Shock oil weights

[richardmid1]

What weight shock oil is best for bumpy tracks? Roughly?

[Chrislong]

This question has not definitive answer as it depends on the piston, the car, the shock positions and springs.

BUT, any setup you find for 8th Rallycross is likely to suit bumpy, as bumpy is the nature of the class - smooth tracks are boring.

[rocketrob]

Originally Posted by Chrislong

This question has not definitive answer as it depends on the piston, the car, the shock positions and springs.

precisely

Originally Posted by richardmid1

What weight shock oil is best for bumpy tracks? Roughly?

there really is no good or "best" answer - only general rule of thumb is that the bumpier/rougher the track surface the lighter the oil, the smoother the track and larger the jumps the heavier the oil (comparatively speaking).

[Chaz]

Then it depends on how hot or to cold

[gnr racer]

Originally Posted by richardmid1

What weight shock oil is best for bumpy tracks? Roughly?

What vehicle are you running?
As has been said lighter oils are more suited to bumpy tracks & larger hole pistons, but then if you are running with BIG jumps v.light oils & large hole pistons may well make your car bottom out on landing

[richardmid1]

Thanks guys. I thought as much. Im running 50 weight at the moment which im guessing is quite heavy? Its a Caster ZX-1 with standard shocks. Ill try some 40. I was on a really bumpy track the other day and although I had lots of saggy suspension the car was bouncing about like the suspension couldn't move fast enough to absorb the bumps.

[Chrislong]

Originally Posted by richardmid1

Thanks guys. I thought as much. Im running 50 weight at the moment which im guessing is quite heavy? Its a Caster ZX-1 with standard shocks. Ill try some 40. I was on a really bumpy track the other day and although I had lots of saggy suspension the car was bouncing about like the suspension couldn't move fast enough to absorb the bumps.

That could be:
too thick oil
too small/few holes in piston
too light spring
or a combination of the 3.

Ideally, find somebody else running the Caster on similar tracks and see what they use in there shocks (Piston, Oil, Spring, Position) and copy that as a starting point.

[richardmid1]

Are stiffer springs generally shorter? If I add spacers to stiffen the springs it increases ride height which I dont want to do.

[Chris Doughty]

pre-load to adjust ride height is different to running a stiffer spring.

you choose the spring rate you want to get the right stiffness and then adjust the pre-load to get the correct ride-height, which on most cars a base setting is so that the driveshafts are paralell to the ground, maybe a little bit lower than that if its high grip

[richardmid1]

Total newbie here, how do I adjust pre load?

[Chrislong]

Originally Posted by richardmid1

Are stiffer springs generally shorter? If I add spacers to stiffen the springs it increases ride height which I dont want to do.

See the bold in your post I have quoted here, this is Preload. Spring rate is totally different.

You will have to replace the springs to the rate required. This is why they are colour coded. As I said - find somebody else who's been running one and checkout there setup.

[richardmid1]

Gotcha! Thank you. Also, if I put thicker oil in the center diff will that give me more drive to the rear? At the moment the fronts are spinning up under hard acceleration.

[Chrislong]

Yep. But again - try and find out what other people are using and copy. If it is transferring so much drive to front, then thicker centre diff oil will reduce this.

You want the balance to be, generally, thick oil in front so to pull out of corner without 'diffing out', equal or thicker oil in centre so not to transfer all drive to the front and waste power wheelspinning, and thin oil in the rear so it works as a diff and can drive through a corner (not drift). I am using a Kyosho MP9 and I have got 7k 9k 2k in it (this is the way diff oils are stated: front, middle, rear). But this is particular to my car, your car is very likely to need different oils but same sort of balance.

Can I recommend to you the Hudy setup book. It really is a bible of information for things like this.

[richardmid1]

Great info, thanks. I have got some 7k oil to try in the front and center, at the moment I think they are empty with just a little grease in!

[dave g]

with the zx1 if your on grass/high grip try 7-7-3,if the grip is lower try 5-5-2

[richardmid1]

I put some 7k in the front and center today and tried it on dusty tarmac with some old tyres, before on this surface with these tires I could not get the back end to break free at all cos it would just understeer like a bitch! Now, if im not careful with the throttle it will do a 180 on the spot! What a difference! Should be good on high grip tracks with some new tyres. What tyres do you recommend for astroturf?

[Chrislong]

There are a lot of options for Astro. For loads of grip try Schumacher Yellow Minipins, and trim pins off 1 row each side at a time to reduce grip.

I like Schumacher Minispikes in Yellow, they provide high grip, but last a little longer. They tolerate a little more rain than the Pins do too.

Hobao Angle spikes, safe all rounder. Wet or dry.

[richardmid1]

Can you simulate different spring rates by the angle of the shocks on the shock towers?

[dave g]

yes and no lol

what it does is change the leverage point on the spring and this affects how the spring feels at the start of travel and to where it becomes coilbound vs the uptravel, and it affects the piston speed.

so you can make the spring feel soft initially then get progressively harder faster or slower.

the spring will feel stiffer on the outside of the wishbone vs the inside of the wishbone,but the piston speed will change as the shock will travel further for the same wishbone movement.


have a look on the hudy site there is an excellant setup guide on there to download and it should help a little more.

[rocketrob]

Originally Posted by richardmid1

Can you simulate different spring rates by the angle of the shocks on the shock towers?

yes - as shocks that are more laid down tend to have more of a progressive performance characteristic, while shocks that are mounted straighter up and down tend to perform stiffer

no - in the fact that just mounting your shocks at a different angle doesn't make up for not buying additional spring sets


utlimately it comes down to the fact that shock oil, springs, and mounting angles are all tuning aids - and the trick is to try different options to find which works best for where you're racing and your own driving style.