Gearing your rig, the effects there-in.

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AoD

AoD

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Hammondsville, Ohio
Alright, so you've gotten to the point where you're wanting to change the gearing in your truck? Well, that's what this guide is going to help you decide on. We'll look at the different parts associated with simple gearing changes, then we'll explain what effects you'll see from gearing your rig.

Clutch Bell

The clutch bell, holds the clutches and is the main output of your motor. It's directly associated with the engine, and it's total RPM. This can play a major effect in the performance of your truck, and can cause many different effects.

Basically, this spins one rotation every time the engine has a complete cycle (rotation of the crankshaft). So, if your truck is running at 10,000rpm, your clutch bell (if the clutch is working correctly) is spinning at 10,000rpm.

A big importance is the teeth amount on the clutch bell. The more teeth on the clutch bell, the more it spins your spur gear per revolution. After I discuss the spur gear, I'll add a small equation to help understand how it works. The key point to remember is, the more teeth on your clutch bell, the more top speed you will have. But remember, the higher the top speed, the less power and acceleration you'll have getting to that top speed.

Spur Gear

This is your main point of contact from the engine to the transmission. This gear is attached directly as an input to your transmission, which in turn gets your drive train going. Most spurs are plastic, and they come in many different sizes. The biggest thing to remember, the spur gear is meshed with the clutch bell, so it spins in direct relation to the clutch bell. The more teeth on a spur gear, the more acceleration you'll have, but you'll see a reduction in top speed.

Simple Driveline Equation

SG / CB = Gearing Ratio

So, an easy way to see this is with whole numbers. Here's two parts that make an easy way to get a gearing ratio with this equation.

50SG / 20CB = 2.50 Final gear ratio

Now, the spur gear has 50 teeth. So, the clutch bell, which has 20 teeth, must spin a total of two and a half times to get one full rotation on the spur gear.

Let's try a stock SG/CB setup, and see what ratio that provides!

49SG / 15CB = 3.2666 final gear ratio

So, which one of these examples will have more acceleration? Well remember, the more teeth on the spur, and the less on the clutch bell give us acceleration. So, here's how it works. For every one turn of the motor, the clutch bell and spur gear are turning the transmission at the final gear ratio. So, at 50SG and 20CB, you're turning the transmission once every 2.50 revolutions of the crank shaft. And in the second example, 49SG and 15CB, you're turning the transmission once every 3.2666 revolutions of the crankshaft.

The more revolutions it takes to spin the transmission turns into more power. As there is two ignitions of the motor in the first example, and three in the second example. That's a general idea, but the higher the final gear ratio, the more acceleration and power you will have. The lower the final gear ratio, the higher your top speed will be.

Finding that right tuning

Now, there's a certain speed to acceleration that every situation needs for perfection. Each person is different, and they may not want the same gear ratio's as anyone else. MotoPsycho has a very good chart that shows combinations of gear ratios. Here's a link to it.

https://www.hpisavageforum.com/forums/showthread.php?t=3867

Now, finding that perfect gear ratio is difficult. But, trying to find the right one for you is the key. Trying different setups is part of the sport, and certainly a good way to get experienced with it. Remember to make sure you mesh your gears together well. An improper mesh can result in a stripped spur gear. Your manual, or this forum are good places to find help with meshing your gears correctly.

Tires, transmissions, and differentials

Now each of these can effect the actual speed and acceleration/power of your model. The most important thing to remember about this is every moving part of the driveline can be an important factor to look at when finding a good gearing ratio.

Tires

These can make a giant difference of speed and power. The bigger the tires diameter the more top speed you will have. A smaller tire will actually provide you with lower top speeds, but higher amounts of power and acceleration. These can actually play a bigger effect on your gearing ratio's than your spur gear and clutch bell.

Transmissions

Some transmissions can be geared higher or lower for more speed or more acceleration. Some companies actually sell kits so you can adjust your gearing further from within the transmission. This usually should be left to an experienced hobbyist, but it is another possibility to look at.

Differentials

Some differentials can have higher or lower gearing ratios then the stock ones. Usually this isn't a factor unless you chose to switch gearing or types of differential. But remember, these can play a factor for gearing.


