45mm vs 51mm, suspension advice, please.

[MartinSE]

I want to renew/upgrade the suspension on my 320i chromie. It's in very good original condition but the suspension feels tired and the car rolls like a yank.

I'm going to change all the bushes that need it and also fit a rear arb to start with. Is it worthwhile seeking out thicker arb's from higher specced E30's like iS, 325, cab or touring and also change the front one?

My engine is standard. It might stay that way but I'd love something more powerful in the future. I'd change for a b25 in a heartbeat if my current engine wasn't in such good nick. Car has done < 65k and is well looked after so I think whatever engine I'd replace it with would be in worse condition.

When it comes to springs and dampers, what are the real benefits of fitting 51mm struts? Would this be sensible to do incase I put a bigger engine in later on? I know there is a larger selection of stuff for the 51mm. I want to use quality gear and lower it perhaps 30mm. H&R or eibach + bilstein seem to be very popular from what I've read here.

I'll probably be filling in with more questions.

Thanks!

[Messenjah]

hi mate im not too sure about the differences but the cxhances are if you buy some 325i struts they willl have the vented discs and brakes being able to dissapate heat better is only going to reduce fdade and be a good thing.

and as you say the availlllibilty of lowering springs is better for the 51mm struts so it has to be a worthwhile upgrade. and also ... if you are going to spend some money on them why dont you get some 51mm struts and a rally design weld on coilover kit and some new strut inserts and make yourself some coilovers. adjustable ride height and massive availibilty of different spring rates. thicker arbs are always a good option and touring ones are the besti beleive. as it goes i have both 51mm struts and touring arbs for sale

[MartinSE]

Messenjah: Thanks for your input. The brakes are the same, I believe. Coilovers are over the top for me, I think, since it's my daily driver and isn't driven on track. Thanks for offering, I'd gladly buy at least the arb's but I'm in Sweden.

[daimlerman]

You will be suprised at the difference that just a new set of dampers will make.
I have fitted Borge gas M-tec spec. ones all round to two E30's now and it has transformed the 'feel' of the cars.
51mm front struts are the way forward,huge range of springs are available if needed.I fitted BMW supplied M-tec springs to one car,lowered it just a touch,around 15mm,and stiffened the ride without making it uncomfortable.The other car(touring)retains standard ride hieght.

[MartinSE]

daimlerman: Yeah, I'm sure it will, with new bushes as well. I think all of the suspension and bushes are original. My dad has a 316 and an iX and both feel like sports cars compared to mine.

I still wonder what difference the 51mm struts actually make. I gather it doesn't have to do with how heavy the engine is since also the iS has them as well.

[Saga]

daimlerman: Yeah, I'm sure it will, with new bushes as well. I think all of the suspension and bushes are original. My dad has a 316 and an iX and both feel like sports cars compared to mine.

I still wonder what difference the 51mm struts actually make. I gather it doesn't have to do with how heavy the engine is since also the iS has them as well.

Tourings are all 51mm strut too IIRC, even the four-bangers like mine.

Since you're in Sweden, perhaps consider the Volvo 240 four-pot caliper swap? You must have a wide selection to choose from! Requires discs and mounting brackets of course. I'm doing the Mazda RX-7 / VW Corrado G60 disc conversion at the moment.

[gareth]

the springs themselves are the same fitment aren't they? just touring/cab/saloon differences in spring rates but they will all 'fit' the same.

the shocks are different obviously

[e301988325i]

Messenjah: Thanks for your input. The brakes are the same, I believe. Coilovers are over the top for me, I think, since it's my daily driver and isn't driven on track. Thanks for offering, I'd gladly buy at least the arb's but I'm in Sweden.

I'm fairly sure it's only the 51mm struts that come with vented discs, but I may be wrong. I'd upgrade to 51mm spec, and the ARB's, doesn't make sense to buy new 45mm dampers when you can UPgrade the bodies.

[scott180gtb]

I have just stripped down my front struts. Both shocks were completely fooked. The seals were perished offering no damping what so ever. Surprisingly I thought the car didn’t drive to bad so I can’t wait to drive it after the upgrade.

