wheel hop continued

[locostv8]

The rear was changed at the same time.

[slngsht]

The rear was changed at the same time.

 

Yes, that is true.

[Al N.]

Does this belong in Tech?

[xflow7]

Does this belong in Tech?

 

Technically. :jester:

[slngsht]

The first reaction is bad shocks, but it sounds like these are new. So....You may be running too much compression. Too stiff and you take out the function of the shock in absorbing the bumps. If the front starts jumping, it doesn't matter how much rebound you have dialed in.

 

What is the condition of your rotors - any chance they are warped or have brake compound built up?

 

I backed off on the compression, and took her for a short drive. This seems to have cured it. BUT, today was a much cooler day, and I didn't have enough time to warm the tires up. So it's possible lower traction due to cooler tires was the reason they didn't hop.

[SR27.Seth]

Sounds like everyone else has had their guess so I will throw mine in too-

First- what makes a front wheel hop off the ground is the stored energy that is thrown into the front components under heavy braking, remember- the coil springs are not the only springs on your car: the tires act as springs as do any front suspension members under bending load. The weight transfer that occurs loads up all of these springs. So where does the energy go?- Well, the coil spring energy should be absorbed by the shock travel- the key is travel- if a shock is not extending or compressing then it may as well be a block of steel. So measure your shock travel with the simple zip-tie method and make sure your not bottoming out or just so stiff that the shock is not traveling. Another question is the 'line' of the shock: is the energy being transfered properly from the center of the tire through the upright and to the bottom shock mount? if anything is flexing (or if the geometry is skewed) then the shock turns into a strut (unless it is mounted on spherical bearings) and you will be creating force and therefore friction between the two halves of the shock- not good. As for the unsprung masses- what can you do- spend a million dollars on 10lb magnesium 17" wheels plus 2 piece carbon rotors and titanium piston calipers and of course play with tire pressures!

[slngsht]

Sounds like everyone else has had their guess so I will throw mine in too-

First- what makes a front wheel hop off the ground is the stored energy that is thrown into the front components under heavy braking, remember- the coil springs are not the only springs on your car: the tires act as springs as do any front suspension members under bending load. The weight transfer that occurs loads up all of these springs. So where does the energy go?- Well, the coil spring energy should be absorbed by the shock travel- the key is travel- if a shock is not extending or compressing then it may as well be a block of steel. So measure your shock travel with the simple zip-tie method and make sure your not bottoming out or just so stiff that the shock is not traveling. Another question is the 'line' of the shock: is the energy being transfered properly from the center of the tire through the upright and to the bottom shock mount? if anything is flexing (or if the geometry is skewed) then the shock turns into a strut (unless it is mounted on spherical bearings) and you will be creating force and therefore friction between the two halves of the shock- not good. As for the unsprung masses- what can you do- spend a million dollars on 10lb magnesium 17" wheels plus 2 piece carbon rotors and titanium piston calipers and of course play with tire pressures!

 

Seth, I think my shock settings were too stiff... backing off on compression was a huge help and the problem is much less pronounced, although at the end of my autox runs yesterday, when I slammed the brakes, I could still feel it. I think playing with the shock settings will cure this problem.

[Davemk1]

Cool. It totally makes sense when you think about it.

 

There is going to be movement up there most any way you look at it. If the suspension is too stiff then something else will take up the load.....like the tires or chassis flex. In either case it's undamped movement with a very rapid rebound. So by softening up the suspension you are allowing it do do it's job so the other stuff can do the jobs they were intended to do.

 

Cool.

 

Dave

[Obi wan]

 

Heh, that's where I've been playing... But my QA1 shocks are 20 out of 24 clicks on rebound and compression. If I jump up and down on the front of the frame, it doesn't even move anymore :lol:

 

My springs are 425 lb/in now... was running 375 until today. I forget my lever ratio, but it is approx. 1.7:1... so my real spring rate in the front is 250 lbs/in now.

 

 

And what's the weight of your car ? (250 lbs in the front is what I have on mine but that's good for the track, not for the road on a 540 kg 's car)

 

Second thing : if your car weight is more or less around 550-600 kg, I think your tires pressure are to high (it should be around 18 psi : 1,2 kg )

 

[slngsht]

I can only wish it was 600 kg.

 

My car should weigh right about 1750 lbs (about 800 kg) without driver in its current config.

 

At the last autox I ran about 18 PSI.

[jbanker]

Mazda,

 

Have you played with your front to rear brake bias adjustment? Maybe you need to dial in a little more rear bias. Just a thought.

 

Jack

[slngsht]

I have not. I will have to do that. backing off the compression on the shocks made a huge improvement. I'm starting to think maybe my car will benefit from a sway bar too.

[JBH]

Mazda:

 

I went back to the beginning of this thread to see you are running QA1 shocks. I have a few questions:

1. What model shocks did you select?

2. Are the compression and rebound separately adjustable?

3. Can you adjust the gas pressure?

4. Did you look at other shock manufacturers and why did you select QA1?

 

Thanks - I am looking at different options and I could use your insights. Also, I run Moton Club Sports on my Porsche 964Turbo so I have a little experience adjusting and tuning shock systems.

