Wcm ultralite motion ratios

[nc7s4]

Hello, does anyone have the motion ratios for the wcm on hand?  I'm trying to be scientific about my shocks and springs setup for next year 

[Croc]

@RGTorque Do you have anything helpful here please?

[RGTorque]

I do not. Sorry. 

[nc7s4]

Motion ratios incoming!  I will measure the actual distance traveled 

 

Not sure if this will be the same for all wcms but maybe a useful reference 

[nc7s4]

MR for front is approximately 0.57

MR for rear is approximately 0.89

 

Info used:

 

Front: 0.81 * cosine (45) = 0.57

Rear: cos(27) = 0.89

 

D1 - 10 7/8
D2 - 13 1/2

D1/D2 = 0.81

 

 

 

[nc7s4]

Getting back to this.  My car can only fit small body shocks and springs. I think that other wcm ultralights can fit bigger outer diameter springs, but if I tried that they would interfere with the rear axles. 

 

So I believe I am stuck with 1.875 id springs and small body shocks.  Small body shocks get expensive quick. 

 

Here's what I am thinking based on those motion ratios above.  To get the wheel rate equalized front and back. We're going to need a slightly softer spring in the back. From looking at the forums it looks like some folks have got a lot softer in the back than I would if I were going for a balanced setup.  Maybe there are other reasons to go softer in the back.

 

So

 

.57 / .89 = .64

 

After lots of searching, the stiffest spring I can find is a 600 hyperco in a 1.875id x 10 inch.  These seem rare!  Other makes stop at about 400 lb/inch

 

600 * .64 = 384

 

The car is slightly heavier at the back so I'd go up to 400.  

 

Softer setup could be 500 / 350

 

Shocks - that I don't know.  Qa1 suggested these but they aren't adjustable 8Q45. 

 

I think that my setup is relatively close to this at 500/500 and the qa1 small body shocks that came with the car. I don't think I will invest in any changes yet and focus on driver training.

 

@charles5448

 

 

Hyperco part numbers for their 1.875 id 10 inch long springs.  This is the best set I've found and mostly seems available from summit etc 

 

 

 

Edited October 20 by nc7s4

[Croc]

Can we go back to basics for the moment?  Some of your numbers are surprising me.

 

I'm not sure what your objective is with this exercise, but I assume this is for a pure track only set up?  No road?  Slick tires? 

 

Assuming I am right, then just ignoring the calculations and applying real world experience, that is a hugely stiff spring for a small light car.  Thinking of my various race cars, thats the type of lb/in I see on a V8 race car with a great iron lump hanging out the front. 

 

Now I know lb/in in a spring is a function of diameter/length but what dimensions are your current springs?   1.875 inches inner diameter x 10 inches long?  Am I reading that right?     How are the shocks mounted - parallel to the outside of the spring? 

 

Not trying to criticize but trying to understand the context for your outcome.

[nc7s4]

Yes these spring rates for the wcm are way stiffer than caterham.  2x stiffer

 

I am using the advice from westtexass2k who ran 550/250, apparently, based on his prior posts here.  I can only assume the force/motion ratios are way different for the wcm vs caterham.

 

Goal is to set the car up for road racing.  Arb, springs and dampers will all work together to address this excessive body roll but right now I'm just considering the spring rates

 

Here are some pics of what looks like too much body roll and how I took the angles.  Not totally convinced this body roll is bad but it looks a lot different from super 7 race cars that are not as rolly 

 

[nc7s4]

Had a little issue with the math.

 

Wheel rate is Kspring*MR^2

 

To solve for the rear spring, assuming 50/50 weight distribution....

 

I think it is

 

Rear spring = ( <Front spring rate> * (.57^2)) / (.89^2)

 

So for a front spring of 550 I'd get a rear spring of 225

 

This math scans with what Loren recommended 

[nc7s4]

@Croc one explanation for the high rate is that this thing doesn't have any arb front or back so they ran the stiffer springs.  I've heard of people fitting an ARB to it but haven't gotten any good images of how to do it.  Would probably be better to run some softer springs with arbs....

