New Product - 928 Racing Spring Perches
07-14-2005, 11:15 AM
#16
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Thread Starter
Warren - I'm afraid I have spent all my efforts widening the track on my 928 and because of that, all my wheel offsets are POSITIVE. - to the outside. I race in classes that permit widening.
But, I have had calls from guys racing the 928 in SCCA regs or classes where the entire tire/wheel must fit underneath the stock fender without modification occording the their rules.... and for them, a wider rim with negative offset is the hot ticket.
Sorry I do not know the offest or rim width numbers that they use.
I bet Dave Roberts does at 928 Specialists - they know that tire/wheel stuff cold.
But, I have had calls from guys racing the 928 in SCCA regs or classes where the entire tire/wheel must fit underneath the stock fender without modification occording the their rules.... and for them, a wider rim with negative offset is the hot ticket.
Sorry I do not know the offest or rim width numbers that they use.
I bet Dave Roberts does at 928 Specialists - they know that tire/wheel stuff cold.
07-14-2005, 02:08 PM
#17
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Hi Carl,
>I sent a question your way, can you help him out?
>... the reader wants to know what offset to use and what you guess the widest
>tire/wheel combo you can fit with the new space gained from smaller spring diameter.
On a street car with up to 1.5 degrees or so of neg. camber the Front springs are not the only limiting factor. The front wheels will also hit the upper control arms (this is being addressed in a future product) just before they will hit the stock coilovers when turning the front wheels "lock to lock" (Note: this varies slightly depending on wheel diameter,etc.). Also the stock sway bars are a limiting factor and "non-factory shaped" larger sway bars are even more of a limiting factor than the coilovers and control arms. For example my 19 X 9.5 70mm offset front wheels with 265/30-19 tires has approx. 1/4" clearance to the stock sized coilovers, BUT only approx 1/8" to the control arms when turned full lock.(running 1.5 neg camber on "S" suspension) and are just touching a factory 28mm sway bar.
However, for a 928 track car guy that wants to run 2-3 degrees neg camber smaller coilovers will give you more clearance to run the same size that clear with stock coilovers and "aggressive" street camber settings. Also for those that chose to use multiple steering rack stops to limit turning radius (not recommended for street cars) these coilovers would certainly allow you to run a wider(via more neg. offset) tire/wheel setup with the higher track camber settings.
For the rear there is no advantage as far as wheel/tire width is concerned. For example with my 315/25-19s on 11" wheels the stock sized Coilovers are approx 3 inches from the wheel/tire,(see first photo) BUT the front of the lower control arm is only 1/2" away (see second photo), the inner rear fender well is also only 1/2 " or so away (photo 2). The stock sway bar is also MUCH closer than the coilover (by a few inches). As a side note, the larger diameter wheel you use the less of an issue the stock rear sway bar becomes.
Based on my experiance for street and agressive street 928ers the smaller coilovers do not allow larger wheel tires sizes without other mods. For a track only 928 with limited lock to lock steering they will allow you to run larger wheels (via negative offset) and tires on the front only with track camber settings which is certainly an advantage on a track car. It is also common practice for most racers to use flared fenders and put the extra wheel/tire width to the outside (more positive offset) so the smaller coilovers are not a big advantage as far as wider wheel/tire widths as flaring the fenders or using aftermarket flares, but they can help some. Of course with the combination of both you could get some REALLY big rubber under there. IMHO the greatest advantage of the smaller coilovers are for track cars due to their lower weight and even more so for the wide range of spring rates available for those racers that truly know how to take advantage of experimenting with different spring rates for specific track layouts and conditions.
Skipping thru all of the above technical issues and in simple terms, I would guess you could run 1/2" or more wider front wheels with the smaller coilovers IF you also modify your steering "lock to lock" range which would not be an issue on a track car.
Hats off to Carl for coming up with a simple solution to allow 928ers to expand their range of spring rate offerings for those who truly need it and know how to take advantage of it! AND especially for selling just the adapters kits for those that want to get their own springs instead of insisting on just selling a complete proprietary package only.
