ex-webby

Hi All

This is the second quiz, and aimed at the more advanced topics (as the previous one was obviously way too easy!!! )

As usual, the questions and answers are based on "most likely", "in isolation", "as a rule of thumb", etc, etc. There will definitely be room for discussion in most things, but try to clear your mind and consider the pure basis of each question.

Section A - Tyres

Question 1
Increasing tyre pressure from a perfectly enflated tyre (assume a theoretical perfect contact patch) will :

a) Increase contact patch area
b) Decrease contact patch area
c) Neither

Question 2
Increasing the width of a tyre and keeping the tyre pressure the same will :

a) Increase contact patch area
b) Decrease contact patch area
c) Neither

Question 3
Adding more vertical load to a tyre will :

a) Increase contact patch area
b) Decrease contact patch area
c) Neither

Question 4
Which one of the following is a benefit of a larger contact patch.

a) Heat dissipation
b) Improved dry traction / grip
c) Improved wet traction / grip

Section B - Roll Centres

Question 5
Lowering a MacPherson strut car (without changing any pick-up points, etc) lowers the centre of gravity :

a) More than it lowers the roll centre
b) Less than it lowers the roll centre
c) The same amount that it lowers the roll centre

Question 6
Increasing the distance between the c/g and the roll centre

a) Will increase body roll
b) Will descrease body roll
c) Will not affect body roll

Section C - Mass

Take two identical powerful rear wheel drive cars. Car A has a higher centre of gravity than Car B

Question 7
Which would accelerate quickest from a standing start?

a) Car A
b) Car B

Question 8
Which would stop the quickest?

a) Car A
b) Car B

Question 9
Which would be able to corner the fastest?

a) Car A
b) Car B

Now, all the same, except Front Wheel Drive

Question 10
Which would accelerate the fastest from a standing start?

a) Car A
b) Car B

---

Submit answers as before :

1:A
2:B
3:B
etc

All the best, good luck!

Simon

Roblad

Here goes nuttin

1=B
2=A
3=C
4=B
5=C
6=A
7=B
8=B
9=B
10=B

Well it was worth a try!!

Fat Boy

These must be right as the bottom of my Guinness glass tells me they are....

A1 B
A2 A
A3 A
A4 B
B5 A
B6 A
B7 A
B8 A
B9 B
B10 B

Andy.F

Haha !

1-B
2-C
3-A
4-B
5-B
7-A
8-B
9-B
10-B

[edited by webmaster to remove potential clues]

ian_sadler

Where did the thread "are so-3s any good end up? cos all the answers are in there

Paul_M

Same as before, all answered before looking at any other replies. Gotta be honest I have no idea about section B so if I get it right it's a total fluke

1:B
2:C
3:A
4:B
5:B
6:B
7:A
8:B
9:B
10:B

Paul_M

LOL... I happened to stumble across that about a month ago, so most of my answers in section A are from my memory of that thread. Didn't go so far as to try and find it again though

TaviaRS

1 B
2 A
3 A
4 B
5 B
6 A
7 A
8 A
9 B
10 B

ex-webby

Guys

Please take care not to post any comments on why you've chosen a certain answer as it may spoil it for others.

All the best

Simon

BruceWarne2

1 B
2 A
3 B
4 B
5 B
6 A
7 A
8 B
9 B
10 B

Faire D'Income

1. B
2. A
3. A
4. C
5. C
6. A
7. B
8. A
9. A
10. A

Carl Davey

iTrader: (3)

Ok, first foray into this forum. Way out of my depth so here goes nothing...

1:A
2:A
3:A
4:B
5:A
6:A
7:A
8:B
9:B
10:B

Awaits explanations with anticipation.

SUBTYPER

1) B
2) A
3) A
4) B
5) C
6) A
7) B
8) B
9) B
10) A

chiark

1:B
2:A
3:A
4:A
5:B
6:A
7:A
8:B
9:B
10:B

mAk78

Not sure what the roll centre is!!
1: B
2: A
3: C
4: B
5: C
6: A
7: A
8: B
9: B
10: B

Twigster

1)b
2)a
3)a
4)b
5)a
6)a
7)a
8)a
9)b
10)b

My first effort, so I hope it goes well!!!

Sbradley

1:b
2:a
3:c
4:b
5:a
6:b
7:a
8:b
9:b
10:b

I think...

SB

Danbo

1:b
2:a
3:a
4:b
5:a
6:a
7:b
8:b
9:b
10:b

Dyney

Seeing as I was at the Sunseaker rally and missed the first Quiz (which I would have won)

1 : b
2 : c
3 : a
4 : b
5 : c
6 : b
7 : a
8 : b
9 : b
10 : b

But I reserve the right to change the answers without prior notice

RRH

1b
2c
3a
4b
5a
6a
7a
8b
9b
10b

ex-webby

And here are the answers...

Section A - Tyres

Question 1
Increasing tyre pressure from a perfectly enflated tyre (assume a theoretical perfect contact patch) will :

a) Increase contact patch area
b) Decrease contact patch area
c) Neither

Answer b)
As a rule of thumb contact patch area is a function of tyre pressure and vertical load alone. More pressure = less area, more load = more area.

