Classic 900 - aluminum or steel/best tires for sport driving

I just bought a late '91 900i(s) with 220,000km. It is in great condition, but only has winter tires on steel rims.

Background: I am in Germany. Aluminum rims are considered a luxury, and fetch a premium price even used. Also, my driving habits are divided between very high speeds on the Autobahn, and very tight turns in the Hartz mountains (but that involves some dirt, so I can't go too low).

I've got an extra set of steel rims from my last car. The question is: How much do aluminum rims affect the performance of this car? I've driven Saab 900s with both types, but not in a way to objectively compare.

I'm looking at either buying new mid-level summer tires and sticking them on the steel rims, or shopping used, where for similar money I could get aluminum rims already mounted with slightly used P6's and the like. Whatever I do, it is only for summer, so I want to go on the wide side, like 205/60. I have noticed a huge performance difference from aluminum wheels on other cars, like VW's, but my last (poor persecuted...blast the bloody a=A7$holes at the inspection...) Saab ('92

390kKm) did really well on humble steel. Everything from Stuttgart to Munich at 180km/h to muddy cow paths in Latvia. There never was or will be be another car like this. Opinions? Robobass
Reply to
robanzellotti
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I can't see why there should be any difference in performance. But changing the wheel diameter for e.g. low profile might change the gearing and the perceived performance on the speedo. It will of course also improve the handling. Performance drivers usually like a lower gearing. (though I prefer relaxed long gearing)

With your fast driving style, you're more likely to hit a stone or a kerb, or even a pothole in the road. That usually puts a big dent in alloy wheels. Steel wheels are much more durable.

Reply to
johannes

in article snipped-for-privacy@q75g2000hsh.googlegroups.com, snipped-for-privacy@googlemail.com at snipped-for-privacy@googlemail.com wrote on

28/04/2007 00:43:

I would go for alloy wheels, rather than steel, but can't cite any "scientific" reason for that - perhaps weight?

The correct ratio would be 205/55 for 15" (standard C900 wheels). On normal

5.5" wide they would be a bit too "fat". On 6" wheels off a 9000 they would suit a little better but the track would not be any wider - in fact it would be 2mm narrow, but who's counting :)

There is a wheel you can get, which is an official SAAB wheel and 7" wide - the offset gives you an extra 3" width in the track and is perfect for

205/55 tyres. IMO, this is a better solution for the C900 than 16" with low profile tyres.

The wheel in question is:

I have seen a few of these wheels come up on eBay in Europe - Belgium and France, particularly, but also Estonia. I was looking for a set myself recently.

Paul

1989 900 Turbo S
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Reply to
Paul Halliday

Expect a rougher ride with low-profile tires. Higher-profile tires have much more "give" and a smoother ride. The advantage of low-profile tires is that there is less "roll" in hard cornering. You're giving up comfort for performance.

My 9-5 Aero has low-profile 17" tires in addition to stiffer suspension. It's definitely a harder ride.

Reply to
Gary Fritz

Saab made a big thing at the time that the aero 3 spokes (and the aero body kit) made a difference to top speed because of aerodynamics (not weight), compared to a steel or standard alloy shod car with no kit.

I would suggest looking for a set of 16" 9000 Aero 3 spokes for the summer on a later 900, with decent tires on, and fit winter tyres to a set of 15" steels for when the weather is less clement (and/or if they salt the roads locally to you). Depending on the weather extremes where you plan to travel, you might find two sets of all season tyres in the different sizes/profiles/widths might be better than a set of wide sticky summer and narrow soft winter tyres

Reply to
Elder

I have the 16" 3 spoke aero wheels on my 9000 and they do look bloody nice. I jumped on the opportunity to buy them when a saab dealer cleared out some stock. They don't fit on newer saabs as they switched from 4 nuts to 5.

However, about the science, I still think it is mostly marketing speak. The 3 spoke wheel was obviously a convenient symbol of the turbo. There was marketing talk that they helped cooling the disc brakes. But wait a minute here:

Suppose that a 'turbo' wheel on the right side is blowing into the disc when the car is moving forward. Then imagine taking off the wheel, while still spinning and blowing air towards the back side of the wheel. Then take the same wheel to the left side of the car (wheel still spinning). Mount the wheel on the left side (wheel still spinning). Which direction will it now roll on the car? To perform the disc cooling function, it will obviously have to roll backwards on the left :-) Hence right and left side 3 spoke alloys would have to be mirrors of each other.

Reply to
johannes

And they are... AFAIK

Reply to
MH

Most of the used stuff I'm looking at is Alu 15"x6" with 205/60. This profile is plenty tall to deal with the smooth roads here (there ain't no Major Deagan Expressway in Deutschland!). The 185/65's I have now are a bit squirrelly up in the 100mph+ range.

Conceptually I figure that aluminum rims not only allow faster accelleration and braking, as since being lighter, there is less rotational inertia, but also, a lighter wheel can move up and down faster, allowing the suspension to react faster to bumps and dips. As I said, the effect probably depends on a lot of factors. I haven't really noticed it with this car, but I'm probably gonna do it anyway to get a bit wider, and also to indulge myself a little. I work hard!

Robobass

Reply to
robanzellotti

I don't believe that this has any significant effect at speeds eh.. under

100mph or so, but I'll have to get my calculator out.

