Handling and braking issues...

Tem · July 23, 2003, 14:27

First of all, the car has the full Sportivo suspension, Member brace set, Front&Rear strut tower bars from TRD and iMR2's Anti-Flex plate. And Bridgestone S03's on non-stock sizes of 205/50/15 and 225/50/15. The alignments are front camber -1, front toe 0, rear camber -1, rear toe-in 0.5. (all in degrees, even the toe)

The car sticks to the road a million times more than the stock, but feels a bit weird. When turning quickly, it kinda feels like the front end turns immediately, but the ass starts turning a bit later. No problems in constant radius corner, just the start of it. Kinda hard to explain, but any ideas or guesses how to cure this...? Set the rear toe to 0..?

Another thingie is that the tyres sidewalls feel a lot softer than the stock A043's. Are they really so, or is the non-stock size causing it. I've tried different pressures, but can't seem to get it right. Since the fronts are the same size as stock rears, I have the stock rear pressure on them now (2.2bar). And since I still have the 20mm difference, I kept the difference in pressures, putting 2.6bar to the rears. The stock pressures are 1.8&2.2bar, don't remember what they are in PSI. What pressures are you guys using on your S03's and on what sizes..?

And the brake issue...if I slam the brake pedal to the floor, the front tyres lock up (well, at least the fronts, can't tell for sure about the rears). But not for good, maybe for 0.5-1 seconds, can't really time it, but you get the idea. This problem goes away with ripless-el-cheapo-tyres. Is my ABS going nuts, or is it just a bit slow in handling that extra grip. Any way to reset/retune it..?

And before anyone asks why I didn't get 195/50/15 and 205/50/15...finnish dealers/importer didn't have any 195/50/15's and they quoted a 6 weeks wait for them (and I needed tyres right then).

Anonymous · July 23, 2003, 15:35

Quote from: "Tem"Kinda hard to explain, but any ideas or guesses how to cure this....

Try playing with the PSI a little.

markiii · July 23, 2003, 15:58

S03 have pretty hard sidewalls. Personally I think it's due to the size of your tyre relative to the rims.

While they will fit (Obviously) you really will get a lot of tyre roll with 205 on a 6" rim.

Tem · July 23, 2003, 22:17

WD, how high you think I could go..? I've had the rears up to 3.0bar (43.5PSI) and it didn't totally cure it...was better than the 2.6bar though. 3bars/43.5PSI just sounds a bit high... s:? :? s:?

mark, I thought about the issue of +20mm on same width wheels myself (but couldn't afford any good&light wheels). But since the stock rear wheels are 6.5" and have 205 tyres, I didn't think the 1/4"/side would really make a difference...can it really be just that..?

Anonymous · July 23, 2003, 22:27

Quote from: "Tem"WD, how high you think I could go..? I've had the rears up to 3.0bar (43.5PSI) and it didn't totally cure it...was better than the 2.6bar though. 3bars/43.5PSI just sounds a bit high... s:? :? s:?

...humm, you tried a little lower?
I dunno now i'm just starting to guess s:? :? s:?

markiii · July 23, 2003, 22:41

Quote from: "Tem"WD, how high you think I could go..? I've had the rears up to 3.0bar (43.5PSI) and it didn't totally cure it...was better than the 2.6bar though. 3bars/43.5PSI just sounds a bit high... s:? :? s:?

mark, I thought about the issue of +20mm on same width wheels myself (but couldn't afford any good&light wheels). But since the stock rear wheels are 6.5" and have 205 tyres, I didn't think the 1/4"/side would really make a difference...can it really be just that..?

I suppose the 225 on 6.5" is probably more of a problem.

I juts bought stock size Eagle venturas for my 15s and it's felt like the car is trying to kill me for the last week or two. The sidewalls are so soft the rears roll on over on the sidewall as you corner hard. Scary Stuff

While S03 are quite hard sidewalls at 225 on a 6.5" rim I'd expect you to get the same problem. There isn't really sufficient wheel to support the tyre.

mph · July 23, 2003, 23:13

I'll agree with mark on this one - 225 on a 6.5" is asking for problems. Ideally you should be thinking 7.5", 7" at a min really.

Tem · July 24, 2003, 22:16

Quote from: "WoodenDummy"...humm, you tried a little lower?
I dunno now i'm just starting to guess s:? :? s:?

Yeah...it starts to feel wobbly with lower pressures. Haven't had any time for this now, but I'll give it a go next weekend...

Mark and mph, I kinda went by this table:
m http://faq.varas.to/rengasvanne.html m

It says 225/50 should be ok with 6.0-8.0" wheel, and 7.0" would be the best. Dunno, maybe the 0.5" really makes a difference then. Can't afford new wheels before winter anyway, so is there any other way to make 'em better..? Just up the pressures and hope the grip doesn't fly away..?

mph · July 24, 2003, 23:30

Have investigated further and it seems as though Bridgestone don't mind the 205/50R15 on a 6.5" rim.

I've posted up the geometry values that Toyota use:
m http://www.mr2roc.org/viewtopic.php?t=564 m
Looks like your value for rear toe could be a little out, though whether that's enough to cause the problems you're having I'm not really sure.

Anonymous · July 25, 2003, 13:07

Given the setup of your car, your not gonig to get a sensible answer unless you find someone running a very similar setup, who has done a lot of setup testing.

I can only assume you are driving on track to be worrying about this, so you need to test with a few changes, I would start with some front toe in, as 0 toe is not the norm. Depending on the size of the circuit you use, you should run 4 lap stints and run sweeps of front toe from 0 to -1 in reasonable steps. Obviously running a lot of toe in is going to worsen your tyre wear.

