536 replies to this topic

[Nikov]

Hi Muncher, where are we up to with this kit?

Cheers

ps Ali uprights?

The tie rods are finalised and i have ones here to be sent out. On saturday I'm test fitting a bracebar to a turbo with a Miltek to check if there is enough room, as soon as that is done the brace brackets will be finalised and sent off for machining.

Ali uprights will be a while longer, to make them perfect and better than anything else around. There's not even a prototype for them yet.

Thanks for the update. As I was a bit premature with my paypal payment do you want to pm me your paypal costs and I'll stick a cheque in the post to cover it?

[Muncher]

Right guys, I'm going to have to close off the group buy for the brace bar and limit it to the 30 people above. The reason for this is the brace bar costs are such that Spitfire will probably be making a loss on the brace bar element. They're happy to provide those who have registered an interest with a kit at that price but don't want to do any more without raising the price. I found out tonight that the Lotus bar which is far from ideal, and is pictured in the first post of this thread is £575 alone!

[myhifi]

Right guys, I'm going to have to close off the group buy for the brace bar and limit it to the 30 people above. The reason for this is the brace bar costs are such that Spitfire will probably be making a loss on the brace bar element. They're happy to provide those who have registered an interest with a kit at that price but don't want to do any more without raising the price.

I found out tonight that the Lotus bar which is far from ideal, and is pictured in the first post of this thread is £575 alone!

Hello Muncher,

Thank you and Spitfire for this offer, and I am glad that my name is in the first 30.

One thing that bothers me though is the setup you have designed for the brace bar. As it is set up I do not see the need for the rose joints : there will not be any play.

Initially, the brace bar was supposed to be tied up on the same axle as the tie rod, transfering the charge to the other side. As you made it, a simple bar without joints will be enough, therefore reducing cost. You should try to fit the brace on the same axle as the tie rod joints, but then I think there is not enough room (undertray and exhaust), could you check ?

Am I clear ? (mechanical english is a first for me...)

Bye, and keep going the result is great with the tie rods already.

Antoine.

Edited by myhifi, 16 January 2008 - 12:54 PM.

[Joe-Turbo]

your english is fine mate, im sure muncher will be along soon enough with answers to your questions

Edited by Joe-Turbo, 16 January 2008 - 01:04 PM.

[Winstar]

Right guys, I'm going to have to close off the group buy for the brace bar and limit it to the 30 people above. The reason for this is the brace bar costs are such that Spitfire will probably be making a loss on the brace bar element. They're happy to provide those who have registered an interest with a kit at that price but don't want to do any more without raising the price.

I found out tonight that the Lotus bar which is far from ideal, and is pictured in the first post of this thread is £575 alone!

Hello Muncher,

Thank you and Spitfire for this offer, and I am glad that my name is in the first 30.

One thing that bothers me though is the setup you have designed for the brace bar. As it is set up I do not see the need for the rose joints : there will not be any play.


Antoine.

I was also thinking what the requirement for the rose joint was, also it's unclear from the picture does the bolt through the rose joint also go through a second hole in the subframe or is it just attached via the flange on the tie-rod bracket.

[myhifi]

I found out tonight that the Lotus bar which is far from ideal, and is pictured in the first post of this thread is £575 alone!

One thing that bothers me though is the setup you have designed for the brace bar. As it is set up I do not see the need for the rose joints : there will not be any play.


Antoine.

I was also thinking what the requirement for the rose joint was, also it's unclear from the picture does the bolt through the rose joint also go through a second hole in the subframe or is it just attached via the flange on the tie-rod bracket.

The Lotus Bar from the first post lacks a decent bracket on the subframe to attain a double sheer mounting. The Spitfire tie rod kit adds this (and more : bumpsteer, machined collet so the bolt does not sheer,...) and it is great. So we should get a mix of both.

[Spitfire Engineering]

Right guys, I'm going to have to close off the group buy for the brace bar and limit it to the 30 people above. The reason for this is the brace bar costs are such that Spitfire will probably be making a loss on the brace bar element. They're happy to provide those who have registered an interest with a kit at that price but don't want to do any more without raising the price.

I found out tonight that the Lotus bar which is far from ideal, and is pictured in the first post of this thread is £575 alone!

Hello Muncher,

Thank you and Spitfire for this offer, and I am glad that my name is in the first 30.

One thing that bothers me though is the setup you have designed for the brace bar. As it is set up I do not see the need for the rose joints : there will not be any play.


Antoine.

I was also thinking what the requirement for the rose joint was, also it's unclear from the picture does the bolt through the rose joint also go through a second hole in the subframe or is it just attached via the flange on the tie-rod bracket.