Yes, this is perhaps more like it. The weight of the wheels doesn't depend on speed (unless close to speed of light :-), so lighter 'un-sprung' weight is an advantage for handling and ride.

Reply to
johannes

you're not allowed to drive 205/60 on a C900 in Germany. Even for the

205/55 you'll need a special allowance from SAAB, unless you have MY87 (I believe). Addtionally you'll need distance blocks for the springs in the back. If you want to avoid this, go for 195/60 and buy "sporty ones" like Yokohamas or Bridgestone Potenza series.

Why do you think so ? Aluminium needs lots of more volume of material in order to gain the same stability as steel. Unless you build your rims from magnesium you won't gain any advantage in weight. Acceleration is more dependant on the diameter of the overall wheel, which you're not allowed to change and braking is more dependant on the tyre (width, rubber type). The rotational inertia is maybe not less, but in most cases better dirtributed in steel rims. (Saab often has this 3-spokes as aluminium). When it comes to suspension the main factor are the shocks... not the rims.

Some people think that the c900 doesn't run very well on 205/55 on

6Jx15 rims, they prefer either the 195/60 or 195/50 on 16" rims. I'll mount my 205/55s next week anyway and try out.

/T.

Reply to
targa

Are you sure? A 205/60 15 should be only 3mm taller than a 185/65 which is listed on Fzs. The inspection thing is a point, but I can do it with the winter tires (If I'm calculating correctly). Also, I'm pretty sure I had this size on my last 900. No clearance problems, and nobody at the T=DCV ever said anything.

What is the weight difference for Saab wheels? I know that the Alu wheels I had on a Golf II were much, much lighter than steel, and I attributed the great performance of that car partly to this.

Robobass

Reply to
robanzellotti

But did you compare steel/alloy performance on the same car, or did you just compare with another car?

Reply to
johannes

Just to throw a few facts into the mix: I think the alloy wheels may be lighter than the steel wheels, but not by a lot. Most aluminum wheels are rather heavy. Originally alloy wheels were a magnesium alloy. The Minilite was a popular choice. I believe my last set weighed in at about 8 lbs each. In contrast, I believe my Saab alloys are close to 40lbs each. They are twice the size, but even so....

Alloy wheels, if lighter, are important in one way: they reduce unsprung weight. Unsprung weight cannot be controlled like the sprung weight of a vehicle. Consequently, we try to minimize it. Alloy wheels today are more of an ornament that a performance enhancement - with the notable exception that in order to get lower (and consequently wider) tires on a car, most manufacturers packed in alloy wheels.

Reply to
still me

Well said. I think there has been an almost transition to alloy wheels. We now expect out pride and joy to have alloy wheel, unless it's a postal van. 20 years ago or so, a car with alloy wheels stood out from the crowd, indeed the wheels were often the target of thieves. I noticed one year at a trip to Denmark that suddenly most cars had alloys. The 200% car purchase Tax in denmark probably means that a small aftermarket upgrade looks more impressive for perceived value.

However, alloys are vulnerable to potholes and kerbing. How often have I seen a flashy Mercedes SL with scraped alloys, it really looks out of place. Did the director lend the merc to his mistress? Better keep my mouth taped over for now...

Reply to
johannes

I'm absolutely sure. That the T=DCV didn't find it was probably just a coincidence. 185/65R15 (perimeter: 1896mm,205/60: 1912mm) is the absolutest maximum diameter in the tolerance. Depending on model year the only allowed 15" tyre sizes are 185/65R15 and 195/60R15(1876mm), this 205/55(1850mm) is allowed in combiantion with the above mentioned little modifications only, AFAIK this also goes for the 195 on 6" rims. For other permieters you need to adapt your speedometer and have it checked by T=DCV (expensive), taller tires might not be approved anyway. Have a look at the german forum

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It has been discussed at lot there.

from:

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16" Aero : 8,25 kg 16" Cross Spoke: 7,90 kg 15" Turbo : 7,50 kg 15" short spoke: 6,75 kg

steel shouldn't be much more...

/T.

Reply to
targa

It's hard to believe that in a country where they are open minded enough to have roads with no speedlimits that they are this particular about using different tires that still cover the load properly :-)

Not doubting it, just surprised!

Reply to
still me

Yeah, We've got a lot of rules here. Even down to the wattage of bulbs that can be sold for bike lights (that's Bicycle!). The standard rear bulb can't take the juice my generator delivers. It burns out quickly, and robs too much power from the front light. I couldn't get a different bulb, so I picked up a 30ohm power resistor and put it into the circuit. Probably illegal.

Thanks everyone for all the advice on tire sizes. I have been looking at used tire/wheel sets, and a lot that are sold as suitable for this car are 205/60-15. I'm not worried about inspection, as I can through on my winter wheels for that, but I'll be sure to test whatever I buy first before I hand over the cash.

Robobass

Reply to
robanzellotti

However, if you change wheel/tyre size in the uk, the insurance companies consider it a 'modification'. We are obliged to declare it and might have to pay a higher premium. If you don't declare a modification, then the car insurance could be void.

Reply to
johannes

Just to clarify, The guy at the bike shop said it was a common problem, but he was prohibited from selling anything else.

Reply to
robanzellotti

Might check out an LED.

Who inspects bicycles ?

Reply to
still me

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