DamonB

Sometimes people think I contradict myself in answers I give but I don't feel that is ever so. These are my fundamental opinions about fast cars and any answer I give is always based upon these. I reserve the right to change my opinions from time to time but as I see it some things cannot and do not change as they are based on inarguable and irrefutable laws of nature

I'm sure guys are tired of hearing me talk about tires but tire grip is all that matters. A racecar is merely a machine that exists for the purpose of eating tires. All else equal the fastest racecar will be the one that gets the most performance in return for eating its tires. That means tires are the most fundamental aspect of the racecar. Anything we do to improve the handling or speed of the racecar isn't really improving the racecar at all, it's improving the racecar's efficiency at turning rubber into speed. Outside of the driver no single item on a racecar has more impact on speed than the tires.

The driver is a part of the racecar. If we have a poor driver we have a poor racecar. It is impossible to make a poor driver better by merely giving him a faster racecar. On the other hand putting an excellent driver in a poor racecar still results in a poor racecar. The driver's job is to maximize the performance potential of his car at all times and therefore if his car doesn't have as much potential as competitors' cars he'll be slower. The only exception is if his competitors prove incapable of extracting the performance from their "better" cars. The driver that extracts 100% of the performance potential from the car is a perfect driver and has done his job the best it can be done. Since the driver is actually part of the racecar we can always make the racecar faster by making the driver better (or replacing him with a driver who already is better!). Racecar drivers are human and thus are imperfect beasts. This therefore insists racecars are always imperfect and that drivers can always go faster, they just don't know how.

Once the tires go on the car they are a given quantity and the goal is to drive the tires in whatever manner they like best; getting the most performance from them for each molecule of rubber we burn off. This insists the goal of the driver should be to drive the tires (car) in a manner that proves most efficient at trading rubber for speed. If he does this fast laptimes will take care of themselves. Any other goal will result in a slower car or at minimum a car that uses up more rubber for no improvement in performance.

Gadd

Hmm... If you get right down to the nitty gritty, doesn’t it really come down to the interface between the rubber and the road? The coefficient of friction of any tire and track is determined by the track surface and the rubber? Also the track is a wear surface, so wouldn’t you need to get the most from every molecule of asphalt all so?

I’m just being the devils advocate. ( I was also trying to find a fault in your logic, and that was the best I could do).

DamonB

No, it comes down to only the tire because the driver is in control of the tire through his driving inputs. There is no control input the driver can make which does anything to the track surface.

Valkyrie

Couldn't you also look at it that the tires (and everythign else) are there to get the absolute most out of the engine?

Cornering, acceleration, stopping... all of these things which are determined by tires (and everything else) are imployed simply so you can gas it out of the corner as fast as possible and then go into the next corner as fast as possible, which is once again trying not to waste the efforts of the engine. You don't win races in the corners...much.

Tires and brakes convert all of your precious motion into into waste heat, whereas the engine's job is to convert energy into GO.

Cheers!

Damon,

From your experience can you comment on the following?

What is the relationship between unsprung weight and maximizing tire contact patch?

Setup 1:
15x7 wheel, 13 lbs heavy
225/50/15 tire
will have a shorter rear end ratio

Setup 2
16x8 wheel
21 lbs heavy
245/45/16 tire
Will maintain almost save drive ratio

Limiting factor is money ofcourse. The 16x8 wheel is a lightweight steel wheel from diamondracingwheels.com about 99 dollars per wheel. The otehr wheel is a Team dynamics 15x7 wheel, also around the 100 dollar a wheel mark.

Tires are going to be:
Toyo RA1, or Hankook Z211s

Car weight = 2820 lbs
RWHP = 225 HP
Torque = 191 ft-lbs
S5TII
Corner weighted
Bilstein coilovers from ISC racing
used for HPDE/Time trial racing.

Current setup is 225/50/16 ToyoRA1 on stock S5 TII wheels

Will there be more performance gain from a wider heavier setup or a lighter narrorwer setup? Typical courses will be Mosport and medium race tracks.

DamonB

That's possible in some cases I guess but tires are tremendously more important than power. You could put a 10,000 horsepower engine in a car and go barely faster unless you also add tires capable of using 10,000 horsepower. Top Fuel dragsters for instance are not limited by power, their traction limited for the entire quarter mile. More power is nearly useless to them because they can't use it anyway; they're already going as fast as the tires will allow.

Power doesn't mean much. All else the same more power is always better but witness nearly every race sanctioning body every year that takes away power and downforce yet the cars go as fast or faster than before. The reason they get that speed back is because the tire company just builds a faster tire...

