Lotus Elan and Lotus Elan Plus 2 Forums

Hi all

I'm having brain fade (no the brakes are fine) - which way round do the trunnions go? - is the RH thread on the drivers side (UK) or the passenger side.

Thanks
Gavin

Hubs and trunnions,

RH thread on RH side

LH thread on LH side

John

Fantastic - Thanks John

I think I had a crisis of confidence because it was too obvious (and I was having yet another senior moment)

All the best
Gavin

Yes, but does it make any difference? Bearing in mind all of the other built in tolerances (both design and manufacture) in the suspension and steering, does the few mm of difference in ride height when turning actually matter or even noticable?

It probably does not matter which side they go on as long as you have one LH and one RH thread. This balances the torque that tries to steer each of the wheels under the weight on thread.

cheers
Rohan

It probably does matter,all one has to do is look at the multitude of bump steer postings...

John

P.S. I still think the bump steer is best not measured from the frame but from " ride height".

Hi John

I don't think the direction of the trunnion thread on any particular side contributes in any significant way to bump steer effects. All the bump steer measurements are done with the wheels straight ahead. Bring in the complexity of what happens with the wheels turned and the suspension deflected due to roll and it all gets to hard The effect of the thread direction is the least of your worries

cheers
Rohan

Triumph will have made them handed for a reason as its cheaper and more desirable to manufacture and stock one common part.

I think they are made in opposing thread direction pairs for the reason that if both say RH threads then turning the Wheel in one direction would be much harder than the other because it would be lifting the whole weight of the front of the vehicle, the other way would have gravity assistance.

On the vehicle I dont think that practically in terms of suspension/steering function it matters what side they are on but if they are symmetrical and can be reversed you would have to swop the uprights and then the steering arms would be sticking out the wrong way, if they can be swopped (and they probably cant) it may still effect the steering geometry, possible the Ackerman angle.

I always wondered if it would effect steering weight by adding or opposing body roll.

I.E. a left turn lifts the left side. therefore fit the trunnion that also lifts that side.

Go with the roll as it were! Otherwise the "trunnion lift" is fighting against body roll.

Although I imagine the actual amount of lift or drop is very small.

Chancer wrote:....

I think they are made in opposing thread direction pairs for the reason that if both say RH threads then turning the Wheel in one direction would be much harder than the other because it would be lifting the whole weight of the front of the vehicle, the other way would have gravity assistance.......

It is not so much turning effort but getting the car to track straight and the wheels to not steer in one direction when the car is moving and the steering wheel only held lightly

cheers
Rohan

Much like castor action, a self stabilising system?

Rick Cranshaw pointed out to me that changing the orientation of the trunnions changes the A-arm geometry and the consequence is a change in front roll center.

Bill

Something like riding a motor-cycle,leaning to the right when taking a left hand bend.....one of my girlfriends did that in the '70's ....never again.

John

This got me to thinking. It seems to me that if the thread on the outside steering knuckle allows it to rise during a turn, that wheel/tire would gain camber, while the inside wheel would drop, loosing camber. Theoretically, this would help in maintaining traction during the turn. Fire away......

john.p.clegg wrote:Something like riding a motor-cycle,leaning to the right when taking a left hand bend.....one of my girlfriends did that in the '70's ....never again.

John

Precisely why I got rid of my pillion seat and fitted a solo seat back then. Seemed every novice had an affinity towards staying vertical instead of leaning with the rider! Much more comfortable seat as well.

Kurt.