Lowering - Affecting stability?

[Jonny5ive]

So late last year I had the Roomster lowered on coilovers guessing at around 70mm drop

Before:

After:

I have noticed of late that the car seems to be a lot more susceptible to turbulence (buffeting) from sidewinds.

On a 180mile round trip down the M1 & M25 yesterday this was particularly noticeable when making *ahem* progress and quite unnerving at times

Does lowering affect the aerodynamics that much? Am I noticing it because the vehicle is not 'absorbing the lean' from sidewinds due to a much stiffer set up?

Any thoughts from the Briskoda Science Massive?

[@Lee]

I'm not a scientist, I leave that to the missus, but just throwing this in there,,,,,,front splitter and a rear diffuser, would that help I wonder?

[blueR36]

Lowering lowers the center of gravity so will help with stability as long as you have had a 4wa . 70 mm is some drop :clap:

[Jonny5ive]

I'm not a scientist, I leave that to the missus, but just throwing this in there,,,,,,front splitter and a rear diffuser, would that help I wonder?

I'd contemplated an LCR front splitter, I may well invest the £25 and see how it goes. Rear diffuser...... the ar$e end of the Roomy (in scout trim) is already sculpted (see pic below)

Lowering lowers the center of gravity so will help with stability as long as you have had a 4wa .

4WA carried out by UNIT18 when coilies were fitted.

70 mm is some drop :clap:

:yes: It needed it, that's for sure

This is how it sits compared to the F-in-L poverty spec Roomy

[@Lee]

F-in-L ,,,,,,,,,,,,,,

[Octygone]

How about a small spoiler on the rear tailgate would that help....I can remember yonks ago when the sierra came out they had to retrofit a lip spoiler as the car moved a bit in sidewinds

[Jonny5ive]

How about a small spoiler on the rear tailgate would that help....I can remember yonks ago when the sierra came out they had to retrofit a lip spoiler as the car moved a bit in sidewinds

Spoilers are available from :shudder: Superskoda.......

[Octygone]

Spoilers are available from :shudder: Superskoda.......

Trouble is ...I'll bet they aren't cheap either

[TeflonTom]

It won't be the height that affects the stability per se... It's more to do with the stiffer spring rates,

the oem springs would have been progressively wound ( starts with tight coils and gradually gets less towards the top), This basically means light bumps make the loose coils at the top compress, and heavier loads are absorbed by the tighter coils near the base of the spring... Ok so your coilovers will have a linear spring ( uniform coil width ) and they are probably a much higher poundage spring than the originals to compensate for the car being lower.. So what you have done is taken away the ability for the body to roll a little with heavy crosswinds...

[Jonny5ive]

So what you have done is taken away the ability for the body to roll a little with heavy crosswinds...

That was what I was trying to string together and came out with "because the vehicle is not 'absorbing the lean' from sidewinds due to a much stiffer set up?"

Thanks Tom

[Robshaw]

It's because you took the bloody roof box off....

[Volvomeg]

I find my octy alot less stable in crosswinds on motorway than my volvo ever was, i just put it down to the octy been lighter than my s40's,

Also find it seems better if rear ends a tad higher than the front then it pushs down the as you drive

[XLBaconDoubleCheese]

I want a vroomster ;(

[Jonny5ive]

f

Also find it seems better if rear ends a tad higher than the front then it pushs down the as you drive

Interesting you say that. I'm looking to wind down the front a little more as I think I'm rocking a little reverse rake

[KenONeill]

Yes, you've lowered the CoG, but do you know where the new Centre of Roll is? It's not impossible that lowering can move the CoR below the nominal surface level, which means that you actually have no geometric roll stiffness.

[nickguzzi]

Vehicles normally have their suspension designed to function optimally at a specific ride height. The unavoidable nasties like bump steer are engineered to be a the bottom or top of travel so there malign influence is less noticeable.

As the poster above pointed out, you may have screwed up the roll centre, altered the scrub radius, the camber values, various offsets, lots of things really, could be quite dangerous for someone who doesn't know what they are doing. Presumably there were no structural/geometric changes to accommodate such lowering?

So your instability could be the result of the lowering to outside the designed normal running range.

