Modern/updated alignment specifications

What size wheels/tires are you using?

This thread has what I used at the front and rear to get the most even tread wear for street driving on my lowered '78 ex-308 when using 16" QV wheels/tires:
https://www.ferrarichat.com/forum/threads/alignment-spec-for-qv.637513/#post-147756351

PS You need to keep positive and negative in mind when talking about camber -- the stock front camber spec is a (crazy ) slight positive camber as you show while the stock rear camber spec is a negative camber (which you don't show).

 

Aaron, this is perfect timing because I have an appointment to an alignment shop next Monday. We have the same size wheels and I’m following Steve’s recommendation for the best even tire wear spec. Image Unavailable, Please Login

 

Those 17" tires will have an even stiffer tire sidewall than a 16" tire so, for sure, you'll need to run less rear negative camber and less rear toe than the stock 308QV rear specs (maybe even less negative rear camber than I did using 16" tires) -- unless you don't mind wearing away the inside rear tread area prematurely .

Had a quick look at the front suspension geometry shown in the 308GT4 WSM, and you probably should be able to increase the caster to 4.5 deg if you want to -- the adjustment range isn't huge, and some may have already been taken up do to the part tolerances, but changing 0.5 deg should be doable except in rare cases.

 

It was also mentioned in a UK Youtubers video on his carb 308 GTS last Summer. I was somewhat shocked to learn that too !!

 

I will assume that is due to greater body flex on a GTS car.

Doug

 

So do we think the positive camber is an attempt by the manufacturer to disssuade GTS owners from trying to drive harder ? By introducing more understeer ?

 

FWIW my ‘82 308GTSi with no shims has neg front camber @1.00 to 1.25 the rear with no shims has neg @0.75 to 1.00. I have SF rear springs in both f&r as the SF front springs sat way to low, the rear has a spring shim to make ride height.

 

A 308GTS has a larger rear sway bar than a 308GTB (putting more load on the rear tire in hard cornering = increases its slip angle under cornering) so decreasing the negative front camber on the GTS (and going to a slight positive camber) would be a way to increase its front slip angle under the same cornering conditions to keep the overall result more similar to the GTB (i.e., targeting both to understeer about equally).

 

I need to ask, is the point to minimize tire wear or maximize traction? the answers are different I think with traction wanting f/r camber near -3 degree then play with springs and sway bars to get the balance you like.

 

For me, getting even tire wear across the tread width (so maximizing tire life). Setting up your car like a DTM car (with a boatload of negative camber at both ends) does get maximum "performance", but you'll be prematurely replacing tires IME.

 

Forgot to ask: If maximum performance is all you want, have you removed most of your car's interior, too?

 

Image Unavailable, Please Login Steve, is this what you call super negative rear camber? This guy probably change rear tires once a week.

 

It wasn't a right or wrong, just trying to understand what "best" or "modern" meant.

I never really messed with mine, its set to OEM spec which for an 84 qv gts is nearly identical to what's in the 1st post. The tires are F225/40-18 R285/35-18. The rears are nearly spent and you can clearly see that rolling around the shop the outside doesn't touch, but I can't really measure a wear difference inside to outside...a little maybe but for sure the center is worn most which I assume is my heavy right foot. The fronts have about double the remaining tread and were installed the same day, they also look pretty even.

I have a rear grip issue, but I think that is mostly a poor spring choice on my part issue (F450/R400). Removing the rear swaybar helped which kind of confirmed its a mismatched f/r spring issue so I never tried messing with the alignment. I'm hoping the car will actually run soon parting sorting all this back on the to-do list.



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You would at -3 deg rear camber

If by "rear grip issue", you mean the car tends to oversteer in hard cornering and the back end comes around (short of going to larger negative camber at the rear) about all you can do is try to increase the tire slip angle at the front relative to the rear -- either by changing the spring rates to put more load on the front under cornering (which isn't so easy to accomplish due to the flexible nature of the GTS chassis and would result in more body roll) or going to less negative camber at the front which is what Ferrari seemed to do. You can see in the 307/84 US 308QV OM specs that they used the same strategy here that they used on the carb 308s as the fronts have very little negative camber (while the rears are at ~1.5 deg negative camber -- which already causes unacceptable uneven rear tire wear IMO):
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and, when using the same size TRX tire all around, they reduced the front camber to zero. I would add that you are running a very wide, low sidewall front tire, and it will have a much lower slip angle under the same cornering loads vs a stock tire -- so you might have to go with a more positive front camber (if you don't want to go to a narrower front tire). Bottom line is that you'll need to decide how much negative rear camber you want to run (i.e., how much uneven rear tire wear you'll accept), then do whatever is necessary to get the front tire slip angle to match the rear tire slip angle (i.e., shift more load to the front, go more positive camber at the front, go to a narrower tire at the front).

 

That is the situation....but I know the springs are causing the excessive rear roll stiffness. I've been going round and round but I thing the final call is up the fronts to 550 along with a stiffer front sway bar, add a sway bar with some adjustment to the rear and see what I have.

