Golf R Observations and Questions

[Corey_R]

Sorry Big_Dave but why would 18's be better still?
Does that mean that 17's and 16's would be even better still?
All depends on the rolling radius of the tyre. In fact some 20 inch combinations could be even better.
Check out this calculator before you fit your tyres and rims

Wheel / tire size calculator / comparer - RIMSnTIRES.com

A very handy tool in checking out after market rims / tyres for your car

Brian, we're talking about the Golf R here. So he means "18's will be better still than the 19's.
And it has nothing to do with rolling circumference. It's to do with rotational weight and to some extent, the more compliant sidewall allowing better bump absorbtion in 18's than 19's.

[AdamD]

I almost exclusively use the paddles. Especially at the traffic lights GP. The delay is still excruciating.

My mileage does vary - the launch/reaction delay on my DSG is, whilst not inperceptible, minimal at worst. Maybe I've just become accustomed to working around any delay subconsiously, but I still drive an auto (MkV 2.0 FSI 6-speed) fairly regularly, and there's very little in it. The GTI is my first non-manual car and I was worried about this pre-delivery, but I have to say my concerns haven't been bourne out. The R I drove felt the same as my GTI.

Maybe your DSG would benefit from a clear/relearn?

[MurphyTheElf]

Maybe your DSG would benefit from a clear/relearn?

Perhaps. Now just have to find somebody in Perth with VCD....

[Brian]

Brian, we're talking about the Golf R here. So he means "18's will be better still than the 19's.
And it has nothing to do with rolling circumference. It's to do with rotational weight and to some extent, the more compliant sidewall allowing better bump absorbtion in 18's than 19's.

Thank you Corey for your elucidation, but I was aware I was posting in a thread with "Golf R' in its title. I'm also aware that Fab_R has 19 inch wheels on his "R" because he's helped me to source a set for my lowly 118TSI (hopefully arriving any minute now).
What I was asking Big_Dave was - why would 18 inch wheels / tyres be faster accelerating than 19 inch wheels / tyres of the same rolling radius? Nothing to do with handling.
His reply made some sense WRT drag cars which can probably obtain a faster tyre peripheral speed due to "ballooning" of the tyres under high acceleration. Maybe the 18s (with their higher sidewall) may obtain some ballooning. However, if the rolling radius of whichever rim / tyre combo you choose is smaller, then the increased gearing effect should produce faster acceleration. If the 18s and 19s have the same radius / diameter / circumfrence, then acceleration times should be the same. Please enlighten me further on your "rotational weight" concept and how it affects acceleration?
Thanks in advance,
Brian

[team_v]

Thank you Corey for your elucidation, but I was aware I was posting in a thread with "Golf R' in its title. I'm also aware that Fab_R has 19 inch wheels on his "R" because he's helped me to source a set for my lowly 118TSI (hopefully arriving any minute now).
What I was asking Big_Dave was - why would 18 inch wheels / tyres be faster accelerating than 19 inch wheels / tyres of the same rolling radius? Nothing to do with handling.
His reply made some sense WRT drag cars which can probably obtain a faster tyre peripheral speed due to "ballooning" of the tyres under high acceleration. Maybe the 18s (with their higher sidewall) may obtain some ballooning. However, if the rolling radius of whichever rim / tyre combo you choose is smaller, then the increased gearing effect should produce faster acceleration. If the 18s and 19s have the same radius / diameter / circumfrence, then acceleration times should be the same. Please enlighten me further on your "rotational weight" concept and how it affects acceleration?
Thanks in advance,
Brian

Very simply (not exactly what happens but suitable enough for a basic explanation)
Force = Mass x Acceleration
Acceleration therefore = Force / Mass
The less mass you have the faster the acceleration if you use the same force, therefore lighter wheels = quicker acceleration

17 are generally lighter than 18's which are generally lighter than 19's.
So smaller (and thus mostly lighter) wheels will likely improve your acceleration times.

This is the reason BBS, Enkei, Oz etc all sell for a premium as they are light weight but strong so you can save 20-30kg when you fit your car with them.
I believe the new BBS FI style wheel comes in at 7kg per corner.

