i know how you feel dd, i tried 175 50 13 on the rears of my sedan, felt more resposeive with the a15, 4080rpm was 60mph or 100kmh. before was 3800 from memory.

The car actually became a bit skittish when pushed hard but felt great. mid range rpm take off was instant and reved all the way to 6500rpm in 4th no issues (dont know what speed either as needle was off the speedo).

in australia the low profile 13's and 12's are hard to get, i was chasing 165 55 13 but importer wont bring less than 40 in. settled on 165 65 13 for fronts at moment.

I lowered my daily driver sedan the other day, I used 280z rear springs with about 2 coils cut. I used a mix of leaves from a corolla + 1200 leaf pack to get the car lower. I drained front drum struts and filled with bel-ray fork oil, also fixing a savage leak from one of the strut legs. On the weekend I put some bilsteins in the rear I had laying around from a bmw 320i, I had to remove the spring seats though, its also got a 120y front swaybar.

The car has been transformed, its so direct now with the extra stiffness upfront and the cornering is fantastic, it has none of the bumpiness it had with the monroe gas shocks on the rear and leaking left strut. The only real complaint I have is its a tad too low.

The wheels are 14" pintara wheels with 175x60 Bridgestone supercats, I get no scrubbing except at full lock on the front of the guard, that would be because of the 3mm spacer to get the tyre away from the strut a bit more and the extra castor we got out of playing with the castor bushings.

Hi DD,

I can see 3 things contributing to the lower body roll, possibly 4.

1. Much stiffer tire sidewalls. They don't deflect nearly as much as the old tires.

2. The aluminum wheels are noticeably stiffer than the steel stockers. You can feel the difference.

3. Lower center of gravity. Not a big change but it should help.

4. Slightly wider track?

The basis for #2 comes from experience gained many years ago. I re-drilled some Fiat mag wheels to fit my Dato. The wheels were the same dimensions as the stock 12" wheels, both in width and offset. The tires were transfered from the steel wheels to the aluminum wheels so the only change was the wheels. The difference was quite noticeable, with the car having a more direct feel to steering inputs.

with grippier semi slick tyres on the stock suspension you should have far more body roll, but seeing as you haven't pushed it to the limits yet I guess you don't know.

If there is a reduction in body roll in normal driving, it must be due to the massive change in your roll centre caused by such a radical change in tyre height.

But I think the biggest change you're feeling is the increased responsiveness of the semi slciks.

There is definitely no increase in the risk of rolling a tyre off the bead in low profile tyres. And certainly not with semi slicks! They can be a pain to break the bead using a tyre machine!

4WDs with monster tyres use bead locks to allow them to run stupidly low pressures (like 4psi) for traction on extreme rock terrain by allowing the tyre to deform over the rocks and keep more tyre in contact with the surface. At less than 14-16psi a 4wd tyre is at risk of popping off the bead. Its a very different thing to passenger car tyres, and has nothing to do with the prefole of the tyre.

even better

with all that dd, you have me convinced and fully informed.

Thanks for the replies. i hope i didnt sound like a know it all. that wasnt the intention, but rather to question your opinion, in order to further my knowledge on the subject.

About the pleasnt sounding jet engine. Its funny how differnt things give a good sound. I am sure the tyre engineers didnt have that in mind when the designed the tyre! The induction sound from my carby sounds awsome when gently accelerating, but again, im sure thats not a design feature.

In the end, the tyres look the part, and like you said, there arnt any downsides to them. Good stuff i say.

Quote:Maybe it is the lowering that did it? I'm just trying to describe what it feels like, a student of steering geometry can set us straight.

Quote:No way. The tires are rated for 960 pounds each, and a 1200 weighs less than half that on each corner. I think you read about the theoretical risk, certain off-road or racing trucks will stress it closer to the limit.

Quote:Let's say this application doesn't get close to a tire-to-bead separation problem. Then I can think of no downsides.

Quote:Not really. The 1200 is not noted for a 'isolated' ride quality to start with. The stock rear suspension is so stiff I don't notice any difference. But in the front, maybe a little harsher. On road expansion joints the fronts seem to 'slap' the pavement a little (is noiser).

These tires also have a really interesting sound like a low jet engine spooling up. It is very faint but pleasant sounding. At about 40mph I can hear it most -- if I listen carefully.

Lower profile tyres have good and bad points as far as cornering goes.

My understanding is that the low profile tyres will help with cornering, but can roll off the bead eaiser than a tall profile as they have very little flex. But too tall, and you get too much flex, which is the reason that bead locks are fitted to 4WDs with monster tyres.
Have you increrased the tyre pressure in the new tyres to compensate with the increased bead roll risk?
And... have you noticed a decrease in ride quality?

The fact that body roll is noticablely better with the lower tyres confuses me somewhat. i would have thought that body roll is more a result of suspension setups rather than the tyres.?

Yes and yes. And maybe even because the car's center of gravity is lower.

There is almost no body roll now when cornerning. There was a lot with the stock 155-SR12 tires. I'm guessing the biggest factor is the short sidewall (profile). The tire is nominally only 1cm wider. But that tread pattern is probably putting twice the rubber to the bitumen.

I haven't pushed it to the limits yet so am not ready to comment on the tread compound. Suffice to say it corners much faster now, how fast I dunno..., but it doesn't scrub the tires (screech) taking corners as the stock tires did.

the tread pattern is certainly made for the bitumen.
You said handling is better, but do you think thats due to the lower profile tyre, or the tread pattern/compound of the tyre?