Ways of reducing the weight of our cars

[fuscobal]

Ok guys, here's the situation I'm in now :

1) 17'' OEM denvers + Kumho V70 R compound on 225/45/17 + R32 front brakes (Carbotech RP2 pads). The weights are 23Kg for the wheel + 21.5Kg for the brakes wich leads to a total of 44.5Kg of unsprung mass

This is the setup I will go to soon :

2) 18" TD pro race 1.2 + Kumho V70 R compound on 225/40/18 + Ap Racing 6pot 362x32 (Carbotech RP2 pads). The weights are 19.5Kg for the wheel + 12Kg for the brakes wich leads to a total of 31.5Kg of unsprung mass

PS1 : The weight saving would be around 13Kg/wheel wich I consider to be huge. From this respect I'm quite sure I will ease my coilover's job of following the track more efficiently and faster. I will also have far better brakes but...I'm not sure the 225/40/18 tires will be as good as 225/45/17

PS2 : I've also changed the arms (TT alloy with adjustable camber) and Hubs (S3 alloy). I've gained 1.2Kg from the arms and 1.5Kg from the hubs + a lot more negative camber (-2.3 as compared to -1 until now). These 2.7Kgs from the arms and hubs brought me more comfort while keeping the fast coilover response ?!?! Since the hub is just a solid piece of metal, I can't see how it can contribute to increasing the comfort other than by it's own reduced mass wich helps the coilover moving more efficiently !

Now, the question comes : Do you estimate the benefits of 13Kgs weight reduction and better brakes will outcome the possible loss of grip from the 18'' as compared to 17'' ? Does anyone know a track test between 17'' and 18'' with the same tire, on the same car ?

[the bruce]

I don't know any test comparing 17" and 18" except http://www.kumhomotorsport.pl/prasa/AutoBild_0205.pdf.
But I have discussed this issue to Raeder Motorsport and some
other mates doing motorsports.
So I'm sure there is no loss of grip with the 18". Raeder prefers
225/40 R18 on Golf and A3.
Most of the professional teams currently also use 18".

[fuscobal]

Yes, Bruce but it depends what tire they use on 18''. I'm afraid that 225/40/18 hasn't got enough sidewall. Racing cars may use 275/35/18 for ex wich has more sidewall !

[the bruce]

No, I have spoken about Golf class touring cars including Scirocco and BMW 1- and 3 series.
Most of them use 240-18 or similar.

I now have found one more review for you:



'White'' ist stock Ambition 17" and ''blue'' is 225/40 R18 Hankook S1 on 8x18,
both with stock suspension.

I currently run 17" on Denvers. I will defintely go for 18" Direzzas when the
Federals are worn.

[_Nathan_]

Slicks use a different system of measurement altogether, a 250/640/18 has an identical diameter to a 220/640/18 and a 320/640/18 - the diameter is a measurement rather than a percentage of the width.

I believe the BMW BTCC cars use 235/610/17 and the WTCC cars run 240/610/17.

What do the Seat supacopas run?

[the bruce]

What do the Seat supacopas run?

Yokohama
210/650 R 18 wet
230/650 R 18 dry

http://www2.yokohama-online.com/ch/motor-sport-event.php?pageID=22114


Volkswagen Motorsport Sciroccos R cup and 24h use 18" as well.

Of course 17" won't be much slower on most circumstances.
Biggest argument for 17" is the price !! And I strongly believe that
17" Direzzas will be faster than most 18" semis.

[_Nathan_]

Thing is without access to the regs it is difficult to know why they are running a given wheel size, wheel size is often dictated by brake size, I have heard people say to run the smallest wheel that will fit over your brakes and certainly don't believe that the bigger the better, the only way to be sure is to do a back to back in the car being discussed with the same driver and an engineer on hand to adjust the geo and damping to suit the tyre. I doubt there is a hard and fast x size is quicker rule that works across all cars and all setups due to the implications of weight, the way tyre side wall acts as part of the suspension, slip angles of tyres etc etc.

Have you compared Michelin Pilot Sport Cups to Direzzas? On my other car the MPSC really is very good indeed for a road legal tyre, I'd be surprised if anything was faster on that car, Golfs may differ obviously.

[the bruce]

Nathan,
I never tried Direzzas on my car and I never tried PS Cup. I cant't afford testing
all makes of tyres.
But I know some people doing motorsports and talk to them nearly every week.
I have some friends doing Autocross as I do and some professinals like Chris Breuer
at Raeder Motorsport. Further on I see what kind tyres win the races.

So that's (just) one basis for my point of view. I want to win. So I'm going to buy
the right stuff that provides first places. The PS Cup is one of the very best semis,
the V70 as well. But the Direzza currently is even better imho.

I know about choosing wheel sizes depending on regs an brake dimensions.
But this does not mean with a smaller brake you better go for smaller wheels.

I also never said ''bigger is better''. I know about ''rotational masses'' and the
damping properties of tyres. I currently have three sets of wheels, 17", 18" and 19".
No doubt - 19" is slowest.

So I'm wondering if you misunderstood me. 


Fact is:

- Raeder recommends 18" for track days (''Touristenfahrten'')
- Volkswagen Motorsport uses 18" on Leon, Scirocco and Golf
- formely many teams used 17"

So you can make your opinion by yourself. 

[fuscobal]

http://www.mk5golfgti.co.uk/forum/index.php/board,27.0.html > Anyone ? 

[_Nathan_]

Hi The Bruce - Sorry, I wasn't saying you had said bigger the better, just saying that I didn't think like that.

All I was getting at is wondering if Seat would've specified 18" wheels if they had smaller brakes? I guess we will never know.

I run 250/640/18 all round on my car despite the road car coming on 19" wheels (235/35/19 & 265/30/19), I'd give 17" wheels a go if they fitted over the brakes.

[fuscobal]

Old steering rack (2006) > 13.4Kg
New steering rack (2011) > 12.2Kg

Just replaced the old worn steering rack with the new gen3 one wich is also 1.2Kg lighter as it seems 

[the bruce]

Any issues with the change ??

Is it bolt directly to the subframe (I guess)?

[Tfsi_Mike]

quite a bit of movement in my steering wheel.  Have some suspect handling atm.  If tyres, alignment and check of ball joints/top mounts/bushes etc doesnt fix it new rack may be another kilo lost :) Depending which one I have on currently

[the bruce]

Seat Leon Supacopa

210/650 R 18 wet
230/650 R 18 dry

Scirocco R cup:

240/640 R18


(AP Racing 356 mm)

[Tfsi_Mike]

Old steering rack (2006) > 13.4Kg
New steering rack (2011) > 12.2Kg

Just replaced the old worn steering rack with the new gen3 one wich is also 1.2Kg lighter as it seems 

Did you bother with polybush?