Mythbusters.

[Abnormal]

For example:
1X 15 inch wheel + tyre weighs 12kg
1X 17 inch wheel + tyre might weigh 20kg.

Have you actually weighed each wheel? This is a very generic statement, which I thought Panic would have picked up.

Part of me want to weigh my BBS 16'' rim vs my STW17'' rim this week end...

its only an example does not need to be accurate.

check out
http://www.wheelweights.net/

[MeanTdi]

its only an example does not need to be accurate.

check out
http://www.wheelweights.net/

Thanks

[Jetta2]

For example:
1X 15 inch wheel + tyre weighs 12kg
1X 17 inch wheel + tyre might weigh 20kg.

Have you actually weighed each wheel? This is a very generic statement, which I thought Panic would have picked up.

Part of me want to weigh my BBS 16'' rim vs my STW17'' rim this week end...

That's why it said "For example" and "might weigh"
Yes, very generic statement, but it is a fact that 17's are heavier than 15's, unless we are talking about the uber expensive lightweight Compomotive, OZ etc alloys which will weigh only slighty more in 17 inch flavour than smaller diameter alloys.

[panic-mechanic]

I saw it but wheel weight isn't an arguement I'm getting involved in.

[VWicked]

Got one,

Will lowering your suspension increase tyre wear as the car has a lower centre of gravity?

[panic-mechanic]

If you just install lowering springs in the front without having your wheel alignament fixed yes it wiil but it's because the alignment is incorrect - not because of lower C of G. If the alignment is correct and you drive the same tyre wear will not be different.

[VWicked]

okay, thats what a guy told me, as since the tdi has alot of torque, it will bite harder with the drop and eat tyres. Im assuming he thinks i will be launching the car more and with the drop...

[panic-mechanic]

Of course if you now drive the car like you are Micheal Shumacher with the Monza race track in front of you then yes it will eat tyres more. If you drive it like you always did then it won't. But why are you wanting to install the drop - purely for 'looks' or becuase you want to drive it harder in corners.... No need to answer - sure you can work it out for yourself.

[Smok3X]

Panic... Since we are on the topic of lowering... Just thought I would ask your opinion on this.

For Drag use only ofcourse... How beneficial on improving traction... would raising the Golf 1 at the back be? By example fitting a shock absorber that stays right up... So that the car sits slanted heavily downwards at the front... So when launching off the line, the front doesnt lift up so much and sort of "squat at the back" when the load transfers. There are tons of MK1 Drag cars with this conversion in Durbs... Was thinking of trying it for the next drag... But would this really make much of a difference?

[VWicked]

Of course if you now drive the car like you are Micheal Shumacher with the Monza race track in front of you then yes it will eat tyres more. If you drive it like you always did then it won't. But why are you wanting to install the drop - purely for 'looks' or becuase you want to drive it harder in corners.... No need to answer - sure you can work it out for yourself.

Thanks Stephan, yes its for handling as well as looks, want to do more track days etc. I wont spend over R 2k for just looks, as I could buy cheeaper N force kits for looks

[panic-mechanic]

raising a FWD car in the back and making it hard(with springs - not the shock) does make a big difference. Sadly that setup is not friendly for everyday use so now your car becomes a basically drag only car. You also want to fit shocks on the front that reists being pulled up - so basically a shock with very hard rebound.

[PoLonY]

raising a FWD car in the back and making it hard(with springs - not the shock) does make a big difference. Sadly that setup is not friendly for everyday use so now your car becomes a basically drag only car. You also want to fit shocks on the front that reists being pulled up - so basically a shock with very hard rebound.

ok im gonna sound major stupid but if you don't want any weight transfer to the rear why not just have a solid suspension setup at the rear, ie welded in one time with no shocks or springs, just solid mounted like engine mounts???

[Scatman]

Howzit @Polony, I think that having a solid rear suspension would almost be suicidal on anything but a perfectly flat surface hey. Like on Tarlton, those bumps would catch the rear of your car off-guard, and you might battle to keep your car straight.