Good question

I cannot say too much about the Lotus design as I do not know why they choose the option they did, though having owned Lotus for over 32 years I can assure you somewhere in the calculation the cost was involved.
Until the latest model was introduced Lotus used a double shear bracket as part of their motorsport upgrade kit.

You need to consider that the flexing of the subframe is 3D that means there is not only a force going across the subframe arms initiated by the cornering reaction through the toe-link, but also, as a result of suspension movement forces pushing only one side of the subframe up and down.
As the car corners there is also a force on the rear as a whole, this force tries to move both arms the same way.
The brace inhibits any individual movement in this plane so both arms move together forming a parallelogram.
You can imagine that if you were positioned on one subframe arm and looking across at the other you will see during the cycle of everyday driving the other side go up and down as the suspension forces act on the subframe, It will seem to move left and right (though actually fore-aft) as the arms move in parallel.
Due to these movements it is not possible to design a rigid fixing that will last for long without the addition of a joint that will allow these forces to be passed on and not used to stress the fixing. That is why a spherical bearing was used. (rod end)
A fixed bar would act as an anti-roll bar as well

The first design was very close to the Lotus solution but when I had it checked by a suspension design engineer he was not impressed by the floating brace, even though it does tie into the mount 1/3 of the way across.
All is fine when the brace and toe links are in direct opposition, but this is rarely the case. Most of the time, and especially when most critical during cornering, the toe link is at an angle to the brace. This imparts a resultant force on the bolt that is not opposed by the brace and the direct result of which in terms of long term fatigue is hard to calculate.

Much better to double shear the original bolt with a bracket that supports it in both planes and ties it to the subframe minimising the bending forces on it in all directions.
The brace is then effectively connected to both subframe and suspension pick up giving better support to the subframe without relying on the bolt to take all the bending forces as the Lotus kit does.
It also leaves the rest of the subfarme alone to flex as and when it was designed to.

The design of the brace bracket does have it bolted to the subframe as well, this larger bolt and the two smaller ones are on the other side of the support plate behind the rear face of the subframe spreading the load nicely across the entire area.

I can guarantee this solution is not cost related 

[techieboy]

Thanks Spitfire - great explanation and it certainly sounds (and looks) like a well designed bit of engineering. And, thanks for deciding to have a go at some uprated parts for the VX, as the choice is severely limited and only likely to get worse as Vauxhall try and erase any trace of it from their collective memories. Nice to hear that decisions you've made aren't based on (low) cost considerations alone.

Edited by techieboy, 16 January 2008 - 03:59 PM.

[Muncher]

Nice to hear that decisions you've made aren't based on (low) cost considerations alone.

I don't think through the development of the tie rod and brace kit at any point has cost of a component even been mentioned, the slotted collets were added, the two part VXT insert was added and the inserts to provide a spanner flat were all added, purely because that was the best way to do it.

Using the spherical joints also allows one side of the brace bar to be further out than the other to clear exhaust components.

[Sam3703]

wow, that's detailed explainations ! indeed the lotus brace is not THE solution but I'm also staring at yours... that's what can be called "complicate engineering"... complicate for low gain, if not nothing If you don't transfer the loads to a not working side of the subframe, as Lotus does with the 3rd clamping point (that's really not optimum but with the constraint of not changing the subframe design)... you simply balance the loads from 1 toe link to the other. Without any local load reduction around, which would have helped in the prevention of the subframe cracking that has already been seen. furthermore you will not avoid bending of the subframe (same effect) because of the rod ends supporting no torque. single (or better : double) shear pivot brace (instead of double shear rod) would have helped the subframe, taking for itself some of the torque created by the lever corresponding to the distance from the toe link rod center to the subframe with this setup you gain : -some strength on the bolt that holds the toe-link on the chassis, thanks to the stiffness of the double-shear bracket & the brace bracket tighten on it -extra weight the brace will remain approximately idle as, when cornering, it will only be loaded by the (small) difference of lateral forces on the 2 toe links. that was not the intent to have the brace useful, one must find a way to clamp it firmly to the subframe, and not in an area loaded by the toe links... I'm working to find a solution, but on the VX220 nothing comes easily (maybe somewhere around the engine mount)

[techieboy]

Nice to hear that decisions you've made aren't based on (low) cost considerations alone.

I don't think through the development of the tie rod and brace kit at any point has cost of a component even been mentioned, the slotted collets were added, the two part VXT insert was added and the inserts to provide a spanner flat were all added, purely because that was the best way to do it.

Using the spherical joints also allows one side of the brace bar to be further out than the other to clear exhaust components.

Sorry if you took offense at that Paul. I wasn't trying to imply it was engineered down to a price; more like the opposite. Well engineered at a sensible price but without compromising on design and/or materials to make it "cheap".

[Muncher]

Nice to hear that decisions you've made aren't based on (low) cost considerations alone.

