Live axles and LSD's.

[ottocycle]

Hello all,

I noticed that nobody had posted here for a while so here goes. See my little blurb in the wanted section.

I think my car needs an LSD. She has snap oversteer when try to exit a corner under power. I have a Ford Escort live rear axle and would like to get a Quaife ATB LSD or find another axle that I can make work. I am thinking I might like taller gearing as I am running out of wind on the main straight at Summit Polnt (my local track). Does anybody have any suggestions as to what type of diff I should look for and what rear axle I should consider. Any suggestions as to what else could be inducing this condition would be appreciated. I had extra weight in the car (an instructor of about 180lbs.) and my shocks were set rather firm. I will be on the track again next Saturday and will set the shocks soft with zipties on their shafts to make sure I am not bottoming them out.

What do you think?

Cheers,

 

Dermot.

Fury/Hayabusa.

[slngsht]

Dermot, just to clarify, you have an open diff now, and when you put the power on coming out of a corner, you oversteer? If that's the case, any kind of LSD will make that condition worse.

[R1 Seven]

I would certainly soften the shocks in the rear. Really, the shocks should not be used to keep the suspension from bottoming anyways. Conversely, you may want to increase the damping on the front shocks as an experiment as well. You may have tried this already, but adjusting driving technique may help as well. I know in my car, I have to ease into the throttle gradually coming out of the turns to keep from spinning the tires as much. Our cars are so light, they get a little nervous at times.

 

I am not sure if you have driven on the new pavement at Summit Point yet, but I did last weekend and it is nice and smooth with plenty more grip. The car will probably drive different just because of that.

 

 

[Kitcat]

Tried stickier rubber?

[sporqster]

I found that a lot of my oversteer was coming from sloppy rubber bushings in my trailing arms, causing the rear end to go into 'four wheel steering mode'. I changed to rod ends with poly races (along with fatter, stickier rubber) and now the car handles much more neutral and predictable... maybe even pushs just a little on track-out.

 

I'm using an Alfa Romeo LSD.

[ottocycle]

Thanks guys for the feedback, keep it up.

You are all partly right , I think. I was back on the track last Saturday driving solo with a few changes. Because of that I cannot definitively say what initiated the improvement. I backed off the shocks to full soft and dialed in more pre load on the front. I ran with tire pressures of 17R 16F. The car ran better but still needs work. I was able to get it to slide a little but it felt like it was on marbles. It was not a comfortable slide and I did not let it happen often. It had rained Friday night and the runoff was wet and muddy. I did not want to be the one who trashed the racing line! I changed my driving style in that I was very gentle with the gas pedal. I am thinking my tires are limiting me. I have Falken Azenis 195 60 14 on her at the moment and I cannot get any heat into them. I would put my hand on them after a 20 min, track session and they would feel barely warm, on a par with body temperature. Theh should have been a lot hotter. I think my choice of tire was bad. I believe the tire is great it is just not soft enough for a car as light as mine (about 1,350 lbs). I willl put them on my Alfa this spring and look for another. (Any suggestions).

I think if I can find a soft 14" tire I will put a slightly wider one on the rear, perhaps 195 front 205 rear. I happen to have an Alfa rear axle and it has an LSD among my spares stash. I might re engineer things this winter and fit it. My rear bushings are good.

Thanks all.

 

Dermot.

Fury/Hayabusa.

[markclow]

I dont mean to hijack this thread but I see you guys are running Alfa axles. What diff ratio are you guys running? I have a Seven built off an Alfa Spider that I want to convert to BEC. My main problem is the 4.5 diff on the back. What did you guys do?

 

Thanks!

[fastg]

I am not sure about the setup issues, but if your looking for a new rear axle look at the 1st gen Mazda RX7, the GSL models have LSD stock and disk brakes. They are light in weight, available cheaply I got mine complete for $95. So check them out if you go that way

 

Graham

[fmorser]

A couple thoughts. Different bike engines have varying final output drive ratios. Try this link http://www.gearingcommander.com/ for the final drive of your engine, or if you are looking for possibilities it offers a wide range of bikes. I use a CBR1000f and the final drive is fairly high at 1.785 so it needs low-ish diff gears to get higher top end or lower highway speed revs. Here's another link http://www.crawlpedia.com/rpm_gear_calculator.htm that you can put your tire size, transmission ratio (final drive ratio), mph speed and ring and pinion ratio to determine approximate rpms. I use a Ford 7.5 live axle and just swapped out 3.73 for 3.08 gears and according to the calculations should get close to 120mph before I run out of engine rpms......assuming the horsepower can push through the wind. The stock 3.73 gears got to about 100mph before I hit the 10,500 rpm redline. I don't know about used ring and pinion gears for alfas, but lots exist on ebay for the Ford and I got my set for $75 I think.

 

hope that helps.

[mel kuipers]

I have a Subaru LSD, and don't get severe oversteer, but do lift the inside rear wheel on tight corners. That causes the inside rear wheel to spin. I am looking to add a front sway bar to keep the front flat, and thereby keep the rear flat. The only time I get oversteer is when I trail brake or engage the throttle too quickly.

[Anker]

You are on the right track. Stronger front sway bar and no or softer sway bar in the rear will correct that problem