My E90 M3 Dedicated Track build (with pix!)

[rhyary]

Originally Posted by tsk94

Are you wondering for wheel rates? The calculation is pretty simple and you could do it even on a phone. It's just spring rate * MR^2 = wheel rate.

I could make a public google sheets spreadsheet I could share if people are interested. You'd just need to input the spring rate and it'll spit out the wheel rate for you. Calculating wheel frequencies is much more difficult as it needs accurate corner weights, unsprung weights and wheel rates - I could also include that but people would need to know their corner weight and rough unsprung weights to make it accurate.

Say you calculate and get the numbers

How would you translate that into a setup?

For example, I had a 900 rear spring (divorced) in the rear and I felt a stiffer spring would help. So I got 1100. All I know it is stiffer and I can rotate the car better.

How would a calculation help me arrive at the 1100 spring?

Please connect for me the calculation and how would I know what I need.

[tsk94]

Originally Posted by rhyary

Say you calculate and get the numbers

How would you translate that into a setup?

For example, I had a 900 rear spring (divorced) in the rear and I felt a stiffer spring would help. So I got 1100. All I know it is stiffer and I can rotate the car better.

How would a calculation help me arrive at the 1100 spring?

Please connect for me the calculation and how would I know what I need.

Well firstly, I'd need to know your front spring rate for reference. Comparing front and rear wheel rates gives a good insight into the steady-state handling balance the car will have. Sway bars also come into play but at the moment we will ignore them, they can later be added into the equation to get a fuller picture.

Since the front MR is so high (0.96), the effective wheel rate at the front is very close to spring rate of the physical spring. Most people are running divorced setups, and a divorced setups wheel rate is very low compared to the physical spring rate of the spring itself.

A 1000lb/in rear spring is roughly a wheel rate of ~330lb/in. If your front spring is in the region of 600-800, your front wheel rate is ~550-730lb/in. You can immediately see that the front of the car is substantially stiffer then the rear. To get a more neutral steady-state handling balance you would want to either increase the rear spring rate (by quite a bit as divorced spring rates increases result in small increases of wheel rate), or soften the front - or a combination of both.

I don't have a public spreadsheet available at this time but can declutter my personal one and make it available to all if enough people are interested..

[b4hand]

Originally Posted by tsk94

I don't have a public spreadsheet available at this time but can declutter my personal one and make it available to all if enough people are interested..

I would be interested. I am looking to upgrade my springs for next season and not sure where to start.

[derbo]

Originally Posted by tsk94

Are you wondering for wheel rates? The calculation is pretty simple and you could do it even on a phone. It's just spring rate * MR^2 = wheel rate.

Front MR: 0.956
Rear MR (divorced): 0.576
Rear MR (coilover): 0.819

I could make a public google sheets spreadsheet I could share if people are interested. You'd just need to input the spring rate and it'll spit out the wheel rate for you. Calculating wheel frequencies is much more difficult as it needs accurate corner weights, unsprung weights and wheel rates - I could also include that but people would need to know their corner weight and rough unsprung weights to make it accurate.

Yes to both.

[rhyary]

Originally Posted by tsk94

Well firstly, I'd need to know your front spring rate for reference. Comparing front and rear wheel rates gives a good insight into the steady-state handling balance the car will have. Sway bars also come into play but at the moment we will ignore them, they can later be added into the equation to get a fuller picture.

Since the front MR is so high (0.96), the effective wheel rate at the front is very close to spring rate of the physical spring. Most people are running divorced setups, and a divorced setups wheel rate is very low compared to the physical spring rate of the spring itself.

A 1000lb/in rear spring is roughly a wheel rate of ~330lb/in. If your front spring is in the region of 600-800, your front wheel rate is ~550-730lb/in. You can immediately see that the front of the car is substantially stiffer then the rear. To get a more neutral steady-state handling balance you would want to either increase the rear spring rate (by quite a bit as divorced spring rates increases result in small increases of wheel rate), or soften the front - or a combination of both.

I don't have a public spreadsheet available at this time but can declutter my personal one and make it available to all if enough people are interested..

750 coil over JRZ
H&R non adjustable solid sway bar front and rear

[tsk94]

Originally Posted by rhyary

750 coil over JRZ
H&R non adjustable solid sway bar front and rear

750lb/in front spring is ~685lb/in wheel rate.

I'd need to know the bar rate of those sway bars to include them into the analysis. Front roll couple distribution is the best analysis that takes into account all of these. I can also create a spreadsheet for FRC but that will take more time.

[rhyary]

Originally Posted by tsk94

750lb/in front spring is ~685lb/in wheel rate.