[Croc]

A couple of observations:

 

1) I am not comparing your spring specs to a Caterham. They are not comparable.  

 

2) Roll is not a monster that needs to be slayed.  When well controlled it is very useful in assisting weight transfer around the wheels while minimizing grip breakaway  - particularly on a light car like a WCM.  Running without an anti roll bar is not always bad - I do the same on my track car - but you are right the springs have to be calibrated to avoid excessive roll.  
 

3) Looking at your photos, I could possibly argue the front on view has some dive to it but photos can be deceptive and that is a downhill corner entry which accentuates the angles.  The math you are doing is good to check seat of pants feel.  The rear view looks normal to me - no evidence of excessive roll.  
 

4) The revised rear spring to 225 feels more what I would expect given the front at 500/550.  Is there a caster limit on the front?  What amount of caster are you using?

 

 

[nc7s4]

Running 4.5° of caster. 

 

Good to know that the pictures don't look unusual to you.  Only reason I have right now to change anything is to get a positive identification on what I am running.  I took some measurements of the wire diameter number of coils, inside diameter and ran it through a sketchy calculator that told me the spring rate. That is why I am guessing they are 500 lb 

 

Could disassemble everything and get them checked, but by then I might as well replace them considering the relatively low-cost of doing so. 

 

My situation is definitely limited by driver skill.  Won't really need any upgrades until the car handling becomes the bottleneck.

 

Nice to have all of this lined up though as I do intend to keep making improvements.  Appreciate your experience with the arb situation.  Maybe not needed after all.

Edited October 20 by nc7s4

[Croc]

 

16 hours ago, nc7s4 said:

Only reason I have right now to change anything is to get a positive identification on what I am running. 

 

This exercise now makes a lot of sense to me.  I was confused earlier. 

 

I suspect your car handles very well.  If you are following guidance by Loren on set up then you are on a home run.  He knows these cars and is a very handy driver on the track. 

 

As you say, making changes to the handling requires some driver evolution.  A track day is not the greatest of ways to assess handling as you cannot always repeat lap after lap due to other cars plus you often need more seat time each session to assess.  When I sort my race cars after restoration/recommissioning it can take quite a few days of private track time to dial out the foibles, recognizing you only make one change at a time and then assess after each change.  

 

One last thing - just because a car feels right in its handling does not mean that it is the fastest that way.  That is where lap data by sector becomes critical as set up may work well on certain sections of a circuit but not others.  In the end it is a mass of compromises.  You just need to get a good baselined set up that works in most places then drive around the issue where it does not.  That becomes driver skill portion missing from your equations above. 

 

 

 

 

[nc7s4]

Out of curiosity why do you think the caterham and wcm are not comparable?  I did a quick search and the motion ratios are apparently almost exactly what I figured the wcm to be.

 

0.57 front

0.89 rear

 

Just trying to reconcile why there is such a huge difference in the recommended setups and the caterhams are running ~200 vs ~500 spring rate 

[Croc]

21 hours ago, nc7s4 said:

Out of curiosity why do you think the caterham and wcm are not comparable?  I did a quick search and the motion ratios are apparently almost exactly what I figured the wcm to be.

 

0.57 front

0.89 rear

 

Just trying to reconcile why there is such a huge difference in the recommended setups and the caterhams are running ~200 vs ~500 spring rate 

 

 

Too many other variables go into the thinking.  I have not see your individual WCM but on the two I have seen I would point to:

1) WCM has wider track

2) WCM has wider tires (more unsprung weight too)

3) Use of anti roll bar or not. 

4) Progressive springs vs non-progressive

5) Overall weight of a WCM is higher than a Caterham - not much but it all adds up.  Honda over Duratec/Sigma is a good chunk of that

 

Small variations can have big consequences. 

 

 

 

[charles5448]

On 10/20/2024 at 8:26 AM, nc7s4 said:

Getting back to this.  My car can only fit small body shocks and springs. I think that other wcm ultralights can fit bigger outer diameter springs, but if I tried that they would interfere with the rear axles. 

