Suspension Setup - good in the wet not so good in the dry

[MikeLMR]

I know we have a few racers around so I thought i would throw this one out here and get some opinions.

Now I have a 1st gen rx-7 and it is very rarely used in the wet so I haven\'t really driven it on wet roads. However when I picked my car up a few weeks ago it was chucking it down.

To my surprise the car handled much better in the wet than it does in the dry, it tracked less and felt much more composed than it does in the dry!

In the dry it feels quite nervous, the front end wonders all over and it tracks quite badly.

My current setup is :-

Standard springs front and rear - standard ride height
uprated shocks - set to full stiff at the front and 1 click back from that at the back
15x7 wheels all round with 205/50R15 tyres (think these might be the cause on the front)
uprated front anti roll bar.

Now I have an uprated rear bar that can go on and I was planning on converting the car to 2.25" springs and adjustable platforms all round (like my \'79 323). Planning to set the rake slightly differently (nose high slightly) and a little lower which unfortunately will give more camber on the front ... I can however correct this with some spacers under the struts to lower the suspension arms to the standard position.

Any idea\'s or suggestions, I suppose if I change all the above I will need to start again but i\'d like to understand why it feels like it does. I am considering ordering some narrower rims for the front with an almost stock scrub radius and width then fit some narrow tyres ... this is however an expensive (circa £350 option)

Cheers ~ Mike

[kev-yorks]

Four wheel alignment check might be in order Mike just to see if its set right. BTW what fuel set up did you end up on it in the end?
Kevin

[MikeLMR]

Microtech LTX-8, 4 bosch coils, 2x500cc injectors, bosch 040 fuel pump and the standard pump acting as lift pump. Throttle bodies were half the set I made up originally on a 45 DCOE manifold.

The engine is out at the moment as I\'m wanting a bit more power than a stock 12a can give (my daily drivers doubled in horsepower in the last two years so my expectations are somewhat different) Not worrying about that though, engine is out and more power is being acquired.

Not sure the alignment is out, it was laser tracked about 500miles ago when I did all the suspension, I think the wet just shows up that I\'ve over tyred it on the front ... take some of the grip away and it\'s nice again.

[oldone]

1st Gens are very nervous when it comes to ride heights.....if you have the weight distribution a lil to much to the rear,and ever so slight negative camber on the front.the car will have its own mind on the road.I am talking of .03 degrees negative and you will fell the differance.This is accentuated under accelaration and high speed driving.
Another problem on the 1st Gens is that all your suspension \'arms\' are prone to bending easily,the slightest curbing,pot holes etc all have an influence on this.On the race cars we used to boltser all the arms with some flat bar to try and curb this problem.On road cars that is the area nobody searches in\\for as all assumes nothing will bend or break under normal use............:cheers  and the list goes on.:wave

[MikeLMR]

I will have to investigate when I get chance, I did set the camber differently when I put the strut tops back in as they are slightly eccentric, I set them so that the arrows both point inwards towards the gearbox. I think that is the max setting for the standard tops.

The car sits ... if I recall correctly slightly nose down at the moment, camber is an unknown but I have a dunlop camber caster gauge and can check that once the new engine is back in the car as I guess it might sit differently due to the weight (and it\'s a bit high in the front without it !)

i could just drive it in the rain all the time ... that won\'t be hard if the current weather holds

[TonyC]

It\'s very hard to make a suggestion on such little info/experience of a car so I won\'t do so. I will say that you would not normally want to set the ride height so the front is higher than the rear. The only time this might be an advantage would be if the car has a live axle on the rear, and you are equalising the roll centres front to rear.

usually, if a car feels better in the wet than the dry it is becuase the lower speed is preventing handling problems that arise in the dry due to excessive flex or movment in the bushes/suspension/frame....

[MikeLMR]

The 1st gen does have a live axle at the rear + a high roll centre due to the watts link being up high on the axle.

It is certainly a common practice to set up a rally car with that sort of rake angle.

[Dominic]

Haven\'t got any first hand experience on this but have done a lot of reading on it (a good and interesting book to read is by Fred Puhn called "How to Make your Car Handle")

Setting the ride height high at the front and low at the back is known to improve handling on the FB. You see lots of FB\'s set up this way. As Tony said, the improvement is due to the different roll centre heights to the front and rear of the car. The McPherson strut set-up at the front gives a much lower roll centre than the rear, which as you said is forced up due to the Watts Linkage. The Watts linkage does a good job in lateral rear axle location (compared to say a Panhard rod which will always return some sideways movement) although is a fair bit heavier. To lower the rear roll centre at the rear axle, one option would be to ditch the Watts linkage and fit an A-arm system (apex of A-arm pivoted at base of differential housing and ends of A-arm pivoted on chassis, forward of the axle and as wide apart as possible). This would move the roll centre from its previous location at the main pivot point of the Watts linkage on the diff housing to the base of the diff housing where the A-arm pivot is located, roughly balancing the front and rear roll centres. This would allow the front and rear ride height to be kept low, helping to reduce body roll and improving cornering capability. The A-arm system is something I\'m considering for my Rx3, mainly because it provides lateral rear axle location while eliminating wheel hop under hard acceleration (due to leaf springs). The alterative is a Panhard rod which will give a higher rear roll centre, prob about the same as a Watts linkage.

I found an old article a while back on improving handling of the FB through a combination of ride height adjustment, new springs, and stiffer anti roll bars. I\'ll have a look for it. :Thumbs-up

[MikeLMR]

If you fit the panhard rod low on the axle (look out for some update piccies on my 323) it will move the roll centre down much lower than the standard watts linkage.

Changing the angle and side that the panhard rod mounts on can aslo be used to change the influence of the rod and load different wheels when cornering ... this is mainly used in oval racing where you can set the car for one handed turns.

If I were to ditch the watts linkage I would go for a panhard rod I think, it\'s simple and is proven to work well enough + it is a road car.

[Dominic]

Yeah, I guess if you fit the Panhard rod very low (if possible) this will help. Not sure whether it will be much lower than for the Watts linkage though cos the new roll centre wont be at the height of the Panhard rod axle pivot, it\'ll be at a point somewhere between the Panhard rod pivots and the other geometry of your specific suspension setup. I\'ve been meaning to find out how to calculate the new roll centre for a live rear axle setup. Guessing at the moment. Wouldn\'t bother changing the Watts linkage to a Panhard rod if the roll centre change is only gonna be small.

[TonyC]

Live axle? fancy that. I was expecting some clever advanced setup. You are ok on the front/rear ride height then. I had tgo get the MGB\'s rear much lower than the front to get it to work properly.

Doesn\'t help much with your wet/dry problem though