45mm strut suitability to track/race conditions

[dlguadiz]

I am slowly turning my e21 320/6 into a track rat and once thought of using the e36 subframe but after some more research and pondering I have decided to stay with the e21 front geometry.

With that out of the door, I found some nice but pricey Mcintyre-type suspension upgrades that I might be able to use, along with RHD e46 purple-tag rack and pinion.

Unfortunately, my 320/6 have a 45mm strut, not the 51mm strut of the 323i and I am concerned about its durability under track/race conditions. Are there any coilovers that are stout enough but fit into this strut?

[OldGray320i]

Fortunately, Koni is making inserts for the 45mm strut tube again.

But, otherwise, finding anything for 45mm unit is nigh impossible.

There are coilover kits that convert it, or you can cut strut tubes off of something else, but either way you cut the stock tubes and weld on the replacements.

Look for my post on coilovers to see what the latter looks like.

Best of luck on your efforts.

[Tom D]

https://www.bimmerforums.com/forum/s...ground-control

[dlguadiz]

I guess we need to break down the problem further. The 'suitability to track' issue has two components -- (1) the hub bearings, (2) the strut/piston size.

From my research, it seems like there are two types of hub bearings: (1) for the m10 cars (part #31211107447), (2) for the m20s and some m10s (part #31211107456). My 320/6 has the latter type which is a relief. This is what I was initially worried about since I'm going to install an m20 327i Frankenstein engine.

Then there is the 45mm vs 51mm strut diameter (every model vs 323i). I am going to probably go the easiest way -- weld in coilovers. I initially balked at this idea since I really like the ability to change modular inserts according to application. Luckily, I chanced upon this dude from NZ on the internet that examined modular coilovers from Tein. Which is what I'm going to try to do.

[Tom D]

two types of hub bearings: (1) for the m10 cars (part #31211107447), (2) for the m20s and some m10s (part #31211107456).

actually there are four different bearing sizes, you've only listed two, one for the outer hub and one for the inner hub and both of those are a different size and part number.

as for your statement above. there is two different size bearing sets known as the "big' and 'small' bearing hubs.

(1) small bearing hubs/spindles were installed on M10 cars starting in 10/1979, these are known as facelift cars.

(2) big bearing hub/spindles were installed on M10 cars until 9/1979, these are known a pre-facelift cars

(3) big bearing hubs/spindles were installed on M20 cars throughout it's production

[dlguadiz]

Thank you for the clarification, Tom.

Before researching any of these, I always thought my 320/6 had the same struts/hubs like the 323i since they are both m20s. Then when I checked the strut diameter my heart sank as I measured 45mm -- I then thought someone replaced it with an m10 strut, and with it, the "small" bearings. Now, after all the research, the 320/6 was some sort of evolutionary step towards the 323i from the m10s -- having the big bearings on the 45mm struts.

[OldGray320i]

Then there is the 45mm vs 51mm strut diameter (every model vs 323i). I am going to probably go the easiest way -- weld in coilovers. I initially balked at this idea since I really like the ability to change modular inserts according to application. Luckily, I chanced upon this dude from NZ on the internet that examined modular coilovers from Tein. Which is what I'm going to try to do.

I don't see that Tein offers anything for the E21, and I didn't see anything "modular". I'd be curious as to what that looked like - mostly for the fun of it at this point.

The modular would have to be akin to what I did, a larger strut tube to welded on to the original spindle assembly if inserts are to be used.

As to changing inserts depending on application, you might want to look at Koni 8611s instead, they are adjustable (separately) for compression and rebound.

Dial it up for what you want without having to change out a damper.

[dlguadiz]

I don't see that Tein offers anything for the E21, and I didn't see anything "modular". I'd be curious as to what that looked like - mostly for the fun of it at this point.

Yes, there are no Tein coilovers for the e21 though I did encounter an e21 race car with e36 front subframe/suspension and Tein coilovers. Its easy to have the front camber plate machined to e21 specs and the lower portion is welded-on anyway. As for the rear, since its going to be upgraded to an e28 subframe, I'll just buy an e39 Koni (M14 fisheye, M10 shaft).

As for the "modular" comment, if your going to weld a coilover to the 45mm strut, what happens when it gets blown? You remove the weld and weld-in another one? Tein so far is the only coilover Ive seen where you can unscrew the shaft/piston assembly so no need to remove the weld. You just buy a new shaft/piston assembly. Kindly refer to this link --> https://stanceworks.com/forums/showt...-BMW-E21/page2

There maybe some coilovers that are modular that I dont know of, but Tein is the most viable for me. There are a lot of Civic front Tein coilovers here with springs rated at around 500 lbs/in. As for the rear, I already have 375 or 560 lbs/in coilover springs and GC sleeves ready to go on an e39 Koni.

