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Discussion Starter #1 (Edited)
Has anyone tried the Spitfire variable rate steering arms? It looks like they allow more camber, and have bump steer adjustment as well as the ability to adjust steering rate up to 21% faster. I did try searching and didn't run across any threads where these (or other variable rate arms) were being discussed. I didn't even know such a thing existed until today, and would be interested in hearing from anyone who has run these, and the pros and cons.

This is a photo I found of them:
1268696
 

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I almost got them, but chickened out ($$$). The adjustability is really neat, and the bearing design is very good, email them and ask any questions.

Fwiw it's an English company with not a whole lot of presence stateside. GRB does stock them though.
Also, I'm running there toe link kit...
 

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Discussion Starter #3
Yeah they seem expensive, but if one wants to experiment with faster ratios they have a range of adjustments, and cost less than a quick rack, so suddenly not so expensive sounding. They should also be a lot less trouble to install. Since I haven't seen an adjustable arm before I am wondering if there's a downside I'm not seeing.
 

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Yeah they seem expensive, but if one wants to experiment with faster ratios they have a range of adjustments, and cost less than a quick rack, so suddenly not so expensive sounding. They should also be a lot less trouble to install. Since I haven't seen an adjustable arm before I am wondering if there's a downside I'm not seeing.
The downsides I see aren't deal breakers per se, but are:

1) I could see the steering link bolt stripping out that notched groove if torque is not maintained on the bolt. I'd use a combo of a nordloc washer and blue loctite. No idea what comes with the kit though.
2) Faster steering will proportionally increase steering effort, whether through this arm or a new rack. So 20% faster is also 20% heavier.
2b) It will also increase the max steering angle, so you may rub at full lock. The easy cure to that is to not go full lock. That's typically only when driving slowly anyway, so again not a terrible thing.
3) Your ackerman angle will change. I am not qualified to guess what this will do to tire wear and handling, but I figure I can give you the keyword to search and see what you can find.
4) Changing the bolt hole when trying to get a different speed will also change your toe angle, so it isn't like it is something where you can frequently move it around. That's where I find "variable rate" to be very misleading. It isn't variable rate so much as adjustable rate. Variable rate steering can be done on the fly, which this can't. Semantics, but important to understand.
 

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Discussion Starter #5
All good points. Yeah I hope that the notches are secure enough! That in particular would be good to hear about from someone with experience with these. I did realize adjusting rate would require setting toe again, but that beats replacing the steering rack if one doesn't like it or wants more or less. I read at the manufacturer's website that they have Delrin rings that could be used, somehow, on the steering rack to limit wheel travel so the wheels won't rub near lock.

I have no idea what ackerman angle is, so I'm going to find out. Does that also change with a quick rack, or is it a negative side effect of this particular strategy?
 

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Discussion Starter #6
OK I guess I knew about Ackerman angle without knowing the name. Would that actually change with this setup? I'm trying to visualize what the arms are doing verse what a quick ratio rack is doing.
 

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All good points. Yeah I hope that the notches are secure enough! That in particular would be good to hear about from someone with experience with these. I did realize adjusting rate would require setting toe again, but that beats replacing the steering rack if one doesn't like it or wants more or less. I read at the manufacturer's website that they have Delrin rings that could be used, somehow, on the steering rack to limit wheel travel so the wheels won't rub near lock.

I have no idea what ackerman angle is, so I'm going to find out. Does that also change with a quick rack, or is it a negative side effect of this particular strategy?
It is unique to this part unless you change the mounting location of the steering rack. If you look from the top view, you make a parallelagram from the steering rod, arm/hub, control arm, and frame. If you change the length of any one of those four arms and only one of those four, your angles all change. If you were to use spacers to lift the rack forward by the same distance you change by moving the bolt hole, you can keep all your angles the same. Again, I don't know either how much this part will change or if it is a positive or negative change, just that it is a change.

A common misconception about bolts is that they carry load. When designed correctly, the friction between the two clamped parts (inner bearing race and steering arm in this case) is really what carries the load, so those notches don't have to be strong IF the bolt is tight. If the bolt loosens though, the load is then supported by the notches, and I'd bet it could wallow them out. So proper torque means this won't be a problem, it just comes down to how strong you want your second parachute should the first one fail.
 

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@sfelise

"The problem with huge amounts of Ackerman is the inside front gets to such a high slip angle that it then gives up. For slow corners the car turns-in fabulous, but then in fast corners it washes out and you get understeer,” Thilenius cautioned. Clearly it is possible to overdose on many of the racing geometry designs, taking them too far or out of context can cause more harm than good.

“On a race track environment like a street circuit such as Long Beach — a track with slow 90-degree corners — I would probably want to run as much Ackerman as I could physically put into a vehicle because I want it to turn in and I don’t have to worry about the mid-corner understeer. If I were to go to a fast open track like Willow Springs, I would run very little Ackerman. The last thing you’d want is push in mid-corner,” Thilenius said."


