View Full Version : Spring rates and Mk1.5's
Making plans for the future as I do and wondered if anyone knew the standard poundage of the stock springs on a mk1b?
I'm putting together the kit I mentioned a while back and will be developing it on KYT2, ride height issues with a Tubby in the back is one of the ones I intend to address. I would like to use 2 1/4 springs to make life easier so once I know what they are originally I can work out something fom there.
To save any hassle I'll prob be posting up my results for anyone to copy, being the small market that it is I don't think I'll be buying my aston on any profits I could make....
Cheers
Edit I've just googled and found 4Kg/mm recommened for the front and 9-10 for the rear??!!??
Diesel Meister
31-12-2009, 19:04
I think this will be of interest to all Mk1 swappers - I've certainly not got the faintest idea what spring or damping rates I need to be using. Something to be resolved once the swap is done then, heh.
4kg front and 10kg rear is what most of the AW11 coilovers come with, and its a nasty setup. 4kg/mm (225lbs/in) isnt a bad front rate, but its way too stiff on the rear (10kg/mm = 550lbs/in).
it comes a lot down to choice and the damping you have available, but on a 4A-GE powered mk1 youd ideally end up somewhere between 175/200 upto 250/275.
on a mk1.5 youre talking about probably 100kg of extra weight in the back, depending on the engine swap? so then your rates will be more like 200/250 upto 250/325. you can roughly add an extra 25lbs to the rear rates for every 50kg of added engine weight (all of my numbers are rounded to the nearest 25lbs).
those are rates for comfortable road use. if you run the car on track then you may want it stiffer, but there are so many variables that come into play. damping being the most important, if youre on stock dampers then youll want to stay soft on springs or youll be bouncing around all over the place. if youre on cheap coilovers then you need to go stiffer to compensate for the lack of bump damping and the excessive rebound damping. Konis offer a nice balance, and are very versatile, you can get away with spring rates from 200lbs/in all the way upto 500-600!! there are also geometry issues at the rear though, which are altered by ride height, which often neccessitate much stiffer rear setups. there is also a popular philosophy on the US MR2OC that removing the anti roll bars and running entirely on spring rate is the best method (with the front considerably stiffer than the rear). it is well proven in auto-x, but its going to be harsh on the road irrespective of the other factors and im not entirely convinced yet.
with regards a kit, Ground Control already have it covered. ive looked at the possibilities of making an alternative setup, and its basically impossible to compete with them on price when they are making their kits in such bulk. they also come with 2.5" Eibach springs at a very cheap price. for an entire AW11 kit it costs about £350 shipped from the US, including import taxes. Eibach springs are about £65/each retail inc VAT in the UK, so youre looking at £260 on springs alone. to make up coilover sleeves and spring platforms (or buy some of the UK options) youre just not going to be able to do it in small volume for under £90. and youve got to do it even cheaper to make a profit. the cheapest 2.25" springs i know of are about £120 a set, which would leave you £230 for making the sleeves, but its still a tall ask.
not trying to put your idea down or say that its not possible. just sharing my own findings which completely put me off the idea. it would maybe be a better bet to offer modified strut cases with platforms welded on to accept the ground control sleeves, since most people dont weld and this is one of the major off-putting factors for them. you can specify the exact spring rates you want when you buy the Ground Control setup as well, so its completely customisable.
Diesel Meister
01-01-2010, 21:06
Thanks Jim - always posting useful advice.
I'm consistently hearing the konis are the only way forward unless I can afford a completely custom setup. It follows that the GC kit makes a good match in terms of flexibility - unfortunately, GC didn't reply to the emails I sent asking for their advice on spring rates for my intended application.
I'm guessing the best guesstimate is based on:
weight of SW20 part (trans, shafts, hubs, wheels / brakes - the latter two unsprung of course); plus
weight of 2GR-FE, plus ancillaries and headers
to give a rough increase in weight for the soring rate calculation.
Time for an email to Paul :)
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