Something I've been curious about for a while - How does AHC maintain alignment at the various ride heights? With uneven a-arms this seem like it would not be possible. How does the AHC front suspension maintain both toe and camber as it moves through the various heights and does it wear the front tires unevenly?
AHC and Alignment Question
- Thread starter Jetboy
- Start date
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All great questions. Whenever I've had an alignment done, I've intentionally turned the AHC height control OFF and the easy accessibility mode (lower when ignition turned off) off. However, when driving above 100km/h, the AHC lowers a bit more than "N". If an alignment is done an "N", is 100km/h slightly out of alignment (sorry to respond with more questions)?
It doesn’t, and does cause extra wear on front tires especially if you do a lot of highway driving.
- Thread starter
- #4
Well - s***. Thanks. That's kind of what I thought intuitively it must do. But then I assumed Toyota must have sorted it out at least with respect to the toe issue. I guess it's just the nature of the system.
The reason I'm asking is that I've been daydreaming of building an adjustable height setup for my Tundra. Rear air is easy and well sorted. Front is challenging. Only option I see as viable is either a bag over coilover setup or a secondary shock mount kit and then run a fox air shock as a secondary, probably with no shims on the piston so it's really only an air spring. Gets a bit complicated and expensive. I really just want to keep it stock height and ride for 99% of my daily driver duty and be able to lift it 3-4 inches for low speed off road duty when I need to get through something that's a bit too much for the stock setup to handle. AHC is pretty close to my dream setup.
Basically this is what I've been thinking about. What I don't like is that the airbag seals against the shock shaft, so it's prone to o-ring leaks. I want this but no o-rings.
Every suspension has a sweet spot where there is minimal toe steer (alignment change with stroke). Get too far out of that zone, and there's no hope to keep alignment at bay.
That said, AHC high was never meant as a general use driving height, which is why its limited to under 20 mph. At that position, camber becomes positive, toes in, and caster is reduced. With more neutral position lift (aka sensor lift), the change in alignment in AHC high becomes more drastic, reducing its utility to a degree. Especially with the loss of droop travel if that's not addressed (AHC Long Travel)
AHC high in the L4 Range is great as it lifts less with lower center of gravity and keeps better alignment to about 50 mph.
Big tires tricks the system to go faster so all of these speed thresholds increase about 10% with 35s for example.
To your questions, it's best to lift with moderation to keep the suspension in its sweet spot. More lift should be achieved in combination with bigger tires that actually lifts the rear axle / pumpkin for real clearance. Done this way, alignment works out great and I have just about perfect wear across my tires. It's important to understand offset plays into this too and that can exacerbate tire/shoulder wear.
For a sensor lifted LX, I would recommend a bit more negative camber, almost neutral toe, moderate caster. LXs with big tires may want caster on the lower end to keep clearance against the body mount. These alignment settings will help make alignments in AHC high better.
That said, AHC high was never meant as a general use driving height, which is why its limited to under 20 mph. At that position, camber becomes positive, toes in, and caster is reduced. With more neutral position lift (aka sensor lift), the change in alignment in AHC high becomes more drastic, reducing its utility to a degree. Especially with the loss of droop travel if that's not addressed (AHC Long Travel)
AHC high in the L4 Range is great as it lifts less with lower center of gravity and keeps better alignment to about 50 mph.
Big tires tricks the system to go faster so all of these speed thresholds increase about 10% with 35s for example.
To your questions, it's best to lift with moderation to keep the suspension in its sweet spot. More lift should be achieved in combination with bigger tires that actually lifts the rear axle / pumpkin for real clearance. Done this way, alignment works out great and I have just about perfect wear across my tires. It's important to understand offset plays into this too and that can exacerbate tire/shoulder wear.
For a sensor lifted LX, I would recommend a bit more negative camber, almost neutral toe, moderate caster. LXs with big tires may want caster on the lower end to keep clearance against the body mount. These alignment settings will help make alignments in AHC high better.
- Thread starter
- #8
What I want is something pretty specific. I've done the full air bag suspension before and wasn't in love with it. What I'm thinking is these goals:
1. 2.0 or 2.5 monotube shocks with progressive valving (even better with internal bypass)
2. Equal or softer spring rate at high height, firmer or similar spring rate at lower height.
3. Low height equal to stock ride height
4. Tall height somewhere around +3"
Air springs like many use to replace the coils fail #2 and #3, which are really the same thing. Air springs along are highly progressive in compression and at higher ride height they are significantly firmer. That's the opposite of what I want for offroad use when I'm at higher height. The beauty of AHC (and possibly the only ride height adjustable system I know of) is the ability to increase height independent of spring rate and it can vary spring rate and shock damping at any height. There's nothing I know if that does that. With air suspension it needs a negative air spring along with the positive air spring to get a proper spring rate through the range of travel. Like a bicycle shock.
The air over coil retains the coil spring linear spring rate at all heights. And ideally for me the air spring would be fully deflated and sitting on the internal bumps when at low height. Then at fully height it would get softer slightly or the same. And a side benefit is that if the air system fails - all you end up with is sitting at stock height with full load capacity. Not great, but not leaving you stranded.
Shocks would be just normal valving. None of the air spring makers would make them for a 2.5" shock body. I asked all of them that I could find. They all first didn't think I knew what size shocks I had, then said that they don't do that size when I confirmed that they were that size. So it'll have to be a 2.0 most likely. I'm okay with that. Just looking for the right air spring to work with the factory coilovers. I think it could be done. And ideally it could be pretty cheap too. A pancake air spring on top of the factory coil spring is all it really needs.
I'd LOVE to see Toyota put AHC in a Tundra. I'm a bit surprised they didn't use it in the Capstone. Would be a popular option I think.
- Thread starter
- #9
My goal is to keep my normal use ride height exactly at stock height or very close. IMO that's the sweet spot where it should ride best on the highway. I was just curious if there was some magic in the AHC that kept alignment geometry because it drops 20mm at highway speeds. For my use - I would limit the high ride height to only offroad use at lower speeds. Just enough to get over trail obstacles and water crossings. Then probably back to stock height.