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Tech Rules: Weightcalculator, from guide base to wheelbase
tamar - 13-1-2008 at 04:29

As some of you may have noticed (well at least Francesc did :D) the new weightcalculator no longer uses the guidebase as a reference but takes the wheelbase as part of its caculation.

But as I expected...the reason why needs some clarification

Because Francesc send me this mail:

Quote:
"Francesc Reyes"
12 januari 2008 12:25:19 GMT+01:00

Hello Tamar
- I see that in the wheight calculator you use the wheelbase as a distance between the front axle and rear axle instead of what you use previously (rear axle and the top of the guide). This modification gives a clear advantage to the Maseratis.

Best regards
Francesc Reyes


Aux contraire mon confrere, aux contraire
The main reason why I dropped the guidebase as a reference to balance the cars is because it was not working!
Although the wheelbase is not a perfect reference it works better and is less advantageous for the Maserati MC12!

Now, for those of you who don't like to read much.... dont... stop reading just check the tabel below and you'll can see for your self. The blue figures are for the wheelbase and red for the guide base.

...for those who want to have more background info ....read on and I'll try to explain!


http://www.slotracinglemans.com/images/pict2008/weightcalc_compare01.png

Searching for an optimum
I assume the reasoning behind Francesc's remark is this: the Masserati MC12 is the longest car, which can now use that advantage to run the longest possible guidebase without any extra weight penalty.

Though this argument is true, this does not mean that this will give them a clear advantage!
A short guidebase is not always a dis advantage and longer is not always better. There's something like an optimum.

To prove my point; the MC12 body is long enough to run a 150mm guidebase, but of all the MC12's that took part in the previous FIA GT races the longest guidebase measured was 146mm, same as the Corvette C6 of Francesc during the Spa doubble race and only 0,5 mm longer than the Slotfabrik Aston!

Now even if you eliminate factors like build quality and driver talent, all the races that had a MC12 in them gave the same impression, that even with the added weight of the weightcalculation there were still factors that gave them an advantage in roadholding....and apparently their guidebase was not one of those.

Tests done by a team trying to find a way to shed some weight of their heavy car showed that the MC12 ran just as well if not better with even shorter guidbases up to 140mm!
Off course with this shorter guidebase the minimum total weight of an MC12 would be around the 206gr!

So what other factors besides height, width and guidebase determine the performance of a car. I checked all the data that we had on the cars and noticed that beside having the longest possible guide base the MC12 also had the longest wheelbase!

The first version of the weightcalculation measured 2 widths and 3 heights of the car, but the weightpenalties still did not achieve what I wanted. So I looked at what else could be measured. Both wheelbase and guide base came to my mind. However I wanted to limit the number of measurements to spare time during TC.
So I picked the guidebase as I thought that it would have a bigger influence on the performance of the car than the wheelbase. Apperently I was wrong!

In hind sight it is always easy to see where you've made a mistake.
First of all the guidebase is a variable factor, where as the wheelbase is not.
Under the "old" weightcalculation car's like the MC12 could reduce their weight penalty simply by running a shorter guidebase like the other competitors. But they still kept the advantage of having the bigger stability of their larger wheelbase.

Now we could use both the wheelbase and the guide base in the weightcalculation but to keep things simple I dont want to have take more than 6 measurements during TC.

Switching to the wheelbase as the 6th factor in the weightcalculation seems like the best option and has the added bonus that all measurements can be taken with the car stationary on the tech block.


That's it for now, more on the averages and how much do they influence the performance in a later post.
One last remark.... the weightcalculation was not changed just to kill the performance of one specific car,I did it to improve the balance of performance within the whole group of cars.