Going Independent rear suspension

Road-race engines and ancillaries - general discussion
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hansmezger
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Going Independent rear suspension

Post by hansmezger » Fri May 02, 2014 2:07 pm

Greetings from Istanbul everyone!

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I have just acquired my 131 Mirafiori 2.0. And I'm currently in the phase of converting it to Abarth straddle replica for road and trackday applications.
I'm a sucker for proper handling and I'm increasing the rigidity of the chassis as much as possible! For weeks I have been scratching my head to go independent on the rear axle.
I have seen a lot of guys using BMW rear end. Which is superb hence the BMW parts here are very cheap and easy to get! But right here I'm having difficulties to understand.

By adding the bmw rear diff,arms and axles I'm changing the overall width of the rear end. So thus meaning a wider rear end? If so the car should handle not very well and resist initial turn-in phase hence the fronts being much narrower compared to the backs.

I would love to here your opinions regarding this issue and how you guys have solved it. Any special advices for which bmw rear setup to use would be great as well!

thank you,
Demir
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Guy Croft
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Re: Going Independent rear suspension

Post by Guy Croft » Fri May 02, 2014 3:47 pm

On tarmac a live rear axle is way better than IRS

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Will01
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Re: Going Independent rear suspension

Post by Will01 » Fri May 02, 2014 5:54 pm

I am with Guy on this, there nothing wrong with using a live axle. I also think it would ruin the original.Fiat dynamics which made the car so good and rewarding If you fitted IRS.
There is plenty you can do with the live axle, best way is to get as much weight as possible off the axle itself, although hard to do. Fit some good hd rubber or pu bushes and new springs and adjustable dampers.
If you still need to improve things you have many options for controlling sideways movement. Dont these cars have panhard rod as standard?
If the escort boys can make the mk1+2 escorts fly and handle well, then it will be easy to do the same on this Fiat
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hansmezger
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Re: Going Independent rear suspension

Post by hansmezger » Fri May 02, 2014 9:22 pm

Very Interesting! For years we have been thought that independent rear suspension is far superior to the live axle... Turns out it's not:)

Will you mentioned about getting out as much as weight as possible from the rear axle. Since I don't have the slightest idea of the workings of live axle. I'm gonna do my homework tonight. Does taking weight from the axle help getting less unsprung mass? If so its very doable in my list:)

thank you!
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Will01
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Re: Going Independent rear suspension

Post by Will01 » Fri May 02, 2014 9:59 pm

Live axle is very heavy and has high unsprung mass. It gives the suspension alot of work to do. There are a few things you can do to take the weight off the axle. Just think brakes, rear arb location, lighter wheels etc. It is however hard to take alot of weight out of a live axle and very expensive. In some cases it is even harder if strengthening is required.
You also want to control the axle sideways movement as much as possible, this makes the rear more compliant and predictable. The better bushes will give more feedback and help reduce play. On live axles with leaf springs it is even more important to use decent bushes to stop twisting of the leafs which can cause weird axle movements.
There are loads of ways to tune a live axle for different requirements, they are very simple and work well for the money. Its a huge advantage to keep camber and toe under full control, which the live axle does effectively. They are great on tarmac surfaces because you dont need to worry too much about excessive movements like you might see off road e.g. Sudden Bump situations. So the added advantages of irs are reduced. Anyway why do you want to make a simple car overly complicated. Hope this helps slightly
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hansmezger
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Re: Going Independent rear suspension

Post by hansmezger » Sat May 03, 2014 11:12 am

Thank you for your reply's. I stoked about the car next up is the locking diff and lots of oversteer hopefully:)
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Will01
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Re: Going Independent rear suspension

Post by Will01 » Sat May 03, 2014 6:10 pm

A proper diff is a very good idea. Either a plate type locking diff or torque biasing diff will help make the rear even more controllable in the corners and alot more fun.
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