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      07-15-2021, 08:27 AM   #45
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Seems odd someone like bimmerworld would recommend 800/1100 based purely on a "300lb/in split." That's just not how suspension works. 100/400 springs would be a 300lb split and actually be a pretty balanced setup since the rear spring rate is pretty much 1/3 as effective as it should be. 800/1100 is massively front biased. Bimmerworld races 328i's though so you'd think they have a pretty well sorted car to base things off of. Maybe their race cars have true rear coilovers? That would make 800/1100 much more neutral handling.

If I keep seeing 128i videos like this I am going to need to sell my 135i. I liked my NA 128i so much better on track. It actually like being at 6,000rpm+ lol and lifting a bit to change the cars balance didn't lose all your boost :/

1:29:9 at thunderbolt is faster than a spec e46. That's a damn fast lap.
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      07-15-2021, 11:19 AM   #46
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Quote:
Originally Posted by bbnks2 View Post
Seems odd someone like bimmerworld would recommend 800/1100 based purely on a "300lb/in split." That's just not how suspension works. 100/400 springs would be a 300lb split and actually be a pretty balanced setup since the rear spring rate is pretty much 1/3 as effective as it should be. 800/1100 is massively front biased. Bimmerworld races 328i's though so you'd think they have a pretty well sorted car to base things off of. Maybe their race cars have true rear coilovers? That would make 800/1100 much more neutral handling.

If I keep seeing 128i videos like this I am going to need to sell my 135i. I liked my NA 128i so much better on track. It actually like being at 6,000rpm+ lol and lifting a bit to change the cars balance didn't lose all your boost :/

1:29:9 at thunderbolt is faster than a spec e46. That's a damn fast lap.
Yeah I had a feeling the 800/1100 wouldnt work for me but oh well worth a shot! Now I know. Yeah I love the 128 so much, i hate that people think I am in a 135 though, especially when they dont lift for a point by haha. Thanks!
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      07-15-2021, 11:55 AM   #47
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Quote:
Originally Posted by bbnks2 View Post
Seems odd someone like bimmerworld would recommend 800/1100 based purely on a "300lb/in split." That's just not how suspension works. 100/400 springs would be a 300lb split and actually be a pretty balanced setup since the rear spring rate is pretty much 1/3 as effective as it should be. 800/1100 is massively front biased. Bimmerworld races 328i's though so you'd think they have a pretty well sorted car to base things off of. Maybe their race cars have true rear coilovers? That would make 800/1100 much more neutral handling.

If I keep seeing 128i videos like this I am going to need to sell my 135i. I liked my NA 128i so much better on track. It actually like being at 6,000rpm+ lol and lifting a bit to change the cars balance didn't lose all your boost :/

1:29:9 at thunderbolt is faster than a spec e46. That's a damn fast lap.
They did run rear coilovers, but the rear rate wasn't that high. It was closer to the equivalent of a 1100 divorced spring - so I was told when I spoke with them about it.

I mentioned that exact point to them as well, the 300 split isn't consistent. As you go stiffer, that same 300# split becomes more front biased.

OP, glad to hear the softer front springs worked out. Nice lap.
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      07-16-2021, 08:14 AM   #48
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The 300lb spring difference is funny, back in my E36 days everyone said you needed to have a 150lb spring rate difference front to rear. Maybe it's just easier to tell people to keep that difference as most aren't planning to run super stiff springs.

But I have to think that Phloozy buying MCS 2WNRs and pushing the limit in TT is very different from most users.

That was an awesome lap, really cool to see a 128 being pushed to the limit. Phloozy do you monitor oil pressure at all? Just wondering how these engines will hold up when on hoosiers and with aero.
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      07-16-2021, 09:12 AM   #49
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Originally Posted by spidertri View Post
The 300lb spring difference is funny, back in my E36 days everyone said you needed to have a 150lb spring rate difference front to rear. Maybe it's just easier to tell people to keep that difference as most aren't planning to run super stiff springs.

But I have to think that Phloozy buying MCS 2WNRs and pushing the limit in TT is very different from most users.

