rear wheel hop

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rear wheel hop; how to stop it?
Topic Started: Tue May 12, 2009 9:08 pm (300 Views)
dave_irl	Tue May 12, 2009 9:08 pm Post #1
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	I'm getting quite a bit of wheel hop/shudder when the back wheels start to spin fairly fast in relation to the cars speed.. If the car is moving quicker or is sideways then its not there, its mainly a 1st gear thing,but its really starting to mess up some of my launches as I always have to back off the throttle for fear of snapping a halfshaft or something. It happens with both the 9Js and my steelies so Im sure its not tyre balance or something. Could it be damper settings? 2 of the 4 subframe bushings are Delrin so I thought that would stiffen the back end up alot.. Any ideas appreciated



Avantdi	Tue May 12, 2009 9:17 pm Post #2
Fastest ship in the Galaxy Posts: 184 Group: Members Member #4,044 Joined: April 10, 2009	had that problem a long while back with a 2.0l twin cam fiat 131 turned out the rear shocks while they looked fine and had no leaks were weak. changed them out and the problem was resolved.You could have a similar issue.



dave_irl	Tue May 12, 2009 9:24 pm Post #3
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	Cool, well the dampers are only in the car maybe 6 months, so I will play around with the damper settings, they are on 14 out of 28 but may well be a tad too stiff. It doesnt happen too much but you know how annoying it is when it does..



Richy190E	Tue May 12, 2009 9:34 pm Post #4
Sales Rep Posts: 1,822 Group: Members Member #1,387 Joined: June 9, 2007	You wanna feel it in my 1978 MG Midget on original leaf springs and dampers



Avantdi	Tue May 12, 2009 9:35 pm Post #5
Fastest ship in the Galaxy Posts: 184 Group: Members Member #4,044 Joined: April 10, 2009	Yes its bloody annoying. My oil burner wont be burning rubber any time soon But that 131 could. It had a 1.4 diff fitted and would launch from the lights like a rocket. Even the gti's of the day could not stay with it, untill it topped out at 95



The Gorilla	Tue May 12, 2009 9:44 pm Post #6
Member Posts: 307 Group: Members Member #3,610 Joined: December 10, 2008	Hi, What suspension set up does the car have fitted ? Could be several things or a combination of them. Sounds like rear wheel tramp, where the rear suspension osalates under load of acceleration, as dampers or springs or both are to soft (maybe leaking], mismatched, or broken spring, etc. Car should be supported/sit on its springs and the damper deals with bump and rebound, as a rule of thumb. Regards, The Gorilla.



dave_irl	Tue May 12, 2009 10:10 pm Post #7
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	-Spax PSX adjustable dampers ("ultrashort" version for lowering beyond 50mm) -H&R -60mm sport/street springs -currently #3 spring pads (will be trying #1 again soon) -EvoII ARB & TE endlinks -Wiechers alu strut brace -adjustable camber arms All I can do at the moment is play with damper settings and adjust ride height a few mm via spring pads..



jeremy	Wed May 13, 2009 5:45 am Post #8
Member Posts: 6,567 Group: Members Member #2,018 Joined: December 9, 2007	Axle tramp? Jeremy



The Gorilla	Wed May 13, 2009 5:58 am Post #9
Member Posts: 307 Group: Members Member #3,610 Joined: December 10, 2008	Hi, Suggestion to try and see what is causing the issue- Set the rear dampers to full soft, and the rear ARB to full soft, and loosen the ARB drop links if adjustable,. so that there is no pre-load on the ARB. See if the wheel tramp is still ocurring ? If yes then, set dampers to full hard, if its still occuring, then the valving of the dampers is mismatched to that of the spring rate. I would guess that the stroke of the rear dampers on a shorter version for a road/track is somewhere around 90-110mm. If the springs are also shorter, when you accelerate the rear suspension 'squats' down under load, and then as the rear starts to rise as the springs uncoil, the damper should absorb the rebound so that the car settles back onto the spring at around ride height. It sounds as if your dampers are not doing this and thus the suspension uncoils at spring not damper rate, this then starts the sequence again but with decreasing rise and fall which creates the wheel tramp/hopping. What are your spring and damper rates in Knm ? Regards, The Gorilla.



