Chassis Question

[thedooga]

Hi there, so I took this to the certifier a few weeks back, he was happy with how I was progressing, but he did question this




So I am gonna cut the hoop an bottom RHS out completely, the car has a roll cage and am going to run bars from the main hoop to the rear chassis legs with a bar to tie the middle in, my question is, it that ok or will i need to add more in? Could also add a upside down V shaped bar to go from the bottom chassis legs up to the middle cross bar? As I need to leave to run the exhaust thru, as original plan was to notch the chassis, but not allowed to do that, Hope it all kinda makes sense?

Cheers, Dylan.

[Chris]

You would be best to discuss that with your certifier as other factors need to be considered which cannot be accurately seen from a single photo.

Based on what I can determine from your post, my thoughts are that a roll cage would not make a great structural chassis crossmember.

[thedooga]

Thankyou for the replay, so cant do that then, Ive emailed my certifier, but obviously with this lockdown I might not get a reply, and would like to keep moving forward, am i able to fabricate the middle section using 3mm steel plate, with a slight curve, to allow the driveshaft to have enough clearance, and also use the 1-3/4 roll bar tube that is everywhere else, to tie in and give support to the rear chassis legs, that will also get tied into the main hoop of the roll cage, or does the middle section need to be completely straight, and also be of no less than 75x50x3 rhs? here is a photo of what im trying to achieve, also the non blue shs is being removed as fouls on the driveshaft, but will be getting replace with 25x50x3 rhs further towards the motor, to mount the seats, i will also try incorporate a type of K frame around the mufflers etc to give support back to the chassis, I have done a build approval but a the build has gone on I have overlooked a few items, and now trying to make it work, sorry for being a pain, its my first proper build.



also if you know of another upload site that is free and doesnt have a watermark?

Cheers Dylan.

[Chris]

Apr 7, 2020 17:37:11 GMT 12 thedooga said:

Thankyou for the replay, so cant do that then, Ive emailed my certifier, but obviously with this lockdown I might not get a reply, and would like to keep moving forward, am i able to fabricate the middle section using 3mm steel plate, with a slight curve, to allow the driveshaft to have enough clearance, and also use the 1-3/4 roll bar tube that is everywhere else, to tie in and give support to the rear chassis legs, that will also get tied into the main hoop of the roll cage, or does the middle section need to be completely straight, and also be of no less than 75x50x3 rhs? here is a photo of what im trying to achieve, also the non blue shs is being removed as fouls on the driveshaft, but will be getting replace with 25x50x3 rhs further towards the motor, to mount the seats, i will also try incorporate a type of K frame around the mufflers etc to give support back to the chassis, I have done a build approval but a the build has gone on I have overlooked a few items, and now trying to make it work, sorry for being a pain, its my first proper build.

also if you know of another upload site that is free and doesnt have a watermark?

Cheers Dylan.

Gidday Dylan,

Unfortunately It is very difficult to assess the suitability of a chassis from pictures, to do so requires detailed information provided, preferably scale drawings in multiple perspectives that include material specifications. So I know this is probably difficult at this time but it should really be discussed and approved by your certifier.

From a simple observation level and if I am understanding your proposal correctly, you want to remove a straight box section cross-member (looks 75x75x3?) and replace it with a curved 3mm plate above and below the driveshaft? Using a "like for like" perspective, they are not at all similar in material or load path, also I suggest the roll-bar should be tied to the chassis, not "be" the chassis.

I understand you have previously been in contact with Justin regarding your build approval, if you are changing the construction of the chassis by more than a couple of minor tweaks, then you might find the build approval is no longer applicable. So perhaps get in touch with Justin to discuss developing your build approval further. As we are all working from home, Justin is available on [e-mail].

Also, you can upload attachments directly to the your posts and they are hosted on the forum.

Cheers

Chris

[thedooga]

Thank you very much for the quick reply, ill get in touch with Justin,