geometry and spring setup

stumo

stumo

Active Member
Trip said:
I just finished off doing the castor mod this eve. It was a very straight forward job to do. :)

Next will be getting my height in order which i'll go for the aggressive 15mm difference front/back. If everything goes to plan early next week i'll take it for a laser alignment and off for more testing





That is exactly what i am suffering. On power while going round a roundabout, Its like the car is RWD and the rear wheels are pushing the car straight forward ignoring front wheel direction. Its like the front wheels are hovering in air :oops: .

With my other car which is RWD, in a similar situation where i suffer from understeer while on power in a long sweep turn, i just tap the throttle (release and press again) to unbalance the rear and off it goes to oversteer :lol: . The Pulsar stayed put and kept on understeering .:doh:
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try the rear toe set to toe out 0.5deg as well as the setup above (as well as toe out at the front too)
 
DanDud

DanDud

Member
keastygtir said:
37psi is the recommended pressure on the original 14" wheels, you should have this at least in a lower profile tyre
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On 14" wheels maybe, but do you realise that after a few laps on a track or a long hard B road the pressures will on average rise around 4psi.

41PSI hot is far too much.

You want to be around the 36 - 38 mark hot.

On the race cars i use to work on we ran them 15psi cold so they would be 20psi hot.
I know these cars only weighed 400 - 500kg's. But the principles the same, and anything over 40psi is far too much pressure in a road car unless it weighs a lot more than an R.
 
DanDud

DanDud

Member
Those are cold pressures Keasty?

Yeah it is, never noticed those threads before. I think a lot of it is down to the different suspension setups people have, combine that with different tyres and pressures and handling and feel will vary a lot.

Trial and error is the way to go, for example iv found that if my rear pressures are the same as the fronts the back end of the car feels looser. Which suits me, but may not someone else.
 
Trip

Trip

New Member
It comes down to personal preference at the end of the day. There are many factors you should consider, mainly make and model of tyre, use and weight of car.

I know for certain because i was instructed from Toyo motorsports division in Italy (which happen to be my sponsor) that I (for my setup) should run the R888 between 25 and 28 psi cold. If they are wrong, i am wrong :).
 
keastygtir

keastygtir

Well-Known Member
Those are cold pressures mate yes.

I am sure that toyo know more than me mate!

I might well try a bit less in the rears tomorrow
 
M

MarkTurbo

Well-Known Member
keastygtir said:
37psi is the recommended pressure on the original 14" wheels, you should have this at least in a lower profile tyre
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37 psi :der: I've never put that much in any low profile road tyre, and its way too much for something like an R888 ;-)

Trip, i'm using the same size R888's as you and i'd start with 28psi front/26psi rear cold pressures for short sprints or hillclimbs
 
keastygtir

keastygtir

Well-Known Member
This is what I find works for me (and some other people) with my 15"s with normal road use. So it my opinion based on other peoples advice and personal preference.

I not sure the wan*** symbol is entirely called for.
 
M

MarkTurbo

Well-Known Member
keastygtir said:
I not sure the wan*** symbol is entirely called for.
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I wasnt aware there was a wanker symbol on this site :? If there was i'd use it more often :lol:

The original question was about a hillclimb set up with 16" semi slicks, so suggesting using the same pressure you use on the road for your 15's is a bit pointless really ;-)
 
keastygtir

keastygtir

Well-Known Member
My response was more toward the understeer/steering feel issues the OP was discussing, which I have some experiance of similar problems but I agree that I dont have a comparable setup.
 
fubar andy

fubar andy

Moderator & N/W Rep
Staff member
Slicks 25 psi (cold) all round - no graining
Road tyres 30 psi (cold) all round - no graining

The chassis is crap compared to today's modern motors. If you compare the modifications we've done today to what was available back then, its leaps ahead of its game.

The simple fact is that the car is always going to under steer unless you are running say slick tyres. I’ve dialled out most of my under steer, but if I push it hard enough then it will let me know and I just back off.
 