Take some time and find that right gearing for you. Whether it is going for 60 miles an hour, or for the maximum power, it is all up to you to decide upon. Some extreme gearing ratios may require some modifications, but can be well worth the time if you do everything correctly. Good luck with gearing your rig, and I hope this small guide was able to help you some way.
 
Last edited by a moderator:
What gearing would you suggest with the LRP Z.28? I'm running the stock setup right now and if I get on the gas hard the truck just flips over. I was thinking going to a 20T CB. Would that be too much?
 
Keithv said:
What gearing would you suggest with the LRP Z.28? I'm running the stock setup right now and if I get on the gas hard the truck just flips over. I was thinking going to a 20T CB. Would that be too much?
Click to expand...


Personally if it was me, I'd be happy with a good bit of wheelies. If you're thinking of getting more speed, and reducing the power and wheelies, try a 47 SG and a 17-18 CB. That'll get you a good bit more top speed, and help reduce the amount of wheelies.

Remember though, with the gearing like that, you also lose the acceleration ability. With each step to a higher speed gearing, your acceleration drops a little bit.

I'd try a few different setups. First try changing the clutch bell, that's going to make a big difference. :)
 
AoD said:
Personally if it was me, I'd be happy with a good bit of wheelies. If you're thinking of getting more speed, and reducing the power and wheelies, try a 47 SG and a 17-18 CB. That'll get you a good bit more top speed, and help reduce the amount of wheelies.

Remember though, with the gearing like that, you also lose the acceleration ability. With each step to a higher speed gearing, your acceleration drops a little bit.

I'd try a few different setups. First try changing the clutch bell, that's going to make a big difference. :)
Click to expand...

Thanks Aod. I'm not looking to stop the wheelies just trying to actually keep it on the wheels. The engine has so much power it just flips right on to the roof, even with the wheelie bar. Ive been getting a little better with the throttle control but its still difficult to keep it from going over backwards.
 
I alredy asked this question in another thread but at the moment i do not want to buy 3speed tranny. I own savage x 4.6 with 5.9 mill(i know it is not the best, but i have it..). What gearing you suggest for more acceleration(torque) over speed(still want some decent speed). At the moment i drive 16/47
 
you can switch up to a 49 tooth Spur or go down to a 15 to CB. There are some options.. If you are running maxx sized wheels with a standard 5.5in tire then you will not want to change it to much as then you will not get any speed out of your truck.
 
I run stock wheels and tires. Then i should try 49/16(can i count on some wheelies if i try hard not that i am so into wheelies but at time to time i want to try). I do not want to buy something unuseful..
 
That should bring some wheelies. You can give it a shot. As the original poster said some trial and error will get you where you want to go. I would not go any higher than 49 teeht on the SG though.
 
I don't know man, almost sounds like a bad tune to me. I was pulling crazy wheelies on 16/47 with a 28. I would lean out your LSN a little. I know that the 5.9 has to run really lean on the low side in order to make good power.
 
i havn't reid it with the phaltline wheels.
but the savage x wheels work well.
the trick is 1st gear play with the throttle let it hit second gear half throttle
then nail it.
The tyre ballooning changes the pivot point.

Once i fix my half tank lean (hopefully with the extra tank will do this i will post a video)
 
I think i need to change my gearing. I'm running flm cen mugen mid tank with an lrp z28 and my wheels don't lift at all. right now i have 18/49
Top end is great but doesnt lift the wheels at all.
 
Are you after wheelies? A good setup puts all the power to the ground, hence no wheelies.

I am in the process of rebuilding with FLM chassie in hopes of reducing my lid surfing.

I was running a 16/47 on a stock 25 set up and could put it on the lid in first or second gear with just the snap of the throttle.
 
Stock setup with my ported polished 25 was on its lid all day. The flm setup with the flm wont lift the front wheels at all.
 
What I tried to say is that I have a LRP 28. You could try a 52 tooth spur, but I do not know if it will fit with the 18 clutch bell. I might have a spare 16 tooth Clutch bell in my parts bin that I might be willing to part with for you to try. I will have to look when I get home
 
I have to mess around with my gearing. I am placing a small order for some parts anyway so i can just add them to that order. Thanks for the offer though.
 
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