Adjusting caster to create heavier off-center steering?

[Lindenwood]

I have been searching for any comments on this, but no luck. Lots of discussions on camber, but I have only seen caster ever mentioned in broad comments about the general ability to adjust “camber/caster” with the UCA carriage or differential turnbuckle movement on some aftermarket arms.

Especially considering MPP now has aftermarket compression arm bushings that are deliberately built and advertised to increase caster, has anyone been tinkering with these adjustments?

 

[MasterC17]

Arguably camber is going to have more of an effect on off-center steering feel than caster to be honest. Caster will have some effect, yes, but not greatly I would imagine. I guess the question is what is your ultimate goal? Personally, I leave the steering in the comfort setting on or off the track.

 

[Lindenwood]

Arguably camber is going to have more of an effect on off-center steering feel than caster to be honest. Caster will have some effect, yes, but not greatly I would imagine. I guess the question is what is your ultimate goal? Personally, I leave the steering in the comfort setting on or off the track.

Thanks!

No specific goal necessarily just yet, though generally I do like a crisp on-center valley with progressively higher off-center weight. Just trying to understand what people have done with caster on these vehicles, and why, since there are now a few options to deliberately adjust (or at least change) it.

 

[MasterC17]

I think it hasn't really been discussed much because there isn't a lot of adjustment possible, and because it doesn't really make a difference in the same way that toe and camber do.

So, in basic terms what we want is positive caster to aid in directional stability. You "need" a minimum amount of caster to have the desired effect, but increasing it beyond that amount is not necessarily going to make much of a measurable difference. Specifically what the minimum is for the Model 3 I am not entirely sure, but I have to imagine the stock settings are a bit beyond that. There is also an upper limit where you could end up completely unloading the inner rear tire during a hard corner which would be undesirable. So, the "ideal" setting is somewhere in-between. Finding that ideal setting however would require an excessive amount of testing, and measuring the changes in terms of lap times would result in pretty small changes. Overall, the reason caster is ending up on the bottom of the list is because it has the lowest input to output ratio in terms of changes, and because it is less of a known quantity than toe and camber are.

To summarize, personally I think putting in the maximum amount of positive caster without ending up with tire rub on the wheel liners is basically the end goal. I don't think you would get more than a degree or two before hitting that limit. How much of an effect this will have on steering feel and lap times I don't know yet, but I will try to find out and report back. FWIW, increasing positive caster would likely actually result in lighter steering feel, as it should take less effort to accomplish the same amount of steering angle.

 

[dsgerbc]

Is there someone here who has a decent CAD model of the 3's suspension that they can share (or weigh in on questions)?
Does it even make sense on our suspension to try to trade static camber for more dynamic camber?
I bought a set of Redwood arms to replace my MPP arms and plan on playing with them with the front shock removed to see what one can accomplish. But doing this all in CAD would be much easier.

 

[dsgerbc]

So, I've added some caster, and been driving around for a few days. Couldn't really feel much of change in the steering effort.

 

[TacoSteve]

With the use of the MPP Caster bearing and UP Fuca I am at 7 degrees of caster. It certainly makes the steering heavier, but I use comfort mode on/off track to negate that effect. Like @MasterC17 said, who knows how much a difference it actually makes in my lap times.

 

[tm1v2]

@Lindenwood What have you modified on your car so far? How has each step affected steering weight?

Also, are you seeking manual steering level of weight? I have to say even stock, on "Sport" it was some of the heavier power steering I can recall.

Lighter wheels lightened up the steering as expected (at any given level), but also improved its feel at the same time. Just recently putting on coilovers + pillowballs + spherical FLCA bearings definitely added heft back, and also really tightened up the steering in general, the steering (and suspension) feels much more taught now. I'm guessing you have those mods and more already, since you're posting this kind of thread, but figured I'd mention their effects just in case. I just got the suspension mods on, haven't gotten the car aligned or driven it hard yet, so can't tell you if feedback at the limit improved yet.

Throughout this (since the car was new) I've preferred the Standard middle mode for steering weight. I absolutely miss the wonderful feedback of good manual steering, but I never found any real improvement in steering feedback/feel from setting modern power steering cars to an extra heavy setting. Too light is bad, yes, but there's no extra feedback from the Sport setting that I can tell vs Standard. Comfort is too light for my taste though, it does feel overboosted and makes feedback more difficult to discern. (But that's the point of a Comfort steering setting of course, so it's nice the car offers it for those who prefer that.)