 

So I believe I am stuck with 1.875 id springs and small body shocks.  Small body shocks get expensive quick. 

 

Here's what I am thinking based on those motion ratios above.  To get the wheel rate equalized front and back. We're going to need a slightly softer spring in the back. From looking at the forums it looks like some folks have got a lot softer in the back than I would if I were going for a balanced setup.  Maybe there are other reasons to go softer in the back.

 

So

 

.57 / .89 = .64

 

After lots of searching, the stiffest spring I can find is a 600 hyperco in a 1.875id x 10 inch.  These seem rare!  Other makes stop at about 400 lb/inch

 

600 * .64 = 384

 

The car is slightly heavier at the back so I'd go up to 400.  

 

Softer setup could be 500 / 350

 

Shocks - that I don't know.  Qa1 suggested these but they aren't adjustable 8Q45. 

 

I think that my setup is relatively close to this at 500/500 and the qa1 small body shocks that came with the car. I don't think I will invest in any changes yet and focus on driver training.

 

@charles5448

 

 

Hyperco part numbers for their 1.875 id 10 inch long springs.  This is the best set I've found and mostly seems available from summit etc 

 

 

 

This is still my first year driving the WCM in Autocross, so there is still a learning curve. Just used to a car that feels a little tighter than this. In reading some of the responses to this post, I think I'm in-line with what the car should be doing. It looks like our cars have a similar amount of roll in corners.

 

I'm still left wondering what the cure for lift-off oversteer would be? My WCM seems to get super light in the rear and really doesn't enjoy braking and turning-in at the same time. Again, this could be skill but once that rear suspension gets a little unloaded, the rear wants to come around while turning. The best way I've curbed this is doing my braking in a straight line and then feeding it minimal throttle while turning. My main question is, would any sort of spring rate adjustment help reduce this?

 

On the note of the spring diameter, my springs rub my axle shafts when that particular corner gets loaded up. We had to make the front mount for the rear diff and it wasn't until after we finished that I noticed how close the axles were to the shafts. Another issue that seems to factor into this is how the diff is mounted at the rear. Unless my car was missing something (which it was missing a lot), it seems like the diff has the ability to pull those rubber bushings through and make the rubbing even worse. You could even see where the bushing on the right side had pulled out compared to the left side and the difference in color of the bushing that is normally not exposed. To (slightly) curb this, we cut out some giant washers to mount on the fuel tank side to keep the rubber bushing from pulling even further through.

 

Sorry brain dump, a lot of words and thoughts there. Just helpful to hear other people's experience.

[nc7s4]

Quick update regarding my new springs and shocks. They do not work!! 

 

10-In heavy springs are too tall.  Even at the top of the shock perch the ride height is too high. 

 

Need to figure out how to fit shorter springs.  I think that only the rear of the car has clearance issues, front will fit industry standard 2.25 ID springs. 

 

The rear of the car will probably still get 1.875 ID springs, but the problem with that is that they are limited in what you can get. It looks like the heaviest 8-in option is 250 lb.  That may be what I end up with in the back.

 

If the front can fit 2.25 in springs then there is any rate imaginable in that size 8 in long.

[MV8]

How did Cory determine those coilovers to be close enough to replace what you have? Did he have specs/part numbers for the originals or take one off the front and the rear then take the spring off to measure? Hopefully not just "eye balled". Were the original coilovers leaking?

 

Just as an fyi, but I did not use a website to guess-timate your spring rates; just your measurements and "maths".

Edited November 1 by MV8

[Croc]

@nc7s4 Bad news I know, but should we move your suspension discussion to your suspension thread to avoid messing with Rashid's rebuild topic?

[nc7s4]

57 minutes ago, Croc said:

@nc7s4 Bad news I know, but should we move your suspension discussion to your suspension thread to avoid messing with Rashid's rebuild topic?

Sure thing. I just wanted to make a note here in case the rebuilder put in the same flawed order that I had recommended earlier!