gearbox and differential ratios

[bloody death]

how do u team up diffs with gearbox by that i dont understand ratio because the ratio on the diffs and gearboxs dont match

[Creative Pudding]

ok, this is relative simple:
GearBox ratio means how much is the difference between the shaft (which comes from the gearbox) and the half-shaft going to the wheels.
So gearBox ratio 1 means both the main shaft and the wheels half-shaft all spinning with the same speed. If the Engine spins 1000, the car is in a gear of ratio 1 (usually one of the highest gear is set to 1, ie. 4th or 5th) and if the diff is also set to ratio 1, then the wheel will spin exactly 1000 rpm as well.

If your diff ratio set to 2, it would means that 2 spin of the main shaft will produce 1 spin on the wheels. However, when you spin less, it will also be stronger. So if ratio is set to 2, it will make your wheel spin 1/2 times of the main shaft AND it will produce 2x more torque.
So higher ratio means more torque, less speed.

When you want to balance a car, you need to take the GearBox, Motor and diff into one.
The gearbox does the same as the diff:
in 1st gear the ratio is high, so the motor rpm goes over the gearbox will be modified with ratio, so in 1st gear lest say a typical ratio is around 3. So it will delivery 3x more torque and 3x less rpm to the diff. Then the diff will use it's own ratio to delivery the torque to the wheels.

Now, when you want to balance them, you need to make sure that:
1. select a gearbox you think is good for you (number of gears, speed, etc).
Then go to drive a bit and check:
2. in 1st gear the car should start, and should have has enough power. If not, your diff ratio is too low.
3. in 1st gear should have a meaning, so if the car spin out too quickly in gear 1, then you cannot really use this gear and it's not a good setup. In this case you need to lower the diff ratio.
4. in last gear you should still have enough power to reach the motor highest RPM. Ideally the power will gone at the very highest rpm, so you still can reach it but nothing more left (no waste)
5. in last gear if your car still "revving" at high rpm, then the differential vs gearbox setup is not ok, the ratio should be lower. This case you either pick another gearbox which has lower ratio at last gear, or you reduce the diff ratio.
6. if in the last gear the car cannot reach the motor max rpm, then your last gear ratio is too low: either change the gearbox to something which has higher ratio at last gear or us a a higher ratio diff.

Summ:
1. gearbox will change the torque based on gears. Every gear has different ratio, so each gear produce different torque.

2. diff ratio will change the torque delivered to the wheel INDEPENDENTLY from the gearbox, because it does apply the ratio after the gearbox is already modified it.

The final ratio comes from the gearbox ratio multiply with diff ratio, which means if both 1, then the final ratio is 1 => wheels spins same speed as motor.

If a car week in every gear, then you need higher diff ratio, if the car too strong in every gear (revving, spinning too much at accel), you will need to reduce the diff
If you have problem in 1st or last gear only, pick another gearbox.


Since every track is different, you might need to adjust this per track! A typical street car is set to be able to reach a good speed with comfort, so you can drive easily in most condition. A race car is set to reach the top max possible torque on a track and it is usually very aggressive. Driving many racing cars required special license and curse to learn, even if you have 20+ years experience with street cars!

If a track is slow, like the backyard you should set the car to make it stronger (so better acceleration on low speed) and if the track is fast like Mount Yanagin or Gutta oval, then you want to reach the max speed of the car and acceleration is less important (you wont stop and start that much, instead keep the car running at high speed)

In a real race world you also need to take the driver into account. Drivers drives differently and some want the car have more power in corners or low speed section, while others use the long, high speed section to win. It is your own decision where you want your car to be the strongest and that is where the GearBox and Differential taking place.

[bloody death]

so sorry i am trying to understand but i cant get my head around it
ok here is what im trying to run and it sucks
engine v8 power 4800ccm
326hp torque 570nm

gear box 5 speed 3.86 1.99 1.29 1.00 0.72

diff 3.08
so can you please help me a little bit more and a very very big thank u

[Creative Pudding]

which car and which track? and what is the problem, is it revving too much or is it just too slow for you?

if you think your car is slow, or you cannot really use the gear 5th, then you should use a diff which is stronger. Try another one around 3.5-4

If your car burn the tires too much, so it spins the wheel a lot during driving (you can hear it you can see it), that means your diff is too high. Use a lower ratio diff (around 2 - 2.5 probably)

[bloody death]

first gear sucks spins a little also the dirt tracks and it is a whela also i forgot to say is it also has weala half shafts and drive shafts does that matter
can u also tell me this
i kinda got some of it so wich one is first gear with gearbox i got that much the 3.86 or1.99 or1.29 or1.00 or 0.72
because those are gear ratio in the gear box right

[Creative Pudding]

yes, the gear box ratios are those numbers!
the first one is is the first gear, 2nd number is 2nd gear.. so 3.86 is your first gear and 0.72 is the 5th. It is under 1, which means it is under driven. (you can see this terms in a few topic)

This gearbox is for high speed, not for any of existing dirt track (yet)! You dont want to switching gears 5 times in those small track, because every shifting is time and until you are shifting your car does not produce power on wheels... This gearbox is for gutta or mount forrest/yanagin.