 

[Lindenwood]

Ironically, I don’t have my M3P yet (hopefully will be delivered in the next few weeks). I already have 17lb 18” wheels sitting in the garage, and have a good list of parts (MPP Coilovers, camber arms, LCA bushings) plus other non-suspension goodies on my short purchase list. Brake improvements are a bit further down the list once I get a better feel for what I really need there. I liked the claimed benefits of the compression rod bushings, and was curious if anyone had experimented with their ability to adjust caster.

I had a couple of Turbo MR2s back in the day before getting into motorcycles and then exclusively off-road vehicles. Only recently did I regain my interest in road performance.

However, I like to tinker, and can’t help but push the mechanical envelops of all my machines, so here I am.

@MasterC17, my primary experience with caster is mostly from motorcycles (and before that, hobby-class nitro-powered RC cars). But even digging back to my dated mechanical understanding is that [positive] caster tends to make the steering wheels align with the direction of travel, which requires increasing force to keep the steering wheels angled off-center. Specifically, turning the steering wheels pushes the contact patch out of alignment with the steering axis; positive caster places that contact patch behind the steering axis, so like a dart with the majority of friction behind the center of gravity [steering axis], the wheels will want to align with the direction of travel (which, at any given moment, is straight). Am I crazy here?

 

[Yperformance]

Anybody have problem with sharp shock and loud bang after increasing caster to 6 degrees.

 

[dsgerbc]

Anybody have problem with sharp shock and loud bang after increasing caster to 6 degrees.

How did you increase your caster? UP or RW control arms? Those could be banging on the chassis.

 

[Motion122]

I have been searching for any comments on this, but no luck. Lots of discussions on camber, but I have only seen caster ever mentioned in broad comments about the general ability to adjust “camber/caster” with the UCA carriage or differential turnbuckle movement on some aftermarket arms.

Especially considering MPP now has aftermarket compression arm bushings that are deliberately built and advertised to increase caster, has anyone been tinkering with these adjustments?

Added caster on my ride but for the camber gain on the outside tire. No notice in steering effort that I could feel.

BTW, I have the UP arms so cater can be easily adjusted in small increments.

 

[P3D-R]

Is there someone here who has a decent CAD model of the 3's suspension that they can share (or weigh in on questions)?
Does it even make sense on our suspension to try to trade static camber for more dynamic camber?
I bought a set of Redwood arms to replace my MPP arms and plan on playing with them with the front shock removed to see what one can accomplish. But doing this all in CAD would be much easier.

Just be careful with this type of an arm adjustment. If you add too much positive caster the arm may contact the chassis under compression. By adjusting caster at the compression rod you mitigate issues with chassis clearance and the FUCA. I have had some chassis contact with similar camber/caster adjustable FUCA so just want to make sure you put the arm through its full sweep and turn the steering wheel as well.

 

[P3D-R]

Anybody have problem with sharp shock and loud bang after increasing caster to 6 degrees.

yes this can happen due to the reasons I mentioned above IF the caster is adjusted at the upper arm. It's a fine balancing act between your camber settings and your caster settings. If you don't run enough camber but run a lot of positive caster you run into chassis clearance issues under compression.

 

[P3D-R]

Ironically, I don’t have my M3P yet (hopefully will be delivered in the next few weeks). I already have 17lb 18” wheels sitting in the garage, and have a good list of parts (MPP Coilovers, camber arms, LCA bushings) plus other non-suspension goodies on my short purchase list. Brake improvements are a bit further down the list once I get a better feel for what I really need there. I liked the claimed benefits of the compression rod bushings, and was curious if anyone had experimented with their ability to adjust caster.

I had a couple of Turbo MR2s back in the day before getting into motorcycles and then exclusively off-road vehicles. Only recently did I regain my interest in road performance.

However, I like to tinker, and can’t help but push the mechanical envelops of all my machines, so here I am.

