The Fingertight Racing Sidecar Project

**Grumph** · 22nd July 2013, 09:39

IMO you're overthinking this - and in the wrong direction too. On a kart track, on Kart wheels and tyres,look at karts for your chassis inspiration.
No suspension - chassis flex takes care of the contact patch movement quite happily, and kart tyres are designed for this.... Sidecar wheel placement is the ruling factor in how a chair turns for a given COG placement,and i don't see this changing.
The swinger has more of an effect on transitional behavior too - all the guff you've been posting relates to a steady state model with stationary weights on board...If the bloody swinger scratches his arse at the wrong time, you're history...

**Drew** · 22nd July 2013, 10:03

Originally Posted by Moooools

Sliding to an extent can be good for a number of reasons. One is to induce an increased slip angle in the rear tyres, and will result in the lateral grip being higher provided that the tyre wants all that slip angle, and the other is to counteract anti-yaw moments and this understeer.

The easiest way to think about this is that the chair has to both move around the corner in an arc, and rotate however many degrees at the same time say 180* for a hairpin. These are separate events (although they affect each other). When you enter a corner the front wheel leads with a force (because you steer it in) and this starts to turn the rig faster and faster. By mid corner the rear tyre has caught up (it always does) and is producing the same amount of force as the rear then the rig is rotating at a constant speed. And then the pilot removes his steering input and the rear tyre is providing more force than the front so the rig decreases it's speed of rotation. This is all just a moment balance game. see: http://en.wikipedia.org/wiki/Moment_(physics)

So the phenomenon of understeer is the front tyre doing not enough work or the rear doing too much, which means the rig will not rotate quickly enough to sustain adequate slip angle on the tyres. And oversteer is the exact opposite.

I have yet to mention the sidecar wheel in all this. Simply put it will just act like a front or rear wheel depending on whether it is in front or behind the centre of gravity of the rig. If the wheel is right at the rear axle you should find that the vehicle has very little understeer on turn in but lots of it mid corner. As you move it forward this understeer decreases until the wheel is inline with the CoG. At this point if the tyre produces any lateral force it acts directly through the centre of gravity and as such cannot rotate the rig. So it effectively has no effect on oversteer or understeer of the rig but can still contribute fully to lateral accelerations.

Taking this a bit further, the sidecar wheel will now have too much slip angle mid corner. However there are no rules against steering the sidecar wheel on a bucket so you may as well link it up to steer a small percentage of the front wheel.

You've obviously got it all figured out better than the guys we have taken inspiration from, in the building of our full sized chair.

I'll leave you to it.

**Kickaha** · 22nd July 2013, 10:09

Originally Posted by Grumph

IMO you're overthinking this

I think he must be University educated

Originally Posted by Grumph

The swinger has more of an effect on transitional behavior too - all the guff you've been posting relates to a steady state model with stationary weights on board...If the bloody swinger scratches his arse at the wrong time, you're history...

I agree with what the old codger sez

**Moooools** · 22nd July 2013, 11:20

Originally Posted by Grumph

IMO you're overthinking this - and in the wrong direction too. On a kart track, on Kart wheels and tyres,look at karts for your chassis inspiration.
No suspension - chassis flex takes care of the contact patch movement quite happily, and kart tyres are designed for this.... Sidecar wheel placement is the ruling factor in how a chair turns for a given COG placement,and i don't see this changing.
The swinger has more of an effect on transitional behavior too - all the guff you've been posting relates to a steady state model with stationary weights on board...If the bloody swinger scratches his arse at the wrong time, you're history...

Yeah good idea. How about we take this 4 wheel vehicle that is built to a very specific set of rules and about half the weight, and just copy the damn thing because ,hey, we are running the same track and wheels. As stated the suspension has nothing to do with contact patch movement, and everything to do with tyre control.
That is truly the worst form of engineering. The vehicles have so little in common it is a joke.

I don't even think you read what I wrote, or if you did you don't know the meaning of steady state. The model is for a transient vehicle and works on the swinger and pilot having two distinct positions, one to the right and one to the left. I will agree that that may miss some of the picture, but it is a better picture than the "well he did it so I will too" approach.

That whole block of shit I wrote said exactly what you said. That sidecar wheel affects how the chair turns. I am glad we are in agreement there. I just don't agree that where people are running them is the best place in a bucket.

**Moooools** · 22nd July 2013, 11:22

Originally Posted by Drew

You've obviously got it all figured out better than the guys we have taken inspiration from, in the building of our full sized chair.

