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      01-18-2016, 10:01 AM   #1
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Would popular H&R springs mitigate hopping?

I have what is called rear axle hopping when driving enthusiastically in Sport+ (DTC on) - do you think a mainly lowering set of springs like the H&R 28896-2 would mitigate it? TIA

Piotr


EDIT: OK, perhaps my post has been too sparse. What I mean is whether any of you guys experienced this unpleasant effect (of the vertical component of the forces at the tire just starting to spin) - and if so, did changing some masses / dumping / springs of the rear axle help eliminate it?
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      01-18-2016, 02:26 PM   #2
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Yes wheel hop is a problem, but my car is stock so I can't help. Try to avoid it. It can break your axles and differential.
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      01-18-2016, 02:34 PM   #3
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I've read that the H and R springs are a bit weak for the car. People have been saying the car basically rides on the bump stops.
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      01-18-2016, 02:46 PM   #4
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Quote:
Originally Posted by pz619
I've read that the H and R springs are a bit weak for the car. People have been saying the car basically rides on the bump stops.
Wow that can't be good. I know I'm probably in the minority but I truly believe that aftermarket stuff is mostly junk and ruins the car.
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      01-18-2016, 03:44 PM   #5
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I fully agree with you; have been searching for pros and cons of some cheap lowering springs option, but will probably look elsewhere.
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      01-18-2016, 08:51 PM   #6
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Aftermarket suspension can be great, but lowering springs are generally hacked together pieces that are not properly engineered for a complex, adaptively dampened suspension like the one on your car.

They may be a great upgrade from the stock mush springs on the average sport-compact sedan, but that really isn't the issue here.

Generally you get movement in the rear axle due to the suspension linkages, not the rate of the springs. This is why the M2/M3 have the rear subframe hard mounted to the chassis. That reduces a great deal of the slop which can occur in the rear axle (while increasing the noise/vibration/harshness of the ride).

Usually to improve that condition, things like stiffer suspension bushings and other suspension components to reduce that flex & slop are where you want to spend the money. I am not familiar with anyone doing urethane bushings for the F2x yet though.
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      01-18-2016, 08:56 PM   #7
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Quote:
Originally Posted by moldcad View Post
I have what is called rear axle hopping when driving enthusiastically in Sport+ (DTC on) - do you think a mainly lowering set of springs like the H&R 28896-2 would mitigate it? TIA

Piotr


EDIT: OK, perhaps my post has been too sparse. What I mean is whether any of you guys experienced this unpleasant effect (of the vertical component of the forces at the tire just starting to spin) - and if so, did changing some masses / dumping / springs of the rear axle help eliminate it?
Looks like someone is operating it as if they don't own it
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      01-18-2016, 09:06 PM   #8
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Quote:
Originally Posted by BentZero View Post
Looks like someone is operating it as if they don't own it
OP is doing something very very wrong if he's consistently experiencing wheel-hop.

He explains that he only gets it when he's "driving enthusiastically".... what? Wheel hop only happens on acceleration in 1st gear and sometimes in 2nd if you're absolutely ripping/abusing the car. Sport+ wouldn't allow enough spin to induce noticeable & consistent amounts of wheel hop either anyways...
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      01-18-2016, 09:45 PM   #9
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Hmm, perhaps the OP has had too many liquid hops. :/
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      01-19-2016, 12:18 AM   #10
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OK guys, to clear things up - the OP (me) experienced hopping only once, and being an engineer with lots of experience (45 years of motoring), and mechanical sympathy for his car, successfully tried to avoid this condition ever after knowing how bad it can be for the car. Now the OP is seeking advise from those more experienced in car mods for means to eliminate even the possibility of it occurring again - and since the OP has been considering dropping his car some 10-15 mm anyway, he started this thread. Thank you all for the answers!

PS. The OP, living in a country where only some 25 years ago the only vehicles available we "creatures" like the Polski Fiat 125p (to mention the one with the same RWD tranny layout), knows hopping all too well from those years - the car was only 75 PS, and it was prone to hopping at almost each harder acceleration. Frankly, the OP expected more of his M235i in this area (the more so that driving an E46 330i for almost 10 years earlier in his life, never experienced hopping at all). But it seems the more powerful engine plus the lower build quality of today's BMWs returned (way - sort of ) the OP to his Fiat 125p days in this regard...

PS. A theory for you guys to consider and constructively discuss: could it be the bushings quality (or generally the rear axle and suspension) aren't quite ready for the LSD the OP has? Because the only so far instance of rear wheels hopping occurred when I floored it in a tight curve - tight enough to impose a very low speed, thus the 1st or 2nd gear of my 8AT (I wasn't even in Sport mode then) - just to exit it with some fish tailing... LSD was at play for sure; an open diff car would lose the traction momentarily - thus not exerting such big forces - while mine did pull with both rear wheels, but lost it for a moment vertically...

