Twitchy rear end under heavy braking

[Robbie C]

Since fitting my KW Coilovers, Neuspeed ARBs (25mm front, 28mm rear), uprated wishbone bushes, rear 15mm spacers and front upper/lower strut braces I've noticed that under heavy braking the back end is quite twitchy and feels like it's struggling to stay in a straight line. (it's been laser aligned since fitting these parts).

Best way to improve this? I'm guessing Bill's/VT's uprated rear beam bushes may help?

Anyone else suffer from this?

 

[PhilW]

Rear brakes binding at all?

 

[andycupra]

its a far more aggressive set up over what you had before, so a tendancy for less understeer and a lively rear end is not a surprise to me, - although its probably more controlable.

How low is the car now?

 

[Robbie C]

Fair point Phil - the car is sometimes parked up for a week or more at a time so it may be binding slightly - I'll take a look.

Not sure exactly how much lower it is over standard but not a silly amount. I'm wondering if it's just a side effect of what I've fitted or whether there's more to it

 

[pj1985]

Strut brace at the rear aswell? Strut braces all round and anti-roll bars all round make it very stiff, some might say to much.

 

[ibizacupra]

are you describing straight line braking hard and rear end twitching or coners?

I found OE ibiza rear brake bias was too high as std, and fitted brake bias valves to the rear circuits, which cured the over braking @ the rear

If you are describing the rear feeling "loose" and "bobbly" thru am open fast undulating corner, then rear beam bushes will keep that beam from moving around (a lot!)

I would'nt expect a big difference in braking stability from rear beam bushes... but overall wheel geometry and alignment can make a huge difference in this respect..

4-wheel laser aligned but to what figures? not stock ones, if lowered for example

 

[PhilW]

The rear bushes make that much difference Bill?

I also find under hard braking on track especially my car feels like its twisting slightly, plus i always find the ABS too intrusive.

 

[ian_cupra]

i found it to be bad under heavy braking on the track due to the ABS, i disabled the ABS for my last trackday and braking was so much better, and rear end felt much more planted, although i did get the odd lock up on the rear wheels, think need to change the biasing a bit to help stop that

 

[p34ch3y]

are you describing straight line braking hard and rear end twitching or coners?

I found OE ibiza rear brake bias was too high as std, and fitted brake bias valves to the rear circuits, which cured the over braking @ the rear

If you are describing the rear feeling "loose" and "bobbly" thru am open fast undulating corner, then rear beam bushes will keep that beam from moving around (a lot!)

I would'nt expect a big difference in braking stability from rear beam bushes... but overall wheel geometry and alignment can make a huge difference in this respect..

4-wheel laser aligned but to what figures? not stock ones, if lowered for example

what you said about the geometry and alignment is what i was told by hrd racing when they fitted my coilovers is was very low but when i was brakeing or going round a corner hard it would try push on abit and dive slighty when brakeing, i cant remember what he said but somethig to do with geometry and alignment when you go to low something is not parelell so i we raised it 10/15mm and that was much betta....sorry to be so vaig cant remember what was said

 

[Robbie C]

Thanks for the replies - I'll dig out the geometry report tonight to see what it's been set to.

It feels unstable at the rear in straight line braking, but as said by others above normally when it's heavy and the ABS intrudes so maybe it's this that's causing it

 

[ibizacupra]

I removed my ABs from my car early on as I would go as far as to describe it as dangerous.
you will need to run bias valves to reduce rear braking effort as it is overbraked hydraulically to the rear, relying on the ABS pump to deal with it (badly)

ABS coming on with my car was rear end not front lock up, so if you add bias valves or reducers to rear brake lines the ABS will not likely have to trigger.

My rear beam bushes did not contribute to straight line braking stability. Bias valves and alignment did tho... big time

 

[Robbie C]

Thanks Bill - think that will be it then as if I think back to all the time's it's felt unstable I'm sure it's when the ABS has kicked in to "help" - possibly locking up the rear by the sounds of it

Think I'll still go for a set of rear beam bushes soon though as I don't always have too much confidence in the back end staying put through high speed corners, especially with the 28mm ARB - is it much work to fit these? Guessing I'd definitely be needing another realignment afterwards.

 

[jay26]

i thort this only happend to me lol bias valve to be on cards too then

 

[PhilW]

Ian, you just pull the fuse for the abs or done something else?

At Llandow the track that i do most of my track days theres a straight flat out section then down to a sharp 90 left, which is pretty much low second gear and coming down from high rpm in third to those speeds is scary as the surface doesnt allow for much grip and the ABS shits itself.

 

[Robbie C]

Well, after a spirited drive home tonight I think I'll be ordering those rear beam bushes off of Bill in the near future - went through a sweeping S-bend in the naughty numbers and just felt the back very nearly step out on me and almost started fish-tailing out of the exit. Made it worse by instinctively backing off the throttle and unsettling the car but didn't dare apply more speed to the equation.

As for the braking stability, it seems that is definitely down to my ABS which I tend to think is actually doing more harm than good

 

[sparkie1984]

im sure ive read that removing abs voids insurance?? as its a safety feature of that car and your removing it.

might be worth checking out if you decide to remove it robbie