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tyre and handling "gurus" - answer me this...
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Author:  simon k [ Fri Dec 07, 2007 8:45 am ]
Post subject:  tyre and handling "gurus" - answer me this...
3 months ago, I did a local motorkhana, and as you do, I put 50psi in my back tyres for it... I forgot, and continued driving around with 50psi until the next motorkhana, when I checked the pressures, 50psi was still there - "oops" I said, "wow, I didn't notice any handling difference at all" I said. I left the 50psi in them, and they're still at 50psi today. The back tyres are pretty much rooted, they're very close to the wear marks, and are badly scrubbed on the inside of the tread from when I had them on the front with the alignment out of whack (too much toe out)

the fronts tend to have about 28-30 in them, give or take... they're in OK condition, say 60%

all 4 tyres are Bridgestone SF226 - according to most people, an average "budget" 10x165 tyre

my mini has Hydrolastic suspension, pumped up to the factory specified pressure, 0.5 degrees of positive camber on the front wheels. About 3" between the tyre and the mudguard at the front, so factory ride height.

today it is PISSING rain in Albury/Wodonga, big storm, lightning, thunder, big puddles, rivers across the roads, you name it...

driving to where I'm working is about 15k's of average city roads, 50k's, a bit of 80, probably 8 roundabouts of different sizes, a few sets of lights. Some of the roads are in good condition, some are pretty miserable. They're all high traffic roads - at least, as high as you can get for an area with 120,000 people

It hasn't rained for a week or so, and has been very hot the last few days. The roads weren't especially greasy, but not "clean"

No matter how reckless I tried to be (when it was safe - no cars, nothing to crash into etc. etc.) I couldn't get the back-end to break away. I even did a handbrake turn on one bit of road and it took a lot of effort to get it to slide...

so why?

why didn't my car have obscene oversteer when I tried to flick it around a roundabout?

why didn't I do 360* spins when I went through puddles?

why did my mini behave the way it always does - straight and neutral?
Author:  Lillee [ Fri Dec 07, 2007 8:56 am ]
Post subject: 
haha very good question. When I had bridgestone at the back, it was very easy to spin! (Ask Gafmo). But mine the rubber was hard and subsequently had bugger all grip.

Just because your tyres are worn does not mean they have less grip per se. A good example is Yoko A008, some people reckon worn ones are better for the track then newies.

Depends on how much Fanging you are giving to her. If you are running a std mini with std power output, I think it would he hard to spin or lose grip in dry conditions... Minis with their low center of gravity can handle quite a fair bit of pounding around corners before they let go. Have you tried pounding her in the wet? I bet you won't be nearly as grippy...

Lastly all I wanted to say actually was that it's handling well cause "IT'S HYDROLASTIC" 8) 8) 8)
Author:  1018cc [ Fri Dec 07, 2007 9:17 am ]
Post subject: 
Lillee wrote:
Have you tried pounding her in the wet? I bet you won't be nearly as grippy...


:lol: :lol: :lol: :lol: :lol:
Author:  simon k [ Fri Dec 07, 2007 9:21 am ]
Post subject: 
Lillee wrote:
Depends on how much Fanging you are giving to her. If you are running a std mini with std power output, I think it would he hard to spin or lose grip in dry conditions... Minis with their low center of gravity can handle quite a fair bit of pounding around corners before they let go. Have you tried pounding her in the wet? I bet you won't be nearly as grippy...


HIM... He's a boy... ;)

fanging my brick? you don't know me well enough Chong... while I've slowed down since my accident a few years ago, I don't take it easy, I give him a good workout every time we go for a drive....

as for power output - the previous engine had 52bhp atw at the MRC dyno day a couple of years ago, this engine is about the same

how about I add this to the mix - I have a very substantial towbar at the back - easily 25kg

hydrolastic, yes.... and I think another big difference is that I actually HAVE some suspension travel, instead of riding on the bump stops like a lot of people do
Author:  sgc [ Fri Dec 07, 2007 9:37 am ]
Post subject:  Re: tyre and handling "gurus" - answer me this...
simon k wrote:
why did my mini behave the way it always does - straight and neutral?


With 0.5 deg positive camber on the front, you're going to tend towards understeer. If you've got crappy rear-end grip, it's going to balance out towards a tendency to drift, but not specifically at either end. That towbar is probably helping you ;)
Author:  simon k [ Fri Dec 07, 2007 9:49 am ]
Post subject:  Re: tyre and handling "gurus" - answer me this...
sgc wrote:
simon k wrote:
why did my mini behave the way it always does - straight and neutral?


