Tyre pressure

[arcturus]

So, starting off with cold tires, sea level at 21psi. Will be taking part in hill climb at 1000mtrs altitude,temperature probably in the 30*c range. what effect will that have on pressures? Do I keep the pressure on the Low side for better grip on corners or on the high side to make steering lighter on tight chicanes? What's the opinion of y'all?

[Clan]

Originally Posted by arcturus

So, starting off with cold tires, sea level at 21psi. Will be taking part in hill climb at 1000mtrs altitude,temperature probably in the 30*c range. what effect will that have on pressures? Do I keep the pressure on the Low side for better grip on corners or on the high side to make steering lighter on tight chicanes? What's the opinion of y'all?

low tyre pressures are not the way to get more grip , you will understeer off the road on a bend . the tread rolls and less contact on the road . i would suggest you use at least 36 psi preferably 40 or more psi if there is much high speed or arduous work for them to do .The tyre treads stay the intended shape then .

The altitude will give the impression of slightly higher tyre pressures but i am not familiar with the altitude versus pressure graph .

[classicswede]

I would be sticking to 30-32psi

[arcturus]

Thanks to all. This was really a tongue in cheek post. Yes,hill climb and altitude but I am in the regularity section. Six runs at exactly the same time at timing points. High speed? I intend to go flat out up hill in second and third gear at about 80 km. Easier to repeat times at flat out speed. About four km distance.

[Vintagewrench]

I race my 67 1800s with the VSCCA and a few weeks ago and competed in the Mt Equinox Hill Climb (3500 feet 5.5 miles and forty turns) for the second year in a row, and have found that lower tire pressures can be used at times to your benefit.

The top half of the course is really rough and bumpy and because of that I run 24 psi in the front and 22 in the rear (195/65/15 Michelin street radials). Did not experience any understeer and because of changes made to the car since last year was able to drop my best time by 35 seconds. Did not experience anymore tire edge wear due to roll under than there would be on a road course and and photos taken of the car during hard cornering did not show more roll under. Tire pressure at the top of the hill rose to 30 psi front and 27 rear.

At Lime Rock Park where the car is run three times a year, 35 psi is used in the front and 32 in the rear.

[Derek UK]

Using higher pressures in the front will increase the tendency to oversteer. Steering turn-in will be sharp but the rear will want to hang out more on parts of the road that have less traction, especially corners when you apply power. A limited-slip diff can help but I would guess you don't have one of those. Hill climbing is generally done at a lot less speed than on the track. Maybe, say, 60 80 rather than 90 to 110 mph so handling characteristics and how you put the power done are a bit different.

[arcturus]

The PV is an old lady. I don't exceed 4000rpm, 80km in third.

[blueosprey90]

My advice is to run the tire pressures (hot) recommended by the manufacturer. Bring a tire gauge with you and adjust your tires just before you go out. If anything, if tires are cold, drop the recommended pressure not more than a pound or two. The tires will heat up as you are driving.

Most cars are designed for understeer, because it is controlled by lifting. Oversteer is when the rear end kicks out unexpectedly - and you have to catch it like when you skid on ice. It is often said that with understeer, you hit the wall facing forward; while with oversteer you hit the wall going backwards.

I've done a lot of track miles at WOT on street radials in two different cars on close to stock suspensions, and unless I'm trying to address a specific issue, I usually run the pressure (hot) recommended by the tire manufacturer. I've only ever really suffered from excessive understeer when my tires got too hot, with resultant increase in air pressure.


Make sure your brake shoes are up to par and that you have changed the brake fluid recently and bled the brakes. And if you lose control and spin, put both feet in.

Have fun!


https://drivingfast.net/understeer/

https://drivingfast.net/oversteer/

[Vintagewrench]

[QUOTE=blueosprey90;2550695]

How did things go for you and the car at the Fall Festival? Hope to see you at the Fall Finale.

[blueosprey90]

^^^

Really well, but I never got the Volvo up there for the Gathering of the Marks on Sunday. I bolted to upstate NY to spend the day with the family. Big bonus points for that run, so I do expect to receive necessary permissions to be at the Fall Finale.

Broke into the 1:11s for the first time.

Crew and I replaced blown head gasket on another MGA, much to the delight of passers by. As a consequence, didn't see much racing and never made it to the vendors area up top.

Here I am on Saturday running 30 psi front, 32 psi rear (cold). For Arcturus, pressures go up about 4-5 psi with hot tires. I'm running different pressures to reduce understeer in the left hand corner. In theory, the higher pressure in the rear means relatively less grip in the rear than in the front, which allows the rear to kick out and help with the turn. At least that's the theory. Not sure it works. But less understeer with the front tires a bit deflated by comparison. In late laps, it helps keep me in front of my Nemesis.

I don't know what is going on in this picture. I'm looking in my mirrors at the yellow car. He's looking past me getting ready to make his move.


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