Bomber suspension - sway bar or spring rate change

[IntrepidMercians]

Hi,
I use the Bomber for what I guess you guys call "bashing" - scooting around the local scenery at a bit faster than walking pace looking for places to crawl.

Sadly we aren't blessed locally with epic rock outcrops or vast forests. :-(

After a fair few excursions I tried the ring and pinion reversal modification to reduce torque twist on steep climbs. The Bomber would have plenty of grip but would try and pull a corkscrew on such a climb. The reversal worked fairly well but eventually I found a sway bar cheap on the auction site, bought it and bolted it on.

The sway bar is the Axial AX31331 RR10 Rear Sway Bar Set described as "Soft". Crikey - if that is soft I'd hate to try an Axial marshmallow!

I need to measure the wire and do some sums to work out the rate of this part, suffice to say that even with the longer bar ends I find it limits rear articulation too much. Cornering is great but now it seems more prone to roll over on off-camber situations. I think this is because in the past the downhill wheel would force compression and keep the C of G low. Now the increased roll stiffness prevents this and presto! the Bomber is on it's roof and the dudes inside have headaches. :-(

A bit of background now before my next idea:
I have been off-roading Land Rover products for years and spent a lot of time tinkering with spring rates on coil-sprung vehicles to get the axle articulation to be as close to 50:50 as possible (results in the vehicle remaning nominally zero pitch/roll in cross-axle situations which is great for driver confidence and vehicle ability).

The coil sprung 'Rover suspension is hampered off-road by the front radius arm / panhard rod setup. I know this is a world away from 4-link front/rear but there are some commonalities.

It is very easy to get lots of travel out of the 'Rover 3-link rear, not so the front. I ended up running rear springs which are quite a bit stiffer than the front which results in the front being forced to comply (against the nature of it's geometry) and thus give a well-mannered twisty truck. In this case spring rates were 133 lb/in front and about 175/200 lb/in rear on a truck of 3000 lb kerb.

I think that the Bomber needs the same trick so I spent a little while tabulating the 14 x 90 and 14 x 70 spring options to see what might be worth trying, there are a few.

I need to sort out the sway bar rate as a benchmark but I think moving to a slightly stiffer rear spring and eliminating the limiting factor of the sway bar may result in a better behaved Bomber when scooting or crawling.

 

[SCREAMER]

I think a softer sway bar is your answer. Going stiff enough on the shock springs to abate body roll will be worse than having a sway bar that's too stiff because at least the sway allows even compression of both shocks at once. I've tried the VP sway, the DLux sway and the Axial sway bars. You are right, the Axial version is way too stiff. Both the VP and DLux sway are much more compliant and very tunable with link mount position options to dial them in to exactly what you like. Give those a look before swapping springs and making the whole rearend too stiff.

 

[mikebecher]

If your primary goal is to reduce torque twist you should also look into an underdrive diff gear set for the rear:Axial Racing - Axial Heavy Duty Bevel Gear Set - 43T/13T. This will also improve climbing and turn radius by effectively making the front wheels spin faster.

 

[SCREAMER]

Underdriving the rear has an adverse affect on handling at speed. It's great for crawlers but not so much on bashers. Same as dragging the rear brakes a little while going down the freeway, squirrelly :shock:

 

[mikebecher]

Underdriving the rear has an adverse affect on handling at speed. It's great for crawlers but not so much on bashers. Same as dragging the rear brakes a little while going down the freeway, squirrelly :shock:

Hey, maybe that's why I can't drive in a straight line ;-)

 

[nd4spdbh]

Can someone explain how the diff reversal helps out with torque twist? Or a link to a thread?

I get id have to run the motor n trans "backwards" from its originally intended but how does it help with torque twist?

 

[SCREAMER]

No, you just swap the position of the ring gear in the diffs from left side to right side. It was talked about in several threads, I don't have a link for each but basically it reverses the leverage being applied to lifting the front left wheel.

 

[nd4spdbh]

No, you just swap the position of the ring gear in the diffs from left side to right side. It was talked about in several threads, I don't have a link for each but basically it reverses the leverage being applied to lifting the front left wheel.

but wouldnt the driveline have to be spun in the opposite direction?

