Back end squirming under heavy breaking

[LDoR]

Lo all,

Question for all you Cupra R owners here.

Over the weekend i was doing some spirited driving when i had to apply quite a bit of heft to the brakes (not fulll pressure mind) as some on coming traffic had decided that overtaking with me heading towards them would be a bad idea.

This was scary enough, but what really got me excited was the way the back got all light on me as though the front wanted to overtake the rear. It was bone dry but the TCS light was seen to flash. The road wasn't the smoothest in the world but it was far from bumpy. I also seem to remember that the LCR brakes in a very straight line.

Now i've only recently put new disks and pads no the fronts - Groved Brembos + Ferodo DS2500 thanks to Bill - but the rears still carry the original disks and pads. Could this unsettling braking action be down to the imbalance in the braking force from front to rear? I haven't recently looked at the rear disks but i'm pretty sure they had a bit of a lip on them and the pads must be getting thin by now.

I plan to take it down to a local garage at one point after work one night but wanted to hear any other opinions here from anybody who might have had the same experience.

 

[Steve_B]

Most likely changing the front brakes that's caused what you describe, the rears do very little over all when you're braking. If your brakes were a bit shagged before you changed them, putting the new disks and pads on the front will have improved the braking at the front but, you've still used the force you would have done with the old brakes.

Had the same once in a crappy courtesy car from a garage, hit the brakes a bit had and it felt like the back was trying to go over the front!

 

[Feel]

Mine's always done it Dor, but the extra braking at the front would make it more pronnouced.

Perhaps the shocks want looking at?

 

[Reg]

The rear brakes should compensate - they have a bias in them. Sounds more like a weight transfer issue. With new uprated brakes on the front, and in that situation where you have really stood onthe anchors, you probably just felt a sharper transfer of weight from rear to front, making the back end light and loose. The traction control sensed that and did what it needed to keep you sunnyside up.

 

[LDoR]

Hmmm, hard to know what to think. I spose i'll try and have them looked at, they might need changing anyway.

I supose what i felt is more down to the horrid FWD weight balance with everything sat over the front wheels. I supose if i want to have a stable back end under heavy braking i need to either fit an air brake or buy that Noble

 

[YerMother]

Does it to me too! Don't worry the ESP sorts it out even when it's switched off!

 

[cupra R con]

weight shift for sure, the R is not that much better than the standard cupra in the suspension department, & the normal cupra is bordering on dangerous IMO.
rebound control on normal shocks is... err, shocking, roll is all but unchecked.
and having a narrower track at the back is an interesting concept.

decent springs & shocks, decent ARB's & spacers for the rear should sort your handling woes.

pricey, but then not much in life is cheap.

 

[YerMother]

When I fitted just the 25mm Neuspeed ARB to my LCR made a big improvement IMO. Back end was more stable around bends and under heavy breaking!

 

[Feel]

...and heavy braking around bends...

I was going to say the same, rear ARB keeps it much more under control.

 

[honeyman]

Yep mines doing it, pain in the ar$e. really need new shocks now. as mentioned switch the ESP off.

 

[honeyman]

Yermother have you fitted the rear ARB only?

 

[LDoR]

Yes the temptation to spend money on the LCR pulls hard on me. I've had thoughts that if i can't find a Noble at the right price that i should go down the IHI + torsen diff route (+ breathing updgrades). Along with that i would think strut braces, new suspension and some big 6-pot AP racing brakes.

 

[YerMother]

Yermother have you fitted the rear ARB only?

I did yes! Just the rear ARB with standard setup!

I now have koni FSD dampers with Eibach springs, 22mm Neuspeed front ARB, 25mm rear ARB and S3 upper strut brace and very happy with it!

 

[Reg]

rebound control on normal shocks is... err, shocking, roll is all but unchecked.

I think in this case its initially a lack of spring strength, combined with compression damping that is a problem. Its when you come off the brakes suddenly and it feels unsettled, thats when the lack of rebound damping shows itself!

 

[Feel]

I think so too.

 

[LDoR]

Ok, continuation of my question.

Garage man said the brakes had 3-4mm left in the pads which he said was enough but i'm sure the pads are at least twice that tickness. I'm sure i replaced my fronts with more on them than that. And the disks have about a 1mm lip on them (each face).

If i was to change them how much would the parts cost and wheres the best place to get them?

 

[Reg]

If you back pads are only half worn, don't waste your money changing them yet - and a 1mm lip is not a problem providing the disc itself is not below minimum thickness (which I can't imagine it would be). The problem here is not the rear brakes, they are only doing around 15% of the work.