Not true; damn near all road races are won in the corners. If they weren't nobody would be using downforce to purposely give up straightaway speed in exchange for increased cornering speed. Races are not won by top speed, they're won by laptime. Downforce results in drastically lower top speeds but much faster laptimes.

DamonB

A wider tire on a wider and heavier wheel is faster until you start carrying around more tire than you need (or have ridiculously stupid heavy wheels but I don't feel your example fits that case). You know you have too much tire when you see straightaway speeds dropping (due to tire friction and aero drag of the wider tire) and the fact that you can't maintain optimum tire temps because you can't get enough heat into the tire.

Your particular question isn't just adding 8 pounds per corner to go from a 225 to a 245 but is also losing acceleration ability due to the 245 also being taller. The key is can the increased grip of the 245 make up for the weight and poorer acceleration compared to your current 225. Short answer is I'm not certain. The weigth doesn't concern me but the diameter does. You're only putting 225 hp to the wheels so you don't have huge power and on tracks with long straights the acceleration difference could be enough to not net faster laps for the wider tire.

I think the difference in tire diameters is enough in the case you listed to change acceleration performance and it would come down to particular tracks and how the car was geared. Assuming you can't change gears I could picture different tracks being faster on the 225 and some on the 245 strictly due to gearing issues since you can't overcome the acceleration deficit with more power; you don't have excess power. Without the diameter issue I'd so absolutely go for the wider tires even with the unsprung weight penalty. Even with the loss of gear in the case of the 245/45/16 I'm still inclined to think they would be faster at most tracks and worst case no faster at some others.

That doesn't help much at all does it?

Mahjik

iTrader: (1)

I'd have to disagree there. Your straight-away speed is directly related to your cornerining speed (unless you are only drag racing).

Say you have say 1/8 mile of straight after a turn. Let's say from a stop, you can get to 70 mph in a 1/8 mile. Now, you are coming out of the turn at 30 and that now llows you go get to 100 mph at the end of the straight. Now, if you are coming out of the turn at 50, what does that do for your ending straight speed just before the braking zone? Yep, it goes up as well.

If you think you can win a race by only straightline speed, you're gonna spend a lot of time sucking exhaust fumes.

Cheers!

Not it actualy explains a lot, but it also makes me ponder even more. I didn't acurately describe my situation as I should.

My current set up is:
Toyo RA1 225/50/16 on 16x7, Stock S5TII wheels. THe tires are shot and I need new ones. Like any other racer out there, whenever one gets the oppertunity to tweak or optimize one shuld take full advantage of it. This will be the first time I've bought new R compuonds. My previous set was bought on the ultra cheap used. Then I stored them for 2 years before I used them.

Current:
16x7, 16 lbs heavy
225/50/16
stock final drive maintained.

Setup 1:
15x7 wheel, 13 lbs heavy
225/50/15 tire
will have a shorter rear end ratio

Setup 2
16x8 wheel
21 lbs heavy
245/45/16 tire
Will maintain almost save drive ratio

Right now it is clear that either Setup 1 or Setup 2 will outperform current setup.

I found with the past season on teh 225/50/16 was just perfect for almost all the straights for the various tracks I visisted. I found with the stock gearing and final drive, I could ring out 2nd and 3rd gear right before I had to brake. Sometimes I would over rev by 500 rpms or so to 7500 or 7600 rpm. I'm worried that with the shorter 225/50/15 tire the final drive will force me to short shift on some of the short to medium straights. I find the less you need to do stuff the better. It's not hard to mis a shift or screw up a braking point because you were trying to downshift and extra gear on the box to be in the right gear.

Most of the courses that I do race on are quite tight and short. So the ability to put down power earlier will be at an advantage. You are right about the point. Will you be able to drop lap times by putting down power earlier or using a smaller diameter wheel to increase acceleration capability. I can not change gearing or final drive on teh R&P.

DamonB

^ With all that more clear I'd say Setup 2 without a doubt will be the fastest. You've already proven the diameter to represent nearly optimal gearing for those tracks so now you're just adding more rubber width on top of that.

Don't sweat worrying about using shorter tires to gain lower gearing and therefore greater acceleration. What's more important is the gearing (engine RPM) fitting the ends of the straights. For blasting out of the corners you just stay in a lower gear a little longer.

I've been in your boat before using someone else's old used R compounds. Even if you do nothing but put new tires of the same size on you'll go lots faster. Race tires that have seen heat cycles and are then stored for 2 years are bricks compared to fresh ones.

Valkyrie

I take that back, I meant that you usually don't PASS in corners... but races are definately won in them (since straight way speed = corner exit speed).