 

[SCREAMER]

Yes, with brushed systems, you simply swap positive and negative leads as long as you're running zero timing. With brushless systems you change direction in the ESC menu. You don't have to "run the motor n trans "backwards"".

 

[nd4spdbh]

Yes, with brushed systems, you simply swap positive and negative leads as long as you're running zero timing. With brushless systems you change direction in the ESC menu. You don't have to "run the motor n trans "backwards"".

Got that, thats easy and what i meant, easy enough for me to change the timing in the opposite direction and change the leads.

What im trying to wrap my head around is how this makes torque twist better by spinning the driveline pre axles in the opposite direction. Is this due to the offset design of the axles?

 

[Alexander_0_1]

^^I'm also not too clear on this. I get that if you reverse the throttle you can reduce torque twist, or at the very least have it affect the longer side of the axle, but what about axles with a centre pumpkin...

Also, people wanna reduce torque, but they use the most torquey gear set of the three (U/D gears), just cause someone is using the axle gears that are slowing down the wheels, doesn't mean it has less...force? I kinda think that if you use the faster gears then you should have less torque, or am I missing something.

I've always thought that torque, and speed, are like two kids sitting on a seesaw, and HP is the lever in the centre, now if you move the "lever" in either direction with the use of a different axle gear set, be it O/D, Standard, or U/D, then you either have more, or less of either torque, or speed, you can't have both, even if you use a giant motor/esc combo, torque and speed still abide by the same rules.

 

[mikebecher]

Underdrive in the diffs works by making it easier for the driveshafts to spin the axles. Imagine just a driveline connected to an axle through a very high ratio diff. It's going to be hard to turn the driveshaft but the axles will spin fast. That force required to turn the driveshaft is what produces torque twist.

 

[nd4spdbh]

I def get the underdrive Difs, that makes plenty o sense.

But the whole reversing the driveline rotation just IMO changes the torque twist direction.

I feel as though moving it the other direction would make torque twist worse as the driveshaft and axle would have more leverage on the left rear shock as its closer to the driveshaft side...

maybe im looking at this wrong.

I really just need to make up my own swaybar setup with some piano wire of the right diameter.

 

[SCREAMER]

It basically gives the effect of the axles having less leverage to twist the chassis And more leverage to twist the wheels. In one orientation, there is greater mechanical advantage between the trans and the chassis that it's bolted to than in the stock orientation. The same amount of force is being applied but it has less affect on lifting the axle.

 

[IntrepidMercians]

I calculated the rate of the standard soft anti-roll bar, results below:

Anti-roll bar
Axial soft 0.455 N/mm
Diameter 2.6 mm
Working length 122 mm
Lever length 78 mm

 

[EeePee]

The pinion gear is still trying to climb the ring gear all the same.

 

[DeathVirus]

I changed my gearing on my Bomber to 11/64 from a 14/64 and I still run the Vanguard 3150kv with a 3s lipo and 2.2 Hyraxes. My torque twist has gotten Significantly worse. I use the Axial “soft” rear sway bar too. I geared down to lower my top speed to handle turns better but also bc it gets so hot down here in Louisiana. What to do?

 

[DeathVirus]

Nvm I found the solution. Changed the motor timing on the castle sidewinder ESC from LOW to HIGH and wow that really fixed it. It runs so good now.

I guess bc the lower gearing gave it so punch but the high timing took a little bit of the punch away and gave it a little top end back. Now my ESC runs cooler bc of the low gearing while keeping the motor cool. After a solid 30mins of full throttle in the grass my temps were 126 ESC, 115 motor, and 86 battery. Ambient temp was 72.

 

[Jim85IROC]

Axial's soft sway bar was the right answer for me. Yes, it's a bit stiff, but that's why it works. There's still more than enough articulation for any crawling I get into, and by forcing the front axle to do most of the twisting, the truck is a lot more stable and predictable in hairy situations. I've experienced absolutely no negatives by adding the Axial sway bar.

 

[Steve g]

I did the same with my wraith, but used the arms from the front kit for the rear, as they are a little longer, making the sway bar a little softer for more articulation

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