Suspension spring loading
 

So my toy car is a bit custom.
I’m having a problem with the rear and I’m hoping there’s a simple solution I missed.

Two people and a full tank is causing tire rub going round corners. The battery is in the trunk and the rubs on that side.

Coilovers were cranked all the way up and that wasn’t good enough.
I swapped the 275lb/inch spring on one side for a 175/350 progressive. Now I want to try to see if that’s enough spring before I do the other. Changing them is a huge pita.

Without resorting to the 5 bags of cement in the trunk approach, is there a simple way to measure deflection under load that I overlooked.

You do not say where it is rubbing, inside or outside of tire. I would say you are fixing the wrong item, the suspension should be able to travel full motion without anything making contact, so wrong rim offset, rubber too wide, loose bushings?

how far inboard are the shock mounts from the rear wheel face?
There are online calculators you can use for to derive spring rates occurring.

Suspension has enough travel without shock to rub in the wheel well. It rubs across almost the full face, but slightly more on the inside. Shock/spring is constraining it in compression rather than say a bump stop.
I could get a shorter shock but when they bottom out it’s ugly too.

It’s all custom, including the wheels.
It’s way too much cost,time,effort to change because the car is assembled - so I’m adding spring rate to fix if I can. It’s fine without two fat asses and a full tank.

There's a lot more to the equation here. Spring rate is determined by load (lbs) to deflect the spring 1". Load rate is the maximum weight a spring will safely carry at a manufacturer's stated compressed height. So, if you have the preload set at full up, does the vehicle sit and drive right? I'm not talking about tire rubbing. Depending on coil / shock length / mid-point travel you may or may not have an adequate spring rate.

If this is a custom deal, you should corner weigh the vehicle, measure spring compression at ride height, then figure out if the spring is matched to your application. Tire rubbing could be too much lateral movement or an improperly set panhard bar angle ( if you have that). But from your OP, not near enough information to provide the correct answer other than what I've already provided.

So your tire tread is bottoming in the wheel well. Can you possible use one of the online spring rate calculator and enter the info you have? One I quickly looked at Hypercoils suspension spring rate calculator.

Do you have enough range of travel on the shock?

Please post pictures of the issue/situation to make it easier for people to help...

Could be a multitude of issues, including incorrect width/offset wheels.....

Cheers

The simplest way to see what's going on is to remove the spring/shock unit, then work the suspension thru its range of motion. Or is the spring/shock part of the suspension, like a Macpherson strut?

changing spring rates will only help until its impact loaded.

what you actually need is longer/stiffer bump stops.

and wider fenders.