Also, with the example of the top fuel dragster, the way I see it is that the tires are there to get the most out of the engine, since the engine is more limited than the tires are, when it comes to design, correct?

You probably have a lot more freedom with the chassis and footwork than you do with the engine, so you have to put the most engine you possibly can into the car, while using the tires to squeeze all the potential out of said engine.

rynberg

You must only watch F1....try watching some touring car or Formula Mazda on Speed channel....

Valkyrie

I'm not suggesting they don't pass in corners... simply that passing on the straight is always preferable, if possible. Someone usually ends up drafting and then passing on the straight by coming faster out of the corner.

If not, passing in a corner usually happens when someone messes up some how (ie, isn't going fast enough...lol).

Reguardless, my argument still stands that tires = tools for getting the most out of an engine.

Mahjik

iTrader: (1)

But's it's more than just your engine. Suspension geometry, driving ability, etc.. The engine is in there, but tires get the most out of the "car" and everything that comes with it.

DamonB

Absolutely not. I already showed you why: every racecar given the chance will add aerodynamic downforce and gladly give up straight line acceleration and speed in return for higher cornering speeds and thus faster laptimes. Grip pays bigger dividends than power. This of course goes hand in hand with the other example I gave which shows that quite often when rules take away power and downforce the cars go just as fast because the tire company makes a faster tire.

You'll also find if you have been around real racecars much that quite often whenever the engine guys find more power for the engine the engineer uses the extra power to just crank more downforce into the car anyway. The car goes no faster on the straights even with more power because the downforce adds more drag, but the laptimes still fall. Grip > Engine. Straightline Speed < Laptime.

Where the cars pass on the track is not an example of anything. Cars pass where there is opportunity. If I'm turning quicker laps than you I'm going to pass you. Where I pass you I don't really care.

DamonB

You have to understand the difference between top speed and laptime. Laptime is the average speed of the car throughout the entire lap. Top speed is merely an instant in time where the car was at its peak velocity for that track. Top speed isn't worth crap; average speed (laptime) is what matters.

It's no different than talking about engines. People always latch onto whatever the peak power of the engine is and claim that number is the engine's power. It is not. The engine's power is the entire area under the dyno curve and an engine with less peak power can easily outrun an engine with more peak power all day long and it happens quite often.

Let's say this pic is the dyno plot of two engines and their peak power is the same. The engine on the bottom however is a much more powerful engine than the engine on top even though if you peak power is the same for each.


Another fact everyone forgets is that the engine only makes all the power it is capable of when the throttle is on the floor. I drive around cars with twice as much horsepower all the time. They only make twice as much horsepower if the driver can keep the throttle fully open. If his throttle is only half open he's making no more power than I am. Power is useless if the racecar can't use it (keep in mind I believe the driver is part of the racecar).

It's no different with handling either. People latch onto skidpad numbers and claim that shows handling. Skidpad numbers are useless; they really only show tire grip at steady state. Given a good tire I could make a school bus turn high skidpad numbers but it's handling would still completely suck.

Valkyrie

Hmm? You seem to be missing my point...

The faster a car can corner, the later it can brake, the more power it can use during a corner exit, and the more speed it can carry into the corner, the faster you will go around the track. So in that way, you have to get as much out of the engine as you can, handling-wise, because straightline speed is determined by how the engine, and straightline speed in turn determines how fast you potentially could enter and exit a corner, does it not?

I didn't really mean that top speed > average speed. Given a certain engine, better tires (and aerodynamics, and everything else that the car has) will be able to get more out of that engine, ending up with a better lap time. The reason I see this is critical is because while you're allowed quite a bit of imagination when it comes to chassis design, tire choice, suspension settings, and aerodynamics, your engine is often very limited, often to where everyone has the exact same engine.

A car will technically go without tires (albiet, very, very badly)... it won't go without an engine, though... (once again, that's not really my point at all.... but I do feel like pointing that out)

Another way to think of it would be that Grip (ie, the handling performance of the tires and downforce of a well-sorted chassis) equals the Time you can stay with the throttle fully open (ie, the potential performance of an engine).

So the more grip you have, the more you can use the engine, the more fast you can go (yes, I know that's bad grammar).

DamonB

A car will go faster with a little more grip than it will with a little more horsepower.

A car will go slower with a little less grip than it will with a little less horsepower.

Tire > Engine

That's really grasping at straws and nearly ludicrous IMO but a car can go just as well without an engine as it could without tires: downhill.

DamonB

Resist the urge to fix driver problems by changing the car. If it's the driver that's broke monkeying with the car can't fix it. Handicapping the car just reinforces the bad habit(s) of the driver.