wet track tyre

[sambb]

kaanage I remember a while back you were looking at running either street conti's or RE003's in the full wet. Did you give that a go? any comparison to your r spec hankooks?

[sambb]

Notso swift, you mentioned in a post on another forum that A050's are good at 30psi hot and over the top at 32psi. In the hillclimbs I do I'll start the fronts at 29psi and rears at 30psi and find that by the end of the run only the fronts have gone up 1psi. Is that the right kind of window to be in for immediate cold tyre grip or do you reckon dropping further would work? Tyre temps are too hard to decipher I find because some runs are as short as 31 seconds and 90 seconds at the most and its not enough to build a picture across the tread. So yeah do those recommendations you gave hold true for stone cold grip too - not sure if having the 'right' pressure but no temperature in the compound changes things?

sam

[Notso Swift]

Those pressures are for a hot tyre, as you will never really get it hot, I think it would be worth starting lower.
Maybe next time give 26 a go, then even try 23, reasonable steps like 3 psi make it pretty easy to feel. While I have tried starting my rears really low (under 20) I probably wouldn't recommend it,
You can always go back if you don't like it

[Martin]

Notso swift, you mentioned in a post on another forum that A050's are good at 30psi hot and over the top at 32psi. In the hillclimbs I do I'll start the fronts at 29psi and rears at 30psi and find that by the end of the run only the fronts have gone up 1psi. Is that the right kind of window to be in for immediate cold tyre grip or do you reckon dropping further would work? Tyre temps are too hard to decipher I find because some runs are as short as 31 seconds and 90 seconds at the most and its not enough to build a picture across the tread. So yeah do those recommendations you gave hold true for stone cold grip too - not sure if having the 'right' pressure but no temperature in the compound changes things?

Only getting a 1 PSI increase makes it a lot easier to select your tyre pressure, you know it's not going to vary a lot
So you need to focus on tyre wear rather than the tyre pressure
Get one of those white paint sidewall marker pens - run a line across the face of the tread, after the run see what's left
Then vary by 3 psi, check again and evaluate how it handled

[sambb]

yeah your right martin - I know pretty much bang on what my running pressures will be because they don't really deviate from starting pressures like on a circuit. Less guess work and hardly any corner to corner variation. Like notso swift alluded to though its finding what pressure works best with a cold compound which is also going to become more important going into winter. So as well as working out what to run in the rain, how soon to switch to r specs as it dries and what pressures to run the R specs on, I have a bit to do. Trouble with hillclimbs is that you get so little seat time for testing stuff.
As far as markers go, the kids chalk would do the trick wouldn't it?
Notso swift TBH I find that running the rears higher than the fronts helps the car rotate on one of the really tight circuits I do. The closer I bring rear pressures down towards what the fronts are increases rear grip. Do you run your rears much lower as a way to get them up to temperature on the circuit? For me because temp doesn't really factor I think it might be that pumping the rears up reduces their contact patch and that's why I get less grip in the rear when I do it. When the tyres are cold maybe the only factor is mechanical grip. For example at King Edward park I started with the rears quite high thinking it'd help me negotiate 'the pinch'. Turns out that that corner was so steep with the inside rear miles off the deck (its the adjacent pic) that it didn't matter anyway but in the corner leading into the top hairpin the car was seriously loose. Dropping the rear pressures to what the fronts were had it much more manageable again. Does that make sense?

[Notso Swift]

Yes it makes sense, the tyre is part of the total Spring rate as well, so the softer tyre can also absorb some of the road noise (helps it follow the road so more contact, more grip)

Chalk will wear off too quick, even paint will be marginal but should hold up, best to aim for a little to much camber than too little

My experiments with very low start pressure also involved lots of toe in, trying to generate more heat

[sambb]

is that rear toe in you are referring to?

[seangti]

I think the chalk should be adequate - they do it in timeattack and we're doing 7 laps (5x hot laps) and much higher speeds and temps than a hillclimb. Run it from side wall to sidewall across the face of the tyre. Use the thick chalk or make it thick. Should be adequate to see if you're using too much sidewall due to low tyre pressures. For this test, I'd start at say 30psi and adjust from there. I'd be cautious going particularly low on pressure for risk of the tyre coming off the rim or making the car snappy when it does run out of grip.

Not sure if the pic will show well, but notice tyre deflection at the bottom of the front. That's turning in at a bit over 100kph, 30psi hot. I start at 24psi but have to bleed between sessions to maintain hot 30psi.

[Martin]

Like notso swift alluded to though its finding what pressure works best with a cold compound which is also going to become more important going into winter. So as well as working out what to run in the rain, how soon to switch to r specs as it dries and what pressures to run the R specs on, I have a bit to do. Trouble with hillclimbs is that you get so little seat time for testing stuff.

As far as markers go, the kids chalk would do the trick wouldn't it?

Notso swift TBH I find that running the rears higher than the fronts helps the car rotate on one of the really tight circuits I do. The closer I bring rear pressures down towards what the fronts are increases rear grip. Do you run your rears much lower as a way to get them up to temperature on the circuit? For me because temp doesn't really factor I think it might be that pumping the rears up reduces their contact patch and that's why I get less grip in the rear when I do it. When the tyres are cold maybe the only factor is mechanical grip. For example at King Edward park I started with the rears quite high thinking it'd help me negotiate 'the pinch'. Turns out that that corner was so steep with the inside rear miles off the deck (its the adjacent pic) that it didn't matter anyway but in the corner leading into the top hairpin the car was seriously loose. Dropping the rear pressures to what the fronts were had it much more manageable again. Does that make sense?

Short hill climbs in winter - tough gig for sure!

Try the chalk but paint marker work much better

Within kart and track racing the convention is to increase tyre pressure in cold conditions
This is done to minimize the tyre contact patch so that heat can be generated to activate the rubber and grip
A smaller contact patch with heat is better than a larger cold contact patch

You would have different objectives at the rear of a FWD
Like you say - trying to get it to rotate
The rears are probably not getting much heat even with higher pressures
You are reducing the rear contact patch to encourage over steer

Another technique is to use lift off over steer to rotate the car
You need to be careful, don't want a heap of over steer, just enough to swing it
You need to be quick to control it (and you'll need toe in at the rear)

Alternatively, don't use lift off over steer, just run toe out at the rear
As long as cornering speeds are low it will help to rotate the car

[Notso Swift]

^^
Agree, if you are softly sprung at the rear you can use toe out to help it
But stiff is faster, if you can handle it

(Insert Benny Hill music)