PPS: after the way the OP composed his answer, please don't suspect him of split personality
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      01-19-2016, 03:06 AM   #11
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Quote:
Originally Posted by Cyberdemon View Post
Aftermarket suspension can be great, but lowering springs are generally hacked together pieces that are not properly engineered for a complex, adaptively dampened suspension like the one on your car.
If I wanted to minimally lower my M235i (10-15mm), and not worry I'm perhaps improving the stance and overall looks, but compromising the ride quality and accelerating the wear of other elements (like adaptive dampers) - which quality product would you (and others of course) advise? The H&R springs I mentioned have two advantages: price and drop distance that suits me, but if they are too soft as some say - what instead then? TIA

Piotr
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      01-19-2016, 07:58 AM   #12
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I won't attempt to offer a single piece of advice, I have not shopped or researched any of the aftermarket options for the 2 series. But as mentioned if you want a drop, for drop reasons (or a stiffer setup) you can research what is out there in the suspension forum. Generally a set of adjustable coil overs which have been properly matched to the car will give you the best pairing, another option people have spoken about is the Dinan Shockwave tune for the adaptive dampers (will not lower the car, but has been said to fix some quirks of the adaptive system). Personally I love the adaptive dampers so I wouldn't want to get rid of them for a standard system.

http://www.2addicts.com/forums/forumdisplay.php?f=522

Since you mentioned you have the LSD and were coming hard out of a tight corner, you have to keep in mind that if the LSD is locked up and you're making a tight radius turn, what you experienced (especially on sticky tires) is fairly natural. The inside wheel and outside wheel were both locked which meant the inside wheel was being forced to move too fast which means it will have to skip. If your tires weren't as sticky, the wheel would have just been able to spin, but because of that it moved to the next softest spot which was your bushings.

It's not fair to try and compare that characteristic of your M235 to your old 330ci - that car had 100 less HP and Tq to put down, which means when accelerating hard out of a turn there is a lot more force to disperse.

Driving habits are important too...if you were getting that much wheel hop it's probably a sign you needed to ease onto the throttle a bit more in such situations, unless you're purposely trying to push the back of the car out.
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      01-19-2016, 10:59 AM   #13
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In addidtion to the LSD potentially causing the wheel hop feeling, the electronic nanny is hard at work with the power of the M235 ripping up the tires on a tight corner. If you want a fair test, turn it completely off, the tires will just spin and slide. As you have mentioned before, the M235 needs more rubber, I can feel the nanny kicking in very often. BMW skimped on rubber with the M235 on purpose. Why? M2.

One remedy that I've found to minimize wheel hop is getting the tire pressure right for your roads and driving style. I have changed the tire pressure in my car to 34.5/36 (morning cold). The recommended 38 lbs in the rear was way to high on my car...hop hop hop, or should I say twitch twitch twitch, the nanny works overtime.

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      01-19-2016, 11:09 AM   #14
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Thank you guys; you confirm mu guesses about LSD being at play there. Also, a lower rear tire pressure is a good idea - unfortunately not always, and you cannot change it at will, during driving.

Anyway: M235i may be a good track car (tracking is less popular in my country), but for auto-crossing - absolutely not, without serious preparation.
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      01-19-2016, 11:36 AM   #15
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Quote:
Originally Posted by moldcad View Post
Thank you guys; you confirm mu guesses about LSD being at play there. Also, a lower rear tire pressure is a good idea - unfortunately not always, and you cannot change it at will, during driving.

Anyway: M235i may be a good track car (tracking is less popular in my country), but for auto-crossing - absolutely not, without serious preparation.
Let's be honest, most stock cars with more than 300hp isn't going to be great at tiny twisty bits. BMW's do great on the high speed bits but the turbo power delivery, narrower rear tires and generally heavy weight don't make this car an AutoX dream. That's what Miata's are for.

Even on track, there is a lot of suspension tweaking on the front end to improve understeer and keep the tires from wanting to roll. But once you're pushing it to that limit on a regular basis you can decide what tradeoffs to make.

For a car that drives so well on the street and still handles great at 8/10ths in factory form, that's a lot to be said. Unlike cars that are so stiff because of their track focused setup that you'll rip your fillings out on a pothole.
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      01-19-2016, 11:46 AM   #16
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Absolutely right - the M235i is a street car, and it would need serious preparation for any kind of extreme use. I'm a very aggressive driver (well, sometimes), and never had a car with mechanical LSD. I think I just must take it into account. LSD usually helps me tremendously, but not in tight twisties.

Thanks for your input!
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      01-19-2016, 12:55 PM   #17
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One more obvious thing: the cars I used before for this driving style quite successfully were much, much weaker, which only allowed me to drift when it was rainy, or actually on snow (using snow tires, of course). This alone explains much lower forces acting on any tire, in any direction.

