Adapting Andy Hollis' spreadsheet to other classes

I'm curious if anyone has tried adapting Andy's formulas to other autocross classes. I worked up a sheet for my Europa in XP here.

Although there are quite a few guesstimates in there.

My biggest questions is where do you reach the point of diminishing returns in regard to HP? Someone could build a 700hp Z06, but would it really be any faster than a 505hp one if they were both built to the extent of the rules?

Also, the formulas don't really account for vehicle width or CoG. I know they both have an impact on the results, is there a reasonable way to compare them mathematically?

Lastly, how are Thrust Factor and Grip Factor changed as you move into higher-performance cars?

Just trying to do some bench racing. 8)

EDIT - Just updated a (hopefully) working link to the spreadsheet.

can't see your link without being a part of that forum. Linkfale.

I was afraid of that. I'll find somewhere else to upload it to tonight.

I think it all depends on how much grip the car has. Let's take your example. If your car has 700hp and it can only use part throttle anywhere without breaking the wheels loose, you are wasting a lot of time. By contrast, if you can use a lot more throttle without wheel spin and get more off corner launch, then the lower hp car is going to be faster. More hp is not always better if it doesn't come with chassis improvements to increase grip and the ability to use it's power.

I've been fooling with, first recreating it for STF, then adapting for various stock classes. The trouble I've found is there is no way on comparing tire compounds (see the results for STF where the 195 Toyo is widely regarded as the best available).

I'll repost the correct link from above here. Just in case no one noticed the edit above.

So....I vaguely recall there was an article (or two?) about picking magic cars based on the magic formulas and a little hand waving. Anybody know when these were published? Is Andy's actual spreadsheet available somewhere out there? I think to Lainford's point, seeing how it fits current class logic would be interesting. I've got a new car I've been kicking around in my head and I'd be curious to see how it bench raced.

Bryce

Well, the most recent one was his STF article in the October 2012 issue.

If you download the document I linked above, it should have the formulas to allow you to input your data for comparison.

You have to be careful trying to come up with magic formulas to predict performance. The sheet I did works pretty darned well for ST, but I suspect will not be as useful for other categories like P/M/SM. It might* be useful for much of Stock and SP, though.

The issues are these:

1) There is such a thing as too much useful power (as has been noted) 2) No accounting for compound (mostly an issue in P/M, not as much of an issue in ST as some might think. 3) No accounting for weight bias (nose heavy, weight over drive wheels, etc.) 4) No accounting for drivetrain (FWD, AWD, RWD) 5) Assumes all cars benefit from mods equally (weight and power increases) 6) Assumes equal quality of suspension

So between cars that are similar (e.g. STR & STF), it works well. For other classes like STX, you have to take the results with a grain of salt.

The STAC uses it as one piece of data...not the "be all, end all".

The width thing is used as a "red flag" for vehicles that are far from the norm. For example, the Fiat 500 hits the numbers around the average for STF, but is 4" narrower. On transition courses, it could well be the best car. But on other courses, it won't be.

Thanks for your reply Andy!