Lowering

[sixafterfour]

Hey, thinking of lowering my car.
I need to lower it alot, (20" tires on 13x7 rims, compared to 22.7 on stock 185/60/14)
So 2.7 inches plus a little more, like 1.3. 4 inches we'll say

So i was thinking i had to do a combination of shorter struts/springs and mods to the suspension. Springs are obvious but how do you think i should mod the suspension? Think i could make a "Z" section to the control arm. and do you think i'd need to mod the tierod ends? too?

anyone do this before?

[Jim-SR]

if you are running much smaller diameter tyres, the chassis is going to be sitting extremely low compared to standard anyway (by 1.35" in your case). if you lower it another 2.7 inches to close up the gap in the arches youre going to be sitting the chassis 4" lower than standard. firstly, im not sure that youd even have enough ground clearance to make it driveable! but more importantly, your suspension geometry is going to be completely destroyed, youll need to move every pickup on the chassis up by several inches to compensate, and that wont be possible.

in terms of shortening the struts, you cant do it by enough with standard length inserts. youll need to get some shortened inserts made up and then shorten the strut cases. or get something completely custom made up, at much expense. what is the reasoning behind such small wheels, and then lowering the car so much?

[sixafterfour]

small wheels dont change geometry.
But what i was trying to say is mod the control arm and shorten the struts so i have similar geometry instead of relocating the pickups.

small wheels because it improves acceleration, less rotating mass, cheaper tires and rims and lowers the centre of gravity without changing the suspension.
lowering it to get rid of the large gap between the arches and wheel and hopefully improve handling(thats what i want to mod the control arms to maintain proper geometry.

[Jim-SR]

small wheels dont change geometry, but lowering the car does. if all you were to do was to put small wheels on then youd be fine. but as soon as you lower the car you are lowering the inside mounting points. the only way to correct that is to lower the outside mounting points, which you arent going to be able to do with small wheels (there physically wont be space). shortening the struts wont change geometry a great deal, it will just mean you arent riding the bump stops at ride height. modifying control arms would work if you had space to drop the lower ball joint down, but you wont have space inside a 13" rim. the only way to correct your roll centre heights will be to lower the ball joint.

the weight of small wheels is obviously a significant enough factor to consider their use, but when you get down to lightweight rims, the tyres weigh more than the rims. a typical 15" tyre weighs in at 14-17 lbs. a typical lightweight 15" rim can weigh in at 10-12 lbs! on a 13" rim youre looking at about 8-10 lbs of rim and 12-15 lbs of tyre. overall youll save 4 lbs in weight, obviously some of that is also rotational, plus youll have a smaller rolling radius. if you were to JUST fit smaller rims, this would be of much benefit. it would like kinda silly with the huge arch clearances, but it would be functional (its probably cheaper and easier to extend the wheel arches downwards lol). youd lower the CofG by about 1.3 inches straight away (which will give you a little freedom on roll centre height). the second you lower the car though you are going to move the suspension geometry and struggle to correct it (there is a distinct lack of space). you can probably get away with lowering it an inch or 2, but 4 inches is going to be too much to work with.

and then youve still got the issue of how to produce struts short enough. your only cheap option will be to find shorter Koni inserts that will fit the strut case in every other dimension, and then to cut the strut case down and re-thread the top closure. but then youll have damping for a car that isnt an MR2. alternatively get some MR2 Konis modified in a similar way (more difficult and more expensive, if you can find someone willing to do it).

to do it properly youd need custom dampers, and then youre looking at something like Ohlins, and a minimum $2000 bill if you can source some Jap spec mk2 Ohlins in good condition and find someone who will modify the inserts and make custom cases (i could do that so its a possibility if you wanted to spend the cash, but it wont be particularly cheap).

[sixafterfour]

mmhmm, i'll take some pics of mk1 suspension parts. I also need to look at the clearances for the control arm and the rim aswell.

i realise i did my math wrong in the first post aswell. I used diametre, not raidus(DOH).
should be 1.35+1.4. so around 3 inches total. Still quite a bit.
I could get away with 1.4" lowering with just struts, maybe a bit less, then move the mountings up along with the balljoint/control arm point.

