Hello gents, I just got my book and was having a look through and was a bit disappointed to see that the book uses a solid rear axle. I was intending to use wishbones and a bmw rear diff. Has anyone done this? I'm no engineer and wonder if its hard to change the chassis to make this happen.

Cheers!

Hi you need to have second book haynes roadster uses ind back end

whats the real advantage of IRS over Live axle in these types of cars...........

mine is Live axle and i cope just as well as IRS

Live axle better at drag style sprints but more unsprung wieght irs bracks away later on corners main advantage is cost of lsd with irs

so stick with the irs? i want this thing to shred corners and peel the tarmac off the straights. I'm not much for drag racing. that's why i'm leaning toward the supra engine

On smooth roads the live axle works very well indeed, it's when the going gets rough that IRS has the advantage.

Live axles get a bad rap because of 70's rep mobiles running cart springs.

A well located coil sprung live axle with properly valved shocks is a lot better than a badly set up IRS on most surfaces you'd be prepared to go quick on.

See Mr Procomp's cars for a good example.

I agree with the above. Procomp setup my live axle, and it is fantastic! More compliant and smoother ride than I ever thought possible. I took a mate out for a whole day across the Cotswolds, and he said it rides better than his tintop (Puma). The biggest drawback as far as I can see is the stigma of having a live axle!

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Originally posted by Mr. Wibble
I'm not much for drag racing. that's why i'm leaning toward the supra engine

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Originally posted by iank... A well located coil sprung live axle with properly valved shocks is a lot better than a badly set up IRS on most surfaces.

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Originally posted by kb58
My brother's Super Stalker has a live axle in it. He drove me down a road that had some bumps in in, and hitting them was like someone taking a hammer to the bottom of the seats.

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The scope for getting a lot of things wrong on a home built car compared to Mr Ford, Mr Vauxhall etc is huge, but there are thousands of people that are doing so.

I am not disagreeing with you, it's just that I am willing to side with pure facts quicker/easier than "what-could-be's"... If you know what I mean!

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Originally posted by MikeRJ
FWIW, I agree with iank; the scope for getting a home spun ISR system wrong is vastly larger than hanging a live axle off the car. That's not a reason not to use IRS of course, but just something to be aware of if you are designing your own with limited experience.

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just a thought, but what BHP are live axles and IRS driveshafts able to cope with? A 3ltr twin turbo has to be pretty big BHP and Torque?

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Originally posted by Dangle_kt
just a thought, but what BHP are live axles and IRS driveshafts able to cope with? A 3ltr twin turbo has to be pretty big BHP and Torque?

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Supra engine

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Originally posted by Steve Hignett
The scope for getting a lot of things wrong on a home built car compared to Mr Ford, Mr Vauxhall etc is huge, but there are thousands of people that are doing so.

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Originally posted by kb58

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Originally posted by iank... A well located coil sprung live axle with properly valved shocks is a lot better than a badly set up IRS on most surfaces.

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I read this all the time and never cared for it. Saying that something well done is better than something poorly done isn't a reason. So, if poorly-educated people make bad engineers, therefore people should not be engineers?

My brother's Super Stalker has a live axle in it. He drove me down a road that had some bumps in in, and hitting them was like someone taking a hammer to the bottom of the seats. I then had him drive my IRS mid-engine Mini down the same road and he was shocked that he could barely feel the bumps at all.

IRS versus live axle can be debated either way on the track, but for everyday street driving, nothing beats the ride quality of IRS.

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The reality is that the car will end up weighing around 750 kg what with the extra weight of the Supra engine and drive train together with the extra reinforcing of the chassis that the weight and power of the motor and drive train will necessitate.

This extra weight will significantly impact on unsprung weight so a live axle becomes a lot more practical.

Then comes the very nature of the motor which is one of extremely high torque which gives a feedback loop of extra weight and bigger tyres which means more traction which requires a stronger and heavier diff and gearbox which means more weight hence more traction ad infinitum.

The above means that you are going to have to apply your mind whichever way you go - whether it is independent or live axle.

With the independent option you will need something that minimises camber change with squat if you want to retain traction for all out acceleration but gives the right camber change with roll for cornering - not that easy to do.

Have fun - you've got a lot of thinking to do if you want a car that is balanced in all aspects and a joy to drive and not just something that spins its wheels with every gentle nudge of the throttle and ploughs straight on in the corner or gives you instant over steer each time your foot approaches the accelerator in a corner.

Talking of balance - you will have to get front - rear weight balance right as well.

Well gents after absorbing all of your sagely advice i've decided to use the nissan SR20det. i get considerable weight savings and I've been told that for a 4 cyl it is quiet torqie. and its easy to tune up. replacement turbo's won't require i sell a kidney on the black market

from a slightly saddened but grateful Mr. Wibble

^^^ An excellent choice

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Originally posted by Mr. Wibble
Well gents after absorbing all of your sagely advice i've decided to use the nissan SR20det. i get considerable weight savings and I've been told that for a 4 cyl it is quiet torqie. and its easy to tune up. replacement turbo's won't require i sell a kidney on the black market

from a slightly saddened but grateful Mr. Wibble

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Live axles work very well indeed they give very good camber control, the main downside comes on rougher surfaces because the sprung to unsprung weight ratio is bad especially on a light car (ie light at the rear corners) traction is also affected by the propshaft torque acting on the rear axle pinion.

To work properly IRS as to be desgined and set up properly for the vehicle ie. just transplanting the complete IRS from a saloon car to a Locost without a redesign isn't a good idea.
IRS always performs better on rough or rippled surfaces but with IRS the camber can never be as near ideal as a live axle.


A de Dion rear end combines most of the advantages of both and a Locost is one of the few chassis layouts that has a suitable layout to accommodate the De Dion tube.

[Edited on 9/10/09 by britishtrident]

"with IRS the camber can never be as near ideal as a live axle"

Really??? on a live axle in any corner the (outside) loaded wheel will always have positive camber - generally not a good thing. With IRS and a roll bar you can design in whatever camber you want - hence the infinite possibility of a whole load of crap or....that illusive perfect solution.

Anyhow what about that rather neglected concept of the mono-shock - very similar to a live axle but with adjustable camber etc

With a live axle roll camber is that of static camber + axle roll due to tyre spring rate, i.e, verylow. In bump camber is the angle from static of the axle, plus static camber, i.e, during bump the camber isn't very good.

For IRS, simply, long swing axle lengths give better bump camber control, with roll camber being controled by the differnce in the wishbone lengths.

As for RC and the consequent roll mements, live axle RC in drive shaft height, giving lower roll moments, and less roll but quicker weight transfere. IRS allowsthe RC to be placed whereever one desires, and they are ususally much lower, giving bigger roll moments, slower weight transfer, and much nicer handling.