With 0.5 deg positive camber on the front, you're going to tend towards understeer. If you've got crappy rear-end grip, it's going to balance out towards a tendency to drift, but not specifically at either end. That towbar is probably helping you ;)


so you reckon with better tyres on the back I'll have more understeer?

alrighty then.... some more detail -

with the ride height so tall (well... compared to most minis) there was 2* of positive camber (as per factory), so I have 1.5* fixed bottom arms on the front

and I don't have a lot of unsprung weight

    lightweight wheels - around 2.5kg
    alloy brake drums on the back


I also have competition bump stops at the back, but generally there's at least 1" between them and the body, so I don't see them making a lot of difference in this situation
Author:  sgc [ Fri Dec 07, 2007 9:57 am ]
Post subject:  Re: tyre and handling "gurus" - answer me this...
simon k wrote:
so you reckon with better tyres on the back I'll have more understeer?


Actually, as retarded as that sounds, yes.. I think so. Positive camber on the front will reduce your front end grip, so increasing your rear-end grip is likely to highlight any shortcomings at the front.
Author:  sgc [ Fri Dec 07, 2007 10:00 am ]
Post subject:  Re: tyre and handling "gurus" - answer me this...
simon k wrote:
I also have competition bump stops at the back, but generally there's at least 1" between them and the body, so I don't see them making a lot of difference in this situation


They'll help control pitching, but if you have the later hydro bags with working restrictors they're less necessary than on earlier cars.
Author:  simon k [ Fri Dec 07, 2007 10:26 am ]
Post subject:  Re: tyre and handling "gurus" - answer me this...
sgc wrote:
simon k wrote:
so you reckon with better tyres on the back I'll have more understeer?


Actually, as retarded as that sounds, yes.. I think so. Positive camber on the front will reduce your front end grip, so increasing your rear-end grip is likely to highlight any shortcomings at the front.


doesn't sound retarded at all... gives weight to the argument some people have that you should put your best tyres on the back of the car - an argument I obviously disagree with

obviously as my rear tyres wear out, I'll get more oversteer, if I let air out of my rear tyres, I'll get more grip and therefore understeer
Author:  Anto [ Fri Dec 07, 2007 10:39 am ]
Post subject: 
For comparative sake, I had accidentally let the rear tyres on my daily hack get embarrassingly low (ie, 10 psi), and the car was going sideways quite a bit. I thought it was just that the tyres on the back were 'budget' at best and are nearly on the markers. No, just that tyres don't function properly with no air in them.

On the understeer vs oversteer argument, my hack is a relatively large FWD and is quite well balanced with new tyres on the front and crap tyres on the back. I would expect when I put new tyres on the back, it will have more of a tendency for understeer.
Author:  TheMiniMan [ Fri Dec 07, 2007 12:08 pm ]
Post subject: 
most of the smarter race guys will pump their tyres up for racing in the wet.
Author:  Morris 1100 [ Fri Dec 07, 2007 7:24 pm ]
Post subject: 
TheMiniMan wrote:
most of the smarter race guys will pump their tyres up for racing in the wet.
Yes, it stops the aquaplaning and lets the tread do its job.
Author:  meeni [ Fri Dec 07, 2007 7:26 pm ]
Post subject: 
doesnt it have something to do with the track temperature not creating the optimum running temp and therefore the tyre not pressurising to its full potential.. (im not sure if this is right but that the reason i would have thought of when i do mine)
Author:  Lillee [ Fri Dec 07, 2007 7:46 pm ]
Post subject: 
1018cc wrote:
Lillee wrote:
Have you tried pounding her in the wet? I bet you won't be nearly as grippy...


:lol: :lol: :lol: :lol: :lol:


Oh grow up!!! (but funny though now that I read it) :lol:
Author:  dove grey 64 [ Fri Dec 07, 2007 7:48 pm ]
Post subject: 
Quote:
No matter how reckless I tried to be (when it was safe - no cars, nothing to crash into etc. etc.) I couldn't get the back-end to break away. I even did a handbrake turn on one bit of road and it took a lot of effort to get it to slide...

so why?

why didn't my car have obscene oversteer when I tried to flick it around a roundabout?

why didn't I do 360* spins when I went through puddles?




i dont think your driving fast enough, a pretty well setup mini will keep to its line and not lose control easily, and the speeds you have to drive at to make them really unstable is quite scary at times.
try some Scandinavian flicks at high speeds, and some left foot braking too.
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