DC5R - Torque steer, tram lining & tyre inflation pressure

[cordz]

A interesting read, but he's hardly empirical about it all. Balloon analogy case in point.

Norm, I was explaining that a car would need to be driven from the left wheels to be forced right. Much like steering a trolley. If the right wheels are travelling slower than the left, and have less grip, the trolley will pull right.

[cordz]

It could be a balancing issue.

[ChargeR]

So after a bit of thinking I have a few poorly researched opinions on what's causing the problems you're having Norm. I'm particularly addressing the tram lining and increased torque steer. I believe it's a combination of a couple of effects:

1. The scrub radius (distance between the point where the steering axis intersects the ground and the wheel centreline) has become more positive because your wheel offset has decreased a lot, which decreases the stabilising effect this has on torque steer. A negative scrub radius improves torque steer because, for example, if the right wheel has more torque applied (differential issues, wheelspin etc.) then that torque imbalance will act to steer the wheels to the right which counteracts the greater torque on the right side tending to turn the car to the left. So you've reduced this stabilising effect.

2. The contact patch of the tyre has become shorter and wider, as shown in the picture below with A being a roughly to scale stock wheel and B a 10.5" wide wheel and tyre (assuming that the total area stays roughly the same). Tyres have something called pneumatic trail, which means that the force acting at the tyre in general acts behind the centre of the contact patch, indicated by the shaded arrows on the picture (The top of the picture is the front of the car). By making the contact patch shorter and wider the distance between this point where the force acts, and the steering axis ground intersection point (SAIP) has become smaller so this makes it less stable as the tyre force doesn't act to self centre as much. This is the same as moving the tail section and rudder of a plane further forward, it won't work as well as it has less leverage! So more tramlining and instability under acceleration results.

3. A second effect of the wide contact patch is that the the extreme outer edges of the tyre are further from the steering axis, and thus have more leverage on the steering axis. So a momentary unevenness on the road or bump will be more inclined to steer the car.

4. Lastly the wider tyre on a wider, larger diameter makes the whole tyre stiffer which means that the tyre will develop more side grip with less angle to the road, or less steering input, which when you consider points 2 and 3 above which decrease the natural stability of the wheel/tyre it combines to make the tyre and hence the steering even more likely to wander over the road as a smaller steering input to the road results in a higher force.

Of these I think the 1 and 2 are most significant, 3 and 4 just compound the issue.



The simplest way to improve this whilst retaining the wheel/tyre you have is to increase the positive caster. This will move the SAIP forward in the tyre footprint, making any forces developed at the tyre/road interface act rearward of the steering axis, which will make it inherently more stable as noted above, by the rudder/leverage analogy. Other than that there is not any economical way to improve the tram lining and torque steer performance, short of putting a narrower, higher offset wheel on the car.

I noticed a big difference in straight line stability when I increased caster to around 6° on my car with 17x10 +18 and 17x9.5 +15 wheels. Not like stock, but a lot better.

[Karl]

Pretty much every FF honda ive driven will pull right under heavy acceleration. Just hold the steering wheel tight. Even my CRV does it!!!!!!!!!!

[Shaun]

How did you even get 18x10.5s on the car? Thats a whole lotta wheel.

[DaRKNT]

How did you even get 18x10.5s on the car? Thats a whole lotta wheel.

Wide body!

[tinkerbell]

I noticed a big difference in straight line stability when I increased caster to around 6° on my car with 17x10 +18 and 17x9.5 +15 wheels. Not like stock, but a lot better.

is it around 0 standard?

did you get 6' from bushes or more aggressive modifications (like re-drilling the top mount!)

[ChargeR]

is it around 0 standard?

did you get 6' from bushes or more aggressive modifications (like re-drilling the top mount!)

I believe OEM spec is 1° for an 02-04 and then they added a little more to bring it to 1.5° for the Type S. I got most of the increase from my offset Todd's upper mounts and only about 1-1.5° from PCi offset LCA spherical bushings.

