9 replies to this topic

[Scruffs]

Hello all,

Am researching dampers today for a giggle, have read Calver's articles on minispares which seem pretty good but I've still got some questions which I'm hoping somebody here might be able to have a go at clearing up.

OK, so I'm lowering scruffs, by how much I don't know because I don't know where I started from, I'm going to wind the hilos up and down 'til I find somewhere I like, whilst giving me enough ground clearance to the first exhaust box (why oh why did I buy a twin box exhaust ). I'm planning to choose dampers based on the centre - to centre length on the front at ride height, then gonna go for a drive and decide where to go from there...but that won't be for a while yet!

What I need to know is what is what isn't designed to control the bump/droop at either end of the car, so I don't end up with broken dampers, bits of suspension falling off or an evil handling car.

At the front I know there are bump stops and droop stops, so I am assuming that these should always control suspension extremities and the damper isn't supposed to limit anything? This would also mean as I lower the front I will get more droop and less bump? Minispares sell modified front damper brackets, which when used with shortened dampers must mean the damper limits droop? If so can you get smaller bump stops to redress the balance?

At the rear there are no stops, so I am guessing the damper is designed to both limit droop and bump? As on the rear there is no static roll centre height change, or changes in toe/bump steer etc. I could go as low as possible before having to modify the arch with about 40/60 bump/droop (Calver's figures).

Basically, for those of you who have thought about it/are bothered enough to have done much work on it, Am I right in what I've said here? Also, what bump/droop do you run at what ride height, and with what dampers? I'm looking at Kayaba Gas-a-jut purely 'cause Calver reccommends them but am wondering whether I'd be better off with something with a little less travel?

Cheers

Al

[Ethel]

Fiddling with the ride height doesn't alter the geometry of the suspension - it just alters where within the range of that geometry your car sits. The requirement for bump and rebound stops will be the same but you're more likely to make use of the bump stops, and hit them harder, so I'd make sure they are in good condition and reinforce where they attach to the subframe.

Not 100% sure but I think the rear subframe makes contact with the inside of the cone to limit travel on the rear. I believe some cars, ERA's?, even used a bumpstop in the centre of the cone?

There is a figure for 'normal' ride height: 13.5 inches measured from the wheel centre to the top of the arch.

[Scruffs]

Fiddling with the ride height doesn't alter the geometry of the suspension

Not on the rear - but it will make a large difference on the front - More neg Camber, KPI increase, toe change, static roll centre will get lower

Cheers for the info on the rear, I take it if I was to use the damper as a bump stop I could ruin it fairly quickly? Am i right in thinking full travel on a stock mini is 3" front and rear? If that is right then I'm not in any danger of doing this as all rear dampers are over 3" travel (according to Calver) and they must be 1:1 ratio on the rear.

I'm just wondering really what %age bump and droop people are running with and whether it works?

[Ethel]

Think you might have slightly missed my point

Yes lowering the car will alter camber etc but it's only done that by moving the geometry to a different point in it's travel. The limit of that travel, where everything goes solid or bits break hasn't changed and you're nearer to it.

I don't know what the wheel travel is between bump and rebound but I'm sure it's a lot more than 3 inches. 3 inches sounds about right to the bump stops from rest.

Incidentally the roll centre doesn't change if you lower a car but it's centre of gravity does.

[Scruffs]

The limit of that travel, where everything goes solid or bits break hasn't changed and you're nearer to it.

That's what I'm concerned about, I don't want to be running something silly like 10/90% bump/droop after lowering because I'll forever be on the bump stops and skidding all over the place

If what you say about the bump stop on the rear is true, and I reckon it is because it makes sense, it shouldn't be an issue. But on the front there has got to be some big issues if it's lowered alot without moving/shortening the bump stops.

I don't know what the wheel travel is between bump and rebound but I'm sure it's a lot more than 3 inches. 3 inches sounds about right to the bump stops from rest.

I got that from here, it does sound a bit small doesn't it? http://www.minispare...le.aspx?aid=283 3rd or 4th paragraph, I'll try and measure it while all the corners are off scruffs

Incidentally the roll centre doesn't change if you lower a car but it's centre of gravity does.

Mate that's a bit of a sweeping statement! I can't say I agree with you on that at all except for a couple of special cases (like rear of a mini), but that's not really the point of this thread so I guess we can store this one up for another day!

[insamoufonyx]

quick question, can you get smaller bump stops, mine failed its mot becasue it was constantly sat on them becasue its so low?

cheers

[GraemeC]

You do not want shorter bump stops - if the suspension is allowed to rise any higher (ie past the limit of the std bump stop) then it will result in breaking ball joints as the angle of the pin becomes too extreme.

If you are riding on the bump stops then your car is too low!!

[icklemini]

GraemeC has it.. i've setup (and sorted) plenty of minis with funny suspensions for road and race.. yes there are ways of getting it lower but on a road car there is no need..

the item on the front that limits droop is the top arm rubber - the one that sits under the top arm.. when this goes then the top arm hitting the subframe will limit droop..

Edited by icklemini, 04 November 2007 - 01:14 AM.

[Scruffs]

OK then, so, *deep breath*

On the front bump and droop are always limited by the stops...lowering gives you less travel in bump and more in droop..I have seen alot of very low minis though, if they can't increase this they must be downright dangerous under braking as you'll be riding on the stops..Anyone got a very low mini? Is it a handful under braking (lots of understeer on turn-in when trail braking, crashing over bumps and generally losing traction??)

On the rear bump is limited by the cone connecting with the subframe, and droop is limited by the shock. Lowering the rear does not change the bump/droop travel - assuming you always change the shock to one that just holds the suspension together at full droop. If you don't change the shock however, if you raise the rear you get less droop and the same bump, and if you lower the rear you get more droop and same bump (more droop until the whole lot drops out the bottom of the car!)

So when I lower my car, I must set it by the amount of bump travel I am prepared to lose on the front, and then select shock length by the fully extended length at the rear, to hold it together...right? I shouldn't have any issues with the shock limiting full droop on the front?

Anyone got any figures for the full wheel travel at the front, and the bump/droop %age at 'standard' ride height for the front (13.5" wheel centre to arch as Ethel says)

Thanks again guys, I don't mean to be a pain, I just want to lower my car properly, and not just slam it to the ground then wonder why it won't handle

[insamoufonyx]

im running on the bump stops with no handling and stoping problems and it will beat anything throu corners lowest part of my mini is about 5cm from the floor

the only problem i ever have is speed bumps, i have to go across diagonaly lol.