Midnight02

iTrader: (8)

Just got weld in LCA relocation brackets installed and they were curious as to what pinion angle we should shoot for.

Car is lowered on Strano Springs, double-adjustable roto-joint LCA's in the bottom hole of the brackets. Street driven with about 8-10 road course track days per year.

I had no idea how to answer the question and the search in this section yielded a few similar threads but no responses.

Anyone care to share?

scj

iTrader: (89)

Here's an article from MWC.
http://www.midwestchassis.com/uploads/3/0/1/4/3014283/pinion_angle.pdf

Midnight02

iTrader: (8)

Thanks for the article. It was helpful to have a starting point and I'll dig a little deeper to see if there's anything I'm overlooking.

The "cliff notes" summary of the article is +0 pinion angle for street driving and road racing and -2 to -4 for drag racing.

KiwiKid

Unless you are running Leaf springs the pinion angle has no bearing on power down, all you are wanting to do is to have a slight angle difference 1-2º down, to pre-load the driveshaft joint.

.boB

iTrader: (1)

Your goal is to have a 0* while under power. Every little bit over or under that will cost you power and efficiency.

When you stomp on the gas, the pinion will rotate upward. So you want it pointing downward a smidgen to compensate for that. How much downward depends on the type of suspension you have. A stock leaf spring will change 2-3*, but a 3/4 link with rod ends will change less than 0.5*. There's a number of articles available on the web to guide you on that.

The big thing to remember is that the pinion angle is compared to the drive line angle (AKA: Power Angle), and NOT the horizon. That's a common mistake.

You should also check your drive shaft angles (not pinion angle) at full droop and full compression. The U-joints can only handle so much misalignment without binding.

KiwiKid

Hi bOb,

Been racing cars on tarmac a looooong time, to long really and whilst I agree with most of your post, I don't agree with you 0º under power. IMO the universal should be slightly loaded, I aim for at least .5º relative to the drive shaft, under power down, not an easy thing to measure with out suspension potentiometer's, but you can still 'knife and fork' it as we used to have to do before Data acquisition became a way of life.

Cheers,

Mark.

.boB

iTrader: (1)

I have only been road racing <10 years. I don't have a big budget to experiment with a lot of variables to see what works best. Especially comparing a pinion angle of 0* to 0.5*.

I am constantly reading and researching suspension design and tuning, looking for stuff that applies to me and my car. Everything I have read - from Carrol Smith to Art Morrison - says to shoot for a pinion angle of 0* under a load.

So what have you found that makes a difference? and why?

BTW, over the internet, that may look like a snotty question, or the beginning of an argument. It's not. You have a different opinion based on years of experience, and I am keen to hear it. If you're willing to share, I'm willing to listen.

Midnight02

iTrader: (8)

Ended up with a 1* difference (downward) and that little bit of pre-load feels nice.

To my surprise, that minor adjustment coupled with the roto-joint LCA's and relocation brackets has it feeling like a different car. Haven't been able to test it out on track, however there seems to be a noticeable improvement in straight line traction.

LS1-450

iTrader: (33)

Are you guys having this discussion based on "live axle" only vehicles or is the topic also related to IRS?

.boB

iTrader: (1)

Both. Regardless of the set up, you still have to adjust pinion angle, drive shaft angle, and power angle. The nice thing about the IRS is that the pumpkin is solidly mounted, so you don't have to try and predict movements. If done right, it's not going to move much.

LS1-450

iTrader: (33)

Thanks for clarifying. Felt like the conversation had more of a live axle kinda vibe & didn't want to say something regarding IRS & then find out that the topic was regarding live axle set ups. Was gonna add that the somewhat solidly mounted pumpkin can be re-enforced in order to significantly reduce pinion deflection, as you have noted. So, I'm still catching up with the conversation. It is an interesting & important topic.


Now, apologies for an off topic question. Have posted in the suspension section asking for C7 guys to post pics of the REAR caster adjustment on the C7 Vette. IMO, it is nothing more than an enhanced toe adjustment when not applied to wheels that swivel (turn). Further, it seems like a precursor
to either a C7R or a C8 all wheel drive set up. If you guys want to comment & discuss further, I would like to start a thread regarding the subject in this section. Please let me know. Again, apologies to the OP. Won't bring it up in this thread again.

.boB

iTrader: (1)

IRS Pinion angle effects drive shaft/U-joint angle, and power transmission, just like a live axle. Too much angle can also cause vibration, just like a live axle. But the nice thing is that once it's set, it's set. It doesn't change as you drive the car.

IRS caster is talked about a lot, but not much is done about it. The problem is that it's so hard to measure and adjust. For most cars, it is what it is.

I don't own a 'vette, and have never really worked on one. Not in the last 30 years anyway. But I understand that there is a way to measure and adjust that on C6's and C7's.

Caster in the rear - just like in the front or on a shopping cart - will help the wheels track better, and make the car more stable. It will also make the car more resistant to turning corners. Gotta find the right balance. If you can dial in a few degrees of caster, I would think that would be a good thing.