Fury first IRS version

[cerberarno]

HI PHers
My freshly bought Fury get this strange IRS version with only a bottom wishbone & the coilover on the top .Looks like a front geometry escort or some
Doesn't seem very ok to me,rigidity mustn't be massive.
My camber set up is different on each wheel & I fell that there are adjustment to do...
The top of coilover protrude behind the seats in a little tower ,not so nice
few q's
Is it known to be good or bad ?
How to setup the camber ?
Is there improvment to do ?

I have in mind to build a top wishbone & relocate the coilover lower , on the bottom one

thanks for help

[Paul Drawmer]

Google Chapman Strut - it's probably all quite good.

[Sam_68]

If it's Chapman strut, it was good enough for the original Elan, but to be fair it's not the best geometry out there.

Change the camber by moving the top mount in and out (unless the wishbone has been designed to be adjustable).

On Elans, the toe is made adjustable by cutting the rear link of the 'Z' frame that forms the bottom wishbone and introducing a turnbuckle.

[Mr2Mike]

OP says it has a lower wishbone, so surely can't be a Chapman strut? It sounds like the OP is describing a McPherson strut.

I thought the Fury was only ever designed to have either a live axle, or a double wishbone IRS using Sierra comonents and fabricated uprights, so this sounds a bit strange. A picture would be a big help.

[Sam_68]

Mr2Mike said:

OP says it has a lower wishbone, so surely can't be a Chapman strut? It sounds like the OP is describing a McPherson strut.

Only practical difference between a MacPherson Strut and a Chapman Strut is that the MacsStrut steers (unless locked in the straight-ahead position by means of a fixed toe control link) and the Chapman Strut doesn't.

In effect, if it has a Z-shaped lower wishbone, its a Chapman, whereas if it has a V-shaped wishbone and a separate toe control link replicating the steering trackrod, it can be considered to be a Mac. Arguably, in its purest form the Chapman strut had a V-shaped wishbone and used the driveshaft as a toe-control link, but that's real anorakism... the Elan didn't, yet even Chapman referred to the Elan as Chapman strut.

Camber adjustment remains the same whatever; obviously if it has the adjustable toe link of the 'MacPherson strut', you should use that for toe adjustment.

[downsman]

I've read a few books about the old Lotus Elan and owned one, and the rear suspension is basically a MacPherson strut.
It works Ok but there is a tendency to toe out if the driver lifts off in bend. Yet another reason to go in slower and to keep the power on

[Mr2Mike]

Sam_68 said:

Only practical difference between a MacPherson Strut and a Chapman Strut is that the MacsStrut steers (unless locked in the straight-ahead position by means of a fixed toe control link) and the Chapman Strut doesn't.

I thought the defining difference was that in the Chapman strut the driveshaft is used as the lower arm (with an extra arm for longitudinal support)?

[Sam_68]

Mr2Mike said:

I thought the defining difference was that in the Chapman strut the driveshaft is used as the lower arm (with an extra arm for longitudinal support)?

Yes, I agree (as above)... it is if you're a purist and take it's first implementation (on the Lotus 12, if my memory serves me correctly) as being the definitive one, but since Chapman himself referred to the Elan's rear suspension as 'Chapman strut', who are we to argue?

ETA: Sorry... you're quite right; I'd said a 'V' shaped wishbone + driveshaft above, hadn't I... you're right, wishbone not necessary; just a radius arm and driveshaft will do. Mr Chapman will be spinning in his grave at my suggestion that a redundant component was necessary.

Gratuitous suspension picture (Lotus 12):



If you're taking a similarly 'purist' approach, one of the defining characteristics of the original MacStrut patent application was that it used the anti-roll bar to provide the additional longitudinal location:



Geometrically, they're all the same, anway.

Edited by Sam_68 on Wednesday 21st December 18:38

[cerberarno]

here is the Fisher's doc



By the way how do I find a longer ratio for the sierra diff , adapted to the bike's box ?

[cerberarno]

I've just realised that my ex Jag E type had the same IRS system

I 'll try to sort the setting & check if all is ok concerning bolts & allignment
I def need to find some softer springs & this won't be easy cf the shocks
thanks for helped this is very instructive

The Fury wellcalled

[Sam_68]

cerberarno said:

I've just realised that my ex Jag E type had the same IRS system

It looks similar, but the E-type system works quite differently: the dampers do not act as locating 'struts' and instead the driveshaft acts as an upper 'wishbone' with an ultra-beefy lower wishbone making up for the fact that there's no proper wishbone or radius rod for longitudinal location at the top:




Geometrically it acts like a crude double wishbone system.

[Sam_68]

cerberarno said:

here is the Fisher's doc...

I'm having to squint a bit, but from that pic it looks like you can adjust both camber and toe by screwing the rose joints that connect the lower wishbone to the upright in and out.

cerberarno said:

By the way how do I find a longer ratio for the sierra diff , adapted to the bike's box ?

