IVA requirements - Chassis & Suspension Modifications

[Jelly_Sheffield]

I have a crazy idea for building a 6x6 vehicle floating around in the back of my head which would ultimately result in needing to pass an IVA.

Whilst I'm stuck away from the workshop (as I will be for most of the next two weeks) I like to play around with designs and design constraints for these ideas and see if it's something I'd actually take further.

The IVA manual, whilst fairly terse generally sets out the requirements fairly explicitly, apart from chassis and suspension design which are notable by their absence.

This is unhelpful as the idea I'm playing with involves modifying the chassis and building a completely new suspension system, leaving pretty much all the other relevant systems untouched.

There also doesn't appear (based on an initial search) to be any definitive standards for the design calculations to determine the strength of chassis and suspension components.

This also makes it very difficult to determine the design weights of the vehicle, which logically would be determined by reference to calculating the imposed load that would exceed the yield strength of the components, divided by some recognised safety factor.

Is there recognised best practice for this, or is it a case of designing it along "sound engineering principles" and seeing if the examiners agree with your decisions/justifications?

 

[Roger440]

I have a crazy idea for building a 6x6 vehicle floating around in the back of my head which would ultimately result in needing to pass an IVA.

Whilst I'm stuck away from the workshop (as I will be for most of the next two weeks) I like to play around with designs and design constraints for these ideas and see if it's something I'd actually take further.

The IVA manual, whilst fairly terse generally sets out the requirements fairly explicitly, apart from chassis and suspension design which are notable by their absence.

This is unhelpful as the idea I'm playing with involves modifying the chassis and building a completely new suspension system, leaving pretty much all the other relevant systems untouched.

There also doesn't appear (based on an initial search) to be any definitive standards for the design calculations to determine the strength of chassis and suspension components.

This also makes it very difficult to determine the design weights of the vehicle, which logically would be determined by reference to calculating the imposed load that would exceed the yield strength of the components, divided by some recognised safety factor.

Is there recognised best practice for this, or is it a case of designing it along "sound engineering principles" and seeing if the examiners agree with your decisions/justifications?

Having looked into this, its down to the examiner to look at it and assess if he thinks its resonable. You are pretty much free to do as you please otherwise. Theres no rules that say it has to drive or handle in a certain way.

I wanted to graft the front of a modern car onto a 50's chassis and asked some questions here about the compatability of the steels involved when it came to welding. Bloody minefield. But IVA dont care.

 

[Jelly_Sheffield]

So if I can provide documentary evidence of a well thought out design with calculations or FEA to demonstrate that the chassis and suspension elements won't fail when loaded as designed, and their inspection confirms my vehicle matches the design documents then it should be fairly straightforward.

I guess if I want advice on appropriate calculation approaches I will have to contact the VCA then.

 

[Roger440]

You dont need to do any of that. I doubt they would know what to do with it anyway. The tester tests the car on the day as you present it. He wont be looking at FEA!

Of course, if you do all that, then its unlikely you will be building anything for them to be concerned about.

I had/have no plans to do anything of the sort. Ill just build it/modify it. Though im using existing suspension from another car. But the chassis will be too my own design utlising only the central section of the original. Everything i could find, and a couple of people i spoke to said that would be fine.

 

[Jelly_Sheffield]

You dont need to do any of that. I doubt they would know what to do with it anyway. The tester tests the car on the day as you present it. He wont be looking at FEA!

Of course, if you do all that, then its unlikely you will be building anything for them to be concerned about.

I had/have no plans to do anything of the sort. Ill just build it/modify it. Though im using existing suspension from another car. But the chassis will be too my own design utlising only the central section of the original. Everything i could find, and a couple of people i spoke to said that would be fine.

I want to build a Hendrickson style Walking Beam bogie with original suspension springs plus a set of helper springs to allow me to both significantly uprate the capacity and improve axle articulation.

Basically everything apart from the walking beam assembly itself, and a custom pinion for the center diff can be achieved using either Toyota parts, or E-Marked OEM parts from the truck world.

But being that I don't have a C1 entitlement (and passing an N2 IVA would be a lot more effort), it needs to stay under 3.5T GVW, so the walking beams, which are under a lot of torsional stress need to be hollow members...

Hence I will definitely need to do proper calculations and possibly have a friend do FEA analysis if that seems marginal just to make sure the beams don't crumple up like twisting a folded crisp packet the first time it's cross-axled.