Braking performance

red_leicester · February 18, 2006, 08:29

Having just driven a friend's Y-reg Alfa 147, and a new Toyota Aygo (oops, sorry AYGO), I've just realised how 'spongy' the brakes are on my 2001 MR2.

The Alfa felt stronger when the brakes were initially applied and pulled up more strongly. The Aygo almost sent me through the windscreen when I put the brakes on at the lights !!!

Is it becuase being lower down in the 2 just makes it feel different under braking? Or should I be getting better initial 'bite' from the 2's brakes. The 2 seems to pull up ok once the brakes are on but as I say there's a spongy initial feeling. The discs and pads are fine by the way; had the once-over from MrT last week when the belt tensioner was changed (£240 s:(

s:( ).

Cheers,Jez.

Slacey · February 18, 2006, 08:33

It's most likeley the fluid. When were the brakes last bled? Mine weren't done all that long ago, but after a track day at Elvingtom they are shot, the fluid probably boiled so mine need a bleed and new fluid too. As they are, in perfect condition they should be more than powerful enough on a stock car.

kanujunkie · February 18, 2006, 10:08

yep, Seans right, mine did this after Donnington, your brake fluid has litterally been boiled and the chemical structure has change to allow it to become compressable and the chance of gas buildup in the system is there as well. The stock fluid is Dot3 and boils at a relatively low boiling temp, change up to a decent Dot 4 or 5.1 and you'll be fine

Tem · February 18, 2006, 12:11

Generally a sportscar should have linear brakes, cause they are easier to control. That means you won't have huge braking power when you barely engage the brakes, like some grocery getters do. If you want massive initial bite (but less control), you can get aftermarket pads.

mrsmr2 · February 18, 2006, 13:19

I think there is a slight sponginess initially. But, only initially.

The 2 has very good brakes and they are progressive.

I find mine don't bite that well on slight pressure of the pedal. But, they are superb as more pressue is applied.

My 406 for example, bites extremely quickly so they feel sharper. Yet they don't brake any better as more pressure is applied. The 2 is the opposite.

I would guess the Aygo is suffering from over servoed brakes (as do most cars now).

When was the brake fluid last changed?

Jason

Tem · February 18, 2006, 14:37

Quote from: "mrsmr2"The 2 has very good brakes and they are progressive.

I find mine don't bite that well on slight pressure of the pedal. But, they are superb as more pressue is applied.

You just described linear brakes. s;)

s;) Little pressure, little power, more pressure, more power.

mrsmr2 · February 18, 2006, 17:30

Possibly, but they feel more linear once the initial pressure has been applied. They don't start off feeling as linear.

Jason

red_leicester · February 18, 2006, 19:46

'More linear' ? You sure that's possible s:wink: :wink: s:wink:

Thanks for the replies, I'll check when the fluid was last changed, but I have a feeling it wasnt so long ago.

They stop fine once you get the pedal down, but it's lask of initial bite I was questioning. Maybe as you said Jason some cars are over servoed so school-run-mum is happy.

Anonymous · February 18, 2006, 21:36

I to was a bit shocked at just how poor the 2's brakes were , my primary car is a diesel renault clio and the brakes are super sharp,ok they are assisted.Very often i am caught out by that initial spongy feel on the 2 and end up sweating thinking will she stop in time. The braking system is apparently fine, i had it checked out at my last service, but it still leaves that, they should be better than this feeling.

proeliator2001 · February 18, 2006, 22:12

I've had a few German cars (or ones using German bits) in the past and they all had breath activated brakes which make using a car with a proper braking setup that much more interesting. What I mean by that is you have to actually press the pedal before retardation begins, which, in my book, makes the '2 a lot more controllable. Plus, I think the '2 has the best standard brakes of anything I've so far owned - it pulls up very quickly once you put pressure on, far quicker than the German cars. Over-servoed setup's just fool you into thinking you have good brakes.

