4.16 rear end.

[Aren Jay]

So I was cruising through some of my old posts and found the one on my 4.44 rear end question. last two posts have the best information.


http://www.izook.com/gearcalc.htm

Have a look it is amazing.

Other great things there too.

so a Marauder with a 4.10 gear set and running 255 55 18 tires has a total gear ratio of 4.16...

The first and cheapest mod should be new tire.

[ctrlraven]

A larger tire should decrease the ratio, not increase it.

Old tire diameter (245/55-18 is 28.6") / (divided by) New tire diameter (255/55-18 is 29.0") x (multiply by) Gear Ratio (4.10) = 4.043.

[Aren Jay]

look at the link

[ctrlraven]

I did look at the link and that is incorrect. Just like with speedometer correction a larger tire will turn slower than the stock size it is programmed to hence the reason why the effective gear ratio will be slightly lower.

[mrjones]

Here's a much better version of the same thing, that one of the guys here did for his MM


http://www.averagegeek.com/Evil_Jim/GearCalc.asp

[Aren Jay]

I did look at the link and that is incorrect. Just like with speedometer correction a larger tire will turn slower than the stock size it is programmed to hence the reason why the effective gear ratio will be slightly lower.


Larger things go further, but turn at the same revolutions.

Turning is not changed.

If you have a stick that is 10 feet long. If you spin around holding the stick end exactly 10 feet from the spinning hub then the end of the stick will be moving 31.4 feet per revolution.

If the stick is 11 feet long, then the distance travelled is 34.54 feet per revolution.

Hence your speedometre will read 60 when you are going 60.9 if you have 255 55 18 tires on your Marauder. You will go faster than the speedo reading.

Tires turn the same number of times you just go further in the same amount of time.

Now for Gear ratio: hmmm.

4.10 is a smaller gear hence it rotates quicker.

A larger tire when compared to a smaller tire has the effect of making the gear, even smaller. Hence increases the gear ratio number.

The gear ratio doesn't change, the end result is that the car is travelling that tiny little bit faster. However I pointed out it is like a multiplier, in that the tire if it was the stock size (in comparison) it would need a higher gear ratio number (rotations) to equate to the same effect. (resultant effect)

Thus the link is correct.

[Breadfan]

A taller tire will spin more slowly to go one rotation, whereas a smaller tire will spin faster to go one rotation.

Translate it into engine speed, a taller tire is like less numberical gear, as the engine crank output will be at a lower engine rpm compared to the rotational speed of the tire. Vice versa for a small tire, it's like higher engine rpm.

Smaller tire gives more numberical gear (i.e. shorter gear). With my drag radials which are 26" tall compared to 28" tall oem tires my effective rear end ratio goes from 4.10 to 4.51.

crtlraven is correct a taller tire will effectively lower the numerical gear value.

Think of it this way a larger tire will cover more distance on one rotation than a smaller tire.

This means a larger tire will get you FASTER (i.e. covering more distance) than a smaller tire however a smaller tire will be easier to turn. That's why shorter gears (i.e. numberically higher) will get us going from a stop quicker but the sacrifice is top speed dpeending on how short the gear is.

[Aren Jay]

A smaller tire and a taller tire will spin at the exact same speed to go one rotation.
ie: 1 rpm.
The taller tire will rotate through a longer distance. Or drive further down the road.

They do not spin at different speeds.

The rim hub spins at the same speed as the rubber. But if you drive on the rim you will not go as far.

The engine is hooked up to the Gear set and drives through the drive shaft the gear set. The gear set that increases the number of rotations for the driveshaft to the axel and wheels/tires. 4.1 x driveshaft = 1 x wheels, results in the engine spinning at a higher RPM which is why a Marauder with it's High RPM engine performs better with the 4.1 rather than 3.55 gear set.

The wheels are on the down or small side of this equation. The bigger the wheel the lower the down side and the higher the driveshaft or gear ratio side.

The driveshaft with a 4.10 ratio has a greater mechanical advantage than a drive shaft with a 3.55 ratio gear.

Want to go faster at the race track, use bigger rear wheels.
Ever wonder why dragsters have the big wheels at the back and the little wheels at the front?

It doesn't really incrase the drive shaft ratio, it just appears to.

[Breadfan]

Yes rpm is the same but distance traveled is faster vs slower depening on size

[Aren Jay]

yes smaller is slower.

[fastcar]

A larger tire should decrease the ratio, not increase it.

Old tire diameter (245/55-18 is 28.6") / (divided by) New tire diameter (255/55-18 is 29.0") x (multiply by) Gear Ratio (4.10) = 4.043.

