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Jun 19, 2005 7:50:27 AM
- 03-turbo911
- Pilot
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- Loc: Bahrain
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- Reply to: zoltan
Re: Looking for spacers
Quote:
zoltan said:
Thanx gnil. Are you sure it's only 5mm...?
I ordered my C4S and got the list at my dealers of all options. Regarding spacers there was only , yes, 5 mm spacers in pack of four. I know it doesn' t sound much at all...I will have to see if one can notice that.!!?? I've ordered it. At least It will hardly change the dynamics .
Jun 28, 2005 8:47:28 AM
- zoltan
- Co-Pilot
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- Loc: Athens , Greece
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- Reply to: 03-turbo911
Re: Looking for spacers
Quote:
03-turbo911 said:
These are two options for the factory sold spacers. The 5mm which comes in a package of four, and the 17mm, of which you get only two, presumably, for the rear wheels only.
Anybody knows the difference if you put spacers only for the rear wheels? Do you get less understeer?
Jun 28, 2005 12:33:03 PM
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Carlos from Spain
- Rennteam Moderator
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- Loc: Spain. , Spain
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- Reply to: zoltan
Jun 28, 2005 3:52:23 PM
- iia
- Pilot
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- Loc: Canada
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Reply to:
Carlos from Spain
Jun 29, 2005 12:28:58 PM
- W8MM
- Rennteam Master
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- Loc: Cincinnati, OH , United States
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Reply to:
Carlos from Spain
Re: Looking for spacers
Quote:
Carlos from Spain said:
I would think you would get more under-steer because you are widening the track at the rear, increasing its grip around the curve making the front more likely to loose grip earlier causing under-steerkind of like adding negative camber on the rear wheels.
I agree with your general sentiment, Carlos.
I think the cause of the under-steer is not that the rear gets more total grip. It's most likely unchanged, but I like your camber argument.
I propose that spacing the wheel further outward from the suspension-arm pivot (chassis attachment) points lengthens the lever-arm working on the rear springs.
This causes a mild softening of the rear spring rate (as seen at the wheels), which simultaneously causes a lessening of the rear roll stiffness. (It might also cause more negative camber, depending on the actual geometry.) Total roll stiffness is comprised of the roll stiffness inherent in the basic spring rate, plus the effect of whatever anti-sway bars are also in use.
A softer rear spring rate has the same effect as otherwise installing a softer rear anti-sway bar. Less over-steer -> more under-steer.
Think of sliding farther out on the teeter-totter.
Jun 29, 2005 12:31:57 PM
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Carlos from Spain
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- Reply to: W8MM
Re: Looking for spacers
Makes a lot of sense Mike 
I was thinking more grip also becuase the wider track would also cause the centrifugal force to have a smaller leverage on the suspension/wheel, since they are more further outward that force from the car's center of gravety would be more parallel to the ground... I don't know if I'm explaining myself correctly
I was thinking more grip also becuase the wider track would also cause the centrifugal force to have a smaller leverage on the suspension/wheel, since they are more further outward that force from the car's center of gravety would be more parallel to the ground... I don't know if I'm explaining myself correctly
Jun 29, 2005 12:50:20 PM
- W8MM
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Reply to:
Carlos from Spain
Re: Looking for spacers
Quote:
Carlos from Spain said:
... I don't know if I'm explaining myself correctly
I think I get what you're talking about.
A wider track could reduce the mechanical advantage of the center of mass acting on the suspension in roll, and give less suspension deflection for a given side load.
Whether this aspect offsets the lower-spring-rate-via-longer-lever-arm contribution is dependent on how high the roll-center of the rear suspension is compared to the center of mass, ... I think
Now, I believe, I'm in over my head
Re: Looking for spacers
Quote:
Now, I believe, I'm in over my head
Well maybe you both are!
But hey! there's no penalty here on Rennteam for that. 
Actually, I find the logic of both arguments entirely palusible and, given that neither of you are automotive or mechanical engineers, really quite impressive.