Let say you have one car only, the same car on each track would have different gearbox-differential for the best performance.

Backyard
In backyard you want a gearbox where you can keep the gears during the whole race. So you start in 1st, 2nd, but then you probably want to keep it in 3rd during each laps. This also required that you take each corner carefully so it wont slip too much and wont slow down too much to shift back a gear.. then up again after the corner. In some cases it is ok to shifting on that track, but you want to keep the shifting of gears as minimal as possible.

Imalona
If you go to a track like Imalona, which is dirt but longer than backyard, you will use 2-3 gears to shifting. On the longer straight you want to reach the highest possible speed, but that's the max you would need, because all other sections are slower. So you try to setup your car to reach this max speed as quick as possible, but you dont need more speed than that!

If you compere backyard with imalona, then in backyard you want a higher diff ratio or gearbox which has less gears and the 3rd gear is somewhere around 1.2-1.6, while in Imalona you want a diff which has less ratio (you can achieve higher speed for longer straights) and/or a gearbox which has 4th or 5th around 1.4 - 1.0

Gutta
If you go to track like Gutta Oval, you want a gearbox with under drive gears, so you have the ratio under 1.0 in 4th or 5th or 6th (whatever is your final gear on that gearbox)
The differential might need to change too, but first get a quick 5 or 6 speed gearbox, then find the differential which still can produce enough power to start the car (you dont need burning tires here) and it will reach the top RPM of the engine at the end of the longest straight only, ideally exactly on the spot where you would start to brake or enter into corner.
using the above example the ratio would be between 1.8 - 2.4

Mount Yanagin and Forrest are a mixture of many section. It would be very hard to tell what gear - differential to use because it is very much depends on how you drive. If you can drive like "go-karts", so you keep the speed at highest and carefully avoid of anything that slows you down, including takeing over others or getting into corners, in this case you drive like this, you want a low final ratio, so lower ratio on diff and gearbox.
However, if you like to drift, sliding, pushing to limits, then you want to have enough power at most of the cases to spin your wheels. This case you want a diff with higher ratio then above.
In most cases changing the diff is enough to adjust the car from "gokarting" to "muscle driffting", but it is very much depends on the power as well.

Drag
On drag tracks or drag racing, you want the highest possible acceleration. This means higher ratios. So continue the above example car, you want a diff somewhere between 3-6 and a gearbox, which has around 3 max 4 speed (gears) and the last gear is close to 1.2-1.4

If you change the engine on this car or you modify so, that the car has more horse power, then you should use slightly lower differential.

The engines not only produce different power, but also has different charasteristic, meaning: each motor has an optimal RPM where it produce the highest torque or horse power.
The panania engines producing the highest power very close to their highest RPM around 8000, while a Buthanbang engine produce the top around 4300 rpm.
Therefor, using this two engine in the same car would means the car would produce the most hp around different RPM. If you want to use BB engine, you want a ratio which will let it run around 4200 as most cases, while if you use a Panania engine, you want to reach 8000 rpm to produce the most torque.

Use a gearbox which has not more then 1 ratio at 4th, because you have a short track

A general "rules":
Use Differential with less ratio ( less then 2.5) if you want your car perform better at high speed
Use Differential with high ratio (more then 2.5), if you want your car perform better at lower speed

If you really get lost in ratios, you should go back to factory setup and use it as a starting point.
Each street config (new cars from bottom of the newspaper), are set to a normal driving mode. It is perfect starting point of tuning. First make a few laps with a factory setup, then you can start to alter it following the rules above.

HINT:
it is wise to write down the factory car's setup and anything else you liked to drive. Make a note about the engine, horse power, gearbox and diff. You can use the parts ID as well, since they are unique and you can buy in shop easier if you know these numbers.
If you have a few of these setup you will get the idea about what works on which car.

[Creative Pudding]

Can you change the title to GearBox and Differential Ratio or something help others to find this, thanks!

[Mad_House]

Originally posted by Creative Pudding:

If a car week in every gear, then you need higher diff ratio, if the car too strong in every gear (revving, spinning too much at accel), you will need to reduce the diff
If you have problem in 1st or last gear only, pick another gearbox.

This. I love this. Very helpful!