talk to me about spacers and "square" wheel/tire configurations

Hi Fol;ks,

I want to experiment with "square" configurations - as is run in spec Boxster.
This means running rear tires/wheels all around. (255/40-17 tires on 17" x 8.5" x 50mmET wheels)

I am told one needs spacers (5mm) in the front to clear suspension. I just test fit rear tires to the front of my car (PSS9, GT3 c ontrol arms, modest lowering) and it fits. Admittedly it is very close to the suspension upright, maybe 3-4mm clearance. But i've driven it a bunch of miles, turned, braked, gone through dips. what DOES concern me is that i'm pretty close to the fender on the outside and fear that under track conditions (heavy lean, take air and land, etc.) it will rub. I put some blue tape on the fender so that I'll have indication of the slightest rub, so I'm trying to test.

For those who have done this and seen it many times (hey you PCA scrutes!), what can you tell me about this?

I will note that the added scrub radius and wider tires already result in significantly more tramlining and modest kickback - jut like the math would say :-)

let's hear it,

Grant

Grant

gee-lenahan-at-gee-mail-dot-com



Edited 1 time(s). Last edit at 08/20/2016 11:04AM by grant. (view changes)

... may be allowed on the fronts only in order to clear suspension and fender well.
Depending on the tire you use, the suspension you have and the aggressiveness of your alignment you may or may not need the spacer when using square configuration.
The Class allows a maximum size wheel of 17 x 8.5.
Wheels MUST be factory cast intended for a Boxster and matching the original offset: front 55mm, rear 50 mm.
The tires are Toyo RR 235//40/17 or 255/40/17 (front) and 255/40/17 (rear) or Toyo RA-1s (rain).
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

The ruels for spec are not important to me, this is not a spec-legal car ( its an S)

I'm curious about clearance of the upright (whcih you say I may clear, and I appear to, just) and the fender (what is your experience there?)

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Here is how it sits (no spacer, PSS9, low not slammed)


Grant

Grant

gee-lenahan-at-gee-mail-dot-com

... PSS9s, it should be fine.
With the OEM struts (not coilovers) there's more of a clearance issue.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Most of us in Spec Boxster run square without spacers. The clearance on the suspension hasn't been an issue. Possible rubbing of the front wheel well liner seems to be the thing that happens, but I'm not even sure that's a 255 tire issue or a general issue with a slightly lowered car. I don't think spacers affect that either way. There are a couple of ways to mitigate that rubbing: 1) push (relocate) the liner mounting bracket (radiator bracket?) forward a touch; 2) replace the plastic push rivets that attach the liner (the heads are tall and more likely to "catch" ) with those torx bit dome head screws that are found elsewhere on the car like the rear bumper underside (the dome head is short and smooth).

The conventional wisdom is that square is generally better (more front end grip / turn in). But on a track that has sustained high speeds (Cal Speedway oval banking section for example) the aero effect of the wider tire may hurt top speed enough to be worse overall than staggered.



Edited 1 time(s). Last edit at 08/20/2016 07:05PM by Trygve (Oakland, CA). (view changes)

I've confirmed from several sources that with my suspension I should have no inner clearance issues, and so far, with lots of street driving includng dips etc., I'm getting comfy that it wont hit the fender either (for me its the fender, not the liner), but truly only experience at the track will tell.

I really like the way it feels so far.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Grant

gee-lenahan-at-gee-mail-dot-com