Rear end wobble
- Thread starter Mez
- Start date
Marsch
Paid Member
I'm running the cup suspenion with H&R's. The tail can come lose in certain situations but it's nothing that can't be controlled/caught with the round thing in front of you. You may experience something I'd describe as a slide swinging if you drive it hard but that's due to the tyre loads in corners and completely normal I'd say. I don't have any "wobble" as you decribe it.
What colour of strips are on the rear dampers and what part number are on the HR springs because this can't happen like you describe the back axle has to be bent or the wrong parts fitted if it was April 1st I would understand where do you live and find a proper Renault specialist to just look and diagnose the car they cant charge that much just to give it a quick drive round the block with you in it or even ask if there is anyone on here near you Shropshire is a bit vague if this is all happening it has to be visible from following behind as you drive along. My feeling is that the car is now so low there is no travel in the suspension at all and bounce is what you will have to expect for what the car looks like when it is parked up or the rubber mounts at the top and bottom of the rear springs are missing a couple of photos would be nice of the rear setup with the wheel removed.
You car could indeed be damaged in some way, but I would suspect the effect of that would be to get worse with speed not better.
There are a number of generic issues you could be experiencing.
Firstly, as has been said, the car is sat on the bump stops negating most of the suspension movement. However this said should not smooth out as speed increases and and significant undulation on the road is going to have you commenting that the car is trying to send you backwards into the ditch rather than a wobble. It also should be very apparent to anyone looking at the suspension on a 4 post lift.
Then you get into the technical stuff. Lowering springs are, if they have been thought about, will be shorter to lower the car. However because this now reduces the total amount or remaining compression (before you reach the bump stops) they are going to be stiffer to resist all the loads before the bump stops. Looking at my standard car there is about a 3" gap between the rear tyre and the top of the arch. Feeling underneath the arch there is about 2" to the arch liner. so using some total man maths assume there is 5" of total suspension compression on the rear. Again assume that to fully compress that needs a 500kg load. That gives us 100kg per inch of compression, nothing like mixing units! Now, if you want to reduce that arch gap to 1" you reduce the total compression travel to 3" or a 40% reduction in travel. However in spring rate terms, using the same 500kg load to get to full compression you now have 500/3 = 166kg per inch or 66% stiffer spring. So what this means is you will naturally bounce a lot more on bumps, particularly of the light rear end.
Taking this further however you get into the damping. If you are still using the standard dampers you are now asking them to do 66% more damping in 40% shorter distance, most particularly in droop when the damper is trying to control the extending spring. Long and short of this the damper is overworked and the suspension is under damped.
This shows up particularly on the high frequency, low amplitude bumps such as broken road surfaces, road joints and the like that will cause the wheels to jiggle and the body to wobble. I have driven cars with "coilies" that quite literally feel like cut and shut cars with the front and read reacting in a totally different way to each other. As speed increases these road imperfections become somewhat less obvious as the car tends to skip over them more and also the tyre compression will take a bit out and the road undulations become more apparent which bigger, higher amplitude bumps, are lower frequency and suspension copes far better. Remember, Renault and it's suspension partners will have spent a lot of time (money and effort) tuning dampers to springs. If they had planned the car to be lower, the OEM damper settings would have been different.
Long answer, but I have seen lots of times where stiffer springs without correspondingly up-rated dampers result in a sh1t ride.
Finally, however, have you actually checked tyre pressures? It never fails to amaze me the number of "help, my car does not drive right" threads that get started, have people say they have looked at every single mechanical issue, only for the OP to come back 8 weeks, yes literally, and say that it is all alright now because they eventually they checked the tyre pressures and one tyre was at 8psi and the other at 32!
There are a number of generic issues you could be experiencing.
Firstly, as has been said, the car is sat on the bump stops negating most of the suspension movement. However this said should not smooth out as speed increases and and significant undulation on the road is going to have you commenting that the car is trying to send you backwards into the ditch rather than a wobble. It also should be very apparent to anyone looking at the suspension on a 4 post lift.
Then you get into the technical stuff. Lowering springs are, if they have been thought about, will be shorter to lower the car. However because this now reduces the total amount or remaining compression (before you reach the bump stops) they are going to be stiffer to resist all the loads before the bump stops. Looking at my standard car there is about a 3" gap between the rear tyre and the top of the arch. Feeling underneath the arch there is about 2" to the arch liner. so using some total man maths assume there is 5" of total suspension compression on the rear. Again assume that to fully compress that needs a 500kg load. That gives us 100kg per inch of compression, nothing like mixing units! Now, if you want to reduce that arch gap to 1" you reduce the total compression travel to 3" or a 40% reduction in travel. However in spring rate terms, using the same 500kg load to get to full compression you now have 500/3 = 166kg per inch or 66% stiffer spring. So what this means is you will naturally bounce a lot more on bumps, particularly of the light rear end.
Taking this further however you get into the damping. If you are still using the standard dampers you are now asking them to do 66% more damping in 40% shorter distance, most particularly in droop when the damper is trying to control the extending spring. Long and short of this the damper is overworked and the suspension is under damped.
This shows up particularly on the high frequency, low amplitude bumps such as broken road surfaces, road joints and the like that will cause the wheels to jiggle and the body to wobble. I have driven cars with "coilies" that quite literally feel like cut and shut cars with the front and read reacting in a totally different way to each other. As speed increases these road imperfections become somewhat less obvious as the car tends to skip over them more and also the tyre compression will take a bit out and the road undulations become more apparent which bigger, higher amplitude bumps, are lower frequency and suspension copes far better. Remember, Renault and it's suspension partners will have spent a lot of time (money and effort) tuning dampers to springs. If they had planned the car to be lower, the OEM damper settings would have been different.
