Hypertech and 3.73 speed fix?

[01camaro]

I had an idea to fix the speedometer by changing to either 3.42 or 3.23 gears in the programmer and reprogramming it to a specific tire size to "trick" it into reading the correct speed. I really don't know what formula to use to get a "new" tire size to trick it. I want 3.73s but I'm not splicing into my wires to do it, especially if I have a programmer and can figure out how to change the speedometer to work right. I'll let everyone know what tire size I find out to use, and I WILL find out.

[StockV6Cam2]

Ok well lets think about this. I would assume that it would multiply how many times the wheel is turning by the circumference of the wheel. You find the circumference from using a 2(Pi)r formula from what I remember.

So say you had a 25 inch tire normally. The circumference would be roughly 78.5 inches. Now multiply that by say 1000 rpms. That means that it should have covered 78,537 inches in that 1 minute. Ok so there are 63,360 inches in 1 mile. So you just traveled roughly 1.2 miles in that minute which would convert out to 72 miles per hour at a 1 to 1 gear (3rd in A4, 4th in M5).

So now the problem comes in where the computer sense RPMs of the wheels when you switch gears. Now obviously the computer takes the revolutions of the driveshaft, not the axles. So say it's calibrated from the factory for a 3.23 gear. This means that the driveshaft spins 3.23 times for every 1 spin of the driveshaft. So say the driveshaft is spinning at 2,500 RPMs. You take 2500 divided by 3.23 and you get the axle spinning 773.99 times in that minute.

So I guess the calculation for MPH would be:

(2 * Pi * (Radius of tire)) * (RPMs / Gearing Ratio) * 60
---------------------------------------------
63,360

So if you figure that the computer is calibrated for 3.23's and a 25 inch tire lets say. And we're cruising in 3rd (A4) at 3000 RPM. That's

(2 * 3.1415 * 12.5) * (3000/3.23) * 60
--------------------------------------
63,360

Which equals = 69.07 MPH

When running 3.73s the equation is.

(2 * 3.1415 * 12.5) * (3000/3.73) * 60
--------------------------------------
63,360

The answer is 59.82 MPH for that one. So this is why our speedo is off w/ the higher gears because the computer still thinks we're going 69mph.

So now lets think about how to trick the computer w/ tire size and a 3.42 gearing. We'll assume the same sitation w/ the computer calibration at 3.23 w/ a 25" tall tire and crusing at 3000 rpm in 3rd. Now lets figure out how tall the tire would have to be to get the same exact reading. This time the equation would be...

(2 * 3.1415 * X) * (3000/3.42) * 60
-------------------------------------- = 69.07
63,360

330684.21X
---------- = 69.07
63,360

Multiply the 63,360 on both sides and you have have.

4376275.2 = 330684.21X

Divide the 330684.21 on both sides and you have.

13.234

That means that you would need to set the tires size to 26.468 inches in order to trick the speedometer into being correct.

Hoped this helped a bit. :D

[ October 01, 2002: Message edited by: StockV6Cam2 ]</p>

[ravenp]

Okay, that's some serious math. My head hurts [img]smile.gif[/img]

Dumb question of the day.

If you get bigger gears(ie 3.08 to 3.42) and leave the tires. You will accelerate faster due to the increase in axle rotations relative to driveshaft rotations correct? Your speedo is off, and some cannot live with that including me.

Now, you go and figure out using the above formula how big your tires need to be to get the speedo back on track.

Bigger tires mean less axle rotations per driveshaft rotation dont' they? So aren't you kinda undoing what you gained from the gear increase?

I realize that the 3.42 is the final drive ratio, and that each each is different...and that's probably where increasing your tire size works.

But increasing the tire size will slow you down due to more power being needed to turn the axle, and not having added any power.

Now my head hurts even more [img]smile.gif[/img]

[StockV6Cam2]

<blockquote>quote:</font><hr>Originally posted by ravenp:
Okay, that's some serious math. My head hurts [img]smile.gif[/img]

Dumb question of the day.

If you get bigger gears(ie 3.08 to 3.42) and leave the tires. You will accelerate faster due to the increase in axle rotations relative to driveshaft rotations correct? Your speedo is off, and some cannot live with that including me.

Now, you go and figure out using the above formula how big your tires need to be to get the speedo back on track.

Bigger tires mean less axle rotations per driveshaft rotation dont' they? So aren't you kinda undoing what you gained from the gear increase?

I realize that the 3.42 is the final drive ratio, and that each each is different...and that's probably where increasing your tire size works.

But increasing the tire size will slow you down due to more power being needed to turn the axle, and not having added any power.

