[IS300 2001]

Hello everybody. I've gradually gotten pretty fed up with how terrible the roads are where I live and decided I can't live with a bumpy ride anymore.

I've had the car lowered on Eibach springs with Koni yellows at the lower perch for a little over 2 years now. Initially, I never thought I would have any issues (comfort-wise) being on lowering springs and stiffer shocks, but the roads are awful. Huge potholes hide in the dark, poorly paved railway transitions are numerous, and some parking entrances are at such crazy angles with the road that even newer Tahoes and similar scrape. I've even seen manholes left without cover in the middle of the street without any warning. Surprisingly, these problems aren't what annoys me most though.

It's the constant small bumps everywhere have made me not enjoy driving the car as much. It makes me feel like I'm destroying it really. Even painted lines at intersections have been done so poorly that crossing over them jolts the car. I was thinking about returning my car to stock height (or at least stock shocks with Eibach springs) but the height isn't my issue. I never scrape the chassis, and rarely the plastic underhang at this point.

I've now been considering going back to 17s as opposed to the 18s I'm running now, hoping that would make a good enough difference to where I could justify keeping my current suspension. I'm not running rubber band tires by any means though, as you can see:

Tire Size/ Diameter (Inches)/ Sidewall (Inches)

215/45/17 (Stock) 24.62 3.81

225/40/18 (Current Front) 25.01 3.50
235/40/18 (Current Rear) 25.40 3.70

245/40/17 (Considering) 24.72 3.86

235/40/17 (Alternative) 24.40 3.70

I'm thinking my current tires aren't really that much a comfort hinderance, so would the 245/40/17s make that much of a difference? I put the 235/40/17 as an alternative because I'm not sure if I could clear the fenders even with more fender pulling.

Also, I've been running the tires around 32 psi (cold), so potentially 245s on 17s with 29 psi would show a reasonable comfort improvement while keeping the car lowered? I'm just trying to brainstorm here...

 

[Hodgdon Extreme]

I think all those ideas are reasonable. The trouble is quantifying how much "comfort" you'd get from each idea.

I think simply swapping to 17s with a meatier sidewall will make a decent improvement, but the bigger difference would be softer dampers... Unfortunately, softer dampers might not appropriately damp stiffer springs - resulting in a bouncy ride.

Another thought are your anti-roll bars. If they are aftermarket, you could realize a nice improvement by swapping back to stock. Keep in mind ARBs have zero effect when both wheels on the axle are simultaneously being jounced - but have a big impact when only one wheel is being jounced!

 

[persocon]

when you switch back to 17s, go with a softer sidewall tire, not something like RE71R
you can even go 16s with soft sidewall, you can even use the rs200 wheels, they come with 16s

 

[TobiasSing]

Those are all the ideas I had. Different tires also have different comforts though, so even that depends. But my only other idea is a set of coilovers with even softer springs. But you'd need even more suspension travel, which is decreased by lowering. Have you thought that maybe something has gotten worse over time as you've had it lowered? Maybe the bushings are going bad?

 

[IS300 2001]

Unfortunately, softer dampers might not appropriately damp stiffer springs - resulting in a bouncy ride.

Another thought are your anti-roll bars. If they are aftermarket, you could realize a nice improvement by swapping back to stock.

I never thought about a softer damper resulting in a bouncy ride when paired with lowering springs - it makes sense though. I read earlier threads of people doing this with the main concern being premature shock wear due to the springs imposing a shorter shock expansion, so this is really a last resort kinda thing.

I did consider switching my front sway bar back to stock and keeping the rear adjustable one in place. I believe that one is more important anyways. I'm glad I ended up going with Eibach as opposed to Hotchkis.

when you switch back to 17s, go with a softer sidewall tire, not something like RE71R
you can even go 16s with soft sidewall, you can even use the rs200 wheels, they come with 16s

This I overlooked, and will certainly take into account when looking for tires. I know 16s would be more comfortable, I just don't know if I want to go that small.. Beggars can't be choosers though.

But my only other idea is a set of coilovers with even softer springs. But you'd need even more suspension travel, which is decreased by lowering. Have you thought that maybe something has gotten worse over time as you've had it lowered? Maybe the bushings are going bad?

I did end up picking up a set of like-new Godspeed coilovers from a junkyard recently and have read good things about them for daily driving. I don't think they're performance oriented really and so there's a chance they could be more comfortable than my current setup. For around $150 I couldn't pass them up.

And all of the front suspension is new. It was pretty old when I got the car and after lowering I ended up replacing it all piece by piece. The front bushings were also replaced, but with polyurethane. To be fair though, they ended up making the ride more comfortable as I think the polyurethane wasn't as rigid as others.

 

[Thatblueis]

Haha polyurethane bushings feel a lot better then no bushing. I have Godspeed coil overs and eibach sway bars on some 225/40/zr18. It's pretty comfy still feels nice and tight I still do feel all the little bumps though. I think if you left the rebound a little loose you'd probably be good. It rides pretty oem feeling. All depends on how you set it up though.

 

[Gosurfun]

2000-2005 IS200/300.
Look for some 16 wheels and use higher profile tyres to give the same or slighty larger diameter, (plenty of online tyre diameter calculators online) for rough roads, with new KYB shocks, it will be the best fix. 16 wheels come on the IS200/300 and the later IS250, Camry ones fit too, look for 45mm offset and 60.1mm centre bore, not many people want them and as a result they are cheap and also the tyres, they fit over the stock brakes as well. Higher sidewalls will go over bumps and potholes a lot easier than low profile tyres, I've taken my 18's off as they make me drive slower to avoid the jarring with the loss of traction, especially while cornering. A hard suspension including the tyres is not one that is good at keeping contact with the road surface. There is a hand sized patch of rubber on each tyre connecting the car to the road, if its not connected well, your not cornering, braking or accelerating to the tyres capacity. A tyre with a larger/higher profile will follow the ground faster than a low profile one, for a low profile tyre the whole wheel and suspension have to move much more to compensate for the reduced give and take of the tyre. Go too wide and aquaplaning or loose gravel and sand will be waiting to get you as well, might look good, but its better to spend the money on better tyres.

The standard KYB IS300 shocks are jap turbo spec shocks already, so going any stiffer is just dumb for rough roads and even normal roads. If you search other posts in this forum, there is a lot of comments on how much better aftermarket replacements are. Unfortunately when the aftermarket shocks have done as many km/miles as the original KYB's, it is extremely unlikely they will have lasted as well. Stay away from Bilsteins and if you want to use them, don't try to lower them, doesn't work. Don't change the stock front sway bar, or if you do don't go any stiffer than an Eibach one. Using a stiffer front sway bar overloads the front outside wheel and makes the understeer the IS300 suffers from even worse. It might feel flatter going around a corner but it goes around slow, slower than a Corolla will with the same tyres fitted.

Replace any worn bushings, Lexus 16 inch ones fit over the stock brakes and new KYB shocks with stock springs, If that doesn't do it for you on the rough roads, buy an RX350 for a soft ride.
.
The stock IS300 suspension, everything inc sway bars and brakes, (the brake pads are the same as the TT Supa pads) have the same part numbers as the later Japanese Chaser turbo JZ powered cars. These cars already have a good quality turbo grade suspension, brakes and wheel package from new. The stock suspension only just starts to get out of shape when getting near the limit, a perfect match, any softer and its too soft, any stiffer and it will be slower as soon as the road conditions aren't ideal.