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-   -   Suspension height on track performance (http://forums.pelicanparts.com/porsche-autocross-track-racing/1004851-suspension-height-track-performance.html)

puddy 08-13-2018 12:34 PM

Suspension height on track performance
 
I recently switched from 18" to 17" wheels on my car. The new wheels are about 1/2" wider than the previous wheels. I'm finding that the new Rear tire on the passenger side is contacting the fender, but driver side rear is fine. My car has welded on turbo flares and it appears that maybe my pass side is not welded on equal to the driver side, it sits a little lower.

So i'll be raising the rear of the car about 1/2" via the coil over shocks. Will this adjustment make any difference to the car handling on the track? And I assume i should be raising them equal amounts to keep the rear suspension balanced? Correct?

wildcat077 08-13-2018 04:48 PM

If it was a street car , i would make both sides even between the top of the wheel and the fender but if a track car , your best bet it to get it corner balanced , although the gaps might end up really uneven !
I usually slip my hand over the rear wheels and just let the top of my knuckles touch the fender
and for the front i try to keep a two finger gap.I had a lot of camber on my 911 when i was tracking it so rubbing was never an issue , even with massive tires ...

puddy 08-14-2018 03:50 AM

OK thanks. It is a street & track car. It was corner balanced earlier this year. I'll try the rears equal height for now.

wildcat077 08-14-2018 05:51 AM

Chris,

Be grateful you have rear coilovers ... i spent half a day on the rear of my 911 fiddling with the torsion bars in order to get the stance i wanted !

puddy 08-14-2018 06:30 AM

Hah yes they rears are super easy to adjust, however I have my fronts sitting a little high now, which I believe I raised previously when I installed 18" wheels, so now that i'm back to 17's I hope I can just drop them down again.

I'm curious what camber setting you use? I'm at -1.2 front and -1.5 rear. Can I benefit from a little more cambre? My car is mostly used on track, probably around 70% on track vs 30% street driving. So tire wear isn't a huge concern.

Dave at Pelican Parts 08-14-2018 10:44 AM

With modern radial tires, more negative camber is almost always a good thing, until you get outside of a fairly large range.

You're not outside it yet. You'll notice better steady-state cornering grip with more negative camber, though you may lose a bit of acceleration and/or braking grip.

--DD

wildcat077 08-14-2018 11:36 AM

Chris ,

It will be hard to get anything more than what you have as far as negative camber without
adding some modifications to your suspension ...
First off , you would need to add adjustable camber plates in front and maybe ER decambered ball joints and perhaps some ER spring plates in the rear !

I was running BFG R1 "R" compounds in 245/40/17 and 275/40/17 at the time on 17 inch Fikses , and i believe the 275's are discontinued now but my camber numbers were around -2.2 and -2.5 front and rear , i toned the camber down now as my 911 is back to street duty only.

A good piece of advice would be to call Chuck at Elephant Racing or Ira at Tarett Engineering , they have lots of experience with 911's and they can guide you through your needs ... all my suspension parts
came from them and Pelican !

puddy 08-14-2018 11:59 AM

Thanks alot fellas, i definitely have some suspension WANTS for next season or two. I was thinking about going to complete KW clubsport 2 way coilovers all around.

puddy 08-15-2018 08:36 AM

Wow it seems my flares are really off.

Perhaps i'm measuring wrong but I measured the length of threads below the jam nuts on my rear coil over bodies for each side.

On the Drive side i had 7" of threads on the Pass side is have 7.75" of thread, which should indicate the Pass side rear is higher as the spring is compressed more. Correct? Yet my distance to the centre of the wheel opening down to the floor is different by about 1/2", the Driver side being higher. Strange.

Same seems to be true for the front but opposite, my Driver side front fender is closer to the floor than the Pass side. I guess i just live with it as I have for the last 4 years!

3rd_gear_Ted 08-17-2018 02:07 PM

Perhaps you should measure the ride height per the "Porsche" procedure. Past posts have described the procedure before with pictures.

Driven97 08-23-2018 07:37 AM

Quote:

Originally Posted by puddy (Post 10142203)
OK thanks. It is a street & track car. It was corner balanced earlier this year. I'll try the rears equal height for now.

FYI you are aware that as soon as you touch a height you completely undo a corner balance, right?

puddy 08-23-2018 11:09 AM

Yes i'm aware of that but my track events for the season are mostly over, i'll get re-balanced next spring.

I tired searching ride height as per "Porsche" procedure and didn't come up with much.

Driven97 08-23-2018 11:44 AM

When in doubt, always look for Bill V's posts. Diagram for procedure is in post #11.

http://forums.pelicanparts.com/porsche-911-technical-forum/960562-euro-ride-height-question.html

Note the Porsche method sets the suspension height independent of tire diameter.

puddy 08-24-2018 11:14 AM

Cool, thanks for the link!

3rd_gear_Ted 08-26-2018 05:40 PM

Quote:

Originally Posted by Driven97 (Post 10154051)
When in doubt, always look for Bill V's posts. Diagram for procedure is in post #11.

http://forums.pelicanparts.com/porsche-911-technical-forum/960562-euro-ride-height-question.html

Note the Porsche method sets the suspension height independent of tire diameter.

Testing, testing:
My understanding is the difference between the two readings using the Porsche method also establish the rake angle of the chassis if you plot it out????

3rd_gear_Ted 09-10-2018 12:52 PM

FWIW
Red Bull F1 - 1.9 degrees rake
Ferrari F1 - 1.5 degrees rake
Mercedes Benz F1 - 1.2 degrees rake


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