Which set of wheels

[George Elliott]

Tony, your question - I dont have a good answer but it always seemed strange to me that F1 Cars had such high profile rubber. For sure unsprung weight would have been considered, plus the constant kerb contact on corners, they seem to steer pretty well on 'em, and grip is an outcome of rubber compound. So why do we have Low profile rubber on modern cars? I can only think its simply - it looks good?

George
944t
964

 

[944 man]

Ive just been looking at the link that you posted Rich (after navigating the frames) and it very interesting. Youre looking at saving approximately 2 kilos per wheel by running on classic Fuchs wheels: even over Fuchs manufactured later design forged wheels. Thats 8 kilogrammes of unsprung weight per set! As well as the weight; think how much that will improve your steering with 2kgs less spinning adding to the gyroscopic force at 1,000 wheel rpm!

 

[turbocabrio]

Nick,
love those 18,s on your red turbo. could you let me know the widths and offsets of your wheels. I have 18 inch cup 3s 8.5inches onfront with offset52 , therears are10incheswith 47 offset.they seem to come out to far.where yours seem to fit much better.cheers.
Paul

 

[944 man]

Youll need an offset of 65mm minimum to 71mm ideal, I think.

Simon

 

[TTM]

ORIGINAL: George Elliott
Tony, your question - I dont have a good answer but it always seemed strange to me that F1 Cars had such high profile rubber.

Stringent rules in F1 suggest the technical solutions they retain should be taken with a grain of salt.

 

[appletonn]

ORIGINAL: turbocabrio

Nick,
love those 18,s on your red turbo. could you let me know the widths and offsets of your wheels. I have 18 inch cup 3s 8.5inches onfront with offset52 , therears are10incheswith 47 offset.they seem to come out to far.where yours seem to fit much better.cheers.
Paul

They are 8.5" and 10" widths with 54 & 45 offsets.

 

[Hilux]

So why do we have Low profile rubber on modern cars? I can only think its simply - it looks good?

20 years ago tyre technology and suspension design was (clearly) simpler compared to today. The suspension systems then (including Mo30) were designed for the car and the tyres on it.

In particular the compliance of the tyre is a big factor which is why bunging mahoosive wheels and rubber bands on 20 year old Mo30 is a pretty pointless exercise in my opinion without regaining control or of the damping and rebound including dedicated variable spring rates and more importantly better/bigger ARB`s to reduce roll.

Modern multilink (and intelligent) suspension is technologically advanced enough to control these almost solid rubber bands and keep the tyre contact patch maximised. Any roll and the tyre contact area is instantly massively reduced as you run on the edges. Tired or even refurbished 20 year old dampers, springs and ARB`s will not cope adequately nor properly and as such is just bling for the road unless done properly for track.

Slicks dont have a low aspect ratio so what does that tell you []

 

[John Sims]

ORIGINAL: George Elliott

....... So why do we have Low profile rubber on modern cars? I can only think its simply - it looks good?

George
944t
964

The lower the profile the larger the wheel diameter the bigger the brake discs. While F1 cars have retro tyres [] look at GT and sports prototypes of 15 years ago and onwards. The diameter of an F1 wheel seems to have changed little in 30 years. There is little doubt the tyre technology has improved greatly though and the tyres are an integral part of the suspension characteristics of an F1 car.

There is also an argument that short side walls are stiffer so the tread has less lateral movement. This is perhaps true and no doubt contributes to the increase in tramlining we experience when going up a wheel size.

Low profile tyres certainly compromise ride quality when on the road, introducing a noticeable increase in choppiness and reduction in damping of small bumps and road imperfections. Having upped the diameter of wheels on two cars recently the only noticeable difference has been in a reduction in insulation from the road surface. I would be hard pushed to suggest a dramatic improvement in handling In short, on the road, the most comfort is available with the tallest tyres you can get.

So, considering the above, there is little that looks more ridiculous than big tall wheels shod with little more than thick rubber bands when you then look inside the wheel an see a tiny brake disc. [:'(]

 

[333pg333]

While there are a lot of crappy new wheels about (we call them Chinese anchors) I think it's possible to find a modern wheel that looks good. It's a safe bet to go for the 5 spoke pattern and almost all of these seem to look good on our cars. It also depends on what other cosmetic mods you do as to the individual flavour of your car. Seems to me that many of you guys prefer the stock appearance which is fine. I also like this, but don't mind a modern wheel if the car has also been updated overall. I think Nick's wheels look great on his red beasty with a few other touches to bring it out of the '80s.

 

[333pg333]

Oh, case in point re slicks with higher profile and a modern Japanese wheel. Horses for courses they say. []

 

[Hilux]

So, considering the above, there is little that looks more ridiculous than big tall wheels shod with little more than thick rubber bands when you then look inside the wheel an see a tiny brake disc. [:'(]

[][] Excellent...........so true

 

[sawood12]

ORIGINAL: John Sims

ORIGINAL: George Elliott

....... So why do we have Low profile rubber on modern cars? I can only think its simply - it looks good?