Well thats my theory

[panic-mechanic]

Exactly right. Jaco Liebenberg wrote off his scirocco at Tarlton for pretty much that reason. They had put rods in to make the rear suspension basically solid. He did a massive run - 10 something and when he backed off and started braking the rear started stepping out and he could not control it. So no - totally solid is a bad idea. You should have some sort of movement still at least.

[Joe]

Nice thread for a change. Pity I missed it all.

[Scatman]

Myth:
A hatchback has a void, or low-pressure zone behind it when its at high speed, and this void actually reduces the top-speed of such a car. This effect can be reduced by fitting a small wing to the rear of the car (top part of the tailgate) that reduces the effect of the void and effectively increasing the top-speed of the car.

I've heard this from a few okes in Rustenburg, would like to know how true it is...

[Smok3X]

Oh so its the springs that must be harder at the back. Yip I can imagine totally pointless and dangerous for a road car... But I wouldnt mind trying it out just for the event, it isnt hard to change rear springs... Mmmm...

[VWicked]

Oh so its the springs that must be harder at the back. Yip I can imagine totally pointless and dangerous for a road car... But I wouldnt mind trying it out just for the event, it isnt hard to change rear springs... Mmmm...

Cant coil overs be a solution? Depending on how high they can go...

[Abnormal]

Myth:
A hatchback has a void, or low-pressure zone behind it when its at high speed, and this void actually reduces the top-speed of such a car. This effect can be reduced by fitting a small wing to the rear of the car (top part of the tailgate) that reduces the effect of the void and effectively increasing the top-speed of the car.

I've heard this from a few okes in Rustenburg, would like to know how true it is...

hmm.. iirc the standard kamei spoiler on a cti is good for an extra 3km/h on top end

[Scatman]

Haha, 3km/h?!
Wow thats amazing. So this myth is plausible?

I know that the Renault (puke) Megane has that characteristic upright rear window to reduce its drag coefficient. Interesting to say the least.

[PoLonY]

Haha, 3km/h?!
Wow thats amazing. So this myth is plausible?

I know that the Renault (puke) Megane has that characteristic upright rear window to reduce its drag coefficient. Interesting to say the least.

same reason the previous gen honda accord had a flat upright boot...

[Scatman]

So then how does the Citroen DS21 compare in this regard? I reckon that it's pretty aerodynamically efficient?





My uncle had one of these, and I thought it was a flippin cool car back then... I still think its forkin heavy though, we battled to push that thing down our driveway

[PoLonY]

no idea, but a cars aerodynamic efficiency is found in its Cd value, the closer to zero it is, the more "slippery" and efficient the shape of the car is, anything under 0.30 is good...

[Scatman]

Yes you get Cd(diameter), Cl(length) and the Cf(friction force)...

Its funny how the beetles' Cd is lower than a lot of the more modern cars out there

[BlueBlob]

Not going to sort out the quoting, but let me answer a few of the questions.

1. Yes, a hatchback creates a vortex behind it that sucks it back. It's simple flow dynamics. The genuine Kamei boot spoiler off the GTi/CTi, makes around a 4km/h difference to top-end, all things being equal, because it lessens the disturbance in the air behind it.

2. Making the rear shocks on a drag car solid helps, yes, but it's unsafe, and it's actually illegal now in SA Motorsport. The rules specifically state that you have to have a fully working shock/spring assembly per wheel. (doesn't apply to rails and F/C's though, but all the pro- and street classes)

3. Raising the rear should work in theory, but I've proved it to be incorrect, at least on my car. I think the problem is that raising the rear on a stripped drag car makes so little difference to weight transfer that you're wasting your time. The best times I've ever run was with a rake of 1cm. Smaller rake I go slower, but bigger rake makes no difference. You want the rear to be hard though so it doesn't squat, but you need to still have a small amount of droop to keep the car semi stable when you hit the brakes.

4. Lowering a car might very well increase the top speed. As will tucking away exhausts that hang out, etc.