Loss of traction in tight corners.

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Loss of traction in tight corners.

Postby lahondal » Sun May 07, 2017 10:31 pm

Hi all.

Im race a 2.8i compact on tarmac stages, and since i have put the new engine (i had a m42 before), im having traction problems on tight corners.

The specs are:

-Gaz gold coilovers on 4 corners, 600/250lbs springs F/R.
-188mm case 4.45cwp, stock plate-type LSD.
-318is front and rear antiroll bars.
-16" tarmac rally slicks.

Last event i have tried raising a bit the rear and undoing the rear arb, and the problem seems to be more or less the same, in tight corners, the inner rear wheel spins a lot on throttle and loss a lot of traction and time.

The LSD suposedly is in good condition but was bought 2 seasons ago and have near 500km of track abuse.

All i want to know, is if this can be a suspension spec problem or simply the LSD is asking for a rebuild....

Anyone knows? Thankss!
lahondal
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Re: Loss of traction in tight corners.

Postby Garry.M » Wed May 10, 2017 7:17 am

Don't know how low you've got the car, but the more you lower it the more camber you get - which would give you less tyre contact on the road. You might also want to play with the rear springs, adding a tender spring in to give some preload with the springs to help push the tyre onto the road. I'm not sure how much droop you have left with the ride height you have the car at,, might be worth checking that too. It sounds like you have the original compact cup Gaz suspension which ws track orientated and could have had shorter dampers. Jack the car up and fit a cable tie onto the rear damper rod and let the car down ,, then Jack it back up and see how much droop you have.
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Re: Loss of traction in tight corners.

Postby lahondal » Wed May 10, 2017 1:58 pm

Well, the rear drop is little, about 2-3cm max i guess, and the rear dampers seems to be a little shorter than used to be in rallying.

I have a helper spring to hold the spring in position when is in full drop but as said, the drop maybe is too small to hold the wheel in floor in the corners.

The corner weight its ok (+-300kg front +-250kg rear, each wheel respectively).

Dampening is in medium to high all four corners. 12/22clicks front, and 16/24clicks rear.

A thing is making me think something is not ok, is the rear stiffness, althought i have 250lbs springs in the back, i am unable to make the dampers travel pushing down the boot.
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Re: Loss of traction in tight corners.

Postby Garry.M » Wed May 10, 2017 6:54 pm

Tender springs are different to helper springs. The compact cup changed the control springs a few times with the last set being an eibach setup with main and tenders on both front and rear. It was a 350 /150 spring setup on the rear. I'd be trying a softer 225lbs spring and a maybe a slightly softer tender around the 175 - 200 lb maybe.? It's trial and error to find the ideal setup,,, especially with the back of a compact
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Re: Loss of traction in tight corners.

Postby lahondal » Tue Sep 12, 2017 9:35 pm

Given that i will have a race in two weeks im going to ditch the helpers and put in a pair of 120lbs tender springs and give it a try.

I have measured the drop and I have 24mm drop but now 8mm or maybe more of this travel takes a long time to extend, 10secs aprox, which i think is causing the major part of the problem.

Anyway for the next race im thinking on purchase a softer spring set all around and see how it drives.

I have checked the breakaway torque of the LSD and is in the 55nm range so i assume its OK as is a stock BMW 188case LSD.

Thanks!
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Re: Loss of traction in tight corners.

Postby jerseypug » Thu Sep 14, 2017 12:04 am

I'm no expert and Gary M seems to know what he is talking about so i can only offer what i have experienced
i have the gaz golds on my compact and ran a 328i engine and never had a problem like you have, i did not use the rear anti roll bar and i did have the diff machined and atlas plates fitted. The Gaz springs are whatever gaz recommended and i was concerned as the car seemed so solid like it was over sprung but I'm very happy with how they work

my road compact has that 328 engine now, standard worn shocks and springs, front and rear arb and the diff is a standard medium case LSD and it never seems to spin just one wheel.

i would look at your diff. what oil are you using? the proper oil from BMW is about £90 per litre so i used a shell oil that i can't find any more then i use Gulf competition oil with a picture of an astin martin on the bottle which seems to work well but is a bit noisy when turning a corner when not on load but it might have been like that before i changed the oil. these 2 cars have been getting abused for some time now, i always start in second gear and the diffs still seem fine
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Re: Loss of traction in tight corners.

Postby lahondal » Thu Sep 14, 2017 5:56 pm

Im using Motul Gear Competition 75w140 on both diff and gearbox. If i have measured correct the diff it should be on stock specs so maybe the car is claiming for more lock on the rear?

