The Piazza shock absorber bible!

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archangel62
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The Piazza shock absorber bible!

Post by archangel62 » Mon Nov 09, 2015 10:00 pm

Hi all!

This article is for those who want their car to handle and ride well, as opposed to just lowering it and hoping for the best. Shock absorbers can make or break a car, and off-the-shelf budget gas shock absorbers are completely useless compared to a decent monotube gas or oil shock. Don't settle for something that calls itself sporty. Get the best for your car, and match the shocks front and rear, as well as to the springs.

When considering rear lengths, please consider that my car has an Australian Piazza diff (4-link, no torque tube). I can't tell you if the overseas/torque tube models will have the same shock mounts or lengths. I would assume so, but PLEASE CHECK FIRST.

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There are a few things you need to consider besides the part number!

- Valving! Shock absorbers use a bump (suspension compression) valving setting, a rebound (extension/after bump recovery) setting, and separate bleed valves which take the edge off of very harsh bumps. All three settings are a factor. Some schools of thought argue that rebound should be about double the bump setting. HBL rear shocks are about symmetrical, possibly to make up for comparatively softer rear springs. Bleed valves will depend on how much you like your spine, the quality of roads in your area and what you use your car for. If in doubt, don't guess, trust an expert. Many shock absorber companies (Koni, Bilstein) allow you to pay to have them re-valved, but it's not cheap.

- Extended length! Has your car been lowered? If in doubt, measure your rear shocks from the base of the pin at the top, to the centre of the eyelet at the bottom, when your springs are just about to reach full droop. This is IMPORTANT, Piazza rear springs would be highly prone to falling out if not held captive by the shock. Fronts most likely won't pose an issue, but it can't hurt to check. Standard rear shock offerings are around 515mm extended length, but mine needed to be 460mm or less. My standard springs were a LOT longer than my lowered rear springs, which measured 250mm free height. This is a guide, you should measure your car.

- Compressed length, if you're riding on bump stops or have collapsed or damaged bump stops, or if you're trying to match a shock from another car. If a shock absorber bottoms out, it will break in a hurry. I take no responsibility for what you do with this information. Some Piazza rear shocks use compressed lengths as long as 325mm, but as short as 291mm. Shorter is better - it means they're less likely to sustain damage. I've never needed to measure front as I feel the off-the-shelf offerings are suitable, whereas the rears simply aren't, due to their extended lengths.

- Layover or effective ratio. On our cars, the front ratio is probably around 66% due to their location along the upper arm. I've never measured, but Geminis are about 66% and eyeball to have similar geometry on the upper arm. At the back, our shocks use a layover of around 45 degrees. Depending on school of thought, this makes them around 50-70% effective. It's complicated ie roll may be different to bump. If you're considering custom valving, talk to the shock company about this.

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With that out of the way, I've researched part numbers from the world's leading shock absorber manufacturers for your driving pleasure.

Koni:

Off the shelf Piazza "red" sports shocks - valving is allegedly good for street and track, but the front part number is the same as a Gemini front (much lighter car) and whilst they're still amazing, they could do to be a little stiffer IMO. The rears are the same as a Commodore wagon live axle rear; the valving might be good, I haven't fitted them to find out.

Front Piazza/Gemini red: 80-2275

Rear Piazza/Commodore Wagon red: 80-2233SP1. Lengths are 311mm-514mm, TOO LONG FOR LOWERED PIAZZAS!

So what if I want a lower and tougher shock?

Front Piazza/Gemini yellow: 82-1886Sport - please note these are physically bigger in diameter and if your wheel gets close to the shock, these may not fit. Check clearance first!


Rear you can get re-valved and shortened for extra cost. Alternatively you can try finding something else suitable.

I had some discussions around the 8040-1277Sport[/b] to suit Volvo 1999-2006 S60, S80, and V70 2wd wagon. Length 456/294 (perfect for my lowered Piazza) BUT the mounting points on both ends need work. The lower bushing needs to be swapped out. Piazzas use a bushing with a 16mm hole; my Piazza diff has metal sleeves for it to mount on. The Volvo shock has a sleeve bonded in it, so the whole bush needs to be pressed out and replaced with the right bush. Furthermore the top pin has 25mm of M8 thread, then tapers to a wider pin - 18mm wide, which would need to be either lathed or ground down to suit the car, which has a ~15mm hole. This may be more trouble than it's worth. They are damped to 1800/750 - I don't know the unit of measurement so don't ask, but the Volvo has a similar layover so they might actually feel firm but suitable as is. I'll report back. Remember, bleed valves make a big difference too, and I have no idea what kind of bleeds they run or how to compare them.

Bilstein

These are "B6" monotube pressurised gas shock intended for street and track. I would estimate not a hardcore all out shock, but a good balance. They are allegedly valved by Bilstein, for a Piazza, which is more than can be said for the Koni's, although I still went for Konis due to lengths, and you can always get both Koni or Bilstein re-valved at a cost. Valving may differ significantly based on springs/driver/roads anyway.

