Working out a BEC project, several questions so far.

[Chris-S]

Great to see this moving along. Keep the updates coming.

[Reliant]

Interesting video here of the famous Hayabusa Turbo Bug :

https://youtu.be/mltCdPF9MGI

This was undoubtedly built at great expense what with the engine built by Holeshot racing (around 350 HP) and the chassis being a one off all aluminium piece designed and made by Zcars...

you can however see one big issue here : the steering (as well as, secondly the sierra diff that is waaaaay too short)

I dont know what they used (maybe the original steering box which is super nice in the standard car because it is like 1 3/4 turns from one end to the other), but here with such output it does look like it needs addressing somewhat.

Paddle shift maybe, but surely steering damper DEFINITELY ?

Edited by Reliant on Sunday 19th August 17:42

[Reliant]

Quick shot of the bug steering set up :



I'm thinking that welding a bracket to the pitman arm and to the chassis kick up rail i will be able to host a damper that would indeed only be reachable by going under the car but at least would avoid the car snaking around when shifting at speed ?

Edited by Reliant on Monday 20th August 06:58

[Chris-S]

I confess, the last time I looked closely at the front setup on a Reliant/Bug was back when I was about 11 and my dad drove one. I was helping him change the kingpin bushes.

But, looking at it now, doesn't it have some pretty serious bump-steer built in as it stands? Anything you can do about the basic geometry to improve it at all?

Random thought, convert to forks, or perhaps wishbones, with a suitable rack??

[Reliant]

Chris-S said:

Doesn't it have some pretty serious bump-steer built in as it stands? Anything you can do about the basic geometry to improve it at all?

Random thought, convert to forks, or perhaps wishbones, with a suitable rack??

I'm not sure it's bump steer thats occuring here. It looks like he's taking his hand off the wheel to shift the gears and that makes the car snake around when the clutch goes back in (plus the HP obviously can't be helping)

The car is moving so fast and if he's using the OE box, the steering is so direct, i have the impression that it could do with some work to get it straight.

I would really rather keep the OE box if possible

[Chris-S]

Certainly, it’s hard to make out what’s happening in that clip, could be a number of things for sure.

A damper wouldn’t hurt, but I’d be tempted to test the bump steer to quantify it, if nothing else. Easily done at this stage and now would be the time to try to improve it if it did prove problematic.

[mikeveal]

Chris-S said:

Certainly, it’s hard to make out what’s happening in that clip, could be a number of things for sure.

A damper wouldn’t hurt, but I’d be tempted to test the bump steer to quantify it, if nothing else. Easily done at this stage and now would be the time to try to improve it if it did prove problematic.

No need to test it, you can see that the set up will generate bump steer.

Difficult to fix completely. Could have been done deliberately to slow drivers down on bumps!

Sorry if I'm teaching people to suck eggs.
There are two rods linking the steering arm to the box, one vertical(ish), one horizontal(ish). As the intersection between these two isn't coaxial with the swingarm bearing, suspension movement will translate to steering movement.

I'd suggest moving the vertical arm backwards, so that the intersection sits as close as possible to the swingarm bearing. Sort of like this:

[Equus]

mikeveal said:

As the intersection between these two isn't coaxial with the swingarm bearing, suspension movement will translate to steering movement.

If the steering link was coaxial with the swing arm bearing, it would introduce bump steer because to reach the steering arm on the upright the link would need to be longer than the swing arm... hence would be moving through a different radius arc.

The current arrangement is correct(ish), as it forces both steering link and swing arm to move through parallel arcs.

[Chris-S]

I was trying to be diplomatic (for a change)

I suggested measuring it to get a sense of just how bad it actually is.

I like that idea to improve it. Looks simple to achieve and really quick and easy to mock up and test the result. Steering will end up a bit asymmetrical and finding space for the Pitman arm on right turns as it rotates back might be tricky, but certainly worth a look.

Less diplomatically, I urge you very strongly to fix that bump steer! It has the potential to be pretty rapid! Steering as it is at the moment will suck the joy out of driving it.

Used to have a Marcos Mantula with chronic bump-steer and that wasn’t much fun until I sorted it out.

[Equus]

Chris-S said:

I like that idea to improve it.

I repeat: making the steering link coaxial with the swing arm will increase its length and arc substantially. It will introduce bump steer, not cure it!

[mikeveal]

Equus said:

I repeat: making the steering link coaxial with the swing arm will increase its length and arc substantially. It will introduce bump steer, not cure it!

