Muffler Contacting Tire on E36

[imstimpy]

This has been an ongoing thing for me, albeit far better now. Nonetheless, I STILL have a problem with the muffler hitting my rear tire under severe corning loads.

I originally rubbed my SuperSprint muffler against the Bridgestone 245/40/17s on 17x8.5+44 wheels. The exhaust mounts had 80k miles on them. It was pretty bad and smoothed out the tread. My solution was to swap out for a Stromung exhaust and all new OE exhaust mounts. This sured up the system and added a lot of clearance against both the suspension and the tire. I thought I had it licked.

The first autocross with this new setup showed I still have contact back there. This time it is with Yoko 245/40/17s on 17x9+42 wheels.

The two solutions I can see so far:
1) The BFH. I can leave everything alone but "massage" the muffler canister a bit. There is a nice greasy spot on the side where the tire hits so I already have the target ready to go.
2) Some sort of lateral support that only restricts movement under lateral load. This is more appealing than a solid mount because it should allow the system to continue shifting and flexing, but in a slightly restrictive manner.

Anybody have any other solutions or care to share their experiences?

-Jon

[lowside67]

rear spacer

[admranger]

BFH is what I used when I had a Supersprint. Worked great but you'll be beating it up pretty good to get the clearance you need.

You could limit travel side to side some, but it won't be pretty (thinking 1/16 cable looped around body of muffler and tied into the spare tire well or something like that. Lowes has a big selection of cable w/crimp ends that you can fool with.

[jayhudson]

When I was shopping for an exhaust, I specifically chose the UUC System U because of weight and tire clearance. I run 255s and have no issues with tire to muff contact.

You might be able to run a small spacer but it won't gain you much. Depends on whether your fenders are rolled, how low your car is and how much negative camber you're running in the rear.

Jay

[Jonathan@BimmerWorld]

1) The BFH. I can leave everything alone but "massage" the muffler canister a bit. There is a nice greasy spot on the side where the tire hits so I already have the target ready to go.

I had the Stromung with 255s for a while and I ended up using a BSH (big soft hammer). I just hit the tire-marked area with a rubber mallet several times and that cured the problem, and didn't really damage the exhaust from an aesthetic standpoint when it came time to sell it.

[fsmtnbiker]

Jon - When I had the Stromung on my car, I ran into the same problem. I never did BFH it, I just cleaned the rubber off when I sold the exhaust. I was planning on using the "make clearance via force" method, since I had all new exhaust hangars and it still had side-to-side movement.

[HabberstadChris]

I run 255s and have no issues with tire to muff contact.

Jay

It is best to stay clear of the muff, particularly when using some big rubber.

Christopher

[chebimmer]

I have seen people zip-tie their mufflers, keeping them from moving side to side at all really. Not sure from where to where they zip-tied though.
Maybe try that Jon.

[jdholder]

I have seen people zip-tie their mufflers, keeping them from moving side to side at all really. Not sure from where to where they zip-tied though.
Maybe try that Jon.

Uh, zip tie??? I think that would last about 4 to 5 seconds. Hammer is your friend.

[chebimmer]

It works and it works well, don't knock it until you try it. Or just knock it, with a hammer
Just something that works for some without damaging the muffler. Worth a try right?

[lowside67]

Wouldnt the zip tie melt?

[Hammer03]

I just had the same issue with my eisenmann and 245 ps2's and azenis. The lip on the side of the muffler was rubbing the sidewall of the tire, heating it up and rubbing off tread.

a little show of force, and it now has clearance I still get a little contact on very hard right hand corners, so I will probably bend the lip up a little more (I didn't get it completely bent up) to completely solve the problem.

[imstimpy]

In my case, it is actually a nice smooth section of the canister so there is no fear of tearing things up. The contact is now less so it shouldn't just melt the tread away like it was before. The stock exhaust actually has the center pinch weld cut away for tire clearance. I don't know if this was from the factory or if it was done after the fact by some previous owner.

As a little aside, I've got 10-15F greater tire temp on the inner shoulder of the tire next to the exhaust.

-Jon

[Jonathan@BimmerWorld]

As a little aside, I've got 10-15F greater tire temp on the inner shoulder of the tire next to the exhaust.

I think that alone is good enough reason to attempt to fix the issue IMHO.

[98ATLe36]

10mm spacers, clears good and IMO looks hot. Thats whats on my car.

[clopez95m3]

It is best to stay clear of the muff, particularly when using some big rubber.

Christopher

Hammer the muff, save the rubber.



Carlos.

[jone30]

Why not weld a bolt on the side of the exhaust and the spare tire well. Then run a cable between the two to limit the amount of lateral movement to the outside.

[bmwpowere36m3]

I just had the same issue with my eisenmann and 245 ps2's and azenis. The lip on the side of the muffler was rubbing the sidewall of the tire, heating it up and rubbing off tread.

a little show of force, and it now has clearance I still get a little contact on very hard right hand corners, so I will probably bend the lip up a little more (I didn't get it completely bent up) to completely solve the problem.

