Lunchbox CVA's

[Boothy 58]

Guys, my 84365 cva short shock set arrived today which are clearly designed for the lunchbox as the instructions show fitting to a lunchie/MP chassis. In the instructions it suggests cutting the rubber tube to create two 10mm bump stops and fitting to the front shocks only.

However it does not show this in the actual lunchbox manual in the cva option section??

It does seem to significantly reduce the travel of the front shocks so I am slightly bothered by it. What have others done? I am guessing it helps the front end with jumps?

Some pics of included instructions:-

[Shodog 1842]

If you don't the tires may rub the body at full compression

[Boothy 58]

Thanks for that, I have not done the body yet so had not spotted that May be an issue

[Boothy 58]

Wow, so I spent half of today messing with these along with doing a third shock mod and I am at a bit of a loss

It seems the spring rates are really weak and although they seem fine at the rear the front is a problem... They literally will not hold the front end up.

I have tried swapping out the springs for the original lunchbox ones but as they are longer I had to compress them and they were just to stiff, so I stole some from my holiday buggy rears as I am fitting cva's and ditching the friction dampers. They were ever so slightly to short so I fitted a spacer clip and they were ok once fitted...

The issue, aesthetics the springs have wider coils and just looked wrong against the rears, so I am back on the supplied (84365) springs with tension clips.

If I place the chassis down the shocks support the tub but if you press the tub down they only return about half way :S

I am thinking that when driving the front will lift naturally but I think it seems too soft for jumps and wheelies and will bottom out as soon as it comes down.

As this is my first lunchie are these the correct settings? The 84365 kit is the correct kit for the cw-01 chassis so I would of thought big T knew what they were doing but it seems far to soft to me.

So how do you guys have yours set? Any suggestions on springs if this is too soft?

Andy

P.s 3rd shock makes a huge difference

[wood5tock 864]

If it's any consolation the Absima after market jobbies on my Lunchie do a similar thing, when its up on the pit stand it all hangs OK. If you put it on all fours it dips a touch on the front. Then, as you say, give it a podge on the front and the nose drops and you physically have to pull it up for it to maintain it's original stance.

I have had a little run with it just inside with wheelies etc and nothing seems to be a miss however, also as you say when you start it up the weight naturally goes to the back and picks the front up (normal run not wheelie mode)

I wouldn't worry too much until you have given it a few runs to test, I'm not. Also don't forget when it comes to landing from a jump etc the tyres will take alot of the initial hit anyway. I haven't even done the third shock mod yet either

What we need is a true expert in 'bouncyness' to set both our minds at rest

[Boothy 58]

Haha! Cheers mate, maybe it's normal then? My worry is crashing down from jumps really, if the front dips too much and bottoms out I am thinking it will cause the forward rolls seen on a few vids?

We need the bouncyness experts

[Boothy 58]

I am tring to work out if firmer oil would help? I am guessing this would make them firmer to push down but if the springs are weak they would struggle more with the return?

Also what difference would the pistons make? I have fitted the two hole type, would the three hole ones make them softer still but help the return?

I am confused

[bromvw 744]

I could be wrong but in principal having three holes in the piston should help . Yes they will be softer in compression but because the oil can return faster they should decompress more quickly as the spring forces the damper to open ? That's as I understand these anyway

[Mokei Kagaku 2909]

I think it's a matter of impossibly getting the best of both worlds; good shock absorbing for handling improvement on any surface and for taking the worst out of landing after jumps. The short suspension travel, large unsprung mass of the gearbox and simple suspension design mean that the potential is limited anyway, regardless of how good shock absorbers you use.

Tamiya's choice of soft springs for the CW-01 damper sets is a clear indication that improved handling on bumpy surfaces was their main goal, whereas harder springs would be more suitable for running fast on flat surfaces and for jumping. And built according to the instructions, the dampers will work pretty well for that, and making changes will most likely only be beneficial if you want to focus on a different purpose, like for instance coming down after jumps. Harder springs, and landings will probably be less "painful", but handling on bumpy surfaces will surely suffer.

And don't worry, with extremely few exceptions, they mostly know very well what they are doing at Tamiya!

[Percymon 2185]

I looked at the original Pumpkin manual last night - at the back of the manula theres an additional section about adding CVA shocks, where it specifies to use the springs from the SuperShot.

When i get round to building my set of 84365s I'll check the included springs against the Supershot ones

I just threw a parts order at banzai again so put som CR-01 setting springs in the basket- they may fit, may not but only a few quid so worth a try

[GregM 1109]

If I place the chassis down the shocks support the tub but if you press the tub down they only return about half way :S

This setting is acutally fine on most cars. The car should sit somewhere intermediate between full compression and full droop. That way, it will be able to decompress the suspension on bumpy surfaces, allowing the wheels to keep in touch with the ground underneath - instead of just bouncing over the bumps.

On cars with dogbone-type driveshafts and double wishbone suspension, the desired ride height is achived when the dogbones are aligned parallel to the ground.

On another note: Single wishbone type suspensions, like found on the Lunchbox, apply friction resistance between the soft semi-pneumatic tire and surface underneath. This friction works against the damper's springs and chassis weight when compressing and decompressing the suspension.

Finding the sweet spot where the suspension is perfectly balanced, not over-/undersprung (spring stiffness and length) or over-/underdampened (damper oil weight and number of piston disc holes) can only be achieved roughly.

