[parapaul]

Just because I don't remember seeing a direct comparison anywhere else on the forum.

E36 M3 front bump stop:



E90 Msport front bump stop:



Side by side:



Yes, it's 5 years old and holy shit, did it need replacing!!

Z4 rear bump stop:



E90 MSport rear bump stop:



Side by side:



Hope that's some help to someone in future

[335iSSA]

WOW those stock ones were in really bad shape, I amazed at how bad!

[Jonny954]

Sorry for the dumb question, but what exactly is the 'Bump stop'...??

[cvc 22349a]

Damn, you're oe bumpstops look bad. Your car must gravitate towards sharp impacts
Thanks for the post. Good info for folks who want to use lowering springs.

[parapaul]

Originally Posted by Jonny954

Sorry for the dumb question, but what exactly is the 'Bump stop'...??

It's not dumb if you don't know the answer

The bump stop isn't really it's correct name any more, it's technically called a micro cellular shock absorber, or something equally catchy. The idea is that the springs do most of the work taking the weight of the car as it bounces along our perfectly made, flat roads and the piston moves in and out of the damper as the springs compress.

The bump stop fits over the piston of the damper, effectively preventing the damper from 'bottoming out' under extreme compression. As it does so, because it's made of foam and has been designed by very clever people who know all about such things, the shape, size and composition determine exactly how it compresses.

This means that as the damper reaches its limit, instead of going "smoothly, smoothly, CLUNK" as it bottoms out, the bump stop adds an extra little bit of "smooth" to the last little bit of compression - and they're an integral part of the whole suspension setup.

People who have changed from stock to sport or aftermarket suspension have reported that the stock bump stops are too long, and when shorter springs are fitted the damper piston no longer has enough travel to do its job correctly - or in extreme cases actually has no travel at all, and the car is effectively riding on the bump stops. Changing from stock to a shorter bump stop gives back to the damper the extra travel that's been taken away by the shorter spring and lets everything work properly again.

Having had mine apart yesterday, there was no need to fit shorter ones to the MSport setup, the OE parts would have been absolutely fine. But given the state they were in, and for the relatively low cost, I'm very glad I had new ones to put on. I can't imagine those horrible old things actually did anything any more!!

HTH

[nitehawk]

Originally Posted by parapaul

It's not dumb if you don't know the answer

The bump stop isn't really it's correct name any more, it's technically called a micro cellular shock absorber, or something equally catchy. The idea is that the springs do most of the work taking the weight of the car as it bounces along our perfectly made, flat roads and the piston moves in and out of the damper as the springs compress.

The bump stop fits over the piston of the damper, effectively preventing the damper from 'bottoming out' under extreme compression. As it does so, because it's made of foam and has been designed by very clever people who know all about such things, the shape, size and composition determine exactly how it compresses.

This means that as the damper reaches its limit, instead of going "smoothly, smoothly, CLUNK" as it bottoms out, the bump stop adds an extra little bit of "smooth" to the last little bit of compression - and they're an integral part of the whole suspension setup.

People who have changed from stock to sport or aftermarket suspension have reported that the stock bump stops are too long, and when shorter springs are fitted the damper piston no longer has enough travel to do its job correctly - or in extreme cases actually has no travel at all, and the car is effectively riding on the bump stops. Changing from stock to a shorter bump stop gives back to the damper the extra travel that's been taken away by the shorter spring and lets everything work properly again.

Having had mine apart yesterday, there was no need to fit shorter ones to the MSport setup, the OE parts would have been absolutely fine. But given the state they were in, and for the relatively low cost, I'm very glad I had new ones to put on. I can't imagine those horrible old things actually did anything any more!!

HTH

Give this man a beer

[zeenon53]

^+1, very informative!

[cvc 22349a]

Originally Posted by parapaul

It's not dumb if you don't know the answer

The bump stop isn't really it's correct name any more, it's technically called a micro cellular shock absorber, or something equally catchy. The idea is that the springs do most of the work taking the weight of the car as it bounces along our perfectly made, flat roads and the piston moves in and out of the damper as the springs compress.

The bump stop fits over the piston of the damper, effectively preventing the damper from 'bottoming out' under extreme compression. As it does so, because it's made of foam and has been designed by very clever people who know all about such things, the shape, size and composition determine exactly how it compresses.

This means that as the damper reaches its limit, instead of going "smoothly, smoothly, CLUNK" as it bottoms out, the bump stop adds an extra little bit of "smooth" to the last little bit of compression - and they're an integral part of the whole suspension setup.