[nikolaz01]

Hi Norm, Iam currently having the exact same symptoms as you.. pulls to the right on acceleration or tram lines when hits a bump or uneven surface and pulls to the right.

Thing is i checked my coil overs(bc coils) for loose nuts or broken springs/shocks couldn't find an issue at all, went to look at the ball joints still minty fresh with no wear or damage.
My wheel specs 17x9+38 tyres 245/45/17 Dunlop Direzza 03g semis, now i borrowed a set of tyres fitted them onto the wheels and guess what??? it went away.

Not saying this is the answer to your problem but you can give it ago.. as it did work for me though. Can't afford new tyres atm when iam ready i will be changing my tyres to avoid this annoying tram lining.

GOODLUCK!!! let me know how you go.

[tinkerbell]

My wheel specs 17x9+38 tyres 245/45/17 Dunlop Direzza 03g semis, now i borrowed a set of tyres fitted them onto the wheels and guess what??? it went away.

well don't leave us all hanging in suspense - what where the tyres!?!??

[Norm]

Hi Norm, Iam currently having the exact same symptoms as you.. pulls to the right on acceleration or tram lines when hits a bump or uneven surface and pulls to the right.

Thing is i checked my coil overs(bc coils) for loose nuts or broken springs/shocks couldn't find an issue at all, went to look at the ball joints still minty fresh with no wear or damage.
My wheel specs 17x9+38 tyres 245/45/17 Dunlop Direzza 03g semis, now i borrowed a set of tyres fitted them onto the wheels and guess what??? it went away.

Not saying this is the answer to your problem but you can give it ago.. as it did work for me though. Can't afford new tyres atm when iam ready i will be changing my tyres to avoid this annoying tram lining.

GOODLUCK!!! let me know how you go.

Thats good to know that your change of tyres has resolved your problem. But unfortunately i'm highly doubtful that your new tyre choice has resolved your symptoms. As ChargeR and tinkerbell state, it is the underlying problem of wider tyres and added traction that is causing the imbalance i'm experiencing. I've booked myself in for a track day on the 17th and I know i'll be combating this issue through the event, but as a learning tool, i'm going to run with the specs and gain some track experience, measure the temperature of the tyres and maintain an optimum PSI of 32-36 on hot tyres and see where the changes in my next set of rim/tyre choice will bring. Only way to know truly is to put them to the test. Unfortunately normal roads aren't the best place to do testing.

[tinkerbell]

I've booked myself in for a track day on the 17th and I know i'll be combating this issue through the event, but as a learning tool, <snip> Unfortunately normal roads aren't the best place to do testing.

exactly!

the 'problems' that exist whilst driving on a road virtually disappear when you hit a actual race terack.

and a whole new set of problems will arise! (mostly involving the creation of heat energy from combustion and friction)

but - the good news is that most racetracks (and some hillclimb circuits) are very much more suited to wild alignments and massive tyres - i think that you might be plesantly surprised as to how much you can fall back in love with your car on the track...

it transforms a wriggling complaining whore on the roads into a divine angel that devours corners and eats up braking zones

if it doesnt seem to do this - change settings til it does...

[nikolaz01]

Thats good to know that your change of tyres has resolved your problem. But unfortunately i'm highly doubtful that your new tyre choice has resolved your symptoms. As ChargeR and tinkerbell state, it is the underlying problem of wider tyres and added traction that is causing the imbalance i'm experiencing. I've booked myself in for a track day on the 17th and I know i'll be combating this issue through the event, but as a learning tool, i'm going to run with the specs and gain some track experience, measure the temperature of the tyres and maintain an optimum PSI of 32-36 on hot tyres and see where the changes in my next set of rim/tyre choice will bring. Only way to know truly is to put them to the test. Unfortunately normal roads aren't the best place to do testing.

Please let us know updates as im curious to know if it has been resolved whilst your on the track