Spring Rate Changes

[thewheelerZ]

I am thinking that we may be able to use stiffer springs. The car feels pretty well set up, but we have gone to a wider tire and it is starting to feel like it is rolling too much. Currently we use off the shelf Yonaka coilovers with 8 and 6 kg (approx 450/350 lb) springs front and rear.  Mazda 626, V6 with about 65% (!!!!) of the weight on the front axle. 

 

I like the the way it drives with a tendency to understeer but fairly well balanced and will rotate when provoked. But I could do with slightly more spring (relatively) in the rear to make it a BIT more loose to drive. 

 

So a couple of qustions:

 

1) is it as simple as upping the spring rates in step with each other? I.e. Add 20% rate to front and rear.  How much increase could be too much for the shocks?

 

2) how much spring rate is enough to make a noticeable difference. Would 10/9 kg springs be in the right general rate?

 

pic for attention, but also will it be any faster with stiffer springs?

 

Edit, side note: why can't I insert pics into a post anymore?

Edited August 2, 2017 by thewheelerZ

[JDChristianson]

With the wider tires did you go to wider wheels?    Would seem like a bit stiffer would be worth trying, with a bit larger increase in the rear vs front

[Xph]

 

Net net, is you want the softest springs you can run which wont bottom out your suspension.  that last little bit is all about ride height...  if you want to control roll, then use a roll-bar and or suspension geometry to adjust your roll center.

Edited August 2, 2017 by Xph

[LAMR2]

That entire video is about road cars going over bumps. He even talks about how it applies to road cars but not necessarily race cars.

[Xph]

2 minutes ago, LAMR2 said:

That entire video is about road cars going over bumps. He even talks about how it applies to road cars but not necessarily race cars.

 

Well the video is about the theory...  in a race car you control more variables than a street car, you expect higher loads..  most "race cars" use specialty tires, with different sidewall characteristics which also come into play in the suspension design.

 

However, the principles are all sound...  you run the softest springs you can which wont bottom out your suspension...  once you identify the corner with the greatest need (usually one of the fronts) you then work on the other corners to balance out the car...   then valve the shock to control the spring rate, and add bars as appropriate...  (all wildly over simplified of course)...

 

But the simple fact remains, race cars only run springs as stiff as they "need"... anything more makes you slower...  the key is to not "shock the tire"  allowing it to keep contact with the track surface and to have as linear of a load change as possible through the course...  linear load changes result in you being able to run closer to the traction limit of your tire.

[Bandit]

3 hours ago, Xph said:

 

Net net, is you want the softest springs you can run which wont bottom out your suspension.  that last little bit is all about ride height...  if you want to control roll, then use a roll-bar and or suspension geometry to adjust your roll center.

 

Get a swaybar.

 

That's a 4k with a ten inch arm. A bit much for 200tw tahrs. 

 

I think. May try.

Edited August 2, 2017 by Bandit

[enginerd]

4 hours ago, thewheelerZ said:

I am thinking that we may be able to use stiffer springs. The car feels pretty well set up, but we have gone to a wider tire and it is starting to feel like it is rolling too much. Currently we use off the shelf Yonaka coilovers with 8 and 6 kg (approx 450/350 lb) springs front and rear.  Mazda 626, V6 with about 65% (!!!!) of the weight on the front axle. 

 

I like the the way it drives with a tendency to understeer but fairly well balanced and will rotate when provoked. But I could do with slightly more spring (relatively) in the rear to make it a BIT more loose to drive. 

 

So a couple of qustions:

 

1) is it as simple as upping the spring rates in step with each other? I.e. Add 20% rate to front and rear.  How much increase could be too much for the shocks?

 

2) how much spring rate is enough to make a noticeable difference. Would 10/9 kg springs be in the right general rate?

 

pic for attention, but also will it be any faster with stiffer springs?

 

Edit, side note: why can't I insert pics into a post anymore?

While all of this theory stuff that has been mentioned above is nice, it's a different story in ChumpCar if you have limited points. Making the best of what you've got is a fun engineering challenge. 

 

Yes, more spring rate will help to reduce roll. Try some higher rates and see what happens. Then try something else. Keep tinkering. Have fun with it. 

 

Just make sure sure you can undo the changes if handling gets worse!

Edited August 2, 2017 by enginerd

[DRVOLKS]

You should try some thing like this

http://www.ebay.com/itm/INTEGRA-SPRING-RUBBER-3-4-TALL-RED-HARD-COIL-OVER-SPRINGS-TYPE-W-HANDLE-RACE-/381283127331?hash=item58c63ed023:g:ThgAAOSwBLlVb2gc&vxp=mtr

I use a few different  ones to dial in the car when scaling it and at the track . and below is my rollcenter now 

Bob Mann

www.DRVOLKS.com

bobtec@comcast.net

[Bandit]

3 hours ago, enginerd said:

While all of this theory stuff that has been mentioned above is nice, it's a different story in ChumpCar if you have limited points. Making the best of what you've got is a fun engineering challenge. 

