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Tiger Avon Chassis
mad_skillz - 30/9/02 at 05:12 PM

Im thinking about building the IRS tiger avon chassis and have just ordered the book, are there any problems with the design eg sizes etc, becauase i know ron champions book has a few problems.
Thanks
Alex

Mark Allanson - 30/9/02 at 05:37 PM

I bought the book thinking I would build it instead of the locost, IRS alrady designed for you and a complete GRP body for about £350. Problems solved!

Read the book and I am now building a locost!

The front end looks well designed apart from the stering column which looks like Professor Pat Pending had a hand in it. The IRS bit tacked on the back is obviously not designed by the same chap who designed the front.There is no triangulation and I really cannot see how it holds together under any amount of power. Read the book and draw your own conclusions!

atb
Mark

Gremlin - 30/9/02 at 07:30 PM

Mark Allanson I to thought this and was a bit disappointed, I also wanted to use the shell to as it was a nice easy way to finish car and I think looks better than the standard shell.

But like you the way the back box which holds the back diff and drive shafts is only tacked onto downward diagonals and am not sure that will hold well under the punishment I may give the car on the track.

If anyone has any good irs alterations to make the original chassis can they let me know, or if anyone thinks it may be possible to fix the tiger shell onto a book chassis some how I would also love to know about that to.

dougal - 1/10/02 at 12:04 AM

i have both books.
what i want is a car that will handle as perfectly as possible aswell as strong enough to cope with the 200bhp+ that my engine will put out.
my conclusions are that both plans will give you good usabe car and probobly as good a car as you would ever need for the road.
but in my opinion the geometery for the front of both cars is not perfect and for such a light car a solid rear axle is rather heavy.
i have designed a better front susp and will use a de-dion rear with a tiger avon mid section with some stiffening work.
pete

mad_skillz - 1/10/02 at 05:10 PM

thanks very much guys
Has any one got any plans for cars ,i have had a look at McSorley 442 which looks quite good but i too think live axle isnt the best way to go and want IRS.

locodude - 1/10/02 at 05:47 PM

Hi Guys
If it's unsprung weight that's bothering you then ok, go for IRS. If you want a track day car with lot's of grip then it's got to be live axle or de-dion. A complete IRS including diff, shafts, hub carriers and brakes weighs more than a live axle! Think about it guys.
Chris PTM

johnston - 1/10/02 at 07:32 PM

i've said it b4 and i'll say it again

how many grp 4 escys were irs???? and a gd 16v vauhall engined one can still hold its own against 4wd cossie's and sub's

interestedparty - 1/10/02 at 09:13 PM

IRS is all about passenger comfort, always has been, always will be. Best cornering results from having the rear wheels held vertically to the road, something which is very difficult with IRS, but which comes free with live axle or de dion

John

Wadders - 1/10/02 at 10:19 PM

IRS is all about passenger comfort, always has been, always will be. Best cornering results from having the rear wheels held vertically to the road, something which is very difficult with IRS, but which comes free with live axle or de dion

Have been in De-deon,live axle,and IRS sevens plus one with inboard rocking arm front suspension, some homebuilt others megabucks kits.Bottom line is they all stuck to the road like poo to a blanket,i.e roundabouts, corners etc at insane skid mark inducing speeds. But surely there is more to the equation than just the type of rear suspension you choose, tyres are important as are,shockers,suspension settings,unsprung weight etc etc etc.
If the roads you will be driving on are racetrack smooth then yes IRS is a compromise
but if they're like the majority of our highways (potholed and bumpy as f*#k)then IRS is a good bet.
Even so unless your a direct descendent of the late Ayrton Senna, or maybe Jon Isons secret love child, then don't worry the suspension will hold up long after youv'e s*#t yourself.

Fun isn'it

Gremlin - 1/10/02 at 11:42 PM

Just seems to me in the tiger book although the irs and suspension may hold up the chassis supporting the bits wont! I would like to put irs on but would prefure to find a diagram where it dosent look like it has been added as an after thought.

