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I'll add some general info here from my professional chassis experience
We make 6061-T6 billet knuckles all day long and then normally cast to A356 or A357 for mass pro.
Every application from trucks to supercars... I can't remember what racing knuckles are made from, but they have a high level of magnesium IIRC.
2000 series material is very popular for brake calipers for weight and stiffness on the highest level of racing like F1. One piece forged mono block machined.
Personally I would certainly make a billet aluminum knuckle, for a high performance application stiffness is more desired then strength. Typically strength is never an issue, its achieving stiffness from moment loads on various axis. You should increase stiffness from the steering ear over stock because the much higher loads of circuit driving than the OE intended (increase tire grip, however your weight is likely reduced from original design). Reduced stiffness will cause a delay and lose steering feel.... so careful lightening up that section in regards to stiffness.
The only thing that largely effects ackerman is moving the pivot point in or out (closer to, or further from, the chassis). Caster/Camber/ride height/toe setting will not have a note worthy effect on ackerman.
Moving this pivot around will also affect bump steer since it will change the length of the tierod. Since we are limited to only moving the outer pivot (the pivot on the rack is fixed unless you build a custom inner tierod), we are limited to how much ackerman can be played with.
Thanks for all the thoughts and feedback from the other engineers, designers, motorsport folk. I'm pretty well set on building with 6061 based on talks with some local guys and from what is stated here. this winter.
I had looked at my numbers for factory ackerman and without really knowing what is really best for the Evo, I thought sticking to factory location would really be best. But thanks for the advice on ensuring we achieve stiffer steering or at least don't let it degrade. I may make my first version with the steering arm a bolt on part so I can play around with different geometries easily.
I know MSI made/makes some billet hubs for the EVO that have a bolt-on steering arm. I honestly thought it looked like a poor design in that it was loading the fasteners in tension and bending. Not good. It did allow height adjustment of the arm though which would probably be better than long *** adjustment shafts. Ideally though, 1-piece hub that use a high misalignment rod end and puts it in double shear while allowing some height adjustment range.
The Sierra Seirra Evo had some 1-piece hub carriers though that looked GREAT for stiffness. They were supposedly MSI units too though, so I'm not sure what was going on there.
Pictures from motoiq.com
Last edited by 03whitegsr; Aug 27, 2015 at 05:05 PM.
I'd be willing to bet 4 lbs or so. Maybe 5. I"m trying to get ideas about the uprights and moving the strut position a little to allow wider wheels without having an insane offset. Basically trying to keep a sane scrub radius with the use of 11+ inch wheels. Probably have to move the strut mounting point inward about an inch. I wanna slap 345's up front
Good freaking lord
I don't want to be snoby/rude but that thing looks terrible from an optimization stand point. However, simplicity, I'm sure it was extremely easy to design and machine
But then again, not spending 15 hours on the CNC to lose 1/2 pound will also greatly reduce costs...
I don't know about that $6,500CAD price, I see it on their website, but Turn-In-Concepts use to sell them for like $1400USD. Complete with Carbon brake shields. That $6500 looks to be a "yeah, we don't really make them any more unless you REALLY REALLY want them." The fact they use to be like ~$1400 tells me an industrious individual could do them for around the same price....not be able to sell them....and decide it's not worth the effort....much like MSI did probably.
Looks like they error'd on the side of bulky. That steering mount location also looks like its taking away Ackerman too. Id have to double check my model at home but the factory location is probably another 1" or so from the rotor.
Looks like they error'd on the side of bulky. That steering mount location also looks like its taking away Ackerman too. Id have to double check my model at home but the factory location is probably another 1" or so from the rotor.
I'll have to agree with your observation. The stock X arm also angles outward which increases ackerman as well.
There could be some side benefits of increasing ackerman.... Reduced ackerman could contribute to being able to carry SLIGHTLY more speed through high speed turns. Response would not be as good and low speed corners may suffer, but there are benefits.
I havn't studied kart geometry but i theorize one of the reasons why they're so responsive, but also very punishing with too much steering angle, is their large amounts of ackerman. If you're full lock on a kart, you scrub a TON of speed. Its better than under steering into a wall when you make mistakes though. Anyone with Kart experience that can share knowledge?
Thanks for all the thoughts and feedback from the other engineers, designers, motorsport folk. I'm pretty well set on building with 6061 based on talks with some local guys and from what is stated here. this winter.
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6061-T6 will be fine. The differences in KIC between the different Al alloys is pretty minimal, and there's not going to be fracture unless there is a crack. Understand the location of your peak cyclic tensile stresses, and monitor for the onset fatigue cracking.
6061-T6 will be fine. The differences in KIC between the different Al alloys is pretty minimal, and there's not going to be fracture unless there is a crack. Understand the location of your peak cyclic tensile stresses, and monitor for the onset fatigue cracking.
I listed the KIC values of the alloys. There is actually very large differences.
EVERY aluminum part has a crack in it. The question is WHERE is that crack and how big is it.
I listed the KIC values of the alloys. There is actually very large differences.
EVERY aluminum part has a crack in it. The question is WHERE is that crack and how big is it.
Yup, I saw it. 20% difference isn't enough to get me excited. I understand the lack of fatigue limit in aluminum alloys, but to say there is a crack in every aluminum component is a bit alarmist IMHO. The issue here is designing the part robustly enough to ensure that the number of cycles needed to induce a crack is at least 10x the number of cycles expected to be seen in the part lifetime.
But I'm not trying to defend 7075. If race car that will not see rain or humid environments, go for 2024, but otherwise, I'd pick 6061 because of its SCC resistance.
Aug 26, 2015, 01:06 PM