Long answer, but I have seen lots of times where stiffer springs without correspondingly up-rated dampers result in a sh1t ride.
Finally, however, have you actually checked tyre pressures? It never fails to amaze me the number of "help, my car does not drive right" threads that get started, have people say they have looked at every single mechanical issue, only for the OP to come back 8 weeks, yes literally, and say that it is all alright now because they eventually they checked the tyre pressures and one tyre was at 8psi and the other at 32!
That is all a very valid point. I honestly think unless its a track or weekend toy, regular sport dampers are far more forgiving on UK roads. Too hard and you dont have the control. Being too low ruins geometry, thats the same for all cars. I went to Eibach springs, replacing H&R for that reason but for the little difference it made I cant tell.
I think Koni are very good, but I would recommend asking the people who supplied the springs, otherwise you need to know the spring specs and ask the damper technical departments.
Tbh the h&r springs are designed around a standard damper, if they were designed for a koni damper they are being mis sold... they are designed to be a stand alone upgrade to factory kit and dampers... Would it not be easier... rather than throwing money at an issue that may purely be a fundamental characteristic of the car and spring combo... to drive to another forum member and swap cars for a section of road or something similar and see if both respond the same if it’s slow speed driving that shows the issue up?
You can spend as much money on a problem as you want, but if it’s how it is it may be that no amount of money will fix the issue your having?
You can spend as much money on a problem as you want, but if it’s how it is it may be that no amount of money will fix the issue your having?
You cannot argue with what Dumdum has said above. It is natural to assume that lowering springs will be shorter and stiffer. Using the man maths from my example above, this in turn will mean a solitary bump that would cause the wheel to move vertically upwards 1" would exert a reaction force into the car of 100kg for the standard spring and 166kg for the shortened spring. The car is going to jiggle a lot more. However trying someone else's car with the same set up will prove one of two things. Either theirs is different or the same. In the first case you then have to find out what is different. In the second case, which is going to be the most likely outcome, what you have found out is those springs with those dampers jiggle and bounce. What you would ideally need to find is someone with those spring and different dampers or those dampers with different springs to find out if the combination is better.
Beyond this there are still some fundamentals in play. There are many scenarios for the spring but the basic one is, it is going to be shorter. As it still needs to be able to support the same weight at maximum suspension compression it is therefore going to have a greater rate. While it may well have been designed to fit withing the original damper travel envelope it is still significantly different to the original damping rate the damper was designed for. This is not an unusual problem. When Mazda launched the MK3 MX-5 in 2006 the pre-launch press shots all showed the car with arch gaps something like this.
The actual UK cars turned up with agricultural arch gaps that you could put an upturned clenched fist in
Many people did not like the look and pretty much from day one Mazda sold an Eibach lowering spring through and fitted by dealers.
The MX-5, just most cars had "base" models right through to the all singing all dancing sport models. All 2.0l cars had sippy diffs and the top of the range sport came on Bilstein suspension. Still the same sill ride height though. It was and still is a very common complaint that the ride when to pieces on the standard suspension when lowered but conversely, that the Bilstein, which was often commented by the old people that generally buy MX-5's was too stiff and jiggly as standard, but that when lowered was a joy.
You don't have to look very far at all to find that what engineers designed and what marketing sells are quite away apart. How many car reviews conclude that the BMW with the optional "sport pack, look at my bling" 19" fat wheels is nowhere near as comfortable as the 17" wheels the designers engineered it for.
So, long winded route to say you actually need to fing someone with a set up that rides like you want it to. That of course may not exist.
Beyond this there are still some fundamentals in play. There are many scenarios for the spring but the basic one is, it is going to be shorter. As it still needs to be able to support the same weight at maximum suspension compression it is therefore going to have a greater rate. While it may well have been designed to fit withing the original damper travel envelope it is still significantly different to the original damping rate the damper was designed for. This is not an unusual problem. When Mazda launched the MK3 MX-5 in 2006 the pre-launch press shots all showed the car with arch gaps something like this.
The actual UK cars turned up with agricultural arch gaps that you could put an upturned clenched fist in
Many people did not like the look and pretty much from day one Mazda sold an Eibach lowering spring through and fitted by dealers.
The MX-5, just most cars had "base" models right through to the all singing all dancing sport models. All 2.0l cars had sippy diffs and the top of the range sport came on Bilstein suspension. Still the same sill ride height though. It was and still is a very common complaint that the ride when to pieces on the standard suspension when lowered but conversely, that the Bilstein, which was often commented by the old people that generally buy MX-5's was too stiff and jiggly as standard, but that when lowered was a joy.
You don't have to look very far at all to find that what engineers designed and what marketing sells are quite away apart. How many car reviews conclude that the BMW with the optional "sport pack, look at my bling" 19" fat wheels is nowhere near as comfortable as the 17" wheels the designers engineered it for.
So, long winded route to say you actually need to fing someone with a set up that rides like you want it to. That of course may not exist.
I’ve cup shocks and H&r springs, rear end can be a bit bouncy on a bad road but there is no wobble of any kind! If you have checked your shocks then replacing them with new ones isn’t going to cure a wobble of some sort, is your car a cup? Just asking as I don’t know if there are any issues with replacing normal shocks with cup ones? I’m sure someone will clear this up.
This is the height mine sits with cup and h&r
This is the height mine sits with cup and h&r
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Yeah mine isn't a cup. I was wondering if I could just put cups on the back too as the front feels great and solid but the back end just bounces about a lot down the road, to the point where my girlfriend won't come in the car as it's, in her words, not suitable for women as it's too bouncy Haha
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