Weight of Roadster?

[Blacktop]

Just wondering what is the expected average weight of a road going version of the Haynes roadster (without driver) using a car engine?

[HandyAndy]

I think the average seems to be around the 500 to 600 kgs range, tho this depends on which engine fitted,

I have the 1.8CVH engine & I,m hoping for around 540kgs , Spuds car with the same engine at his SVA test was 520 kgs, I think that was with a full tank of fuel but no driver/passenger in the car.

cheers
andy

[Blacktop]

I am looking at using a MX5 donor. Do you know how these engines compare in weight to the cvh and pinto?

[CTWV50]

I'm using an mx5 1.6 too and would be interested if people new the answer to this, all I can add is that my research has suggested that the 1.6 engine and running gear could be as much as 50kg lighter than the mx5 1.8! Worth considering! :)

[CTWV50]

Andy is your chassis 2mm or 1.6mm anyone know the weight difference ? I guess it would be one third heavier, correct.

[deezee]

I calculated this in AutoCAD a while ago, whilst bored at work. Sadly we lost a lot of the forum to some hacking and I can't find the post. From recollection, the increase in weight from 1.6mm to 2mm is only around 6kgs more.

[CTWV50]

Ok flicking through the original locost book there's picture of the guy holding the chassis, apparently it weighs 35lb which doesn't seem very much at all, about 15kg! so 2mm steel will add maximum 5kg! Not much. Answering my own questions here but what-the-hell!

edit: Ooops didn't see your post deezee! So 6kg then!

[HandyAndy]

As a rough guide, a fully welded chassis using 2mm walled steel with the basic CP plates fitted will be approx 70kgs in total, give or take a few kgs depending how much you have welded onto the main frame of the chassis( if you have fitted diff plate hangers/wishbone brackets etc).

Chris...just be aware that when using the MX5 as the donor there are a few parts of the chassis that are longer than book spec, its not alot, approx 0.5mtr, this is basically to accommodate the new diff cage arrangement. The overall dimensions of the length/ width of the chassis etc are the same as book spec details.

cheers
andy

[CTWV50]

As a rough guide, a fully welded chassis using 2mm walled steel with the basic CP plates fitted will be approx 70kgs in total, give or take a few kgs depending how much you have welded onto the main frame of the chassis( if you have fitted diff plate hangers/wishbone brackets etc).

Chris...just be aware that when using the MX5 as the donor there are a few parts of the chassis that are longer than book spec, its not alot, approx 0.5mtr, this is basically to accommodate the new diff cage arrangement. The overall dimensions of the length/ width of the chassis etc are the same as book spec details.

cheers
andy

So I will be ok with 7x 6m 25mm and 3x 6m 20mm? CP plates? Checker Plate? Is the locost book a bit out on the locost weight 15kg really seems too light!?? And does the 6kg weight difference between 2mm and 1.6mm still stand for the roadster? Too many questions I know but I'm about to order the steel within the next few days hopefully.

[deezee]

The book refers to the Chassis Plates as CP. I've just calculated all the box section required for the build as around 12 metres of 19mm and 37 metres of 25mm (lengths of all box section + 10% waste). Based on these figures you can work out that the weight of a BARE (box section only) chassis in 1.6mm is going to be 51.26 kgs and in 2mm as 63.13 kgs. So around a 1.9% increase in estimated total vehicle weight (600kgs). This is based on the density of the mild steel as being around 7,800 kg/m3.

I'm proper out of my league for guessing exactly how much stiffer / stronger the chassis will be made out of 2mm versus 1.6mm.

[ozzy1]

From what i recall from 1.6mm to 2.0mm there is an increase of 25% in weight for an increase of 30% in torsional rigidity.

[CTWV50]

Thank you both for that information, I really am bold over by the helpfulness of this forum. I hope I can contribute as much one day. Sorry I seem to have taken this thread off in another direction.

[verbel]

Not to make new post, I think is the good practice to mix square and round tubes. This could lower a wieght a bit and increase stiffnes. At least this is my goal to make when my build will start. Main structure 25x25x2mm and all braces and other with round tubes + some reinforcements.

My only consideration is if the roll axis and other performance bits change significantly if i will use MX5 front uprights, wishbones modded for that and rear sierra ones. I plan to use zetec (tuned to 180hp) with t9 and sierra diffs are way cheaper than miata. Coz i doubt that its possible to mix miata rear uprights and driveshafts with sierra diff.

cheers

[shh120m]

at the end of the day, a few kilos here or there wont matter. for example as a little runt of 9 stone wet a 600cc bike is fast to me but slow to my 16 stone dad.(sorry dad)