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Chassis Tubes

Simon - 19/6/02 at 01:54 PM

Hi all,

I will be ordering tube shortly, and was wondering if there are any advantages / disadvantages to using 1" sq for transmission tunnel. I appreciate a slight increase in weight and an extra Ł2.50 on my metal cost. I like to think engine will be replaced with R V8 eventually, so think strength may be in order

Thanks and regards

Simon

JohnFol - 19/6/02 at 01:58 PM

I guess weight is the main one, and the reduction if 1/2" space. Not sure why having stronger tunnel is suited to a V8 as it is not load bearing . . .

john_s - 19/6/02 at 08:23 PM

I've made my trans tunnel from 1" section on the grounds that my diff is fixed at the end of it (i'm using a sierra diff).

I decided that the extra strength may offset the slight extra weight.

John.

stephen_gusterson - 19/6/02 at 10:31 PM

I also made my tunnel out of inch section. In my car, I tapered the top of the tunnel towards the rear. thats cos the shaft runs in the lower section, and the top being tapered gives a bit more room for seat belt clasp mounted on the seat ala sierra - and a bit more elbow room. It may also be that the triangulated shape is a bit stronger?

atb

steve

stephen_gusterson - 19/6/02 at 10:35 PM

quote:
I guess weight is the main one, and the reduction if 1/2" space. Not sure why having stronger tunnel is suited to a V8 as it is not load bearing . . .

I would say that it does have a load bearing aspect.

It gives the centre of the car a bit of a 'backbone' - although some cars just have hoops instead of a solid tunnel - but then perhaps stiffness suffers.

On standard road cars, most still retain a 'tranny tunnel' section of some sort to avoid a low strenght flat floor.

On my car, which is a morgan replica based on a morgan, the tranny tunnel is most certainly important, as it takes a rear end impact force into the chassis and my car has doors, which requires the sides of the car to be modified, possibly reducing stiffness. I made my tunnel strongly.

atb

steve

stephen_gusterson - 19/6/02 at 10:36 PM

On my car, which is a morgan replica based on a morgan,

read 'based on a locost'

atb

steve

Simon - 19/6/02 at 10:47 PM

Hi Chaps

Thanks for replies.

Steve - you got that in a bit quick - Morgan based on a Morgan, not such a silly idea - people have being doing Cobras based on Cobras for years!! Locost based on Locost -there's an idea. Build your own Sportscar etc and Race It - for Ł1.75

Jon,

I'm using entire rear Sierra subframe, and want a sturdy mounting. Other reason is using only one size sq and one round hopefully reduce waste, and therefore recoup my Ł2.50 cost. As for the 1/2" - I'm building four inches wider than book. Gotta be able to get wife in!

ATB

Simon

johnston - 2/7/02 at 07:15 PM

Well i'm usin the 1" tubin for mine cos its cheaper (but then thats ireland for ya)

merlin - 2/7/02 at 09:02 PM

Just for information -
Having studied a series 2 lotus 7 chassis recently the transmision tunnel was a piece of rolled 18 guage ali ! not much of a backbone there! Also the floor section has no cross members and the seats bolt directly to the ali floor which is in turn 'stiffened' by the tunnel.

If you look at the chassis in general modern chassis such as the Locost/Cat/west etc have about 50% more tubing in their construction!

Obviously safety issues have changed over the years but if the great Mr C designed such a perfect chassis why change it?

If it aint bust don't fix it!

stephen_gusterson - 2/7/02 at 10:12 PM

quote:
Just for information -
Having studied a series 2 lotus 7 chassis recently the transmision tunnel was a piece of rolled 18 guage ali ! not much of a backbone there! Also the floor section has no cross members and the seats bolt directly to the ali floor which is in turn 'stiffened' by the tunnel.

If you look at the chassis in general modern chassis such as the Locost/Cat/west etc have about 50% more tubing in their construction!

Obviously safety issues have changed over the years but if the great Mr C designed such a perfect chassis why change it?

If it aint bust don't fix it!

stephen_gusterson - 2/7/02 at 10:18 PM

quote:

Obviously safety issues have changed over the years but if the great Mr C designed such a perfect chassis why change it?

If it aint bust don't fix it!

Perhaps years and lots of miles of sevens on the road have shown how the cars can or might fail, and the car has been beefed up as a result.

I read a library book about the seven once, and it went into detail of how the rear axles used to fail. Chapman mounted the rear axle on just one swing arm. The result was that the axle used to split along the casing. Rather than use two arms ala locost, he welded a strip along the top.

Its been said that lotus killed more of their drivers than any other marque in formula one. Rint might agree, cos something broke causing his crash.

There was also a quote on TOL once, that was how great a particular Chapman design was, using a single bolt to hold 3 suspension assemblies together. If that one bolt fails, 3 bits fall off!!!!

My strategy is to build the car strong. A few extra kilos here and there arnt gonna be a big problem. I wouldnt want st Peter asking me if the 0.2 secs off the 0-60 time was worth dying for.

atb

Steve

cymtriks - 10/7/02 at 08:46 PM

Take a look at my suggested mods in the "macspeedy - chassis poll"
The tubes in the tunnel don't do much but the basic frame as built to the book is getting marginal so it counts. With my mods in place the tunnel tubes can be deleted giving a frame which has less tubes overall and is 10 percent lighter and 100 percent stiffer in torsion. This ties up well with other members comments regarding the lighter structure in the Caterham tunnel.

johnston - 10/7/02 at 09:42 PM

I do a lot of work on rally cars and have worked on cars as small as 1.3 suzuki swifts right up to grp a ex works imprezza's (with a fiat 131 with golf vr6 front suspension and drive shafts mated to a atlas axle dif housing) and 1 thing that has been drumed into my thick skull is to finish first you've got to finish i.e. if somethin breaks your at best going to lose a lot of time and at worst your going to put a lot of people int hospital (driver navigator marshalls and most important spectators) and this is the principal i think should be used to build our locosts if something breaks your not on a stage but on a public road or isn't up to the job its not just the builder thats going to get hurt.