You mean like unequal tire scrub radii and stuff ?

Yeah! The fun stuff. When I study the geometry I don't see a massive issue with unequal link lengths. Obviously there is an issue, but it seems to me that it would be amplified by the amount of ackerman you have setup. So, if you didn't have any ackerman and the links stayed straight the whole length of travel it wouldn't be an issue. Obviously it will never travel straight the entire throw, but you get what I'm saying.

Just thought a discussion on the topic would be interesting. Perhaps not.

lol

Even if the links start straight (vertically and horizontally), as the spindles travel, the links progressively move away from their straight nature horizontally, and the servo horn rotation moves the links away from straight vertically. If the links are different lengths, then the rates of change are not equal, thus the ackermann (vert&horz) and bumper (vert) are both different from left to right - which is not ideal.

My take on this...

As the servo-saver moves, the more it travels through its arc so the less lateral movement you get from the steering arms. As the arms get shorter, the less lock you get for a given travel of the servo saver.

Therefore, the issue here is not one of Ackerman, it is one of unequal steering from left to right. IF this is corrected by altering the end points, the overall effect is that you have less lock overall and therefore less steering overall.

Foam tyres do not have a single contact patch. Despite the scrub of the offset axle and inboard kingpin, foam tyres work because each part of the tyre is able to generate its own slip angle. With that in mind, the amount of lock you can achieve will dictate the amount of steering you can achieve.

One short link that limits the lock you can get is more of a problem than any effect on the Ackerman angles you set. Ackeman is actually set by the steering blocks, not the steering links. What is affected is the amount of lock you get from each wheel which looks like Ackerman, but it is actually just differences in among of steering lock.

Too much play is made of the Ackerman angles on cars with foam tyres. Since the tyre does not behave like a rubber tyre, it is the amount of lock applied to the inner and outer wheels that translates into different steering feel, not the Ackerman angle. In reality, a 12th car's cornering behaviour is more affected by the instantaneous steering centre than by the Ackerman or differences in lock from side to side.

The reason a steering servo must be in the middle is to maximise the lock you can get from each wheel. The total amount you can achieve is dictated by the shortest link, so having each link equal increases total lock. Yes, I know you dial it back on the rate, but try driving a 12th car where the servo is offset 5mm one way. Once the lock circles are balanced on the Tx, the overall lock will be reduced a lot!

Congratulations to the guy who can tell the difference of a 0.005" off-centre position of his servo. Firstly you couldn't measure that accurately enough and secondly there is so much play in the whole front suspension that it could just as easily be a fraction more slop on one side of the whole front suspension, or one ball joint with a fraction more slop than the other. 0.005" is about the thickness of a human hair - forgive my scepticism...

So, I trued my first set of tires this week and it seemed to go well. However, when I mount them on the axle, the rear tires seem to be a little lopsided. Only thing I can think of is that I didn't have them properly centered on the truing station, even though I double checked that part. So, two questions

1. Will a little off-center wiggle in the rear tires (trued at 43mm) kill the performance of my little pan car? Enough to throw them away and start over?

2. What's the trick to getting the wheels aligned on the Hudy arbor? I already have the Team Tamale adapters and was using those. The CRC wheels are a very tight fit on the arbor.

Thanks!

@SlowerOne

Nice share mate! I learn a lot from your post above.

On the subject of tires with a little out-of-round wiggle to them, they will typically warp their plastic material a little over the course of a run and run true. If it is making the car jump then you may have more of a problem, but I would run them in a practice and see if they come off true.

When it comes to cutting tires, just be sure to watch the rim, not the foam, and make sure it spins super true before cutting. I don't own a Hudy arbor, but if I can tell that the rim is spinning out-of-round on the truer I adjust it. It takes me a long time to true tires.

That is some fantastic insight man, thanks!

So, other than the affect on streering lock, do you think it has any affect? Okay, you can tune the end travel and get it so the car turns the same radius each direction, but other than that affect what do you think?

Regarding Ackerman though - if you make it extreme you can clearly see the difference between the inner and outer tire's radius, is that not all Ackerman is?

Thank you very much. This really helps me a lot!

Hi guys, looks like out local 1/12 class will be running 17.5 this season. Would you recommend a high torque rotor in this class, or the regular rotors? We run on a 40x80 ft track with CRC carpet.

I'd like to hear others thoughts about the topic of wobbly wheels as well. Especially if the truer has been eliminated as a problem.

From what I've been told, it's the tightening of the screws into the rear wheels that usually causes it.
If the screws aren't evenly tight etc it can 'pinch' the plastic of the rim which can distort it slightly.

Zen Racing developed a rear axle to remove this problem. Dave Spashett helped design it.
The hubs have small 'lugs' that fit through the holes on the wheels and M2.5 screws that attach the wheels;



A review of it;
http://www.thercracer.com/2014/01/re...tive-lock.html

Interesting...

I'll have it with me at the worlds if you want to take a look

That is why I like rim designs that have flat area where the screws go through...you can use a washer on rims like Ulti rims which help to keep from over torquing the screw and distorting the rim.