That was an awesome lap, really cool to see a 128 being pushed to the limit. Phloozy do you monitor oil pressure at all? Just wondering how these engines will hold up when on hoosiers and with aero.
So after driving the 800/1100 setup I can see someone pushing less hard loving it. They were easy to drive slightly under the limit and produced decent times. The issue was when you started to push harder the car would get upset. Bimmerworld still thinks the setup can work with shock tuning but imo it doesnt fit my driving style.

I need to really think about oil pressure. This was my first time running hoosiers and I just kind of threw them on and went with them. I'm scared to see what rears its head now that i have a lot more grip and Gs lol
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      08-02-2021, 03:46 PM   #50
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Stumbled on your build here and it's got me thinking twice about spring rates...

I'm about to go with YCW 1-way adjustable coilovers. I was originally shooting for the usual 1:3 front/rear spring rates (i.e. 6k/18k) to maintain the nearly 1:1 wheel ratio front/rear. But now reading that you have more like a 1:1.5 spring ratio with your 650/1100 I'm second guessing it. To add more confusion to the mix, when I emailed YCW asking for their recommendation based on my specs, they suggested 8k/18k or 1:2 spring ratio.

My car is going to be very similar to your build, similar weight 128i. You are at a higher skill level than I am, though.

Do you feel like the 650/1100 is a good fit now in terms of front/rear bias? Or if you could do it over again would you try to have it more rear biased?
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      08-02-2021, 05:05 PM   #51
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Originally Posted by wootloops View Post
Stumbled on your build here and it's got me thinking twice about spring rates...

I'm about to go with YCW 1-way adjustable coilovers. I was originally shooting for the usual 1:3 front/rear spring rates (i.e. 6k/18k) to maintain the nearly 1:1 wheel ratio front/rear. But now reading that you have more like a 1:1.5 spring ratio with your 650/1100 I'm second guessing it. To add more confusion to the mix, when I emailed YCW asking for their recommendation based on my specs, they suggested 8k/18k or 1:2 spring ratio.

My car is going to be very similar to your build, similar weight 128i. You are at a higher skill level than I am, though.

Do you feel like the 650/1100 is a good fit now in terms of front/rear bias? Or if you could do it over again would you try to have it more rear biased?

I am happy with the 650/1100 I am at now but I also have a wing and splitter, are you running that as well? I think it may be too stiff with no aero but could be wrong. I ran 450/1050 for a while when I had no aero and it did well but was pretty prone to oversteer so I think 650/1100 works better for me. The 800/1100 was way to pushy on the maxxis, I am still curious how it would have been on the hoosiers.

After trying all those setups I don't think I would recommend the 1:3 approach as it was a bit much to handle. Watching this video from last year on 450/1050 you can see I'm battling the rear end almost every corner.



With ALL of that said I only did 1 event on the 650/1100 on Hoosiers so time will tell as I get used to it if I want to change anything.
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      08-02-2021, 05:34 PM   #52
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Quote:
Originally Posted by Phloozy View Post
I am happy with the 650/1100 I am at now but I also have a wing and splitter, are you running that as well? I think it may be too stiff with no aero but could be wrong. I ran 450/1050 for a while when I had no aero and it did well but was pretty prone to oversteer so I think 650/1100 works better for me. The 800/1100 was way to pushy on the maxxis, I am still curious how it would have been on the hoosiers.

After trying all those setups I don't think I would recommend the 1:3 approach as it was a bit much to handle. Watching this video from last year on 450/1050 you can see I'm battling the rear end almost every corner.

With ALL of that said I only did 1 event on the 650/1100 on Hoosiers so time will tell as I get used to it if I want to change anything.
This is great info, thanks!

You're right, I am not running aero yet so I probably don't need to go as stiff. The YCW Recommendation of 8k/16k I believe equals 448/896 so that would be a little softer. Based on your comments, The spring ratio would be 1:2 front/rear which may be a tad oversteer prone, but I can probably dial that out with a stiffer front sway bar if needed. It should fall somewhere between your 450/1050 and 650/1100 in terms of front/rear bias.

