19" to 18" Bumpy

[Mimzie2763]

I just recently had a tire shop install my TE37SL 18x9.5 +45 - 5x120 and some Michelin PS4S 265/35ZR-18.
I have noticed there is some bumpiness at low speeds. I know the wheels and tires were balanced.

Is this normal with new tires?

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[Tickle]

I haven't noticed this.

 

[Icehawk]

Check the tire pressures.

 

[chopsuey34]

Are they significantly lighter than stock? I read on CivicX that the suspension is tuned for the heavier stock wheels, so if the aftermarket wheels are too light, the springs & struts are too powerful and cause harshness and more bumpy riding. Can anyone comment?

 

[Icehawk]

Are they significantly lighter than stock? I read on CivicX that the suspension is tuned for the heavier stock wheels, so if the aftermarket wheels are too light, the springs & struts are too powerful and cause harshness and more bumpy riding. Can anyone comment?

IME, that's pretty negligible unless we are talking large changes.

 

[Tickle]

I dropped about 9lbs or so at each corner. Again I can't sit here and say I have noticed this.

 

[Mimzie2763]

I guess I will go back to the tire shop and let them look at it. Maybe it is just in my head idk.

 

[TypeRD]

I would drive on them a bit. Tires require some break-in. I would be surprised if they have a defect, but it does happen. I had a set of Bridgestones once that were “bumpy” at low speeds. It was barely noticeable and I doubt anyone else would notice. At first I thought it was just the roads, but that wasn’t the case.

Also, be sure your tires are properly inflated. Smaller wheels w/ larger tires don’t require as much air as the stock setup, so don’t use the factory inflation recommendation. Someone else in the same aftermarket wheel/tire size situation as you (in another thread) found a calculator and iirc the proper amount of pressure is ~31 psi front and ~29 psi back. I’d start with that, then inflate or deflate 2 or 3 psi to your liking.

 

[chopsuey34]

I would drive on them a bit. Tires require some break-in. I would be surprised if they have a defect, but it does happen. I had a set of Bridgestones once that were “bumpy” at low speeds. It was barely noticeable and I doubt anyone else would notice. At first I thought it was just the roads, but that wasn’t the case.

Also, be sure your tires are properly inflated. Smaller wheels w/ larger tires don’t require as much air as the stock setup, so don’t use the factory inflation recommendation. Someone else in the same aftermarket wheel/tire size situation as you (in another thread) found a calculator and iirc the proper amount of pressure is ~31 psi front and ~29 psi back. I’d start with that, then inflate or deflate 2 or 3 psi to your liking.

Which calculator did you use? I'm thinking of upsizing my tires and I'm not sure with psi to use.

 

[TypeRD]

@chopsuey34 It wasn’t me who used the calculator. It was another member with a wheel/tire setup like yours. I think it may have been this : https://tiresize.com/pressure-calculator/

 

[VarmintCong]

Are they significantly lighter than stock? I read on CivicX that the suspension is tuned for the heavier stock wheels, so if the aftermarket wheels are too light, the springs & struts are too powerful and cause harshness and more bumpy riding. Can anyone comment?

I’ve replaced heavy stock wheels with 17-18lb OZ wheels on several cars before, and usually notice more road feel and a bumpier ride. I think a heavy wheel acts as another damper.

I don’t think springs and dampers should need to be tuned for wheel weight, from what I remember of spring equations in engineering school. If they work for one weight they should work for another weight.

 

[elusiveaura]

Slightly off topic but care to post a pic of your wheels on your car? What color?

And back on topic, were your wheels/tires road force balanced? I know that helps with mine

Thanks!

I just recently had a tire shop install my TE37SL 18x9.5 +45 - 5x120 and some Michelin PS4S 265/35ZR-18.
I have noticed there is some bumpiness at low speeds. I know the wheels and tires were balanced.

Is this normal with new tires?

 

[Cornercarver]

Other than the bumpiness, are you seeing any actual benefit from the switch in cornering, handling, braking, steering response, etc.? I don't want to rub it in, so not asking about ride quality.

Less un-sprung mass at each wheel is usually a very good thing...if the suspension settings are dialed in for that weight.

 

[TadashK]

Have you checked the tire pressure as someone told above?
It is very important if you change tire profile and load index.
I just calculated appropriate tire pressure.
If you change stock 265/30R19 to 265/35R18,
appropriate TP should go down from F34psi R32psi to F27 R25.
These numbers are based on stock ETRTO load index 93 to popular JATMA LI 97.

Do you understand? Stock tires might be different from Japanese one.
Sorry for my poor English.

 

[Icehawk]

Until we know the tire pressure of the current setup... likely it's still very high from mounting the tires. I have experienced new tires feeling a bit stiffer than the ones they replace (same tire/size) for a few drives though.

I'll disagree with these tire pressure calculators you guys are referencing - that's just about load which is not something we need to worry about here. I have a lot of experience with tires and pressures from autocrossing, we can have a discussion about that if desired but I absolutely would not recommend 25psi on tires you are going to use on public roads.

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