working on my 6n2 today I saw a small air dam under my splitter, the either side a small diffuser like device to reduce pressure in the wheel arches.

Got to admit, I'm not expert on aerodynamics. What's the score with the rear diffusers on the cup cars? Or is that more about stability at speed than streamlining?

The Mk2's and 3's.

I'm skeptical about the alloys reducing 0-60 by half a second. How did you measure it?

An engine under tray would do a bit to reduce your drag as the air gets trapped in there producing drag. There's just as much chance as getting tho wrong as right, do I'd recomend lots of research. Keep us updated though, should be interesting

Got to admit, I'm not expert on aerodynamics. What's the score with the rear diffusers on the cup cars? Or is that more about stability at speed than streamlining?

The Mk2's and 3's.

like this cup?

or Berg cup?

I think it'd have to be a sledge design so that it'd be forced against the floor of the car by the turbulance, but even then, the idea is to have a little vacuum under the car for handling/stability.

I don't wanna touch this, tbh. I think my only offer should be not so much hypothetical opinion on how my model aeroplane works, but of my experience as a roofer/cladder.

When we left sheets of roofing/cladding materials on the roof of buildings, we had to strap them down like we were preparing for a tsunami. See, it's a sheet of metal only when it's not moving - but get wind under it, and it becomes a human-sized razor blade, a 60mph guillotine.

If it does end up being torn from your car by the forces that hold up Boeings, whether or not it takes the floor with it, it will slice through the air until it makes contact with an object, then slice through that too. Unless it wraps itself around something like wet paper, and that's only gonna happen if that something is hard enough to take the weight of it ten times over.

The least aerodynamic parts of the underside are the engine bay and specifically rear axle/boot area. A plastic sledge-type undertray for each will be relatively safe (won't do a child any good in the face, but not as bad as a 4ft long Stanley blade), put one either end and you can't go wrong, surely? Apart from the vehicle behind coming at you like a giant toboggan when skidding on it..

with the secure mounting, nothing will come off. not at any speed on the road. high tensile steell bolts and jobs a good 'un.

The standard alloys weighed over 7 kg and the new ones I bought from a member on here two months ago.

They were small r14 specially designed light weight alloys weighing 5kg (maybe 4.9kg).

Remember some of us guys talking about the formula about light weight alloys. i.e taking off 1kg on rotational weight is equivalent to 10kg. This is a formula, some call a myth that is on many light weight alloy websites trying to induce more sales.

Well it is true. If the design is right it works and it has for me.

I have done many tests using a (don't laugh) stop watch. both ways on same stretch of road. And have been consistent in doing my tests when I got my Chip + then again when I got the 4-2-1 manifold and again with de-cat.

Now listen carefully. I was in the 8 second range before these alloys were put on and now I am in the 7 second range. Any normal human being will see the number 7 is different to number 8.

Now go to this link: http://www.torquestats.com/modified/index....ubmit=Calculate

Taking off 100kg from 1000kg with bhp of 115 will take off more than half a second in the 0-60. Nearly a second.

I have been lean in my measurements and made sure I am UNDER-ESTIMATING. I think it is actually more. But half a second will cover it no doubt.

Those who talk before "so called wasting money" and gathering figures should be more open.

Make sure not to go R15. The weight should be to the center as much as possible. Smaller wheel diameter. Don't go bigger.

"Losing 1kg of rotational weight (ie wheel weight) is the straightline performance equivilent to removing 10kg from your car" http://www.potn.co.uk/lightweight_wheels.php :)

Edited 26 June, 201214 yr by damunk

Don't confuse inertia and mass.

@damunk

So have you changed your rolling radius?

And how were you measuring your speed?

Edited 26 June, 201214 yr by MaxMax

@ Madmax

Rolling radius same. I found it hard to find the r14 in light weight alloys but g40jon had some.

I remember him giving me a smile and telling me I'm going to be well impressed on performance and boy he was right.

£160 pound and in mint condition.

I've always used stop watch technique and if I am bad then I am consistently bad so I know how it dropped from each modification as you would say.

I've ordered some fibreglass parts from Germany. Front two doors, Bonnet, back hood and front two wings for approx 1000 Euros. They said that I will have the parts 25 days from money and it's been over 3 months and still nothing from them :(.

