Strut Brace

Ultra Racing, in Malaysia. Their kits can be cheaply bought on eBay.

They do make a kit of tubular frames to surround the floorpan in Mk 4 series cars. 2 strut bars + 1 frame around the front subframe + 2 frames beneath floor + 1 frame around rear axle mounting points.

Not all of them fit all cars: some bars made for TT Mk 1 do not fit the Leon, other made for Golf Mk 4 do not fit the TT.

It's like a poor man's version of an autocross roll cage.

Nautilus said:

Ultra Racing, in Malaysia. Their kits can be cheaply bought on eBay.

They do make a kit of tubular frames to surround the floorpan in Mk 4 series cars. 2 strut bars + 1 frame around the front subframe + 2 frames beneath floor + 1 frame around rear axle mounting points.

Not all of them fit all cars: some bars made for TT Mk 1 do not fit the Leon, other made for Golf Mk 4 do not fit the TT.

It's like a poor man's version of an autocross roll cage.

Click to expand...

Yes basically. What you have done is pretty cool. Do you have measurements of the bar and place on holes on the bar? Out of interest would in not be better to have a solid bar

Sent from my Nexus 6 using Tapatalk

Bar is a square-section steel tube, 30x10mm, 1.5mm walls, 880mm long, 835mm between hole centers, fitted with 2 x M12 bolts with washer heads through rivet nuts in the holes. To fully compress the rivet nut, you need strong bolts, at least 10.9 grade, with big washer heads. Total weight in the 2 lbs range.

Solid bars of similar shape are very heavy and weaker compared to tubes. A solid steel bar from the hardware store (35x6 mm section) flexed even more than a tube. It was literally like a single leaf from a truck leaf spring. A fellow with an Audi S3 (8L, which has the lower subframe brace from factory just as LCR does) complained the S3 brace flexed just like that: he pulled himself up from the brace while the car was on jackstands and it wobbled under his weight like a big leaf spring. There is a reason most companies use steel tubes to make braces.

30x10mm tube can't be flexed by hand tools and vibrates little on the work bench. Once bolts are tightened, bar is in tension like a very hard spring and can be vibrated by a rubber mallet.

Same thing happened with Wiechers upper strut bar (forged aluminium): once tightened to the max, it's tensioned and it will become a very hard leaf spring. Even so, it has proved useful in the last 11 years it stood on the car.

Nautilus said:

Bar is a square-section steel tube, 30x10mm, 1.5mm walls, 880mm long, 835mm between hole centers, fitted with 2 x M12 bolts with washer heads through rivet nuts in the holes. To fully compress the rivet nut, you need strong bolts, at least 10.9 grade, with big washer heads. Total weight in the 2 lbs range.

Solid bars of similar shape are very heavy and weaker compared to tubes. A solid steel bar 35x6 mm section flexed even more than a tube (it was literally like a single leaf from a truck leaf spring). There is a reason most companies use steel tubes to make braces.

30x10mm tube can't be flexed by hand tools and vibrates little on the work bench. Once bolts are tightened, bar is in tension like a very hard spring and can be vibrated by a rubber mallet.

Same thing happened with Wiechers upper strut bar (forged aluminium): once tightened to the max, it's tensioned and it will become a very hard leaf spring. Even so, it has proved useful in the last 11 years it stood on the car.

Click to expand...

Thank you for the info.

Sent from my Nexus 6 using Tapatalk

Reasons for the need of strut bracing:

Leon frame rails are very strong, but attached to the bodywork structure at 3 points, as we can see:



At the strut tower, at the bottom plate below front seats and again at the bottom plate before the pedals. This last place is where subframe fits.

People took great pains throughout 2 decades to strengthen the Mk4 subframe. Since it's a steel sheet box and therefore vibrates. (There was a good reason people at VAG, far better schooled than most of us, replaced the steel-sheet subframe with a cast aluminium one in the Mk5 and above!)

But they ignored the actual chassis structure. Subframe is flexibly attached, by 4 bushings. We use stronger bushings, of urethane, aluminium or steel, to stop it from moving side to side. The frame structure is big and strong, laser-welded, but only made from closed box steel at the frame rails proper, at the rails below the seats and the U-shaped structure behind the rear seat.

The rails by themselves are united only by 3 things:

- front bumper (bolted);
- structure around lower edge of the windscreen (welded, with 2 short sheet-steel braces);
- structure before pedal box / firewall (welded, but flat section, not boxed).


The engine space is a pretty big void with a perimeter around.

So a cross brace between frame rails strengthens the perimeter and drives up the stiffness of the big spring which is the bodywork.

Also experimented with an Yamaha Body Damper in the car's frame, fitted behind rear seat, between strut towers, just below and parallel to the Wiechers brace. Set the damper with 2 threaded bars between strut towers, to keep it in tension by threading the bars (1/4 of a turn, not more - the damper normal travel is about 1 mm).

First impression: road noise from the rear decreased. That is, it dampened those vibrations in the audible spectrum. Ran same trail before and after: winding road with some small hard bumps.

Then added the second Yamaha Body Damper from the pair in the (already-braced) front subframe. The effect was far more easily felt:

+ Dampened engine noise at most rpms;
+ Dampened resonance in the car's frame around 3500-4000 rpms;
+ Front end feels more "planted" to the ground (less tramlining on small hard bumps)

On same tyres, at 5°C (41°F) it feels like previously at 20°C (68°F)

Followed the rule of COX Japan for fitting, as displayed for a Mk 5 Golf here:



Transverse fitment, snug into the car's frame by threading, rear one with rod towards right, front one rod towards left of the car.