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Classic 900 - aluminum or steel/best tires for sport driving
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#11
 
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Re: Classic 900 - aluminum or steel/best tires for sport driving -
04-29-2007
, 05:56 AM
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in article 4633871F.2BA6F692 (AT) siz-nospam-efitter (DOT) com, johannes at johs (AT) siz-nospam-efitter (DOT) com wrote on 28/04/2007 18:40: 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. If you're referring to the curly Aero wheels, then they are - the wheels are rotational. When I had a new set of tyres fitted to my set, I drove around for a day, or two, before noticing that they had the sides wrong on the front. I duly went about swapping them over and realised that my rotational tyres would then be the wrong way around. I returned to the tyre fitter and pointed out their error, the fitter pointer to the rotation lines and assured me it was okay. I tried to explain again, but the fitter kind of sniggered and went to find his Manager. They could clearly be seem laughing about it in the office and then the Manager came out to see me. He also pointed to the rotation arrows and assured me that the tyres were on the correct sides. I pointed to the rotation arrows and the wheel and he went white, then red, then yelled the at the fitter who swapped them over  Paul 1989 900 Turbo S http://saab.go.dyndns.org/ |
round, but they're not of the curly types, just three wide bars to the rim.
#12
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Hm interesting, I didn't know that. My 3 spoke aero wheels are the same all round, but they're not of the curly types, just three wide bars to the rim. |
"directional" and even shows the left and right wheels in one frame.
http://jpowell.tripod.com/saab-wheels/#90003spoke
--
-Fred W
#13
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johannes wrote: Hm interesting, I didn't know that. My 3 spoke aero wheels are the same all round, but they're not of the curly types, just three wide bars to the rim. SAAB Wheel info and pictures. Note the oval slotted wheels are marked "directional" and even shows the left and right wheels in one frame. http://jpowell.tripod.com/saab-wheels/#90003spoke -- -Fred W |
part exchanged them at dealer for the 16" 3 spoke "Super Aero" with exposed
lugnuts.
#14
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and assured me that the tyres were on the correct sides. I pointed to the rotation arrows and the wheel and he went white, then red, then yelled the at the fitter who swapped them over |
I know they don't get paid as much as say dentists, but is there any
place where you get poorer service and more misinformation than tire
shops? I once had a guy insisting that the first number referred to
the height of the tire and the second to the width. HE SOLD TIRES FOR
A LIVING!!! And, there is a certain big chain where you go in to get
something like a flat fixed or a simple rotation. The clerk must fill
in pages and pages of forms on the computer and then print out
kilograms of paper in triplicate. Then you wait and wait, and when
they are finally finished they have always managed to screw something
up. They should be working for the government!
Robobass
#15
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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. |
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.
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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 |
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.
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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! |
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.
#16
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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. |
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 TÜV ever said anything.
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Why do you think so ? Aluminium needs lots of more volume of material in order to gain the same stability as steel. |
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
#17
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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. 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 TÜV ever said anything. Why do you think so ? Aluminium needs lots of more volume of material in order to gain the same stability as steel. 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. |
just compare with another car?
#18
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On Wed, 02 May 2007 13:13:58 GMT, johannes johs (AT) siz-nospam-efitter (DOT) com> wrote: 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. But did you compare steel/alloy performance on the same car, or did you just compare with another car? 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. |
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...
#19
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you're not allowed to drive 205/60 on a C900 in Germany. 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 TÜV ever said anything. |
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 TÜV (expensive), taller tires might not be approved anyway.
Have a look at the german forum www.saab-cars.de. It has been
discussed at lot there.
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What is the weight difference for Saab wheels? I know that the |
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.
#20
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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! |
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
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