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Unespected handling due to shock oil change - please explain

Unespected handling due to shock oil change - please explain

Old 10-06-2003, 11:14 AM
  #16  
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Tires/inserts are the same front / rear - schumacher Dragon with sorex type A firm and double belted with gaffa tape.

Springs front: HPI green = 480 gF/mm
Springs rear: HPI pink = 272 gF/mm

Piston number 5 and shock oil 80, that equals 60 wt with stock pistons. Currently 70 wt front.

Shock position is stock front and rear.

Camber links front is stock, but rear they are the longest possible, yet parrallel to the a-arm.

Downtravel front/rear: 2/1 mm rear.

Ride hight front/rear: 6/6 mm

10 degree caster, zero kick up.

Toe front/rear: 1/2 deg.

Body: HPI ford Mondeo (handling pretty close to HPI Stratus)
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Old 10-06-2003, 11:36 AM
  #17  
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Originally posted by Cole Trickle
Tires/inserts are the same front / rear - schumacher Dragon with sorex type A firm and double belted with gaffa tape.

Springs front: HPI green = 480 gF/mm
Springs rear: HPI pink = 272 gF/mm

Piston number 5 and shock oil 80, that equals 60 wt with stock pistons. Currently 70 wt front.

Shock position is stock front and rear.

Camber links front is stock, but rear they are the longest possible, yet parrallel to the a-arm.

Downtravel front/rear: 2/1 mm rear.

Ride hight front/rear: 6/6 mm

10 degree caster, zero kick up.

Toe front/rear: 1/2 deg.

Body: HPI ford Mondeo (handling pretty close to HPI Stratus)
I'm no expert on the Pro 2, but I can already see a few inconsistencies in your setup.

The front spring rates are almost double those of the rear - this is unusual, HPI normally recommend only one grade difference. Wheel rate is also important, and I think your rear probably feels much softer than the front at the wheel. Most cars are set up with fairly similar wheel rates front and rear, or with a stiffer rear wheel rate.

Secondly, it's a mistake to assume that a certain piston is the "same" as another piston with a lighter/heavier oil. Static damping may feel the same, but once the car gets going, the "pack" and other dynamic damping phenomena will be very different. What you have is piston 5 and 80wt - 60wt oil doesn't come into the equation.

Thirdly, your downtravel (droop) seems backwards. Normally less would be run on the front than the rear, or similar amounts all round, not less at the rear.

Fourth, I would ensure the camber link changes you've made still let the car gain negative camber as the suspension compresses, and not positive camber at any point in the suspension movement. Large differences in roll-centre front to rear also make a less consistent car (e.g. a short andled link in front, and a long parallel link in rear won't work well).

Everyone's opinion in car setup are different, but I would say...

1. Stiffen the rear springs to be closer in rate to the fronts (or soften the fronts, if the car lacks turn in).
2. Set the damping so the front and rear have a similar feel, nice and smooth (not springy, and not slow).
3. Increase droop all round to 3mm. This will make the car have more of a feeling of grip all round the track, and keep the wheels on the ground - it will also help stop some of the twitchy behaviour limited droop can cause. You can dial in less droop at a later date once you have the cars springing and damping set right.
4. Consider returning the camber link settings to standard.
5. Consider racing without the one-way, or adjust the radio for less steering. It seems to me that in an attempt to make the one-way work, you've comprimised the car's overall setup.

Without seeing your car it's hard to say, but I think that your tail has been rolling excessively at a slow rate, and lifting the inside wheel as well when you corner. This will give a feeling of low grip and a lack of responsiveness, especially later in the corner entry.
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Old 10-06-2003, 12:30 PM
  #18  
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Default Unexpected handling

Cole Trickle;

I think 'sosidge' stated it perfectly.

What you are trying to achieve is a Car that is perfectly balanced Front to Rear, which will be faster and ultimately easier for you to drive.
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Old 10-06-2003, 02:08 PM
  #19  
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Cole,

Often stability and grip are seen as one and the same.
They are not.

Although you might feel it like they're the same.

Well I'll try to explain with an example.
See it like this.
Your car has very soft springs, and very high grip tires.
Now I start exagerating. And a top heavy car.
It would have a lot of grip, but no stability.
It would hang in every corner, and stay hanging into this direction, until the weight starts to shift, then it might flip over to the other side.
It still would have grip but as you can imagine, it would not be stable.

I hope you got a little of what I try to explain.
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Old 10-06-2003, 03:27 PM
  #20  
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Default Re: Unespected handling

Originally posted by popsracer
Guys;

Are you mixing Tire compounds Front to Rear?