[mt1104]

the difference in 45mm and 51mm is just damper choice really, that and the 51mm are slightly stronger - but I doubt this will be noticed on a road car. It also goes the other way, as the 45mm ones will be *slightly* lighter and so will have less unsprung mass - but again I don't think even the stig could tell the difference.

I'd get some 51mm if you can, as there's more choice in terms of available dampers, iirc the only uprated dampers available for 45mm inserts are bilstein b4s, and some other dubious ebay ones. Though having said that, I have a set of B4s on my rear and they match the front boge mtec items extremely well.

The biggest difference I made was fitting a rear ARB (I had a standard 318 when I started), really tightened up the car. I used a 14.5mm rear and a 20mm front one, I think the tourings and cabs had 22mm front ones - but remember if you fit that your car will have more tendency to understeer.

[MartinSE]

My front discs are vented.

mt1104: I've been looking around and the nice options like H&R and bilstein don't seem to be available for 45mm. Why is there more tendency for understeer with thicker arb's?

I've just contacted a guy who offered me touring arb's front/rear for ~£45 + shipping which to me sounds fair so I think I'll jump on that.

[mt1104]

its the ratio of front / rear ARB thickness will make the car either lean towards under / over steer, so thicker front ARB will mean more understeer, thicker rear ARB will mean more oversteer. So you have to match them, to the car as well to your driving style. Ideally you want the car to be neutral on the limit, so you can basically tell it what you want it to do.

iirc the H&R ARBs are 24mm front and 16mm rear, giving a ratio of 1.5 - assuming H&R have done their homework and aimed to make the car more neutral (of course this will be slightly out as they probably did their tests on their own cup springs), with a standard sport / touring rear ARB which is 14.5mm, to get the same ratio as H&R you ideally want a 21.75mm front ARB. So after all that it looks like the 22mm front ARB your going to get will be more or less spot on.

Though on the other hand, it could just mean H&R were epically lazy and just scaled up OEM spec.

[harry_p]

the 51mm struts are definately a good idea on any e30, not just large engined / hard driven ones.

the strut is a structural part of the suspension, remove the topmount and the wheel will wobble all over the place. every force that acts on the wheel other than directly through the travel of the damper will try and bend the damper rod and strut housing, every time you brake or corner.

a thicker rod gives more strength so it is better at resisting bending, so puts less force on the bushings and seals, giving a smoother ride, more controlled geometry and longer damper service life.

i would also suggest that a thicker front antiroll bar on an otherwise standard e30 will infact increase front end grip. the reason being that most e30s run very little castor or negative camber, and they roll quite a bit. under hard cornering the outside front wheel will tend to roll into positive camber, leaning hard on the outside edge of the tyre. by using a thicker front arb the car rolls less, the tyres stay flatter to the road surface and front end grip is increased.

[MartinSE]

harry_p: I'm convinced!

They guy selling me the ARB's also happens to have touring struts. Is there anything I sould ask concerning the condition since I'll buy them unseen? Same goes for ARB's + related bits.

[MartinSE]

Bump

I'm wondering if there is anything I should ask before buying second hand struts. Do they wear? They are from a -89 ~130k 325i touring. Seller told me the strut bearings might be worn. Can I keep my current ones or are they different? Also, do I just fit my current brakes and wheel bearings?

Thanks

[mt1104]

brakes should be a simple swap, wheel bearings on the other hand are a bit of a pain to do yourself, doable but a pain. Depending on your budget I'd be very tempted to buy some new ones and have them fitted while the struts are off the car to save time and money in the long run.

I've done the same, upgraded to 45mm, and one of the 51mm struts I brought was slightly bent, unnoticeable to the eye but it made the car follow the road and generally inconsistent steering. I brought a replacement and it sorted it. So to your initial question, struts don't generally wear no, but be careful of unseen accident damage.

Also, I assume by strut bearings the seller means top mounts? again depending on budget you aught to replace these as well.

But as with all things, prices start to mount up quickly, especially if you use the recommended bmw rubber.

[E30star]

Spax do 45mm inserts too.

But yeah, 51mm for me, stronger and better availability for inserts etc. For example, we don't do coilovers for 45mm struts, but do for 51mm struts.