I like the GAZs, as you state they seem oversprung (600/250 is wayyy hard) but works well even on bumpy surfaces. Only downside is i feel the rear a little, only a little bouncy sometimes, but clearly i have a problem to solve on the rear axle that i havent discovered yet, so probably the problem are not the GAZ or their valving.

With 250 springs on the rear should be able to push the rear down with my weight? If I push down the rear is almost impossible to get down the shocks. My entire weight (95kg 8) ) only get it down by maybe.....1centimeter?

Must try the new tenders and then think in another problem if that dont solve the problem in part at least.

Thanks, will post the results.
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Re: Loss of traction in tight corners.

Postby Garry.M » Sun Sep 17, 2017 9:31 am

Your droop figure of 24mm seems very low,, I have 70mm on my compact..
The Gaz dampers will be valved very much towards race circuit use,, so I'd think that the rebound valving might be a contributing factor to your wheel spin issue. Might be worth measuring the free length of the rear springs then measuring their length when the weight is on them. If you look at a std spring, I think you'll find that even on full droop they have a small bit of tension on them (not loose on the arm) - so they will always be "pushing" the tyre in contact with the tar.
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Re: Loss of traction in tight corners.

Postby lahondal » Thu Sep 21, 2017 12:18 pm

Im going to fit the new tender this afternoon, so i will can measure the compressed and extended lenght of the springs.

I have talked with GAZ in the past for changing the rear strut rods to a longer rods, as i think this make me able to run more drop at the same height. Compression travel is a lot a lot more than extension travel, so i think i can do it with good results.

When i ordered the GAZ dampers, i ordered them as tarmac rallying dampers althought i tell him i feel better with hard suspensions and that is why him recommended me the spring rates i have now, but i supose he valved the dampers for tarmac rallying and not for circuit racing.
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Re: Loss of traction in tight corners.

Postby Overthelimit » Thu Sep 21, 2017 9:04 pm

Softer springs at rear and rebuild the diff. The static prdload does not necessarily translate into
Good lock up under power. We have a 328 plate diff with 3 sets of plates, a tuned m3 motor, both anti roll bars connected and traction is never a problem on tarmac unless both wheels are spinning. Keep the back higher than the front or it will understeer. And dont lower the front too much, bottom arms should be higher at the car end else it affects the front geometry (so i,m told).
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Re: Loss of traction in tight corners.

Postby mrfuzzyfelts » Fri Sep 22, 2017 1:21 pm

LSD problem it sounds like. I had the same. Played with suspension, ARB's etc etc

Fitted a Gripper diff and it has been spot on since :mrgreen:
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Re: Loss of traction in tight corners.

Postby lahondal » Fri Sep 22, 2017 6:32 pm

Yesterday i have fitted the tender springs. I havent been able to try the car but definitely they make a change in the suspension behavior, as now they extend all the way down in less time than before.

And also i have realised that i have 300lbsx8" springs in the rear. I thought i had 250lbs springs but not.

LSD 3 disc kit ordered as you have recommended me, they are advertised as "sintered discs" instead of normal LSD discs.
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Re: Loss of traction in tight corners.

Postby Overthelimit » Sat Sep 23, 2017 12:06 am

I use JCB lsd oil and change it once ayear or after about a dozen rallies.
No lsd problems in four years.
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Re: Loss of traction in tight corners.

Postby lahondal » Tue Sep 26, 2017 7:48 pm

Last race went well as we have achieved to finish in fourth position over many m3 with dogboxes and ahead we only had a 997gt3, an m3 e36 with s54 engine and samsonas dogbox, and a very well built clio sport with sequential gearbox and 240hp.

The tender springs definitely done a good job, dampening was decreased at the same time so both have contributed to gain a lot of traction in my opinion.

But softening the rear make the bouncy problem bigger, as 300lbs springs need big dampening force, and im thinking on trying a few pounds lower springs F and R, 400F/200R. For next season.

Next step, rebuild the LSD and repair one trailing arm and a wheel that were damaged in a right corner i take too fast....

Anyone have a pair of disc trailing arms? Here are becoming rare and prices are rising.

I want to replace both arms as i feel a lot more oversteer in left corners than right corners. Try with 2 good known arms and see what happens.
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Re: Loss of traction in tight corners.

Postby lahondal » Tue Sep 26, 2017 7:53 pm

https://www.youtube.com/watch?v=42F_7zLugfI

Here is a good example for what i have named loss of traction, MIN 0:40

And throughout the whole stage the left oversteer.
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