More spreadsheets
Posted: Mon Jul 02, 2007 4:34 am
Well, I was over at a fellow Elan owners house looking at his car. As usual, we got into trouble asking questions for which there was no readily available answer. The basic question was what speed will the car go for various differential ratios. The other question was what is the theoretical top speed of the Elan (theoretical since we know the car is so under geared it can't get close)
Many of you know I have this monster spreadsheet that can give some of this information, but only a piece at a time.
Getting home, and awhile later, I had adapted the original into a tool for answering the question. Input the rpm and tire data, and is has a two dimensional matrix of R&P values down the left and gearbox ratios across the top. The R&Ps are all the combinations of pinions from 7 to 11 and ring gears from 31 to 41. I mean, if you can present one result, why not choke the world with more results than can be assimilated or used?
Since this Elan was running with low profile tires, I figured it would be useful to have a sheet that gave speed values for different tire sizes. So quickly I made a sheet that extracted the tire size data from the big spreadsheet, and used that with different gearbox ratios to display speed given rpm and diff ratio.
This was so much fun, I made another sheet that showed speed for different R&P values and different rpms, for a constant tire size and gearbox ratio.
Well, there are 6 ways to display the variables, but I stopped here. If anyone wants any of the other 3 ways, I'll whip up the sheet, but this spreadsheet is getting close to 1mb, although it zips down nicely.
The last thing was to generate a sheet that would estimate the top speed of a car. Now, this is a very slippery area, since many of the factors involved in the calculation can only be estimated, and the estimates have a rather large margin of error. And there are many ways to agglomerate all the aspects that go into calculating vehicle drag.
So, given all those caveats, the first cut came up with some plausable lies (estimates). I would be most interested in others experience in this area, suggestions for improvement, comments on how I goofed up, etc.
Have fun.
David
1968 36/7988
Many of you know I have this monster spreadsheet that can give some of this information, but only a piece at a time.
Getting home, and awhile later, I had adapted the original into a tool for answering the question. Input the rpm and tire data, and is has a two dimensional matrix of R&P values down the left and gearbox ratios across the top. The R&Ps are all the combinations of pinions from 7 to 11 and ring gears from 31 to 41. I mean, if you can present one result, why not choke the world with more results than can be assimilated or used?
Since this Elan was running with low profile tires, I figured it would be useful to have a sheet that gave speed values for different tire sizes. So quickly I made a sheet that extracted the tire size data from the big spreadsheet, and used that with different gearbox ratios to display speed given rpm and diff ratio.
This was so much fun, I made another sheet that showed speed for different R&P values and different rpms, for a constant tire size and gearbox ratio.
Well, there are 6 ways to display the variables, but I stopped here. If anyone wants any of the other 3 ways, I'll whip up the sheet, but this spreadsheet is getting close to 1mb, although it zips down nicely.
The last thing was to generate a sheet that would estimate the top speed of a car. Now, this is a very slippery area, since many of the factors involved in the calculation can only be estimated, and the estimates have a rather large margin of error. And there are many ways to agglomerate all the aspects that go into calculating vehicle drag.
So, given all those caveats, the first cut came up with some plausable lies (estimates). I would be most interested in others experience in this area, suggestions for improvement, comments on how I goofed up, etc.
Have fun.
David
1968 36/7988