Jun 29, 2005 1:13:23 PM
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Carlos from Spain
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- Reply to: W8MM
Re: Looking for spacers
You make it sound so clear when you put it into your own words, you can tell which of the two of us is an engineer (eventhough not automotive) 
I would think maybe since the increase in track from the spacers is so small relative to the overall track that the effect of the lower-spring-rate-via-longer-lever-arm contribution you decribed is more relevant since the increase in the overall distance wheel-to-suspension arm pivot would seem greater relative to the overall wheel-pivot distance. OK, again I think I just confused things further with my ramblings and wordings
I would think maybe since the increase in track from the spacers is so small relative to the overall track that the effect of the lower-spring-rate-via-longer-lever-arm contribution you decribed is more relevant since the increase in the overall distance wheel-to-suspension arm pivot would seem greater relative to the overall wheel-pivot distance. OK, again I think I just confused things further with my ramblings and wordings
Re: Looking for spacers
Quote:
GM Austin said:
Quote:
Now, I believe, I'm in over my head
Well maybe you both are!
After reflecting on my enthusiasm to spout off on a subject I barely understand, I can only imagine what is going through the mind of an actual suspension engineer while reading this end of the thread
When I read certain energetic exchanges on some radar-detector web sites, I have to exercise mountains of self-control so as not to post sarcastic comments. I apologize in advance if I create this temptation for real suspension experts.
Jun 29, 2005 3:03:29 PM
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Carlos from Spain
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Re: Looking for spacers
Did a quick search, no explanation of the reasoning behind it but wider rear track does seem to increase understeer
http://www.roadrunner-region-pca.org/tech.htm
http://www.roadrunner-region-pca.org/tech.htm
Re: Looking for spacers
Quote:
Damian said:
My miniscule intellect can only grasp these concepts if I consider them in both extremes:
Vehicle *A* (with spacers) would tend to plow--or oversteer, while *B* (w/o spacers) would more closely follow the front wheels.
Nice photo, but remember that with the rear weight bias of the 997, the car in figure B would oversteer (rear sliding out in the turn) and not strictly follow the front wheels if the grip of the tires is exceeded (high speed corner). This is probably the point you were making (less understeer), but I just wanted to be clear...
Re: Looking for spacers
Quote:
Grant said:Quote:
Damian said:
My miniscule intellect can only grasp these concepts if I consider them in both extremes:
Vehicle *A* (with spacers) would tend to plow--or oversteer, while *B* (w/o spacers) would more closely follow the front wheels.
Nice photo, but remember that with the rear weight bias of the 997, the car in figure B would oversteer (rear sliding out in the turn) and not strictly follow the front wheels if the grip of the tires is exceeded (high speed corner). This is probably the point you were making (less understeer), but I just wanted to be clear...
Doh! Thanks, Grant. I meant *A* would exhibit more UNDERSTEER , *B* would tend to exhibit more oversteer.
I edited my prev post.
Jun 30, 2005 12:56:35 AM
- Evo_Dubai
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- Loc: UAE,Dubai
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- Registered on: Jun 16, 2005
- Reply to: 03-turbo911
Re: Looking for spacers
Quote:
03-turbo911 said:
These are two options for the factory sold spacers. The 5mm which comes in a package of four, and the 17mm, of which you get only two, presumably, for the rear wheels only.
Can you give me the code of the 17mm spacer.. I went to the dealer but they said they don't have a 17mm only the 5mm
.... So please can anybody give me the code for the 17mm.. Thanks.
Re: Looking for spacers
Quote:
Grant said:Quote:
Damian said:
My miniscule intellect can only grasp these concepts if I consider them in both extremes:
Vehicle *A* (with spacers) would tend to plow--or oversteer, while *B* (w/o spacers) would more closely follow the front wheels.
Nice photo, but remember that with the rear weight bias of the 997, the car in figure B would oversteer (rear sliding out in the turn) and not strictly follow the front wheels if the grip of the tires is exceeded (high speed corner). This is probably the point you were making (less understeer), but I just wanted to be clear...
So do you think that if you put 5mm all around it would be better?
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