Rear tyre wear / alignment question (related to the 70mph humming?)

I'm still trying to get to the bottom of what this humming is at 70mph....
The mech I saw on Saturday thought the inner edge of my rear passenger tyre was feathering a bit - but I couldn't see it or feel it to be
honest...and I know what a scrubbed tyre looks like.
However, it has got me thinking about that now, and I've noticed that when I get home from work (approximately 13 mile journey at on average 40/50mph) the inner edges of BOTH rear tyres are warm to touch...whilst the rest of tyre is cool, especially the outer edges, which are completely cold.
The tyres don't look like they are wearing oddly, but the very inner row of tread does feel like it's been sort of flattened/worn to the road.
The first 4 wheel alignment I had done in November, just after I'd had the new tyres put on.
Here's the printout:
http://www.randcjones.plus.com/website/Nov%2005.jpg ]November 2005
Naturally, after i'd put the lowered springs on in January, I drove around for a week to let things settle, then took it back to have the alignment done again - but this time on 528i Sport with lowered suspension settings.
http://www.randcjones.plus.com/website/Jan%2006.jpg ]January 2006
After I'd had the January alignement done, I ended up having to replace the rear top mounts (that was when the spring was squeaking), and I haven't been to get yet another alignment done yet, as I didn't think it'd have made that much difference.
Is the warm tyre thing normal and do those alignment settings look ok? (apart from the front castor)
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Russ (www.e36coupe.com) wrote:

Yes, they look OK. But did they properly weight down the chassis per BMW spec? If not, then your camber may still be excessive as the BMW specs are in the "weighted" position which would increase the camber some.
Also, the specs are generally for the car with OE size tires. Your tires and wheels are bigger so any camber effect will have a greater effect on the road pressure difference from edge to edge.
Finally, I recall you mentioning using the M5 specs for your lowered car. M5's are notorious for wearing out the inside edges of the rear tires. But they handle great!! Things that make you go Hmmmm....
--
-Fred W

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Hi Fred
Thanks for your reply.
Yes, the car was correctly weighted on both occasions.
I've heard the M5 munches tyre inner edges, although I'd also gathered that was due to monster torque being transmitted to the road.
Any thoughts on the warm inner tyre edge thing though? Is that normal in your opinion?
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You have lowered the springs. The suspension geometry tries to keep the wheels in the vertical plain, however nearer the end of the travel the wheels will tend to splay in (top) and out (bottom). By positioning the wheels a few inches higher your normal suspension travel will now take place in the top end of the suspension 'window'. This will mean that more load and energy will be transmitted through the inside edges, particularly when the car squats down as you accelerate away.
It is bad enough when Alpina take a well designed car and start messing with it, but at least they have all the drawings etc. and cooperation of BMW. When ambitious amateurs start messing then problems are never far away: -
turbo - blown head gasket chipped - burnt valves big tyres / wheels - tyres scuffed in wheel arches body kits - unpredictable aerodynamics lowered suspension - bent mountings, poor handling, increased road noise any of the above - higher or void insurance
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yeah thanks R. Mark, that's really constructive. I wasn't asking your opinion on modifying my car.
I understand how the suspension works. I also know that a drop of a mere 25mm on the rear is more than acceptable on standard shock absorbers. Any more than 40mm requires replacement to stop the shocks wearing out as the standard shocks have a 'neutral' positio - as in there is resistance to expansion as well as compression, and it's not adivsable to make the shock operate far outside of that neutral window. I am also aware that going even lower than 40mm will need to be accompnied by camber correction kits - due to all of teh above, I chose a reputable spring manufacturer that woudl give a drop of less than 30mm.
The suspension does not try to keep the wheels in a vertical plane, BMW STANDARD suspension has a slightly negative camber.
The Eibach springs fitted lower the front of the car by 30mm and the rear by 20-25mm. This is actually the same drop as BMW offer on their 'low slung M-Tec' setup. Which is a BMW option, I might add.
You may alos want to ask yourself what is considered 'modified' about retrofitting STANDARD 17" BMW wheels to my car?
For your information, Alpina use the Eibach springs that I have just fitted, so they are obviously a bunch of misguided engineers too.
You seem to have been seriously misinformed and your pompus statments need some refinement as well:
Turbo - agreed, much aggro if not done correctly at great expense Cheap chip done by cowboy outfit = burnt valves or similar due to incorrect fuelling, timing, etc. Big tyres/wheels don't scuff anything if they are the correct offset and size. Body kits - seriously, how many BMW's have you seen with ridiculous body kits? Any bodywork modifications done that I've seen on our forum have been MTec parts. Lowered suspsension - bent mountings is a new one on me. Poor handling is only applicable if it's cheap gear and hasnt been adjusted/4WA properly. Where you live and part your car overnight has a bigger bearing on your insurance than delcaring you've put alloy wheels on your car.
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I think it's more down to the lowered suspension. I have std E34 fitted with BMW dealer fitted M-Tech suspension, and 17" wheels, which results in a slight negative camber. This causes slightly more wear on the inside edge of the rear tyres. I expect a lowered E36 rear wheels have a similar negative camber.

If the lowered suspension does give negative camber, I'd say it is. The inside edge of the tyre is doing more work, so I'd expect it to be warmer. Mike.
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I guess that's it then.
Just seems odd how there's very little /no variance between the standard suspension camber and the new lowered setup (Jan 2006)
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Russ (www.e36coupe.com) wrote:

I would say so. They are tilted inward, so there is significantly more pressure on the inner edges than the outers when going in a straight line. But then, we don't fit wider tires so we can go in a straight line, do we?
I think you should make every effort to drive faster in the corners to equalize that rear tire wear... ;-)
--
-Fred W

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Lol!
Thanks for your input again Fred.
"But then, we don't fit wider tires so we can go in a straight line, do we? "
Well...it seems some people do...
;o)
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