 

Yes, more spring rate will help to reduce roll. Try some higher rates and see what happens. Then try something else. Keep tinkering. Have fun with it. 

 

Just make sure sure you can undo the changes if handling gets worse!

I love old school! 

[mender]

1) Only part of your roll resistance comes from the springs, so changing them proportionally won't maintain the car's balance unless your springs and bars were perfectly matched before the changes; unlikely but it might. Better to set up your spring/cycle rate then tune the handling balance with sway bars (actually anti-roll bars. Hmmm; what would happen if someone placed an anti-roll bar inside the car next to the roll bar ... )

 

2) Most people can't detect less than a 15% difference in overall cycle rate (bounces per second in the vernacular) but can detect a 15% spring change in one end.

 

A good target is around 2 cycles per second with the rear being slightly higher. There's a fair bit to be said about rapid recovery from transients; most people are more comfortable with a car that settles quickly than one that floats. Tires seem to have an optimum range as well. This might be of interest:

http://www.smithees-racetech.com.au/performancefactors.html

Edited August 3, 2017 by mender

[mender]

9 hours ago, Xph said:

 

Net net, is you want the softest springs you can run which wont bottom out your suspension.  that last little bit is all about ride height...  if you want to control roll, then use a roll-bar and or suspension geometry to adjust your roll center.

The premise in the video that you have a spring that reaches either end of its travel with 0.40" of wheel movement is a little hard to swallow, at least for club racing. In actuality, under normal circumstances the wheel with the higher rate will arrive at the track surface in the dip sooner than the lower rate one.

 

Recovery time is reduced by higher spring rates as long as the corner isn't under-damped. Weight transfer time decreases with higher spring rates, which in terms of achieving a neutral or average corner weight is better. A poorly set-up car will have trouble maintaining a specific ride height, resulting in unneeded weight transfer and tire loads during the time that is required to return to ride height, as seen by a car that drops almost to the track then rebounds or one that gets lifted by a bump or curb.

 

Skiers talk about a quiet upper body when doing moguls. Watch what happens when they either compress too much or get bounced up: longer recovery time, sometimes in the hospital.

 

A question asked of me by a very smart chassis guy: if you increase your spring rate, how should you adjust your shock in compression and in rebound?

Edited August 3, 2017 by mender

[tommytipover]

10 hours ago, mender said:

A question asked of me by a very smart chassis guy: if you increase your spring rate, how should you adjust your shock in compression and in rebound?

 

There is the key. I don't think I'm smart enough to answer but my gut tells me you'll need more damping in both directions with a rate increase. I think most of us want more rate than our off the shelf, non-adjustable shocks can damp but as a compromise, can get away with a little more rate than is "textbook proper"

[Xph]

1 minute ago, tommytipover said:

 

There is the key. I don't think I'm smart enough to answer but my gut tells me you'll need more damping in both directions with a rate increase. I think most of us want more rate than our off the shelf, non-adjustable shocks can damp but as a compromise, can get away with a little more rate than is "textbook proper"

 

Some of us search for minivan or other sedan shocks which can be used with slight modification for our application, allowing us to control stiffer springs.  Its also possible to modify the motion ratio of your shock in chump, moving the mounting points on the control arms (for some cars)...  which changes the effective rate of the spring and shock without needing to change the spring and shock itself.

[mender]

48 minutes ago, tommytipover said:

 

There is the key. I don't think I'm smart enough to answer but my gut tells me you'll need more damping in both directions with a rate increase. I think most of us want more rate than our off the shelf, non-adjustable shocks can damp but as a compromise, can get away with a little more rate than is "textbook proper"

HInt: resistance to wheel movement changes with spring rate.

[JDChristianson]

1 hour ago, mender said:

HInt: resistance to wheel movement changes with spring rate.

These are the black art sort of things that keep even F1 teams with all the kings men and such testing the cars on track with real drivers.  If it were easy surely they would have the technology to just calculate the right answer and skip testing 

 

 

[tommytipover]

3 hours ago, mender said:

HInt: resistance to wheel movement changes with spring rate.

Ohhhh, so less bump more rebound?

[mender]

5 hours ago, tommytipover said:

Ohhhh, so less bump more rebound?

Yes, as a starting point. It's good to understand trends and how they can affect other things to try and avoid tolerance stacking.

 

As JD mentioned, despite having seven post shakers to run the car through its paces in the lab and getting things within a reasonably small range, track testing is the final answer.

