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Discussion Starter #1 (Edited)
tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

Some very interesting facts about how tyre weight differ per manufacturer and even manufacturer Spec in the same size and also the myth that 20" is far heavier then 19".
If I didn't mention the manufacturer spec (eg RO1, N1, N2..) then it is the standard aftermarket tyre. All tyres here (except Hankook, their good test results are bought...) are on the same high quality level!
Some weights:

REAR:

tyre size 305 30 20

Conti 6 FR XL: 12,8 kg
Michelin PS4S: 13,8 kg
Pirelli Zero NO (strongly reinforced for Porsche 911! but more grip): 13.1kg
Pirelli Zero RO1 (Audi R8 Gen2) : 12.1kg
Hankook: 13,86kg (smallest width of all, in fact one size smaller wide then all others)

=> weight saving potential 1.76kg per tyre

tyre size: 305 30 19
Conti 6 FR XL: 10,99kg
Pirelli P Zero N2 : 14,3kg
Pirelli P Zero RO1: 13,21kg
Michelin PS4S: 12,669kg
Michelin PSS: 12,56kg
Hankook Ventus S1: 13,262kg
=> weight saving potential 3,3kg per tyre!!!

FRONT

Tyre size: 235 35 19

Pirelli P Zero: 10.2kg
Pirelli P Zero RO1: 9,87kg
Conti 6 FR XL: 13,427kg (no typo mistake!)
Conti 5P FR AO: 9.8kg
Hankook Ventus V12 evo 2: 10,022kg
Hankook S1 Evo 2: 11kg
Michelin PSS: 9,96kg
Michelin PS4S: 10,22kg

=> weight Saving potential 3,67kg per tyre, but except Conti 6 they are pretty close around +/- 100g. Choice of exact tyre is by rear as much bigger differences

Tyre size: 245 30 20

Conti 6 FR XL: 9,96kg
Michelin PS4S: 10,38kg
Pirelli P Zero: 11,2kg
Prielli P Zero RO1: 9,67kg
Hankook S1 evo: 10,32kg
=> Weight saving potential 1.5kg per wheel

Tyre Size: 255 30 20
Pirelli P Zero RO1: 10.4kg (I am currently running this)
Conti 6 FR XL: 10,67kg
Michelin PS4S: 11,62kg

Conclusions:
1) A lot of unsprung weight can be saved by choosing the right tyre brand & model
2) the choice of tyre is led by the rear one as there are the most differences

19" versus 20":
remarks:
the rear tyre 305 30 20 is actually one size taller and more rumber, comparing to 305 30 19 the "right" tyre would be 305 25 20 (less rubber so less weight). But not interesting for me.
the front tyre 245 30 20 is also one size wider then the direct comparing one 235 35 19. 235 30 20 shouldn't be used front as LOI is spot on and no reserves here, more chamber then OEM due to coilover and you are above the limit.

With the right manufacturer tyre setup the 20" ones (being one size wider front and one size taller rear) are lighter then the lightest 19":
Pirelli P Zero RO 1 in 245/305 30 20 is front 19,34kg and 24.2kg rear, so 43.54 kg or -1.5kg in total lighter compared to the lightest 19" tyre combo one

a) closest is Michelin PSS in 19" with being 19,92kg front and 25.12kg rear per wheel, so 45.04kg in total.
b) in 235 30 20 and 305 25 20 I am sure there is another 1-1,5kg possible, so direct compared sizes its between 2,5-3kg less unsprung weight in 20" compared to 19".
c) the tyre is the most outside part of the wheel so the influence on unsprung and rotational mass is the biggest one on the car! -1kg tyre weight counts more then -1kg wheel weight.
 

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Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

Very interesting and useful info, Helldriver. Thanks for posting.
 