Thanks again, your build is a big inspiration.
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      08-02-2021, 05:36 PM   #53
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Quote:
Originally Posted by wootloops View Post
Quote:
Originally Posted by Phloozy View Post
I am happy with the 650/1100 I am at now but I also have a wing and splitter, are you running that as well? I think it may be too stiff with no aero but could be wrong. I ran 450/1050 for a while when I had no aero and it did well but was pretty prone to oversteer so I think 650/1100 works better for me. The 800/1100 was way to pushy on the maxxis, I am still curious how it would have been on the hoosiers.

After trying all those setups I don't think I would recommend the 1:3 approach as it was a bit much to handle. Watching this video from last year on 450/1050 you can see I'm battling the rear end almost every corner.

With ALL of that said I only did 1 event on the 650/1100 on Hoosiers so time will tell as I get used to it if I want to change anything.
This is great info, thanks!

You're right, I am not running aero yet so I probably don't need to go as stiff. The YCW Recommendation of 8k/16k I believe equals 448/896 so that would be a little softer. Based on your comments, The spring ratio would be 1:2 front/rear which may be a tad oversteer prone, but I can probably dial that out with a stiffer front sway bar if needed. It should fall somewhere between your 450/1050 and 650/1100 in terms of front/rear bias.

Thanks again, your build is a big inspiration.
I think that's a perfect starting point. I often wonder if I'm too stiff in general even with the aero
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      08-03-2021, 09:28 AM   #54
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Quote:
Originally Posted by wootloops View Post
This is great info, thanks!

You're right, I am not running aero yet so I probably don't need to go as stiff. The YCW Recommendation of 8k/16k I believe equals 448/896 so that would be a little softer. Based on your comments, The spring ratio would be 1:2 front/rear which may be a tad oversteer prone, but I can probably dial that out with a stiffer front sway bar if needed. It should fall somewhere between your 450/1050 and 650/1100 in terms of front/rear bias.

Thanks again, your build is a big inspiration.
I run the YCW with 8k/16k but i sent them out to be custom valved for it. I like this setup the best I've had on the car. 4k/12k "street" setup they sell is too soft. Maybe for a stance car it would be good. I ran 6k/16k for a while and it was pretty good until I tried 8k/16k. The little bit of extra front spring rate gives you a little more front bump travel without being so stiff that you then need helper springs. I like where the car is at right now but it could be stiffer. I am now running 285s all around. Going to be moving to ohlin's dedicated track soon which is 12k/18k So I am curious to see how that feels... I hear a lot of hype.

Moving from 6k/16k to 8k/16k definitely induced a little under-steer in slow speed corners in autocross. However, the car also slaloms way better now for a net gain (I've been faster). Driving style matters for sure and you'll need to adjust/re-learn every time you make a change.

I know I have preached on here a lot about ride frequency and how the rear motion ratio is low... but that is usually said within the context of people complaining about terminal under-steer and how to fix it. Run more balanced spring rates. However, many people's counter arguments in those conversations are also true... that a race car doesn't need to be tuned for flat ride. I think due to braking and what not it's more realistic for a racecar to have more of a 60/40 spring rate bias. Spring rates like 650/1100 result in about a 62% front spring rate bias which is a little high. With sway bars tuned for more front roll stiffness that number likely increases to closer to 70% front roll couple distribution depending on what sways you run. That's where it becomes a balancing act of staying within that golden range where a little front bias might help but too much and you'll just induce excessive under-steer leaving time on the table. 450/900 (8k/16k) is closer to 57% front spring rate bias and before factoring in sways feels like a pretty good starting place on paper.

IDK if I am using all of the terminology correctly and explaining it well.. I am paraphrasing from resources like this: https://robrobinette.com/Suspension_Spreadsheet.htm

Quote:
*Front Roll Couple Percentage describes lateral load transfer distribution front to rear and subsequently the handling balance. It is the front roll stiffness divided by the total roll stiffness which is a ratio, front to rear, of the vehicle's total roll rate. Higher than 50% means the front wheels take more weight while cornering and the handling progresses toward understeer but for most cars around 55% gives balanced handling on the track while approximately 75% is best for autocross. For powerful cars a higher FRC% can help prevent power-on oversteer so a turbocharged Miata will typically need a higher FRC% than a normally aspirated Miata.

