Need Ideas: Failed French homologation due to braking distance (1 Viewer)

[Phat1842Many]

Hey guys,

So I'm almost out of the woods with my US market '99 LX here in France. I took it to Bordeaux for the test and it passed everything except braking.

For the test they load the truck down to rated capacity, measuring by putting it on a scale. So removing my heavy sliders wont help; they'll just add more weight bags to compensate. Then they take it up to speed, about 55 mph, and nail the brake pedal. I failed by a small margin.

I'm going to get braided SS brake lines (can you recommend some?) and do a fluid flush. All the pads and rotors are good.

The ABS computer has always felt... eager to me. Like it lets the tires slip too much. Referencing that braking issue that causes emergencies, I'm suspicious of mine because it makes that pumping noise ALL THE DAMN TIME. If the ABS is slipping I think that means the hardware is up to task. At least the lines/pads/rotors/fluid aren't the weak link in the chain. Right?

All that said, I think the real issue is my Toyo OC tires. They don't have the contact patch surface area or bite of the stock (or similar) tire. Because the brakes as a whole feel fine. So I think I'm gonna just find a hundy I can swap tires with for the test. If you can think of anything else or correct me please do.

Cheers

Phat-

 

[pavieSD]

Swapping tires will probably do the trick, see if you can find someone with AT tires and make sure the tires are warmed up before the test. I don't think stainless is going to make a difference on the brake lines, I'd just put some new OEM ones on there if you're concerned about the lines bulging from age.

The only other thing I can think of would be to swap out the pads for a more aggressive compound pad. OEM's are great for durability and low dust, you basically want something that's the opposite, maximum bite.

 

[aging fleet]

Agree with pavie, a less aggressive road tire may get this done.

 

[Manhattan]

Can you crank your torsion bars more? The more the truck is nose diving, the less the rear brakes/tires are helping.

Side note: I'm a branding guy - not a physicist...the weight transfer thing was just the first thing to come to mind

 

[jLB]

I believe I've seen "big brake kits" for the LX/LC from stop tech or brembo, but I'd agree with the previous posts that swapping tires is probably your best bet.

I don't know the details on the tires that you are running. I do know that the LT285/75R16 BFG AT weighs in at ~60lbs, compare that to factory style P275/70R16 Michelin LTX M/S at ~40lbs. It's only 20lbs per tire (100lbs total) BUT it is ~50% more rotating mass which has more inertia, and a longer lever for the braking system to overcome.

Any chance you might be able to beg/borrow/steal a factory spec set of serviceable wheels/tires anywhere over there just to pass the test?

 

[e9999]

my gut-thought is that if the tires are not locking up and sliding, which hopefully the ABS is preventing, then the tire tread should matter comparatively little for braking, everything else the same. Then again, I've had some good Tempranillo with dinner...


added: while the statement above is factually correct I believe, on further thought, I should add that it is also true that the ABS control scheme when active will likely result in "worse" treads resulting in worse braking since the worse tread will likely slip earlier at which point the ABS will reduce the braking torque, generating thereby less braking overall. So as far as technical control goes, the issue would then become dependent on whether the inspector tries to lock up the brakes or not..

 

[Sandroad]

I think better tires will do it. Tests on the Tire Rack and Consumer Reports sites show remarkably large differences in stopping distances among tires, on the same vehicle. The LC brakes are easily capable of locking the wheels but the ABS can't do its job well if the tires slip too easily.

 

[Sandroad]

Forgot to add, get the brake pump noise checked out. Whether or not that's a factor, it's not something to ignore.

 

[GregLCA]

Can you crank your torsion bars more? The more the truck is nose diving, the less the rear brakes/tires are helping.

Side note: I'm a branding guy - not a physicist...the weight transfer thing was just the first thing to come to mind

^^^^ THIS.

I don't know if "Cranking" is the right term, as that seems to imply raising the vehicle even higher. But certainly anything you can do to lower the vehicles CG is going to keep the tires working harder, and help to keep the rear end from unloading.... if the rear end is lifting up in the air, it's not contributing much to the braking efforts.

Are you allowed to play around with air pressure at all? There might be some benefit to reducing air pressure to "fatten up" the contact patch for the braking tests.


-G

 

[CanadianRockyCruiser]

You need Michelin tires to make the french people happy that you bought their products.

Also, load down the back with baguettes and a few cases of cote-du-rhone. That should fix your brakes in proper french style.

After the test, throw up a white flag and admit defeat. This may seem like a fail, but in France, that should get you a pass.

 

[n55luvr]

how difficult is it to retest? If it is easy and free I'd first try dropping tire pressure about 20%. I've seen studies showing lower than normal tire pressure can result in shorter stopping distances. Greater contact patch = less chance ABS comes in to play.

 

[Sandroad]

I'm also not a physicist, but I do wonder where they add the weight to bring it up to rated capacity? If all the added weight is in the cargo area, you may have too much braking from the rear and not enough from the front? So, give it some thought before raising the front with the torsion bars just to pass the test. That may lighten the front brakes so much they won't be effective at all.

 

[hj 60]

Let a drunk French friend do the test, without brake pads.
When we competed wheely sprint at Orgères-en-Beauce they always managed to get two dutch riders to compete each-other to eliminate one.
La France, c'est nous

 

[ppressle]

+1 on making sure the tire pressures are in spec or a little low. If that doesn't do it, upgrade the tires to some good street tires.

 

[bctlex]

how difficult is it to retest? If it is easy and free I'd first try dropping tire pressure about 20%. I've seen studies showing lower than normal tire pressure can result in shorter stopping distances. Greater contact patch = less chance ABS comes in to play.

I would start experimenting with different tire pressure because this is the cheapest route. If this does not work, then replace brake pads with more aggressive pad. Just to note, some brake pads work better when they are warm, so I would make sure to warm up the pads before the test. After that, then consider replacing the tires. I am a Michelin fan, and the Michelin LTX MS2 gripped really well on panic stop in our 01 Sequoia.

Good luck, and report back what you observe.
Chris

 

[chuckscap]

Buy some nice inexpensive soft street tires and turn your overdrive off and your ECT power switch on. Gearing and rubber are your friends