Barry
Diamond Level Sponsor
The attached Excel spreadsheet allows quick "what if" calculations for tire size, gearing, speed and RPM for Alpine conversions using a 5-speed transmission.
Any of the data INPUT cells (highlighted in "tan") can be changed and the OUTPUT values will automatically recalculate (all of the other cells are locked for editing, but the contents can be viewed). Garbage inputs will result in garbage outputs (GIGO). The INPUT data shown are for 155/80-13 tires, an Alpine 3.89 rear axle and a '94+ Mustang V6 T-5 transmission with a 3.35 1st gear and a 0.72 5th gear.
For most engines, the “Maximum usable RPM” value will be approximately 500 RPM more than the RPM at which maximum HP is developed. Again, for most engines, the RPM at which maximum HP is developed will not exceed 5500.
Based on a suggestion from Michael King, this version of the spreadsheet has a section that calculates the tire diameter and tire revolutions per mile based on the tire size inputs. Calculating tire diameter is straightforward, but actual tire revolutions per mile are always greater than would be suggested by the tire diameter. The spreadsheet ESTIMATES the tire revolutions per mile based on a “rolling diameter” that is 3.2% smaller than the actual diameter. Because the tire revolutions per mile value is ESTIMATED, it does not automatically transfer to the input column. ACTUAL tire revolutions per mile can be obtained from your tire maker or tirerack.com (click on "Tires by Size" on the left hand side, enter your tire size in the drop down box, click on "Proceed to Tires" and the click on "Specs"). Stock tire size on an Alpine is about 914 revolutions per mile.
A typical 1st gear MPH / 1000 RPM value for a performance vehicle is 6-8; 5 MPH / 1000 RPM is a very "short" 1st gear and 9 MPH / 1000 RPM is a very "tall" 1st gear.
The calculated value for MPH in 4th gear @ maximum usable RPM requires that sufficient power is available to reach the calculated speed.
When you click on the attachment, it should download to your computer and / or open automatically (subject to settings on your computer). As always when downloading a file from a website, it is good practice to save the file to a specific location and scan it with appropriate anti-malware software before opening the file. According to Kaspersky, the file was clean when I uploaded it, but the bad guys are always developing new tricks.
Please let me know if you have questions or suggestions for improvement.
Thanks to Andrew Masse for enabling xls attachments.
Barry
Any of the data INPUT cells (highlighted in "tan") can be changed and the OUTPUT values will automatically recalculate (all of the other cells are locked for editing, but the contents can be viewed). Garbage inputs will result in garbage outputs (GIGO). The INPUT data shown are for 155/80-13 tires, an Alpine 3.89 rear axle and a '94+ Mustang V6 T-5 transmission with a 3.35 1st gear and a 0.72 5th gear.
For most engines, the “Maximum usable RPM” value will be approximately 500 RPM more than the RPM at which maximum HP is developed. Again, for most engines, the RPM at which maximum HP is developed will not exceed 5500.
Based on a suggestion from Michael King, this version of the spreadsheet has a section that calculates the tire diameter and tire revolutions per mile based on the tire size inputs. Calculating tire diameter is straightforward, but actual tire revolutions per mile are always greater than would be suggested by the tire diameter. The spreadsheet ESTIMATES the tire revolutions per mile based on a “rolling diameter” that is 3.2% smaller than the actual diameter. Because the tire revolutions per mile value is ESTIMATED, it does not automatically transfer to the input column. ACTUAL tire revolutions per mile can be obtained from your tire maker or tirerack.com (click on "Tires by Size" on the left hand side, enter your tire size in the drop down box, click on "Proceed to Tires" and the click on "Specs"). Stock tire size on an Alpine is about 914 revolutions per mile.
A typical 1st gear MPH / 1000 RPM value for a performance vehicle is 6-8; 5 MPH / 1000 RPM is a very "short" 1st gear and 9 MPH / 1000 RPM is a very "tall" 1st gear.
The calculated value for MPH in 4th gear @ maximum usable RPM requires that sufficient power is available to reach the calculated speed.
When you click on the attachment, it should download to your computer and / or open automatically (subject to settings on your computer). As always when downloading a file from a website, it is good practice to save the file to a specific location and scan it with appropriate anti-malware software before opening the file. According to Kaspersky, the file was clean when I uploaded it, but the bad guys are always developing new tricks.
Please let me know if you have questions or suggestions for improvement.
Thanks to Andrew Masse for enabling xls attachments.
Barry