I'll leave you to it.

Yep. I am sure am glad I haven't told you already that I am referring to bucket sidecars here, and explained why I thought there was a difference. Otherwise your point would seem invalid.

**Moooools** · 22nd July 2013, 11:33

Originally Posted by Kickaha

I think he must be University educated

I agree with what the old codger sez

Ahhhhh. The old 'university educated'. Too much thinking and not enough doing.
I would say 'University educated' is a stretch for me. Although I am at Uni I spend most of my time on this:

https://www.facebook.com/UoAfsae
www.fsae.co.nz

Which is where I learnt most of what I am going on about.
We design and build a new one each year and and race it over in Aus. And do all of our testing at Mt Wellington.
I can't say I appreciate most of the rubbish that university itself teaches but it is good for the bit of paper at the end.

But if by 'university educated' you mean 'Doesn't just look at someones work and assume they had it right, and tries to correlate real world outcomes to the physics that govern them' then yes. Yes I am.

**Moooools** · 22nd July 2013, 11:34

Holy shitstorm Batman.

Who would have thought people wouldn't like being told I think they are wrong?

**Drew** · 22nd July 2013, 11:38

Originally Posted by Moooools

Yep. I am sure am glad I haven't told you already that I am referring to bucket sidecars here, and explained why I thought there was a difference. Otherwise your point would seem invalid.

The further forward you put the chair wheel ya condescending twit, the more it fights the front wheel when turning right. Do you get that? It is not allowed to turn with the steering. So it's direction is fixed.

Put it right in the middle, and when you turn it is being dragged across the road surface.

**Moooools** · 22nd July 2013, 11:41

Originally Posted by Drew

The further forward you put the chair wheel ya condescending twit, the more it fights the front wheel when turning right. Do you get that? It is not allowed to turn with the steering. So it's direction is fixed.

Put it right in the middle, and when you turn it is being dragged across the road surface.

It is not allowed to turn with the steering? In buckets it is. I don't know about your full sized rules.

I do see what you are saying but you are assuming that the Yaw axis is at the rear wheel. Which it only is for initial turn in. Mid corner the rig will turn about its centre of gravity. And initially there is fuck all load on the chair wheel at turn in. I would rather have it working correctly when there is the most load on it, right in the middle of the corner.

**Grumph** · 22nd July 2013, 13:11

Originally Posted by Moooools

It is not allowed to turn with the steering? In buckets it is. I don't know about your full sized rules.

I do see what you are saying but you are assuming that the Yaw axis is at the rear wheel. Which it only is for initial turn in. Mid corner the rig will turn about its centre of gravity. And initially there is fuck all load on the chair wheel at turn in. I would rather have it working correctly when there is the most load on it, right in the middle of the corner.

Oh great, he's read the rules....If he ever gets it finished with a steerable sidecar wheel, would someone please video the ensuing shitstorm for the benefit of those of us who can't be there...thanks.

Carry on, never let it be said i discouraged anyone...

**Kickaha** · 22nd July 2013, 13:59

Originally Posted by Grumph

Oh great, he's read the rules....If he ever gets it finished with a steerable sidecar wheel, would someone please video the ensuing shitstorm for the benefit of those of us who can't be there...thanks.

Carry on, never let it be said i discouraged anyone...

Full size rules specifically state it must be steered only by the front wheels, buckets dont have that rule

The Seymaz had sidecar steering back in the seventies when it was allowed

**Grumph** · 22nd July 2013, 16:17

Originally Posted by Kickaha

Full size rules specifically state it must be steered only by the front wheels, buckets dont have that rule

The Seymaz had sidecar steering back in the seventies when it was allowed

I know - i too can read the rules - and i've got a pretty good drawing of the Seymaz layout too.

In this case i suspect polling the class competitors prior to cutting metal may be a good move. I don't want to do a husaberg with rule interpretations but i'd be surprised if the others in the class were happy to let it run.

**Henk** · 22nd July 2013, 16:39

The others in the class are pretty relaxed at the moment, I had thought that side wheel steering was out but mools is right, nothing said in the bucket rules where it is disallowed in the full size variants. To be honest at the moment there isn't that much of an arms race going on, just getting numbers on track is a bonus, I guess when things hot up at the front this will change, at the moment I think most of the teams out there are still getting their heads around how to ride the smaller rigs and getting them set up so they work close enough and are able to finish a meeting without falling to bits.