My plan is is to keep the car looking standard yet have that power. I will continue with the aero underneath. It will make a big difference. (5-7mpg extra)

Edited 26 June, 201214 yr by damunk

Wouldnt cutting holes in the arches reduce the air pressure around the tyres too? I noticed some cars now have vented wheel arches

I have registered to EcoModder.com

This is a fantastic site for this kind of stuff and the folks there are ultra-friendly when it comes to modifying the aero work.

I am studying this subject. It is exciting :)

@ Matt: The newer cars come with wheel wind deflectors which are peaces of plastic carefully positioned to deflect the wind away from wheels and arches. Drilling holes could be a bad idea if you end up getting it wrong. Especially with not having wind tunnel available. But in theory it could all work if you really put your mind to it. :)

Edited 26 June, 201214 yr by damunk

A stop watch is in no way an accurate way to time 0-60, far too much human error and reaction comes into play, plus inaccuracy in the speedo itself. You would have just as much chance of an accurate figure using this method as you would just plucking a number out of the air

A stop watch is in no way an accurate way to time 0-60, far too much human error and reaction comes into play, plus inaccuracy in the speedo itself. You would have just as much chance of an accurate figure using this method as you would just plucking a number out of the air

True. It is not a accurate way. You have to do it maybe 10-12 time each way then take a average. Thats the best one can do without devices JUST to get a idea that your mods are making a difference.

You can prob buy devices for this kind of reading aswell as mpg readers. With changing alloys but keeping to R14's can that alter speedo reading?

Edited 26 June, 201214 yr by damunk

There is no point doing 10-12 runs and taking an average when the figures you are taking are all inaccurate. No one has the reactions to hit start and stop at the exact time they start to move and when they hit 60, plus the 60mph shown on the clocks isn't even 60, so non of the figures are correct. There's no way sticking a lighter set of alloys on knocked .5 of a second off the 0-60 of a 6n polo. Half a second may not sound like much but when you talking 0-60 its a fairly big number

Another discrepancy that needs to be taken into account with your way of measuring 0-60 is the weather, wind direction will play a part in it but also air temp, moisture ect. The weather conditions on all test days would have to be exactly the same for your results to mean anything.

Fair play for doing all this but if your gonna make claims like "lighter wheels knocked half a second off my 0-60 times" then you really need some evidence to back this up, and driving up and down a road with a stop watch isn't going to cut the mustard

The tire profile being different would change the speedo reading, the larger the difference, the more difference it would make to the speedo reading

Edited 26 June, 201214 yr by Mclovin

There is no point doing 10-12 runs and taking an average when the figures you are taking are all inaccurate. No one has the reactions to hit start and stop at the exact time they start to move and when they hit 60, plus the 60mph shown on the clocks isn't even 60, so non of the figures are correct. There's no way sticking a lighter set of alloys on knocked .5 of a second off the 0-60 of a 6n polo. Half a second may not sound like much but when you talking 0-60 its a fairly big number

Another discrepancy that needs to be taken into account with your way of measuring 0-60 is the weather, wind direction will play a part in it but also air temp, moisture ect. The weather conditions on all test days would have to be exactly the same for your results to mean anything.

Fair play for doing all this but if your gonna make claims like "lighter wheels knocked half a second off my 0-60 times" then you really need some evidence to back this up, and driving up and down a road with a stop watch isn't going to cut the mustard

And thanks for the

The tire profile being different would change the speedo reading, the larger the difference, the more difference it would make to the speedo reading

Your saying "no way" and I think it should stop there because you've got that into your head and any evidence will still cloud your one way thinking.

However with the Fibreglass parts and also the aero mods I am pretty sure I will be at around 7.0 second at the minimum. I am not guaranteeing it as you you say "no way" which you imply "impossible" but I am going in the right direction "with my stop watch".

Thanks for the "The tire profile being different would change the speedo reading, the larger the difference, the more difference it would make to the speedo reading"

I've kept it the same so hopefully my speedo is right incase of cameras.

Edited 26 June, 201214 yr by damunk

You still have the same factor of error

I mean the light weight alloys have given me more performance than the 4-2-1 manifold. Best thing I have bought for this car by a long shot.

£160 for the alloys and I'm trying to sell my original genuine VW ones on here but no ones interested becuase of some scuffs.

Edited 26 June, 201214 yr by damunk

Don't confuse inertia and mass.

Rotational inertia and mass are quite heavily linked

Remember some of us guys talking about the formula about light weight alloys. i.e taking off 1kg on rotational weight is equivalent to 10kg. This is a formula, some call a myth that is on many light weight alloy websites trying to induce more sales.

