wrestling with the steering
Discussion
So I left work early and enjoyed a couple of hours in my Sports round the Suffolk coastal roads. What I noticed today is the amount of effort I had to put into the steering. On the sort of damaged and rippling surfaces I encountered, I didn't really feel comfortable accelerating hard or taking my hand off the wheel for a gear-change, for fear the steering would jerk. Even a kerbside drain at moderate speed (say over 40) results in a fair amount of steering movement. The car felt unnuaturally lively and not particularly safe. It was absolutely fine on smooth roads. It was absolutely normal under fast weaving too. Is this bump-steer normal ? Have I suddenly lost my chest-hair ?
Bump steer can be reduced / eliminated by moving the steering rack up or down. Factory have a good crib sheet to explain how to do it. I followed their instructions to determine how much correction was needed then had a local machinist make me up a set of new rack mounts - it seemed easier than filing the chassis (as suggested by factory) and it will never move.
I would venture to say this is actually somewhat normal. The car only has 2.5 turns lock to lock on the steering rack so the steering wheel is going to jerk back and forth over potholes and really rough sections of road. I notice it more at low speed. That being said, I believe the steering rack ratio we use is better suited to a track. I run a rack with 2.2 turns lock to lock. I also generally run zero front toe in to make the car even more nervous for very tight twisty tracks. The first thing I'd do, though, is check that your rearmost lower suspension bush at the back of the car is still good. That bushing wears out pretty quickly and can really upset the handling of the car. Next, I'd check the camber and toe settings. There should be detailed procedures for this in the build manual, but you can ask us for help on this bit too. Bumpsteer's probably the last thing I'd check.
Cheers!
-Mack
Cheers!
-Mack
I'll second that, the steering is very sensitve. Just see what happens when you turn the wheel from side to side just a little, the car moves. Contrast that to a normal production car that pretty much does naff all. I have long come to the conclusion that on really bad stretches of road a normal car is far easier to drive quickly (or at least feels like it!). The best practice is not to fight the steering and let it do what it wants, you probably find it does actual go straight!
Thanks all, particularly BigMack. There is some play in the rearmost lowest wishbone bush. That explains it.
I agree that Ultimas react super-fast to sharp steering inputs. I like that and it's well worth the normal & non-worrying levels of 'kickback'. As someone pointed out, you just relax your hands and let it find its own path of least resistance. Like riding a mountain bike fast through a sandy bit.
cheers
I agree that Ultimas react super-fast to sharp steering inputs. I like that and it's well worth the normal & non-worrying levels of 'kickback'. As someone pointed out, you just relax your hands and let it find its own path of least resistance. Like riding a mountain bike fast through a sandy bit.
cheers
The Bumpsteer I corrected was on a Can-Am. Prior to correction the car would dart over bumps and undulations. Now it it rock solid. The steering response it still razor sharp, you just don't have to make constant corrections. Honestly if the rack is just bolted into the chassis it can be a mile out. Mine was and it is easy to fix.
When my car was new it felt a bit more nervous than I was expecting. I then redid the suspension alignment only a lot more accurately (prictice makes perfect I guess) and dialed in a bit more camber and a bit less toe in and it was a lot more sorted.
I agree with Mack that checking the bushes and general setup would be a very good idea.
What sort of tolerance is acceptable when checking for bump steer and what's the easiest way to measure it? I feel another job's about to be added to the winter work list...
I agree with Mack that checking the bushes and general setup would be a very good idea.
What sort of tolerance is acceptable when checking for bump steer and what's the easiest way to measure it? I feel another job's about to be added to the winter work list...
I know of two GTR's that had the bump steer checked and had up to 18+mm of bump steer and their cars were set up by the book...... in both instances it was 'dialed out' to be less than 1mm. so worth checking.
Rear bushes wear very quickly and IMO are worth replacing as regularly as the oil (£5-10 from Wisbeck engineering!).
Rear bushes wear very quickly and IMO are worth replacing as regularly as the oil (£5-10 from Wisbeck engineering!).
Yes, sounds like bump steer is worth checking! I checked mine yesterday and it had 1mm with the standard factory holes. I had checked it before and thought it was pretty close to dead on. I was going to dial it out to zero but thought it not worth fiiddling with at the moment, b/c I'm going to upgrade those outer tie rods to rose joints and will dial it out on that end. I received another email from someone who tested two cars that had quite a sizeable amount however.
Very sorry to have overlooked this as being an issue! Wow. 18+mm!
Cheers!
-Mack
Very sorry to have overlooked this as being an issue! Wow. 18+mm!
Cheers!
-Mack
Hi Phil, yep it is the one that appeared in Ultimatum a few years back. Unfortunately, for reasons I can't fathom, the writing is in a shade of yellow and does not show up on my scanned copy!
Not sure if it will even fax to be honest.
So cannot do anything with it, other than post it!
Not sure if it will even fax to be honest.
So cannot do anything with it, other than post it!
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