hillclimb tyre pressure advice

[sambb]

After some advice on starting/cold pressures for:
1: advan AD08R standard size and
2: bridgestone RE003,

This is for hillclimbing where there is zero opportunity to get heat into the tyres and the total run goes for 1min. ie I need stone cold grip by the first (20metres away) corner.
I know that on the track you might set the yoko's somewhere around 30psi and the street tyres around 35psi but I'm pretty sure that won't hold true when I can't get a pressure change into them. Even if each was set optimally for what I'm doing, I'm actually wondering if the RE003's might go better than the yoko's in terms of giving instant cold grip
thoughts!

[Stuwey]

My daily Polo is (or at least was) on RE002s. My mini is on A048Rs. Without doubt, after corner 1, the Yoko's have more grip, damp or dry.

My Polo went up the Collingrove Hillclimb on the RE002s, and it was definitely quicker once I dropped the pressures down to around 32 (front) cold. It was a chilly cold winters day though, with no track temperature at whatsoever.

Never competed in the mini on bitumen, so can't comment definitively but i'd be surprised if a road tyre would outperform an R-Spec ADVAN.

Run the Yokies, maybe 32psi?

[brad]

I'd run low - maybe as low as 28psi.

I was driving a Corolla yesterday at 24psi & couldn't believe how much grip it had. Felt like I was driving a pudding & response wasn't terrific but you could hook it around corners.

[seangti]

Both tyres are for street, Yoko having a track oriented intent though still not a semi. Probably ideal for hill climb though. As such, perhaps start around the 30psi, check at the end of the run to see what it's doing. I'd be surprised if it's gained 2psi. I can't see you doing much about that on cold tyres and within a minute.

Would be looking at suspension geometry, taking note of pressure variation front to rear. May also be worth getting a tyre temp sensor (pyrometer) to see what heat is being spread across the tyre and fiddle with geometry and pressures accordingly. A good GPS laptimer may help too, understanding max g'force achieved.

Also bear in mind an old tyre takes longer to heat. My old semi's are useless in the first session (5 laps) and improve thereafter.

Please share your experiences, keen to see.

[sambb]

So just to confirm are you guys saying that the pressures should be pretty similar 30psi (+/- 2psi) even though the tyres are fundamentally different? Brad when you said to even go as low as 28psi, was that for the bridgestones?
The weather report is saying max 16 degrees so it'll be a cold morning and 40% chance of rain. If its just patchy damp yeah the yokos would be fine but if it turns out to be properly wet I'm worried the yokos might be a bit skitish - I'm virtually on the indicators. The **** of it is, I have to make a decision now on which tyres i'll run on the front as I don't have a spare pair of front rims so have to take the punt and commit. Might have to play it safe in case it rains and put the bridgestones on and give myself enough time to scrub them in before saturday practice. grrrr decisions!

[seangti]

Will you be doing hill climbs often? If so, pick a tyre you'll be running in the future and make incremental adjustments on pressure. Wouldn't; worry too much about one tyre or the other initially. Higher tyre pressure will make it more progressive when it slides, but sacrifice grip. First you need a benchmark to make adjustments from.

If you run the Bridgestone, start with higher than 30psi, would be more like 34-36psi as you don't want to rip a tyre off the rim.

[brad]

I meant for either.

It's just a club level hill climb isn't it? You're meant to make mistakes & adjust as you go along.

seangti - you won't rip a tyre off a safety rim at 28psi - not at the speeds the OP will be doing on a "first outing" hillclimb (unless he's really good). I used to run as low as 26R / 20F in the dak-dak.

[sambb]

The hilclimbs are run just about once a month until october when it goes a bit more quiet over the break. This will be my first hillclimb. I'm not getting ahead of myself obsessing about times in all this, I'd just have preferred to have been going there with tyres I'd been on for a while and understand. To have to switch to bridgestones and slimey new ones at that due to the threat of rain is a bit of a bugger.
In the future, once I get another rim i'll be able to have the yoko's for dry events. I've spoken to a few people about street style 'semis' and got the feeling that federal RSR's grip almost instantly and that the AD08R's are nearly as good in that department but a little better when its patchy damp so I'd go with either of those. The bridgestones will be the daily/wet event tyres.
The event I want to feel sorted by is the last King Edward Park hillclimb that may ever run which is in October - this weekend though will just be finding my feet.