+1. The calculator is wrong. The 255/55/18s will make it LESS than 4.10. This is one reason I'm hesitant to switch!!!

fastcar:burnout:

[fastcar]

Please see responses in body of text:
A smaller tire and a taller tire will spin at the exact same speed to go one rotation.
ie: 1 rpm. NOT TRUE. THE CIRCUMFERENCE OF A BIG TIRE IS GREATER THAN A LITTLE TIRE. RPM IS NOT THE SAME AS SPEED (THOUGH IT IS SOMETIMES CALLED 'ENGINE SPEED'. FOR EXAMPLE, A 460 WITH A 3.85" CRANK HAS GREATER 'PISTON SPEED' THAN A 302 WITH A 3" CRANK AT THE SAME RPM. DO YOU SEE HOW SPEED IS NOT THE SAME AS RPM WITH RESPECT TO THE PISTON? SAME WITH BIGGER TIRES.

The taller tire will rotate through a longer distance. Or drive further down the road. THIS CONTRADICTS YOUR PREVIOUS STATEMENT ABOUT SPEED. IF EACH TIRE ROTATES THE SAME NUMBER OF TIMES PER MINUTE, BUT ONE TRAVELS FARTHER, OBVIOUSLY IT HAS A HIGHER TREAD SPEED.


They do not spin at different speeds. DON'T CONFUSE RPM WITH LINEAR SPEED AT THE TIRE SURFACE. YES THE RPM IS THE SAME IN EACH CASE. BUT, WHAT HOW FAR DOES ONE ROTATION GET YOU DOWN THE TRACK? YOU CAN'T SAY THAT THE LINEAR SPEED AT THE TREAD IS THE SAME FOR DIFFERENT DIAMETERS. MULTIPLY 'ROLLOUT' (CIRCUMFERENCE) BY RPM TO FIND OUT HOW MUCH DISTANCE YOU COVER PER MINUTE. YOU WILL SEE YOU GET MORE WITH A BIGGER TIRE.

The rim hub spins at the same speed as the rubber. But if you drive on the rim you will not go as far. NOT TRUE. THEY SHARE THE SAME RPM, BUT ONE HAS A GREATER CIRCUMFERENCE THAN THE OTHER, SO A DIFFERENT LINEAR SPEED. YES. THE LARGER THE DIAMETER THE FARTHER YOU GO, BECAUSE THE TREAD SPEED IS MUCH HIGHER. DON'T YOU SEE A CONTRADICTION IN YOUR STATEMENT?

The engine is hooked up to the Gear set and drives through the drive shaft the gear set. The gear set that increases the number of rotations for the driveshaft to the axel and wheels/tires. 4.1 x driveshaft = 1 x wheels, results in the engine spinning at a higher RPM which is why a Marauder with it's High RPM engine performs better with the 4.1 rather than 3.55 gear set. AGREED. YOU CAN GET THE SAME RESULT WITH A LOWER PROFILE TIRE, OR BY GOING TO A 17 OR 16 INCH RIM.

The wheels are on the down or small side of this equation. The bigger the wheel the lower the down side and the higher the driveshaft or gear ratio side. IT DOES NOT WORK THIS WAY. THEY DON'T ADD UP TO ZERO. THEY MUST BE MULTIPLIED.

The driveshaft with a 4.10 ratio has a greater mechanical advantage than a drive shaft with a 3.55 ratio gear. AGREED. AND A TIRE WITH LESS DIAMETER HAS A GREATER MECHANICAL ADVANTAGE THAN A LARGER TIRE.

Want to go faster at the race track, use bigger rear wheels. FASTER, MAYBE, BUT NOT QUICKER!!! YOU GET LESS MECHANICAL ADVANTAGE WITH A LARGER TIRE.

Ever wonder why dragsters have the big wheels at the back and the little wheels at the front? THEY USE BIG WHEELS BECAUSE THE CONTACT AREA BETWEEN A LARGE TIRE AND THE PAVEMENT IS GREATER THAN BETWEEN A SMALL DIAMETER TIRE AND THE PAVEMENT. THE BIG WHEELS ACTUALLY HURT THEIR MECHANICAL ADVANTAGE, BUT IT'S OK, BECAUSE THE 4000 FT/LBS OF TORQUE THOSE MOTORS MAKE EASILY OVERWHELM THE TIRES, AND THEY NEED DISTANCE MORE THAN FORCE AS THEY APPROACH 320 MPH. DID YOU KNOW THAT AS THE TIRES GROW TALLER DOWN THE TRACK, THAT IT HELPS THEM GO FASTER? NOT SLOWER. FASTER!!!