I don't think through the development of the tie rod and brace kit at any point has cost of a component even been mentioned, the slotted collets were added, the two part VXT insert was added and the inserts to provide a spanner flat were all added, purely because that was the best way to do it.

Using the spherical joints also allows one side of the brace bar to be further out than the other to clear exhaust components.

Sorry if you took offense at that Paul. I wasn't trying to imply it was engineered down to a price; more like the opposite. Well engineered at a sensible price but without compromising on design and/or materials to make it "cheap".

No offence taken at all

[Spitfire Engineering]

wow, that's detailed explainations !

indeed the lotus brace is not THE solution
but I'm also staring at yours... that's what can be called "complicate engineering"... complicate for low gain, if not nothing
If you don't transfer the loads to a not working side of the subframe, as Lotus does with the 3rd clamping point (that's really not optimum but with the constraint of not changing the subframe design)... you simply balance the loads from 1 toe link to the other. Without any local load reduction around, which would have helped in the prevention of the subframe cracking that has already been seen. furthermore you will not avoid bending of the subframe (same effect) because of the rod ends supporting no torque. single (or better : double) shear pivot brace (instead of double shear rod) would have helped the subframe, taking for itself some of the torque created by the lever corresponding to the distance from the toe link rod center to the subframe
with this setup you gain :
-some strength on the bolt that holds the toe-link on the chassis, thanks to the stiffness of the double-shear bracket & the brace bracket tighten on it
-extra weight

the brace will remain approximately idle as, when cornering, it will only be loaded by the (small) difference of lateral forces on the 2 toe links. that was not the intent
to have the brace useful, one must find a way to clamp it firmly to the subframe, and not in an area loaded by the toe links...
I'm working to find a solution, but on the VX220 nothing comes easily (maybe somewhere around the engine mount)

Possibly it was too detailed
OK, normally the toe link is only transferring the forces to the subframe. This is fine as long as everything is a strong as it should be.
But I am led to believe though that this is not the case, especially when high grip tyres are used there are two problems ….
The first is that the ball joints are not strong enough in single shear and sometimes fail as they do regularly on the Elise.
The second problem which is Toyo Elise and VX specific is that the subframe flexes too much on the outer side when cornering causing changes in Geo and possibly even causing stress fractures as you mentioned.

The solution to the first problem is to replace the ball joint with a quality bearing and also to take the opportunity to double shear the inner mount.

The second problem is to support the subframe in some way without re-designing it as you mentioned. The advantage of the brace is you share any loads that come through the toe links to the subframe across both sides of the subframe effectively halving the load. Remember, the high forces are only generated in the outside wheel where a significant proportion of the weight has transferred.
Not quite true of course as the effect on the inner wheel which is being dragged outward is to pull on the toe-link not compress it, so both forces are acting in the same direction though the forces involved here are light compared to the outer so the overall effect is to share the high load on the outer toe-link across both arms of the subframe.
This is how the brace kit functions.
The total load is not the problem, the problem is the individual load induced by cornering on the outside tyre.


So you are correct, the load is only “balanced” but across the subframe rather than the links, allowing both arms to take the force simultaneously. For the “non- working” part of the subframe the brace uses the other arm as it is not working very hard at the same moment the other side is.
This causes a major reduction on the amount of force each arm of the subframe has to endure in turn as no single arm has to take the full cornering force anymore. This will lead to a substantial reduction in subframe distortion and a reduction in stress induced fatigue.
It will also increase the rigidity of the subframe in that plane helping to keep the geometry correct under load. Further restriction in one plane will often cause a restriction in another as the component cannot twist etc until it has moved significantly.

The second part of your post I cannot quite understand enough to comment I’m afraid.
Though I think it is based on the assumption the total force is the issue?
Are you saying the force generated on the inside wheel is also too great for the frame?

If there is an option to locate the brace to an additional location on the VX frame I cannot see any reason why this could not be investigated, though you need to be very careful as you will be aware in case you cause the area to become too rigid which creates it’s own bunch of problems and may cause stress cracking elsewhere.

The VX subframe is not the same as the Elise one though similar; how the differences are reflected in stress pattern across the chassis and subframe I have no idea.

Unless you wish to spend a lot of time and money doing a thorough stress analysis of the subframe and suspension system or really know what you are doing and prepared to take the consequences may I humbly suggest it is best left as it is?
If your experience and knowledge is such that you can modify it safely then that is a great bonus and I am sure many here will wish be involved or at least share the result with you.

The gains from the brace are substantial, relatively safe, simple, easy to fit, and even good value.

BUT the choice, as always is yours 

The extra weight mentioned by the way including the rod ends, boots, brace brackets, collets and bolts is less than 1KG! and will support over 3 tonnes, substantially more than forces generated by the suspension, impact notwithstanding.