@MasterC17, my primary experience with caster is mostly from motorcycles (and before that, hobby-class nitro-powered RC cars). But even digging back to my dated mechanical understanding is that [positive] caster tends to make the steering wheels align with the direction of travel, which requires increasing force to keep the steering wheels angled off-center. Specifically, turning the steering wheels pushes the contact patch out of alignment with the steering axis; positive caster places that contact patch behind the steering axis, so like a dart with the majority of friction behind the center of gravity [steering axis], the wheels will want to align with the direction of travel (which, at any given moment, is straight). Am I crazy here?

If you adjust the upper carriage to get you nearly symmetrical caster you'll generally end up around +5.8 to +6.2 degrees of caster between 365 to 375mm ride height hub to fender. At least that is what I have found on the hundreds of 3's I've aligned and setup suspension on. I always adjust my upper carriage to get the left and right numbers to line up within a few tenths. Call me anal, I don't mind. I think it's very subjective but for road course +6.5 seems to be nice and for autox they like lots of positive caster so I see guys pushing +7.0 to get that dynamic camber. If you're a drifter than FULL MAX positive until your tire hits your fender well and then it just self clearances. Zipties FTW!!!! lol.

 

[Yperformance]

Thanks so very much for the input. I am using Meghan Racing FUCA. I have got caster up from OEM 4 degrees to 6 degrees each side. You are right the odd pothole ridge in concrete causes the FUCA to impact the mount. Car is on MPP suspension about 1.5 inch lowered.
3 degrees neg camber on front 2.25 on rear.
Am getting some contact on FUCA both OEM and the Meghan. Have stiffened the damper a tough but not helped much. Have reduced negati camber a bit, no chang problem persists. Any further thoughts. Should I rubber pad the top of the control arms say 1/4 inch?

 

[Motion122]

Thanks so very much for the input. I am using Meghan Racing FUCA. I have got caster up from OEM 4 degrees to 6 degrees each side. You are right the odd pothole ridge in concrete causes the FUCA to impact the mount. Car is on MPP suspension about 1.5 inch lowered.
3 degrees neg camber on front 2.25 on rear.
Am getting some contact on FUCA both OEM and the Meghan. Have stiffened the damper a tough but not helped much. Have reduced negati camber a bit, no chang problem persists. Any further thoughts. Should I rubber pad the top of the control arms say 1/4 inch?

That is not a whole lot of caster from the factory at only 4 degrees. I am seeing most cars right around 6 or more.

Low speed rebound damping isn't going to help with your situation. You can compensate the easiest with higher static height, then with higher spring rates. increase gas charge and high speed damping aren't possible with MPP.

 

[dsgerbc]

Thanks so very much for the input. I am using Meghan Racing FUCA. I have got caster up from OEM 4 degrees to 6 degrees each side. You are right the odd pothole ridge in concrete causes the FUCA to impact the mount. Car is on MPP suspension about 1.5 inch lowered.
3 degrees neg camber on front 2.25 on rear.
Am getting some contact on FUCA both OEM and the Meghan. Have stiffened the damper a tough but not helped much. Have reduced negati camber a bit, no chang problem persists. Any further thoughts. Should I rubber pad the top of the control arms say 1/4 inch?

Your best bet is gonna be buying MPP arms.

Your other and pretty sub-optimal option is gonna be trying to limit bump travel. With fixed length MPP/KW shocks *I think* you're gonna need some rigid spacers on the shaft above the bumpstop. Ask MPP.

 

[Motion122]

Your best bet is gonna be buying MPP arms.

Your other and pretty sub-optimal option is gonna be trying to limit bump travel. With fixed length MPP/KW shocks *I think* you're gonna need some rigid spacers on the shaft above the bumpstop. Ask MPP.

Limit compression travel? Not ideal but could work. Find some shock packers of the correct ID and thickness and you are good.

Shock Packers .125” Thick, Fits Shock or Strut Shaft with .625” Diameter, 10 Pk | eBay

This new item is used to limit travel on your shocks.

www.ebay.com

 

[Yperformance]

I am surprised that there were marks on the original OEM arms. I can see the issue with the Meghan arms not being curved. Only makes a difference of about 1/4 if an inch. But I guess every bit counts. Like the idea of the slip in spacers to test. I am working on setting up the MYP for autocross EV-X series You guys are really helpful.