Question 2
Increasing the width of a tyre and keeping the tyre pressure the same will :

a) Increase contact patch area
b) Decrease contact patch area
c) Neither

Answer c)
As above. It is not a hard and fast rule, as certain compounds / tyre constructions can alter this property slightly, but almost without fail, the only way you can theoretically change the area of a contact patch is by altering the tyre pressure or load on it. A wider tyre would theoretically create a wider and shorter contact patch, a narrower tyre would create a narrow, long contact patch.

Question 3
Adding more vertical load to a tyre will :

a) Increase contact patch area
b) Decrease contact patch area
c) Neither

Answer a) see above

Question 4
Which one of the following is a benefit of a larger contact patch.

a) Heat dissipation
b) Improved dry traction / grip
c) Improved wet traction / grip

Answer a)
This is a slightly tricky one. In theory, the grip a tyre produces is a function of the compound, and the load on it. If you increase the load, you increase the grip, but the grip per square inch remains the same. If you reduce pressures in order to increase the contact patch area, but the load remains the same, there will be more rubber on the road, but the load per square inch will reduce, meaning the overall grip stays the same. The difference is that the tyre is able to share the load across the contact patch, so deals with the heat better. This (plus reduced wear, etc) does however tend to increase the grip of the car once the tyres are being used. A heavier car will heat up the tyres quicker than a lighter one, so you'd be better off with a larger contact patch area on a heavier car in order to still have grip from the tyres once there is heat in them.

Section B - Roll Centres

Question 5
Lowering a MacPherson strut car (without changing any pick-up points, etc) lowers the centre of gravity :

a) More than it lowers the roll centre
b) Less than it lowers the roll centre
c) The same amount that it lowers the roll centre

Answer b)
Except in very unusual circumstances (would need to be very odd geometry) the roll centre moves faster than the c/g. Which has the bizzare effect that lowering a car may actually make it roll MORE.

Question 6
Increasing the distance between the c/g and the roll centre

a) Will increase body roll
b) Will descrease body roll
c) Will not affect body roll

Answer a)
Whether the roll centre is above or below the c/g, increasing the distance between them will make the car roll more. If the roll centre is ABOVE the c/g, it will have the REALLY odd effect of the car naturally leaning INTO the corners, not away from them.

Section C - Mass

Take two identical powerful rear wheel drive cars. Car A has a higher centre of gravity than Car B

Question 7
Which would accelerate quickest from a standing start?

a) Car A
b) Car B

Answer a)
The higher the c/g the more load transfer you get. In the case of a RWD car, you want as much load on the rear wheels as possible during a straight line standing start in order to give the rear tyres as much grip as you can.

Question 8
Which would stop the quickest?

a) Car A
b) Car B

Answer b)
Assuming the car is set up correctly, a lower centre of gravity will stop you quicker. If you only had brakes on the front of the car, then the reverse would be true.

Question 9
Which would be able to corner the fastest?

a) Car A
b) Car B

Answer b)
In all normal cases, a lower centre of gravity is beneficial for cornering as the tyres share the load more evenly which means more grip.

Now, all the same, except Front Wheel Drive

Question 10
Which would accelerate the fastest from a standing start?

a) Car A
b) Car B

Answer b)
Keeping as much load as possible on the front wheels during acceleration.

All the best

Simon

ex-webby

Answers in short format...

1:B
2:C
3:A
4:A
5:B
6:A
7:A
8:B
9:B
10:B

Allan

iTrader: (1)

1:B
2:A
3:A
4:B
5:B
6:A
7:A
8:A
9:B
10:A

Allan

iTrader: (1)

LOL..... didn't notice you've already given the answers

Andy.F

"As increasing the load on the car also increases the contact patch area, the load per square inch does not change, so the grip theoretically stays the same."

Disagree Simon
If increasing the width of the tyre does not increase grip then I don't understand how we can tune a cars handling by altering the weight transfer between axles ???
I always thought that as the load increases on a tyre the grip increased to a lesser level.

Andy

Andy S.

Glad I did this on a peice of paper I applied single seater rules to some questions and got completely different answers, When you are running 5 degrees of negative then some of the answers dont work!

ex-webby

Andy.F

Deepest apologies, and thank you for pointing that out, you are absolutely correct. I have no idea what I was on when I wrote that explanation, but I've edited it to make more sense now.

All the best

Simon

Andy.F

Cheers Simon

I think we need further discussion on tyres, I'm fairly sure that the contact patch size is not directly proportional to tyre pressure, the tyre construction will have a big effect on this as some of the force against the road will come from the sidewalls and carcase strength/resistance to deflection. For example, when my tyre on my old Cavalier is down at 10 psi, there is no way it has a contact patch area of 101 square inches !! (Assuming a corner weight of 460kg)
This completely throws out the 'std' answers to some of the questions regarding grip on wider tyres, weight transfer etc.

Do you know of any tyre experts we could throw some questions at ?

regards

Andy

Chris_P1

Well i supose i best have a go after the last fluke, or maybe Don really did teach me something. I though it was all about having a laugh and wearing out my tyres !!!

1 B
2 A
3 B
4 B
5 B
6 A
7 A
8 B
9 B
10 B

Chris_P1

Doh, The answers are there now ?