Lap times - GTST vs GTR

[Sydneykid]

Hi guys, this subject has a large number of possible arguments. Personanly I think the killer for the GTR's is weight, for example our R32 GTST weighs 1245kgs and the R32 GTR 1558 kgs. The 25% extra weight in a GTR means that in order to go around a corner at the same speed it has to have ~25% more grip, in order to stop as well it has to have ~25% better brakes and in order to accelerate as well it has to have ~25% more power.

So if I have a GTST that has the same power, suspension, tyres and brakes it will be faster than a GTR over one lap, maybe even for 2 or 3 laps. But over say 20 laps, and the higher the power output, the more the rear tyres on the GTST start to go away. That's why the GTR was, and always will be, Godzilla of the Touring Cars.

[Duncan]

totally agree....a gtst with the same size tyres on good quality suspension *must* be quicker thru a corner than a gtr of the same model

weight is a killer.

On the other hand, drive out of the corner may be better in a gtr. perhaps not depending on tyre and diff quality and driving style.

[fatz]

yup gtr's r for *****s

[CSV Imports]

The G-sensor is the gold coloured box located under the centre console, in the very middle of the car. Rotate it by 90° and fix it in its new position. Advantages: results in a far higher degree of front wheel drive torque split in cornering conditions; is the easiest of all modifications. Disadvantages: results in some wheelspin in straight-line acceleration at high revs; power understeer can occur; in wet conditions the car is still a little unpredictable. Summary: Gives an easier car to drive but isn't the ultimate mod.

[fatz]

rotating the g sensor also makes it drive like one of those hyundi wrx shitter

[Roy]

LOL, i was going to say the same thing about GTSTs with properly sorted suspension and tyres, but was scared i would get flamed, so couldnt bring myslef to argue the point:)

My next bone to pick is big brakes...two identical GTRs, with identical 355mm rotors, identical tyres and suspension, but one has 6pot/8pot AP/Brembos and the other has std 4 pot Brembo caliper. (assuming equitable pad compunds)

Will they stop the same for the first half dozen laps around the track? I say yes:)

I was making an idiot of myslef recently when i was trying to tell a guy that a certain monster car with race car brake package wouldnt stop any quicker then a car with a much more sedate braking package. I was trying to say the suspension and tyre package would account for any difference more then the caliper / rotor package.

My thinking, you want shorter stopping distances get your suspension and tyres sorted, you want improved resistance to fade then go for the bigger rotors and monster calipers.

[Silver-Arrowz]

Wow! I always thought bigger rotors/calipers would have much more braking capacity than smaller rotor/caliper. What's the reasoning behind this?

[Roy]

I’m not saying in right:) Its just my thinking:(

But the biggest basic thing is no matter how quickly you can slow the brake rotor, you have to be able to maintain grip with the road. Comes back to their being two forms of friction. One is when something is stationary, the other is when something is sliding. Call it static (nothing sliding) and Kinetic (sliding)

So the thing to remember is that Static Friction is higher then Kinetc.

So think about the circumference of the tyre, now imagine it being cut and laid flat and is essentially a never ending length as its rolling.

When there is no slip between the tyre and the ground, that’s static friction. The higher of the two. When there is slip, ie a brake lock up then that is kinetic friction. Hence if you lock your brakes you not only lose control of steering you actually take longer sto slow.

So no matter how quicky you can slow the rotor, the tyres movement relative to the ground dictates stopping distances. This is on the proviso that you have enough braking capacity to lock the tyre.

So that is some thinking behind the tyre scenario.

[Roy]

Now suspension. What happens when you brake heavily? The weight of the car is transferred forward meaning that the front suspension squats.

So ppl are aware that lowering your car excessively messes with your camber, well the compression of the front springs under heavy braking can also increase the camber.

And when the camber is increased all of a sudden you don’t have the same width of tyre in contact with the road, mening you will have less grip. The of course no road is perfectly smooth so the spring and damper must have the ability to absorb the undulations and ensure the tyre remains in contact with the road, otherwise you get brake lockup. And remember kinetic friction is lower so you get increased stopping distances.

So that’s some of my thinking behind tyre and susp. (not all but most:))

[Roy]

So moving onto rotors and calipers.

It’s the job of the rotor, pad and caliper to slow the rotor and in turn wheel. It does this by transferring the energy of the rotating rotor into heat. The rotor needs to be able to absorb this heat and be able to transfer it to the cooling medium air in order to ensure that temps do not increase to the point where the brake fluid or brake pad increase to outside their optimum efficiency.

Good pads will have high friction coefficients and the ability to operate at high temperatures.

Two piece rotors with aluminium hats are not only lighter reducing unsprung mass allowing the suspension to respond quicker to undulations on the road, and whereby ensure the tyre remains in contact with the road… but also cool more effectively.

Now the idea of the larger rotor is that it had larger mass so therefore able to absorb more energy (heat) and transfer it to the air (cool) Larger diameter rotors also transfer more torque as they offset the pistons/caliper/pads further away from the wheel centre. Try pushing or stopping those spinning hotel doors, where do you push them from…the furthest point from the centre. It’s the same thing with trying to slow a spinning rotor.

