Wheels?

[SimonExtreme]

So, I have taken the plunge and bought a car (more in another post later). A few minor bits need sorting out and these include the wheels being tatty. I am aware of all the problems restoring the Mags and have already had it confirmed that these wheels are OK and can be restored.

However, it seems a bit scary to be driving a car where the wheels are £1000 a corner, if you can get them. What do other people do? Do you just grin and risk it? Or do people have an everyday set of alloy cups and bring the Mags out for special occasions? Or should I just leave the wheels as they are and just accept that they don't look their best.

One issue with getting a set of "standard" cups is the weight difference which I believe is 3.5kgs. That is a lot of unsprung weight and I know that with other cars I have owned, you can feel the difference. On my Evo I had wheels that were 3.8kgs less than standard and the braking was noticably better. Now, Evo's have totally cr#p brakes so this might account for it. Can you feel the difference on an RS?

So, what do I do?

 

[Melv]

Just drive the bl**dy thing and stop worrying!!!!

[]

Mel

 

[lee fulford]

I bought my car fitted with 18" speedline split rims (as fitted to the cup cars)

Recently I bought a set of original magnesium wheels and fitted some extra sticky tyres(pilot cup sport thingies)..Yes the wheels are lighter but by the time I'd fitted those heavy tyres the difference in weight was negligable. (picture me standing on the bathroom scales balancing a wheel on my head)

The car feels harsher over bumps with the mags because the tyre has less give in the sidewall and the brakes are simply awesome whatever wheels are fitted.

You have to ask why the race cars fitted 18"

lee

 

[Melv]

".......You have to ask why the race cars fitted 18"......."

That's easy!! Better grip, better cornering, better braking........

The '90 and '91 Cup Cars ran 17"'s, then upgraded to 18" for the '92 season, not only because of the above, but also because the German DTM series were running 18" Pirelli PO slicks, so the tyres were readily available. It also meant that they could play around with the suspension more -the 17"'s gave very little leeway in terms of setup to give the optimum performance.

Roland Kussmaul, the engineer behind the weight reduction programme on the Cup Cars (now Chief Engineer for Porsche and a 964 owner.....) reckoned he cut 3 seconds a lap off the time at the Weissach test track by fitting 18" wheels.

Mel

 

[SimonExtreme]

ORIGINAL: Melv

".......You have to ask why the race cars fitted 18"......."

That's easy!! Better grip, better cornering, better braking........

Interesting. Autofarm convinced me that 18" wheels actually made the handling worse. They say that the car is more skittish, harder to drive on the limit and that in practice, the lap times would be about the same anyway! Moving to a lower profile has the same effect as firming up the suspension.

As for the braking being improved by 18" wheels, this will only happen if the moment of inertia of the wheel and tyre is reduced. The extra contact area doesn't (IMO) help. If the 18" wheels were the ame weight as the 17", it would almost certainly mean that the moment of inertia has moved away from the centre. Therefore, you would need more braking power to prevent the extra inertia of the wheel. And the difference is more than you think. Some Evo driving fiends in France did a test on this and found that to get the same effect, 18" wheels need to be nearly 2kgs lighter than a 17" to get the same braking effect from a given force.

As for why they upgraded to 18" wheels in '92 and why they were 3 secs a lap quicker, I suspect that it was done because a really sticky tyre was available and it was more ecinomical to use the same tyre for 2 classes. We regularly see that lap times of cars can be changed significantly by tyre choice. To know the real effect of the wheel size change, you would need to compare times using tyres of the same tread pattern, compound and wall stiffness.

 

[Timmy]

Isnt it also going to get to a point (in the near future) when the mags become unserviceable through porosity and we all have to look for alternatives anyway? (or £5k a set if they are still available)

I remember my mate having to bin £1000s of what appeared to be perfectly good minilites as they couldnt hold air anymore.

 

[oldtimer]

just a comment or two.

Suggest you use the (mag) wheels you have, dont bother about refurb, second Mel's advice here.
The cost of the wheels new is not to be confused with the cost of getting a second set of mags in good order , that would be more like £300 each.
The driving force for a second set of wheels is to fit different tyres eg slick or semi-slick, and you can get perfectly fit for purpose used original Porsche wheels eg from Jasmine who have a wide selection. I use ex 996C4 ,1998 vintage ( non twist ) 55 offset. I was not prepared to have a second set of mags..nb mag is a misnomer , still an alloy with lots of aluminium present.

 

[SimonExtreme]

Thanks for your replies. I am interested in the comment from Old Timer that you can get second hand decent mags for £300 a corner. Are there any recommended sources, please.

As for just driving the car, that's what I want to do. However, the wheels are one of the few things that lets down the overall appearance and I do want to get them reconditioned. The problem is that Diamond Styling would need them for rather a long time and I don't want the car off the road. If you guys had told me a second set was a good idea, that would have been an easy solution. Back to the drawing board.

 

[Melv]

Simon

More than happy to lend you a spare set in the down season.

Mel

 

[SimonExtreme]

Mel

That's a very generous offer that I may well take you up on. I am truely overwhelmed by how helpful verybody on here has been and many thanks, once again.

 

[rskiwi]

Simon, is you car LHD, if so the 18" wheels will make the steering so much heavier. Also the lower profile of the tyres also affects the steering. I had a set of speedlines 18" looked great but the car was not very nice to drive at low speed. When I put the Mags on it transformed the car. By the way I have a spare set of Mags just in case!
Jeff

 

[oldtimer]

Hey Des , sell the man a set of sturdee mags if not sold already !
I think Simon went RHD , so we are talking power assisted steering , but agree with rskiwi that 18 inchers not so clever for normal road use.

 

[PhilRS]

ORIGINAL: oldtimer

Hey Des , sell the man a set of sturdee mags if not sold already !
I think Simon went RHD , so we are talking power assisted steering , but agree with rskiwi that 18 inchers not so clever for normal road use.

Might as well ask since this is generating quite a bit of interest. Everything being equal
(i.e. proper set-up, same tyre type--e.g. corsa or cup, and so forth), on the track, is there
a significant difference in handling between the 17 and 18 inchers? In principle, the answer
should be yes (the footprints of the 18 inchers is bigger front and rear). If so, what are
the main seat of the pants differences?

 

[Melv]

Phil -read my post above.

Mel

 

[lee fulford]

Tres strange

As posted previously...I found the car alot less pleasant with the 17" mags albeit the sidewalls on the sticky tyres have much less give and so do not absorb the bumps too well.

I figured thats why most RS owners complain about the ride for everyday use...I must say that contrary to this I dont find the ride a problem or the steering at all heavy... thats with the 18"s.

lee