Classing cars by weight

blamkin86

blamkin86

Well-known member
I'm just wondering if there's a "formula" SCCA uses to decide that two different cars are competitive based on their weights.

For example, let's say you have two identical cars - same CG, wheels, aero, all of it exactly the same. The only difference is, Car A has 200RWHP while Car B has 300RWHP.

For the sake of argument, let's say Car A weighs 2000 lbs.

How much should weight Car B be classed with?

The "dumb math" says that Car B has 50% more power, so it should weigh 50% more. Of course this makes no sense, as that means the cars are equal (lbs/hp) on the straights, and Car B is slower everywhere else. Car A is clearly the better car: It is better in every corner and braking section, and even if it left the corners at the same speed as Car B, it would just keep up with Car B until it was in a braking zone again.

So, how much would you make Car B weigh for it to be competitive with Car A?

Thanks for your thoughts.
 
By my understanding (in general reasoning)

1) Lower weight will accelerate faster.
2) Higher horsepower will have higher top speed.

Given you have enough straightaway (like at Daytona), the lighter car will exit the corner first but the more powerful car will pass the lighter car when the the lighter car reaches terminal velocity. For us HP guys, that is about at the exit of Nascar 4. Add a draft off the lighter car and the more powerful car zings past on the high side of Nascar 3.

Also, more HP also means more torque which means more acceleration.

I will add more weight for more horsepower any day.
 
Dug89":24tukkxf said:
I will add more weight for more horsepower any day.
Click to expand...

...Until you don't have enough tire to finish a race...

STU cars are limited to a 245 tread width DOT car, and some are running at 3800lbs with well over 300hp. they can go like hell, but they can't stop and can't turn!
tire management really becomes an issue with those cars. My car with 150hp runs same size tire and they last multiple race weekends as hard as I can drive, while the heavier cars throw a set of tires away at the end of one weekend, and their tires start falling off about 20 minutes into a race.
 
It's is a very complex calculation to get from HP and weight to lap times. But it can be done ....

Weight will affect everything .... acceleration, breaking, handling, etc. HP will only affect acceleration. RPM in unrestricted (cam and valve) motors will spin higher, which allows shorter gears, and thus greater torque multiplication. And on, and on .....

I'd think that this would be the perfect opportunity for the use of simulation software like Bosch Lapsim. It wont be perfect, but it will allow a quantitative understanding of changes rather than the usual "I think .....".

I've said for years that the club should be providing this kind of thing to support these decisions. I suspect that CRB egos trump technology, and the thought is "I don't need a computer to tell me how to setup a car ...."

Such a shame, because this technology would be useful in just about every category/class.

-Kyle
 
Well there are other ways to slow down the car that is to fast.

I recall one story of a car with a downdraft carb, the hood was so close to the top of the carb, at speed the carb would suck the hood down and choke the intake. That set-up will really cut the top end speed.

I am sure there are many other solutions to the high speed problem.
 
Well yes a rod out the side of the block will really reduce the top speed.

I know a siezed rocker will do the trick as well, since the valve will open but not reliably fully close causing a terrible miss.
 
I know it's complicated - I'm surprised we don't even have any ballpark guesses.
Given how much the club imposes parity by weight, how do you know if your car is classed fairly?
 
blamkin86":2bn0hh6p said:
I know it's complicated - I'm surprised we don't even have any ballpark guesses.
Given how much the club imposes parity by weight, how do you know if your car is classed fairly?
Click to expand...

If I win, my car is classed fairly.

Where's that tongue in cheek emoticon?
 
I would say go over to the IT website, but its been down for a while. They have a formula that works petty well to get most cars in the ball park for classing and then its a matter of observation to tweek weights. Get in touch with the ITAC and see if they'll share.
Chris
 
Log into SCCA web site and the IT process can be found in the Resources Tab, under Club Racing Manuals.
 
You must log in or register to reply here.
Back
Top