Last edited by bbnks2; 08-03-2021 at 10:12 AM..
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      08-03-2021, 09:37 AM   #55
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Originally Posted by bbnks2 View Post
I run the YCW with 8k/16k but i sent them out to be custom valved for it. I like this setup the best I've had on the car. 4k/12k "street" setup they sell is too soft. Maybe for a stance car it would be good. I ran 6k/16k for a while and it was pretty good until I tried 8k/16k. The little bit of extra front spring rate gives you a little more front bump travel without being so stiff that you then need helper springs. I like where the car is at right now but it could be stiffer. I am now running 285s all around. Going to be moving to ohlin's dedicated track soon which is 12k/18k So I am curious to see how that feels... I hear a lot of hype.

Moving from 6k/16k to 8k/16k definitely induced a little under-steer in slow speed corners in autocross. However, the car also slaloms way better now. Driving style matters for sure and you'll need to adjust/re-learn every time you make a change.
Also good info, thanks! I would be ordering them from YCW with the 8k/16k and they would be custom valving them to match. If I remember your other posts correctly, you were one of the early adopters of YCW coilovers, right? How have then been working out with the updated springs?

EDIT: Sorry, didn't mean to hijack your thread Phloozy but I figured this is all somewhat related to the topic at hand lol
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      08-03-2021, 10:10 AM   #56
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Originally Posted by wootloops View Post
Also good info, thanks! I would be ordering them from YCW with the 8k/16k and they would be custom valving them to match. If I remember your other posts correctly, you were one of the early adopters of YCW coilovers, right? How have then been working out with the updated springs?

EDIT: Sorry, didn't mean to hijack your thread Phloozy but I figured this is all somewhat related to the topic at hand lol
yeah sorry I like to rant. I can't complain about the YCW. They have done everything I have needed them to and YCW has made a few revisions based on feedback (sway bar mounting tabs are beefier now). They feel better custom valved with what feels like much more rebound damping. They are in-line price wise with BC or FA... That's what expectations I would hold for them. The hardware is everything it says it is but it's the damping that matters most I suppose. It would be interesting to do shock dynos on both but it's expensive.

I guess I'll have to wait and see how they compare to something like the Ohlins. Shipments are delayed until September right now, unfortunately.
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      08-03-2021, 10:57 AM   #57
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yeah sorry I like to rant. I can't complain about the YCW. They have done everything I have needed them to and YCW has made a few revisions based on feedback (sway bar mounting tabs are beefier now). They feel better custom valved with what feels like much more rebound damping. They are in-line price wise with BC or FA... That's what expectations I would hold for them. The hardware is everything it says it is but it's the damping that matters most I suppose. It would be interesting to do shock dynos on both but it's expensive.

I guess I'll have to wait and see how they compare to something like the Ohlins. Shipments are delayed until September right now, unfortunately.
Anyone that's seriously competed on Ohlins complains that the bodies are too long and they dont have enough travel. If you plan on competing seriously, i would stay away from Ohlins DFVs.
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      08-03-2021, 11:27 AM   #58
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Anyone that's seriously competed on Ohlins complains that the bodies are too long and they dont have enough travel. If you plan on competing seriously, i would stay away from Ohlins DFVs.
Any suggestions? These are things often overlooked by people as they hype a product based on a brand name. I'll be sure to compare and contrast to the YCW (which have a short stroke that I've complained about). The car in general has a lot of packaging constraints which limits what you can do especially when lowering the car. There is a limit in how short the strut body can be though while still being able to operate with limited hysteresis. External reservoir might be the way to go ultimately but right now I am invested in the idea of these new "dedicated track" Ohlins being a simple plug and play suspension that performs.
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      08-03-2021, 11:33 AM   #59
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I am not familiar with all of the options for this car. I will say that my MCS 2 way remotes have zero issues with travel at my current ride height setting, the same as what Phloozy ran on his Ohlins to barely avoid bottoming out. At these settings, I probably have another 1-1.5 inches of travel left.

Phloozy switched to MCS 2 way non-remotes, not sure if those are better for him in terms of travel or not.