dave_irl	Wed May 13, 2009 2:09 pm Post #10
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	The ARB is not adjustable, nor are the endlinks, though if it came to it I could easily disconnect both sides for a quick (straightline) test. H&R replied to my mail suprisingly quick today, they say the front spring has 70N/mm, the rear spring 75N/mm (these are for the H&R 29613-1 -60mm springs). No reply from Spax yet. Thats the thing about the tuning parts that are not "all out motorsport", you don't get the info too easily. Springs and dampers are bought in terms of ride height alone with no knowledge of rates.. Lesson learned I guess! (But I did buy them around 2 yrs ago, lots learned since!) The right way to do it would be buying the proper kit like Mikael got, though I must to say, my self made kit handles pretty good for my needs. Will updated if/when Spax reply/I ring them..



pentoman	Wed May 13, 2009 2:53 pm Post #11
Resident OVP Expert Posts: 2,697 Group: Members Member #11 Joined: November 6, 2005	If you read the.. Autocar? road test of the 2.5-16 they say the same - make a quick wheelspin start and it suffers from what feels like terminal axle tramp, and that's from a road test of a brand new car. If Mercedes couldn't get rid of it...........



Big Ben	Wed May 13, 2009 3:42 pm Post #12
Member Posts: 4,905 Group: Members Member #155 Joined: January 26, 2006	Changing the rubbers in the thrust arm and the top support strut to something with less give (poly bush) would help. Tramp is normally caused by torsional loads and is most noticable in cars with solid rear axles. My old Sd1 used to suffer horrendously after I tuned it and I actually had to fabricate an anti tramp bar which restricted forward movement of the top of the axle under power! Unfortunately, cars which are developed with a smooth ride often behave this way!



jeremy	Wed May 13, 2009 3:50 pm Post #13
Member Posts: 6,567 Group: Members Member #2,018 Joined: December 9, 2007	I had axle tramp, when I first got my 2.5-16V, and posted about it, but I just got round the problem by riding the clutch, just a little bit mind, thereby negating the problem. I just didnt snap the clutch pedal up. When I think about it , my acceleraton is just as good, even better perhaps. Jeremy Edited by jeremy, Wed May 13, 2009 3:52 pm.



Martrider	Wed May 13, 2009 4:26 pm Post #14
Longest build time in history? Posts: 1,531 Group: Members Member #2 Joined: November 2, 2005	Didn't Racing or Jereto or Tobjorn or somebody have the same with their 2.5-16 turbo running stupid boost? I remember a post about what he did but i think i would be inclined to go with Gorilla's theory and say that the occilation is due to a mis-balance of damping force to spring rate. With thos adjustables i would assume stiff is the way to go, but then of course you are putting more stress on other suspension arms and components. Have a check, but don't be too vigorous and be sad when you break something.



The Gorilla	Wed May 13, 2009 7:08 pm Post #15
Member Posts: 307 Group: Members Member #3,610 Joined: December 10, 2008	Hi, Dave_irl- The H & R Spring rates are a bit strange? 70nm and 75nm is circa 400lb front and 450lb rear ? The rule of thumb for a front engined rear wheel drive car at around 1100 to 1200 kg is about a 1/3rd more rear spring rate for fast road / Track cars. I would have expected around 400/450 [70/75nm] front and then 575/ 600 lb [100/110nm] rear. That said there are always exceptions to the rule and I run 180nm front [1000lb] and 140nm [800lb] rear springs and 300nm front damper at 75% travel with 200nm rear damper at 50% travel, on my E30 M3 Track Car. It is however almost undriveable on a normal road. When you know what the rating is on your dampers, and subject them to being OK, I would look to replace the rear springs with stiffer ones. Sorry I forgot that the 190 runs the ARB's fitted directly to the wishbones and there are no drop links as such. Regards, The Gorilla.



merc190uk	Wed May 13, 2009 7:38 pm Post #16
Steve Posts: 7,517 Group: Admin Member #1 Joined: November 1, 2005	interesting thread Dave and will be good to see if you find a fix my standard 2316 did it once but now it just lights them up



dave_irl	Wed May 13, 2009 8:12 pm Post #17
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	jeremy Wed May 13, 2009 3:50 pm I had axle tramp, when I first got my 2.5-16V, and posted about it, but I just got round the problem by riding the clutch, just a little bit mind, thereby negating the problem. I just didnt snap the clutch pedal up. When I think about it , my acceleraton is just as good, even better perhaps. Jeremy Thats the thing, when driving normally it doesnt, but when I intentionally bang out the clutch with lots of revs to induce mega wheelspin up through 1st and 2nd gear (in the wet on my steelies) thats when it happens. Tough on the car I know but hey thats what Im building it for. Thanks for the thoughts on the ratings G, hopefully Spax will get back to me or Ill be on the phone to them. It doesnt really bother me that much, its all part of the learning curve and development of the car! BB I will look at the arms and see what can be done. The camber arm is rosejointed already so not much flex there.. We'll see whats next. Thanks all (waiting patiently for more rain now lol)



Martrider	Thu May 14, 2009 7:11 am Post #18
Longest build time in history? Posts: 1,531 Group: Members Member #2 Joined: November 2, 2005	You are the only person other than Garden Nursery owners in the UK that is WAITING for rain at this tme of year! It sounds like the springs you have are the weak point, but as you say it's all part of the learning curve! Keep going dude.