[speedy_w_beans 4277]

On another note: Single wishbone type suspensions, like found on the Lunchbox, apply friction resistance between the soft semi-pneumatic tire and surface underneath. This friction works against the damper's springs and chassis weight when compressing and decompressing the suspension. Finding the sweet spot where the suspension is perfectly balanced, not over-/undersprung (spring stiffness and length) or over-/underdampened (damper oil weight and number of piston disc holes) can only be achieved roughly.

I was going to say something similar to this. When I've checked Lunch Box / Mad Bull suspensions in the past, I'll leave one tire on the table and float the other tire in my hand so the friction is reduced. Plus, the Lunch Box has a lot of toe-in if built per the instructions, and that toe-in will cause the suspension to lift the front end while driving forward. You can see it just by pushing the car along by hand.

[Percymon 2185]

When you look at photos of lunchies quite often they look lower at the front - not always but quite often.

[wood5tock 864]

When you look at photos of lunchies quite often they look lower at the front - not always but quite often.

Tis true

[stevepi 7]

Have you tried the "hard" oil as well as the clips to preload the springs? Also make sure you get all the air out of the oil by pumping them, not like that :-) to make sure all the airs gone as this can also effect their performance.

Steve

[Boothy 58]

Cheers guys

All very helpfull, always learning with this hobby

[Boothy 58]

Spot on about the front lifting when pushed forwards

The only thing I have noticed is the imbalance in the tyres, you can feel the thing bob a little when pushed forwards on both front and rear wheels. It's not something I have noticed with other cars?

It may be the bigger tyres but my monster beetle does not do it, it's obvious when you spin the front wheels. So is that normal for a lunchie? I don't think I did anything wrong putting them on the rims as they look like they are sat down fine.

[speedy_w_beans 4277]

Yes, my Lunch Box has terrible tire imbalance. So does my Mad Bull. It's not so noticeable on the rear end where there's a lot of mass with the gearbox, but on the front with just the suspension arms, I can spin the tires by hand and see/feel the bobbing. The answer is to go full throttle so the vibrations go away!

There are balancing products on the market, such as putties and tapes. See here for examples:

http://www.amainhobbies.com/index.php/cPath/89_2049_254_282/n/Tools-Setup-Tools-Car-Setup-Tools-Wheel-Tire-Balancing

I imagine you could get the same effect with other household or automotive products too.

[Percymon 2185]

Well i cracked open a packet of the same shocks today.

I decided to build as per instructions at the rear of the lunchbox manual rather than the shock instructions, with a few alterations in bold..

At the rear i've gone for 3 hole pistons with the x3 spacer under the piston to limit stroke (shock kit and lunchie manual say 2 hole pistons and x3 spacer)

for the front i replaced X3 spacer (mentioned in the shock kit, but not in lunchie manual) with the much shorter x1 plus a 3mm o ring (there are spares in the shock kit so nothing else needed) but kept with 2 hole pistons. This has the effect of increasing down stroke, so increasing the overall shock length (albeit not as much as no spacers as per lunchie manual) . This won't make any difference to the static ride height/shock compression but will marginally help to keep tyre contact under mild acceleration (this is also helped by fitting the Pro-line tyre foams). Added the 10mm rubber tubing at the front

All four shocks currently sporting the medium and thickest preload spacers from the x parts trees.

Shock kit yellow light oil used on all four

When built the springs just about filled the gap from top cap to lower spring platform, but with the preload spacers they seem so far to be performing as i'd expect (off the vehicle)

It'll be a few weeks before they get attached to a chassis so can't comment on dynamic performance yet.

[Percymon 2185]

It'll be a few weeks before they get attached to a chassis so can't comment on dynamic performance yet.

Said shocks are now installed on my pumpkin project - I would say the front shocks compress ca 2mm once the body is fitted (no battery).

After pressing the chassis down, the shocks do return most of the way to their static position - in a running situation i'd expect them to fully return as the weight would be transferred to the rear on acceleration.

I didn't compare the spring to the supershot one sorry - mine seem to be as i'd expect so no reason to compare really.

Whether mine are different due to how i built them, or the different shock oil , or just different spring quality control I don't know.

Edit - having read back on the thread one important point is that you are not using any preload adjusters, which will have an impact on the spring rate / ride height....

[Skottoman 306]

I want to know more about this Pumpkin project! Do you have a thread?
Cheers,

Skottoman

[zomboided 374]

I want to know more about this Pumpkin project! Do you have a thread?

Cheers,

Skottoman

This! Looks very cool (and makes me want a Pumpkin...)

[Percymon 2185]

I want to know more about this Pumpkin project! Do you have a thread?

Cheers,

Skottoman

No thread Scott - as usual I buy one project and it turns into two. The shell above came from a used pumpkin. The wheels and TS-39 paint were in the spares box as were the white cvas. I just saw an opportunity to build up a white chassis, especially with HK prices for the chassis tub and d parts.

The old pumpkin chassis have been 'aged' and us having a different body fitted, one which is requiring some adjustments

[Boothy 58]

Hmmm, that's interesting then. Mine do have the preload spacers fitted, I have one of each of the widest ones on each shock. I have just stuck one extra of the next one down on the fronts but it has not really made a difference.

I built the rears in the same way as the fronts just without the rubber tube stops and they return fully, the fronts return about 50% of the way up from bottoming out on the rubber stops.

Which oil have you used Percy? The only difference I can see between the front and rear is that when pushing down on the rear the tyres move in the direction of rotation giving no resistance but on the front the tyres push outwards and must be dragged in as the springs de compress.

Andy

[Percymon 2185]

I'm using team associated 35wt oil all round