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Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

It is part of the whole picture, we must measure rolling radius (as it effect gearing and acceleration) of each individual set up to properly declare winner here
 

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Discussion Starter #4 (Edited)
Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

It is part of the whole picture, we must measure rolling radius (as it effect gearing and acceleration) of each individual set up to properly declare winner here
I expect the winner would be even clearer the 20" if comparing the actual same sizes in rolling radius 235 30 20 and 305 25 20 with 235 35 19 and 305 30 19. Was not asking for that precise data as not of interest for me. Asked for some data just to proof this too, see below.
Also the flow or rotation forming technology enables the wheel producers to offer 19" and 20" with nearly the same low weight for reasonable pricing and the difference to a real forged lightweight wheel in the same size is around 1-1.5kg per wheel for triple+x cost. So with the right tyre you can even compensate that in 20" but not in 19".

Done that whole picture for me. The gearing is a bit too short in the frist 3 gears on V8, especially if you modify the engine to 480hp, less curb weight plus soon RWD. With using 305 30 20 I catch 3 bunnies at the same time...lengthen the gearing a bit, having a bit more sidewall rear for more grip and a very slammed look while being on OEM ride height (speed bumps, parking garage...) with a 15mm lowered GT coilover suspension.
Front to cure understeer and have a matching rolling radius to rear the solution is 255 30 20. With the right tyres I only have a tiny bit more unsprung weight then OEM 19" setup, thats the real surprise.

Far more interesting is
- that 19" and 20" setups (tyre+rim) are in general quite even in weight, when choosen right
- some OEM tyre specs rise or lower the weight signifcantly
- that a 235 can weight more then a 255
- how much you can save in unsprung weight just by using the right tyre (brand/model/width).
Was surprised myself when I got all this data.

Also interesting and surprising is that I can go far wider with 9x20 and a 255 30 20 tyre and have only a tiny bit more unsprung weight compared to already lightweight OEM doublespoke 8.5x19 with 235 35 19 with the right tyre and wheel setup (that costs 2k). For 6k with OZ supertourismo 20" I could get another 1.5kg front and 1kg rear off with the downside of having a 8.5 front plus a rim load rating of 430kg compared to 700kg now (more stable wheel, not unimportant on bad mountain roads).
 

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Discussion Starter #5 (Edited)
Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

just some more data in the direct comparing size 235 30 20 and 305 25 20

tyre size 235 30 20:
Conti 6: 10.18kg
Michelin PS4S: 9.7kg


tyre size 305 25 20:
Conti 6: 11,88kg
Michelin PS4S: 12,19kg

so a set of Conti 6 is 20,36kg + 23,76kg= 44,12kg
set of Michelin PS4S is 19.4kg+24,38kg= 43,78kg

the lightest 19" Michelin PSS were 45,14kg, again heavier by 1.3kg then direct comparing sizes in 20".
or if you choose wrong and use in 19" the Hankook its a 22kg+27.72kg=49,72kg, means you are +5,94kg:eek: heavier then the 20" combo Michelin PS4S or +6.18kg:eek: compared to lightest 20" tyre combo Pirelli Zero RO1. Thats the weight saving potential people spend >6000Euro for a set of forged lightweight OZ wheels....
Again surprise is that the 245 30 20 and 305 30 20 combi is even lighter then the smaller 235 30 20 and 305 25 20. So its not only sidewall size.....
sometimes wider is lighter and better :)


another thing to mention, in 305 25 20 there are no OEM spec tyre avaliable. OEM have their qualified reasons not to use a 25 tyre height in 20";)


To be clear, we are talking here about weight saving only through the choice of tyre of unsprung and rotational mass.
Unsprung weight you can multiply with factor 4 or 5, means your car is 6.14kgx4 or 5=25-30kg heavier with the wrong 19" tyres, the damping is less precise with less comfort and you have more wear on everything that is affected by damping eg dampers, springs, ball joints....
rotational mass you can multipy with factor 10, means with the wrong 19" tyres your engine has to speed up 6.14kgx10=61.4kg more weight which results in less HP , torque and more fuel consumption plus higher brake wear as the +60kg have to be stopped too. And +60kg is significant here!!!
 