You're right. I'd not taken the length of the steering arm into account. When you add that in, it looks about right.

[Chris-S]

Apologies, I didn't see your reply before finishing mine. No need to get snippy!

But, I still believe it would be worth the effort to quantify the amount of bump steer at this stage. Maybe it's pretty good as is, but I'd want to make sure myself.

[Equus]

Chris-S said:

Apologies, I didn't see your reply before finishing mine. No need to get snippy!

I wasn't being snippy... just didn't want the OP to waste a lot of time and effort making the situation much worse, with not one but two people confidently saying 'this is the way to fix it'!

Certainly, it's worth doing a plot of current bump steer to see if there is a problem, and if so, how big it is.

I suspect that the bigger issues may be gyroscopic (which is why bikes fit steering dampers, of course) and down to the fact that there will be bugger all weight on the front wheel under hard acceleration, though.

[Reliant]

hi

thanks for all your input.

I'm not under the impression that a stock Reliant has bump steer, but I do know you can flip it around quite well thanks to its super direct steering.

that said,what technique do you use to test the stock setup for any bumpsteer ?

A guy who built a GSXR1000 bug used a rack from a Vauxhall Astra (I think). I have a couple of photos of the setup but cant really make out how he went around setting the links up etc it looks weird. But he said he did that to have a less direct steering action to avoid zigzagging up the road when driving fast

[Equus]

Reliant said:

that said,what technique do you use to test the stock setup for any bumpsteer ?

Disconnect the coilover and move the suspension through its working range by hand. If the bump steer is bad, you'll be able to see it by eye.

OIf it's less bad, or you need an accurate reading, you can make up a bump steer gauge basically by attaching a flat plate or sheet of wood to the face of the wheel, then using a couple of dial gauges to measure the difference in 'toe' as you move the wheel up and down through its working range.

Google 'DIY bump steer gauge' and I'm sure you'll come up with the details, or it's covered in Allan Staniforth's books.

[Mr2Mike]

Equus said:

Chris-S said:

I like that idea to improve it.

I repeat: making the steering link coaxial with the swing arm will increase its length and arc substantially. It will introduce bump steer, not cure it!

What am I missing? For any given steering angle, the distance between the end of the (hub end) steering arm and any point coaxial with the leading arm pivot will remain exactly the same over the entire suspension travel. Even if the leading arm could rotate through 360 degrees this would remain the case.

In practice the link at the steering box end could not be made coaxial with the suspension pivot over the full steering range, so some bump steer would be introduced as the steering angle increased either side of straight ahead, but that happens on plenty of four wheeled cars as well. Actually you could do it by using a hydraulic ram for steering, but that would be a non-starter for a road going vehicle.

[Equus]

Mr2Mike said:

What am I missing? For any given steering angle, the distance between the end of the (hub end) steering arm and any point coaxial with the leading arm pivot will remain exactly the same over the entire suspension travel.

That would work in the straight ahead position, but as soon as you move the steering, the Pitman arm moves the rear end of the steering tie rod out of coincidence with the leading arm of the suspension. and you've got conflicting arcs.

[Chris-S]

Equus said:

I wasn't being snippy... just didn't want the OP to waste a lot of time and effort making the situation much worse, with not one but two people confidently saying 'this is the way to fix it'!

Certainly, it's worth doing a plot of current bump steer to see if there is a problem, and if so, how big it is.

I suspect that the bigger issues may be gyroscopic (which is why bikes fit steering dampers, of course) and down to the fact that there will be bugger all weight on the front wheel under hard acceleration, though.

It's all good. I quite agree - wouldn't want the OP wasting time on my say-so either, but it "looked wrong" so thought I should say something at this point, hence my original post to have measure. At first look, I thought the suggested solution might work, but as always, am happy to accept I'm wrong. If I am of course

I'm keen to see this project finished (although not as much as the OP I'm sure). I always had a soft spot for the Bug - I had a model of one as a kid and it was always a favourite.

Anyway, back on yer 'eads.

[Mr2Mike]

Equus said:

That would work in the straight ahead position, but as soon as you move the steering, the Pitman arm moves the rear end of the steering tie rod out of coincidence with the leading arm of the suspension. and you've got conflicting arcs.

As I mentioned...

[Chris-S]

Any progress? Itching to see how it’s coming along, and I promise to keep any further “helpful thoughts” I might have to myself