[OldGray320i]

For the fronts, it's why I went with welding on larger strut tubes for use with strut cartridges. One goes bad, pull it and throw a new one in.

Depends on what you want to do with the car, though. I wanted a simple and affordable stock style set up. If you're doing major work like swapping subframes, the world is your oyster.

[OldGray320i]

Tein so far is the only coilover Ive seen where you can unscrew the shaft/piston assembly so no need to remove the weld. You just buy a new shaft/piston assembly. Kindly refer to this link --> https://stanceworks.com/forums/showt...-BMW-E21/page2

Ah, now I know what you're talking about. That's common among a lot of the affordable coilover builders.

When I sent the units for the Miata back to be rebuilt, I sent just the threaded cartridges. BC, Tein, everybody uses those.

[dlguadiz]

BC, Tein, everybody uses those.

I am aware of BC Racing and I know they have e21 coilovers, 45mm and 51mm. But made in Taiwan coilovers just doesn't cut it for me. I'm an IT engineer and Ive worked with both Taiwanese and Japanese engineers both in Taipei and in Yokohama. Lets just say I share the same attitude towards quality as the Japanese. Taiwanese, not so much.

For the fronts, it's why I went with welding on larger strut tubes for use with strut cartridges. One goes bad, pull it and throw a new one in.

Believe it or not, I am also considering this option. I have two e30 51mm front strut lying around and I could actually cut these and weld them unto the 45mm. At what length did you cut both tubes? What strut cartridge did you use?

[OldGray320i]

I am aware of BC Racing and I know they have e21 coilovers, 45mm and 51mm. But made in Taiwan coilovers just doesn't cut it for me. I'm an IT engineer and Ive worked with both Taiwanese and Japanese engineers both in Taipei and in Yokohama. Lets just say I share the same attitude towards quality as the Japanese. Taiwanese, not so much.




Believe it or not, I am also considering this option. I have two e30 51mm front strut lying around and I could actually cut these and weld them unto the 45mm. At what length did you cut both tubes? What strut cartridge did you use?

I don't know a lot about Tein (certainly know of them), but for damping, the internals matter more than the externals. Damping profiles matter as well, so goes without saying if you do go Tein, ask them if they'll mod the damping to work well with e21 motion rates and so on.

My tubes are 14" long and came off of a 91 Volvo, so that's what I have; the anecdotal spec on the board here is cut 2" off the stock strut for coilovers, and I believe top of the spindle to the top of the housing is 16.5" (all measurements I note here are top of spindle assy to top of strut housing). So in theory, I'm about 2.5" shorter than stock. HOWEVER, I left about 1.5 of the stock tube on as a guide, so my internal space is about 12.5 for a strut cartridge.

For inserts, I'm running a Koni 8610-1437. Single adjustable rebound only. The 8611 series (same cartridge size) is a double adjustable, sounds like you might want that.

I'm hoping to get the car one the ground this weekend, we'll see.

[dlguadiz]

For inserts, I'm running a Koni 8610-1437. Single adjustable rebound only. The 8611 series (same cartridge size) is a double adjustable, sounds like you might want that.

Thank you for pointing me in the right direction. It helped reduce my research time by a lot. For the record, the Koni 8610-1437 double adjustable equivalent is Koni 8611-1259, but requires a 1/2" diameter hole at the bottom of the strut for the second adjuster. I post here some more similar Koni race inserts with measurements for the others...

Koni Inserts - Race.jpg

...ask them if they'll mod the damping to work well with e21 motion rates and so on.

Do you know the base motion ratio of the e21?

I tried to measure mine using a laser for the angle and a ruler for the D1/D2 values. Its 0.998 Front and 0.995 Rear. Since I don't have a base figure, I cant tell whether I'm doing it right or not. I do know that it changes as you adjust the camber or put in an e28 subframe in the rear but a base value would help.

The e36 and e30 motion ratio has been discussed by their respective forums and are as follows.

e30 Front: 0.92, Rear: 0.64
e36 Front: 0.94, Rear: 0.67

I'm hoping to get the car one the ground this weekend, we'll see.

Nice! I hope it turns out really great!