The Gorilla	Thu May 14, 2009 7:57 am Post #19
Member Posts: 307 Group: Members Member #3,610 Joined: December 10, 2008	Hi, The point raised by Pentoman in regard of the Autocar article suggests that the reason that Merc themselves had this issue with hard launches, is related to the rear SLS. If you run to hard a spring with a SLS system then the SLS will not function correctly. You would remove the wheel tramp and more than likely replace it with a very skittish rear that is always moving around on the springs due to them being a lot stiffer than the SLS. This may in part explain why the H&R rear spring kit is only 75nm, as H&R will have worked from the manufactures original specs. Dave_Irl - the reason the car does it in 1st and less in 2nd is to do with weight transfer under increased load caused by fast accerlartion. In a normal pull away the weight transfer is nominal, but under load, ie] hard accerlartion the rear suspension loads up as the rear wheels bite, which moves the weight balance of the car rewards, at which point the springs and dampers should compress [bump] some so as to keep traction. As the car moves forward the springs and dampers should return [rebound] to their normal ride height. It sounds as if yours in being to soft are then 'over pitching' so as you pull away the springs and dampers are 'bouncing' up past normal ride height, as they now have rebound inertia, whereby the whole cycle is then repeated with decreasing movement. Correct spring rates and the dampers are effective, to weak or stiff and the dampers to a point are unable to function correctly. Regards, The Gorilla.



bri957	Thu May 14, 2009 8:05 am Post #20
Member Posts: 1,468 Group: Members Member #1,134 Joined: April 2, 2007	Dave This place will make you custom springs. They supply Prodrive and Demon Thieves among others. They are pretty good value too I think. D. Faulkner Springs LLP, Greensleeves, Northfields Lane, Westergate, Chichester, West Sussex, PO20 3UH ENGLAND. +44 (0)1243 543049 +44 (0)1243 542133 sales@dfaulknersprings.com



dave_irl	Thu May 14, 2009 8:33 am Post #21
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	Demon Thieves, lol, yeah Im feeling that lately actually.. Thats a handy looking website, thanks Bri.. When I find out what the damper rates are, Ill have another look. Looks like decent prices, cheaper than new dampers anyway!



dave_irl	Thu May 14, 2009 9:10 am Post #22
I love offset. Posts: 8,729 Group: Admin Member #6 Joined: November 2, 2005	Spax have just replied: Quote: Dear Dave, Damping force is determined on speed and adjustment, what speed do you want the KNM at and what setting are the dampers set to out of the 28 points ?? If you are getting hop in the vehicle try adjusting the dampers to a harder setting. Kind Regards ... I replied with the 75N/mm and 14 clicks, we'll see what he says. I don't really know what speed I want, which is the problem..



Racing	Tue Oct 27, 2009 7:49 am Post #23
Member Posts: 788 Group: Members Member #384 Joined: July 1, 2006	All good advice,while i believe Gorilla tossed the general recomendations for front and rear around. Regardless. Another issue to check out is actualy rear axel inclination and angles for the propshaft. Look the numbers up in the WIS and adjust accordingly with the shim at the fron of the rear axle housing. Also make this shim much bigger in dia to spread load into structure. Also have in mind that the rear subframe structure of the W201 isn�t more than 2mm thick in places,why some intelligent reinforcing of the sub might be an idea as well. Anything but solid pucks in the subframe mountings is a waste of time. Gorilla is 100% correct though in that we�re talking uncontrolled oscillation. Issue is that there really is no quick fix as some of the problem dates into the substructures of the rear setup flexing. If you are hellbent on alleviating the problem at hand it IMO starts out with ripping the rear subframe out of there and start by seam welding all the scarf joints. Then add a number of plates in critical areas to alleviate flex.Be aware that the rear axle cap is part of the structure,and that loads indeed make the steel of the sub twist under load/unload. Reinstall and THEN evaluate what the suspension does with rear diff angles asf taken care of.



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