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Rally Suspension

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On 23/02/2018 at 1:25 PM, NVZEE said:

Here’s another car to use for ideas, Dylan.

https://www.silverstoneauctions.com/datsun-240-z

Basically that Z is a tribute car not a replica, there are no claims in the sales blurb that the original car was replicated mechanically. I'm surprised that Alan did not jump on it.

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7 hours ago, 260DET said:

Basically that Z is a tribute car not a replica, there are no claims in the sales blurb that the original car was replicated mechanically. I'm surprised that Alan did not jump on it.

Probably because words fail me. Either that or because I'm on a weather-related go slow after a couple of days of 'Beast From The East' blizzard conditions here in Ye Olde Englande.

 

From the sales blurb: "This evocative 240Z is a super replication of the Nissan works car that was driven by Rauno Altonen and navigated by Jean Todt in the 1972 Monte Carlo rally finishing in a very creditable third place."

"Super replication"? It's actually nothing like it. Nothing. Not unless you count red and black paint, a kids art project idea of a carnet number plate and some '5' stickers as 'close enough'...

They credited Goertz in the blurb too. That's a top-scoring double fail in Z History Bingo. House!

Cars like this are built to purpose, and that purpose is modern historic 'regularity' type events rather than stage rallies. Compliance with modern safety regulations and a bias to practicality is enough to make such cars stray a long way from true period Works specifications. I'm sure it's a good car, but claiming "super replication" of a real period Works car is well wide of the mark. 

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I'm very happy that JDMjunkies has invested the time and work needed to put together his really helpful article on S30 suspensions. It certainly helped me a lot. I've had my 240Z prepared for long distance rallying and it has an FIA HTP, with the work that lies behind that done.  The suspension uses adjustable base spring platforms, and is modified with Bilstein inserts. Both the struts and the dampers were modified by Gartrac (https://www.gartrac.com/)  The springs are 2.25 inch OD, front spring rate is 185lbs/in and rear 225lbs/inch. Lengths are 12 in (305mm) front and 14 inch (356 mm) rear.  The car has done about 10,000 regularity rally miles with this setup, with one damper rebuild. But now the whole system including the insulator mounts, top bearings and bottom mounts are showing wear.

Recently I weighed the car on Proform 7000 lb wireless scales.  This is the result for the car with driver but no passenger aboard (I know, I know but full roll cage, extra electrics and no weight reduction because the marketing department thinks it looks good) all in kg:

image.png

image.png

I must admit that the 80kg heaver front left than right and the 46kg heaver rear right than left was difficult to understand. The car is left hand drive so some of the front difference must come from the driver, the steering console/column, pedal box, plus the fact the carbs and manifold are on that side. As to the rear there is a built in fire extinguisher behind the pax seat. and the fuel tank is 'taller' on the pax side and the fuel pumps are also there. Still.....

However taking these figures to be correct then with symmetrical spring lengths the car will not sit level.  I assume there was always a weight difference left to right which is why the service manual shows different, as commented by JDMJunkies,  front spring lengths each side (on page FA-20 on my copy) at 373.5mm LH and 386 mm RH uncompressed (note opposite heavier side to mine) to give an identical 201mm 'installed height'. The rears are shown identical. I guess that even if the lengths - or adjustable bottom mounts are set to bring the car level, the behaviour will be different on each side if the springs and dampers have to deal with significantly different weights on them, although with different lengths at least the spring travel will remain the same on the heavier side.

So I'm trying to find out what to do.  I'm looking at short term fix of fitting Eibach springs which have rates similar to the existing, but an inside diameter of the springs of 76mm, which I've been told 'are better'.  But what I'd really like to do is redo the suspension from first principles. That is deriving the unsprung weights by weighing, work out the suspension frequency with different spring rates, and chose an appropriate damping rear in compression and rebound. Of course all this could be short circuited if I could get the information for the works cars in period, which must be closer to correct than anything I can calculate.

So if anyone just happens to be sitting on this info and would share it, there is at a good meal with drinks waiting here in Switzerland

 

Edited by nickmaris

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17 hours ago, nickmaris said:

Of course all this could be short circuited if I could get the information for the works cars in period, which must be closer to correct than anything I can calculate.

