to 70psi rears I`m told ... not sure if hot or cold but still rather high ! Used to have a road going 1.4 Ibiza and just increasing a few psi in the rears used to help that......felt more stable. Can`t attribute any science to all this .... just `feel`
my colways were orrible if they got over 40psi on track. used to iam for about 30 hot - and i mean hot ! The big XJS's i was helping at the weekend were set at 24psi cold, on unlop DO1j's
One of the funny things with setting cold tyre pressures for track use... Low tyre pressure allows lot's of rubber deflection, this deflection of the tyre heats up the rubber more quickly, which then transfers the heat to the air inside and causes it to expand increasing pressure. If the tyre starts to cool on slow laps etc then the tyre pressure decreases, deflection increases and the tyres heats up again Starting off with a higher pressure might be assumed to give a much higher hot pressure - but the higher cold pressure greatly decreases the rubber deflection of the tyre when you go out on track. This means it takes longer for the rubber to heat up, and can mean that ultimately the tyre gets less hot - so heating up the air in the tyre less and causing less increase in tyre pressure from cold to hot. If you look in the car's owners manual it often states to use a higher tyre pressure for high speed driving. Although specialised tyres (slicks etc) will have their own rules that are completely seperate from road tyres I believe that there is a lot of room for experimentation with road tyre cold and hot pressures. It's also worth remembering that *hot* pressure is a very hard thing to consistently repeat. Even on the same track, with the same 20 minute session (for example) doing the same lap times your tyre temps when you come in will be greatly affected by factors like ambient temp, track temp, wet/dry track etc, even how fast/slow your cool down lap is and how far you have to drive round the paddock before you park up and check the pressure. Unless the regs exclude it i'd consider pricing up a nitrogen tyre inflation kit as it has definite benefits for pressure consistency.
Yoko`s advice to me was car specific - I gave them all the details of the then suspension and different types of tyres I used - A520`s / AO32R`s. For track use (Coombe) - their advice was to start with the standard cold set pressures and do a session of ~ 6 laps then immediately take the hot pressures and note the rise over cold. They advocated leaving the front pressures as standard which I always have after experimenting with higher and finding that the car was less stable under braking. As for the rears they advised letting the tyres cool back to cold set then increasing them a few psi at a time and repeating the 6 lap exercise. Each time noting the increase over cold. What I found was - the A520`s would only give 4 / 6 psi rise at the rear whereas the AO32R`s would give 9 / 10 psi. Their advice was to continue increasing the cold set pressures up to ~ 40 psi and see how the car felt along the way. Eventually deciding on what worked `for you`. As I`ve said before am not sure of the science of this but possibly increased pressure = increased temperature = better grip, noting that 32R`s are a much better / softer compound. Even the 520`s at 40psi cold are much better than at standard. I have consistently followed this advice for track / hills / sprints and as said before it works for me....gave the then set up an extremely stable and consistent rear end. In addition ..... one of the best mods I`ve done was to replace the worn standard rear beam bushes with Bugpack Urethane type .... transformed / stabilised the rear no end. Car now has a totally different set up so will start all over again when it`s run in but I`ll be giving Yoko a call to discuss. Hope this helps !
I'm keen to hear your thoughts on that (i know you've said it's just your best guess, but keen to hear the logic behind it)
interesting read. my mix of tyres is probably not ideal with rears being boggo falken road tyres, reasonably sturdy sidewall. The Bridgestone RE070's have very very firm sidewalls akin to slicks, so airpressure is'nt holding the sidewall up.. less pressure softer sidewall more tyre flex more heat... makes sense. higher initial pressure, less sidewall flex, less heat less pressure rise from heat.. makes sense. firm sidewall vs pressure vs heat gain from work.... God knows.. experiments to learn I guess and check wear rates and lap times.
You can’t go generalising about rear tyre temps on FWD cars, whether an initial high or low temp works is completely dependant of the specifics of the car in question. Tyre compound, sidewall ratio, roll stiffness, dynamic camber, scrub radius and spring rates are just a few of the influencing factors, change any one of these and any ‘rule of thumb’ is worthless. That’s not even considering such things as track surface coefficient, ambient air temperature and downforce.
`Dex` Higher pressure = higher temp = better grip ? As I increased the rear cold set pressures the resulting hot pressures showed an increasing differential and a more stable rear end. The (my) physics being that the higher the initial pressure the more volume that is subjected to the work of the tyre (force acting on the pressure) resulting in greater molecular activity within the air volume that generates more heat that enables the rubber to `work` more effectively ......... up to a point. (Always noting the tyre manufacturer maximum inflation pressure on the sidewall). Plus the fact that the rubber itself is helping to generate heat. ...now standing by to be shot down by the scientists out there
a racer i race against said he runs his particular car (which is a race winning car) at pressures at hot temps on the max spec'd for the tyre.. which is higher than I have ever run mine. Might try my previous starting point 35psi cold pressure (road) and see what happens I guess. There are soooooo many variables as said previously. suck it and see.
Thanx for saying that Dex, I've said exactly the same before and been slated for it. As far as road tyres are concerned, through my own experimentation I have found higher initial cold pressures to work much better. I found them not to go off so quickly. But its also down to driving style. I prefer the tyres sliding slightly rather than the tyre walls flexing and rolling. Also Sprinting and Hill Climbing is very different to Circuit Racing due to the simple fact that you spend much longer on track. When sprinting the tyres don't have as much time to warm up and so a good "feeling" is needed straight away. Were as with circuit racing you can afford to sacrifice some initial feeling and grip until the tyre warms up to its racing temperature. Its a compromise either way. Sean
I was involved with the Formula Women Mazda's and always found it strange that the cold pressure for the Avon tyres was over 40 psi. This was recommended by Tim Harvey who was the consultant/presenter for the series. Seems to fit with some of the comments above though.
To me it seemed (with road tyres) that you are subjecting the tyres to far more cornering force than you would on the road. This will create more force trying to flex the sidewall and lift the tread off the track (and start to run on the shoulder and the sidewall) Since it's high tyre pressures that stiffen the sidewall it strikes me that for track i'd want to be running higher pressures than on the road. So it's a matter of how i get those pressures - either start with low pressure, let the rubber move and heat a lot, heat the air so it expands - but by the time i've *pumped* the tyres up with the expanded air how close have i got to cooking the rubber of the tyres? (and how long have i been abusing the sidewalls when they weren't properly supported. So i start with higher tyre pressures, i get far less sidewall deflection and don't get the initial soggy feel of underinflated tyres. The tyres warm up progressively, but they only need to get up to operating temperature - they don't need to get hot enough to pump themselves up. Jamesa2 - "As I increased the rear cold set pressures the resulting hot pressures showed an increasing differential and a more stable rear end." Is that a higher differential as a percentage of the start/finish pressures, or a higher number of psi difference? (or both...)
Dex `Differential` - the more the cold set was increased the greater the difference between the cold and resultant hot pressure. Cold set of 40psi gave a greater hot pressure than the hot pressure resulting from a cold set of 30psi. I recall suggesting this principle to Keith R (Smith) some time ago and when he tried it in one of his races it appeared to improve his situation.
tyre construction will dominate this hot v cold pressure I think. always used to run my road tyres on 35psi cold... >40psi when hot. The 28psi cold on my fronts went to 40psi hot at the last race on very firm sidewall tyres. I will definately try my old road settings on the next race and see what happens.