It doesn't really incrase the drive shaft ratio, it just appears to. THE LARGE TIRES GIVE YOU AN DECREASE IN EFFECTIVE REAR END RATIO, NOT AN INCREASE.[/QUOTE]

I recommend a basic book on physics. Look at the sections covering mechanical advantage. You must understand, RPM is NOT speed. Speed is distance over time. (D/T) But RPM does not specify a distance, so it can not be speed. I know this may come as a surprise to you, but it's true. It's a good gauge, though, of knowing how many times per minute your engine has rotated. But, to get vehicle speed, or piston speed, you need tire diameter or length of crank. Hope this helps.

fastcar:burnout:

[Aren Jay]

OK, so the gearing advantage, which is an illusion as the gearing doesn't actually change is such that larger tires make it seem as if the gear ration is less not more. A lower number not a higher one.

ok

But the speedo thing that
wrong, is not wrong which is what confused me.


I did look at the link and that is incorrect. Just like with speedometer correction a larger tire will turn slower than the stock size it is programmed to hence the reason why the effective gear ratio will be slightly lower.

The RPM (quickness) of the tires doesn't change, the resultant MPH is higher.

Which means that the gearing ratio is such that it gives you a lower number or larger gear ratio, if you had the original sized tires on it. You don't though and you still have a 4.10 or 3.55 gear ratio but you also get the MPH (speed) benefit as if you did.

Does that really change the mechanical advantage though?

As for the dragster tires, you are right for the patch, and wrong about other parts of it.

Larger rear tires, mean higher top speed and less RPM of the wheel/tire drive shaft and engine to reach the end of the track.

Using smaller wheels is a bad idea.

Tires grow because of the low tire pressure, and the centifical force.

[fastcar]

OK, so the gearing advantage, which is an illusion as the gearing doesn't actually change is such that larger tires make it seem as if the gear ration is less not more. A lower number not a higher one.

ok

That's correct. Larger tire = less effective gear ratio (numerically lower)


But the speedo thing that [ctrlraven] brought up is not wrong which is what confused me. The RPM (quickness) of the tires doesn't change, the resultant MPH is higher.

I think ctrlraven was trying to say that when you put bigger tires on the car, the speedometer will read low at a given RPM, because they will be moving you a greater distance each time they rotate (because of their greater circumference) and, so, your MPH will be higher.


Which means that the gearing ratio is such that it gives you a lower number or larger gear ratio, if you had the original sized tires on it. You don't though and you still have a 4.10 or 3.55 gear ratio but you also get the MPH (speed) benefit as if you did.

A little tough to follow. We need to use a convention when speaking of rearend ratios. 4.10 is 'lower' than 3.55, but numerically higher. 3.55 is 'higher' or 'taller' than 4.10, though numerically lower. Specify which you mean, it will be clearer. The original size tire gives you a lower effective gear ratio (numerically higher) than the taller 255 tire.


Does that really change the mechanical advantage though?

GOOD GRIEF YES! Man, you've got to listen. You can't cheat nature. If it effects distance or speed, it is effecting mechanical advantage!!! Mechanical advantage is always at play when you discuss gearing or tire size. They are both the same. If you want the same mechanical advantage in your Marauder with 255s, you will need a slightly lower rear gear than 4.10.


As for the dragster tires, you are right for the patch, and wrong about other parts of it. :confused:


Larger rear tires, mean higher top speed and less RPM of the wheel/tire drive shaft and engine to reach the end of the track. Of course... That's what I said...



Using smaller wheels is a bad idea. If wheel spin is a problem, than I agree. But, if you want more mechanical advantage, and you can't spin the tires, a cheap way to get off the line faster is by using lower profile tires. It could be like going from say a 3.55 to a 3.73. That could be really good, depending on your budget, and torque output.:)


Tires grow because of the low tire pressure, and the centifical force. Yes, you are right. It's kind of neat, because its like having a VARIABLE rearend ratio or gear box that you do not need to shift. It shifts gradually, and automatically as the tire grows. It really is a good thing for dragsters. Works nicely...

Anyway, I hope this helps. If you really want to figure out what your new effective rearend ratio will be after you install 255s, just repost and we'll go through it. It will involve rollout which can be inferred from tire size. Should be interesting...

fastcar:burnout:

[Dragcity]

Smalller = quicker

Taller = Faster

Dragracing 101....

There is way more to it than that, but that is 101....