Reinforce Upper Front Suspension Chassis Tabs?
 

I noticed in a picture of Carter T's SSM FD that he had the upper front suspension A-arm chassis tabs' attachments to the chassis reinforced. I suspect that was preemptive to deal with the increased lateral loads provide by the big race tires he runs. However, I have never run across any commentary of this being a failure/weak point on the FD when run in autocross. I have my car set up now for ASP on Hoosier A7's and like Carter would like to prevent the tabs from being torn off the chassis. After years of runs on Kumho Victoracers and recently 100+ runs on the A7's, I so far see no failure developing. It looks like a tedious job to weld on the reinforcements and would like to avoid having to do it if not really necessary at my preparation level. (I understand that this is a safety modification allowed by SCCA SP rules as apparently some of the really "ancient" cars that run in SP were never designed to handle the loads of modern race tires.) Has anybody seen or known of failures at this area?

Cheers, Philip

So I have no advice to offer regarding failures, but i thought i would chime in as I came across this reinforcing plate setup last night:

https://www.rhdjapan.com/jun-front-u...rx-7-fd3s.html

I assume if someone is making these there must have been a need.......

I think I can see how that would work. Not what I had in mind but the reference and comment is appreciated.

Ones modified down here are usually as a result of something like Susprog3d having been run, or one method of chasing castor. Bulk of the load is in the lower arms, boxing the mounts wouldn't hurt though....only seen them damaged in competition from an off....can't imagine how those RHD ones work/fit either!

Hey Phillip,

I did that modification during my build following the advice of a fellow racer that had an issue. Although I am running as he did all solid rod ends for suspension attachment points which might be causing the extra stress on that area. Although I never have had an issue since the modification I believe it worked and or was not needed but better safe than sorry. It was a pretty basic job that was not difficult to do.

CT

Thanks Carter for the further insight to the reason for your modification. My car has always had the OEM bushings which would reduce the magnitude of an impact load to to the tabs, however I just installed eccentric nylon bushings in the upper A-arms to gain additional camber and caster. Ran them in the first event this past Saturday.

I need to find a welder who thinks its a "pretty basic job that is not difficult to do".

Cheers, Philip

I think I was the racer Carter referred to lol. And yes the a-arm tabs started ripping out, primarily I would guess from years of hard braking with grippy tires. Besides that the large plate that the UAA mounts are welded on to also started to pull away from the frame. I know I am not the only person to have had this issue as I just recently was contacted by a race fabricator who had same thing happen on a customers car. Boxing the UAA mounts as well as drilling through and welding the large plate, plus welding around the plate seams should fix the issue. I had mine fixed about 10yrs ago and have not had a problem since. Unless you are doing a fair amount of racing with grippy tires I don't think this issue would happen, though.

--Andy M.

Thanks for the input Andy. My car is prepared to ASP rules and runs 295-15 A7's which only have a 23" diameter, thus less leverage on the chassis tabs than the big tires on a SSM or XP car, but I have been keeping an eye on them none the less. It has been in a 6 to 8 run event every couple weeks this summer, and started as a SS car years ago before the Z06's took over. I thought I had it prepared to the full extent of SP rules, but looks like I better consider that reinforcement mod also which has become SP legal in recent years. My primary site is at the old WW2 concrete ramp in front of the hanger at the Chanute AFB in Rantoul, IL, and it has some areas that are pretty rough. A late model CAM C Mustang snapped the ball joint stud at the bottom of the front strut at the last event there two weeks ago.

Cheers, Philip