| Author |
Message |
Hubert Otlik (Hugh)
Intermediate Member
Username: Hugh
Post Number: 1384
Registered: 1-2002
| | Posted on Friday, September 12, 2003 - 12:41 pm: | |
>>Race cars can get away with absurdly low suspension settings (and make the wheels fit the wells) BECAUSE they have stiffer springs and thereby smaller body movements with respect to forces being applied at the contact patches.<<
They also have rewelded/redesigned suspension points and geometry ( if we're talking about production based models), much shorter shock bodies, track specific spring rates and bench dyno'd shock valving... oh... I hear JRZ calling... off to get my shock... |
Mike Charness (Mcharness)
Member
Username: Mcharness
Post Number: 978
Registered: 8-2002
| | Posted on Thursday, September 11, 2003 - 4:56 pm: | |
You'll find that wheel spacers make it look much better, reducing the visible gap just by pushing the wheels out slightly. Then you don't have those other concerns mentioned here.
Search the archives... there are good pics of 348's with spacers. In fact, if I remember correctly, one of the FChat sponsors, Paul Hill, makes them and has them on his 348.
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Mitch Alsup (Mitch_alsup)
Intermediate Member
Username: Mitch_alsup
Post Number: 1031
Registered: 4-2002
| | Posted on Thursday, September 11, 2003 - 10:02 am: | |
Beware: There are two issues with respect to lowering:
1) there is a twitch in the front end geometry when transitioning from max acceleration to max braking. It is controlled by the front ride* height. When you lower the car, the twitch gets worse.
2) After you set the front ride height, you can use the rear ride height to control oversteer/understeer relationship. Lowering the rear induces understeer (or reduces oversteer). You can use this if you change the ratio between the tront and rear tires.
If you do end up lowering the car, lower it with a set of scales so that the corner weights are put proper durring the process.
*Race cars can get away with absurdly low suspension settings (and make the wheels fit the wells) BECAUSE they have stiffer springs and thereby smaller body movements with respect to forces being applied at the contact patches. These cars never encounter speed bumps or pot holes.
You are starting with ~4.2" of ground clearance, things like Vipers and Vettes start with 6.0". |
Mark Eberhardt (Me_k)
Member
Username: Me_k
Post Number: 677
Registered: 5-2002
| | Posted on Wednesday, September 10, 2003 - 10:15 pm: | |
"so is lowering the only way to decrease the gap?"
yes, the only practical way. Normaly, when you go up in wheel diameter, you go down in profile, so the tire outside diameter stays about the same. |
neal (95spiderneal)
Junior Member
Username: 95spiderneal
Post Number: 247
Registered: 3-2002
| | Posted on Wednesday, September 10, 2003 - 7:43 pm: | |
so is lowering the only way to decrease the gap? |
John Dixon (Qvb)
New member
Username: Qvb
Post Number: 21
Registered: 8-2002
| | Posted on Wednesday, September 10, 2003 - 3:12 pm: | |
Another problem is you will be raising the car half an inch, which will not be attractive and will adversly affect your center of gravity. |
Hubert Otlik (Hugh)
Intermediate Member
Username: Hugh
Post Number: 1366
Registered: 1-2002
| | Posted on Wednesday, September 10, 2003 - 2:26 pm: | |
It'll raise the gearing, essentially slowing accelration, and increasing top speed. Also, 18's , usually, weigh more than 17's; therefore, you're increasing unsprung weight which has as effect on your shocks (as the heavier mass affects the dampening; i.e., your ride will be harder/harsher). Also, increasing unsprung weight has a a quadratic effect on the car, not a linear; every pouund of unsprung weight affects the car like four pounds of sprung weight.
Here's a good wheel calculator you can use, to try and get w/in your preferred rolling diametere:
http://www.miata.net/garage/tirecalc.html |
neal (95spiderneal)
Junior Member
Username: 95spiderneal
Post Number: 245
Registered: 3-2002
| | Posted on Wednesday, September 10, 2003 - 2:12 pm: | |
i am not happy with the fender gap around the tires of my 348 spider and would like to use 18" wheels with same tire profile i have on 17" rims now. this would increase overall diameter. i want to avoid lowering the car also. what effect would this have on the cars gearing? besides speedometer error would it increase acceleration and lower top speed?
thanks |