BBS FI - Perfect precision Individual - Ultra-light - Forged
The new high end product line combines technology and a unique design to a perfect and individual match.
The special technological manufacturing process reduces weight so that the FI in 19" x 8.75" weighs 7.4 kg (16.31lbs.) only! As a result the performance is increased significantly as well as driving comfort.
The FI emphasizes the unique character of the car.

Technology:
Forged blank made of aviation quality aluminum alloy.
The design is 5 Axis CNC milled for a unique look for each car.

Specials:
Weight reduced by back milling between the spokes.
Flow formed inner rim for a maximum of stability at a minimum of weight.

[Corey_R]

Rotational Weight isn't my concept. It's a basic concept of car design which is particularly important in performance cars and in motorsports. It's entirely based in physics where it's called Rotational Inertia or Moment of Inertia

I'm sure everyone already understands the important of weight reduction to performance. Most people also have heard of "unsprung" vs "sprung" weight. The basic theory of that is that you aim to reduce as much unsprung weight as possible. So much so is the importance of this, that it is beneficial to reduce your unsprung weight, even if you then need to add additional sprung weight to meet a minimum weight requirement in motorsports.

But there is also rotational weight. Rotational weight can be both sprung (crankshaft, gears, drive shafts etc), and also unsprung, wheels, brake rotors etc. Chad Knaus said in a recent "NASCAR Performance" show that in order of important is rotational weight (most), unsprung and then sprung (least). The reason reduction of rotational mass is most important is that the engine must accelerate its mass PLUS overcome its rotational inertia.

Doing a google search brought up articles specifically on this topic in relation to motorsports:
Auto Racing

In many cases, car handling can be improved by increasing the diameter of your car's wheels matched with a lower aspect ratio tire. The drawback of this is that most plus sized wheel and tire combinations are heavier than the stock smaller wheel size with a taller tire sidewall. This can make for slower 0-60mph and 1/4 mile times.

So reduction of the rim size reduces the weight and thus the rotational inertia.

I also don't think you should immediately discount "handling" as a requirement for straight line acceleration... but that's harder to quantify, although we already know that even on a GTI, the 17" wheels have beat out the 18" wheels around a track...


Edit: Oh, and team_v got in whilst I was writing that up. Cheers mate... it's good to find a 2nd person who knows what I'm talking about

[HPSOV]

There is an inherent delay of about 1 second (which is huge) that can't be overcome with fancy footwork.

I have no delay in my DSG....
The only time there is a delay is when the hill-holder activates, which only seems to be on a significant upslope. It seems to hold the brakes on for a full second regardless of what I do with the accelerator (I can be revving against the brakes, then all of a sudden it lets the brakes go and you're off with a jolt). I have found to get around this you must go straight from the brake to the accelerator, no hesitation. Normally (say on a level road where I knew the hill holder wasn't going to be a pain), I would take my foot off the brake when the lights go green, the car starts to roll a bit, then when the car infront has started moving enough I start accelerating. On a hill I cant do that, I have to wait until the car infront has moved enough that I can go, then I go straight from brake to accelerator and the hill holder doesn't cut in.

[Lex200]

I have no delay in my DSG....
The only time there is a delay is when the hill-holder activates, which only seems to be on a significant upslope.

I find the hill-holder very frustrating. Mine activates on only minor slopes and makes takeoff unpredictable and rough.

Can the hill-holder be adjusted to activate with more/less slope? Can it be turned off?

[HPSOV]

Can the hill-holder be adjusted to activate with more/less slope? Can it be turned off?

I would love to know the answer to that too!!!
My WRX had hill-holder, it would hold until you moved the clutch, it was awesome. Maybe the DSG one should hold until it senses some accelerator then let go, rather than this completely arbitrary 1 or 1.5 seconds or whatever it is.

Have a go at getting from the brake to the accelerator very quickly, it seems to stop it activating completely for me.

[Brian]

Edit: Oh, and team_v got in whilst I was writing that up. Cheers mate... it's good to find a 2nd person who knows what I'm talking about

Many thanks Team_v and Corey for the explanations. I guess when it comes down to it, the only thing that matters is the time on the clock at 100km/h or the end of the quarter mile! I may have shot myself in the foot for getting the 19s for the TSI, (arrived just after I posted earlier) but lucky the Bluefin from Superchips arrived not long after.
I'll cease to hijack this thread now and let it go back to the mighty "R" and not physics