Shock length question - FF02 and similar

[Mad Ax]

I was doing a search for "FF02 shock length" both here and on the greater web and struggled to find a good consensus.  I've found posts that said "shocks for TT01 or M-chassis will work" - yet TT01 and M-chassis have different length shocks.  I've just finished converting an M03 to FF02 by fitting TL01 arms and a 3Racing chassis extension and want to fit some good shocks for racing.

Currently it is wearing some CVAs that I think came from a TA02T truck.  Fully extended, they are about 63mm in length, but at the front they have to compress to 60mm to fit and the rear compresses to 56mm.  If I use these I will rebuild them with a spacer to reduce overall length.  I have just fitted a set of 55mm TRF shocks from my TL01LA and the rear looks perfect, but the front looks to be slightly too short.  As in - the rear wishbone is extended a little (as you'd expect with a touring car lifted from the ground) but the front wishbone is compressed very slightly off horizontal.  I can understand tuning a spring so the wishbone is horizontal at sag, but this one won't even go horizontal when the wheel is tugged down.  (I forget if there is a spacer in the TRF shock to limit shock length - if TRF shocks will go to 60mm, this might be the answer).  With the chassis at rest, the ground clearance / ride height is visibly lower at the front.  It seems wrong to me that a standard car (even a parts-bin special) would have different shock lengths front to rear, and furthermore, would need different shock lengths to other cars of the time.

This morning I measured some other touring cars to see what length shocks were installed (lengths taken centre-to-centre of the mounting eyes with shocks at full extension).  Note that most of these cars have been modified at some point so there is a possibility the shocks have not been built to book specs.

FF01 race car, Tamiya alloy shocks: 56mm

TB01 Rally spec, Tamiya CVAs: 62mm

TA02 Rally, Tamiya CVAs: 55mm

TL01 Scale Truck, Tamiya CVAs: 60mm

TL01LA race car, Tamiya TRF: 55mm

M03 race car, Tamiya TRF: 50mm

M03 Rally car, 3Racing shocks: 50mm

TT01 shelfer, Tamiya CVA: 50mm

Unfortunately my TT02D and my TA03F are hidden away at the back of the storage area and I don't have time to dig them out to measure.  I think the TA03F is still wearing vintage Tamiya alloy shocks and it would be interesting to know their length.

As far as I can tell, my car needs a 60mm-ish shock at the front and a 55mm shock at the rear.  Is there a TRF or other good alloy shock I can buy that will assemble to these lengths, or will I have to stick with CVAs?

[ThunderDragonCy]

@Mad Ax The kit FF02 setup is same as the TL01. The reason for your confusion is "kit vs racer". The kit uses 55mm super mini length cva shocks, but they give quite a lofty ride height. If people are racing (and usually restricted on mods they can make like Iconic rules) the simplest way to get the car to a sensible track ride height is to run m-chassis 50mm shocks. This just drops the whole chassis into that 5-7mm ride height area without having tonnes of droop. 

[ChrisRx718]

This is interesting...

I have an FF02 shelfer and just measured the front dampers at 55mm eye-to-eye. I wouldn't want them much shorter than this - the suspension arms and driveshafts are pretty much horizontal.

However; on the back I have the same 55mm setup and I suspect these would be better suited to 50mm, as the arms are sitting at a slightly raised angle. Compressing them until they're 'flat' with the horizontal and re-measuring, 50mm would be spot-on.

So 55mm front, 50mm rear?!

[svenb]

I think the low friction damper set states 55mm front and rear, medium spring spacer front nothing rear, 1?hole piston front 3 hole rear. 

Would need to double check. 

[Mad Ax]

On 6/23/2020 at 9:47 AM, ChrisRx718 said:

This is interesting...

I have an FF02 shelfer and just measured the front dampers at 55mm eye-to-eye. I wouldn't want them much shorter than this - the suspension arms and driveshafts are pretty much horizontal.

However; on the back I have the same 55mm setup and I suspect these would be better suited to 50mm, as the arms are sitting at a slightly raised angle. Compressing them until they're 'flat' with the horizontal and re-measuring, 50mm would be spot-on.

So 55mm front, 50mm rear?!

This is very interesting.  I was starting to wonder if I'd made some mistake in assembly, or if the FF02 used different front arms.  The rear (with 55mm shocks) looks exactly as I'd expect it to look, but the front seems too low (at least for a stock setup).  However I have just gone back to my PDF copy of the Absolute FF02 Book of Rules for the 306 Maxi and the shock shaft length for the stock friction shocks are labelled as 27mm front and 23mm rear.  So, it does look that the extended length for the standard shocks should be 4mm different from front to rear.

I'll have another look later with some 55mm shocks and see if I'm happy with the angle of the front wishbones.  If so, I can use a 55mm shock set and install spacers to level out the rear end.  If I feel I need a little more travel at the front then I can stick with the CVAs.  Ultimately I'd like to have TRFs for racing but in all seriousness I'll race it 3-4 times this year and I'm really not fast enough to tell the difference between CVA and TRF.

[ChrisRx718]

Every day is a school day!

It's going to bug me now that my 'shelfer' 306 Maxi is potentially incorrect; sporting 55mm dampers all-round. But if I correct it now, the ride height will be wrong. I can't simply change the body post as I was a fancy pants and installed them horizontally to allow for a still-not-painted-because-I'm-lazy cockpit set:

[ThunderDragonCy]

@ChrisRx718 Liked because 306 

[Mpsiweb]

here you have a shock length diagram :

 

[ChrisRx718]

2 hours ago, Mpsiweb said:

here you have a shock length diagram :

Unfortunately that was written before the FF02 was released, so it refers to the FF01 which was the only FF chassis at that time.

I remember looking into this and as @Mad Ax also spotted; the FF02 manual states the rear damper shaft lengths are 4mm different (shorter on the rear), so it makes sense to run 55mm front, 50mm (or 51mm) rear.