February 19, 2019, 08:21:22 PM

Author Topic: Big tire alignment for FC  (Read 710 times)

Offline Supe

Big tire alignment for FC
« on: May 09, 2018, 12:20:02 PM »
For those of you on 275-315 tires in an FC, what are you running for track alignments?  I'm starting at ground zero again on the new setup.  Leaning towards 1/8" out back, 1/16" out up front.  Particularly interested in rear camber, and front castor settings.  I've got a bad scrub radius, so I'm worried about going to heavy on castor and making the thing impossible to turn/nightmares in the bumps like it used to be.

Offline largeorangefont

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Re: Big tire alignment for FC
« Reply #1 on: May 09, 2018, 12:35:33 PM »
I run 1/16 toe out front, 7/32 toe in rear. The extra rear toe helped a lot.

Im -2.9 camber in front, about -1.5 rear. I just have slightly more than stock caster, a little extra is built into my camber plate.

I actually need a bit less front camber, Im wearing the inside of my tires a bit more than the outside. The car is pretty good over the bumps.
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Offline Supe

Re: Big tire alignment for FC
« Reply #2 on: May 09, 2018, 12:55:37 PM »
Thanks.  I may give the extra rear toe a shot.  I suspect I'll have issues putting power down out of low speed turns. 

I have Ground Control camber plates, so probably the same deal on castor.

Offline largeorangefont

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Re: Big tire alignment for FC
« Reply #3 on: May 09, 2018, 09:34:29 PM »
Yea the extra rear toe made the car much more consistent. I started out with 1/16 toe in rear. I dont feel like I lost anything, the car still rotates very well.
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Offline Bowtie7

Re: Big tire alignment for FC
« Reply #4 on: May 10, 2018, 08:33:06 AM »
Totally agree with more toe in rear. Sat in on a seminar with hoosier tire a couple years ago and they mentioned same on powerful, big tire cars. I stumbled onto it so felt good to know that my thinking was in the right direction. Made the car way more stable. Camber sounds about right too. To much negative will not leave as much of the tire in contact so less traction is the result. I think we run 1.25 in rear on 315 tire.
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Offline Supe

Re: Big tire alignment for FC
« Reply #5 on: May 10, 2018, 09:33:18 AM »
Thanks guys.  I'm on 275 NT01's now, but am going to 315 NT01's on a 10.5 wheel.  Sounds like I'm going to go with:

-2.5 camber front
-1.5 camber rear
1/16" toe out front
7/32 toe in rear
5-6 degrees castor (5 if I can get it based on manual rack/scrub radius - current setup wanted to center the wheel in bumps, so you had to hang on for dear life)

Offline largeorangefont

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Re: Big tire alignment for FC
« Reply #6 on: May 10, 2018, 02:17:26 PM »
I think that is a great place to start.
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Offline jwvand02

Re: Big tire alignment for FC
« Reply #7 on: May 11, 2018, 12:50:17 PM »
I think that is a great place to start.
What changes would you make for a 255 tire?

Offline largeorangefont

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Re: Big tire alignment for FC
« Reply #8 on: May 11, 2018, 08:47:52 PM »
I used to run 255s all around. That alignment will be good with 255s. You could crank the rear toe in up slightly to a full 1/4 in. Make sure to dial in the front camber perfectly to get the best braking performance. The biggest improvement I saw going to 275s all around was increased control  and improved performance under braking.
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Offline jwvand02

Re: Big tire alignment for FC
« Reply #9 on: May 14, 2018, 09:51:44 AM »
thanks!

I'm doing all of the reliability and safety stuff (IR baffle, accusump, roll bar) this year and progress has been slow. Hoping to get some wide fenders and put those on this winter

Offline 346fc3s

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Re: Big tire alignment for FC
« Reply #10 on: August 25, 2018, 07:17:42 PM »
a 315 on a 10.5" wheel won't be ideal.  You'd probably have more luck on track with the 275 on a 10.5" wheel.  Going too wide with the tire will give you slower response and a vague feeling on center, it will also make the car take longer to take a set.  You also won't gain as much grip as you should with a tire that wide because your contact patch won't be flat. 
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Offline Supe

Re: Big tire alignment for FC
« Reply #11 on: August 26, 2018, 04:23:07 PM »
You also won't gain as much grip as you should with a tire that wide because your contact patch won't be flat.

As much as I hear this being said, I have never met anyone who has actually gone slower on the bigger tire without a HORRIBLY mismatched wheel/tire combo, and usually on stock or near stock power levels.  Conversely, everyone I know who's thrown a 315 Hoosier on a set of 10" or bigger wheels has gone quicker than on 275's.

Offline 346fc3s

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Re: Big tire alignment for FC
« Reply #12 on: August 26, 2018, 06:20:30 PM »
We tried it on the mx5 cup cars.  We ran a 225/45/17 BFG R1s on a 7" wheel in the series, going to a 9" gained .5 seconds a lap at MSR Houston.  This was on a 1:42ish lap time with a couple pro drivers.  Going down to a 215/45 on the 7" wheel didn't change lap time at all but it did make the car easier to drive and more consistent.  Tire wear was also more even with properly sized tires and temps were more consistent.  The drivers both liked either the small tire/small wheel or large tire/large wheel.

I just said you won't gain as much grip as you should, not that you wouldn't gain any grip at all.  The wider tire may give you more overall grip but it will react differently, not in a good way, it will also take longer to come up to temp, wear unevenly and have a shorter useable life due to that uneven wear.  I know there are bandaids to fix some of these issues but isn't it just easier to get the correct size wheel?
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Offline Supe

Re: Big tire alignment for FC
« Reply #13 on: August 27, 2018, 02:01:30 PM »
In a 17", not really.  Just not getting there without big $$$, and considering the hits my wheels have taken while hill climbing, it's not worth the expense for the ROI.