I know, this is contrary to the trend, but I'm dialing in the suspension on the 2002 SC430 I bought a few months ago and I've started wondering whether the way to iron the famous "jitter" out of the suspension is to go to a smaller wheel (offsetting with higher profile tires to wind up at the same overall diameter). I know, not cool. But maybe more fun to drive.

I'm kindof a nerd and am thinking that maybe the reason for the jitter is that Lexus basically took a suspension design from one of their sedans, slapped on larger diameter wheels and tweaked the suspension to get things sortof right. My theory is that a smaller diameter wheel will move some of the mass of the wheel closer to the axel, which means less overall weight and centrifugal force, which in turn will mean less work for shocks/springs to dampen things out.

Part of the reason I'm thinking about this is to also get rid of the bad behavior when hitting bumps. I'm pretty sure I'm gonna be bending a lot of wheels with the current setup and that a little more tire between the rim and the bump might help that too.

Lessons I've learned so far from you guys;

- run-flats are a problem. I agree, I replaced them with regular tires and the ride got a lot better

- check for hub rings!! Can't say this enough. I had the tire guys check three times and it wasn't until I walked out with the manager and actually watched them rotate the tires that we "discovered" that they hadn't put the hub rings in. Without hub rings, you're fighting a no-win deal. That solved the 55 mph vibration problem. So let me add my 2 cents. Check for hub rings!

- Check the suspension. If you've bought an older SC like my '02, it's quite likely that you've received a few gifts from the prior owner (like I did). In my case, bent wheels and beat up front suspension components. Replacing bushings and control arms in the front helped a lot.

So the car rides a lot better than it did but it still jumps around a lot (the jitter) and I've still got a vibration problem on the rear at around 80.

I know, it wouldn't look as cool as the 18 inch rims. But the amount of time I drive the car vastly outweighs the time I, or anybody else, looks at the car. :-)

Anyway, what do you think? Possible good idea? Completely stupid bad idea? Any thoughts appreciated.

 

I think this is a plausible idea. It MIGHT solve the problem, but in my opinion not completely. If you go to a smaller wheel, please don't go any smaller than 17s. Haha. If you really want, I would put the 17" 10 spoke 06 GS300 wheels on the SC. I saw one with them on and it really looked good. If they were 18s I would def. slap them onto mine.

My setup would be 17x7.5 wheels (at the narrowest) and probably put on some 245/45-17. If you wanted to go smaller, I'd say 235/45-17 (the size they used on 98-05 GSs.) Just my two cents.

 

Have you tried a shop with a Hunter RoadForce machine to work on radial runout? Costs much more but in the hands of a knowledgeable tech who knows how to use the machine to its full potential, it might solve your problem.

 

Fellow members, I have to agree about the ride,it sucks.I have often thought the 17inch option would be a good one,just waiting for someone to bite the bullitt and give us some feedback.Lextasy has some nice lexus 17s that are supposed to fit all sc430's,they were originally made for the LS and the ES350.OconnerSTP I hope you try those 17s and tell us how you like them,I just bought 18s and I'll trade ya!,thats how happy I am

 

Thanks lads.

JohnnyCake -- I've had the folks at Discount Tire road-force balance them. I'm not sure if they use a Hunter or some other flavor of balancer but the tech was getting tired of me coming back so he went crazy one day and was pretty sure the tires were balanced.

The tires are kindof the next step in the incremental improvement campaign. I had enough other stuff going wrong that it was hard to justify swapping them out until now. Now I've got a pretty good case that I've got at least one bad tire and I'm pretty sure the Discount Tire guys will swap them even though I'm way beyond the normal 30-day replacement date. I'm not outside of 30 days away from when they got the tires mounted correctly.

But that upcoming swap of tires is what got me started thinking about changing the wheel size too. This would be a convenient time to do that swap.

Playa3uhh, I hate to drive you crazy, but I may even drop down to a 16 inch wheel. That would get me an extra inch of tire between the rim and the road, a 17 only gets me half an inch. Anybody know what sedan suspension ours is based on? I'd be curious to see what the stock tire on that suspension is.

Hmm. I suppose I have to worry about clearing the brakes... Have to cogitate about that...

Thanks for the encouragement -- I'll may be able to swap the rims/tires tomorrow. I'll let you know how things work out.

 

I cured the jitter in my car by adding bigger sways, different coilovers which lowered the car and staggered 20" wheels. I've recently gone back to the stock 18" wheels. One of the benefits of the 18s is a much smoother ride as there is more rubber between the wheel and the road, the 20s were harsh, but the I have noticed the jitter has come back a bit with the 18" wheels.

 

If I had to guess on the suspension, I would think the suspension is based on the GS430. It's a guess, but I think it's the best observation. The 2GS used 16" wheels for some time and ride is pretty good. My 01 GS has a 215/60-16 setup. On the SC I would think that a 235/50-16 would suffice. Again, just a guess. Just my two cents!

 

Aren't you defeating the whole purpose of the SC's designed ride? You will gain comfort and lose much of the sportiness of the ride. I hate to think how your SC will corner when pushed, riding on 16" wheels and balloon tires. This car wasn't made for a sedan-like ride; that's what the GS, ES and LS are for. Of course it's your car and you can do what you like.... just my 2cents.

 

<grin> Yep, IntDiamond that's why I kicked off the thread the way I did. My idea of a really fun time is going through a 35mph marked corner at 50! Woohoo! I'm a geezer who shouldn't be pushing this car under any circumstances. So I'm not suggesting that most of you folks would want to do this. I bought the car for the way it looks, the V8 sound and the convertible top. I drive like your granny and routinely get 25-28 miles per gallon so I really don't need high-performance feet on this car.

Having said that, here's another update. I talked to the guy that drives/diagnoses all the "tough cases" in the service department at Maplewood Lexus -- Todd. He has a huge advantage over me in that he knows how the car "should" handle, since he's driven hundreds of them with all kinds of different wheel/tire configurations.

He says 16 inch wheels won't fit, they don't clear the calipers. He says lotsa folks up here in St Paul drive 17s with winter tires on them. Why anybody would try to drive this car in the winter leaves me puzzled, but that's another story. Anyhoo, he said that the handling/ride don't change that much and he thinks I'll be disappointed with the results.

Interestingly, he confirmed bt430's point that people running 20 inch wheels like the handling better -- less jitter. That's got me scratching my head. When I scratch my head, I pause and find out more scoop. So here's a question to you 20 inch people. What's it like going over bumps with those big rims and low, low profile tires? I would think it would feel like you're running on wagon wheels, since now there's even less tire between your rim and the bumps.

Anyway, I ain't making any moves soon on this. I've got one more Smart Person to talk to but he isn't getting back from vacation until a few days from now.

 

By the way.....welcome to clublexus, OConnorStP.

 

Currently running Michelin Sport Pilot (zp) 240x40x18 on my sc430. Last eweekend drove from L.A. to Sacramento up I-5. Pushed her up to 90 mph, no problem, 100 mph, no problem. Steering steady as a rock, ride smooth as any big car. While I would like to fill up my wheel well a little more, I'm not sure how much comfort I'm willing to sacrifice for looks yet. There is a reason Lexus put 18" on the car.

 

Just wondering, why did you deviate from the stock size (245/40-18) and go narrower? Does it make the ride better?

**Wait I just realized that this isn't a size. Maybe you made a type?

 

You're correct, 240 is a typo. It should have been 245.

 

Welcome to CL, please keep us posted