People who have changed from stock to sport or aftermarket suspension have reported that the stock bump stops are too long, and when shorter springs are fitted the damper piston no longer has enough travel to do its job correctly - or in extreme cases actually has no travel at all, and the car is effectively riding on the bump stops. Changing from stock to a shorter bump stop gives back to the damper the extra travel that's been taken away by the shorter spring and lets everything work properly again.

Having had mine apart yesterday, there was no need to fit shorter ones to the MSport setup, the OE parts would have been absolutely fine. But given the state they were in, and for the relatively low cost, I'm very glad I had new ones to put on. I can't imagine those horrible old things actually did anything any more!!

HTH

That's the primary function of bumpstops. It's my understanding BMW also engineers them to be a secondary spring so they can use softer springs for ride comfort yet increase spring rate for better handling during hard cornering; sort of like a progressive spring
So, you didn't change springs but switched to these shorter bumpstops? I'm curious if you'll experience a bit more body roll, dive and squat..

[parapaul]

Sorry - I replaced them along with the springs and dampers.

Although, also for reference, the stock bump stops from the MSport setup would have been absolutely fine with Eibach springs, there would have been plenty of travel left in all of the dampers.

I don't know how long the bump stops are from the non-sport setup, it's possible they're what caused the reported problems.

[irish320d]

Would anyone know what sort of bump stops i would need with the h&r race cup kit?
I had my car on a ramp today and found out i have NO bump stops left on the rear!
Any help greatly appreciated as i need to order some asap

[parapaul]

TBH you'll probably be fine with the standard MSport ones.

[irish320d]

Thanks

[bamboostk86]

where can i buy these?? thnx

[parapaul]

Your local dealer.

[Dr. G]

How squishy are those bump stops? Can you compress them via hand?

[parapaul]

From memory, (because it was about a year ago now) they're a similar consistency to a cold squash ball. If you're from the US and not sure what squash is, it's like racketball with a smaller, less bouncy ball, but that's probably not a great help

Yes, you can compress them by hand.

[Suntzu]

I'm ordering my Eibach Pro-Kit with B4-S as per your recommendations.
I'm still a little confused by bumpstops.

It's hard to get the E36 and Z4 bumpstops in australia and they are $130 each!

Can I just use MSPORT bumps stops or get aftermarket ones that are:

FRONT: 55mm (guessing from your shots)
REAR: 65mm

Noting I am on STOCK SE bumpstops right now. I could get them cut but they are 7 years old.

Hows the Pro-kit + b4S working long term? Any issues with 4 people plus luggage? Hoping they arent to soft.

Appreciate your advice so I can get this underway.

PS: whats the internal diameter of the shaft in case i go aftermarket?

[parapaul]

Standard MSport ones will be fine

After about a year I'm still very happy with my setup. Not soft at all, just perfectly damped. No problems at all under full load either.

[Suntzu]

OK great. I have source Msport bump stops at the local BMW stealer for a much lower cost. They are about 10-15mm bigger than the ones you used.

I have also sourced the B4-S despite bilstein trying to ram B12 down my throat and telling me I cannot order B4S in Australia!

Got the Pro kit springs coming and all new spring rubbers upper and lower front back.

All up its costing the same as a B12 kit sourced from the motherland - blighty - but thats ok as I am shit scared of having hard ride at the tend age of 39 years!

Im pretty much taking your recommendations (and two or three others who followed) because you guys seem to be very sensible and have well thought out comments and objectives for your cars.

I will report in with a review in a few weeks.


Front sway bar is also on the horizon but we will try springs/shocks first.

thanks a heap!

[parapaul]

Good luck look forward to hearing what you think.

[jzepeda]

Will you confirm the part number for me.
31332225377 fronts and 33536770350 rear. I want to order them from tischer but when I put the part numbers in they have a left and right, isnt it the same?

from the pictures they seems right.

[thecadman99]

Originally Posted by parapaul

It's not dumb if you don't know the answer

Having had mine apart yesterday, there was no need to fit shorter ones to the MSport setup, the OE parts would have been absolutely fine. But given the state they were in, and for the relatively low cost, I'm very glad I had new ones to put on. I can't imagine those horrible old things actually did anything any more!!

HTH

Thank you, Thank you, Thank you, for sharing.
I'm getting ready to tear down my Eibach pro-kit/BMW Performance suspension (on it when I got the car) to check how much travel I'm actually getting.

My car is very firm (but WOW does it handle), and I'm getting some bounce.

The PO had the PS installed so I have no idea what bumpstops are on there.
Hopefully they ARE too long and I can reduce the bounce with some new stops.

Your post will be a big help in determing what stops (I mean "Auxillary Shock Absorers" hehe) I have.