Now my head hurts even more [img]smile.gif[/img] <hr></blockquote>

If you actually changed the physical tires to be bigger yes it would undo the reason for the gears. But that's not what we're doing here. We're tricking the computer into *thinking* that we've made the tires bigger so that it calculates the correct speed. So you get all the performance and a correct speedo/odometer :D

[Dewey]

I'm confused. Doesn't the HPP3 allow for gear changes, tire size changes, and speedo fixes?

HPP3 Info

[StockV6Cam2]

It only allows for gear changes up to a like a 3.42 from what I understand of it.

[Dominic]

The new version is supposed to work up to 4.56's

[john00v6a4]

<blockquote>quote:</font><hr>Originally posted by Dominic:
The new version is supposed to work up to 4.56's<hr></blockquote>

he is correct. when i used mine it said it could work up to 4.56's

[StockV6Cam2]

Well now you guys who can only switch up to 3.42 on the pcm know how to trick it so it'll read the correct speed [img]smile.gif[/img]

[ravenp]

<blockquote>quote:</font><hr>Originally posted by StockV6Cam2:


If you actually changed the physical tires to be bigger yes it would undo the reason for the gears. But that's not what we're doing here. We're tricking the computer into *thinking* that we've made the tires bigger so that it calculates the correct speed. So you get all the performance and a correct speedo/odometer :D <hr></blockquote>

See, if I would have read that closer, that would have made sense [img]smile.gif[/img]

Thanks...

&lt;/head hurting&gt;

[ravenp]

The Odometer will still be off though if you change the tire size in the computer but not actually the tires, correct?

[StockV6Cam2]

<blockquote>quote:</font><hr>Originally posted by ravenp:
The Odometer will still be off though if you change the tire size in the computer but not actually the tires, correct?<hr></blockquote>

Nope, if you change the tire size in the computer and leave them how they are. The odometer will be correct. The PCM calculates it off of the same principles as the speedometer. So both the speedo and odometer will be correct.

[Silver3800V6FBodyKY]

I'm not what others have said in this post, but if you want to use the HPP3 to change the speedo, and it doesn't have the 3.73 option, you have DECREASE the tire height on the HPP3, not increase it. If you increase the tire height on it, it will only make the speedo farther off. HPP3's smallest tire height is 24", that's enough to fix the speedo for gears. But you shouldn't have to do this since the new version has all gear options.

[StockV6Cam2]

<blockquote>quote:</font><hr>Originally posted by Silver3800V6FBodyKY:
I'm not what others have said in this post, but if you want to use the HPP3 to change the speedo, and it doesn't have the 3.73 option, you have DECREASE the tire height on the HPP3, not increase it. If you increase the tire height on it, it will only make the speedo farther off. HPP3's smallest tire height is 24", that's enough to fix the speedo for gears. But you shouldn't have to do this since the new version has all gear options.<hr></blockquote>

Maybe you should try reading my post where I mathematically proved that you'd have to increase tire height to compensate for a higher gear.

[Silver3800V6FBodyKY]

<blockquote>quote:</font><hr>Originally posted by StockV6Cam2:


Maybe you should try reading my post where I mathematically proved that you'd have to increase tire height to compensate for a higher gear.<hr></blockquote>

Well bud, your math is wrong [I'm not exactly a stranger to math (engineering major)].

http://www.camarov6.com/cgi-bin/ulti...&f=16&t=000513

I have the HPP3 on my 2001 and I have 4.11:1 gears, but the HPP3 doesn't have that gear option, so what I did was trick the PCM using tire height as the variable.

The whole goal is to get your PCM to think that you have stock tire height, but a changed gear ratio, you can do this two different ways: change the ratio on the PCM, or change the tire height. Since you can't change the ratio because it's not an option, you have to alter the tire height on the HPP3.

What you want to do is put the gear ratio on the HPP3 as high as possible: 3.42:1. Then you need to figure out what tire height you need to simulate 3.42:1 gears, and a changed tire height that would be the same as 3.73:1 gears and the tire height you have now.

Obviously you would go with a smaller tire height because when you lower the tire height, you simulate lower gears ( 3.73 gears are lower than 3.42).

I'm not sure what math you did up there, but this is all you have to do:

3.42X = 24Y

X = Your tire height right now.
Y = What gear ratio you are going to be simulating.

EX: I have 26.1" tires.

[(3.42)(26.1)]/24 = Y

Y = 3.72

So right now, with the HPP3 set at 3.42 gears, and a 24" tire, I am simulating 3.72 gears with 26.1" tires.

This works because tire height and gear ratios are inversely proportional. It is a very simple concept, no need for using pi, or RPMs.

So basically just multiply your tire height by 3.42, and divide the products of those two by 24, and that is the gear ratio that you are simulating.

Sorry man, but you've been owned.

[ October 01, 2002: Message edited by: Silver3800V6FBodyKY ]</p>