small bumps are harsh in rear of car

[chris82]

This is a problem that developed over time. The rear was fine when everything was first installed (new shocks), but within the past few months, going over smaller, sharper bumps, has gotten a little harsh. It's like you can feel the impact throughout the car. It's not ruining my experience but it just doesn't feel normal. There is also a knocking noise which I'm pretty sure is related. I've adjusted my tire pressure to spec, increased and decreased rebound and compression settings, but it does not make much of a difference. It's like the shock isn't absorbing the bumps like it should, but it's only in instances where the shock would be using the high speed compression, so i'm talking about sharper bumps. Anything else and the car handles beautifully. I think there could be play in the lower shock mount? But I think I would feel that all the time. On highway driving, it's fine.

So I bring the car to the local indy.
They said they had to tighten up quite a few bolts for the rear suspension arms. They weren't 'loose', but they definitely weren't to the proper torque specs. So they tightened them all up, thoroughly inspected my rear suspension, lubed up anything that needed it, and checked all the bushings and everything is good according to them. They told me they spent a lot of time on the car to see if anything was wrong, and they've always been good to me so I trust them. So after this check up, the rear felt much tighter and everything in general felt better, but did not entirely solve my issue.

All the suspension arms and bushings are stock, so they have 50k miles. The tires are Michelin PSS in 245/35/18 size, and they have at least 75% tread left, the spring rates are ~400 at the wheel, the shocks are JRZ RS and they were put on in the spring.

Any ideas?

[Suprgnat]

With 600/700 spring rates and a motion ratio of .960^2 and .569^2, the effective rates are weird and your ride frequency is all out of whack ?

[_Ryan_]

Are you on the bump stops?

[chris82]

Originally Posted by Suprgnat

With 600/700 spring rates and a motion ratio of .960^2 and .569^2, the effective rates are weird and your ride frequency is all out of whack ?

The motion ratio is not a problem nor something I care about tbh, and it wouldn't make a difference here mainly because this isn't a problem that existed when I first had everything installed. It's only developed in the last 3-4 months so that leads me to believe that something could have worn out, like a bearing or bushing, but I don't know what? Anyways, my point was that my front spring rate is much, much higher, yet there is no issue, and people run up to 800 in the rear of this car without this issue (and I'm only on 700lb).

Originally Posted by _Ryan_

Are you on the bump stops?

It's not a big enough bump to get near a bump stop, and there are no bump stops on them anyways. The car isn't slammed or anything, it's set up to have plenty of travel for street or track. I'm not having any other issues other than these small bumps, like a small sharp bump.


Appreciate the help!

[Suprgnat]

Originally Posted by chris82

this isn't a problem that existed when I first had everything installed. It's only developed in the last 3-4 months

Didn't realize that (cuz I can't read) or I would have guessed the bump-stops too. Since that's not the case, maybe it's an issue with the high speed compression circuit.

[chris82]

Originally Posted by Suprgnat

Didn't realize that (cuz I can't read) or I would have guessed the bump-stops too. Since that's not the case, maybe it's an issue with the high speed compression circuit.

Yea, I forgot to mention that part in the original post, it's updated now. It definitely seems like it could be a problem with the high speed compression. It's not like this problem is detrimental to the driving experience, it's just odd

[chris82]

So the indy wants to take the shocks out to see what is going on. They will be checking upper and lower shock mounts, frame, etc. Looking forward to the results!