If you think your ultimate stopping power is poor, you should get the whole braking system checked as my '2, with full on pedal pressure, will eject anything through the windscreen that isn't nailed down!

red_leicester · February 18, 2006, 22:58

Sorry Jason, just realised what you meant by 'more linear'. s:oops: :oops: s:oops:

fstsven · February 20, 2006, 08:17

Welcome to the world of properly set up sportscars! s:wink: :wink: s:wink:
The cars you used as a reference (147 and AYGO) have brakes that are, as in most bread-and-butter cars today, WAY over-servo'd... They fool you into thinking they've got the best brakes in the world by nearly locking up the whole system as soon as you THINK about even TOUCHING the middle pedal. That's probably to cater for inexperienced drivers not putting enough pressure on the pedal in emergency situations; call it a cheap "brake assist" system... s:roll: :roll: s:roll:
Now, in a "proper" sportscar, like ours, braking power is directly related to pressure on the pedal: low pressure~low braking power, high pressure~high braking power. This makes sure that the driver can easily and precisely modulate braking power, even to the edge of lock-up.
The MR really has great brakes: very good stopping power, solid pedal feel and one of the best ABS systems I've ever driven (only comes in when you really need it, for as long as you really need it)
Those cars you mentioned have brakes like an on-off switch; you really DON'T want that in a driver's car.

On note though; if your pedal really does feel "spongy", get them checked, because the MR should have a nice, firm middle pedal...
Greets

red_leicester · February 20, 2006, 12:27

Quote from: "fstsven"Those cars you mentioned have brakes like an on-off switch; you really DON'T want that in a driver's car

That's a very good point. The replies like Greets do make sense, you want control rather than full-on braking force when your foot feathers the brake pedal.

BenF · February 21, 2006, 00:18

Quote from: "mrsmr2"Possibly, but they feel more linear once the initial pressure has been applied. They don't start off feeling as linear.

Jason

Hmm, sounds like there may be a little air in the system? You should get positive pressure from the top of the pedal - if there is air in the system the pedal will drop a little way before the brake pads bite.

Either way, flushing the fluid and putting some new DOT5.1 is recommended.

mrsmr2 · February 21, 2006, 12:07

OK, cheers Ben.

The 2 I test drove before I bought mine felt exactly the same so I assumed it was normal.

It's overdue a change anyway. Pity Mr T only do the change at 2 years of age instead of 20k miles service.

Jason

Anonymous · May 6, 2006, 10:44

Quote from: "fstsven"Welcome to the world of properly set up sportscars! s:wink: :wink: s:wink:
The cars you used as a reference (147 and AYGO) have brakes that are, as in most bread-and-butter cars today, WAY over-servo'd... They fool you into thinking they've got the best brakes in the world by nearly locking up the whole system as soon as you THINK about even TOUCHING the middle pedal. That's probably to cater for inexperienced drivers not putting enough pressure on the pedal in emergency situations; call it a cheap "brake assist" system... s:roll: :roll: s:roll:
Now, in a "proper" sportscar, like ours, braking power is directly related to pressure on the pedal: low pressure~low braking power, high pressure~high braking power. This makes sure that the driver can easily and precisely modulate braking power, even to the edge of lock-up.

Chaps, a bit late in the discussion: but after scanning this and a few other threads it seems clear that faulty/cooked-fluid scenarios aside most people confuse pedal feel with stopping power... as Greets has described above.

Try driving a non-servoed race car brake system and you'll experience this in extremis (as I did in a comp driving Lotus Elises in Jan). I'm pretty fit and I was using an astonishing amount of force to get anywhere near threshhold braking (= the point of optimum stopping power, just before the tyres lock up - or ABS kicks in ABS equipped cars). Easily 3 to 4 times the force I use even on a track-day in my 2.

Other factors that no one has mentioned are tyre compound, tyre type and age, ambient temperature and current tyre temp, the incline of the road you're on, and how much weight you have on board. (with a passenger in my stopping distance is increased by a noticeable percentage).

The feel of your brake pedal is relevant but the ultimate stopping demonstration of your 2's braking will be when your system is warm, your tyres (pref. newish in great condition!) at some decent operating temperature (generally about 5-10mins of standard driving at a reasonable speed) and then getting stuck into yr pedal to threshhold (ie when your tyres are about to skid/lock up/stop moving - ie lose useful traction, but BEFORE they do - in ABS spyders this is when ABS is triggered).

Given that it's the control input that will tend to save your life and car in an emergency I recommend learning how to brake hard but smoothly up to traction threshold rather than just jumping on the things. (think easy in-pushing on firm but steadily- then harder till the ABS does it's banging but all in about a second or two).

For anyone who hasn't an experience of threshhold braking it'll feel pretty late and deep, but that's what the set up of our cars is meant to allow, for the reasons that Greets has described.

If you want to take it further, find safe tarmac or a skid pan etc, and disable your VDC/traction/ABS systems (2 fuses marked ABS in the L-shaped fuse box under the front bonnet) and go to town on the pedal at different speeds. You'll start to quickly discover lockup and the difference without ABS.

right - enough from me i think. s:wink: :wink: s:wink: