Best wheel sizes for track days

[944 turbo cabrio]

Hi,

maybe I'm just plain dum but using the search I don't find any hits as to the possibilty of using 10" wheels in the rear on the late 944 Turbos.
I am sure it is possible but what ET would the wheels need to be?
Also: what are the road racers here in this forum thinking is the correct wheel combo front and rear - 9&10 or 8&9 inch (or maybe 9&9 inch)

Thanks in advance for answer to this tedious question.

Happy Easter

Niels

 

[Hilux]

I always err towards what the manufacturers put on the car originally and rather than overtyre the rear a lot of racers even them up

 

[944 man]

Id suggest using 8" rims all around, or possibly 7". The reasons are two fold - firstly the tyres will be a damned-sight cheaper and secondly: you cant work your suspension until youre working your tyres, and youll never get massive rear tyres hot (also a mismatch will cause indersteer and the greater the difference the greater the pushing).

If you were asking about a N/A car, then Id suggest 7"x15" all around, with 195 track focussed tyres - looking for larger and fatter wheels/tyres is usually folly, in my experience/opinion.


Simon

 

[Neil Haughey]

I even run smaller circumference than stock, the Dunlop DZ03 currently on there are 225x45-16. Only gears the car down by a tiny amount but fits tighter on the rim due to less sidewall to move around and helps reduce inertia in the wheel/tyre package, hence why the original mini had tiny wheels.

 

[Neil Haughey]

I should add that a lot of this is down to the power and weight of a car. My S2 only weighs 1130 kg in its current trim and of course only has NA power which means a little over 200 lb/ft of torque. A tuned up turbo will be sticking out considerably more so you may find you end up needing bigger tyres in order to cope with the traction problems. Personally I would invest in either a rebuilt LSD (if the car already had one) or a decent after market LSD before going mad with big tyres though*.


*- Even my S2 is a pig to get off the line now, the 200Kg reduction from a stock S2 means it spins up the rear tyres very easily off the grid, BUT I have so far experienced only the faintest problem on corner exits, pretty much peddle to the metal out of corners and this is on a car with no LSD.

 

[944Turbo]

Cold tyres off the start Neil? My 100cc kart would spin easily on cold slicks with a heavy right foot, but on a hot day I have had it a long way up on 2 wheels just by turning hard.
Tony

 

[Neil Haughey]

No choice really though Tony, on a long race like a 40 minute CSCC one we have to start with the pressures well down to give enough head room up to the pit stop. At Silverstone for example I started at 23 psi, went north of 30 psi after 15 minutes for an early pit, I had Paul Follet helping out that day so he bleed mine back down to 29 psi for the next phase (I am sure the badly oversteering handling characteristics I had that day helped with heating the rears []). For sure one can chuck the car around like a nutter on the green flag lap but as you know its difficult to get heat into the rear tyres whilst rolling along at a slow pace in a 40 car grid (some of the PCGB club racers do indeed chuck the car about to warm the tyres). I am sure on hot tyres its better but I haven't tried a launch yet on hot tyres. Will also depend on compound, I have been using the H1 endurance compound, they last forever but as is the way you need to get heat into them to work properly, they do seem to last ages though. Softer tyres obviously give grip quicker but I can't imagine anyone will be using softs/mediums on track days as its a false economy to my mind.

 

[944 turbo cabrio]

Thanks for your thoughts - after end of engine build I will have approx. 350 BHP and 500 Nm so I think I will need minimum 9" at the rear.
I already have a LSD and will fit GAZ Gold coilovers shortly + I will up-grade to Powerflex bushings. The car is however in no way bantered for weight so I am carrying more weight than most of you

I will use trackday tires and I am looking for new lightweight wheels to match. I am limited to 17" or 18" due to brake size (17" preferred to keep weight and gearing lower). I need however to kill the eternal understeer I am experiencing so far and I am now looking forward to see how the mods will turn out

In a perfect world I then I guess I should have 9"&9" or 9"&10" but for the 10" wheels I am unsure what Et number that will fit a 944 Turbo Cabrio. Anybody knows?

Cheers to all!

 

[944 man]

I will agree with Neil first, before offering another likely to be controversial opinion: Id gear down too, which I thought that Id mentioned (195/50 or less on 15").

With regards to understeer, accepted 'wisdom' usually goes along the following lines: if youre suffering understeer then you need to increase the stiffness of the rear anti-roll bar.... This is boll*cks! If you have grip at the rear but the car is pushing, then you need to add grip at the front, dont lose it where you do have it. All that gets you is a very loose and much slower car; but internet wisdom seldom gets as far as testing...

Id be looking at the front wheels and tyres first, looking to find the missing grip in the easiest possible way. Having a large difference between the front and rear wheel rim / tyre sizes is certainly going to encourage understeer. Id be considering reducing any excessive rear width too, both for the reasons I mentioned in my earlier post, and because, if theyre too wide, you simply wont be able to add enough width/grip to the front.

I dont feel that this contradicts my 'never lose grip' advice, because were reducing a surfeit of grip; as opposed to reducing the cars ability to grip (such as you would by hobbling it, by increasing the rear ARBs stiffness in order to loosen the previously gripping rear), if you see what I mean?


Simon

 

[Neil Haughey]

Good point actually to add, even on an S2 running equal width tyres all round its usually the outside front tyre that takes a pasting. I have the memory of seeing the state of that tyre on the white EMC S2 after the first race at Snett last year etched in my memory bank. Corum really took its toll and the tyre looked shot.

With the engine sat bang in between the front wheels there is always going to be a natural understeer tendency. Some tune this out with suspension fiddling but I am not convinced it works in overall performance terms. Watching different racers there is basically 3 driving techniques one can use to combat corner entry understeer;
1) Heavy trail off the brakes to spit the car side ways on turn in, in essence causing the car to drift into the corner, needs to be caught with throttle tap and counter steering to stabilise the car at a slight yaw angle
2) More conventional trail braking which isn't really combating the understeer rather using it to enable the trail braking and carry more speed on entry
3) Aggressive steering input on corner entry, similar effect to 1) and likewise will require throttle and steering inputs to stabilise the car.

I haven't mastered any of the above yet myself and these are pretty advanced techniques, I just watch the fast guys like a hawk to see what their cars are doing.

 

[GPF]

ORIGINAL: 944 turbo cabrio
maybe I'm just plain dum but using the search I don't find any hits as to the possibilty of using 10" wheels in the rear on the late 944 Turbos.
I am sure it is possible but what ET would the wheels need to be?

Hi Niels

Leaving the "what's best" to others, I have 10J x 18 ET 50's at the back with 285 30's and no spacers.

My fronts are 8.5J x 18 ET 50's with 245 35's and a 1mm spacer to clear the calipers.

The wheels were previously on a G reg Cab by the way.

Other offsets may also work - my wheels sit right at the outside of the arches and I think there is good inboard clearance for the rears, but not much at the front - only because the m030 calipers are very tight to the inside of the wheel but I think that's because of the design of my particular wheels.

 

[pauly]

ORIGINAL: GPF

Leaving the "what's best" to others, I have 10J x 18 ET 50's at the back with 285 30's and no spacers.

My fronts are 8.5J x 18 ET 50's with 245 35's and a 1mm spacer to clear the calipers.

Ah but big wheels don't suit the car, it won't handle properly, and the ride will be terrible. [].

 

[Diver944]

My track wheels are 9" ET 55 all round with 275/40/17 at the back and 245/40/17 at the front. They fit fine with no rubbing issues even at extreme lean angles with the tyres nice and hot.

With your 350bhp I do not think you'd really need to go any wider than 275 and 9" at the rear to give you enough traction

 

[333pg333]

There is quite a lot of space at the rears. A friend has just bought some 996 turbo twists and fitted 11" on the rear of his recently turbocharged S2 however the fronts are only 8" so I feel this is too much of a difference.
As others have mentioned, keeping the stagger between front and rears work well on our cars. I've run 10" all round for a couple of years on a modified Turbo. I believe with 350bhp you could run something similar.
Offset are et 60 which required a little bit of massage to the fronts. If you don't have the wheels already there is a Japanese brand called Enkei which make a few different sizes for our cars (5x130 bolt pattern).
They're cheap, strong and light. Model NT03.

 

[GPF]

ORIGINAL: pauly

ORIGINAL: GPF

Leaving the "what's best" to others, I have 10J x 18 ET 50's at the back with 285 30's and no spacers.

My fronts are 8.5J x 18 ET 50's with 245 35's and a 1mm spacer to clear the calipers.

Ah but big wheels don't suit the car, it won't handle properly, and the ride will be terrible. [].

Well, that's your opinion Pauly - which no one asked for. Mine is that 18's do suit the car - which no one asked for either![]

As for the handling, I didn't realise you had put 8.5 & 10x18's on your car and tried them, or is that also just an opinion?

I have tried them, and my car handles just fine, thanks.

 

[pauly]

ORIGINAL: GPF

ORIGINAL: pauly

ORIGINAL: GPF

Leaving the "what's best" to others, I have 10J x 18 ET 50's at the back with 285 30's and no spacers.

My fronts are 8.5J x 18 ET 50's with 245 35's and a 1mm spacer to clear the calipers.

Ah but big wheels don't suit the car, it won't handle properly, and the ride will be terrible. [].

Well, that's your opinion Pauly - which no one asked for. Mine is that 18's do suit the car - which no one asked for either![]

As for the handling, I didn't realise you had put 8.5 & 10x18's on your car and tried them, or is that also just an opinion?

I have tried them, and my car handles just fine, thanks.

[] Actually I have 10J and 8J X 18's on my car, can provoke a bit of understeer around mini roundabouts though so may try a thicker rear AR bar [8D]

 

[333pg333]

Wider fronts than 8"s will help with understeer.

 

[pauly]

ORIGINAL: 333pg333

Wider fronts than 8"s will help with understeer.

My comments were tongue in cheek about wheel dia [], when a NEW poster asks about 18 inch wheels there often follows a history lesson on how the cars were originally designed around 15 inch wheels. I don't doubt there are several factors that affect understeer/oversteer including camber, ride height, spring rate, tyre compound, roll stiffness, brake and throttle use, slow in and fast out v constant corner speed etc, etc.

 

[333pg333]

Sorry, I don't get over here much and miss the subtlety at times. [&:]
It totally depends on what one wants their car for in my opinion. What the factory designed and built can often still be the best option...but also remember that in this instance they didn't even have 18" tyres back then...as an example.

 

[GPF]

Unfortunately, your irony was lost on me.......sorry mate. []

The 245/285 combo doesn't seem to suffer from understeer - or maybe I'm just not going fast enough!

I presume you have tried more right foot just after turn in? []