13 replies to this topic

[Ross Stonefeld]

on the seventhgear.com forum Parker Johnstone (last drove CART in 97) said based on studies by the teams, 10lbs is worth about a tenth of a second.

On a car with less power that'd be more right? Same for a car with less weight?

The cars I race are 1140lb empty. Horsepower is listed at 150 but I think its more like 135 because of the restrictors and stuff for tuning purposes.

Anyone care to guess on weight/tenths?


Last time I drove I was about 205lbs and set fastest lap of the race. The guy I was dueling with for the lead was Id say 140-150. Hard to tell, he's tall but quite thin. I was within about 7tenths of the track record. Im wondering how much the weight penalty cost me.

[Ross Stonefeld]

Oh yeah...

http://www.skipbarbe...00/news201a.jpg

We use low profile tires too. Did we ever figure out why low profiles are good? Why would you want them on an open wheeler?

My theory is its because these things are really really softly sprung and dampened and less side wall would mean less flex in the tire?

[ray b]

205 is alot of mass in 1195 lb car 1/6or 1/7
of total mass XdeltaV.
drag race computer can tell you axcel. times
as the mass changes so will the times
lower gears may help if top speed isn't factor
brake times+distance higer to but less than axcel..
10/10's corner speeds lower too.you must drive good.

I allway use 50 tyres on street cars and wish that
lower sized 15" could be had like 40 or 35 ar type
yoko makes 45 now but limited sizes in 15"

[Ross Stonefeld]

Its a series where we all have identical cars. No setup is allowed and we draw at random from a hat before the event. So I thought it'd be a case where we could accurately calculate stuff like that.


MY weight killed me when I went karting in the UK...geez it was bad

[ray b]

desk top dino is one program for axcl times
but there are many others.
in a car with less power mass is more important
as lesser power to mass =slower times to speed.
g-tec hand held may be big help to record times.

[Schummy]

I'm a tech expert here but I suppose the real correlation is between the % increment in weight and the % decrement in lap time. It's must not the same 10lb in a small formula car or in a "monster" NASCAR car type, nor a tenth in an small oval or in a Spa lap.

Best regards everyone.

[Engineguy]

Hey Ross, maybe you should change that "Will race for food" signature. lol

Seriously, all racing series should weigh the car with driver... a small hassle, but you've gotta wonder if there is a large body guy out there somewhere that otherwise has the talent to be World Champion. On the other hand I guess there aren't any F1 drivers that could play in the NBA.

[Ross Stonefeld]

Looking at the math, I think something is wrong. I think 10lbs = 1/10th in an Indycar must be off.

Lets just assume that in a Formula Ford its the same. I was about .6 off the track record, at a track where they race constantly, so everyone knows how to get around the place. I could see that happening realistically, I could easily be 145lbs and healthy at my height (60lbs drop, 6 tenths off track record)

Now, if we factor in what the weight penalty is in a Formula Ford and look at the times again, it just doesnt make sense. Otherwise my fastest lap Ive done minus weight advantage would be an unholy lap time, nevermind an absolute 100% balls out perfect lap. I'd have set a time that would have shamed the top 1% of the top 1% of kart racers in the US. Guys (and gals) who race shifter karts, been racing for almost a decade. Guys that have won competitions that involved them test driving Indycars (in a massive cone defined parking lot, but still). Im pretty confident in my ability, but lets be realistic. The difference between the best driver in the world and the also rans is only fractions of a second. If we take away my weight penalty we're looking at lap times people dont even think is possible

[Schummy]

Well... when I said "I'm an expert here" in my former post obviously I meant "I'm NOT an expert here" LOL, I'm sorry I appeared to be rather pedant

[Axe007]

And does anyone know how does weight distribution over the length of car affect its performance? In what way?

[Engineguy]

Axe,

As you concentrate weight toward the center of the wheelbase you lower the polar moment of inertia. This allows the car to "rotate" easier (i.e. turn in)... it takes less steering tire grip to start the the rotation. It is also easier to stop the rotation (i.e. catch a potential spin). An F1 car with virtually all its mass well within the wheelbase is about as good as you can get, short of removing the fuel tank to squeeze the driver and engine closer together, but you won't get very far without fuel, and you can't move the tank because you need to keep the fuel at the CG because its weight varies as its used up. Reducing the mass of the gearbox is about the only thing left to have much effect since it is furthest back.

Conversly, a car with a higher polar moment of inertia is harder to get rotating. A Porsche 944 comes to mind, with the engine mass centered at the front axle and the transaxle fully behind the rear axle, and bumper mass at the extremes too. Once you start the rotation, it wants to continue rotating (spin). The 944 comes to mind as I spun one going from dry pavement to sheer ice and it spun around about 300 times before stopping. Well,I lost count after 3 or 4, but it seemed like 300.

[PDA]

A good, easy to understanf illustration of polar moment of inertia is to watch a figure skater doing a spin movement. They start out slowly with their arms extended and one leg extended (high polar moment of inertia - significant mass (arms) far away from the centre of rotation) and then pull arms and leg in close to the body (low polar moment - all mass concentrated at the centre), causing them to increase rotation speed considerably.

[PDA]

Having said that, they try to get 45% of the weight on the front wheels to maximise braking efficiency (proportion of tyre contact patch front to rear is 45/55). This is very important. That is why lighter engine and gearboxes have been developed in recent years, as it reduces the weight concentrated towards the rear, and because overall weight is much less than the legal minimum, allows ballast to be added forward and low to centralise the weight and at the same time achieve the ideal front to rear distribution, and bring weight up to the legal minimum.

[Ross Stonefeld]

According to the new official F1 magazine, the article on pit strategy; 10kg is .4 seconds I imagine that effect will increase as power or weight decrease

Though what they list as tire degradation numbers, vs fuel penalty; doesnt explain how people can do fastest laps soon after pitstops