I had the same problem with my eisenmann race and 17x8.5" Kosei w/245s. I ended up first hammering the "lip" up and then decided to cut it off just in the offending area and welding it back up.

[Mike S]

This has been an ongoing thing for me, albeit far better now. Nonetheless, I STILL have a problem with the muffler hitting my rear tire under severe corning loads.

I was gonna give you some grief about all the weight of a muffler hanging back there, but I haven't had my coffee yet this morning.

I don't know how big your muffler is, but I've used Borla and Magnaflow and never had that problem. Not that you want to spend more money on the project, but perhaps a smaller muffler would take care of it.

I'm on 265/18s and never had any contact, though I will admit the exhaust is 0% stock and may be routed slightly differently behind the cat to smooth out the flow. Let's compare cars in S.D.

Mike

[NeilM]

BMW provided a clearance relief in the muffler to accommodate the wider rear tires fitted starting with the 96 model year. This isn't necessarily incorporated in aftermarket parts. I had a similar problem with my SuperSprint that led me to study the situation and come up with a simple and effective solution. One that, by the way, doesn't involve repeatedly buying new mufflers until you find one that works.

Firstly, it's important to recognize that the muffler's lateral positioning is partly determined by how you tighten up the flange bolts where the cat back muffler assembly joins the rest of the exhaust. One of those pipes is a slip fit and the other isn't, so varying the tension on the slip fit pipe bolts will move the tailpipes from side to side in the rear valance slot. I like to slip a spacer on either side of the tailpipes to keep the system centred during installation.

The other issue is that the rear exhaust hangers, by design for whatever reason, provide essentially no lateral locating force. You can fix that very easily by positioning a large fender washer on the outside of each hanger's centre bolt. The washer will restrict the ability of the hanger webs to move laterally, and so stabilize the muffler position.

Working these two things will allow you to position the muffler properly and know that it won't move around enough to touch the tire.

Of course judicious use of a BFH is still an option. However I was concerned with possibly breaking internal welds in the muffler canister.

Neil

[Hammer03]

I had the same problem with my eisenmann race and 17x8.5" Kosei w/245s. I ended up first hammering the "lip" up and then decided to cut it off just in the offending area and welding it back up.

I'm afraid thats what I'm going to have to end up doing. I was really surprised by how strong that lip was and how much force it to to get it to bend up.

Problem is, BFH I can do myself, grind/weld I can't

[emosound]

The other issue is that the rear exhaust hangers, by design for whatever reason, provide essentially no lateral locating force. You can fix that very easily by positioning a large fender washer on the outside of each hanger's centre bolt. The washer will restrict the ability of the hanger webs to move laterally, and so stabilize the muffler position.
Neil

I had this tire rub issue, and fixed it with the big washer on the end of the mounting post on the right side of the muffler. In my case, one of the 4 "legs" in the rubber mount was also broken. After the washer was installed, I had no rubbing. I still haven't replaced the rubber mount....

-Paul

[bmwstephen]

BMW provided a clearance relief in the muffler to accommodate the wider rear tires fitted starting with the 96 model year. This isn't necessarily incorporated in aftermarket parts. I had a similar problem with my SuperSprint that led me to study the situation and come up with a simple and effective solution. One that, by the way, doesn't involve repeatedly buying new mufflers until you find one that works.

Firstly, it's important to recognize that the muffler's lateral positioning is partly determined by how you tighten up the flange bolts where the cat back muffler assembly joins the rest of the exhaust. One of those pipes is a slip fit and the other isn't, so varying the tension on the slip fit pipe bolts will move the tailpipes from side to side in the rear valance slot. I like to slip a spacer on either side of the tailpipes to keep the system centred during installation.

The other issue is that the rear exhaust hangers, by design for whatever reason, provide essentially no lateral locating force. You can fix that very easily by positioning a large fender washer on the outside of each hanger's centre bolt. The washer will restrict the ability of the hanger webs to move laterally, and so stabilize the muffler position.

Working these two things will allow you to position the muffler properly and know that it won't move around enough to touch the tire.

Of course judicious use of a BFH is still an option. However I was concerned with possibly breaking internal welds in the muffler canister.

Neil

Doing a bit of a thread revival here as I found Niel's post very helpful. I thought I would add pictures to illustrate. The biggest difference (aside from the part numbers) between the s50 vs s52 muffler is in fact that the pinch weld beside the left rear tire. The s52 had a provision of the pinch weld cut to accommodate the wider rear tire setup in the latter models (17x8.5) as depicted here:

S50


s52 exhaust

Now to Niel's point, aftermarket exhausts may not accommodate this as some members ran into this issue running Super Sprint, Stromung, and even Eisenmann. Only ones I am aware of (by design) to not worry about interference with the rear tire are Dinan, bimmerworld, and UCC.

I am currently running an Eisenmann Sport Muffler with DS1's (17x7.5) with 235 width rears. And I have just abouth 1 inch of clearance between the rear tire (muffler is centered with valence cut out). I can imagine that running DS2s (17x8.5) with 245 rears or larger could run into clearance or rubbing issues.