Brake Upgrade dribble

[Duncan]

Interesting point re tyre size, I have heard that before....would be interested on SK's comments since he was sitting across the table at the same time

I always thought bigger tyres meant more contact patch, but the arguament was that at the same car wieght and same pressure, the same amount of tyre will be touching the road no matter what the size since it is just the car's weight pressing down and the tyre pressure holding it up.....

[Roy]

F=uN So irrespective of tyre size the Normal force will always be the same.

But if you have a 5kg block with a contact surface are of say 10sq.cm, then the same 5kg block with contact surface area of 20sq.cm. Which will be the first to start to slide if i exerted a 1kN sideways force?

[dangerous_daveo]

From Autospeed I think...

Turns out I was wrong, I was thinking suspension, go softer suspension so the tyre doesnt have to work so hard, mostly the tyre walls. Personally Id still stick to 17s at the max, I feel the sidewall movement, and the added air helps handeling on the street on rougher roads.

"

So, what about tyre pressure? Obviously, tyre pressure plays a very important part, but there are clearly limits on both sides of the tyre pressure equation. At the higher end, there is the maximum tyre pressure that can be sustained before there is damage to the carcass. At the low end, you don't want the sidewall almost collapsing, generating massive heat, and have the tyre slipping on the rim. So, you can play around with tyre pressures to optimise your set-up, but there are limitations.  

A simple way to find out approximately what pressure is optimal for your combination is to draw a chalkline across the width of the tyre, drive for a bit, and look at the wear pattern of the chalkmark. Wearing more quickly in the centre indicates pressure that is too high, and wear on the edges indicates too low a pressure.  

One issue to consider is that, for wet weather driving, despite what you may have heard, it is better to increase your tyre pressure, not reduce it. The reason is that there is a relationship between tyre pressure and the speed at which there is the onset of aquaplaning. In the Imperial system, the equation is 9 times the square root of the tyre pressure. So, if your tyres are at 25 psi, if you drive into a puddle that is deeper than your tread depth, you will aquaplane at 45 mph (72 km/h), whereas if your tyre pressure was 36psi, you would aquaplane at 54 mph (87 km/h). The advantages are obvious.  

As far as tyre profile is concerned, the main benefit is one of handling - the lower sidewalls give reduced sidewall deformation under lateral loading, which results in improved steering response and a more stable contact patch.  

Conclusion  

Summarizing, what factors are important in terms of tyre grip? Tyre width has no direct relation to the amount of grip generated; it is a secondary factor, and the width basically relates to cooling potential and so the tyre compound that can be used. The size of the contact patch has no bearing on the amount of grip generated at all, apart from the extreme of where the compound is getting so hot that it no longer acts as a solid (and therefore doesn't follow Amonton's Law). The tyre pressure has no direct bearing on the level of grip (apart from aquaplaning), but it does have a bearing on the heating and cooling characteristics of the tyre. Having a lower tyre profile gives improved handling through reduced sidewall stress and improved contact patch shape stability."

Hope that helps.

Quoting myself from another topic. But I think that sums up to a degree the tyre width thing.

But lets say a mate put a 3sgte in to a corolla where a 4age should be, he would want bigger brakes correct due to the significant increase in front end weight???

[Roy]

LOL...its a simple equation:) But id rather be given 265 rear tyres then 225 rear tyres:)

[Merli]

Very interesting.

"In the Imperial system, the equation is 9 times the square root of the tyre pressure. So, if your tyres are at 25 psi, if you drive into a puddle that is deeper than your tread depth, you will aquaplane at 45 mph (72 km/h), whereas if your tyre pressure was 36psi, you would aquaplane at 54 mph (87 km/h). The advantages are obvious."

Is aquaplaning that direct a calculation? This seems almost unbelievable to me, considering that some tread pattens are much more adept at displacing standing water than other tread patterns. That calculation above ONLY takes into account tread depth, and not tread pattern (or perhaps displacement abilities measured in "mm of H2O per metre")

Also, in that conclusion from the quote above, he (Julian Edgar?) only lists the factors that DON'T affect tyre "grip", and he never answers the question he poses in the first sentance of that conclusion.

[Merli]

LOL...its a simple equation:)  But id rather be given 265 rear tyres then 225 rear tyres:)

Why? If both tyres supposedly give the same amount of grip? :confused: :kick:

Another thing to consider is that it's a generally accepted fact that staggered tyre setups (235 front/265 rear), give more traction than a 235 front/235 rear setup. At the same time it increases the car's tendancy to understeer, as there is less grip in the front than the rear.

These are commonly accepted facts, but seem to contradict the "tyre width don't mean sh1t" theory? :confused:

[GTRgeoff]

Sorry, perhaps I'm not reading this right... But how can you discount those factors so willy nilly?

That's like calculating trajectory, "assuming no air resistance or friction"? These are integral parts of the calculation? :confused:

Yeah sorry mate, I should have been more specific. The deformations of an obviously mismatched tyre size due to the pressure or load will cause the contact patch to have uneven loadings, so "high points" will load more and generate more heat. The width, diameter relationship still has to be reasonable.