So if anyone just happens to be sitting on this info and would share it, there is at a good meal with drinks waiting here in Switzerland

The suspension specifications for Nissan's Works 240Z and 260Z rally cars - as used in period - are a moving target. They changed for every major event, according to the nature of the event but also with a natural evolution of improvement.

So, for example, 1970 RAC Rally specs were different than 1971 Monte Carlo Rallye specs, and 1971 East African Safari Rally specs were different again, and so on.

I think your Gartrac-built Bilstein monoshock setup is getting close to ideal for the nature of event you are taking part in. I have a very similar Gartrac/Bilstein set myself. Some very successful cars have used an almost identical setup and you just need to fine tune with rates. I think if you go back to first principles and build something else from scratch you might well end up with something fairly similar to what you've already got.

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Hi - of course you're right.  Still say Monte Rally specs would probably be closest to the kind of use my car gets.  I was under the car today, measuring the rear road clearance (and so indicating ride height?)per the service manual which is given "at the transverse link mount lower end" this is ambiguous - could be the outboard end of the lower wishbone/transverse link or it could be the inboard end where it connects to the cross member. Anyway they give 261 mm without load.  I got 170mm outboard and 190mm inboard within +/- 2 mm or so. So if my measurements are correct my setup is  lower than stock despite running 185/70 R15 tyres. This with 7 litres of fuel and a spare tyre and jack but nothing else in the car.

I'd very much like to have a more comprehensive comparison of our two cars.  Btw -have you looked at Tein suspensions? 

Nick

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Don't quite understand why what the factory used back in the day, way back in the day, is still apparently considered to be the ultimate. There are successful Z cars around of recent build that have been built with what works now.

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On 5/14/2019 at 8:40 AM, 260DET said:

Don't quite understand why what the factory used back in the day, way back in the day, is still apparently considered to be the ultimate. There are successful Z cars around of recent build that have been built with what works now.

I don't think anyone is saying that. On the other hand, some people seem happy to dismiss factory settings and data without even knowing what they are.

It's all useful. And when you are restricted to period-correct and/or FIA homologated parts then the parts that the factory used in period are far more relevant than any fancy remote-reservoir WRC type struts. Personally speaking, one of the things I like about owning old cars is the fact that they are old. Period tuning parts appeal to me. I don't necessarily care about "what works now", and I certainly won't be fitting that new inboard rocker arm design rear suspension system to any of my cars. Yes we all have to be pragmatic - I am pretty much forced to use modern tyres, oils and fuel in my cars - but a '32 coupe with an Ardun headed flattie is much more my cup of tea than a '32 coupe with an LSX crate engine, even if the LSX is "better"...

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I've checked over the 240Z that won Bejing-Paris a couple of years ago, it was basically a standard car enhanced by using technically superior materials and with a ferocious attention to detail, something that Japan would approve of. It's not always about using advanced systems, in this case it was just about building a near perfect car without changing any of the original systems. Which in itself is an enormous tribute to the original design.

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1 hour ago, 260DET said:

I've checked over the 240Z that won Bejing-Paris a couple of years ago, it was basically a standard car enhanced by using technically superior materials and with a ferocious attention to detail, something that Japan would approve of. It's not always about using advanced systems, in this case it was just about building a near perfect car without changing any of the original systems. Which in itself is an enormous tribute to the original design.

Interesting that you should cite that car. I shared some correspondence with John Coffey when it was being built, as he was interested in period data as well as reference rates for modern Bilstein monotube type struts, which he chose to use for the car.

Of course, the P2P event is something quite different to the period special stage rallies like the RAC, Monte and Safari. They were pretty brutal by nature and highly competitive. Real car breakers. In some events the Works team were changing all four corners of the car more than once during servicing. 

 

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5 hours ago, HS30-H said:

Interesting that you should cite that car. I shared some correspondence with John Coffey when it was being built, as he was interested in period data as well as reference rates for modern Bilstein monotube type struts, which he chose to use for the car.

If you're referring to the car that John Coffey built, I don't believe that's the car that won the event, and 260DET is likely referring to a different car, as IIRC, the winners were from Australia.