 

WRT sway bars, I look at them as a means for fine tuning your suspension system. The springs and shocks are the core of the system - a sway bar offers a means for tuning in the suspension (balancing under and over steer behavior) once you get your springs and shocks set. I am not saying it is true in your case, but if wrong choices are made in spring rates or shock settings, a sway bar may have limited benefit.

 

 

[slngsht]

Mazda:

 

I went back to the beginning of this thread to see you are running QA1 shocks. I have a few questions:

1. What model shocks did you select?

2. Are the compression and rebound separately adjustable?

3. Can you adjust the gas pressure?

4. Did you look at other shock manufacturers and why did you select QA1?

 

Thanks - I am looking at different options and I could use your insights. Also, I run Moton Club Sports on my Porsche 964Turbo so I have a little experience adjusting and tuning shock systems.

 

WRT sway bars, I look at them as a means for fine tuning your suspension system. The springs and shocks are the core of the system - a sway bar offers a means for tuning in the suspension (balancing under and over steer behavior) once you get your springs and shocks set. I am not saying it is true in your case, but if wrong choices are made in spring rates or shock settings, a sway bar may have limited benefit.

 

 

At the point I bought the QA1's I was not anywhere near the point of tuning the car... I needed to get my piece of junk on the road. I stumbled on QA1 because Rotus used to use Carrera shocks, which is now QA1.

 

These do have seperate adjustments for rebound and compression... 24 clicks on each.

 

I don't recall the model number of the shocks. I don't see an obvious way of adjusting the pressure in the shocks.

 

The reason I brought up sway bars, is that it seems to let the shocks do their dampening, I need some wheel travel, however, I would still like to keep body lean under control, and sway bars would help me achieve that. Perhaps my roll center is too far from my center of gravity?

 

I am NOT experienced in this stuff, so my advice is... um... free, and you know what they say about that...

[WestTexasS2K]

Maybe a little stiffer front springs will also help reduce the weight transfer from back to front. Helping keep the rear planted if you run out of shock adjustment.

[slngsht]

Maybe a little stiffer front springs will also help reduce the weight transfer from back to front. Helping keep the rear planted if you run out of shock adjustment.

 

That was the first thing I tried... went from 375 to 425. I think it made some marginal improvement, but biggest improvement was backing off the compression so far.

[WestTexasS2K]

I run 600s in the front and my car is a little lighter than yours. I think you could stand a bit more up front. Are you using sway bars?

[JBH]

Ok...I am surprised or maybe just confused. Actually, suspension settings for different cars may be a good topic for a separate thread, but some of that has been covered here and there

 

Since you brought it up, My SLR is set up with 175 lb/in in front with progressive rears (not sure of rate), so it seems surprising you would run spring rates of 425 or as high as 600! Is this just differences in geometry between our cars?

 

My car exhibits little roll and is nicely balanced under braking and through turns. I might go as high as 225, but after that I start to worry the car gets too stiff and will become unsettled. I am not sure if some of Mazda's problem is being too stiff in front.

 

Just for reference, I'll list the specs on my car setup:

Springs F/R: 175/Progressive

Bump Rubber F/R (mm); 42/42

Dampers F/R: Bilstein M1/M1

Camber F/R (degrees): 1.3/1.8

Toe in F/R (mm): 1.5 / 2.0

Castor (degrees) 4.7

Ride Height F/R (mm): 120 left, 122 right /145 left, 136 right

Rollbar diameter F/R; 18mm / 1/2"

Wheelbase F/R: 2225 / 2330

Tires CR500 F/R: 175/55-13 / 205/55-13

Wheel width F/R (inches): 6.5 / 8.5

[yellowss7]

JBH, check out the Tire warmer thread down in Autox. Davemk1 shared the spring rates of his Birkin...

 

"For what it's worth I'm running 350# springs in the front and 175# in the rear. If I were to change anything i'd drop them by 25# all round but It's not in the budget at this point. That said the set up works very well on my car as it sticks very well and has near ideal balance."

 

My Superlight is sprung like yours. Interesting. Tom

 

 

 

[WestTexasS2K]

I would suppose that the location that the shocks are mounted would have alot to do with the spring rate. If the leverage arm is shorter a lighter spring would act stiffer than the stiff spring with a little more leverage applied. The mounting point on the control arm and the angle of the shock would effect spring rate too. JBH you are also running a sway bar. The Ultralites do not. That is why I had asked if he used a sway bar. If you are running a sway bar a lighter spring could be used depending on the size of the sway bar. I was simply suggesting that if slgsht hadnt tried it, to give a look. If you run out of shock adjusment then you can start to adjust spring rates instead of replacing or revalving shocks which is more expensive way to do it. Springs are realatively cheap . It sounded like slgsht had used up the shock adjustment just trying to give him somewhere else to look. What do I know Im probably all wrong.