Sam's build thread

[metalhead]

I'd tend to agree with you, particularly at this time of year. At the last few events, in much cooler weather, I haven't really seen any significant ongoing tyre pressure/temperature rise through the day (I see it each run, but it drops back to the same before the next run). And the tyres are barely getting any signs of heat/melting around the tread blocks at those events.

I think, as Gary suggested a while back, that for my car the less than ideal geometry means that a bit of sidewall height, and therefore flex, can be a good thing. Not to mention how it helps with traction on launch, which is a fairly large factor in a hillclimb, particularly for a rear wheel drive car that's large and heavy with a reasonable amount of horsepower.

[sambb]

yeah at Bathurst one of those guys that double drive the orange datto 1200 coupe with the carby SR20 were saying that they go much better on the track with lower profile tyres but that for the hillclimbs the plumper sidewall gives them better times.
I still think that if you went narrower at the front and changed nothing else that it would just tend towards corner entry understeer. Do you have a limi in yours?

[sambb]

There is a god and his name is Ari. Still cant believe this vid - just mental. The famous line at 2:05. In my opinion at 2:00 he knew he was ****ed and that they were going to hit the wall but was just an iceman waiting to see what he could do about it when it happened. I think even Ari soiled himself. And then check out how hard he still goes afterwards with the puncture - again at 3:04, so calm sliding towards the wall and just knocks it down a gear and drives out of it. An artist! Makes current F1 look like a video game.

YouTube

[Sydneykid]

yeah at Bathurst one of those guys that double drive the orange datto 1200 coupe with the carby SR20 were saying that they go much better on the track with lower profile tyres but that for the hillclimbs the plumper sidewall gives them better times.

Assuming the Datto 1200 still has its steel leaf spring rear end then it almost certainly has too much rear spring, so a softer tyre (higher profile) will reduce the total spring rate. Similarly if they aren't running a rear swaybar (most leaf sprung 1200's don't because the leaf spring acts as an anti roll bar) then a taller sidewall will tolerate the higher levels of roll. In the same vane if it doesn't have a floating rear end with appropriate toe and camber, then a more flexible sidewall will help.

Crossing over set up tips from a 70's RWD car with live axle leaf springs to a 00's FWD car with independent suspension all round is a garden path that I wouldn't suggest following.

Cheers
Gary

[Sydneykid]

For hillclimbs we really need to look at using the softest compound tyre available, what we used to call a "qualifying tyre", good for one flying lap only. These days more often used in time attack with one slowish warm up lap, one flying lap and then half a lap slowish cool down, then throw them in the bin and put on new set for the next run. The other choice used to be a wet weather compound, we used to buy them without groves and then cut our own for wet weather, occasionally they accidentally found their way on for qualifying on a cold morning The Yokohama A050 soft compound would be my choice for hillclimbs, they don't need a lot of heat build up.

I think I mentioned it before but just in case, I'd strongly suggest before each run running the car up on the jack and dragging the brakes. There is lot of heat transfer from the rotor through the rim to the tyre. Obviously in a 2WD situation that means only 2 tyres are pre warmed, so be aware. As Sam has done previously, on a FWD car a medium compound on the front pre warmed works pretty well with a soft compound rear. For RWD car I'd strongly suggest warming up the rears, for a good launch, just be aware of the understeer from the colder fronts. Of course if anyone asks you are warning up the engine and the transmission.

Cheers
Gary

[sambb]

Crossing over set up tips from a 70's RWD car with live axle leaf springs to a 00's FWD car with independent suspension all round is a garden path that I wouldn't suggest following.

Cheers
Gary

yep your right, wasn't attempting that! just that I've noticed a few people say that all things being equal, that they find cold tyre grip is better with a taller sidewall. Could it be something related to the fact that in the hillclimbs people tend to run their tyres at or below the hot tyre recommended pressures for their runs and that taller sidewall tyres maybe tolerate that better than lower profile ones?

[Sydneykid]

yep your right, wasn't attempting that! just that I've noticed a few people say that all things being equal, that they find cold tyre grip is better with a taller sidewall. Could it be something related to the fact that in the hillclimbs people tend to run their tyres at or below the hot tyre recommended pressures for their runs and that taller sidewall tyres maybe tolerate that better than lower profile ones?

If the car is set up correctly then the lower profile tyre should always be better, with emphasis on if the car is set up correctly for that track on that day. It's just that in general a taller profile is more tolerant to a "not quite right" set up (and/or not quite right tyre pressures).


Cheers
Gary

[sambb]

gotcha. thanks

[metalhead]

Thanks Gary, good info.

That video of Ari is awesome! Nutter...

Sam, yeh, I'd say you're right about the results of narrower fronts. Yes, I have a limited slip. It's the factory clutch lsd, but with solid steel clutches, and with the preload springs removed such that it only locks up under power - but it locks up very effectively when the right foot is down. Makes it very progressive and predictable/controllable, though arguably slightly less effective and with no residual limited slip effect when off the power.

[sambb]

So its more like a one way now. That'd help with turn in too wouldn't it, not being pushed from behind as you brake into the corner.

Yep Ari is the man. Having had a mk2 Escort and a Peugeot 205Gti its impossible not to be a fan boy of him. You see interviews of him now where he comes across as so cultured, relaxed and very thankful that he survived the Group B era, but jeez put a helmet on him and the nutter emerges. He talks about how he felt that he was no different to a dancer or a composer, that he was an artist and dusty roads were his canvas. Legend