Administrators RTz Posted June 5, 2011 Administrators Share Posted June 5, 2011 I'll have to see if I can get you a picture of the rear mod they did. I'd be interested in seeing that too. Back to the front bridge... Would there be any benefit in taking it higher up on the strut? Would that help stiffen the strut tube, or would it be dead weight?... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 5, 2011 Share Posted June 5, 2011 Someone could do some FEA on it and tell you for sure, but for my $.02, the middle of the strut tube is an unsupported span, and the strength is close to the base. Quote Link to comment Share on other sites More sharing options...
Matt 78Z Posted June 7, 2011 Author Share Posted June 7, 2011 Wow, I was away from the pc for a day and I get all this! 1. Yes I am going too fast into the corner, most of the time. I tried various speeds and lines. The best seemed to be swing it wide under no throttle then as it straightened out roll into the throttle. -Doing this it will push the front tires but no where near as bad as when I try to take it tight around the cone. 2. The majority of the time I can keep cranking on the wheel and feel the tires biting, one of my favorite things about these cars. When they start to slide I either back off just enough to keep it turning, or depending I can give it more throttle and slide the back around. 3. Really unless we are talking 180's or tighter it is fairly neutral. I try to go by the "if you can still turn in your not going fast enough and if you can't still turn in your going to fast" idea. In most cases I am able to hold the car to this line. 4. At the moment the tires are worn out, I'm taking that into account. I've had it on A6's so I know how much better it will stick with the same configuration and it is significantly better. However the understeer is still there. This is why I'm thinking I can make a few minor mods and get it better. 5. I was running too much pressure. I dropped the fronts to 30psi down from 36(normal street setting) and the rear I have at 34, at 36 the rear was pretty loose. This helped front bite and calmed the rear enough to feel more balanced. 6. I have been adjusting the illumina's. I run the back 1 or 2 settings stiffer than the front, this is helping to rotate the rear as well. So it sounds like I'm going in the right direction, I just need a few parts and to better my driving. I had this car down for a year and have to admit that I'm slower than the car and late, so getting back more seat time will help. I'd never seen the front strut bracing, looks like something to do. I saw the pictures of the rear bracing and am leaning towards that as well. I did think about trying the stock rear sway bar. I'm going to get camber plates and add caster also. I'm gonna hold off on the subframe re-drilling till I try these other methods. I'm going to slow down and use 2nd gear more Oh and get some darn tires! Thank you, you've given me lots of good info and things to try. I'll report back with progress, normally I try one thing at a time like making carb adjustments. Quote Link to comment Share on other sites More sharing options...
johnc Posted June 7, 2011 Share Posted June 7, 2011 I've seen a number of cars with the strut bridge but I've never really known a reason to install it. I've yet to see a bend or failure in that area that wasn't caused by hitting something - hard. I'm of the mind that the welding itself would cause more distortion in the alignment of the spindle to the strut tube then any inherent flex that might exist at 1.25G lateral supporting, what, 600 lbs. vertical? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 7, 2011 Share Posted June 7, 2011 The spindle itself is a lever arm that is about 3.5" from the middle of the bearings to the back side of the casting, and there is the "ear" that the spindle is machined out of which is another little lever arm for the strut to work off of as well about 1" long from the center of the spindle to the main thicker part of the casting. If the spindle came straight out of a solid casting, I don't think I would have done this mod. I think the effect here that we should be most concerned about would be camber loss in cornering. There may be some issues in supporting the weight of the vehicle vertically as well, with some corresponding neg camber loss under braking, but I think it's very analogous to the strut tower bar, where what you're trying to do is keep the neg camber and not lose it to either that ear flexing over under load in the case of the gusset or the strut tower flexing out under load in the case of the strut tower bar. Weight transfer = lateral g x weight x cg height / track width. Say that is 1.2g x 1200 (weight of one axle) x 21" / 53", or 573 lbs. So that outside tire is now having 1173 lbs of vertical pressure, but that's just the vertical load, and that doesn't account for the effect of the horizontal loading of the suspension through the twisting effect of the spindle as the tire tries to fold under the car. Here my math gets fuzzy, but I think if you just added the length of the levers to the 1' from the hub to the ground, you're going to get 1.375 x the weight, so really we're talking about 1612 lbs, but I think that is an oversimplification and too generous, because it is the convoluted shape that the forces are acting through that makes the structure weaker than the force would otherwise suggest. I think a large offset wheel would also skew the numbers further. Testing would tell the effects for sure, but for those who don't have the facilities to test, this is an easy modification to do and whatever distortion would be caused by welding is easily adjusted out by me, and certainly by most who would bother with this modification. Quote Link to comment Share on other sites More sharing options...
johnc Posted June 7, 2011 Share Posted June 7, 2011 I dunno... in thirteen years of racing and pulling from .85 to 1.2 lateral Gs at autocrosses and race tracks the front struts on my 1970 240Z never had a fatigue failure and neither Erik nor I had a camber loss issue (based on tire temps) that could remotely be tied to spindle flex. The hub/bearing combo is a different story. Sometimes a mod that looks good on the Internet just adds weight to the car. Quote Link to comment Share on other sites More sharing options...
Leon Posted June 7, 2011 Share Posted June 7, 2011 I dunno... in thirteen years of racing and pulling from .85 to 1.2 lateral Gs at autocrosses and race tracks the front struts on my 1970 240Z never had a fatigue failure and neither Erik nor I had a camber loss issue (based on tire temps) that could remotely be tied to spindle flex. The hub/bearing combo is a different story. Sometimes a mod that looks good on the Internet just adds weight to the car. Agreed. I'm not convinced that strut flex has any noticeable effect on camber. It may give piece of mind if that's what you're after, but in the end it's just unnecessary unsprung weight, IMO. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 8, 2011 Share Posted June 8, 2011 Weight of a .060" thick gusset and the welding wire to glue it in place isn't more than a couple ounces at most. I'm sure the weight of the sectioned part of the strut housing that I removed was greater than the weight of the gusset. Trying to think of an easy way to test flex now, because it would be good to have numbers to work with instead of intuition. Quote Link to comment Share on other sites More sharing options...
johnc Posted June 8, 2011 Share Posted June 8, 2011 Weight of a .060" thick gusset and the welding wire to glue it in place isn't more than a couple ounces at most. I'm sure the weight of the sectioned part of the strut housing that I removed was greater than the weight of the gusset. Trying to think of an easy way to test flex now, because it would be good to have numbers to work with instead of intuition. Just need a fixture on top to hold the top of the tube and bolt the bottom of the strut to a plate. Then put a bottle jack on top of a scale under the spindle. I think you'll find that's a pretty stout casting. If you really want to check it you can bolt the steering arm, ball joint, and LCA in place. I'll bet you'll find more flex in those three components then in the spindle casting. Quote Link to comment Share on other sites More sharing options...
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