Have you been to a specialist consultant like Center Gravity?

At any sort of legal speeds, mechanical grip provided by the suspension/tyres will overwhelm aero artifacts.

[vindaloo]

Looking at this from a "grunt's" perspective...

It's a car with a big-high arse end on it.

Stiffer springing will mean that things happen faster from the driver's perspective.

Wonders at how often the OP has pressed on whilst driving in gusting high side winds?....

I can't quite believe that a side wind would push it onto the bump stops. Rapid cornering would be required to do that.

Depending on your POV it's a driver thing, deal with it... Or... You've broken it, fix it!

HTH

J.

[fabdavrav]

Also in "simple terms" you have altered the areodynamics under the car which is the worst bit..............the car is now way lower so when you make "progress" the air under the car is getting quished.......the underside of the car is not fully flat so this will be causing turbulance......which could make the car "lift" or even affect the fuel consumtion!

[KenONeill]

Also in "simple terms" you have altered the areodynamics under the car which is the worst bit..............the car is now way lower so when you make "progress" the air under the car is getting quished.......the underside of the car is not fully flat so this will be causing turbulance......which could make the car "lift" or even affect the fuel consumtion!

I see where you're coming from, but lowering a car almost always reduces the amount of air flowing under it, which makes it more aerodynamically stable and improves fuel economy slightly as well.

[Jonny5ive]

Whoaa!! Science overload. Good information folks thanks

[SimonK24]

Try raising the rear a little bit Barrie. From your picture, if the car was empty it looks too low at the back to me. I've ****ed about with mine for long enough on and off the track, and found the best setup now I think. Mine handles best with some positive rake (rear higher than front). Some of the cars on here are slammed right on their arses, I bet they are horrible to drive....

On my fabia the Weitecs still have the rear adjuster in, but lowered as much as possible, the front is a little amount lower than the rear. Don't forget though when you start driving (and also luggage, fuel etc) the rear will squat, levelling the car out.

We have some horrific winds sometimes (must lay off those curry's parp ), I've noticed more instability with mine too recently, but I put that down to stronger winds than the car itself. That and the fact I'm back on 16's which have a narrower track than the 17's.

[Jonny5ive]

Try raising the rear a little bit Barrie. From your picture, if the car was empty it looks too low at the back to me.

Indeed it is empty, and only going to be more empty with the rear seats out on track.

I've booked a week off in Feb to carry out a bunch of stuff car related, I'm firmly of the opinion that either the rear needs to come up a bit, or drop the front a bit to get some 'positive rake' on the go.

I'll also experiment with and LCR splitter on the front.

Also need to do:

• Replace front pads with DS2500
  
• Paint and fit SEAT Sport upper strut brace
  
• Get to Shark for a map tweek
  
• Fit HID's
  
• Repair and repaint Roofbox :'(
  
• Looking at 5mm spacers for the front
  
• Modify and fit VW damped grab handles
  
• Remove redundant phone cradle and wiring
  
• Repair/Replace ASV
  

[SimonK24]

Edited

Indeed it is empty, and only going to be more empty with the rear seats out on track.

I've booked a week off in Feb to carry out a bunch of stuff car related, I'm firmly of the opinion that either the rear needs to come up a bit, or drop the front a bit to get some 'positive rake' on the go.

I'll also experiment with and LCR splitter on the front.

Also need to do:

• Replace front pads with DS2500
  
• Paint and fit SEAT Sport upper strut brace
  
• Get to Shark for a map tweek
  
• Fit HID's
  
• Repair and repaint Roofbox :'(
  
• Looking at 5mm spacers for the front
  
• Modify and fit VW damped grab handles
  
• Remove redundant phone cradle and wiring
  
• Repair/Replace ASV
  
• Respray in red
  
• Source postman uniform
  
• Find suitable trackday helmet for cat
  

[jonnynewns]

My octy and the mother's estate is shocking in cross winds. Hella scary. Passats are much better in cross winds. Put it down to a Skoda safety feature.

[j0hn]

Edited

• Respray in red
  
• Source postman uniform
  
• Find suitable trackday helmet for cat
  

Hahahahahah