At Daks Toyota we neither recommend it or modify cars but we can give you information so that you know exactly what you are getting into when you take that decision else where.
It depends on which is the lowest ground clearence point – more specifically whether it is part of sprung mass or unsprung mass.
If the lowest point of the underbody is part of unsprung mass, it would move with the wheel and might not be so critical. To improve its ground clearence, you would have to increase the tire rolling radius.
If the lowest point is part of sprung mass, it might actually get worse as the suspension system compresses. So it is more critical than the former. To improve the ground clearence, you can increase the suspension ‘ride-height’, stiffen the suspension while increasing the static height, increase the tire rolling radius or try and raise the part with lowest clearence by adding shims to the closest mounts.
Disclaimer: This should be done only in design phase by the car makers and not by the customers / service workshops. Disturbing suspension geometry can have serious effects on the stability of the vehicle – not to mention other critical settings like ABS and even engine tuning (if you change the wheel radius).
If your car has softer suspension and there is more travel , then the car will feel bouncy and ride height will change more . Causing the cars under body to hit the speed brakes .
While we brake just before approaching speed brakes the car front end or the under body will hit or screech.
There is insert for this in the suspension coil its called as “Coil spacer”
This may not raise your ground clearance , but has effect when you driving your car. It prevents suspension travel.
It really depends on what car you have, the kind of suspension mechanism its riding on and how much flexibility the entire package offers. On the face of it, most modern cars are designed to have a ride height that provides optimal stability for everyday use, which is imperative to the safety of the vehicle and passengers especially if you go onto a highway, or corner around bends. Yes, certain manufacturers do under-tyre their OE offerings in the wake of reducing costs or increasing off-the-shelf mileage (especially in cost-conscious markets such as India). I wouldn’t recommend anyone should play around with the mechanics of the ride height, unless you’re really experiencing a lot of grounding and you drive in very rough terrain, or on bad roads. If you have a front wheel drive vehicle (which is the most common drive mechanism today), it’s better not to alter anything on the front side as it will significantly impact tyre life, grip and vehicle braking. On the rear, what you can check with an experienced mechanic or service advisor is how to place rubber bushes (they will have to be fixed) where the dampers are attached to the torsion beam. This is a very crude method, but it is the cheapest alternative if you’re carrying around heavy loads, which makes your vehicle grind while going over humps and bumps. I wouldn’t recommend this method at all, if you’re driving around on highways speeds as it can affect vehicle stability, grip and braking.
The next method is to alter the ride height by using a tyre that has a higher profile. Or upsizing using larger rims and wider tyres. You might have seen some manufacturers provide smaller rims and slimmer tyre configuration on their cheaper variants. For example, the Suzuki Swift L and V variants ship with 14in rims while the Z variants ship with 15in rims. Although, both variants offer very similar ride heights, owing to lower profile tyres on the 15in rims, it’s possible to place slightly wider tyres on the 15in rims which will slightly increase the ride height of the vehicle. But again, overkill in upsizing can lead to tyres touching the inside of wheel wells, which can be very dangerous. It is recommended you consult an experienced tyre salesperson or your service advisor at the authorised service station about how much you can upsize. For a car like the Honda Brio, which has tiny wheel wells, there is not much room to upsize the tyre, against what ships with the OE. Tyre upsizing can improve ride height on the smaller cars by up to 0.75cm, but it may feel like a lot at times when you have been grounding your vehicle regularly.
The third mechanism will be to play around with the suspension system, altering the dampers and struts which I would not recommend in the real world because most mechanics would not have the experience and know how to do a proper job, and you will end up playing with the dynamics of road behaviour which will impact the safety of occupants and others on the road. If you’re a professional rally driver, you should be in consultation with technically sound professionals who can provide you with the know how but I am doubting that’s the case since you’re posting the question here and not on a technical forum.