Suspension - the journey

[Magpie]

Have started on the next part of the journey now that the data collection is over... suspension .....

A great reference book is Competition Car Suspension by Allan Staniforth.

The purpose of this journey is to fine tune the car and make some informed decisions and as much as possible avoid trial and error methods of testing. Track time these days is limited and best used to get more consistent.

A few years ago I had a chance meeting with Danny Nowlan of ChassisSim and it was then I decided that this was the way to go. However, until now I did not have sufficient data to utilise ChassisSim.



The beginning... this is the next big job, measuring up the car.


Some points to consider:
1) Ride height is ground to the Chassis reference.
2) When a shock is in compression it records a positive (increasing) value and in rebound a negative (decreasing) value.
3) Calibrate damper pots to what you see at the springs.
4) Unsprung weight (wheels, tyres, brakes, wishbones, uprights etc - Competition Car Suspension by Allan Staniforth)
5) Sprung weight (Total weight - unsprung weight)
6) Motion Ratio - the movement of the spring for a given amount of wheel movement (the shock travel can be used for this value, however the spring ratio will also be needed). This has been previously done for both the dampers and the sensors.

Ride Height Measuring
1. Measure to a point on the body (fender) with the tyres at normal pressure and with its normal weight in it (driver).
2. Also measure to a point on the lower control arm. Not important where but must be used all the time. For this I use a longacre ride height tool as it has a magnet that holds the tape to frame. Indicator shows height as the car moves up and down. This is locked off at a measurement (not critical).
3. Jack the car off and remove the wheel.
4. Lower the car so that the measurement in (1) is the same.
5. Raise the lower control arm to match the measurement at (2).
6. Measure the ride height from the point that you want to use. For my purpose I used the bolt that attaches the hub.
Mine:
RL - 177 mm FL - 162 mm
RR - 175 mm FR - 163 mm






Unsprung Weights
NB8B suspension parts Rear - 18.557kg unsprung (excluding wheels). Assumed calipers at 3.5 and excluded the drive shafts.


Front NB8B suspension parts - 19.064kg unsprung (excluding wheels)

[ozace]

serious exercise you have going in there

[manga_blue]

The old FCM spreadsheets already have many of the measures you're looking for. Send me a pm with your email address if you don't have a copy.

[Magpie]

serious exercise you have going in there

[brendanstacey]

I did my Honours thesis at Uni for Danny. Very knowledgeable and even more eccentric! You'll learn lots with Chassissim and really understand how changing front/rear roll rates can help!

Would you be able to post your pickup points when/if you manage to measure them?

How detailed are you thinking of making your car model? You going to assume things like CLA and CDA or just assume some established numbers?

[Magpie]

Very knowledgeable and even more eccentric!

I met Danny in person last year at WTAC, however been chatting for a few years. You get the sense of his eccentrics from his videos

Would you be able to post your pickup points when/if you manage to measure them?

Will do. Started to do it on the weekend, however transfereing the front upper chassis mounts was not possible with a plumb bob. Plan is to put a large sheet of paper under the car, tape it down, mark out some reference points then transfer the points to the paper. This way I can then pull off the arms and transfer them with a plumb bob.

How detailed are you thinking of making your car model? You going to assume things like CLA and CDA or just assume some established numbers?

I only have old numbers on CLA/CDA when I did some coast down testing whilst the car was road registered. I could attempt to recreate some of these on the track, but only going one way would negate some of the accuracy. However the back straight at QR should be long enough to do a coast down.

The old FCM spreadsheets already have many of the measures you're looking for. Send me a pm with your email address if you don't have a copy.

Thanks, will look at these. I had an old copy of this somewhere at home...

Interesting that Shaikh assumes that only 2/3 of the total weight in the suspension is unsprung, however in Competition Car Suspension by Allan Staniforth it is wheels, tyres, brakes, wishbones, uprights etc and for the rear drive axles.

A quick data input for my setup (NA) was Hz of 2.08 and 2.13 (F/R) with a FRC of 51.6%. However if I change the weight dist %, update the unsprung weights to what I have collected it changes to 2.15 and 2.09 Hz (F/R) with a FRC of 51.6%.

What I'm trying to do is get a baseline to work from be it Shaikh's, ChassisSim or Allan Staniforth's, in the end it is just a 'number', like tyre pressures, alignment etc but it then allows changes to be evaluated against. I'm being careful to choose the method that I will continue using as changing will cause new problems. I do not want a repeat of my Innovate/Racepak data logging decision...

[brendanstacey]

I only have old numbers on CLA/CDA when I did some coast down testing whilst the car was road registered. I could attempt to recreate some of these on the track, but only going one way would negate some of the accuracy. However the back straight at QR should be long enough to do a coast down.

If you want some help or advice with these I'd be happy to help as I've done measured them on a couple of cars before. I also think doing a ride height sweep would be insightful considering your current front aero setup! Again I'm happy to help since I just enjoy this stuff

Interesting that Shaikh assumes that only 2/3 of the total weight in the suspension is unsprung, however in Competition Car Suspension by Allan Staniforth it is wheels, tyres, brakes, wishbones, uprights etc and for the rear drive axles.

A quick data input for my setup (NA) was Hz of 2.08 and 2.13 (F/R) with a FRC of 51.6%. However if I change the weight dist %, update the unsprung weights to what I have collected it changes to 2.15 and 2.09 Hz (F/R) with a FRC of 51.6%.