But I must admit when I experienced the violent hopping for the first (and the last) time, I was unpleasantly surprised.
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      01-29-2016, 09:46 AM   #18
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Quote:
Originally Posted by nike001 View Post
OP is doing something very very wrong if he's consistently experiencing wheel-hop.

He explains that he only gets it when he's "driving enthusiastically".... what? Wheel hop only happens on acceleration in 1st gear and sometimes in 2nd if you're absolutely ripping/abusing the car.
How do you know all that if if never happened to you?
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      01-29-2016, 06:44 PM   #19
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Wheel hop is a result of dynamic changes of contact patch of the tires, position and direction of the tire relative to the road surface.

This in turn is a result of dynamic changes of position of the control arms under power, primarily changes of toe-in. This is true for any vehicle without exception that experiences wheel hop.

At a certain threshold a tire's contact patch decreases and it loses grip. It then snaps back to a position with an optimal contact patch and grip until it again "pulls" the control arms forward so much that the tires again reach a position with significantly less grip, and the cycles goes on and on.

The position of the control arms changes because of the weak parts in the assembly - linkages - that is bushings. So the magic word to correct the problem is BUSHINGS.

No springs, nor shocks, nor sway bars, nor LSD will have a significant impact on wheel hop if the key factor in this equation, bushings, are crap.

Sudden appearance of wheel hop is often a symptom of bushings failure and they are the first thing to look at for damage, tear&wear. Sometimes simply using new bushings will cure the problem. In some extreme cases things like a failed shock may be the reason for wheel hop but usually you'll know it because of other symptoms.

Stiffer bushings will not allow a change in the position of the control arms, and therefore the wheels, so as to produce those cycles of less grip and more grip. In essence, the movement of the control arms needs to be as limited longitudinally (primarily) as possible.

The crappier the tire to begin with the less likely the wheel hop phenomenon is to occur. The wheels will just spin. The stickier the tire the greater the threshold when wheel hop occurs, so logically, using a grippier or wider tires (or both) may significantly decrease the chances of wheel hop but... But the stickier the tire the more dramatic and damaging the wheel hop is if it still occurs (if a higher threshold is reached).

One other thing that may influence wheel hop is torque delivery. Ideally, to avoid wheel hop it should be immediate and more or less linear. If, say, after an engine tune it "explodes" into a peak this may be the reason for sudden "pull and snap back" behavior of the wheels that was not present on the stock car.

Typically, if you increase power output of the car and/or remap your engine power/torque output you also need to, and I should say it's a must for any serious tuner, increase stiffness of the control arms' bushings (rear axle in case of a RWD car, or front axle in case of a FWD), so they can handle the increased torque and its peaks.

Sometimes (but that's usually only the case with purpose build sports cars) engine and gearbox bushings need to be stiffened as well to ensure more immediate and linear torque delivery.

Last edited by x233; 01-30-2016 at 06:04 AM..
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      01-30-2016, 02:04 AM   #20
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Thanks for the analysis - quite accurate, and adding to what's already been said.

For now, I simply must never forget my M235i is quite another beast than my Golf 7 R - the latter can be floored inside even the tightest twisties (this is where it really spreads its legs)... But it has 4 wheels to accommodate all this torque, plus the very capable Haldex system.
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      04-03-2016, 01:29 AM   #21
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I'm coming back to this old subject because - after having replaced my winter tires back to my MPSSs - I'm experiencing rear axle hopping under full load acceleration, and this time not inside a corner!

While the explanation of this ugly phenomenon offered here was convincing in the circumstances I described originally (too much grip, too much rotary speed difference inside a curve, LSD not allowing the inner wheel to slip and release some loads) - it certainly worries me that it now also happens in the straight line, WOT acceleration.

So, I'm asking again: did any of you with LSD on their M235is experienced it at least once? If not, where do you think I should look for a reason? The first thing that comes to my mind is failing rear shock(s), but I'm only at some 16,000 km on the clock.... I'd really like to listen to your opinion before I take my car in - the service guys know nothing, at least at my local BMW dealer...

Waiting for any suggestions...

PS. Oh - as to the header of my thread it may be confusing; I do not have H&R springs - the suspension is completely original oem. Also, in the meantime I realized that if I ever do upgrade, it will not be just springs - but probably some good coil-overs like KW, keeping EDC functionality. But this I'd only want to do after my suspension needs replacement anyway.
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Last edited by moldcad; 04-03-2016 at 01:38 AM..
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      04-03-2016, 09:07 PM   #22
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Ask them to check everything but bushings first. No matter what advice you get here that is what you need to do.

PS: I think I got a hint of wheel hop a couple of times recently on aggressive acceleration on cold wet pavement when I switched to wider and much grippier summer tires. but it was raining and about 5 C outside. Maybe our cars are prone to have that. Maybe it was too cold for the tires. Or, maybe I should check my bushings, too.
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