Now by offsetting the caliper further from the rotor centre, you apply more stopping force with the same applied load to the brake pedal. So provided your tyre is constantly in contact with the ground and not locking up, you are able to slow the rotor quicker, in turn slow the wheel and car quicker.

But the important thing here to consider is that even if youca n now slow the rotor quicker, if you cannot maintain the contact patch and maintain no slip between the tyre and road, you aitn going to stop any quicker:(

[Roy]

Now for pads, this is the part where im a bit confused.

Forgetting calipers that take very thick pads for endurance racing (none of us are ever going to use a single set of pads in one day of thrashing around the track) the more pistons you have the more even the pressure on the pad. This ensures the contact patch between the pad and rotor is maximised. So by maximising the contact patch you are maximising the amount of friction available.

Now this is the part that is a little grey to me. If you look at 8 pot Brembos etc, instead of just using two large pads, they actually use 4 smaller pads. Think about someone stepping on you with a high heel (conventrated load) then with a pair of sneakers(distributed load)

Looking at cars like the BMC M3 CSL and its front brakes it ueses pissy callipers with big rotors but has great stopping power. I think they are twin piston sliding callipers!

With the larger pad area and increased contact patch there is less heat generated per sqr cm of pad as the energy is absorbed across a larger cross section.

So I think when you start looking to need 6pot and 8pot callipers I think we are kidding ourselves. Think, not sure, as I believe the improvements that can be made are never realised as the tyre will lock relative to the road well before you can take advantage of the extra pad thickness/area/volume

[Roy]

Wow! I always thought bigger rotors/calipers would have much more braking capacity than smaller rotor/caliper. What's the reasoning behind this?

...PHEW:)

I wonder if anyone is going to even bother read my dribble:(

[Abo Bob]

I did.

[Snowman]

Troy - are you trying to say that the reason Benno can out brake me by MILES given that we run the same tyres is due to his suspension set-up rather than these massive fark off things? LOL.

Na.

[Snowman]

BTW - GTST's continued to get owned big time down South on the weekend.

How many GTST's in the 1.20's? How many GTR's in the 1.20's? (Or if you and your car's insane into the 1.16's)

How many R31's even on the track? :confused: Must have been all been at the supermarket.

[Roy]

No doubt they are impressive brakes, but have you discussed with him where his braking marker is.

Even that would be misleading as he has an aero package working for him so corner speed would be higher then yours so doesn’t have to brake as late. The again he is arriving at corners quicker….so many variables:) Drive down the straight side by side at 200km/h and both jump on the brakes at the same instance and see who stops first. It would be interesting to see the difference:confused:

As for GTST getting owned, that’s the main reason I was pissed off about the fark up with my car. I am dieing to find out if my thoughts hold any water. As for comparing the lap times of the GTST guys, that aint fair. Every single GTR had semi slicks, and every single GTR had susp work and every single GTR had PFC with the exception of Ronin 09.

Now lets look at the GTST guys, INASNT had about the best package there but still didn’t have tyres or any experience at the track. He did a good job, but on merit the car should have been at least 5 seconds a lap quicker going on Gareth / Geoff’s pace, who both had crap rubber, basically std suspension:(

My car isn’t the end all be all, far from it, but its at least got susp work, tyres and a bit better power then std much like many of the GTRs you guys were running. How much slower is it? It will be interesting to see how I go around PI and Sandown when I get my car back…I hope I have a bit more success with Race Pace next week otherwise it could be 2007 until I get the car back to a track...Apparently he can do something with a rooted std diff

[Roy]

Just thought of something that may help make it all make sense. Look at V8 Supercars. Take the Holdens, why is once car able to out brake another? Comes back to suspension setup and drivers ability to brake heavily as the chassis is well behaved. They all run same tyres, very similar callipers, same size rotors (vanes etc may differ) and very similar suspension pick ups etc.

[fatz]

have to organise a track day down south and get my r31 out and go hunting gtrs

pussies

[Snowman]

Roy - in the first session Benno was "toying" with me. Just staying far enough in front of me so that I couldn't pass - then would give it a squirt just to show how much more power than me he has.

Anyways.... down the main straight we'd travel at exactly the same speed. (He just wanted to see what it was like to do it "that slow" BASTARD) At the end of the straight I'd have to brake at the 150m mark and still nearly lost it. He was braking at the 125m mark and doing it easy. And boy did that give me the shits.

Yes he has that big big big wing. Yep his suspension is probably a lot better set-up than mine. But he also has THOSE brakes. He doesn't have them for endurance as his car goes into meltdown after 3 or 4 laps.

HE says they stop him a lot quicker than standard calipers / rotors. (But does say that the suspension set-ups have to be right in order to get the benifit of them). Right now I am in no position to argue with anything he says.

[Snowman]

And don't worry fatz - next year I'm going to come to Syd to set the record straight. Can't have these northerners thinking GTST's are faster than GTR's.