I personally do NOT like to mix compounds (except with Foams) as it is easier to keep a balanced set-up with the same Tires/inserts at both ends of the Car. Otherwise you need "Strange" set-ups that require stiffer Springs at the Rear than the Front and IMHO, the Car will be faster with the balanced set-up (though slightly harder to drive).
I run foams, either 40 shore all round or plaid/purple.
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Old 10-06-2003, 04:07 PM
  #21  
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Default Unconventional set-ups

fatdoggy;

Sorry my post was not directed at you personally.

Do you run a Front One-way also? If not that may give you the Steering that you need.
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Old 10-06-2003, 11:59 PM
  #22  
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If you put the one-way in, you increase the amount of front steering, entering and exiting the turn, that it tends to change the balance, all things being equal - ie. if your car is fine, then you put the 1-way in, you will have to adjust to regain the balance.

You could stiffen the front (take steering away from the front) or soften the rear.
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Old 10-07-2003, 04:38 AM
  #23  
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Originally posted by PizzaDude
Cole,

Often stability and grip are seen as one and the same.
They are not.

Although you might feel it like they're the same.

Well I'll try to explain with an example.
See it like this.
Your car has very soft springs, and very high grip tires.
Now I start exagerating. And a top heavy car.
It would have a lot of grip, but no stability.
It would hang in every corner, and stay hanging into this direction, until the weight starts to shift, then it might flip over to the other side.
It still would have grip but as you can imagine, it would not be stable.

I hope you got a little of what I try to explain.
That helped me, I think I'm on the right direction of thinking now.
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Old 10-07-2003, 05:14 AM
  #24  
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Thanks for the valuable input.

I see your points and are considering one of two: striagthen up the setup with or without the one-way.

Thing is, I really like the turn in with a one-way and on-power steering coming out of the corners, meaning earlier acceleration.

However, stability have been the problem. It aint a problem, when I practise, then I'm one of the fastest. But in races when the heat is on, I sometimes crash too often - not in every race, but yet too often.

I think I'll start with the one-way, and if it's too hard, I'll try with a traditional diff. By the way, that'll save 8 grams rotating mass.

Plan is to set down travel at 3 mm all around, get springs closer and set rear camber link to stock pos. See how it runs. If still lose in the rear (it've always been mid-coner), I'll try with thicker shock oil all around.

And now for some detailed questions:

Originally posted by sosidge
The front spring rates are almost double those of the rear - this is unusual, HPI normally recommend only one grade difference. Wheel rate is also important, and I think your rear probably feels much softer than the front at the wheel. Most cars are set up with fairly similar wheel rates front and rear, or with a stiffer rear wheel rate.
What is wheel rate?

I havent seen HPI's recommendation, is it in their faq? Originally, Dr. Diff suggested white progressive rear and yellow progressive front for carpet. That is 50 gF/mm or 3 spring rates different. But granted, mine is much more different.

I forgot to mention, I'm running anti roll bars, softest (pink) rear and hardest front (purple).


Secondly, it's a mistake to assume that a certain piston is the "same" as another piston with a lighter/heavier oil. Static damping may feel the same, but once the car gets going, the "pack" and other dynamic damping phenomena will be very different. What you have is piston 5 and 80wt - 60wt oil doesn't come into the equation.
I know about packing, that's the reason for running piston #5 and 80 wt, instead of 60. Our track got some bumps. On HPI cars going one piston number up, is equal to going 10 wt down - when talking regular (static) dampning.


Thirdly, your downtravel (droop) seems backwards. Normally less would be run on the front than the rear, or similar amounts all round, not less at the rear.
This is one point I have to re-check.


Fourth, I would ensure the camber link changes you've made still let the car gain negative camber as the suspension compresses, and not positive camber at any point in the suspension movement. Large differences in roll-centre front to rear also make a less consistent car (e.g. a short andled link in front, and a long parallel link in rear won't work well).
The camber links front/rear are relative close. At least front is stock and rear is only changed "one point" from stock - front and rear are both parrallel with the A-arms.


2. Set the damping so the front and rear have a similar feel, nice and smooth (not springy, and not slow).
This is the hard part, "feel" is a wide definition. Some guidelines like "springs from 150-250 gF/mm suits 40-50 WT" or something like that.


Without seeing your car it's hard to say, but I think that your tail has been rolling excessively at a slow rate, and lifting the inside wheel as well when you corner. This will give a feeling of low grip and a lack of responsiveness, especially later in the corner entry.
It would definately be nice, to race with guys like you. Probably fun and definately valuable to share some experiences.

