top arm angle on very low cars
Turbo Mini Forums

Hi guys,

Are there any tricks / quick fixes to helping out the front suspension geo when running really low? My top arms are at a silly angle and are only a few mm from hitting the subframe even at rest...

I'm going to be converting to coilovers and cutting out the bump stop side of the subframe ( and alot more) which should help prevent any fouling but it doesnt really help with the overall geometry. My rose jointed bottom arms are wound right in and the wheels still sit with some negative camber, which i dont really want when running cross ply slicks.

Im contemplating making a tubular subframe or at least part tubing and changing all the pick up points back to a sensible angle, but its a big job, string computer stuff looks complicated, and ive got a baby on the way, so if i want to get racing at all next season, then a quick fix is probably more realistic!

Are there any tried and tested methods that go some way to helping without a complete rework of the front suspension / subframe? I had thought about creating some new arms / wishbones and raising the top arm pick up point slightly, but im thinking that will play havoc with bump steer etc.

cheers,
Nick

The quickest fix is to put hydro top arms on. These have the knuckle joint further out and do help. Geometry is the same, but the pickup point increases the effective spring rate.

Yes, you can remove the bump stops to give clerance, but it's a good idea to add a bump stop on the damper.

I also had extra short dampers made as well as raising the top pickup point of the damper.

Finally I added an ARB to stiffen it all up and ran the stiffest front doughnuts.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Standard Bump stops went long ago . I mean the metal of the arm hitting the metal of the subframe! yeah, ive added these to the dampers as well as raising the top pickups.



Looking to ditch the doughnuts etc when i move to the coilovers. I run an ARB on the rear but havent felt the need to run one on the front but maybe worth looking into.

Yeah, I meant the metal bit. I cut mine back a couple of inches.

with the hillclimb slicks giving so much grip I really needed to stiffen up the front. Even with the yellow dots cones on the front the front is soft when lowered.

For info I ran mine with the bottom arm horizontal at rest. Is yours lower than that?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Just to be sure....did you already solid mount the subframe without spacers as the Miglia boys do?

No the car is solid mounted but with spacers.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

Ok, that would be a good start to restore suspension geometry / articulation. Just redo the engine mounting points so it drops down an equal amount as the subframe is raised....and than Bob's you mother's brother.

If you're running it low then you'll probably want to look at raising the engine to keep the driveshafts at a sensible angle. That's the next job on my list.

Not sure about the bottom arms, it's all in bits now. You can see in this picture how bad the lack of damper travel, driveshaft and top arm angles are though...

I'm currently running solid subframe mounts and solid engine mounts. Don't really want to raise the engine if I can avoid it but I guess there is a sweetspot between centre of gravity and suspension Geo...

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Edited by nky_84 on 21st Dec, 2016.

Yeah, it's hard to tell on that photo, but keeping the bottom arm horizontal at rest is as sensibly low as you want to go. So that might be a tweak to start with.

It looks like you need shorted dampers. I had some made to my specific length, iirc around 25mm shorter than the 'lowered' dampers that are available for minis.

I wouldn't raise the engine, keep that weight as low as possible. Nick only need to do it as he's on 10" wheels and planning to drive over speed humps!

The main issue is that we use 13" wheels on 20" slicks meaning it's on stilts to start with.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I'm in the same boat as nick, and the main reason for raising the engine was so the cv's sit properly in the pot joints. If you don't, then for 180 degrees the cv's ball bearings are outside the pot joint. Slide your cv boot back and check.. Only other way to fix it would be to get an extended driveshaft, but then ull never be able to have your driveshaft horizontal again because it'll bottom out in the joint.. If that makes sense

Its not exactly a quick fix but raising the inner pivot of the top arm an inch or two will do wonders for the geometry. Combine it with a bottom ball joint spacer of the same length and switch to coil overs mounted as close to the wheel as you can get them and i should think you will see a massive improvement.

I tried the bottom ball joint spacer and it was terrible. It increase the scrub radius and made the car uncontrolable on exit of tight corners. I went slower at a number of events.

Top arm pivit point moving seems more sensible, but only works if using coilovers and I wanted to stay with rubber cones so never did it.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

That's where I'm at currently.

Top arm pivot has been raised an inch. Made my own lower coilover mounts to push them out as far as possible. Upper coilover mounts are as high as I can get them, Ideally I'd have moved them inboard but that's way out of my skill level.