[kaanage]

My question is why AD08R? Yes, they are VERY grippy and from all accounts, you could run them as a daily tyre but if you get another set of rims that let you easily switch, then I'd get a set of full semis as they are quicker. I posted up a video last year of the PoD vs a Clio last year where the Clio was miles more powerful but the PoD made up the difference through the turns - the Clio was on AD08Rs and the PoD was on A048Rs. The AD08Rs would probably be a bit better in the wet but then I'd run the RE03s (what I intend to get as my "wet" track tyres once I wear out the Conti Premium 2s).

On a hillclimb, you won't have enough distance to get tyres properly warm so I'd be starting around 32psi to make sure steering was responsive from the start. And I agree with Stuwey that the track tyres will outgrip the road tyres in any conditions that aren't properly wet. I broke in a set of A048Rs in the hills on a cool morning and scared the $hit out of myself with the corner speed that the PoD was holding without it ever feeling like it was near the limits. When I reached the end of the 18km of twisties, I pulled over and found the tyres barely warm to touch (plus that I had a sore neck)

But since you're starting out, the RE03s will be a lot more progressive on breakaway so I'd hold off the AD08Rs until you get the extra rims.

[sambb]

righto. I always thought that proper semis needed to be brought up to temperature before they'd properly grip. Thats why I'd only really looked into 'street semis' like 595's, AD08R and hankook RS-3 thinking that they'd get there quicker. Yeah I mean if you think a proper semi would grip from the get go (I can't even do an effective burn out with my open diff axle tramper) i'll definitely look into that because the plan is to just use street tyres in the wet and swap on a pair of semi fronts when its dry.
I've been running the AD08R's on the front as dailys after my dunlop sport maxx R/T's evaporated after only 15,000km. yeah i've definitely found that the AD08R limit is higher in damp conditions than the dunlops provided you are carrying some speed and can lean on them a bit. In really slow speed corners though I've found them to be a bit treacherous as it gets wetter. But they let go very suddenly in the wet and don't tell you they are about to in the way that the street tyres had thats for sure. Its just a question of keep them on and hope it doesn't rain or get the RE003's on and hope it will!
The AD08R's are nearly out of legal tread so i'll probably save them for a few more events and then i'll look into the dedicated semi's like you said.
If I do get the RE003's put on whats the quickest way to scrub off the greasy new top layer. Will a quick flog on a favourite stretch have them ready?

[Stuwey]

and swap on a pair of semi fronts when its dry.

Nooooo!

Even grip all the way round the car, please. Be it high or low, you want the back of the car to grip the same as the front!

[kaanage]

Again, total agreement with Stuwey - putting the semis on the front and leaving the street tyres on the rear will turn you around as soon as you think about lifting off mid turn. I once scrubbed in a single A048R on a rear rim and it TOTALLY screwed the handling of the PoD, making the car understeer in a diabolical way and turning in very strangely as the car would seem pivot about that tyre - it was weird enough that a Polo GTi driver following me on that cruise commented on how odd the car looked in the turns.

But they let go very suddenly in the wet and don't tell you they are about to in the way that the street tyres had thats for sure. Its just a question of keep them on and hope it doesn't rain or get the RE003's on and hope it will!

This!

If I do get the RE003's put on whats the quickest way to scrub off the greasy new top layer. Will a quick flog on a favourite stretch have them ready?

Street tyres (any tyres really, except GP 125 slicks) seem to scrub in almost immediately IME once you lean on them a bit so about 4 corners into a decent fang on a dry road should do it, I would think.

