Tyre Pressure

[freedom_honda]

Hi,
Does higher tyre pressure gives you more grip? or does lower tyre pressure gives you more grip?

because i was reading some articles on the internet. and some say higher pressure = more grip, but some say lower pressure.

Thanks

[Jersey Tom]

Higher or lower than what?

Every tire / car combination has an optimum pressure Front and Rear (or Left and Right.. or LF / LR / RR / RF).

If you had all flat tires, you wouldn't have much grip. If you ran 120psi all around you wouldn't have much either. There's a sweet spot, gotta find it. FSAE car might be in the teens, small open wheeler in the 20s, stock car 15 to 60, who knows.

[majicmeow]

As has been mentioned, every car and every tire will be different.

In the case of F1, every tire is the same, so the amount of pressure with vary by team based on chassis design, track conditions and driver profile. Every single car will be setup differently to suit each drivers needs. If a driver wants more oversteer, the front pressures may be reduced slightly or the rear pressures increase slightly etc... On certain cars, they may have to run low(er) pressures consistently compared to other teams due to design limitations.

Here is a BASIC!! rundown of how tire pressure can affect traction. Keep in mind, this is BASIC theory only

If the tire pressures are too low for example, the tire will exhibit more sidewall flex. This is detrimental because the flexing of the tire in an extreme amount allows the car to move relative to the contact patch. Think of a flat bicycle tire... you are able to rock the entire bike side to side whist the tire's contact patch remains in the same position. This causes a degree of unpredictability and the car will feel like it is wobbling down the track.

Keep in mind, this is always going to happen, regardless of tire pressure, but the less it happens, the better/more predictable the handling of the car will be.

Another problem with running low tire pressures is that the contact patch tends to actually become two small contact patches at the very edge of the tires. You'll notice on a regular car tire that has been under-inflated for long periods of time, that the center of the tread is relatively un-worn while the outside edges are usually quite badly worn. Making two contact patches work together can be incredibly hard, if not impossible.

Over inflating a tire causes exactly the opposite of both of these problems. Sidewall flex, though still present, becomes too little! This is bad because more and more of the effect of a bump will be transmitted to the suspension. This can cause the car to bounce, the tires to hop over bumps instead of absorbing them, or generally just drive unpredictably over rough surfaces.

Also, the more inflated a tire becomes, the less of a contact patch you will get in return. Again, using a car tire as an example, one that has been over-inflated for a long period of time will show you that the center of the tire is very badly worn while the outside edges are hardly worn at all.

So, where does that leave you? The optimal goal is to use as much of the tire as possible at all times while cornering. Using a large portion of the tire keeps wear consistent and temps lower. That is where camber and suspension geometry come into play to work along side the tires, but thats another thread all together...

Obviously, there are exceptions to the rule, again, depending on design and drivers etc...

[marcush.]

anyone who happened to go racing with the slightest seriousness soon realised that
as soon as the pressure rises above optimum ,you loose traction.
Having said that ,the pressure rise is really depending on a lot of factors not easily controllable for the guy who sets the cold pressure before the race/stint starts.
Assuming the tyres are all the same ,there´s still differnt tyre gases (still allowed?),ambient ,tracktemps,stickertyre-scubbed-used tyre(how many laps done?),setup of car ,weight distribution,driver style/talent,stint (how many laps to be covered,fuel in )and a lot more to be considered to hit the bell just right ...
So really ,one rather errs to the low side with pressure and reminds his hero to please avoid the curbs in the first lap...

[donskar]

Hi,
Does higher tyre pressure gives you more grip? or does lower tyre pressure gives you more grip?

because i was reading some articles on the internet. and some say higher pressure = more grip, but some say lower pressure.

Thanks

The other responses have been far more technical (and accurate), but there has always been a sort of "street smart" that raising the tire pressure just a few pounds over spec will give you slightly better handling. Back in the dark ages of 1960s-70s when some of us were still running bias ply tires we'd always pump the tires 2-4 pounds over spec before a rally or autocross (gymkhana). From my seat of the pants chassis dyno (call it a one-post test rig )this is probably true, but has NO bearing on race car tire settings. In the competition arena very small increments of tire pressure can make a noticeable difference (at least that's what the drivers and engineers say).

On a semi-serious note, "do NOT try this at home; these are trained professionals." I experimented with tire pressures on a rally stage, LOWERING the pressures by several pounds. I sort of succeeded, because the lower pressure had a VERY big impact on handling -- I ended up on my roof.

[Ciro Pabón]

Well, I'm here with donskar. I know little about pressure, actually I don't measure pressure, but I know a bit about tuning. And from what I know, my recommendation is NEVER MEASURE TYRE PRESSURE (sorry for yelling): it won't lead you anywhere. What you want to measure is the temperature.

I use a tyre probe (Digatron brand, I'm not sure about the english name of this thingie), the one you insert into the tyre.