You can see where the outer CV's are in relation to the diff outputs so I definitely need to raise my engine.

The problem I see is that: Now the bottom arm is above horizontal already at rest and the top arm is more horizontal that it would be normally (as the arm pivot is moved up) is that the wheel will have less camber compensation in compression. worst case it might go positive.

Adding the lower arm extenders will help, but as above, this increases your scrub radius. Maybe ok with skinny 10" wheels, but not an option with 7" 13s with slicks.

Edited by wil_h on 22nd Dec, 2016.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

When i do the metro im planning to ditch the bottom ball joint and use a bush in the bottom arm instead. Then i can make an offset extender if needed to correct the KPI/Scrub radius issues. The only way i can see of doing it without making hubs to suit from scratch..

Raising the upper inner joint alone will reduce the front roll centre height and will reduce camber compensation.

Both upper and lower inner points need to move up the same amount to improve the angle of the ball joints and maintain anything near the original kinematics.

Edited by Aubrey_Boy on 24th Dec, 2016.

Absolutely Aubrey. What I said but better!

Looking at Nicks car, as the cones are not used, why not just cut the subframe towers down and modify the lower mounts to bolt to the floor. Then you can have the suspension in a sensible position.

The bump steer can just about be corrected with extended track rod ends connections to the steering arms.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

If you do move the inner joints of the upper and lower arms to correct things and don't move the rack then the inboard steering rack ball joints are no longer in line with the upper and lower arm inner joints, when this happens the problem is bump steer correction.

If you don't correct for all of these 'problems' it just leads to having to run a much stiffer wheel rate than is really necessary and to keep the bump steer manageable.

Colin Chapman: "Any suspension will work, if you don't let it..."

Edited by Aubrey_Boy on 24th Dec, 2016.

I've seen it done on a few cars, not just Mini's and as mentioned above it's and extension of what is done with Miglia's

EDIT: The caveat I would make is that if you cut down a front subframe to move the suspension pick up points up (which is what I would do) that you really have to address the coil over issue:

A rubber coned Mini has damping from both the rubber cones and the dampers, even in standard form the dampers on a Mini are near to falling rate which is understandable due to the 'added' damping from the rubber cones themselves.

With coil overs all of your damping is from the dampers / coil overs themselves.

Many people cite that rubber cones are rising rate, I have measured several, new and old in a 'static' form and they behave in a pretty linear rate in my opinion and others I know have found the same.... The rising rate mainly comes from the kinematics, these kinematics are not present when you fit coil overs to the standard damper pick up points.... You have to move the damper upper point inboard or the lower point outboard so that the coil over angle is always less than 90 degrees to the upper arm angle even at full bump, if you can't do that you will always have to run a much stiffer spring than is really necessary and will probably complain that coil overs are sh1t compared to rubber cones as seems to be the case in a lot of instances.

There seems to be this philosophy that Mini's only handle well on rubber cones, in my opinion it's not just the rubber cone it's the installation ratio which makes it rising rate. Yes there are coil springs which replace cones.... Most I have tested are softer than a rubber cone when tested at what I will call a 'static' rate, steel springs are not sensitive to frequency, rubber is sensitive to frequency so rubber cones I have measured are not only stiffer but get stiffer with frequency compared to the steel springs I have tested. But a properly mounted coil over solves all of these issues.

Edited by Aubrey_Boy on 22nd Dec, 2016.

What an amazing thread this has turned in to.

Great input Aubrey, learning lots.

I even stick with rubber cones on the rear and accept the additional weight as I know I can make it work.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I think im going to have a go at making a string computer / modeling things in one of the digital ones e.g http://www.racingaspirations.com/apps/susp...try-calculator/

Trouble is the car is in bits, so i might have to reconstruct some of it to take the measurements..

I like the logic of chopping out some of the subframe and dont see a problem with raising the floor mountings but moving the rack by the same amount does sound quite tricky, especially when you start to get into pedal proximity and i would probably need to adjust the steering wheel mountings too...

@Nick - assume you havent driven the car with that top arm mod as yet? That looks pretty straight forward, but im guessing if you drive / model that its going to be pretty horrible / impossible to drive at the limit...

Slight hi-jack/ off topic, are you able to share your results from testing the rubber cones Spencer? Would be interesting to see the difference between standard, red dot, yellow dot etc if you have that information?