16 replies to this topic

[ls2lxhatch]

While you have both racks can you confirm the part numbers and the number of turns from lock to lock for each rack?

My UC rack #9940277 is 3.25 turns lock to lock. According to my calculations this works out at 18:1 which is the quickest of the Torana racks. The published ratio for #9940277 is the slowest at 25:1.


This is the information I have previously collected from the forum. According to Toranamatt69 the front wheel moves 65 degrees from lock to lock. 34 degrees in and 31 degrees out.

9932244 18:1 65 * 18.0 / 360 = 3.25 turns lock to lock.
9942632 20.4:1 65 * 20.4 / 360 = 3.68 turns lock to lock.
9940277 25:1 65 * 25.0 / 360 = 4.51 turns lock to lock

[Toranavista]

The published figure for the UC rack doesnt sound right to me.

[ls2lxhatch]

I agree, I think it is more likely that the UC is 20.4:1 than 25:1.

I have heard that the A9X rack has the same part number as the UC rack and the ratio is 25:1. The A9X ratio would have increased due to the longer steering arms fitted to the A9X. I do not know if the arms are responsible for the increase from 20.4:1 to 25:1 or there was also a different gear set.

According to the LX Gregorys manual the ratio is 16.5:1 however I believe this is the LH not the LX.

As the steering ratio is difficult to measure and affected by steering arms I think the best way to compare racks is to measure how far the tie rod moves for 1.5 turns of the steering wheel.

The tie rod on my UC rack moves around 55 mm for 1.5 turns of the wheel.

Edited by ls2lxhatch, 28 March 2009 - 03:35 PM.

[Toranavista]

[quote name='ls2lxhatch' date='Mar 28 2009, 04:34 PM' post='383259']
I agree, I think it is more likely that the UC is 20.4:1 than 25:1.

yes that sounds right to me

[ls2lxhatch]

If you measure how far the tie rod moves when you turn the steering 1.5 turns you will be able to work out the difference between the two racks. The steering ratio is a combination of the rack ratio and the steering arms.

The LH rack with LH arms is either 16:1 or 18:1 which works out at 2.88 and 3.25 turns lock to lock respectively.

The LH rack with UC arms will be slightly slower. We should be able to estimate the ratio once you have measured the tie rod travel on both racks.

The UC rack with UC arms is most likely to be 20.4:1 which works out at 3.68 turns lock to lock.

The most likely scenario is that the difference between the UC and LH racks is negligible and it is not worth fitting the LH rack.

[76lxhatch]

That was with the suspension at full droop so it may not be 100% accurate, but it wouldn't be too far off.

Should be the same, shouldn't it? The rack doesn't change angle

[ls2lxhatch]

If we assume that the UC rack is 20.4:1 and 3.68 turns from lock to lock. The travel for 1.5 turns is 55 mm therefore the total travel for 3.68 turns would be 135 mm.

Using the above figures. A rack that travels 63 mm for 1.5 turns of the wheel would require 135 mm / ( 63 mm / 1.5 ) = 3.21 turns for lock to lock (135 mm) which is close enough to the figure for the 18:1 rack.

It appears that these figures then confirm the LH at 18:1 and the UC at 20.4:1 although I have not had time to measure if the total travel is actually 135 mm. If the total travel is not 135 mm then all bets are off.

Another way to calculate the difference between the UC rack and the LH rack is 55 mm / 63 mm * 3.68 = 3.21

On this basis the 25:1 rack would travel ( 135 / 4.51 ) * 1.5 = 45 mm for 1.5 turns.

I think that kills the theory about the steering arms being solely responsible for the ratio difference between the LH and the UC. I also think the difference in speed between the 18:1 and 20.4:1 is probably not worth the slightly heavier steering.

My power rack at two turns lock to lock works out around 12:1.

Edited by ls2lxhatch, 07 May 2009 - 03:08 AM.