I recommend to buy one of these if you're serious (ehem) about karting. Insert it into the center and edges, at an angle, more or less half a millimeter or so. Of course, be careful not to puncture the tyre (it has happened to me).

That's the best instrument when you want to check pressure, forget about measuring the pounds per square inch or pascals or whatever (I don't know why almost all tools I have use imperial units...).

Bear in mind that the tyres cool very rapidly after leaving the track: no matter how quick you are, you will get readings below the 165-185 fahrenheit recommended by manufacturers. Be consistent and use a laptop to register what you measure, that's all. I take the time since the car leaves the last curve until I get the reading, for every reading. I also annotate the time since the car stops, which is different for every circuit, just to look for consistency.

Another very important measure is totally subjective: check for shiny tyres. No kart tyre I know can survive over 200º F, they will destroy in minutes.

Temperatures are always different in both sides of the thread, of course (unless you're on a drag track... ).

If both temperatures are the same, something's wrong. The "outer tyre" HAS to be hotter. For example, check this:



What you're looking for is for the same temperature differences among left/right tyres.

If it's raining, lower the pressure a little or the tyres will get cold.

[Jersey Tom]

IR trumps needle pyrometer by miles for chassis setup (camber and pressure). I'd use pyrometer as a durability check.

If you do use a pyrometer, be sure to use it the right way. Go deep! At least 3/16" (4.5mm) on most race tire. Maybe only 1-2/16" on a stock car tire. You shouldn't be able to puncture the tire... go in at a angle and get as much of the needle "submerged" as possible. Don't stab it violently.. but when you put it in you'll feel just a bit of resistance when you hit the cords.

Also, you've got to stick the thing a couple times quickly in one area, to get a reading. Don't just put it in once and let it settle for 10 seconds, as I see a lot of folks do.

[Scuderia_Russ]

Well, I'm here with donskar. I know little about pressure, actually I don't measure pressure, but I know a bit about tuning. And from what I know, my recommendation is NEVER MEASURE TYRE PRESSURE (sorry for yelling): it won't lead you anywhere. What you want to measure is the temperature.

I disagree to a point. If I sent a driver out on a set of tyres with the following cold pressures - L.F. 15 psi, R.F. 16 psi, R.R. 15 psi, L.R. 14 psi on a clockwise circuit with the aim of achieving 20 psi across the rear and 21 psi across the front. I'd have to ensure that the pressures came up to or were dropped to the desired pressures before I could start to get reliable / useful temperature data.

[Ciro Pabón]

Well, to make it simple, I think that you look for a pressure that gives you a temperature that gives you more grip.

So, the answer to the original question is:

Lower or increase pressure to get the temperature recommended by the factory.

Regular cars AFAIK (AFAIK!) have tyres designed to as much "grip-insensitive" to temperature as posible. In that case, follow the manufacturer instructions (I think, please correct me if I'm wrong).

If you're using racing tyres, take in account the tips given by Tom and Russ about the right method of measurement.

I don't know if there is anything more to it.

[flynfrog]

Pressures have more to do with temps across the tire.

I know Ciros example is a kart but on a suspend car changing springs or weight balance has more to do with the over all temps between tires while tire pressure has to do with the temp across.


example

Code: Select all

 O   M   I   I   M  O
140 180 140 110 80 110
 O   M   I   I   M   O
200 250 200 140 140 140

The left front tire has to high of pressure.
the Right front is probably close on pressure but the spring is too soft. Once the tire is up to temp it should be close.

The left Rear has to hard of a spring is but once the correct spring is in the pressure is probably close.

The Right rear is perfect. How ever once we changing the springs in the left rear and right front it will probably need to be tweaked.

And this is why race car tuning is referred to as a black art.

These numbers assume camber is correct if you had a tire

Code: Select all

 O   M   I
120 150 190

you are running to much camber

[flynfrog]

grr formating got messed up

[Jersey Tom]

Key to FF's bit, is you should aim for that even temp spread mid-corner.

[flynfrog]

Key to FF's bit, is you should aim for that even temp spread mid-corner.

Depends on the tires or series for an oval race usually 10 laps in if you expect cautions ect. You might not be able to cool off the tires between corners.

[Belatti]

Well, I'm here with donskar. I know little about pressure, actually I don't measure pressure, but I know a bit about tuning. And from what I know, my recommendation is NEVER MEASURE TYRE PRESSURE (sorry for yelling): it won't lead you anywhere. What you want to measure is the temperature.

Quite odd for a kart racer / kart tunner. I don´t know if it is because the type of tires karts use arround here, but it is a standard among kart races to keep an eye closely to hot tire pressure not to pass 14 psi. Usually 12psi to start on cold tires. They told me if you run a higher pressure the tires turn to soap in a matter of minutes.

Of course I´m starting in the world of karts and have still A LOT to learn.