35's and AHC ... too bouncy now?

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lx4dp

Joined
Sep 6, 2023
Threads
9
Messages
73
Location
CALIFORNIA
Any members running AHC with 35" AT/MT tires noticing a significantly stiffer ride?

My rig went from a svelte, road-gobbling luxury liner to a choppy SCUD missile, crashing and bucking over every ripple in the pavement. More plainly: ride quality is about 100% worse than before. If the old system was on a scale of 1 to 10, comfort was 1, normal was 2.5, Sport+ was 4, and now, the new scale would be, comfort 7, normal 8, sport+ 9. Its harsh everywhere. Lil bumps echo thru the cabin, large bumps crash, woops seem to max this thing out (I now "pucker" when I see highway transitions coming towards me).

Prior to the recent mods, the sweet spot was Normal mode for daily driving. Sport+ was slightly jittery except on smooth pavement, and Comfort worked well for rough roads. Now, however, all modes feel overly firm.

Recent changes include:
  • Falken Wildpeak AT4 – 35" x 13"
  • 18" Method wheels
  • Body lift
  • Adjustable UCA
  • Thicker sway bars (currently planning to revert to OEM to test)
  • Perry Parts bump stops for 35's

I’ve lowered tire pressure to 32 psi front / 34 psi rear with only a negligible difference compared to 36 psi all around.

I’m considering lowering the AHC height (reversing the sensor lift) by ~0.5–1.0" to see if that helps.

I wasn’t expecting OEM-level plushness with 35s, but I also didn’t expect the truck to feel like TNT detonating under every road imperfection. I don't want to completely lose all civilized manners in my daily.

Has anyone had success improving ride quality with:
  • perch spacers
  • AHC sensor adjustments
  • different tire brands
  • something else?
  • Could the bump stops be affecting me more than I think
Curious what others have experienced. Thoughts on how to start tweaking. Stellar Built is doing some fender work next week so curious what others are thinking here so I can give some feedback and have some alternatives to restoring some ride back.
 
I've written Falken's help / support team. Here's that email. Trying to get the range they "recommend" without getting some boiler-plate-see-manufacturer-placard-in-the-door type response.

"
Hi Falken team,

I'm running Wildpeak AT4W – 325/65R18 (Load Range D) on a Lexus LX570 (~6,250 lb curb weight). Current pressure is 34 PSI cold.

After moving to these 35" tires, ride quality became significantly firmer than the previous setup. Before I consider changing tire models, I’d like to experiment with inflation pressure tuning to see whether ride comfort can be improved.

I understand the fundamentals of load vs. inflation pressure and that the sidewall maximum pressure reflects the pressure required to carry the tire’s maximum rated load, not a recommended operating pressure. I also understand that pressure adjustments must account for vehicle load, speed, and heat buildup.

For normal highway driving (45–90 mph) on a vehicle in the 6,200–6,800 lb range, could you share Falken’s recommended safe operating pressure range for this specific tire? I'm primarily trying to determine the practical lower bound that still maintains safe highway operation (ie. can I get down to 30 or 28 PSI for daily tuning while I'm travelling on the highway without cargo). I’ll obviously increase pressure when carrying cargo or towing. I am VERY experienced off-roading / towing driver; just looking for Falken's guidance.

Very much I love the look and performance of these tires so far. I just don't love that every single imperfection in the roadway RIPPLES through my cabin. I've let these tires "break in" so I'm pretty sure I'm at the point of tuning PSI and I'd like guidance on the range from Falken. Thank you gents!

Thanks very much."
 
You changed a bunch of stuff at once. I would highly recommend reverting back to stock swaybars asap. Your plan of reversing sensor lift is also a good troubleshooting step.
 
lx4dp said:
  • Thicker sway bars (currently planning to revert to OEM to test)
  • Perry Parts bump stops for 35's


I’m considering lowering the AHC height (reversing the sensor lift) by ~0.5–1.0" to see if that helps.
Click to expand...
You might find yourself bottoming out on those extended bump stops even on normal roads if you're not fairly highly lifted on AHC (especially above 65 mph when the suspension drops).
 
I feel like the AHC is irrelevant in the Bump Stop equation. I feel like the front lower arms are bumping off of the frame and body height wont matter much. I suppose geometry is a potential issue here with the UCA's changing angle but this wouldn't have much effect at the LCA's, IMHO. In the rear, I'll need to look but I think the bumps are coming off a frame extension and the axle so again not much body height or AHC will change here.
 
Anyone think I should be worried running tires at 30-31 psi all the way around?
 
Stiff sway bars have a big adverse effect on comfort of any vehicle. Get rid of those and test again. If you like the comfort (due to those tires you should not expect back to stock comfy) but you get much body role, eliminate sensor lift and test again. It is easy to see if the stops are causing problems - in normal driving there should be no contact.
BTW if you still have the old wheels, just put those on first and see how much the new tires are the problem - kind of set or reset expectations.

AHC - your tuck is almost new for a 200 but make sure all is Ok.
 
lx4dp said:
I feel like the AHC is irrelevant in the Bump Stop equation. I feel like the front lower arms are bumping off of the frame and body height wont matter much. I suppose geometry is a potential issue here with the UCA's changing angle but this wouldn't have much effect at the LCA's, IMHO. In the rear, I'll need to look but I think the bumps are coming off a frame extension and the axle so again not much body height or AHC will change here.
Click to expand...
FWIW, I was hitting my extended bump stops in the rear before I went from moderate to maximum AHC lift. This was noticeable when going over expansion joints on the interstate. From your initial description, it sounds like there's hardly any suspension actually at work.

More to Bloc's point, getting as many things back to stock as possible should help you rule out causes.