[OldGray320i]

Thank you for pointing me in the right direction. It helped reduce my research time by a lot. For the record, the Koni 8610-1437 double adjustable equivalent is Koni 8611-1259, but requires a 1/2" diameter hole at the bottom of the strut for the second adjuster. I post here some more similar Koni race inserts with measurements for the others...

Koni Inserts - Race.jpg




Do you know the base motion ratio of the e21?

I tried to measure mine using a laser for the angle and a ruler for the D1/D2 values. Its 0.998 Front and 0.995 Rear. Since I don't have a base figure, I cant tell whether I'm doing it right or not. I do know that it changes as you adjust the camber or put in an e28 subframe in the rear but a base value would help.

The e36 and e30 motion ratio has been discussed by their respective forums and are as follows.

e30 Front: 0.92, Rear: 0.64
e36 Front: 0.94, Rear: 0.67



Nice! I hope it turns out really great!

I'm afraid I do not - and I can't recall if I've seen them anywhere or not. Based on what you listed for the e30 and e36, as strut based cars, it seems you're not far off, though I'd think the e21 should be a little closer (at the front). For the rear, e30/36 both have the spring up underneath the body, so those MRs make sense; e21 rear spring is as far outboard as the fronts, so makes sense the numbers are close front to rear.

In any case, both Feal and RedShift will sell you an e21 kit, if you went that way, both legit motorsports entities. The Miata has Feals on it, and it's the best of the budget coilovers out there for the Miata, my opinion. Great valving for auto-x, more than passable on the street with 725/450 springs. Redshift has glowing reviews from guys on the grassrootsmotorsports board, various cars. You might ask if they'd have the MRs for the e21.

Thanks for the well wishes, I'll post up once I get mine on the ground.

Cheers.

[mxl556]

Beware of new Koni Sports, 86 1957SPORT, they may (probably) not fit inside stock strut housings. At least they did not fit into my stock 45mm housings.
I ordered a set and had to return them, ended up losing shipping for no reason. Now I am waiting for a refund.

Max

[dlguadiz]

Beware of new Koni Sports, 86 1957SPORT, they may (probably) not fit inside stock strut housings. At least they did not fit into my stock 45mm housings.
I ordered a set and had to return them, ended up losing shipping for no reason. Now I am waiting for a refund.

Max

Thank you for the warning. To clarify for those who are following this thread, this concern is for the unmodified 45mm strut housing, not the modification OldGray and I were discussing (e.g. put 51mm tubes on 45mm strut).

Were you able to measure the diameter of these new shocks? If you follow the link provided by Tom D. earlier, the ID of the 45mm strut is around 40.13mm and the diameter of the KONI shocks that fit is around 38.32mm

[dlguadiz]

Beware of new Koni Sports, 86 1957SPORT, they may (probably) not fit inside stock strut housings. At least they did not fit into my stock 45mm housings.
I ordered a set and had to return them, ended up losing shipping for no reason. Now I am waiting for a refund.

Max

I think I know what happened. There was a mix-up in the order and 45mm shocks for the 51mm struts were sent instead of the 38mm shocks for the 45mm struts -- 45mm shocks just wont fit on 45mm struts.

[OldGray320i]

Got the car on the ground, still need to a) drive it more, and, b) nut and bolt a few things, but just a quick drive and fling it around a corner, and oh em gee, awesome.

I'm on 8k/5.5k (448/300lb) springs, with 8610-1437s/NC Miata Konis, cut cut about 1/2 in off the bumpstops supplied with the front-1437s, and some shorter Koni bumpstops on the rear, and with some generic hankook street tires, it's a gem.

I didn't know what to expect, but first blush, better than what I thought I'd get.

We'll see what more driving brings.

If you want to go the shorter/ bigger diameter (i.e. ~51mm tubes) housings with the Koni double adjustable inserts, I think you'll be more than fine.

And from the Goodwin racing site, looks like there will now be Miata NC race units, and the body appears to be threaded. You do have to get spacers for the lower mounting eye, and mod the top hats/play with upper mount and spacing, but if the damping profile isn't too far off, it would be easier still than what I did. 20230228_152853.jpg

[Retoropak]

I welded volvo 51mm tubes to my knuckles. and used koni single adjustable race inserts. A1 racing spring hats and threaded sleeves,350lb/400lb spring combo. It was a bit stiff for the daily duties but tolerable. It handled great.
I am reusing the inserts in my e36/e28 suspension swap.

Here is the write up with some part#s

https://www.bimmerforums.com/forum/s...3#post30007523