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Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

Somehow you missed important factor of rotational mass distribution from center. More mass further out from center is bad. So your 20 wheel set up might be equal in weight to 19, but having heavier rim barrel further out will diminish any gains from "lighter tire" you might have in 20 size.
 

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Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

Somehow you missed important factor of rotational mass distribution from center. More mass further out from center is bad. So your 20 wheel set up might be equal in weight to 19, but having heavier rim barrel further out will diminish any gains from "lighter tire" you might have in 20 size.
The information on 19's vs 20's on weights and sizes is very helpful. Its just rarely (almost never) the case that a larger diameter wheel is better for performance, handling, steering and ride even at same OD tires.

So what Andy notes here is correct. Rotating inertia which is referred to here is directly proportional to diameter to the 4th power...20^4/19^4 = 23% greater rotating inertia in simple terms...at the same weight but 1" greater diameter. More complicated than that in taking the whole mass/mass distribution...in which they are not typically for equivalent stiffness. Increasing rotational inertia is quite detrimental to acceleration and deceleration.

For a 20" wheel to equal a 19" in weight it is likely is not as stiff, which is critical for vehicle dynamics (especially handling and steering).

Reduction in overall unsprung mass with all else equal is good, but within a small range (and even larger) the suspension can readily be tuned for ride and handling.

The biggest "pro" for larger wheels typically involves ability to use bigger brakes if they are needed for fade during track running. But there are obvious rotational inertia and weight tradeoffs again depending on brake choices. And then of course many like the bigger wheels for aesthetics.

So the wheel/tire weight and size information posted here is great, but larger wheels are not a great path for better performance or vehicle dynamics.
 

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Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

A very technical answer but how do you justify that they just look good LoL.
 

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Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

LOL...I included that DaveL! Nothing wrong with that...you are just far more likely to go slower than faster!
If I want to go really fast I take the motorbike out (carbon fibre wheels and Ohlins suspension front/back and steering damper)
 

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Discussion Starter #13 (Edited)
Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

@andy: I didn't miss the rotational mass distribution from center. the tyre is the furthest out, so 1,5kg on the tyre is worse and 75% of tyre weight is outside. Overall diameter of wheel+tyre 19" and 20"is nearly the same, so 20" wheel the weight +300g in my case is further out but lighter tyre saves 1,5kg even further out=less rotational mass overall in 20".

The information on 19's vs 20's on weights and sizes is very helpful. Its just rarely (almost never) the case that a larger diameter wheel is better for performance, handling, steering and ride even at same OD tires.

So what Andy notes here is correct. Rotating inertia which is referred to here is directly proportional to diameter to the 4th power...20^4/19^4 = 23% greater rotating inertia in simple terms...at the same weight but 1" greater diameter. More complicated than that in taking the whole mass/mass distribution...in which they are not typically for equivalent stiffness. Increasing rotational inertia is quite detrimental to acceleration and deceleration.

For a 20" wheel to equal a 19" in weight it is likely is not as stiff, which is critical for vehicle dynamics (especially handling and steering).

Reduction in overall unsprung mass with all else equal is good, but within a small range (and even larger) the suspension can readily be tuned for ride and handling.

The biggest "pro" for larger wheels typically involves ability to use bigger brakes if they are needed for fade during track running. But there are obvious rotational inertia and weight tradeoffs again depending on brake choices. And then of course many like the bigger wheels for aesthetics.

So the wheel/tire weight and size information posted here is great, but larger wheels are not a great path for better performance or vehicle dynamics.
in general I fully agree on what you wrote. And on most cars I went 1" down from OD e.g. BMW 1M from 9/10x19 to 9.5x18 all around.
The R8 Gen 1 seems to be an exception as Audi developed it as street daily supercar and then "applied" its Audi typical security understeering setup. The front tyre is on purpose too less wide combined with a suspension setup that supports that understeer, so R8 is far slower on street tyres then it could be but with a wide security spread. A 305 on the rear is needed for spirited performance driving on streets even with the V8, i think we all agree on this.