What I'm trying to do is get a baseline to work from be it Shaikh's, ChassisSim or Allan Staniforth's, in the end it is just a 'number', like tyre pressures, alignment etc but it then allows changes to be evaluated against. I'm being careful to choose the method that I will continue using as changing will cause new problems. I do not want a repeat of my Innovate/Racepak data logging decision...

Just thinking out loud, as I haven't read this anywhere so it might be a stupid idea, but one way to measure the unsprung weight might be to have everything unsprung on the car like normal and have the car in the air on ramps/stands, and then jack up a scale to the tyre just before you start loading the springs, or you could just remove the springs and do the same?

I agree that some weight from all the components should be lost to sprung weight, as things like the drive shafts and wishbones are also supported by the body, which is sprung.

[manga_blue]

A quick data input for my setup (NA) was Hz of 2.08 and 2.13 (F/R) with a FRC of 51.6%. However if I change the weight dist %, update the unsprung weights to what I have collected it changes to 2.15 and 2.09 Hz (F/R) with a FRC of 51.6%.

You zeroed in immediately on my two favourite measures. I always aimed for somewhere around 54% FRC and bounce frequency about the same as yours except with the rear around 10% slower than the front. I tried mine once at 51% FRC and the car was almost undriveable because of oversteer. It's all very individual though. Everyone has different driving techniques and I assume yours is altered a fair bit by having aero. Aero was never permitted in my classes.

What I'm trying to do is get a baseline to work from be it Shaikh's, ChassisSim or Allan Staniforth's, in the end it is just a 'number', like tyre pressures, alignment etc but it then allows changes to be evaluated against. I'm being careful to choose the method that I will continue using as changing will cause new problems. I do not want a repeat of my Innovate/Racepak data logging decision...

That's really the key to it. It's simple once you have one or two simple measures to base your adjustments on. I've always regarded these as purely starting point static measures. The reality is that you have to follow up with seat time and lap logging to see what happens in the real world with the effects of differing wind speeds, different power outputs as you use the gears, not to mention bumpy tracks and the like.

[Magpie]

If you want some help or advice with these I'd be happy to help as I've done measured them on a couple of cars before. I also think doing a ride height sweep would be insightful considering your current front aero setup! Again I'm happy to help since I just enjoy this stuff

Many thanks, will do a PM up soon or make a post as this may help others.

Just thinking out loud.

The issue is the bind in the bushes.

That's really the key to it. It's simple once you have one or two simple measures to base your adjustments on. I've always regarded these as purely starting point static measures. The reality is that you have to follow up with seat time and lap logging to see what happens in the real world with the effects of differing wind speeds, different power outputs as you use the gears, not to mention bumpy tracks and the like.

110% agreed!

At Morgan Park one of the layouts (B) is very very bumpy and it just so happened that I would the rebound up to 4 clicks from hard... even with a harness my teeth are sore Some comments from people watching were that the car was bouncing all over the pace.

We swapped to D after this and I left it at 4 from hard and again it was 'difficult'. Next session on D had the front at 6 clicks from hard and wow what a difference!

Will post some of the data to give an insight into what can be done. However I have a concern for my RR as it has more noise than the other 3. Could be play in the sensor mounts, binding in the bushes, bent component down there (damper/arm). I have a feeling one of my offs at Lakeside may have caused some damage down there. However to me the car feels fine...

By the way improved my PB at Morgan Park on layout E so the changes worked! The BC ER's were set on 6/4 (F) and 4/4 (R) clicks from hard with 10/8 springs. Note the ER's have seperate bump and rebound.

[brendanstacey]

Many thanks, will do a PM up soon or make a post as this may help others.

No worries

The issue is the bind in the bushes.

I would picture the bind to be negligible if they're greased up, or at least compared to the unsprung weight anyway the shouldn't provide too much extra force? Alternatively you could remove the bushes place them on top to keep their weight?

[Custardtart]

SuperPro bushes seem the least susceptible to binding and you could tap in some zerk fittings?

[greenMachine]

SuperPro bushes seem the least susceptible to binding and you could tap in some zerk fittings?

Not to derail this thread ... but no, seriously NO.

Have a close look at the picture upthread of the NB8B arms - they came off my racecar. Those are delrin bushes (white) and a few poly/bronze (red) where compliance is required. They are not polys, most certainly not Superpros (some of which had to have the pins hammered out before being replaced with these). Poly is a bad choice for bushings, end of story. Instead of derailing this thread further, I would point people to the bushings megathread on MTnet.

[Magpie]

Not to derail this thread

They are very close to being installed! Having the rear dampers put on the shock dyno next week. This is to either see if there is an issue with the dampers and get some force plots

If there is no issue with the damper then the rear arms will be the first to go in

[Magpie]

I would picture the bind to be negligible if they're greased up, or at least compared to the unsprung weight anyway the shouldn't provide too much extra force?

After doing the rear suspension on the weekend I can tell you that the OEM bush setup has a lot of 'resistance' and will 'spring' back when pushed down. This is due to having to be torqued when the car is on the ground.

The new setup literally falls down under its own weight even when torqued up! I may put a set of scales under the setup and see what the unsprung weight is and compare the values.