hey up,

drivein back from the sva and the car is all over the road, as the suspension compresses over bumps the car moves across the road and usually towards a HGV!!!

ok the car is far from set up because of no millage on the road, i incrased the shocker pre load which reduced the twitchyness but still dangerous! if i increase the pre load much more i will shake my fillings out!

im assuming that this is bump steer??

any ideas guys for a basic set up to work from??


cheers

bob

why dont you take it to a wheel alingment place?

Bump steer should be pretty visible - stand on the car with the bonnet off and bounce to see how much the wheels diverge....

atb

steve

[Edited on 28/6/04 by stephen_gusterson]

check daves comments in http://locostbuilders.co.uk/viewthread.php?tid=3285

mine did that till i changed the front springs,what poundage you got?

i had 275 lb at the front and it tramlined worse than my alfa,fitted 375 lb and its sorted all the probs out.
it felt like it was too hard,throwing the whole car across the roads when hitting pot holes etc,now its brilliant

John, sounds like you have fitted harder springs now for a better ride, the way you have written it, is that right ??

Jason

thats right,i was going to go softer still,good job i listened to other peeps

You had 275lb/in spring which were causing bangs on pot holes and skitish handling, you have now fitted 375lb/in springs instead.

I make this about 1/3rd stiffer than before.

So as deckman was suggesting you have gone HARDER not softer to aleviate handlng and ride issues???????

As syd suggests most locosts are rather stiffly sprung in the first place. In my experience skittishness can be reduced by reduction in spring rates, removing a bit of toe, backing off on the stataic camber and moist importantly getting good tyre pressures, so i dont understand the going stiffer bit.....

It is of course possible that the issue you had originally was actually bumpsteer in which case limiting the vertical wheel movement by increasing the spring rate would make it a lot better, but at the expense of overall handling.

As i say im not entirely sure i understand, so any futher info would be of interest.

Cheers guys

theoretically, to a point stiffer springing would be better on a perfdectly smooth track, however on the road this doesn't really apply. Conrod's mk has a shortened rack so shouldnb't suffer too much from bump steer, having said that it does eem strange that going up in spring rates has improved the handling, so it could be bump steer related...

Ned.

stressy,excatley what i said,i was going to get softer ones but after many conversations i decided to try the harder ones,i was supprised when it worked,dont ask me i only drive it ps i now have a collection of springs surpluss

[Edited on 29/6/04 by theconrodkid]

Hi Bob,

Come and give me a ride in it and i'll sort it out for you FOC.

Kind regards,

Darren

I estimate that a 275# spring gets reduced to about 95# wheel rate mostly because of the mounting distance from the wheel (assumed 1/3 of the way along the wishbone and with Cortina uprights) and the mounting angle (assumed 30%).

If the unsprung weight per wheel is also about 275#, a 1G bump could put a car with short shock travel into the bump rubbers.

I think most people would be happier with a front spring rate of 300-350# (for the type of car I used for the estimate).

The rear's a different story. With a solid axle, a 175# spring also has a wheel rate of 175# for 2-wheel bumps. For 1-wheel bumps the wheel rate's a bit less because the springs are offset from the wheels. The wheel moves more than the spring, meaning that leverage is being applied to the spring.

I think rear rates can sometimes be lightened up a bit, but weight of the car, driver, passengers, road conditions, etc., are so variable that I don't want to throw out a number. IRS might need a heavier spring.

Pete

BTW, I'm guessing bump steer or toe for Bob's problem

Edit: Fixed a gross over-generalization.

[Edited on 29/6/04 by pbura]

I don't think springs should be the source of handling ills such as tramlining. Sounds more like a alignment issue. Springs should basically be there to hold the vehicle off the bumpstops, and to extend the shocks after bump. Naturally the firmer the shock the stiffer the spring, an unfortunate consequence. A thought....Do people tend to use heavy springs to counteract roll since many don't seem to use roll bars? Cheers!

I've got 325lb springs on the front. Zero toe in/out, zero camber. Bump steer should not be the problem if you have MK modded rack as I have.

The big surprise for me was how low the dampers are set, try starting at 4 or 5 clicks and working up, front and rear. Also get the tyres started at 18PSI.

The only moan I have about my Indy is the low self centreing action, but this seems to affect lots of other LSIS.

TYRE PRESSURES ?????

Try about 14 to 20 psi

20 front and 18 rear seems best,any softer and they get a bit loose

I've got the same spring rates as conrod using the gazmatic coil overs and the heavy pinto lump,it does drive nice and seems to be getting better with less pressure in the tyres as people have said.

My set up is as zetecs regarding toe in and camber,i'm very pleased with the ride.

oh tyres are 15" 195/55

hmmm, spring rates!!! There's a can of worms!!

On bumpy roads (i.e. English roads) soft is best, but only works with good dampers. With soft springs the dampers travel a lot more, and therefore fade much more quickly.

As a guide on the really soft spring front, my autograss car (which only runs offroad, but on very bumpy tracks) which is mid-engined so not quite the same, uses 120lb front springs and 200lb rears, thats with a VX XE 16v engine in the back. It handles very well on these. This car weighs about the same overall as a lightish seven (around 500kg)

My rwd Peugeot 205, which weighed around 875kg, used 200lb springs on the front and 180lb on the back.

My Opel Manta used 400lb on the front and 160lb on the back but this weighed 1075kg and was very front heavy.

To use low springrates you need correctly sized anti-roll bars and good dampers, but in my opinion (after working on a good few competition cars over the years) soft is the way to go on anything that is not on slicks on a perfectly smooth track.

Look at rallycross cars, these are ridiculously softly sprung, and have very little in the way of anti-roll bar poundage, but they handle on any surface, especially if it's bumpy, but again, look at the quality of the dampers used, cheap ones would go off after a couple of corners.

Before deciding on spring rates, give consideration to what the springs are doing. In many cases, particularly when static weight is low, raising spring rates simply makes the tyres do more springing, and unfortunately the tyres have very little in the way of damping, meaning that wheel control is reduced, and handling compromised.

Softer springing gives the job of wheel control (rather than just propping up the car) back to the spring, enabling the wheel to follow the lumps and bumps in the road much better.

All that a car's "handling" does is present the best possible tyre contact patch to the ground at all times. As you can read in many books, this is always a compromise between controlling the roll motion of the car and the pitch motion of the car in order to keep the tyre square to the ground.

Soft springing allows the wheel to remain in full contact with the ground for more of the time over bumps, good roll control then allows the square face of the tyre to remain in good contact with the ground during the roll that is caused by using the soft springs.

I have had enough now so won't go into camber change and all those complicating factors but soft is best, given correctly rated anti-roll measures (not necessarily anti-roll bars in their conventional sense)