Thanks for the help, I look forward to try it out.

Last edited by Cole Trickle; 10-07-2003 at 05:19 AM.
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Old 10-07-2003, 07:07 AM
  #25  
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Hi Cole,

Wheel rate is how stiff the suspension feels at the wheel itself. So a very stiff spring, mounted a long way in on the wishbone, will feel similar in "wheel rate" to a soft spring mounted a long way out on the wishbone.

Anti-roll bars are a funny beast in my opinion, I tend to set the car up without them at first, then fine tune the car with them, to take a little grip away from a certain end. I've only ever used them on a smooth carpet surface, cars ride the bumps better without them.

For HPI springs, I'm just repeating how the recommended setups tend to be.

By the way, going up 1 on the piston isn't the same as 10 wt - if you were running 30wt, would the damping be like 40 if 60 was like 70? No. Bigger hole pistons can work better for bumpy tracks though.

As for a "rough" spring/damper oil starting point, it's hard to be precise when not every piston/oil combination works the same. As a total guess, I would run the springs around 300g/mm with 40wt oil, the 500g/mm range with 60 or so. While you're experimenting with setup, it's better to have lighter damping instead of heavy damping, that way you can truly see what the springs are making the car do, without the damping giving a false impression.

I know what you mean about a car that's fast in practice, but less so in a race. On an empty track, I would choose to run my car with more oversteer, because then I can throw it around, and feel fast. But as soon as you put other cars on the track, the oversteering car is more likely to get hit as it drifts mid-corner. You also have to set the car up so it's driveable even if you're off the racing line, e.g if you're overtaking, or you get "rubbed". A bit of understeer is normally safer.
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Old 10-07-2003, 08:41 AM
  #26  
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Default Dr. Diff suggested

Cole Trickle;

These "suggestions' may have been made before the new 'Pro Linier" Springs came out.

If you are up to it. Try going to a more traditional set-up. Start by changing ALL 4 Shock Pistons to #3's. Then use some 45wt Oil in the Front and 40wt in the Rear. If the Car feels lazy, go up 5 or 10wt at each end equally.

The Yellow/White Spring combination may be a little stiff for running on asphalt. Even then there are several Springs inbetween for fine tuning.
Spring rate selection is always a compromise between Side Grip and Chassis roll. You want the least amount of roll, but not at the expense of Grip.

If you do try any of our suggestions, make sure to tell us how they worked for you.
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Old 10-07-2003, 08:54 AM
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Default One-Way tips

Here's a couple of things I've found about one-ways.

1. If you have too much freewheeling on tight tracks, put some 5000wt diff oil in the one-way bearings. It will slow down the freewheel without slowing down on-power drive.

2. Check your dual rate on your radio. Mine goes down to 65% with a one-way vs. 80% with a diff. That will calm the rear down a bit too. When i get ass-around a few times, I turn down the dual rate.
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Old 10-07-2003, 11:25 AM
  #28  
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Default Re: Dr. Diff suggested

Originally posted by popsracer
Cole Trickle;

These "suggestions' may have been made before the new 'Pro Linier" Springs came out.

If you are up to it. Try going to a more traditional set-up. Start by changing ALL 4 Shock Pistons to #3's. Then use some 45wt Oil in the Front and 40wt in the Rear. If the Car feels lazy, go up 5 or 10wt at each end equally.

The Yellow/White Spring combination may be a little stiff for running on asphalt. Even then there are several Springs inbetween for fine tuning.
Spring rate selection is always a compromise between Side Grip and Chassis roll. You want the least amount of roll, but not at the expense of Grip.

If you do try any of our suggestions, make sure to tell us how they worked for you.
You're right about that the suggestions is quite old and HPI have released some springs afterwards.

You're talking about asphalt, I'm running on carpet. However, there's a few bumps. So I think around white/yellow (300-350 g/mm) would be a good starting point.
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Old 10-08-2003, 11:10 AM
  #29  
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Originally posted by sosidge
By the way, going up 1 on the piston isn't the same as 10 wt - if you were running 30wt, would the damping be like 40 if 60 was like 70? No.
Hi sosidge

I dont understand this example?
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Old 10-08-2003, 11:12 AM
  #30  
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Default Re: Dr. Diff suggested

Originally posted by popsracer
If you are up to it. Try going to a more traditional set-up. Start by changing ALL 4 Shock Pistons to #3's. Then use some 45wt Oil in the Front and 40wt in the Rear. If the Car feels lazy, go up 5 or 10wt at each end equally.
Popsracer;

Is this suggestion for asphalt or carpet?
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