Piazza front: 24-008839 - these list an "F parameter 261/108" - I assume this is valving but I don't know the unit of measurement so don't ask!

Piazza rear: 24-003179 - there is no R parameter listed. They're "the same length as a standard shock" - but the distributor didn't know the length, so there's a chance they may not suit lowered Piazzas. You can have them shortened at an extra cost. The extended length can be shortened using an internal spacer which just limits full extension, apparently this is easily done by the factory.

A friend on the Piazza FB group, Daisuke-san, has suggested that UBS-UCS Bighorn front shocks can be used for the front of a Piazza if the lower bushings are changed. If Piazza items are not available, these could be an option. I would suggest speaking to a Bilstein distributor first to check the compressed length, just in case.

Spax

In my humble opinion, Spax don't quite have the reputation that Koni and Bilstein have, but I've heard they're still very decent. I'd suggest asking about on-car adjustment, as neither Bilstein nor Koni truly have this, and it could set them apart. Thanks to IPTOC for tracking down the Spax information for me!

Piazza front: G165, max length 393.3mm, min 259.9mm, stroke 133.4mm.

Piazza rear: G169, Max length 469.2mm, min 295.8mm, stroke 173.4mm. These will suit some but not all lowered Piazzas. They're about 10mm too long for my springs, but may suit others and are a hell of a lot better in length than the standard Koni listing.

Spax should also have a lowered option for the Piazza, but I'm not sure on the part numbers.

==============================================

But Drift Panda, I hate reading and want a simple answer that's entirely at my own risk! What should I buy?

I've had good experiences with Koni's in other cars, but you will need to check lengths and possibly get the rears shortened. In Australia, for rough 2015 prices, fronts at around $350-400. Rears would be around the same in standard trim, if you have them shortened and re-valved it's around $622/pr.

If you have a slightly lowered car but don't have any brand loyalty, check your extended rear heights and consider Spax. They're the simplest off-the-shelf solution for a lowered Piazza.

If you have a standard height car, any of the shocks listed would be great for you.

If you want what is arguably the best shock available, based on [non-Piazza specific] lap times and the glowing recommendations of rally drivers, get the Bilsteins, but if your car is lowered, you will need to have the rears shortened. They will probably be the most expensive option.

Aren't you glad this damn Gemini drivin' filthy drifter got into Piazzas? :heart: hahaha.
Last edited by archangel62 on Wed Dec 02, 2015 12:22 pm, edited 2 times in total.
Indigo - '76 TX Gemini sedan, G180W+T project,
Abigail - '81 TE sedan, white, G180W ITB project,
New Hotness - TG Gemini drift car, orange, 4ZE1+T
Tardis - 1986 Piazza 4ZC1-T, black, forged, 136rwkw @13psi
Coupe - TX coupe grip car, "do it later", G180W+twin carbs
Trevor aka Jimmy's Gem - Grandpa-spec TD
BA Falcon - Tow car

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IPTOC
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Post by IPTOC » Tue Nov 10, 2015 4:34 am

No problem, anytime! (I am Giorgetto....!)
It may be of interest that Spax DO offer shorter versions of both G165 and G169 as catalogue options, specifically for lowered cars!
1988 Isuzu Piazza HBL Auto - Ebony Black
1988 Isuzu Piazza HBL Manual - Romanesque Silver
1851 Cellar chock full of Isuzu spares!!

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archangel62
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Post by archangel62 » Tue Nov 10, 2015 9:50 am

Thanks for that! I've just edited my original post :D
Indigo - '76 TX Gemini sedan, G180W+T project,
Abigail - '81 TE sedan, white, G180W ITB project,
New Hotness - TG Gemini drift car, orange, 4ZE1+T
Tardis - 1986 Piazza 4ZC1-T, black, forged, 136rwkw @13psi
Coupe - TX coupe grip car, "do it later", G180W+twin carbs
Trevor aka Jimmy's Gem - Grandpa-spec TD
BA Falcon - Tow car

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archangel62
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Posts: 232
Joined: Sun Aug 14, 2005 7:07 pm
Location: Adelaide, South Australia

Post by archangel62 » Wed Dec 02, 2015 12:23 pm

I have edited my post after not having much success with the Volvo option! I still think it would be doable but may cost more and/or be more difficult... The distributor I've been dealing with wasn't keen on the idea so I'm still considering which I'll go with!
Indigo - '76 TX Gemini sedan, G180W+T project,
Abigail - '81 TE sedan, white, G180W ITB project,
New Hotness - TG Gemini drift car, orange, 4ZE1+T
Tardis - 1986 Piazza 4ZC1-T, black, forged, 136rwkw @13psi
Coupe - TX coupe grip car, "do it later", G180W+twin carbs
Trevor aka Jimmy's Gem - Grandpa-spec TD
BA Falcon - Tow car

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