To generate more grip front so you cure the understeer, get a neutral setup with a quite small secuirity spread and drive on the max grip level with street tyres you can do 3 things:
1) more tyre contact patch => wider tyre front
2) far more negativ camber front
3) less tyre contact patch rear
yes you could also modify the anti roll bar...not a good idea as they are quite well designed for street use.
suspension can be modified too but with given anti roll bars and not compromising street drivability too much the space for modifing it to cure understeer is small and is accutally need to achieve the goal=> GT coilover suspension, eleminates the understeer caused by suspension and reduces body roll but understeering security setup with 235 stays...

well you need:
1) a 255 tyre front with 305 rear and a 255 35 19 has too much sidewall for cornering but a 255 30 20 is perfect from sidewall and is performance wise better then the 19" and lighter. 255 30 19 would need a 305 25 19, only Hankook makes it and too less sidewall for grip on normal street roads. As you wrote "20^4/19^4 = 23% greater rotating inertia in simple terms" the wheel barrel as a significant weight part is further out on a 300g heavier 20", but a 1.5kg heavier tyre even further out is compromising the rotating interna even more then 19". My 9x20 wheel is 10kg flow formed, the 9x19 is 9,7kg and both have a load rating of 700kg, very sturdy wheel and surprisingly light. So overall the 20" rim+tyre is better in unsprung and rotational mass plus performance better then 19".
2) or you have approx -2,5 degrees chamber front and -1 rear and the 235/305 combo which comes with the downside of a) compromised straight on stability b)bad bump steer and c) 70% reduced tyre life front
3) you can reduce to 285 rear with 235 front, well even not enough grip then for a V8 and your overall grip level is far lower.
so in this case of R8 Gen1 and spirited street use 20" is better then 19"...and lighter overall.

totally different picture on a track car with semi or slicks, here 18" is the way to go. no question.
 

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Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

Helldriver, glad you agree with what I wrote. Some notes on understeer. My 2012 R8 V10 coupe scales at 45.5% front at curb. 245/305 matches that distribution nearly exactly. So that is what I run..in 19's. And frankly should have stuck with the 235 for my steering feel...for the street.

However, one thing to remember for the street. You will want understeer/stability if an evasive maneuver is required or even dropped throttle in the middle of a good corner is needed for an animal or otherwise. Something unforseen.

The true evasive maneuvers Audi and we developed for on the Ford GT involve testing for events like the double lane change where vehicle yaw rates reach 600-700 degrees/sec and steering wheel rates of ~600-720 deg/sec. Incredibly high...effectively a rate of 2 revolutions of the steering wheel per second. For racing or otherwise the entry yaw and steering rates are typically 1/3 or 1/4 of that or even less for smooth drivers...even on corner entry or "catching" the car. Except in situations like the chicane at Monaco. Or running in the wet. Or catching a car at Indy...which is rarely caught if she steps out. So none evasive maneuvers/corners do not require the same level of understeer though even the very best pros benefit from some on entry.

Flow formed isn't likely to meet forged for stiffness. So I guess I don't agree that the R8 understeer needs to be "cured" for the road (and I have broken the rears loose before the front on aggressive 30-40 tight round abouts) and wouldn't go this route to reduce understeer if that is what I wanted because of the reasons I mentioned. But if you want to reduce understeer and this is a path you like then that is all good. It just read like your position was that the larger wheels were a "win-win" and obvious solution. They are not, from my perspective.
 

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Just curious...

You recommending going 20" 305/30 instead of 20" 305/25. Is that not more then 5% difference when using 20" 245/30 front? Im just worried about the quattro.
 

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Discussion Starter #17
Just curious...