The usual suspects (e-bay, various specialist suppliers/manufacturers, occasionally the Locost group small ads, etc.). you're (probably) looking for a 3.14:1 Sierra diff (or maybe a 3.38). Type 'Sierra 3.14 diff' into Google and see what shows up.

[cerberarno]

Thanks Sam

But I think in the fury , the shafts are acting as control arms / wishbone to
the Shock wouldn't hold on itself this function
It musts apply a lot of side pressure on diff & spindle bearings
I guess in a sierra the diff isn't that much loaded with those huge trailling arms !
I will check all of that , I wanted an IRS fury for the improvment in handling compares to live axle but for instance I believe this is worst !!

[Furyblade_Lee]

I have not had a Fury for a few years, but you are correct there are 2 types of Fury IRS. The Sierra type current IRS and yours, the very first Fury IRS. My friends know a lot more about it that me, one had one with a Fireblade engine, but I am not sure about the specifics. Give Steve Hughes a call at FurySportsCars and he will tell you about it, he has built dozens and knows all about your version.

[one eyed mick]

Cerberano I would imagine you would need either a 3.9 or 4.1diff to let the bike engine sing esp in the higher gears, they are out there and can be found with a little resarch probably some one on here will be able to help .I have recently changed from a 3,37 to a 3 .62 in my RH 2.1 pinto ,it is now usable in all 5 ratios HTH

[Sam_68]

cerberarno said:

...I think in the fury , the shafts are acting as control arms / wishbone to
the Shock wouldn't hold on itself this function.

Is there just a single bolt at the bottom of the damper, where it mounts to the upright then? I must admit, this is what your diagram seems to show, but then the damper assembly also appears to show the twin bolt positions you'd expect to mount a strut to an upright and it doesn't appear to show any sort of radius arm at the top. There's no way that bottom wishbone looks beefy enough to resist the braking torque on its own? Is there any plunge on the driveshafts?

Any chance of a photo of your suspension with the wheel off, which would make it all clear?

one eyed mick said:

Cerberano I would imagine you would need either a 3.9 or 4.1diff...

DEFINITELY NOT!!

Do the calculations, by all means (use Google to look up the rear ratios for your engine, then feed them into one of the readily available gearing calculators you can download online, if you're not familiar with the calcualtions involved), but I'm pretty sure you'll find that with a bike engine this would give you stupidly short gearing... like flat out at 100mph with the engine screaming at 12K rpm in top sort of gearing!

Edited by Sam_68 on Thursday 22 December 12:54

[Mr2Mike]

Sam_68 said:

DEFINITELY NOT!!

Do the calculations, by all means (use Google to look up the rear ratios for your engine, then feed them into one of the readily available gearing calculators you can download online, if you're not familiar with the calcualtions involved), but I'm pretty sure you'll find that with a bike engine this would give you stupidly short gearing... like flat out at 100mph with the engine screaming at 12K rpm in top sort of gearing!

Edited by Sam_68 on Thursday 22 December 12:54

The BEC guys are always after the taller ratio Sierra diffs but they are relatively rare.

[one eyed mick]

ok 3.62 diff ,0.82 5th gear ,205 x50 x15 tires 6k rpm = 140 mph
3.9 """""" "" "" =130 mph
4.1 """ =125 mph
where does your 12k rpm at 100 mph coms from ?

[Arthur Jackson]

That looks like a standard 'Locost' type IRS with the exception of the strut, I'd be very surprised if the Sierra driveshafts are doing anything other than transmitting drive...!

[Sam_68]

one eyed mick said:

ok 3.62 diff ,0.82 5th gear,205 x50 x15 tires 6k rpm = 140 mph
...where does your 12k rpm at 100 mph come from?

From the overall 1.69:1 6th gear ratio of the OP's ZZR1100 bike engine.

As I pointed out, I was speculating/guesstimating on the effect of the short gearing, but since you labour the point, some slightly more accurate figures:

• Max rpm of ZZR1100 engine = 11,000
• Divide by primary reduction ratio of 1.637 = 6,719rpm
• Divide by 6th gear ratio of 1.035 = 6,492rpm
• Divide by your suggested 4.1 final drive ratio = 1,583 rpm x 60 minutes in an hour = 95,010 tyre revolutions per hour
• Divide by 874 revs/mile for a 205/50 x 15" tyre = 108 miles per hour.

With a 3.9 diff, you'd see 114 mph, but remember that's with the engine absolutely screaming its nuts off at maximum rpm.

With a 3.14 diff, you'd get a theoretical maximum speed in 6th gear, at 11K rpm, of 142mph. That's overall gearing of 12.9mph/1,000rpm in top, which is still very short by car-engined-car standards (modern cars tend to be in the region of 23-25mph/1000rpm in top, for relaxed cruising and fuel economy), but it's about as good as you can get with the available Sierra final drive ratios on a BEC.

Disclaimer: Figures for ZZR gearing and tyre revs. mile are from a quick Google and it's been a long day in the office, so somebody feel free to correct me if I've fked up the sums completely.