[sambb]

I know I know I agree. For the street I'd be putting on another set of dunlop sport maxx R/T fronts to keep it all the same if I could but they are discontinuing in that size and they are now over $220 a tyre. Thats why RE003 is in the picture.
As for the AD08R's on the front that was really just an experiment to see how much of the dull polo steering and poor forward traction under power was tyre related (the dunlops have a really soft sidewall) or if I'd need to throw money and effort at steering rack rebushing/big geometry chgange etc. In all honesty I just don't have the coin to go to a seperate set of semis all round anyway.
I do understand the risks re lift off oversteer. The track is very tight and outright speeds don't get very high (its all second gear really) so spots where a mid corner lift could get me out of shape are few. There's none of that high speed building high g's stuff that does give you the heebies if you chicken out. If you watch the vid there is a down hill section at the end that could definitely be a lift off risk though. Being uphill too and front drive the only time i'll really get oversteer is corner entry on lift/brake but at those low speeds my rear dunlops are ssoooo progressive so I back myself. Through a similar uphill stretch where I like to go locally, I've got to be literally trying to loop it to get it to step out going uphill. If it s wet on the day though, that will be a different matter if I still have the AD08R's on for sure though. You're absolutely right .....its a calculated risk.

here's the course:

https://www.youtube.com/watch?v=OWiAUokdU-c

here's where the risk will be:
https://www.youtube.com/watch?v=lO351ek0Q4k (at 1:30)

[sambb]

Well the event is done. It was such an unreal spectacle. I'm not sure about how the track days go down but the hillclimb had such an amazing carnival atmosphere. There was everything from formula vees, dallaras, lolas, penskes, right down to my humble little shopping cart. The most insane class was formula libre. Almost all of them were hyabusa powered missiles, supercharged, turbo charged etc.
M. Oastler (the nsw champ) did it in 33.95. To but that in perspective thats 10 seconds quicker than an improved production 200SX around a course that is 720m long - mental! The guy has worked for mclaren and BAR apparently so figures. Me - my best was 47.17. All I really cared about was that I improved on each run which I did (except for the first run after lunch when the tyres cooled right off and front pressures in the AD08R's got down to 29psi).
For me the times were better when I had 33psi in the fronts. Lower and I had trouble turning it in without it pushing and poorer steering feedback. Higher and I couldn't get traction on corner exit. The rears more or less stayed fixed at 33 ish psi. During the event today it took about 45 mins for everyone to cycle through so the tyres had a chance to cool for each run. On saturday practice though unbelievably (to me) one 48 sec run would add nearly a psi to the fronts. When I had the chance to do 3 sort back to back runs the car got less and less traction under power (even though they were getting sticky) and I couldn't believe the fronts were nearly 36psi when I parked it. You guys that do sustained laps/track days must have to dump so much air to keep the pressures where you want them.
How do you guys launch the car? I tell you what traction control sucks a##se. In the end the best thing I found was to hold the clutch at the bite point with the handbrake on and 2000rpm for an unmolested launch. Did anyone ever find out, is it just brake force modulation that shuts things down or is there a boost cut too because it felt like it? - woeful. The way a datsun 1200 coupe with a sidedrafted SR20 launched... now that had me pining for my escort back!

[kaanage]

That sounds like you had a fun day out

I suspected that you needed some pressure in the fronts to start with since you start from cold in a hill climb (missed by 1 psi, though :p). With track sessions, I basically start with pressures low enough to get the tyres to 32-34psi when they are fully warmed (when EVERYTHING you run over sticks to them) which rarely takes more than the out lap as I basically build speed over the course of the lap, feeling the grip increase with each corner.

With track days, you get timed on flying laps so launching isn't a requirement - a good thing for me since the PoD is such a slug.

I do understand the risks re lift off oversteer. The track is very tight and outright speeds don't get very high (its all second gear really) so spots where a mid corner lift could get me out of shape are few. There's none of that high speed building high g's stuff that does give you the heebies if you chicken out.

The guys setting really quick times don't build corner speed - they turn in pretty much on the limit which is why some element of stability is required so can go in a touch hot without instantly flying off the track. I'm not sure I could commit that much on a hill climb - I'll find out someday, I guess.