George
944t
964

The lower the profile the larger the wheel diameter the bigger the brake discs. While F1 cars have retro tyres [] look at GT and sports prototypes of 15 years ago and onwards. The diameter of an F1 wheel seems to have changed little in 30 years. There is little doubt the tyre technology has improved greatly though and the tyres are an integral part of the suspension characteristics of an F1 car.

There is also an argument that short side walls are stiffer so the tread has less lateral movement. This is perhaps true and no doubt contributes to the increase in tramlining we experience when going up a wheel size.

Low profile tyres certainly compromise ride quality when on the road, introducing a noticeable increase in choppiness and reduction in damping of small bumps and road imperfections. Having upped the diameter of wheels on two cars recently the only noticeable difference has been in a reduction in insulation from the road surface. I would be hard pushed to suggest a dramatic improvement in handling In short, on the road, the most comfort is available with the tallest tyres you can get.

So, considering the above, there is little that looks more ridiculous than big tall wheels shod with little more than thick rubber bands when you then look inside the wheel an see a tiny brake disc. [:'(]

F1 cars have their wheel diameters limited to 13" by regulation so they can't go bigger even if they wanted to. Lower profile tyres on modern cars are really just there for aesthetics. It is generally accepted that 944's handle better on 17" or even 16" wheels and the same is true with modern cars - I think BTCC touring cars only have about 15" or 16" wheels. In fact modern suspension can make higher profile tyres work even harder to produce more grip than a lower profile tyre. The compliance in the sidewall can be exploited to maximise the contact area. It's like everything - there will be an optimum. What that is on any given car will probably vary but it is not the case that the lower the profile the better.

Also unsprung weight drastically improves the response of the suspension, again increasing grip. This is because there is less inertia for the suspension to deal with when the wheel is bouncing up off a bump allowing the suspension to maintain more positive pressure onto the wheel and improving grip.

 

[D7MPJ]

thanks guys,lots to think about then, was going for cup 3's but seriously considering cup 1's now in 17's

 

[Neil Haughey]

Well it seems I was right about the 968 16" cup 1's, about 1 Kg per wheel lighter then D90's but the Fuchs another 1 Kg lighter per wheel again. Depending on which calculation you believe 1 Kg on the wheel is worth up to 4 kg in performance terms due to the energy required to accelerate that mass up to several thousand rpm.

With regards to modern cars and suspension design I have an MX-5 running on stock rubber bands to make a comparison with. It has a smoother ride on surface imperfections then my 968 does for example but because they have used softish springs and stiff dampers the ride and handling goes to pieces on bumpy roads. Modern BMWs seem to be the same as well.

 

[944 man]

The reduced gyroscopic force is even more important than the overall reduced weight and the reduction in un-sprung weight.

 

[333pg333]

So in theory having larger brake discs and wheels/tyres should increase understeer?

 

[TTM]

ORIGINAL: 333pg333
So in theory having larger brake discs and wheels/tyres should increase understeer?

Absolutely.
Larger diameter = higher polar moment of inertia, and if I remember correctly, I=mr²/2

 

[944 man]

Another inescapable physical fact, is that increasing the rolling radius of your front wheels will reduce the effectiveness of your brakes...

It isnt understeer, its the gyroscopic force which resists your attempt to turn it away from centre. You can use a bicycle heel to demonstrate both problems. Hold a cycle wheel on its spindle in your hands and it will be easy to turn, as though you were steering the cycle: now get someone to spin the wheel quickly and youll see exactly what gyroscopic force is and realise how great an effect it has. With regards to the brakes: get someone to hold the wheel in a similar fashion and spin it as quicky as you can. Now stick your finger in the spokes at their far end by the rim, in order to slow down the wheel: easy. Now spin the wheel again and attempt to slow down the wheel by sticking your finger in between the spokes, but for the sake of the example do it in the middle of the weel, simulating a constant brake disc size but an increased roadwheel diameter..... Thats why larger road wheels decrease your braking effort, because the braking force remains constant whilst the leverage that the wheel has over the brakes is increased with diameter.

 

[944 man]

Similarly; you can increase your braking effort be reducing the rolling radius of your front wheels. If you do this all round then it can usefully shorten your overall driven ratio too, which can be very useful; and its far cheaper then sourcing a different final drive. []

If anyone sees me sprinting over the next year or two with 15" Fuchs and spray-on tyres, then youll know why.....

 

[944Turbo]

But you need to take the tyre size into account and look at the total diameter and therfore its effect. For road use at least most people with bigger wheels use smaller tyres so overall the diameter remains the same. In motorsport the wheel size is regulated and I am sure that in F1 they would rather have less rubber so they could control the movement with dampers rather than having all that undamped air springing.
Tony