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On 5/12/2019 at 8:05 AM, nickmaris said:

I'm very happy that JDMjunkies has invested the time and work needed to put together his really helpful article on S30 suspensions. It certainly helped me a lot. I've had my 240Z prepared for long distance rallying and it has an FIA HTP, with the work that lies behind that done.  The suspension uses adjustable base spring platforms, and is modified with Bilstein inserts. Both the struts and the dampers were modified by Gartrac (https://www.gartrac.com/)  The springs are 2.25 inch OD, front spring rate is 185lbs/in and rear 225lbs/inch. Lengths are 12 in (305mm) front and 14 inch (356 mm) rear.  The car has done about 10,000 regularity rally miles with this setup, with one damper rebuild. But now the whole system including the insulator mounts, top bearings and bottom mounts are showing wear.

Recently I weighed the car on Proform 7000 lb wireless scales.  This is the result for the car with driver but no passenger aboard (I know, I know but full roll cage, extra electrics and no weight reduction because the marketing department thinks it looks good) all in kg:

image.png

image.png

I must admit that the 80kg heaver front left than right and the 46kg heaver rear right than left was difficult to understand. The car is left hand drive so some of the front difference must come from the driver, the steering console/column, pedal box, plus the fact the carbs and manifold are on that side. As to the rear there is a built in fire extinguisher behind the pax seat. and the fuel tank is 'taller' on the pax side and the fuel pumps are also there. Still.....

However taking these figures to be correct then with symmetrical spring lengths the car will not sit level.  I assume there was always a weight difference left to right which is why the service manual shows different, as commented by JDMJunkies,  front spring lengths each side (on page FA-20 on my copy) at 373.5mm LH and 386 mm RH uncompressed (note opposite heavier side to mine) to give an identical 201mm 'installed height'. The rears are shown identical. I guess that even if the lengths - or adjustable bottom mounts are set to bring the car level, the behaviour will be different on each side if the springs and dampers have to deal with significantly different weights on them, although with different lengths at least the spring travel will remain the same on the heavier side.

So I'm trying to find out what to do.  I'm looking at short term fix of fitting Eibach springs which have rates similar to the existing, but an inside diameter of the springs of 76mm, which I've been told 'are better'.  But what I'd really like to do is redo the suspension from first principles. That is deriving the unsprung weights by weighing, work out the suspension frequency with different spring rates, and chose an appropriate damping rear in compression and rebound. Of course all this could be short circuited if I could get the information for the works cars in period, which must be closer to correct than anything I can calculate.

So if anyone just happens to be sitting on this info and would share it, there is at a good meal with drinks waiting here in Switzerland

 

Nothing weird going on here. You have adjustable spring perches so you just need to corner balance the car, preferably laden to race spec. Looks like it has a 49% front and 51% left distribution as it sits so you should be able to get within 18kg at 50.0% corner balance. Either raise the RF and LR, lower the LF and RR, or a combination of both.

image.png

 

Note: you can't adjust Left % or Front % when corner balancing, that's based on the CG of the car, but you can change the diagonals. The diagonals in your measurements are off by 5% which tips off that a corner balance will take care of most of your worries.

Edited by LeonV

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Thanks for that very helpful guidance.  My 'adjustable' perches have frozen solid (exactly 2 year un-adusted) but as soon as they are freed, I'll follow your suggestions. Do you have guidance on ride heights and where to measure them?

 

with best regards

 

Nick

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12 hours ago, nickmaris said:

Thanks for that very helpful guidance.  My 'adjustable' perches have frozen solid (exactly 2 year un-adusted) but as soon as they are freed, I'll follow your suggestions. Do you have guidance on ride heights and where to measure them?

 

with best regards

 

Nick

Hi Nick, I usually measure from the rocker or pinch seam to make sure there's some rake in the body for aero purposes. These are measured before, during, and after the corner balance on a leveled-out 4-post alignment rack. Make sure the car is level when doing the corner balancing and the wheels are allowed to settle after lowering from the jacks or else you'll be chasing a moving target.

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On 5/18/2019 at 5:36 PM, 260DET said:

I've checked over the 240Z that won Bejing-Paris a couple of years ago, it was basically a standard car enhanced by using technically superior materials and with a ferocious attention to detail, something that Japan would approve of. It's not always about using advanced systems, in this case it was just about building a near perfect car without changing any of the original systems. Which in itself is an enormous tribute to the original design.

And a second go https://www.facebook.com/P2Pcar86/?tn-str=k*F

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