Then decide where to go on alignment...which brings me back the the original question of what "modern" means. I don't know what Aaron is trying to optimize. I'm after good autoX results and tolerable tire wear....which means the rear camber is going to land somewhere between the current -1.5 and what is probably optimal traction at -3. I've not given any thought to the front beyond I'm pretty sure max traction is around -3 camber again. Caster....I've not thought much about it.....so I'll be watching Aaron's results I guess

 

That's the problem -- you don't want max traction at the front -- you need about equal tire slip angles at the front and rear. With the engine at the rear (i.e., most of the weight at the rear), the rear is going set the traction limit on a 308 -- then the front needs to be degraded to match that same rear behavior.

 

I'm pretty sure that's not quite right. Being as my current knowledge is mostly limited to what doesn't work well on a 308 I have only 2nd hand success info I hesitate to say anything but the most general straight from the book stuff For sure the rear tires will be under more load which will cause more heat, but that's why the rear gets wider tires with sizes adjusted to equalize load/temp. What you're saying sounds more right what tire size are fixed and certainly when they are equal but that is not the case with my car. I know Aaron talked about going up to 235 fronts with his 255 rear....that seems like that would get him back to overloaded rear and trying to balance it out.

There is also the ability to vary the f/r roll stiffness to change the f/r cornering loads and the f/r spring rate to change braking/accel weight transfer. I know I have this screwed up on my car at he moment. again, if stock suspension is the order of the day, there is not a lot that can be done, but that is not the situation with my part which has adjustable coil overs and basically unlimited spring rate and sway bar options to try.

This represents my entire knowledge.....a book I bought years ago to help with our fsae car design
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Well, I find this discussion fascinating.
I am not a suspension guru either, nor do I have any suspension tuning software.
I am however concocting a real Frankenstein 308 of sorts and, like mk e, have to start somewhere and make adjustments accordingly and see what happens in the real world.
I am way out in no man's land as a starting point, My car started life as a GTB. I back halved the frame in chrome moly while increasing the wheelbase to 288 GTO specs (car is receiving GTO bodywork). I also increased the rear track 1" and switched to Mondial 3.2 rear suspension. The front remains 308 spec. but all control arms front and back were made from chrome moly tubing in a 288/F40 design. The upper arms ended up weighing 1,5 lbs. less than the factory stamped arms and the lowers ended up 2 lbs. less each and of course I took advantage of the full width of the bushings where they press into the arms unlike the factory pieces. Bushings are Energy Suspension polyurethane for now. Wheels are Compomotive 17" "star mags"......9" wide front & 11" rear with the same outside split rim barrel. Front sway bar is a much beefier one from the last group buy here on fchat. For the rear, I came up with a splined bar to run through the lower rear frame tube kind of like the Daytonas ran higher in their rear framework. It is actually meant for a Jeep CJ I believe but the length was right and I selected a diameter that retained the ratio the factory had between front and rear bars. I have splined arms that I have yet to finalize and attach to the rear lower control arms but I figure I will use the factory location on those to start. I plan on going the QA1 adjustable route for now but have not selected any spring rates as of yet and would appreciate any and all feedback in that regards. I suppose I should mention that it is running a longitudinally mounted Cadillac Northstar sitting extremely low in the chassis backed by a Porsche G50/50 box.
Again, I don't claim to know what I am doing and am open to any and all advice/opinions/feedback etc. The car has been lightened to the extreme, doors are full carbon fiber. It will not be a dedicated track rat but I'm sure will find its way to the track now and again. I'm sure mostly street duty will be the order of the day.
To further complicate the suspension unknowns there is also another situation. The Porsche box has to be run upside down which put the axle flanges way up high. In an effort to re-establish the factory location of those in relation to the hubs, the engine was dropped to the point of requiring a dry sump pan and system. Of course that also means very low center of gravity. Another concession that was made was flipping the lower frame rails upside down. As most of you know, the control arm fork mounts are offset in the rails so this effectively raised the level of the entire rear suspension. In other words, the rear geometry is all correct, just sitting in a different and higher plain than the front. Trouble? I selected a taller tire for the rear to begin to compensate for this.
Whether all of this is just one big hot mess at this point I don't know.

 

As most of you know, luckydynes is hardcore into auto-x and has posted in the past on this subject. I know he has advanced past these older threads but still good references:

https://www.ferrarichat.com/forum/threads/go-fast-chassis-setup-for-your-308.277744/

https://www.ferrarichat.com/forum/threads/desperately-seeking-camber-308.197820/

https://www.ferrarichat.com/forum/threads/i-just-made-solid-suspension-bushings-for-my-308.323864/

Maybe he will chime in and update us on his more recent set-ups.

 

I was just talking suspension with Sean....springs specifically. I'm 450/400 and he is 580/350. Quite a difference in f/r roll stiffness as a result.

 

Interesting.
It would be great if you and Sean could (or already have) corner weighted your cars so I could compare to mine. That might help me get in the ballpark.