CdA figures for TVRs
Discussion
This year the TVRCC Challenge Cup (formerly Tasmin Challenge) runs classes based on power to weight ratios. To work out the power output of the cars we use GPS data loggers. However: mass, rolling resistance, CdA (drag x area) and weather conditions are needed to work out the numbers. Most of these can be found easily enough except CdA which so far has been guesstimated at 0.65. This wouldn't be too bad if everyone have the same model but we're now seeing Griffiths and hopefully a Cerbera soon. Obviously we want to be as fair as possible so does anyone know (or know where I might be able to find) coefficient of drag factors and frontal areas for TVR models? I thought I'd put this to the Pistonheads knowledge bank since google is being uncooperative!
Cheers
Matt
PS Next round is at Snetterton 30/31st May.
Cheers
Matt
PS Next round is at Snetterton 30/31st May.
Quite often the Cd is quoted worth a look fro that on the net, the Cda is Cd x frontal area, which I'm sure can't be too difficult to measure?
You can also calculate Cda from coast down testing.
Suggestion: Take a frontal pic using a zoom lens, with a known size square in the picture eg 10cm square piece of paper, bit of photoshop chopping & you'll fit x number of squares in. Might take an hour two.
You can also calculate Cda from coast down testing.
Suggestion: Take a frontal pic using a zoom lens, with a known size square in the picture eg 10cm square piece of paper, bit of photoshop chopping & you'll fit x number of squares in. Might take an hour two.
cptsideways said:I've not had any joy so far but will keep looking.
Quite often the Cd is quoted worth a look fro that on the net,
cptsideways said:In theory yes but in practice its very difficult. Simon Bowes who races the orange griff tried it a few times in his road car and came up with very inconsistent numbers. The trouble is the ground has to be level (although I suppose an average of two runs could be done) and it has to be a completely windless day.
You can also calculate Cda from coast down testing.
cptsideways said:That's a great idea.
Suggestion: Take a frontal pic using a zoom lens, with a known size square in the picture eg 10cm square piece of paper, bit of photoshop chopping & you'll fit x number of squares in. Might take an hour two.
As soon as I get my Fujifim s5000 (ordered yesterday 
) I'll do that. Cheers.Ask TVR?
Now that they have discovered the joys of playing in wind tunnels to optimise aerodynamics, maybe they have taken the opportunity to work out the CdA figures.
Even if they only have number for the Tuscan S, Sagaris and Typhon it could form a good starting point for a guestimate for older models.
Now that they have discovered the joys of playing in wind tunnels to optimise aerodynamics, maybe they have taken the opportunity to work out the CdA figures.
Even if they only have number for the Tuscan S, Sagaris and Typhon it could form a good starting point for a guestimate for older models.
0.65 is way way too much.
www.teknett.com/pwp/drmayf/tvr.htm for Chimaera/3000S and Tasmin data based on a simulation program called Car Test.
The problem is that playing with spoilers/splitters etc will affact the cDa figure quite significantly.
www.teknett.com/pwp/drmayf/tvr.htm for Chimaera/3000S and Tasmin data based on a simulation program called Car Test.
The problem is that playing with spoilers/splitters etc will affact the cDa figure quite significantly.
Surely these factors all cancel out, what the handicap *should* be doing is measuring absolute acceleration versus speed rather than trying to calculate actual brake horse power, correct to flywheel, estimate weight, subtract wind resistance, add your date of birth and so on. At the end of the day acceleration versus speed is the only thing that matters.
greenv8s said:
Surely these factors all cancel out, what the handicap *should* be doing is measuring absolute acceleration versus speed rather than trying to calculate actual brake horse power, correct to flywheel, estimate weight, subtract wind resistance, add your date of birth and so on. At the end of the day acceleration versus speed is the only thing that matters.
I've been musing on that point recently..
for a pure comparison on driver performance each car should be allowed an identical amount of performance, so a nice slippy shape should need less BHP than say a rag top with no roof ( i.e. me
) so how would we caluclate performance ignoring drag ect to equal out the cars... ???
shpub said:Excellent
0.65 is way way too much.
www.teknett.com/pwp/drmayf/tvr.htm for Chimaera/3000S and Tasmin data based on a simulation program called Car Test.
The problem is that playing with spoilers/splitters etc will affact the cDa figure quite significantly.
Can that program be downloaded from anywhere or somehow sourced for little cash?Graham said:Surely the DL1 software should be able to do it? When my
Surely these factors all cancel out, what the handicap *should* be doing is measuring absolute acceleration versus speed rather than trying to calculate actual brake horse power, correct to flywheel, estimate weight, subtract wind resistance, add your date of birth and so on. At the end of the day acceleration versus speed is the only thing that matters.
I've been musing on that point recently..
for a pure comparison on driver performance each car should be allowed an identical amount of performance, so a nice slippy shape should need less BHP than say a rag top with no roof ( i.e. me
so how would we caluclate performance ignoring drag ect to equal out the cars... ???
exams are over I'll have a fiddle. We've got to work to the regs though so power is what's important.Actually Pete, the regulations limit Power to weight ratio, which gets us a bit closer to your ideal.
Problem is that we have to have something measurable, and adjustable (like weight). What is the number we should put in the regs to limit "acceleration vs speed".
The Power to weight limit is effectively restricting acceleration. It is a limit in the regs which everyone knows before we start and can adjust to remain legal. It ignores Torque - Differences in Torque will have a much bigger impact on performance than differences in CDa.
Sure, different drag co-efficients will have an effect on speed and acceleration, and in the extreme Graham shouldn't have been able to beat Steve Lewis at Cadwell with his drop top - but he did. The idea is to race different TVRS against each other for the fun and spectacle. In order to make the playing field sensibly level we need some metric which can be measured and adjusted. This limits the cost needed to be competitive.
Problem is that we have to have something measurable, and adjustable (like weight). What is the number we should put in the regs to limit "acceleration vs speed".
The Power to weight limit is effectively restricting acceleration. It is a limit in the regs which everyone knows before we start and can adjust to remain legal. It ignores Torque - Differences in Torque will have a much bigger impact on performance than differences in CDa.
Sure, different drag co-efficients will have an effect on speed and acceleration, and in the extreme Graham shouldn't have been able to beat Steve Lewis at Cadwell with his drop top - but he did. The idea is to race different TVRS against each other for the fun and spectacle. In order to make the playing field sensibly level we need some metric which can be measured and adjusted. This limits the cost needed to be competitive.
mattjbatch said:
Matt, take a look at the figures for BMW. Do these numbers correspond to the figures you got from the Kumho chaps?
To be honest I can't remember what the bimmers numbers were.
I have the figures in a spreadsheet:
M3 E46 - 0.660
M3 E36 - 0.630
M3 E30 - 0.630
Z3 - 0.773
Gassing Station | General TVR Stuff & Gossip | Top of Page | What's New | My Stuff