IRS Bump Steer

[THark88]

So my IRS is currently out (doing gears, bushings, sway bar links, lowering springs, shocks, etc...) and i have a set of adjustable outter tie rod ends to go with it. i have no stock bump steer measurements and frankly don't have a way to measure it. also, besides youtube videos i have 0 understanding of the bumpsteer.
My question is, when i take it to get aligned, would they correct what ever settings the tie rods change or no ?

or should i keep the stock on and get everything else done and aligned then have a shop install the bumpsteer kit ?

i'm doing all the other work (besides gears) , so i hate that i don't feel confident in doing these ... but i just don't have the measuring device, nor the understanding of it.

thoughts? opinions?

 

[52merc]

Adjusting bumpsteer is not something most alignment techs would do our have the equipment to measure. If you have a high performance (racing) alignment shop nearby you might get lucky. Adjusting bumpsteer will change toe so bumpsteer should be adjusted before the alignment.

There are a couple of good articles about bumpsteer on the internet. Just google "bumpsteer" and a dozen good articles come up. I'm cheap and didn't want to spend the money to buy a bumpsteer gauge as it would only get used once or twice, so I made my own based on the MM gauge. MM has a good explanation on how to measure bumpsteerb using their gauge. Although most of these articles discuss front suspension, it applies to IRS as well.

 

[THark88]

Is there any difference in front vs rear ?

 

[52merc]

The basic theory is the same. The geometry is obviously different. If the car is a driver, then you want to avoid toe-out on the front or rear as this causes an unstable straight line drive (but improves cornering). Some racers use toe-out in both the front and rear to promote cornering.

I thought about a nasty comment like, 'Ya, one is on the front, and one is on the back' but thought better of it.

 

[FIREBALL]

The bump steer and alignment should be done at the same time. My car is lowered 1 3/4 inches and my rear outer tie rod ended up with a 1/2" spacer. If your car isnt lowered or lowered 1" or less then you generally dont need the bump steer in the rear. The front is a different story---if the car is lowered 1" or more than bump steer adjustment helps. My spacer in the front ended up at 3/4". If you dont get the bump steer adjusted professionally then a general rule of thumb is when car is sitting on ground the front tie rods need to be horizontal in the same plane as the lower control arm. The rear tie rods horizontal to the ground. These are only ball park adjustments and much better to get it professionally adjusted.

When your suspension travels up and down when cornering or going over irregular surface and bumps (hence the name bump steer) your toe will change either in or out, if its bad enough it will cause the car to not handle well and when going over bumps or cornering it will make it feel like the car is trying to steer itself one direction or another (not good) adjusting the bump steer is a compromise to limit the change of toe and keep the car from being unsettled . There are plenty of bump steer articles and explanations, just google.

 

[THark88]

i'm lowering it 1.6" (vogtland springs, convertible) while i do the IRS stuff.....

 

[scottydsntknow]

Full Tilt Boogie tie rods or don't even bother. I hope that is what you are talking about. The stock ones are flimsy and the ends are worse. You hit the gas and the rear will want to steer the IRS half the time till you get the good tubular ones.

 

[FIREBALL]

Full Tilt Boogie tie rods or don't even bother. I hope that is what you are talking about. The stock ones are flimsy and the ends are worse. You hit the gas and the rear will want to steer the IRS half the time till you get the good tubular ones.

I only went with Maximums Motorsports tie rod end bump steer kit, but you are probably right, ---should have went with the whole tubular tie rod kit. But I do wonder how much of the problem are the tie rods and how much of it are the control arm bushings causing the rear steer?, I mean how do we know or has it been proven that the stock tie rods have much flex?. In my mind It would be a large amount of flex to to the point of almost giving it a permanent bend to cause rear steer, But no matter I will be going with the rest of the kit pretty soon.

 

[01yellercobra]

I only went with Maximums Motorsports tie rod end bump steer kit, but you are probably right, ---should have went with the whole tubular tie rod kit. But I do wonder how much of the problem are the tie rods and how much of it are the control arm bushings causing the rear steer?, I mean how do we know or has it been proven that the stock tie rods have much flex?. In my mind It would be a large amount of flex to to the point of almost giving it a permanent bend to cause rear steer, But no matter I will be going with the rest of the kit pretty soon.

The only thing I've seen as far as the stock tie rods are them flexing on high horsepower cars on the dyno. It was a trip to watch. In the case of the bushings and such it's probably a matter of stacked tolerances causing the issue.

 

[FIREBALL]

Wow on a dyno in a straight line with little suspension travel they flexed thats crazy. Pardon my ignorance but what is stacked tolerance and is that referring to all the rear bushings or just the control arm bushings?

 

[01yellercobra]

Wow on a dyno in a straight line with little suspension travel they flexed thats crazy. Pardon my ignorance but what is stacked tolerance and is that referring to all the rear bushings or just the control arm bushings?

Stacked tolerance is adding the play for everything. Say like there's 1mm of play in the bushing, 1mm of play in the tie rod, and 1mm of play in the cross axis joint. Adding those up gives you 3mm of movement.

 

[jrgoffin]

Here’s some reading on the subject: Chassis & Steering

 

[2DXTRM]

Have a look into the Kenny Brown "Rear Steer" kit and replacement outer rod ends.

Kenny Brown IRS Rear Steer Kit for 1999–2004 Mustang SVT Cobra | Shop Kenny Brown
IRS Outer Tie-Rod End 1999-2004 Cobra/SN95 IRS Equipped Mustangs | Shop Kenny Brown

 

[01yellercobra]

Or go with the FTBR heavy duty links and save a few bucks along with getting something a tad stronger.

FT 1860

 

[scottydsntknow]

Or go with the FTBR heavy duty links and save a few bucks along with getting something a tad stronger.

FT 1860

Yep. The FTBR stuff is superior to Kenny Brown and cheaper.