I am aware that lower profile tyres will put more strain on the soft stock suspension and therefore increase body roll (which is already an issue) due to the thinner tyre sidewall and added grip transferring more inertial energy to the springs…
However, the roads in my country are full of bumps and potholes so I would not like to stiffen my suspension or lower the ride (also because it’s already not too good at absorbing bumps stock, and the new wheels are not going to help).
After doing some research both online and within this community, I saw that the best option for me would be to upgrade the sway/anti-roll bars: either at the rear only to reduce FWD oversteer, or both the front and rear.
Does anyone have experience with specifically upgrading the sway/anti-roll bars on their Daihatsu? Do you know of any websites that sell them to fit my Sirion?
Increase the rear spring rate. Load travels diagonally. Keep the front rate as close to std as possible to keep front traction high. Sway bars couple one side to the other. Remember they are a torsion bar. You end up with a bump on ones side of the car acting on both sides with a sway bar. So if you have lots of bumps and pot holes they are not the solution. Big sway bars are okay for billiard table smooth roads. Increasing the front sway bar will only make is understeer like a dog. What is the solution for front wheel drive asphalt rally cars? No sway bars and testing spring rates. Now you spoke of “not too good absorbing bumps”. No your shocks/dampers/struts control the spring frequency, I am going to take a wild guess and say that your “roll” is because you are underdamped. Double or even triple the rear spring rate and see if you can at least find some Koni reds for the rear and play with the adjustable rebound.
Firstly, thank you for your swift reply. I did not think that a sway bar would cause issues with potholes and uneven surfaces…my impression was that stiffer springs would be problematic in this situation.
My priority at this point is reducing body roll without sacrificing comfort due to the lower profile tyres (and without spending too much to be honest). In order to play around with adjustments in spring rate, I assume I would need to install new, adjustable shocks like the Konis you suggested, correct? Or is possible to change the springs only on the stock shocks?
I am very new to all this so I appreciate your detailed explanations, thanks again.
Just change springs. Why do you think body roll is an issue? Better to think lateral grip, under steer/oversteer. Roll is weight transfer. Springs need to be firm enough to manage this and not blow through travel such that you hit bump stops. On a road car std front springs are usually spot on and rears never anywhere near hard enough.
A problem with sway bars is they link both sides of the car. Rally and off road race cars don’t use sway bars if they can help it.
Thanks again. I’ll see what local chassis tuning companies think since they know the roads here well and can give a good assessment of my car’s current stock setup.
I’ve fitted an Ultra Racing 19mm ARB on my M101 Sirion and can confirm that bumps on one side definitely are felt on both sides now - e.g. pot holes, or speed humps are felt on both sides now. It does help on smooth roads, but there are fewer and fewer of those around here these days!
I would like to try @Mr_Gormsby 's suggestion of stiffer rear springs, not least because they are super easy to change - can anyone suggest forms in the UK who might be able to make springs to a specification? I can find lowering springs for the M101 Sirion, but I want to keep standard ride height if possible.
I do like to use a spring in a std diameter like 2.5" diameter with ends ground flat and modify the spring seats to accept them. I’ve done this even if I had to cut the bases off the chassis and put smaller diameter spring seats in. That was I can buy a few different springs and do some testing without braking the bank on full custom.
It does fit, but needs some persuasion to do so, and needs mounting upside down. If you made your own brackets for the rear beam you could make it work better I think.
Once fitted, it works fine though.
Option B is to try and find a YRV, some/most/all of these had the RSB as standard, and the rear beam is exactly the same as the Sirion M100/101 so its a straight bolt-on.
haha, yeah I suspect postage might be prohibitively expensive!
In that case the Ultra Racing RSBs are good, I got mine from a seller in Malaysia and IIRC it was approx 90 GBP delivered, via FedEx. Communication was good and delivery prompt.
Fitting was fiddly but do-able, you need to compress the Myvi bar to get it to locate on the brackets, then do up the bolts a bit at a time on each side. Once on, its rock solid though.
Something to be aware of, the UR RSB did foul on my exhaust where it goes over the rear beam - whether that’s due to the rear section of my standard exhaust being a pattern part or not I don’t know, and I ended up modifying the rear section slightly to fix this. Basically I cut out and re-welded a section to give better clearance.
Subsequent to that I went over to a full custom stainless setup which obviously clears it all fine.