I think that the faster notch will give you more Ackerman, so it sounds like having that tuning option might be nice to have for a track car. All this is without firsthand experience of that arm myself though, so take it more as a conversation starter than ender. I am wanting to shop for some kind of arm this winter if I get to a suspension refresh, so I have been curious about this anyways. @eldonz do you have any input?
 

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THis part reminds me of the 'variable camber' lower wishbones on my S2 Seven. They were of course also variable toe and variable everything

I finally made blocks that fixed the lower trunnion in one place and made the car handle properly for the first time, probably ever. Prior to that it was truly frightening to drive

One does not want adjustable, well, anything. One wants to put it in a place and have it stay there.

This part does not seem that likely to do that
 

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@cyow5 In circle track, we would take the left front control arm and change the position of the control arm point to increase the ratio the tire would turn with respect to the right front. What we were trying to do was get the inside tire to track a shorter radius compared to the outside tire. Normally, this is a function of ackerman but for most cars this is fixed and not adjustable. This is what the manufacturer starts referring to as asymmetric setup. I haven't quite wrapped my head around having one control arm at a different length than the other. This would bias the car for turning in on direction over the other. So, if a track had a lot more lefts than rights, I could see this making a difference. For street use, I would not do this. The correct approach to make the inside tire track shorter than the outside is ackerman. As far as the bolt slots, I would not to be concerned with them getting strip out. I have used these type of slots in suspensions and never had one strip itself out.

Later,
Eldon
 

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Discussion Starter #11
So in the the few articles I have now read about ackerman, it seems intertwined with dynamic toe, bump steer, slip angles, and tire loading and I am pretty sure I have no idea of what to expect from making changes to the steering rate using these arms. If the ackerman is substantially changed when changing the steering rate with these it almost feels like the actual steering rate change might be the less important adjustment than the ackerman change. Then just add in that I'm equally unsure about setting the adjustable bump steer with these arms and they start looking like trouble!
 

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Interesting ackerman steering was used on my 30' catamaran as well while not on the 27' model. I had assumed it was to keep the blades from stalling in a tight turn with the wider beam.
 

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@sfelise I was told by a Lotus chassis dynamics engineer that if our cars had better bump steer that we would not need as much negative camber. Setting bump is something that isn't difficult but is time consuming. The neat thing is that you can actually make bump work for you to help create some dynamic toe out under suspension compression to help low speed turn in. This can help create the same effect that ackerman is trying to create.
Later,
Eldon
 

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Discussion Starter #14
@eldonz that makes sense, but I have no practical experience with these adjustments. I'm curious about how to set the bump steer to allow less negative camber. Especially if it's something that can be adjusted without a race team LOL. I was reading about using ackerman in conjunction with static toe. In the simplest terms it seems there is a trade off between low speed and high speed cornering grip using ackerman, so race teams might adjust it depending on track. Some of the articles referenced things like slip angle friction plots for tires, and logging suspension travel and steering angle, in general it looked like something that would be hard to adjust effectively without all this data.
 

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Discussion Starter #15
@eldonz When you mentioned better bump steer, did you mean no bump steer or a tiny bit of bump out?
 

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@sfelise For most cars you would want this to be as close to zero as possible. For racing purposes, you would adjust it to get the benefit desired. I know that was a vague answer but it all depends on your end goal. You would think that I want toe out when the front is compressing but do you want both sides or just one? Too much toe out can cause a "Dead Spot" in the steering wheel. By this I mean the car does not react when turning the wheel until you put enough in to it. This is caused because both wheels are pointing out and you have to overcome this before the car reacts. Creating bump steer is a crutch to fix a problem that cannot be fixed. The best approach is to get the ackerman correct but this is set by the manufacturer and is fairly involved if you want to change it.
Later,
Eldon
 

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Also interested to hear if anyone is running this. In regards to the slotted hole, the website also talks about a street version with only a few discrete mounting holes rather than the slots. That is the option I am looking at
 

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Discussion Starter #18
Yeah I'm also interested in the discrete holes setup. I contacted Spitfire via e-mail. They responded right away and were very helpful. They said that there is no change to the Ackerman curves when using them symmetrically (adjusting to the same hole on each arm), as "The arm holes focus on a common point, same as OE". I'll admit I am trying to visualize this, and I keep thinking that a shorter arm will increase inside wheel rotation in the range we turn the wheels verses a longer arm, but they say otherwise.
 

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Yeah I'm also interested in the discrete holes setup. I contacted Spitfire via e-mail. They responded right away and were very helpful. They said that there is no change to the Ackerman curves when using them symmetrically (adjusting to the same hole on each arm), as "The arm holes focus on a common point, same as OE". I'll admit I am trying to visualize this, and I keep thinking that a shorter arm will increase inside wheel rotation in the range we turn the wheels verses a longer arm, but they say otherwise.
As long as left and right increase or decrease at the same rate, I can see how ackerman will be maintained (or at least minimally affected). Kinda like how 1/2 times 2 is 1.
 
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