I'd need to know the bar rate of those sway bars to include them into the analysis. Front roll couple distribution is the best analysis that takes into account all of these. I can also create a spreadsheet for FRC but that will take more time.

The H&R are 42.5% stiffer than M3 stock.

[dogbone]

Originally Posted by tsk94

Well firstly, I'd need to know your front spring rate for reference. Comparing front and rear wheel rates gives a good insight into the steady-state handling balance the car will have. Sway bars also come into play but at the moment we will ignore them, they can later be added into the equation to get a fuller picture.

Since the front MR is so high (0.96), the effective wheel rate at the front is very close to spring rate of the physical spring. Most people are running divorced setups, and a divorced setups wheel rate is very low compared to the physical spring rate of the spring itself.

A 1000lb/in rear spring is roughly a wheel rate of ~330lb/in. If your front spring is in the region of 600-800, your front wheel rate is ~550-730lb/in. You can immediately see that the front of the car is substantially stiffer then the rear. To get a more neutral steady-state handling balance you would want to either increase the rear spring rate (by quite a bit as divorced spring rates increases result in small increases of wheel rate), or soften the front - or a combination of both.

I don't have a public spreadsheet available at this time but can declutter my personal one and make it available to all if enough people are interested..

Hey Trevor. I really appreciate you jumping in on here today with this info. I have learned a lot today.

I just realized my measurements are garbage. Been crawling around under my car and didn't do it right. My neighbor next door has a lift where the wheels sit on ramps. Maybe I'll bug him to let me put the car on his lift.

Anyway, thanks again.

[tsk94]

Originally Posted by dogbone

Hey Trevor. I really appreciate you jumping in on here today with this info. I have learned a lot today.

I just realized my measurements are garbage. Been crawling around under my car and didn't do it right. My neighbor next door has a lift where the wheels sit on ramps. Maybe I'll bug him to let me put the car on his lift.

Anyway, thanks again.

No problem! Happy to help.

I'm making a simple spreadsheet for calculating wheel rates (roughly) that I'll share this afternoon.

I have a much more extensive spreadsheet for calculating front roll couple distribution (which also calculates wheel rates, among other things). I can clean it up and post that at a later date as well.

[derbo]

Originally Posted by tsk94

750lb/in front spring is ~685lb/in wheel rate.

I'd need to know the bar rate of those sway bars to include them into the analysis. Front roll couple distribution is the best analysis that takes into account all of these. I can also create a spreadsheet for FRC but that will take more time.

The biggest topic I always see is the ride frequency being higher in the rear is ideal for a passenger car but what about HPDE weekend car?


I need to do more research on chassis development.

[tsk94]

Originally Posted by b4hand

I would be interested. I am looking to upgrade my springs for next season and not sure where to start.

Originally Posted by derbo

Yes to both.

Originally Posted by derbo

The biggest topic I always see is the ride frequency being higher in the rear is ideal for a passenger car but what about HPDE weekend car?


I need to do more research on chassis development.

There's no definitive answer to this topic for a track application, many people have different schools of thought on the matter. Some believe it also applies to track/race cars, while others don't. Two very different approaches, but both can be made to work with tuning other aspects of the chassis and setup accordingly. I fall somewhere in the middle but need to do more research and experimentation myself to better formulate my opinion regarding what frequency ratio is optimal for a track car.

[//steve\\]

^ I do think that's one common problem is some people want to math their setup to death. I think driving style may even come into play. That said I know people that aren't super experienced with tons of seat time want to try and get as close to "perfect" as they can right out of the box. I think I fall into this scenario more often than I'd like to admit.

[rhyary]

So the goal of the calculation is to equalize the front/rear effective wheel rate as a basis for neutral car then fine tune.

The reason that you can't buy 1000 for the front and 1000 for the rear and call it "neutral" is because the "wheel rate" front and rear is not the same.

Did I understand the issue correctly?

[tsk94]

Originally Posted by rhyary

So the goal of the calculation is to equalize the front/rear effective wheel rate as a basis for neutral car then fine tune.

The reason that you can't buy 1000 for the front and 1000 for the rear and call it "neutral" is because the "wheel rate" front and rear is not the same.

Did I understand the issue correctly?

Somewhat. The idea is to find a neutral handling balance for you with the rest of the setup tuned accordingly to achieve such a balance. We use things like wheel rates, wheel frequencies and measures like front roll couple distribution to provide numerical values to a range of real world handling balance characteristics.

You will most likely not want to equalize front and rear wheel rates though, as the car will be heavily oversteer biased and will need many other aspects of the setup tuned to make it work nicely. That's not to say to say you couldn't make it work. If you ran no rear sway bar, a big front bar, had the rear very low with lots of toe in and had the front end relatively high it would help - but still be very oversteer biased.