[Sam3703]

convinced !

although I would still use pivots instead of rod ends

for the record, I think the main difference between your analysis and mine, is that you consider the side force of the inner wheel as negligible
that can be true on hi CG vehicles/stiff suspension as we see on some rallycar based on standard road vehicles
on lightweight (and low CG) ones, that's a bit different
I've recently calculated the anti-roll components of a 550kg light sportscar, and, when cornering at 1.3G side acceleration, the outer wheels sustain 250kg side force, where the inner still sustain 100kg side force each, that's not negligible


but I give up, you're right saying transferring the load to other "unloaded" parts of the subframe may take the risk of failure of that zones, not designed for that... that's why I did not reach to a solution (the only one I see would be to bolt/weld the brace on many points of the frame to spread the load... that's not what I want to do)

I keep the order
but I hope you're fast manufacturing it as i'm currently preparing the speedster to receive it

[Muncher]

convinced !

although I would still use pivots instead of rod ends

for the record, I think the main difference between your analysis and mine, is that you consider the side force of the inner wheel as negligible
that can be true on hi CG vehicles/stiff suspension as we see on some rallycar based on standard road vehicles
on lightweight (and low CG) ones, that's a bit different
I've recently calculated the anti-roll components of a 550kg light sportscar, and, when cornering at 1.3G side acceleration, the outer wheels sustain 250kg side force, where the inner still sustain 100kg side force each, that's not negligible


but I give up, you're right saying transferring the load to other "unloaded" parts of the subframe may take the risk of failure of that zones, not designed for that... that's why I did not reach to a solution (the only one I see would be to bolt/weld the brace on many points of the frame to spread the load... that's not what I want to do)

I keep the order
but I hope you're fast manufacturing it as i'm currently preparing the speedster to receive it

With any luck the fit on the turbo will go to plan on saturday, the final brackets will be drawn up on saturday night and given to the laser cutters on monday morning.

[Spitfire Engineering]

convinced !

although I would still use pivots instead of rod ends

for the record, I think the main difference between your analysis and mine, is that you consider the side force of the inner wheel as negligible
that can be true on hi CG vehicles/stiff suspension as we see on some rallycar based on standard road vehicles
on lightweight (and low CG) ones, that's a bit different
I've recently calculated the anti-roll components of a 550kg light sportscar, and, when cornering at 1.3G side acceleration, the outer wheels sustain 250kg side force, where the inner still sustain 100kg side force each, that's not negligible


but I give up, you're right saying transferring the load to other "unloaded" parts of the subframe may take the risk of failure of that zones, not designed for that... that's why I did not reach to a solution (the only one I see would be to bolt/weld the brace on many points of the frame to spread the load... that's not what I want to do)

I keep the order
but I hope you're fast manufacturing it as i'm currently preparing the speedster to receive it

Honestly I am not trying to convince you this is just the way I see it with a knowledge of the Elise setup.
As an example, the figures you calculated above would see a total load of 350kg across both arms of the subframe, with a maximum of 250kg per wheel depending which way you are cornering.
The brace will change that to 175kg per side either way. A 30% reduction in maximum force and the resultant distortion.
As you can imagine as the car weight increases and the CofG rises this split becomes larger to the point where the inside wheel lifts and 100% is on the outer wheels.

Can you please calculate using the the actual VX weight, front rear split and estimated CofG? that would be more realistic. I appreciate not all the force on the subframe is from the toe link most is from the lower wishbone where the weight sits, but it will be indicative of the % split anyway.

Ta



Gaz
Be nice

[Joe-Turbo]

think the standard vxt is 929kg, n/a about 850kg?

[Spitfire Engineering]

I meant to add the other reason that this extra fixing cannot be added to the current design nor a different end fitting used due to the tube used. Although this will support over 3 ton (actually more, in compression it is nearer to 4 but I added a margin and gave the tension figure as it was lower) it will not take much in the way of bending loads, nor can you weld to it without changing it's propereties. The tubes are best in tension and compression. for other loads another design, probably in steel is needed. If anyone wishes we can always look at other options later and send the plans to a friend who is more than capable of the stress analysis. But expect the cost to be neare to the Lotus kit.

[Sam3703]

I am capable of stress analysis, I just miss free time to build the model I'll do the calc for the VX asap... where do you estimate the CoG is ?

[Spitfire Engineering]

I am capable of stress analysis, I just miss free time to build the model
I'll do the calc for the VX asap... where do you estimate the CoG is ?

Well what have we got, a line half way through the engine and box (box is low) versus most of the suspension components which are centre wheel height along with the subframe. the main chassis is mostly below but also around centre wheel height, fuel tank is chassis height. pax is are higher and lots of plastic and fibreglass.
Lets say between the wheel centre and 10cm above.

have you the Lotus suspension tool?