Driving DynamicsDriving techniques (trail braking, power slides, donuts, scandinavian flicks, etc), and vehicle dynamics (roll centres, c/g weigh transfer, etc)
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Can anyone explain what the 'bump stops' are for me please ?
I've read when you lower your car it can hit the bump stops on uneven surfaces, would this explain why my car seems to bottom out whilst turning at speed on uneven roads, like it just slides/jumps wide of the apex ?
I'm pretty sure I'm not going to fast
Reason I ask as I was looking at the roll center adjustment kit, but it says it retains the original height of the bumpstops, I thought I'd want to change this ? No ?
Bump stops are bit of rubber that stop your shock knackering itself when it runs out of travel. When the shocks bottom out your are hitting the bump stops.
When the car is lowered you hit the bump stops sooner (less travel in the shocks).
Your looking at bump steer mods, not bump stops. Bump steer mod is about retaining oe geometry, as when you lower the car The arms don't sit level so it just brings them back in line.
As above says bump stops are there to stop the shock travelling to far, if you don't mind me asking how low have you done it as it might be your shocks are knackered anyway
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TD04 Hybrid, small turbo, bigs balls.
The STi uses quite long progressive bump stops unlike most cars which use a shorter rubber cylinder.
The car uses these to creat a progressive spring curve without the fancy springs. original cars will sit on them when cornering anyway. They touch when you lower the car by 1" or so.
The roll centre of a car is determined by taknig the strut top mount and drawing an imaginary line at 90" to it inwards. then draw the line from the outer ball joint to the inner lower arm pivot and where the two lines intersect draw back to the car's tyre contact patch on the same side.
When you do this on both sides it should cross over at the point the car rolls about. The distance of the centre of gravity to this point creates a roll moment which creates the body roll.
If you lower the car, the centre of gravity also lowers. BUT, unfortunately the lower arms angle changes and the strut becomes slightly more upright too as the lower arm outer swings up and out. this means the intersection points is much further out and lower so by the time it comes back it crosses far lower. Thus you need stiffer springs not only to stop bottoming out but to avoid the extra roll.
Getting the longer outer balljoints restores the lower arm angle giving increaed negative camber in roll, raises the roll centre back up and allows you to avoid harsh spring rates and reduce roll at the same time. Win Win.
Suspension 101- don't ask me about rear beams, unequal length wishbones, etc. I can bore for England.
As above says bump stops are there to stop the shock travelling to far, if you don't mind me asking how low have you done it as it might be your shocks are knackered anyway
Its not stupidly low, it was so I raised it up a bit
Coilovers should be fine, bought a set of BCs from the group buy on here, only 4 months old
Quote:
Originally Posted by Markyscoob
The STi uses quite long progressive bump stops unlike most cars which use a shorter rubber cylinder.
The car uses these to creat a progressive spring curve without the fancy springs. original cars will sit on them when cornering anyway. They touch when you lower the car by 1" or so.
The roll centre of a car is determined by taknig the strut top mount and drawing an imaginary line at 90" to it inwards. then draw the line from the outer ball joint to the inner lower arm pivot and where the two lines intersect draw back to the car's tyre contact patch on the same side.
When you do this on both sides it should cross over at the point the car rolls about. The distance of the centre of gravity to this point creates a roll moment which creates the body roll.
If you lower the car, the centre of gravity also lowers. BUT, unfortunately the lower arms angle changes and the strut becomes slightly more upright too as the lower arm outer swings up and out. this means the intersection points is much further out and lower so by the time it comes back it crosses far lower. Thus you need stiffer springs not only to stop bottoming out but to avoid the extra roll.
Getting the longer outer balljoints restores the lower arm angle giving increaed negative camber in roll, raises the roll centre back up and allows you to avoid harsh spring rates and reduce roll at the same time. Win Win.
Suspension 101- don't ask me about rear beams, unequal length wishbones, etc. I can bore for England.
Thanks for that, very informative
I think the roll centre adjustment kit will be ordered shortly !
Hope you have this on subscribe because if you can bore for England, then I can ask for Scotland
Bump stop explained ?