[sixafterfour]

no pics tonight. The stock struts are pretty much right against the knuckle. So serious mods would have to be done to the strut.
How control arm however has lots of room.
http://www.twobrutal.co.uk/forum/images/recovered/2009/01/143.jpg
Just using that for reference, and thats a 2nd gen not a first gen but the suspension is similar.

Where the middle bolt is, just outboard hack that off. From there reweld, add some metal whatever it takes to move the joint up(using a jig to keep the same geometry, but up 2-3 inches or so) then find a coilover thats shorter, possibly from another car(ex. corolla) possibly mod it and go from there.

[Jim-SR]

heres a picture of someone in the US who has already made tubular suspension arms. this is about as much space as youll ever create at the rear of an MR2's suspension

http://www.twobrutal.co.uk/forum/images/recovered/2009/01/144.jpg

struts will have to be shortened from the top, youve got less than half an inch to play with above the driveshaft

if you then lower the chassis 3 inches, youll need to lower the lower ball joint by a similar amount (it wont be quite as much due to lower CofG), and im not sure youll have the space to do it. on the inboard mount you can maybe change that subframe bracket so that it raises it up an inch or 2 without problems. that MIGHT be enough. but with a 13" rim, your lower ball joint is already going to be extremely close to touching the rim, so i just dont think youll have space to move it any lower there.

youre going to have to compromise somewhere, its just a question of whether you will compromise performance from geometry more than you will gain from the other benefits of smaller wheels

there is possibly a safer compromise in super lightweight 14" rims. youll lose a lb or 2 less in mass, youll lower the CofG by 1/2" less, but youll be able to maintain much closer to stock suspension geometry, also with room to change it for improvements later! on the 13" setup youre limited to one geometry setup that isnt ideal, and cant be easily changed in future due to lack of space

[sixafterfour]

http://www.twobrutal.co.uk/forum/images/recovered/2009/02/11.jpg
http://www.twobrutal.co.uk/forum/images/recovered/2009/02/12.jpg

Rear suspension.
Those are 13x7 rims with 3" back spacing, so a total of 4" back.
Now in the second pic you see the profile pic of the contol arm. Where the bolt in the middle is offset quite aways back.
So by doing something like the attached picture(assuming you kept the geometry the same) and used a shock/spring/damper combo that lowered the same amount you could have an decent setup.

[Jim-SR]

the "middle" bolt isnt the problem though, thats just the strut arm that supports the control arm. you could move that around a bit, but youll change geometry at the same time.

the issue is that you need to move the outer ball joint lower. if those wheels are the actual wheels youre going to be using then you may be able to move the low pivot point inboard a little to give clearance to lower the ball joint as far down as you like. however, if you are going to run wheels with any additional inboard width than those then youve got a maximum of about an inch that you can lower that ball joint. which means in theory you can only lower the chassis around 1.5" before youll run into problems will roll centre heights and camber change characteristics

[sixafterfour]

i dont think you understood the attached picture.
The middle bolt doesn't move. the ball joint has to move UP, not down. As the further the wheel moves up the closer it gets to the chassis and the lower the car gets.

[Jim-SR]

as the chassis lowers the inboard mount moves down.

if the inboard mount moves down but the outboard mount doesnt then your control arm is now pointed upwards (from inside to out). you want it to be the opposite of that

the only way to correct it is to move the outboard ball joint lower

smaller wheels lower the car but dont change the geometry. shorter stuts (including compressing the strut) lower the body (think of the wheels as being fixed in place, they essentially are, move the chassis, its easier to picture that way) which lowers the inboard mount and inclines the control arm upwards. lowering the outer ball joint will restore the control arm nearer to its original angle

you want the control arm below parrallel (low on the outside) for optimum camber change characteristics and for a more ideal roll centre height. if its above parrallel then you will create issues.