How much does it need to be lowered by? What size springs do I need?
how much drop?
Moderator: martauto
I want to lower the arse end of my m30 project car, it's currently got the standard 325i springs. The front height has dropped with the extra weight of the m30 and is perfect for daily driving. I just want to lower the rear so it matches up nice with the front.
How much does it need to be lowered by? What size springs do I need?
How much does it need to be lowered by? What size springs do I need?
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Rtaylor2208
- E30 Zone Addict
- Posts: 3004
- Joined: Mon Oct 11, 2010 11:00 pm
- Location: Ayr, Ayrshire, Scotland
Going on the picture I would say -30 as it looks like 4x4 suspension on the back compared to the front.
Be aware that there's more to a spring than ride height.
Lowering by adding weight will not change the spring stiffness, however the new rear spring will probably be stiffer than the old, and this will change the balance of the car - in this case giving it more over-steer due to increased load transfer at the rear end from the stiffer springs.
You should really aim for a stiffness increase on the front end to match the increased weight and increase in rear stiffness, but a shorter free length to give the ride height you want.
Suspension tuning is a bit of a black art unless ou have access to vehicle dynamics modelling tools like ADAMS Car.
Lowering by adding weight will not change the spring stiffness, however the new rear spring will probably be stiffer than the old, and this will change the balance of the car - in this case giving it more over-steer due to increased load transfer at the rear end from the stiffer springs.
You should really aim for a stiffness increase on the front end to match the increased weight and increase in rear stiffness, but a shorter free length to give the ride height you want.
Suspension tuning is a bit of a black art unless ou have access to vehicle dynamics modelling tools like ADAMS Car.
I had exactly the same issue with my m30 conversion. Standard 325 front springs upfront and an arse in the air, after trying a couple of options I went -30 and used the thinnest spring pads I could get.
Have you got a rear arb fitted?
Have you got a rear arb fitted?
eibachs or koni would be a good move.
Just wondered what arbs you had cos you mentioned the handling. Mine started life as a 316 so skinny front arb and no rear one at all. I think cab and touring ones may be thicker than saloons. My springs were off a breaker, no idea of make tbh.
I don't know what the spring rates are for the various options I'm afraid. Generally the shorter you go the stiffer it will be to control bump movement. Go with the most road focused lowered spring you can find for the rear, and the most track focused standard height spring you can find for the front. I hate to say it, but this is one area where coil overs make life easy. Pretty much any spring rate you want combined with an adjustable platform to set the height independent of the free length.
The other way to change the balance as Johnnle30 mentions is ARB's. A thicker ARB will give moe load transfer, and thus make that end 'looser' So if it's a bit tail happy after some lowering springs you can either remove any rear ARB fitted, or beef up the front one. The down side of tuning with ARB's is that their effect is proportional to the lateral acceleration, fine if you only ever drive on a dry road, less fine when it'ss wet, as the natural balance of the car will start to come through again. You could tune them for the wet road, but then they'll be out for the dry etc.
The other way to change the balance as Johnnle30 mentions is ARB's. A thicker ARB will give moe load transfer, and thus make that end 'looser' So if it's a bit tail happy after some lowering springs you can either remove any rear ARB fitted, or beef up the front one. The down side of tuning with ARB's is that their effect is proportional to the lateral acceleration, fine if you only ever drive on a dry road, less fine when it'ss wet, as the natural balance of the car will start to come through again. You could tune them for the wet road, but then they'll be out for the dry etc.
I'm looking into finding out more information on this car having just purchased it and was wondering what setup you went for in the end on it?
Haven't had the chance to look underneath but would appreciate any help or links to any posts relating to this car.
Haven't had the chance to look underneath but would appreciate any help or links to any posts relating to this car.
this is why I love owning older cars is being able to find out information about them as well as history and so on.