Front roll couple distribution is a better mechanism for analyzing true steady-state handling balance, as it's easier to interrupt and takes into account many more factors then simply just the wheel rates. Wheel rates are simply the first part to a bigger picture.

For example; people hear 800lb/in spring rates for the front and don't think twice about it. But you mention a 1800lb/in divorced rear spring and most will think you're nuts. But the reality is that the wheel rates with these setups are ~730 in the front and ~600 in the rear. So while 1800 sounds very high, it's all relative to the MR and what the resulting wheel rate would be. I'm not saying a 800/1800 setup would be ideal by any means, simply an example.

Keep in mind, no matter what spring setup you go with, the resulting chassis setup will vary to get it just right for you. Individual driver preference also plays a huge role. Some might prefer a much looser setup, and choose different spring rate setup accordingly compared to the guy that prefers a setup with slight understeer. And on top of that spring rates are just 1 part of chassis setup - but when looking at steady-state handling balance they are one of the most important factors.

[tsk94]

To elaborate on my above post:

When I said equalizing front and rear wheel rates is likely not the optimal approach, I'm referring specifically to the E9X M3 platform. Other platforms will be different. FWD cars are a good general example of going against this point. They often have very stiff wheel rates, even relative to the front - but making a FWD car go fast around a track is very different then our front engine RWD cars.

I don't think it would be optimal on our cars (equalizing front and rear wheel rates), but again that's not to say you couldn't make it drivable, or quick for that matter, if the rest of the car is setup around it accordingly.

My goal is to take what on paper makes sense for spring rates, then fine tune the rest using other methods. Rather then taking spring rates as given and then doing massive changes to ride heights, alignment etc. to make a given spring rate work.

[dogbone]

hehe to your point-----I spoke to someone today that is very knowledgeable about this stuff. I wanted his input. Ultimately, his answer was a question----"How does it feel??" For him, comparing rates of divorced to coilover wasn't all that useful. He said the feel of it ends up being the most important thing. Basically, every car is different and every driver seems to have different preferences. To nail it all down, you gotta go out and see what it feels like.

I liked the feel quite a bit. I just think I want to try the 12k in the rear. Something is telling me that I will dig that.

[tsk94]

Here's a google sheets spreadsheet for calculating wheel rates and approximate wheel frequencies:
https://docs.google.com/spreadsheets...p-FDeDMek/copy

I put steps/explanations in the spreadsheet itself so it's pretty straightforward to use.

Regarding the unsprung weights. They will vary the frequencies slightly, as like I mentioned everyone's will be different depending on what tires, what wheels, what brakes and even things like control arms they use. However, unless you have your exact unsprung weights, just use the approximated ones in the sheet. These are fairly accurate and won't alter the wheel frequencies much from their 'true' values for your car. You need to make quite large changes to unsprung weights to affect frequencies noticeably.

[dogbone]

[QUOTE=tsk94;26964647]Here's a google sheets spreadsheet for calculating wheel rates and approximate wheel frequencies:
https://docs.google.com/spreadsheets...it?usp=sharing

It looks like the doc is View Only. Any trick to be able to use it?

[SYT_Shadow]

Originally Posted by dogbone

Hey Trevor. I really appreciate you jumping in on here today with this info. I have learned a lot today.

I just realized my measurements are garbage. Been crawling around under my car and didn't do it right. My neighbor next door has a lift where the wheels sit on ramps. Maybe I'll bug him to let me put the car on his lift.

Anyway, thanks again.

You gave me wrong measurements??

[tsk94]

[QUOTE=dogbone;26964683]

Originally Posted by tsk94

Here's a google sheets spreadsheet for calculating wheel rates and approximate wheel frequencies:
https://docs.google.com/spreadsheets...it?usp=sharing

It looks like the doc is View Only. Any trick to be able to use it?

I thought the make a copy option would work but it appears to be greyed out. Let me see if I can fix it.

[dogbone]

Originally Posted by SYT_Shadow

You gave me wrong measurements??

No---haha----I gave you what you told me to measure. But don't make me swear on it.

[tsk94]

Can someone try the link now and let me know if it works? When you open it now it should ask if you want to make a copy, click yes. Then you should have access to the spreadsheet and be able to edit it. You will need a google account for this but I assume most do. Otherwise I can post the original link which has an option to download the spreadsheet so you can open it in Excel.

If you have a google account:https://docs.google.com/spreadsheets...p-FDeDMek/copy

If you don't have a google account/want to download the sheet and open it in Excel: https://docs.google.com/spreadsheets...it?usp=sharing
- Go file, download, excel doc