Scrub radius, strut angles and alignment setup

[Compelica]

Hi everyone,

Trying to get line up my thoughts for my suspension install and alignment this weekend.

I am installing Tein Flex As with 10mm wheel spacers on stock rims and suspension components. Another thread has mentioned that the stock setup has about 0.75 inches (or 19mm) of positive scrub radius, so having 10mm spacers would further increase that amount.

In order to reduce scrub radius, I am thinking if I could attain the desired negative camber by using the camber plates, and then using camber bolts to bring more positive camber back - by doing so I would assume I could get less positive scrub radius while keeping the slightly wider track.

This car is a street car with the occasional canyon runs. The height is planned to be at 145mm/135mm rear and front at pinch welds respectively. The spacers are to increase track and to fill some flush while at it. Toe is to be at 0, and camber to be targeted at around -1.7 degs.

Any thoughts and opinions would be much appreciated - thanks.

[NoHaveMSG]

You should be able to hit what you want by doing that. I think my Flex Z’s would do well over -3 with just the plates so there should be enough adjustment to crank them over, then stand up the spindle with a camber bolt.

[Compelica]

Originally Posted by NoHaveMSG

You should be able to hit what you want by doing that. I think my Flex Z’s would do well over -3 with just the plates so there should be enough adjustment to crank them over, then stand up the spindle with a camber bolt.

Thanks. I found this article some time later which at least supports that thought process.

https://grassrootsmotorsports.com/fo.../133011/page1/

Problem is that I'm likely just going by feel here; have no idea how much positive scrub I am reducing, but I suppose any reduction would be beneficial given the 10mm spacer.

[Racecomp Engineering]

I prioritize getting as much camber as I can at the lower mount rather than the camber plate. Doing it this way gives you a more beneficial SAI, which IMO outweighs the benefits of getting more camber from the top mount (and there are some positive effects including the effect on scrub radius like you've said).

You'll notice a lot of strut based motorsports-level cars including the STI Nurburgring racecar I crawled all over and under has (roughly) center fixed location top mounts and got it's camber at the lower mount. Some of it is application dependent.

Still can't go nuts with wheel offset and spacers, but for less than -2 degrees of negative camber and a 10mm spacer it's not going to make toooo much of a difference either way.

- Andrew

[autoracer86]

Originally Posted by Racecomp Engineering

I prioritize getting as much camber as I can at the lower mount rather than the camber plate. Doing it this way gives you a more beneficial SAI, which IMO outweighs the benefits of getting more camber from the top mount (and there are some positive effects including the effect on scrub radius like you've said).

You'll notice a lot of strut based motorsports-level cars including the STI Nurburgring racecar I crawled all over and under has (roughly) center fixed location top mounts and got it's camber at the lower mount. Some of it is application dependent.

Still can't go nuts with wheel offset and spacers, but for less than -2 degrees of negative camber and a 10mm spacer it's not going to make toooo much of a difference either way.

- Andrew

I was told the same thing by my shock builder get as much camber from the lower bolts first

[Compelica]

Thank you everyone!

[gpvecchi]

The 14R60 by TRD aka Griffon Concept uses ET 30 on the front, I assume because of a compensation for the increased camber.
Is is possible to calculate the scrub radius reduction according to the different camber?

[new2subaru]

Originally Posted by Racecomp Engineering

I prioritize getting as much camber as I can at the lower mount rather than the camber plate. Doing it this way gives you a more beneficial SAI, which IMO outweighs the benefits of getting more camber from the top mount (and there are some positive effects including the effect on scrub radius like you've said).

You'll notice a lot of strut based motorsports-level cars including the STI Nurburgring racecar I crawled all over and under has (roughly) center fixed location top mounts and got it's camber at the lower mount. Some of it is application dependent.

Still can't go nuts with wheel offset and spacers, but for less than -2 degrees of negative camber and a 10mm spacer it's not going to make toooo much of a difference either way.

- Andrew

If that's the case, would group N top mounts work with an adjustable front lower control arms? Could you get as much as -3.5 - 4 camber with SPL's?

[Racecomp Engineering]

Originally Posted by new2subaru

If that's the case, would group N top mounts work with an adjustable front lower control arms? Could you get as much as -3.5 - 4 camber with SPL's?

I use OEM top mounts (I'll probably switch to Group N eventually) with Cusco adjustable lower arms. With that, my KW/RCE coilovers, and the OEM crash bolt...I'm at over -3 degrees with a little more adjustment available. Probably not -4.

Couldn't tell you the limit on the SPL front arms.

- Andrew

[new2subaru]

Originally Posted by Racecomp Engineering

I use OEM top mounts (I'll probably switch to Group N eventually) with Cusco adjustable lower arms. With that, my KW/RCE coilovers, and the OEM crash bolt...I'm at over -3 degrees with a little more adjustment available. Probably not -4.

Couldn't tell you the limit on the SPL front arms.

- Andrew

Thanks, Andrew. I may try it just to see what I can get just out of curiosity. I have the car in the air and doing a bunch of work now.

ETA It's right on their website

"Camber Adjustment
One of the biggest improvements to cornering grip you can make is increasing the front camber angle from the weak factory spec (0.0 to -0.75°) to a more proper -2.5° to -4.0° of front camber. This also will significantly improve tire life by reducing heavy wear on the outer portion of the tread that occurs due to insufficient camber angle while cornering.

Elongating the lower arm will add more camber without the need for adjustable camber plates or eccentric bolts that could potentially slip. However, pairing the SPL LCAs with camber plates allows you more adjustability options for inner and outer tire clearance as well as elongating the track width while retaining a specific camber angle"

[gpvecchi]

Elongating lower arms will also increse track...

[Racecomp Engineering]

Originally Posted by new2subaru

Thanks, Andrew. I may try it just to see what I can get just out of curiosity. I have the car in the air and doing a bunch of work now.

ETA It's right on their website

"Camber Adjustment
One of the biggest improvements to cornering grip you can make is increasing the front camber angle from the weak factory spec (0.0 to -0.75°) to a more proper -2.5° to -4.0° of front camber. This also will significantly improve tire life by reducing heavy wear on the outer portion of the tread that occurs due to insufficient camber angle while cornering.

Elongating the lower arm will add more camber without the need for adjustable camber plates or eccentric bolts that could potentially slip. However, pairing the SPL LCAs with camber plates allows you more adjustability options for inner and outer tire clearance as well as elongating the track width while retaining a specific camber angle"

Just be sure you have sufficient engagement on the turnbuckles.

- Andrew

[new2subaru]

Originally Posted by Racecomp Engineering

Just be sure you have sufficient engagement on the turnbuckles.

- Andrew

100% and I would never take something like this to "maximum" Safety first.