Timing is the only way to determine improvements, other than fairly course subjective views on turn in etc. Soyou need to lap consistently within a few tenths before you start changing things.

Of course, you will probably find that you can improve your laptime far more by driving around this, adjusting your entry line so you maximise speed into the corner, as you don't have the horsepower to maximise the slow in fast out line.

As for your braking, you need to improve your braking style, as you have to load the front tyres up more gradually before you can get maximum braking effort from them, if anything you should be disabling the ABS completely, as it will limit your braking on the limit in the dry for sure, and even in the wet, it is often an unwelcome distraction.

Lastly read up on driving techniques, turn in dynamics, tyre slip angles etc because it may just be you need to understand better how the car is working, and adjust your driving style, not your setup.

James.

Anonymous · July 25, 2003, 14:00

Quote from: "jblackmore"Lastly read up on driving techniques, turn in dynamics, tyre slip angles etc because it may just be you need to understand better how the car is working, and adjust your driving style, not your setup.

As I understand it Tem is already a good driver.

Tem · July 25, 2003, 22:42

Edit: Oops, doublepost...mods, feel free to delete this one.

Tem · July 25, 2003, 23:14

"Given the setup of your car, your not gonig to get a sensible answer unless you find someone running a very similar setup, who has done a lot of setup testing."

Of course that would be the best thing, but I don't see that happening. And I think the 2nd best choice is this s;)

s;) Talking with ppl who know the car, didn't mph even have the Sportivo as well..? And then testing the theories/guesses. (I wish I had the time to just play with the settings for full weekend or so...)

"I can only assume you are driving on track to be worrying about this"

Well...do I have to answer that? s:roll: :roll: s:roll:

I do drive on tracks as well, but obviously most of the miles come from public roads. I want the car to handle well on "real life roads", not on the smooth track, that's why I chose the Sportivo in the first place. It would be too soft and too expensive, if my main concern was driving on track.

"I would start with some front toe in, as 0 toe is not the norm."

Wouldn't toe in just make the car harder to turn..? A straight line is always boring, so I try to have fun in places where they don't exist. I had some 0.5deg toe out in my prev (AW11) MR2 and I loved it. I actually want to set some toe out for this as well, once I get these sorted out...

"Timing is the only way to determine improvements, other than fairly course subjective views on turn in etc."

I'm not really looking for the absolute fastest laptime as I don't do any races on tracks. I'm looking for easy and predicted handling on the limits. IMHO that makes the car faster on public roads. You know...when you're taking corners at the limit and really enjoying it...and then there's some gravel or bumps on the road. I have to "trust" the car, to be able to explore the limits and have fun.

"if anything you should be disabling the ABS completely"

I'd prefer ABS, but if it keeps acting up on me, I'll probably do that. Been thinking about it for some time already...

Quote from: "mph"Have investigated further and it seems as though Bridgestone don't mind the 205/50R15 on a 6.5" rim.

That's good to know, thanks s:)

s:)

I see my rear toe is right on the acceptable range limit. I guess I'll give it a go, reducing it that is.

Quote from: "WoodenDummy"As I understand it Tem is already a good driver.

Thanks, s:oops: :oops: s:oops: but I'm not so sure about it s:? :? s:?

darrenjuggins · July 29, 2003, 12:01

Hi Markiii,

Ventures ? why ?

I purchased some of these back in 2000 when I couldn't get hold of any Bridgestones.

THe car handled trerribly, the rear end was all over the place under quick direction changes.

Spoke directly to Goodyear, who where great and said I should have never been sold them for my car as they are not designed for the toyota mr2 set up (funny they put them of the MGF though!!!!, maybe they want MGF drivers off the road!!!)

anyway, long story short, they agreed if I took it steady they would buy the tyres back of the supplier who would then give me the bridgestones when available......

think I covered about 5k on them (slowly) before my bridgestones came in !!!!

Are you changing them for yoko's or bridgestones ? stock potenza are only £70 per corner anyway ?

Cheers

Darren

markiii · July 29, 2003, 12:07

Darren,

Great to know it's not just me. Thats exactly the sensation I get when rapidly changing direction and it ain't fun. Great for getting the back end on islands though.

I doubt I'm going to get these swapped as I order them from the net directly and requested these specifically. As they are gorgeous tyres to use on the other halfs SLK. Unfortunately the same can't be said about the 2.

Running them way over stock pressures (rears are at 40psi) has helped, but I will be changing them as soon as funds allow.

back to the F1s I think.

Mark.

Comer · July 29, 2003, 13:29

Quote from: "markiii"As they are gorgeous tyres to use on the other halfs SLK.

Flash g*t. My other has got a Clio and she doesn't like me driving it!

markiii · July 29, 2003, 13:51

not driving it through choice old son, handles like a barge compared to the 2. Unfortunately even though she came out of the company car scheme, she still has the company car mentality. Which means I've had to replace her fleet department in getting everything sorted out on it.

Tem · August 12, 2003, 08:09

Seems like the weather has cured my problems...at least I can't really think of anything else. It was over 30C (+45C in the sun, God only knows how much on dark tarmac) when I had those problems...and now when the temps are around 20C, I don't have these problems anymore...tried to play with the pressures last weekend and yesterday again and even the worst settings aren't as bad as the best when it was hot.

Anyone else noticed that S03's don't like warm weather..? s:? :? s:? Somehow I can't believe the temps could make that huge difference...

(20C=70F, 30C=85F, 45C=115F)