It doesn't look like you're running wheel spacers but what is the offset of your wheels? Smarter people may have something to say about this.

Lastly, I wonder how much of this comes down to having 75 lb tires at each corner plus a 30-ish lb wheel (stock was around 70-80 lbs total vs 105+ for you).
 
I'll go up in body lift (AHC sensor lift), I'll revert sways, I'll lower tire pressure to 30psi. Go from there. Anyone think 30 is too low for our 3 ton monsters, let me know.
 
lx4dp said:
Anyone think I should be worried running tires at 30-31 psi all the way around?
Click to expand...
lx4dp said:
I'll go up in body lift (AHC sensor lift), I'll revert sways, I'll lower tire pressure to 30psi. Go from there. Anyone think 30 is too low for our 3 ton monsters, let me know.
Click to expand...

These are your tires:
1773359495499.webp


Because they are an LT-Metric tire, the MINIMUM safe cold tire pressure for these tires for on road use is 35psi. That is also the RCTIP (Recommended Cold Tire Inflation Pressure) for these tires on your LX570.

If you run these tires at speed, on road, below 35psi you run the risk of overheating the tires and (at best) shortening tire life, and (at worst) experiencing tire failure.

Additionally, you mention you are using Method wheels - are they at least 9" wide as approved by Falken for use with these tires?

HTH
 
Gaijin, thanks for response.

Is this your experienced opinion or are you getting the statement of “35 min at cold temps”from somewhere? Having replied to my inquiry already, Falken doesn’t have a minimum psi (or aren’t willing to share it with me).

Just trying to sort out what’s experienced opinion vs common sense vs technical data. Thanks.
 
Do you still have stock wheels and tires to throw on for a quick drive to see if anything changes?

That’d be my first step

But, I’m guessing it’s not tire related
 
When you say you are running Perry bumps for 35s, what do you mean?

Front
Product Height
AHC Equipped: 41 mm
OEM Up-Travel: 45.3 mm
-1/4" Up-Travel: 52 mm

Rear
Product Height
AHC Equipped: 50 mm
Regular Length Shocks: 75 mm
Extended Travel Shocks: 105 mm

If you are using the tallest bumps, you might be riding on them, which will make your ride quality go to crap.

Did you do the install and check for tire clearance or did a shop?
I'm wondering if 13" wide tires and unknown offset wheels required limiting suspension travel to keep the tires out of the fenders.

Do you have any pictures?
 
lx4dp said:
Gaijin, thanks for response.

Is this your experienced opinion or are you getting the statement of “35 min at cold temps”from somewhere? Having replied to my inquiry already, Falken doesn’t have a minimum psi (or aren’t willing to share it with me).

Just trying to sort out what’s experienced opinion vs common sense vs technical data. Thanks.
Click to expand...

Technical data:
Screenshot_13-3-2026_74457_www.toyotires.com.webp


The Load/Inflation tables published by TRA (Tire & Rim Association) show the allowable range of tire pressures. LT-Metric tires are limited at the low end at 35psi.

HTH
 
I think pretty much all the suggestions have been covered here. You changed too many things at once to be able to narrow down the culprit.

1) put the stock wheels and tires back on. That should confirm or rule out the tires. Just my guess, probably not the tires, as I have 35x12.5 load D tires and it rides pretty good.

2) Why did you get aftermarket swaybars? With AHC, they should not be needed. If you need more level cornering (i.e. canyon roads), put it in "sport." Thicker swaybars generally do not affect ride quality when you hit a road imperfection that impacts both sides of the vehicle at the same time (like a perpendicular expansion joint) but can add quite a lot of jitteryness and head toss if you hit a road imperfection that only impacts one side (like a pot hole)

3) Perry Parts extended bump stops should only be used if you have increased suspension travel via spacers and rear lower shock relocation. Otherwise, the stock bump stops (or PP standard bump stops) are correct. If you do not have "AHC Long Travel" you should not be using the extended bump stops. You will be riding the bump stop instead of the suspension. :edit: @turbo8 beat me to it.

You're not going to kill yourself trying lower psi as an experiment, but if you have to lower a LT tire to 28psi just for ride comfort, something is else is wrong. If you do much experimenting with this, get an infrared heat gun and check tire temps after short/medium drives.

:edit: LETS SEE SOME PICS!
 
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For reference, I run 37s (KM3s and KO2s) with no AHC lift, so not apples to apples, but my ride is silky smooth (except at 55 because my KO2s seem to balance like crap). The folks above have hit it, but an easy test would be swap to the original swaybar and remove the bump stops, then go for a drive. You aren't going to bottom anything out around town so I wouldn't bother to put the original bump stops back on, you're just trying to gauge ride difference. If you're getting some fender massaging done in the future, I would also drop that AHC lift to improve comfort, but that's my personal soap box opinion.
 
@lx4dp where in California ya located?
 
Just to cross check

- it's not the tires. I've run 35s and 37s for years. LT-E and RTs Sometimes at 42 to 45 PSI because I'm towing. Wheel tire packages into 100 lbs. A healthy suspension will soak this all up.

- Focus on the suspension. Definitely can be bump stops.

- I'd key in on ahc sensor lift if you haven't augmented and pressures are super high. Along with a lot of installed weight. This essentially has the globes bottoming out, especially if compounded by any globe wear.
 
Another vote for it probably being the bump stops. I've had 35" Nitto Ridge Grapplers Load F and even that with AHC was buttah.

Also pretty much zero reason to need thicker sway bars with AHC. Ditch those 1000%. Even with AHC deleted, the stock AHC bars are still pretty adequate with a traditional shock/spring combo lift and big tires. I went with a thicker rear bar because I drive a bit too fast up and down the mountains here, but it's definitely acceptable without upgrading.
 
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