Oh, sorry for the long winded reply, but it is not a simple subject and requires thought, planning and some experimentation to get it right and more importantly to get it SAFE.
>I sent a question your way, can you help him out?
>... the reader wants to know what offset to use and what you guess the widest
>tire/wheel combo you can fit with the new space gained from smaller spring diameter.
On a street car with up to 1.5 degrees or so of neg. camber the Front springs are not the only limiting factor. The front wheels will also hit the upper control arms (this is being addressed in a future product) just before they will hit the stock coilovers when turning the front wheels "lock to lock" (Note: this varies slightly depending on wheel diameter,etc.). Also the stock sway bars are a limiting factor and "non-factory shaped" larger sway bars are even more of a limiting factor than the coilovers and control arms. For example my 19 X 9.5 70mm offset front wheels with 265/30-19 tires has approx. 1/4" clearance to the stock sized coilovers, BUT only approx 1/8" to the control arms when turned full lock.(running 1.5 neg camber on "S" suspension) and are just touching a factory 28mm sway bar.
However, for a 928 track car guy that wants to run 2-3 degrees neg camber smaller coilovers will give you more clearance to run the same size that clear with stock coilovers and "aggressive" street camber settings. Also for those that chose to use multiple steering rack stops to limit turning radius (not recommended for street cars) these coilovers would certainly allow you to run a wider(via more neg. offset) tire/wheel setup with the higher track camber settings.
For the rear there is no advantage as far as wheel/tire width is concerned. For example with my 315/25-19s on 11" wheels the stock sized Coilovers are approx 3 inches from the wheel/tire,(see first photo) BUT the front of the lower control arm is only 1/2" away (see second photo), the inner rear fender well is also only 1/2 " or so away (photo 2). The stock sway bar is also MUCH closer than the coilover (by a few inches). As a side note, the larger diameter wheel you use the less of an issue the stock rear sway bar becomes.
Based on my experiance for street and agressive street 928ers the smaller coilovers do not allow larger wheel tires sizes without other mods. For a track only 928 with limited lock to lock steering they will allow you to run larger wheels (via negative offset) and tires on the front only with track camber settings which is certainly an advantage on a track car. It is also common practice for most racers to use flared fenders and put the extra wheel/tire width to the outside (more positive offset) so the smaller coilovers are not a big advantage as far as wider wheel/tire widths as flaring the fenders or using aftermarket flares, but they can help some. Of course with the combination of both you could get some REALLY big rubber under there. IMHO the greatest advantage of the smaller coilovers are for track cars due to their lower weight and even more so for the wide range of spring rates available for those racers that truly know how to take advantage of experimenting with different spring rates for specific track layouts and conditions.
Skipping thru all of the above technical issues and in simple terms, I would guess you could run 1/2" or more wider front wheels with the smaller coilovers IF you also modify your steering "lock to lock" range which would not be an issue on a track car.
Hats off to Carl for coming up with a simple solution to allow 928ers to expand their range of spring rate offerings for those who truly need it and know how to take advantage of it! AND especially for selling just the adapters kits for those that want to get their own springs instead of insisting on just selling a complete proprietary package only.
Oh, sorry for the long winded reply, but it is not a simple subject and requires thought, planning and some experimentation to get it right and more importantly to get it SAFE.
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David Roberts
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David Roberts
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07-14-2005, 03:18 PM
#18
Developer
Thread Starter
Excellent photos and an excellent response! I knew DR would have the tire/wheel info.
They really show that the tires rubbing the springs are not the issue - the tires will hit the swaybar and the tracking arms long before that.
When we designed the spring perches - it was to get into a spring series where we could get any rate we wanted easily, and less unsprung weight as a by-product. Somebody said they could add more negative camber now cuz the springs are smaller - but looking at DR's pics - it makes me wonder...
They really show that the tires rubbing the springs are not the issue - the tires will hit the swaybar and the tracking arms long before that.
When we designed the spring perches - it was to get into a spring series where we could get any rate we wanted easily, and less unsprung weight as a by-product. Somebody said they could add more negative camber now cuz the springs are smaller - but looking at DR's pics - it makes me wonder...