tubular control arms

[funkyflynz]

Hi,

Is is ok for control arms to be made of 1"x .095 wall chromoly with 5/8 " welded bungs in the end that are threaded for adjustment?

[Justin]

Hi there

The specs for tubular a-arms are all contained in the HCTM. The requirement for the material specifications will be determined by the vehicles weight, and also the function of the arm, for example whether or not the arm has the spring attached (meaning that it carries the weight of the vehicle) will have a direct bearing on the requirement.

The specs contained in the manual are all based around mild steel ERW - if you want to use an alternative material, it's specifications will need to be the same or better.

Also a point to make is that if you are building a custom IFS, this may be required to be assessed and approved by the TAC as part of the build approval process - www.lvvta.org.nz/approvals.html#design

If this is not the case, and you are only replacing the suspension arms, then this Information sheet may be relevant - www.lvvta.org.nz/documents/infosheets/LVVTA_Info_01_2012_Custom_Suspension_Arm_Inspection_Approval.pdf

I hope this helps

Cheers, Justin

[funkyflynz]

Thanks Justin,

The specs in the HCTM specify ERW or seamless tube, not 4130 chromoly.

Chrome-Moly, DOM and ERW tubing weigh about the same but it is important to note that Chrome-Moly is the strongest, followed by DOM and finally ERW being the weakest of the three.

You can take advantage of Chrome-molys much higher strength by using thinner walled tube, thus saving weight.

It would be good to know the acceptable wall thickness' for UCA and LCA when using Chrome-moly please.

Aug 27, 2012 8:03:47 GMT 12 Justin said:

Hi there

The specs for tubular a-arms are all contained in the HCTM. The requirement for the material specifications will be determined by the vehicles weight, and also the function of the arm, for example whether or not the arm has the spring attached (meaning that it carries the weight of the vehicle) will have a direct bearing on the requirement.

The specs contained in the manual are all based around mild steel ERW - if you want to use an alternative material, it's specifications will need to be the same or better.

Also a point to make is that if you are building a custom IFS, this may be required to be assessed and approved by the TAC as part of the build approval process - www.lvvta.org.nz/approvals.html#design

If this is not the case, and you are only replacing the suspension arms, then this Information sheet may be relevant - www.lvvta.org.nz/documents/infosheets/LVVTA_Info_01_2012_Custom_Suspension_Arm_Inspection_Approval.pdf

I hope this helps

Cheers, Justin

[Justin]

Hi again. After re-reading what I have already written I wasn't very clear in what I was saying.

We only provide a spec for mild steel. If you wish to use an alternative, then the alternative will need to have the same or better strength specifications when compared to mild steel. This data will be available from the supplier.

Also to note, the person welding these arms should have experience in TIG welding chrome molly tube - there are pre and post heat treatment processes which may be required, to prevent chill hardening and other issues.

The Hobby Car Technical Manual has a section in the 'Attachments' section which provides the requirements for welding critical function components, including the qualifications required by the welder, and also of the NDT requirements.

I hope this helps.

[funkyflynz]

Cheers for that,

Im looking at a kit they sell in the states, not making it myself. Just want to make sure it can be approved before i buy it and ship it here.

The kit is for street cars and had been around for a long time, but doesnt match up with the HCTM in a few areas, such as using thin wall chrome-moly for control arms and threaded "spuds" welded into the end of each arm. A fairly common setup but not "ideal" according to the HCTM.

Appreciate your feedback.

[Justin]

This document may be relevant, if you are only replacing the suspension arms. www.lvvta.org.nz/documents/infosheets/LVVTA_Info_01_2012_Custom_Suspension_Arm_Inspection_Approval.pdf