If you run 17x9s up front, your front ride height will be limited by making sure the spring perches dont contact the tire. From there, the car is front camber limited unless you go to extreme measures like Phloozy and I have. Once you get the strut past 3.5* of camber, you start losing the ability to access the top of the strut for shock adjustment.
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      08-03-2021, 11:48 AM   #60
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Originally Posted by Mach3M3 View Post
I am not familiar with all of the options for this car. I will say that my MCS 2 way remotes have zero issues with travel at my current ride height setting, the same as what Phloozy ran on his Ohlins to barely avoid bottoming out. At these settings, I probably have another 1-1.5 inches of travel left.

Phloozy switched to MCS 2 way non-remotes, not sure if those are better for him in terms of travel or not.

If you run 17x9s up front, your front ride height will be limited by making sure the spring perches dont contact the tire. From there, the car is front camber limited unless you go to extreme measures like Phloozy and I have. Once you get the strut past 3.5* of camber, you start losing the ability to access the top of the strut for shock adjustment.
No travel issues on the 2 way non remotes! But yeah, the ohlins had travel issues and I am glad I switched but they were good enough to Win SCCA T4 locally! So who wants to buy my Ohlins?!
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      08-03-2021, 11:56 AM   #61
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This is exactly where I have ended up, looking at running a 6" spring on my Ohlins in order to clear the 17x9. This means minimal preload to avoid coil-binding the spring.

At the same time, I've been designing a custom camber plate to move the strut under the tower like you say. The one positive there is the Ohlins are bottom adjust, but that's a very valid concern for top-adjustment struts. It does sound like remotes are the way to go with the limited packaging up front.

3DM's website says they can upgrade the R&Ts to the dedicated track kit, that makes it seem like the dedicated track is just spring/valving changes and not necessarily physically different strut bodies.
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      08-03-2021, 12:29 PM   #62
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This is exactly where I have ended up, looking at running a 6" spring on my Ohlins in order to clear the 17x9. This means minimal preload to avoid coil-binding the spring.

At the same time, I've been designing a custom camber plate to move the strut under the tower like you say. The one positive there is the Ohlins are bottom adjust, but that's a very valid concern for top-adjustment struts. It does sound like remotes are the way to go with the limited packaging up front.

3DM's website says they can upgrade the R&Ts to the dedicated track kit, that makes it seem like the dedicated track is just spring/valving changes and not necessarily physically different strut bodies.
I had MCS custom build mine with a shorter stem so that my rebound adjuster fits below the strut tower, so it's definitely a possibility.
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      08-04-2021, 11:54 AM   #63
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That's the problem with an off-the-shelf 1-piece design like the Ohlins. Oh, sure it has more total travel. However, it's inherently restricted to a manufacturer pre-selected range of ride height and spring rates. If you take it outside of that range, it becomes inherently compromised. If you want to properly run outside of that, it becomes a custom affair.

Meanwhile, yes the total travel is compromised on the 2-piece design, found on YCW/RedShift/etc. However, it can be combined for a wider range of ride heights and spring rates. The other drawback here is that if you don't know what you're doing, it's just as easy to get wrong as it is right.

I don't know what RedShift run standard, or what options they offer, but YCW have a 110mm travel shaft standard and can run 130mm travel shaft with the optional extended reservoir that extends down into lower mount cavity. However, as best I can tell, this is actually more valuable for a street setup than a track setup. Based on the Swift metric spring data, the 110mm setup can already meet or exceed the 'usable stroke' of the vast majority of spring we'd be discussing here. Even without going into coil bind, exceeding the engineered usable stroke of the springs can unnecessarily damage them. So going for 130mmm on those springs would merely allow you to do more potential damage to your springs more often. Thus to get the parts working together properly, there shouldn't be any need for longer stroke in a track application. If you're bottoming out with the 110mm, it simply means the springs and/or bars (depending when the bottoming is occurring) are not stiff enough.

That being said, it has crossed my mind (but I never had reason to ask) that for additional full-travel lowering on a track biased setup, they may also be able to combine the 110mm stroke shaft with a shorter body by using the extended reservoir.
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      08-05-2021, 03:30 PM   #64
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Originally Posted by Driven5 View Post
That's the problem with an off-the-shelf 1-piece design like the Ohlins. Oh, sure it has more total travel. However, it's inherently restricted to a manufacturer pre-selected range of ride height and spring rates. If you take it outside of that range, it becomes inherently compromised. If you want to properly run outside of that, it becomes a custom affair.

