eCtune

What size tyres does the speed read out assume the car is running? I run 23.4\" drag slicks at the moment on track but may shift to 24.5\" next year depending on what I do with my gear ratios. I'm looking at running Y21 ratios until 5th which will be a 4.7FD S80 5th (longer) but with a 3.7FD to give me more traction in the 1st/2nd & enough room at the top end in 4th but still with a 5th for VMax Bill

std tire size on most hondas is 195/55/R15, or the equiv diameter. (23.4'') to bump in in diameter and keep the right mph reading you'll have to change the final drive value to compensate for the 4.5% increase in distance traveled per revolution of the tire. As to what tha value would be, I'm not sure I'm away from all of my calculation spreadsheets at the moment. When I get a chance I'll update.

As you say my plan is to fudge the gear table values so the MPH on the data logging is right. I have a spreadsheet I made years ago to help me with gear ratios/tyre choice etc I just want to know 100% what eCtune has as a \"built in\" tyre size. Thanks for the reply Bill

it's not so much eCtune, more the Honda ECU having that built in. As far as I know all honda tuning programs use the same default circumference of the tire to calculate vehicle speed. NOTE: this could be a decent addition to any program to edit the default tire circumference value. All though your speedo will be off even if the ECU knows the right speed. (tunerview to the rescue)

Your right it would be a good addition Thanks for your help. The 3.7FD looks like it might be ok as it's \"30% stronger than OEM\" so it should take my 400/500hp Bill