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Trip

Trip

New Member
MarkTurbo said:
The original question was about a hillclimb set up with 16" semi slicks, so suggesting using the same pressure you use on the road for your 15's is a bit pointless really ;-)
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Pointless indeed since tyres would also work work at a lesser teperature. With the extended diet i've done on my car, it should be close to 1000Kg so you cannot really compare the pressure for a full weight pulsar either.

My problem is that my coilovers are already hard for a pulsar, removing more weight from car only made it worse :sad: .
 
campbellju

campbellju

Moderators
Staff member
Trip, whether hot or cold, you use your tyre pressures to set the shape of your tyre. There are always different tyre compounds available to change wear characterisitcs.

As the front of our cars are heavier then theory and most people's experience is to add a few psi extra in the front. At 34psi front, 32psi on my road car that is not stripped, the tyre wall is the same height front and back. This means whether right or wrong its about the same shape/profile.

As a general rule, try to avoid handicapping grip at any end to compensate for a poor reaction at the other end.

Toyo are suggesting 25psi which for me given the front of cars are nearly double the weight of the back doesn't sound right. Mark is using 28/26 cold temps but I expect Malta gets warmer than UK. Tyre pressures are easy to play with and you should always do this as a starting point. Try 26/24 and 28/26 and see which you prefer. This is gives you a baseline.

I moved from 4/3 springs to 5/4 springs to give a more over steer biased car that is still usable on B roads. Your 8/7 springs are even more biased to oversteer. They could be an issue but I would change them last rather than first. The stiff springs is why I think you need to raise your front pressures a little.

The rear ARB could be set to the stiffest setting and that might help. I would use that to balance the ride height difference front and rear that others have already suggested. If you have too much difference and the rear is twitchy you could always back the ARB stiffness off.

The rear spacer I would lose for the moment. It will improve rear end stability which will also reduce turn in. A 5mm spacer is quite small so you could always play with it again at the end.

Geometry is very important. Do the castor mod with a rough camber mod. Our cars don't run enough castor. The whiteline bush adds negligble castor, Whiteline say 1deg but I think that is with rounding up. I'd agree with what Stu says, try the -2.2degs Stu suggests as a starting point with the castor mod. Leave toe zero all round until you have understood the rest of the cars characterisitcs. Like the spacer, it can easily be done at the end.

As side from the fact that you don't know what your geometry is set to, my guess for the cause would be damper settings. Everytime I've made a major change to the cars balance or setup I've needed to adjust the dampers. Often I've thought I've completely messed it up until they were tuned in. What setting are your dampers set too? They may be too stiff alll round or out of balance front/back. Dampers setttings are a lot down to driving style but try to use as little as possible rather than starting from the max and backing off.

Good luck with trying things out and be patient. Everytime I change things significantly it always takes me a while to get everything balanced again. There is no magic wand or perfect setting for all conditions.

Jim
 
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Trip

Trip

New Member
Thanks Jim,

for the damper setting, i've only tried it with soft front and hard rear. A 5mm spacer was needed on the back to prevent tyre hitting the springs. I can always put a 5mm on the front to get it balanced.

what do you mean by: As a general rule, try to avoid handicapping grip at any end to compensate for a poor reaction at the other end
 
campbellju

campbellju

Moderators
Staff member
Sorry Trip, not very clear. You could increase the relative grip at the front by reducing the level of rear grip. You are better as a general rule to optimise the available grip at all 4 corners and shift the weight (not mass) at the right time with ARB's, springs and dampers.

Easier said than done.

What damper settings have you used, ie number of clicks front and rear.
 
PobodY

PobodY

Moderators
Staff member
PobodY said:
I'm sure that someone who knows how to do this properly will post shortly. It will probably come down to "use 5 clicks on your rear shocks, but only 3 clicks on the front ones".
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Jim, you'd be someone who knows what they're doing... and we've finally got to "how many clicks"...

I'm not saying that I'm right, just that I thought we might get to this.
 
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