Don't confuse inertia and mass.

...and don't believe everything you read on a lightweight wheel manufacturer's website. Especially when there's not even an attempt to back it up with any physics.

My plan is is to keep the car looking standard yet have that power. I will continue with the aero underneath. It will make a big difference. (5-7mpg extra)

I think you've missed a decimal point in your mpg claims for the undertray. I don't have much experience in the area, other than knowing what we managed to achieve at work with a shopping hatchback a similar size to a 6N and several hundred grand budget for glass-fibre spoilers, splitters, undertrays and extensive wind tunnel time at MIRA. What we ended up with were tweaks very similar to VW's Polo Bluemotion. You'll notice a difference if done properly, but if you think you'll get 7mpg improvement from that you're kidding yourself - unless you spend all your time at 110mph...

Remember some of us guys talking about the formula about light weight alloys. i.e taking off 1kg on rotational weight is equivalent to 10kg. This is a formula, some call a myth that is on many light weight alloy websites trying to induce more sales.

Don't confuse inertia and mass.

...and don't believe everything you read on a lightweight wheel manufacturer's website. Especially when there's not even an attempt to back it up with any physics.

My plan is is to keep the car looking standard yet have that power. I will continue with the aero underneath. It will make a big difference. (5-7mpg extra)

I think you've missed a decimal point in your mpg claims for the undertray. I don't have much experience in the area, other than knowing what we managed to achieve at work with a shopping hatchback a similar size to a 6N and several hundred grand budget for glass-fibre spoilers, splitters, undertrays and extensive wind tunnel time at MIRA. What we ended up with were tweaks very similar to VW's Polo Bluemotion. You'll notice a difference if done properly, but if you think you'll get 7mpg improvement from that you're kidding yourself - unless you spend all your time at 110mph...

For some alum sheets £50 pounds 4-5 strut bars at 5 quid each. And lots of time and effort and though process. Got to be worth it if you like D.I.Y.

On ecomodder.com

There is a guy with a polo diesel 1.4. Doing the same thing and I'm following his project. It's great.

Apparently 30% drag is from under car aero. i.e wheels, wheel arch etc & reducing 0.1 CD is equivalent to approx 100kg.

That is why newer cars tend to have flat belly pans and other under car aero dynamic feature. I am very surprised how this can be overlooked.

Basicaly your 6n is quicker than a g40s 0-60 because of your wheels?

With roughly the same power (from your estimates) as a g40 plus more weight?

I've kept it the same so hopefully my speedo is right incase of cameras.

Try finding when your car actualy hits 60mph before timing it

Basicaly your 6n is quicker than a g40s 0-60 because of your wheels?

With roughly the same power (from your estimates) as a g40 plus more weight?

I've kept it the same so hopefully my speedo is right incase of cameras.

Try finding when your car actualy hits 60mph before timing it

I think his focus is more on the timed delta rather than the true 0-60 time. That actual figure is pretty much irrelevant in this case, his point being by reducing rotational inertia and unsprung mass he achieved a quicker acceleration (whether the figures are accurate remains to be seen )

Basicaly your 6n is quicker than a g40s 0-60 because of your wheels?

With roughly the same power (from your estimates) as a g40 plus more weight?

I've kept it the same so hopefully my speedo is right incase of cameras.

Try finding when your car actualy hits 60mph before timing it

I think his focus is more on the timed delta rather than the true 0-60 time. That actual figure is pretty much irrelevant in this case, his point being by reducing rotational inertia and unsprung mass he achieved a quicker acceleration (whether the figures are accurate remains to be seen )

Thank you for this. I am trying to say that by reducing each wheel weight by over 2kg each I have improved acceleration up to 60 by half a second.

And I'm saying that's bollocks. Sorry if that seems harsh, but I could say that stripping the paint off my car made it half a second quicker to 60, and I could back this up with wildly inaccuratly obtained data that only exists in my head.

Now the theory would be there to back up my claims to a degree, after all I would of made my car lighter, but that doesn't mean its had any noticeable effect on it hitting 60, or on anything for that matter.

You claim to of knocked 3 seconds off the standard 0-60 with only the use of an air filter, decat, manifold and lighter alloys. If only it was that easy

You are using stuff that you have read on the internet to try and back up your claims of how much improvement your wheels have made. Unfortunately, for the most part the internet is full of shit