You recommending going 20" 305/30 instead of 20" 305/25. Is that not more then 5% difference when using 20" 245/30 front? Im just worried about the quattro.
No problem. ABS/ASR/ESP work fine from +1% till +8% front to rear. From 5% till 8% the limited slip diff front has to work a bit more, only a point you need to take care about if you driving a lot and long time above 250kmh as it gets hot. With RWS you don't care at all as front slip diff is not there anymore :)
Its not a real quattro, its a rear wheel biased hang on 4 wheel drive with 15%/85% in normal mode and max 30%/70% Front/rear. The OEM tyre setup is between +1.4% till +2.7% larger rear tyre compared to an equal front/rear diameter as with all other Quattro Audis.
I ran 245/30/20 with 305/30/20 for about 10000km without any issue but mine is optimised as a mountain pass "racer". The 245/305 combo puts more load on the front diff (see above, its +6.x%), if you are running for longer times(!) high speed above 250kmh then I suggest to use a different front diff oil to compensate for that. Mountain passes are 50 till 160kmh speed range, so no issue at all.
...now I am running 255/30/20 and 305/30/20, that what I recommend to used when a 305/30/20 rear and this is fully within the ratio for the front limited slip. With the Pirelli combo I drive its +3,8% front/rear, calculated with the real exact tyre dimensions given by Pirelli. Not with a tyre calculator that take a theoretical average tyre size.
the 245/30/20 fits optimal with a 295/30/20, that what I am running in Winter Conti 830p tyres and a world difference to all 235/295 19 inch winter tyres avaliable. Thats the OEM 20" winter tyres for R8 Gen2.
 

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Discussion Starter #18
Re: tyre weight, tyre weight saving potential and 20" are lighter then 19" (surprise)

Helldriver, glad you agree with what I wrote. Some notes on understeer. My 2012 R8 V10 coupe scales at 45.5% front at curb. 245/305 matches that distribution nearly exactly. So that is what I run..in 19's. And frankly should have stuck with the 235 for my steering feel...for the street.
clear why because your V10 is 80kg heavier and more rear biased weight distribution then the V8 plus more hp rear. you would need a 325 or 335 rear but then 235 is too small front, I think I wrote that too that a V10 needs more rear. With your 245 front, did you adapt toe in to compensate for the wider tyre? Then you get your 235 "feel" back.

my lighter R8V8 is further reduced by -180kg weight (so total 1495kg with 75l gas tank full) is different here even more as even less rear wheel biased. With 235/305 19 my front understeers way before the rear. so I could reduce tyre size rear (less grip overall) or heavly increase camber front (bump steer!!!), both not a good option as slower at the end. with 255/305 in 19" the grip front was ok with slight oversteer overall but tyre wall was too high. So I went to 20" as this gives me the right front tyre 255/30/20. Surprisingly the 305/30/20 Pirelli NO has more grip then Michelin Supersport, Conti 5P in 305/30/19 so overall corner grip level is even higher then with 19" combo.

So I went with 255/30/20 and 305/30/20, -1.4 degrees camber around (max. OEM GT camber), 0 toe in front and +8' rear. Thats setup behaves exactly like the Gallardo superleggera. On the absolut limit I get slight short understeer and if I stay on the throttle then the rear comes soft(!) to oversteer. do I loosen the throttle shortly during the understeer, understeer continous a bit more and then neutral all 4 grip and "guide me" around the curve like on rails.
Very good controlable and predictable. If understeer appears I know exactly that the rear end comes and can prepare to react accordingly. Sure if I miss then to act accordingly I am spinning the R8 like the blades of a helicopter with no chance to resuce it....for an experienced driver like me a good fast setup, for a noobie or 60years average banker a noGo.
On my "house mountain pass" I am significantly faster with much higher curve speeds with this set then with 235/305 in 19". Harry's laptimer tells me exactly where I am faster and slower...
 

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Discussion Starter #19
Choosen the 20" setup and tyres carefully, I had proven above its lighter in total and even safes unsprung weight compared to already light OEM 19" and has a far higher grip level and curve speed. Optics is far better too. Mission accomplished :)
 

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Helldriver, thx for your reply and for sharing your experience with us!

Ok so maybe many in this forum reading your info are that "noob 60y old banker" guy that only been test driving a few laps on a track wanting to start improving weight and handling of the car. What is your recommendation of rims+tyres+camber set up to start with?
Im driving a R8 V10 2009 with standard 19" 235/35 295/30 today
 
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