Edited August 3, 2017 by mender

[mender]

4 hours ago, JDChristianson said:

These are the black art sort of things that keep even F1 teams with all the kings men and such testing the cars on track with real drivers.  If it were easy surely they would have the technology to just calculate the right answer and skip testing.

Considering the smart guy in question wrote an extensive and detailed book on race car suspension, was offered a significant postion in a top NASCAR team (can't say who or what) and was invited to speak at an F1 symposium, I think he might be able to get pretty close to the right answer before even getting to the track.

[JDChristianson]

37 minutes ago, mender said:

Considering the smart guy in question wrote an extensive and detailed book on race car suspension, was offered a significant postion in a top NASCAR team (can't say who or what) and was invited to speak at an F1 symposium, I think he might be able to get pretty close to the right answer before even getting to the track.

Oh certainly they get close, and they know what direction to go with changes to get results they need, I didn't mean to imply that really smart chassis engineers aren't good at it and close.    Its also not uncommon to see pro teams show up to a race and they've completely missed the set up somehow and are scrambling like mad for two days to get close to what they hoped for.   If a chump team can make and educated guess and then test and make changes in the right direction, they are doing pretty damn good in my opinion.

[Ron_e]

At a recent F1 race:

 

What happened to Lewis?

We got it wrong, we had it wrong all weekend.

 

The "it" was the suspension.

[Ogren-Engineering]

 

 For Chumper tires at near 1lateral G;  Try about  75% of the static weight per wheel for front spring rates. This assumes front struts with a 85-90% strut travel.to wheel ratio. IE ;     750# per wheel = about 550# springs.  Most FWD go faster with no front bar. The car may lean more but the lap times and balance is almost always better  bar free. 

  For balance ,  add wheel spacers to the rear , increase spring rates  /wheel rates  to near 90% of static weight . Add rear bar until the inside wheel comes up 3 in . When you get it right , you will be able to trim the balance with rear air pressure . low 40s  to 45 will roll faster.  

 Trying to get the rear tires to track out side of the fronts is the key to really flying the FWD.  As they get out, they take more  dynamic loading reducing the front tire loading, allowing the fronts to go faster.  Some  slight 1/8in toe out for the rear along with 2 * camber willl crispen up the turn in.  If you can't get the car to go straight, reduce the toe out a little. 

 The stock edition of Bilstein HD should control the higher rates well enough for Chump. 

Edited August 4, 2017 by flyinglizard

[thewheelerZ]

thanks for the replies guys.  Some good info here. 

[Bandit]

On 8/3/2017 at 8:16 PM, flyinglizard said:

 

 For Chumper tires at near 1lateral G;  Try about  75% of the static weight per wheel for front spring rates. This assumes front struts with a 85-90% strut travel.to wheel ratio. IE ;     750# per wheel = about 550# springs.  Most FWD go faster with no front bar. The car may lean more but the lap times and balance is almost always better  bar free. 

  For balance ,  add wheel spacers to the rear , increase spring rates  /wheel rates  to near 90% of static weight . Add rear bar until the inside wheel comes up 3 in . When you get it right , you will be able to trim the balance with rear air pressure . low 40s  to 45 will roll faster.  

 Trying to get the rear tires to track out side of the fronts is the key to really flying the FWD.  As they get out, they take more  dynamic loading reducing the front tire loading, allowing the fronts to go faster.  Some  slight 1/8in toe out for the rear along with 2 * camber willl crispen up the turn in.  If you can't get the car to go straight, reduce the toe out a little. 

 The stock edition of Bilstein HD should control the higher rates well enough for Chump. 

Concerning the wider rear track, that's what Olds did with the SCX. Rear axle was out of the Beretta GT.

 

 

Along with dual rear bars.

 

The Archers did ok with the Quad 4.

 

First hand experience-Thing cornered like a beast for the day.  Had to pull the abs fuse due to picking up the inside rear when driving hard on the back roads. ie-Mid 90's when I had mine. Red '92.

 

Unfortunately it had A/C, like 95% of them. No Torsen.

 

Considered buying one of the old Archer Express cars 10 or so years ago. Should have for the price. 4 figures. The 92 is legal for Chump btw. Around 1200 built.

Edited August 20, 2017 by Bandit

[DRVOLKS]

On spring rate when we where a Thompson Speed way on a test date the drivers said the car was a bit bounce going in the the hard rights. So I installed one more spring rubber

in the left front spring and all drivers said it fixed the bounce and they dropped there lap times. SO some times small change like this can lead you to the right fix.

Bob Mann

www.DRVOLKS.com

bobtec@comcast.net

[ross2004]

Is a spring rubber 10 points/each?