http://www.speedworldmotorplex.com/calc.htm

Okay, I put 3.73s in along time ago or at least it seems like it. I havnt got the speedo fixed yet. Don't think I will either. But anyways, I ran a test on a site. I measured the wheels and what gears I had. As directed below. .

Tire diameter in inches: 25.68
Gears: 3.73
RPM: 2K
MPH: 40.98

Tire diameter in inches: 25.68
Gears: 4.10
RPM: 2K
MPH: 37.28

While my speedo said 45 mph at 2K rpm. I was right be side my wife on the phone. She said I am going 35 mph. 10 mph difference in speedo. Also, as you know now. That is closer to the 4.10 speed then the 3.73s. Is this correct? Is this test worthy!
:wrench <~~~ If I only felt that good about it!

I would not suspect the calculator on that page is wrong.
If what you said is all true, the wife's car's speedo is off... or perhaps your tach.. or both.. or some other factors or combination of factors.

I would not suspect the calculator on that page is wrong.
If what you said is all true, the wife's car's speedo is off... or perhaps your tach.. or both.. or some other factors or combination of factors.

The car she was in was cought on one of those hwy radars that were posts your speed as you past and it was right on. This was a few weeks prior. Thats why we choose that car. My rpm gauage has to be close. Because how could I not tell when the rpms are up with the flows 40s. Now the web site page could be wrong. I dunno. . .

But I bought the gears off of Ebay with less then 500 miles on them and his reason was. He wanted to go with higher gears. Im guessing he wanted 4.10s. But you can never trust some of them guys on there. But sometimes the gears just seem to high for me. If these are 3.73s. I would never get 4.10s. This would be as high as I would go. . .

I'd do another test and try it at different speeds, noting the rpms and speed for each. Have your wife drive at 25 for a set distance with you beside her, then 35, then 45 on up and see if it's consistently off. If it is, I'd consider installing that speedo gear. Either that or use a grease pencil to mark the correct speed on your speedometer ;).

The formula seems too simple for the page to get it wrong.. but you never know.

MPH = (RPM x Tire Diameter) divided by (Gear ratio x 366)

This page has several handy formulas so you can do it on paper.. calculating the effects of changes in RPM, tire diameter, gear ratio, etc.
http://www.offroaders.com/info/tech-corner/reading/mph-rpm.htm

There is a speedo gear to correct your speedometer. I believe it is the purple one, got mine at SVPU.com - installation about 10 minutes.

You have non-stock rims/tires on your car. This is a second factor in the equation that you have not considered.

Here's another calculator I like because of the graph. I know what the transmission gear ratios are for the markviii, but not the vii.

http://www.geocities.com/z_design_studio/transmission_z28_6.html

http://www.speedworldmotorplex.com/calc.htm

Okay, I put 3.73s in along time ago or at least it seems like it. I havnt got the speedo fixed yet.
...
T a k e i t t o t h e t r a c k .

You have non-stock rims/tires on your car. This is a second factor in the equation that you have not considered.

Thats a good point. I did over look that.

3.73 Stock Wheel Size

225/60 16 ~ 26.63"
2k @ 42.49

3.73 w/ My Wheels/Tires

245/45 17 ~ 25.68"
2K @ 40.98

T a k e i t t o t h e t r a c k .


I won't make it back. Unless I drive 35 mph the whole way back. . .

Purple gear.....just do it and be done

I won't make it back. Unless I drive 35 mph the whole way back. . .

Well, pull your data from the 'timeslip' forum then. It never belonged there anyway!

Okay, when I went to my grandmothers house. Guess what was on her street? A radar, with digital display! Awesome huh! Well, here me go. I tryed to go at 2k. But the thing just beeps the number. And chages from 37 to 40. So, I went slower. 1500 rpms. My speed at 1500 was 27/28mph and if the calculations are right on that site. It would be for 4.10s. It would have to be 30 mph for 3.73. Here it is. . .

3.73 w/ 25.68 Tall Tires
1500 rpm @ 30.73

4.10 w/ 25.68 Tall Tires
1500 rpm @ 27.96

T a k e i t t o t h e t r a c k .
T a k e i t t o t h e t r a c k .

Okay, when I went to my grandmothers house. Guess what was on her street? A radar, with digital display! Awesome huh! Well, here me go. I tryed to go at 2k. But the thing just beeps the number. And chages from 37 to 40. So, I went slower. 1500 rpms. My speed at 1500 was 27/28mph and if the calculations are right on that site. It would be for 4.10s. It would have to be 30 mph for 3.73. Here it is. . .

3.73 w/ 25.68 Tall Tires
1500 rpm @ 30.73

4.10 w/ 25.68 Tall Tires
1500 rpm @ 27.96

WAAAAYY too complicated. Use the mile markers on the freeway and a stopwatch.

T a k e i t t o t h e t r a c k .

What in the hell will that tell me! I been there done that and now im going back. But what does that say. I can't get hooked. You have better 60 times then I do!

You have non-stock rims/tires on your car. This is a second factor in the equation that you have not considered.

You smarty, you!

Tee-hee!

Murderously Yours,

MACHVII

What in the hell will that tell me!
...

Reaction time
60 foot time
1/8 mile time
1/4 mile time
trap speed
(depending on the track) weight of the car with and without the driver

Dude. With all of the information above, there are a dozen calculators on the net that will give you a BOOK FULL of information from just one run!

Am I misunderstanding your question?

Reaction time
60 foot time
1/8 mile time
1/4 mile time
trap speed
(depending on the track) weight of the car with and without the driver

Dude. With all of the information above, there are a dozen calculators on the net that will give you a BOOK FULL of information from just one run!

Am I misunderstanding your question?


Yeah, I got all that. . .

Dude.
Read this post out loud and maybe you'll see your answer.

You asked:

"While my speedo said 45 mph at 2K rpm. I was right be side my wife on the phone. She said I am going 35 mph. 10 mph difference in speedo. Also, as you know now. That is closer to the 4.10 speed then the 3.73s. Is this correct? Is this test worthy!"

I answered:

"T a k e i t t o t h e t r a c k ."

You asked:

"What in the hell will that tell me!"

I answered:

"Reaction time
60 foot time
1/8 mile time
1/4 mile time
trap speed
(depending on the track) weight of the car with and without the driver"

You replied:

"Yeah, I got all that. . ."

My final reply on this subject is:

"Then you have all the information you need to answer your FIRST question of Is this correct? Is this test worthy!"

If you ran a 17 @ 92mph at the track, then what that means is you ran a 17 @92mph at the track.

If you ran a 12 @ 122mph at the track, then what that means is you ran a 12 @122mph at the track.

If you changed gears without changing tires then you need to reread every post about traction and performance and the trade offs of every modification you make on your ride. You're still my Boy and we all love you like a step child but sometimes you need to shorten the question or stay focused on one aspect of one thing. I, on the other hand, need two Ibuprofen and a glass of water :confused:

John "Just-Not-Understanding-The-Question-Sometimes" Dancy

I ran a 15.1 sec @ 94 mph I can easly do better. With the right timing and some better tires. I could get into 14s. Like I should be running. Then with some DRs a low 14 run would be nice. Then with a can of 100 shot. Low 13s isn't asking to much. BUT, I am only spraying 3rd ar 3K. Or something like that. I just need to make up for a weak 2nd to 3rd shift.

But anyways, I do not care to know what I am running. I just want to know, if I have 4.10s or 3.73s.I know, I beleive I have one size to small tires. But just getting it correct. Just knowing what I got. Thats all I wanted to know.