I recall a recent article in Racecar Engineering magazine, van Valkenberg suggested maybe extending metal wire filaments out into the free airstream to aid cooling. That guy is one hell of a lateral thinker.

[GTRgeoff]

I think, Andrew, that you are right at the point of needing to tinker with some handling setup programs. You are certainly asking the right questions. The understeer can be initially countered with some extra castor. I have 235 front and 255 rear and had understeer issues before pulling in some more castor. Of course I can still induce understeer.

I think Roy just needs a 33, everything is BIGGER.

As mentioned earlier, the wider rubber allows for greater heat dissapation, particularly when staying the same diameter or limited to near larger sizes. A general rule is just get the widest allowed on for track for the heat control aspect. On normal road rubber my best time is usually the first or second flyer, and I get slower the more laps I do, but semi's work for longer.

[Roy]

Why? If both tyres supposedly give the same amount of grip? :confused: :kick:  

lol, like i said, its theory that i reckon gets lost on the way from the pub to the track. Give me wider rubber thanks:)

[Abo Bob]

I think I see the heat dissapation issue now. My new 17 inch rims also are wider at the back whereas before they were the same all round. I use these for the track.

Last time at the track I felt that the rear tyres held up longer than before (both cheap street tyres) allowing better corner exit speeds. I've always controlled understeer with my right foot although do people think that I'd have higher corner entry speeds with 245's all round or is more likely that the wider rubber on the back gives you higher exit speeds making the entry speed seem slower when in actual fact the entry speed is the same as it was before I put the wider rubber on the back???

I can also concur with my fastest laps being earlier in the day. About laps 4 to 7. Even after lunch when I would have thought that the tyres would have cooled down I'm slower. Maybe I should eat lighter lunches.

[Roy]

LOL...i always find the opposite at Wakefield. Purely because of the amount of track time you get at their open practice days, in the afternoon im always quicker. It could be because track temperature, lighter fuel load or im just starting to get my eye in after all the laps earlier int he day?!?!?!?!

And ive only ever had to fight my car on two occassions, both times i had semis on the rear and street tyres on the the front, and the thing had a fiar bit of frotn end push:( Other then that my car has always been fun and easy to drove, with a pretty neutral chassis:thumbsup:

I loved Doughboys R33 GTST though. It was so much firmer and had lots of grip. The thing moved around and was so controllable:thumbsup: It had monstrous 165/35/18s DO1Js on the back and 255??? on the front. No way on earth my car wiht pi55y little 235/17s had near as much grip:(

[Duncan]

no mate, thats becuase you were driving a decent car instead of a 32

[dangerous_daveo]

no mate, thats becuase you were driving a decent car instead of a 32

But he said R33, not cefiro... What ARRRE you talking about

With the tyres tho, is it not the sidewall movement that relates mostly to the heat, and the performace/handeling caracteristics of a tyre? And the semis have better side walls? Is that right or not?

[Duncan]

Yeah sidewalls on r tyres are *heaps* harder than regular tyres......if you are feeling nasty watch a tyre person trying to fit them to a rim

[dangerous_daveo]

Yeah sidewalls on r tyres are *heaps* harder than regular tyres......if you are feeling nasty watch a tyre person trying to fit them to a rim

LoL, I might just do that. I'll go have even more fun, and tell them that as far as I know the set I have are the only ones in Australia that'll make them sweat!

[Roy]

When fitting a tyre to my rim they botched the seal. I was driving aorund for 2-3 days bedire i noticed the car pulling to one side. So fixed up the pressure that was down around 14psi. Checked it again 3hours later and it was back down to 20psi. They sidewalls are that stiff that i couldnt readily tell the tyre was flat visually or when driving. Of course they replaced the tyre and 2nd time round didnt botch the fitment:)

[GTRgeoff]

That's why you get a set of less expensive track rims.......so they don't wreck them

[Roy]

Ok. So with Brembo 8 pots for the front and Brembo 4 pots for the rear, i just need to suss out what size rotor i can get away with running and do some master cylinder sizing calcs:)

They are going to look tuff, but im betting they dont do a whole lot for stopping distances:(

[Ronin 09]

mate, i say go 2 x 4 pot callipers on the front - just need another bracket and seeing that you're already doing some master cylinder calcs - it will be all good

[Roy]

mate, i say go 2 x 4 pot callipers on the front  - just need another bracket and seeing that you're already doing some master cylinder calcs - it will be all good

LOL...thought about that ages ago, problem is there isnt anywhere where you can bracket them off from the hub.

As much as id love to machine up custom hubs like we did for a Formula SAE car, its a road car and im not an indepedently wealthy car enthusiast with the time and money to fark things up 3 times trying to get it right...especially when there are easier ways:)

Scary thing is just speakign to a few places, they are saying that there is no way i can fit 343mm rotors inside a 17" wheel with a caliper this size.

If this is the case then im going ot have to pass on them. There is no way i want to be paying for 18" wheels and rubber...just cant afford it:(

If someone seriously wants soem truly big brakes then PM me and ill give you the details of the guy selling them. Landed they will be approx $2,000-2,150