Rorty - 4/10/02 at 03:28 AM

If anyone wants to send me the drawings of the Avon, or any other chassis for that matter (or even have something scratch built for a fee), I'm quite happy to make alterations/improvements. I have 16 years experience designing chassis for road and track, both tubular and monocoque.
Cheers, Bob.
www.rortydesign.com

Findlay234 - 5/10/02 at 06:47 PM

irs isnt designed for passenger comfort!!!!!!!

its to reduce the unsprung weight of the car. its the same reason people use alloys, not just to look good, alloys weigh less. if live axle and de dion were the best in racing then why dont f1 and rally use it? a wheel when reaching a bump will bounce up and then be forced back down by the spring, with the lighter wheel and axle it will be pushed back onto the surfce of the road faster, a wheel in the air has no grip. that is why in irs the axle diff is supported by the chassis.

Findlay234 - 5/10/02 at 06:47 PM

irs isnt designed for passenger comfort!!!!!!!

its to reduce the unsprung weight of the car. its the same reason people use alloys, not just to look good, alloys weigh less. if live axle and de dion were the best in racing then why dont f1 and rally use it? a wheel when reaching a bump will bounce up and then be forced back down by the spring, with the lighter wheel and axle it will be pushed back onto the surfce of the road faster, a wheel in the air has no grip. that is why in irs the axle diff is supported by the chassis.

Findlay234 - 5/10/02 at 06:47 PM

irs isnt designed for passenger comfort!!!!!!!

its to reduce the unsprung weight of the car. its the same reason people use alloys, not just to look good, alloys weigh less. if live axle and de dion were the best in racing then why dont f1 and rally use it? a wheel when reaching a bump will bounce up and then be forced back down by the spring, with the lighter wheel and axle it will be pushed back onto the surfce of the road faster, a wheel in the air has no grip. that is why in irs the axle diff is supported by the chassis.

interestedparty - 5/10/02 at 07:09 PM

quote:
if live axle and de dion were the best in racing then why dont f1 and rally use it?


F1 cars (due to having to resist huge downforce loads) don't have enough suspension movement to make a de dion set up worth it.
Aren't rally cars supposed to be built in approximately the same way as the production cars on which they are based?

Of course IRS is about reducing the unsprung weight. What better way could there be of improving passenger comfort?

John

Rorty - 5/10/02 at 09:10 PM

IRS is neither for weight saving, nor passenger comfort.
In most cases, an IRS setup is heavier than a comensurate live axle.
Most automotive developement comes from the race track. IRS was devised as a means of tuning the suspension, passenger comfort is an added bonus.

interestedparty - 5/10/02 at 09:27 PM

quote:
IRS is neither for weight saving, nor passenger comfort.


Actually that's wrong. Passenger comfort is a big consideration with manufacturers. A good example would be the TR4 which started with live axle and was upgraded to IRS with virtually no other changes. Reason, passenger comfort

John

johnston - 5/10/02 at 09:46 PM

f1 cant do it cos gbox is in the way

yes rally cars have to be based on the road car version but they also have to contend with bombin down forest tracks not just snooker table smooth tarmac

i only no 1 guy who has converted a live axle rally car to irs his main reason was weight ie his fiat 131 ran a 4ha axle which was bloody strong but took 2 people to lift and counted for bout half the weight of the car

and only reason he didnt swap to a atlas axle was cos he couldnt easly get shafts with the fiat pcd

but he did end up with atlas diff and diff housing mated to golf vr6 shafts uprights and struts

Viper - 27/10/02 at 07:42 PM

lets put it this way..can you adjust rear camber with a live axle? can you adjust rear toe in/out with a live axle without bending the axle casing? and how about squat? to adjust squat on a live axle you would end up tipping the nose of the diff is that a good idea? so ok irs is possibly a tad more expensive but not allways heavier and then there is the real handling advantage in less unsprung weight, in this set up the only disadvantage i can see is the lack of diff ratios...

johnston - 27/10/02 at 08:18 PM

raising or lowering the diff nose by moving your trailing arms is the norm on race/rally cars not only does it change the dive/squat charcterisitics it also changes the oversteer/understerr caracteristics

Viper - 29/10/02 at 08:10 PM

On classic rally and race cars i agree but there is not a lot out there today that runs a live axle, i thought the only reason that Mk2 GP4 cars had trailing arms etc was because that its a better set up than leaf springs..off the top of my head i can't think of any purpose built modern race cars that use live axles unless you include oval cars but they use live axles because its the rules they have to abide by...i look forward to the replys to this thread its a good un.