| Author |
Message |
James Glickenhaus (Napolis)
Intermediate Member
Username: Napolis
Post Number: 1236
Registered: 10-2002
| | Posted on Wednesday, May 07, 2003 - 10:25 am: | |
Joel
that worked for my MK-IV:
7000rpm
2.5 rear
27in dia
225mph
(It was clocked at 233 on the Mulsanne) |
Mitch Alsup (Mitch_alsup)
Member
Username: Mitch_alsup
Post Number: 628
Registered: 4-2002
| | Posted on Wednesday, May 07, 2003 - 9:57 am: | |
speed = RPM/(tranny_ratio*diff_ratio*pi*rolling_diameter*60/88)
pi = 3.141592653.....
rolling_diameter in feet (driven wheel with tire)
60 MPH = 88 ft/sec
speed in MPH |
Joel Belser (Driver)
New member
Username: Driver
Post Number: 37
Registered: 9-2002
| | Posted on Wednesday, May 07, 2003 - 8:33 am: | |
The formula is: (RPM x Wheel Diameter)
---------------------
( Final Drive Ratio x 336)
Remember that your final drive ratio is your rear end ratio x top gear ratio. On many cars this will be less than the rear end ratio due to overdrive top gears. |
Mike Procopio (Pupz308)
Member
Username: Pupz308
Post Number: 349
Registered: 10-2002
| | Posted on Sunday, May 04, 2003 - 5:33 pm: | |
Are you making the assumption that you tach is correct? These have error in them, too. During my emissions test, the tach read 200-300rpm less at true 2500 rpm as determined by hooking onto one of my plug wires...
Recommend handheld GPS, a cop who's also a friend to do the radar thing, or drive by one of those radar-based speed displays on the side of the road... The best test is to have, say, two markers at 1000ft and do the timing test.
My speedo indicates 43 at a radar-based road speed display value of 40... 78 308.
Non-OEM wheel/tire sizes will of course affect the reading...
|
Jeffrey Davison (Jeffdavison)
Junior Member
Username: Jeffdavison
Post Number: 116
Registered: 7-2002
| | Posted on Sunday, May 04, 2003 - 2:11 pm: | |
chart is for a Camaro 6 speed, But just plug your numbers in place and the chart will adjust itself:
http://www.geocities.com/z_design_studio/transmission_z28_6.html
Jeff Davison |
Patrick S. Perry (Psp1)
Junior Member
Username: Psp1
Post Number: 147
Registered: 3-2001
| | Posted on Sunday, May 04, 2003 - 1:51 pm: | |
The easiest way to check your speedo is with a handheld GPS receiver. Most of them will give you a speed reading that will update every few seconds. |
stephen r chong (Ethans_dad)
Member
Username: Ethans_dad
Post Number: 257
Registered: 3-2002
| | Posted on Sunday, May 04, 2003 - 1:06 pm: | |
Hello All,
I was wondering how to determine theoretical speed thru engine speed and final drive ratios; very much like the graphs shown in owners manuals. I was hoping to get a rough estimate of how accurate my speedometer is or isn't.
If anyone has the math for this, I'd be most appreciative, and also the best way to calibrate a speedometer. |