Meanwhile, yes the total travel is compromised on the 2-piece design, found on YCW/RedShift/etc. However, it can be combined for a wider range of ride heights and spring rates. The other drawback here is that if you don't know what you're doing, it's just as easy to get wrong as it is right.

I don't know what RedShift run standard, or what options they offer, but YCW have a 110mm travel shaft standard and can run 130mm travel shaft with the optional extended reservoir that extends down into lower mount cavity. However, as best I can tell, this is actually more valuable for a street setup than a track setup. Based on the Swift metric spring data, the 110mm setup can already meet or exceed the 'usable stroke' of the vast majority of spring we'd be discussing here. Even without going into coil bind, exceeding the engineered usable stroke of the springs can unnecessarily damage them. So going for 130mmm on those springs would merely allow you to do more potential damage to your springs more often. Thus to get the parts working together properly, there shouldn't be any need for longer stroke in a track application. If you're bottoming out with the 110mm, it simply means the springs and/or bars (depending when the bottoming is occurring) are not stiff enough.

That being said, it has crossed my mind (but I never had reason to ask) that for additional full-travel lowering on a track biased setup, they may also be able to combine the 110mm stroke shaft with a shorter body by using the extended reservoir.
Yes the ycw are about 110mm and the Ohlins appear to get down on the internal bump stop as early as 75mm with about 100mm total travel per fe1rx's data. Many other lighters cars have 6-7"+ of front wheel travel whereas we end up with about 4.5."

Based on that I've realized that you don't really have much of a choice but to run really stiff front springs with a short stroke strut. Many of the "mid-range" front spring rates will result in bump stop engagement. Especially so on a roadcourse where the cars velocity is higher.

I think 700lb/in is a good place to start up front. I have no hard data on this but I believe that in a 3300lb BMW you will see close to 2000lb of outside corner load in a turn. At 700lb/in your 4.3" of strut stoke will have used about 1" of static compression (1" of rebound travel) given a ~650lb sprung corner weight. That leaves an additional 3" or so of bump travel less your bump stop. Add in a sway bar and effective wheel rate in roll is closer to 900+ meaning you can support that 2000lb cornering load even with a small bump stop in place to prevent bottoming out the struts.

700lb is the cutoff where I would want to run a helper spring to re-gain rebound travel if I were to run any higher of a spring rate. 75/25 bump/droop distribution is already pushing it. I think 60/40 is where most people want to be. The Dedicated Ohlin's appear to be 12k (672lb)/18k (~1000lb) and also run a front helper. It will be interesting to see where the bump/droop travel lands and work the math backwards to see just how much it gets into the bump stops up front in a turn. Maybe they are a longe stroke strut... I am leaning toward the helper should be removed on this setup though and just deal with having limited rebound travel.

Take these numbers with a grain of salt but...

If 800/1100 pushes too much then I'd probably look to increase the rear spring rate to achieve closer to a 60% front roll couple distribution. To land close to 60% you would need something like a swift Z65-178-260 (1500lb). Not sure if anyone has experimented with going that high with the rear rate but that's how the basic math plays out. Also not sure on the spring length either. Maybe it doesn't actually take that much spring due to other complexities in calculating roll couple but that's what my understanding of the basic math shows...

Maybe my perception will change when I have the ohlins 12k/18k in hand which are heavily front biased on paper. If my car magically handles insanely well ( i know some very fast drivers are already using them) then I'll have to try to figure out where the magic comes from (maybe the damping?).
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      08-05-2021, 05:36 PM   #65
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Quote:
Originally Posted by bbnks2 View Post
Quote:
Originally Posted by Driven5 View Post
That's the problem with an off-the-shelf 1-piece design like the Ohlins. Oh, sure it has more total travel. However, it's inherently restricted to a manufacturer pre-selected range of ride height and spring rates. If you take it outside of that range, it becomes inherently compromised. If you want to properly run outside of that, it becomes a custom affair.

Meanwhile, yes the total travel is compromised on the 2-piece design, found on YCW/RedShift/etc. However, it can be combined for a wider range of ride heights and spring rates. The other drawback here is that if you don't know what you're doing, it's just as easy to get wrong as it is right.

I don't know what RedShift run standard, or what options they offer, but YCW have a 110mm travel shaft standard and can run 130mm travel shaft with the optional extended reservoir that extends down into lower mount cavity. However, as best I can tell, this is actually more valuable for a street setup than a track setup. Based on the Swift metric spring data, the 110mm setup can already meet or exceed the 'usable stroke' of the vast majority of spring we'd be discussing here. Even without going into coil bind, exceeding the engineered usable stroke of the springs can unnecessarily damage them. So going for 130mmm on those springs would merely allow you to do more potential damage to your springs more often. Thus to get the parts working together properly, there shouldn't be any need for longer stroke in a track application. If you're bottoming out with the 110mm, it simply means the springs and/or bars (depending when the bottoming is occurring) are not stiff enough.

That being said, it has crossed my mind (but I never had reason to ask) that for additional full-travel lowering on a track biased setup, they may also be able to combine the 110mm stroke shaft with a shorter body by using the extended reservoir.
Yes the ycw are about 110mm and the Ohlins appear to get down on the internal bump stop as early as 75mm with about 100mm total travel per fe1rx's data. Many other lighters cars have 6-7"+ of front wheel travel whereas we end up with about 4.5."

Based on that I've realized that you don't really have much of a choice but to run really stiff front springs with a short stroke strut. Many of the "mid-range" front spring rates will result in bump stop engagement. Especially so on a roadcourse where the cars velocity is higher.

I think 700lb/in is a good place to start up front. I have no hard data on this but I believe that in a 3300lb BMW you will see close to 2000lb of outside corner load in a turn. At 700lb/in your 4.3" of strut stoke will have used about 1" of static compression (1" of rebound travel) given a ~650lb sprung corner weight. That leaves an additional 3" or so of bump travel less your bump stop. Add in a sway bar and effective wheel rate in roll is closer to 900+ meaning you can support that 2000lb cornering load even with a small bump stop in place to prevent bottoming out the struts.

700lb is the cutoff where I would want to run a helper spring to re-gain rebound travel if I were to run any higher of a spring rate. 75/25 bump/droop distribution is already pushing it. I think 60/40 is where most people want to be. The Dedicated Ohlin's appear to be 12k (672lb)/18k (~1000lb) and also run a front helper. It will be interesting to see where the bump/droop travel lands and work the math backwards to see just how much it gets into the bump stops up front in a turn. Maybe they are a longe stroke strut... I am leaning toward the helper should be removed on this setup though and just deal with having limited rebound travel.

Take these numbers with a grain of salt but...

If 800/1100 pushes too much then I'd probably look to increase the rear spring rate to achieve closer to a 60% front roll couple distribution. To land close to 60% you would need something like a swift Z65-178-260 (1500lb). Not sure if anyone has experimented with going that high with the rear rate but that's how the basic math plays out. Also not sure on the spring length either. Maybe it doesn't actually take that much spring due to other complexities in calculating roll couple but that's what my understanding of the basic math shows...

Maybe my perception will change when I have the ohlins 12k/18k in hand which are heavily front biased on paper. If my car magically handles insanely well ( i know some very fast drivers are already using them) then I'll have to try to figure out where the magic comes from (maybe the damping?).
Completely agree, math says to go with the 1500lb springs but seems insane to me lol
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      08-06-2021, 01:23 AM   #66
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That's largely because the stock ('flat') ride rate distribution is overseer biased and gets a surprisingly large portion of its roll rate and natural understeer bias from the sway bar(s). As you increase the spring rates, the same sway bar(s) contribute a decreasing proportion of the roll rate. So if keeping the same f/r ('flat') ride ratio, as the spring rates rise, it transitions from a steady state understeer characteristic to a steady state oversteer characteristic. Once you reach your desired handling balance, any further increase in spring rate would require a proportional increase in sway bar rate. At dedicated track car spring rates you can get into some absurd front bar sizes to keep it balanced, so the most common alternative is to run proportionally higher front ('pitched' ride) spring rates at the expense of 'flat ride' characteristics.

At more street friendly rates, the 'flat' ride ratios should generally work better... Well, that's the fundamental theory at least. There are obviously many other factors that influence this as well.
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