Wheel sizes

[stevieboy]

You might have seen this on the "gossip" board but i thought i'd try it here.
I have recently bought a Roadster TF. it has 16" wheels on the rear and 15"on the front. Why? and what would be the effect if any if I put 16"on the front also?

[dj2k21]

Hi, as I believe wabbit said on your other thread, its how it was designed. Most rear engined cars nowadays have larger wheels on the rear. With fitting same size wheels you can do it but just ensure you retain stagger on the tyres.. ie wider on the back, its essential to any rear drive car

[Jrichards20]

Unless you know how to control your car sideways constantly leave stock sizes. There are a few debates about this, the larger sizes on the rear produce more understeer to stop the back kicking out at every corner. But then some racing drivers will say that as much grip as possible is better. Unless you know what you are doing, leave this standard tyre and wheel sizes that are available by searching tyres sizes or wheel sizes in the search bar.

[dj2k21]

I think thats a bit exaggerated to be fair. I have 18's all round with a substantial power gain over stock and its never snapped and span on me, although I do maintain stagger is vital, I dont think the actual size of the wheel is all that important in all honesty.

[Wabbitkilla]

I'm not arguing here, but you have to remember that tyre/wheel width isn't everything.
Toyota optimized the car for road driving, so the best compromise of handling and comfort is the standard size tyres and wheels.
Dynamics like tyre width and profile depth affect how the tyre handles the loads it's put under in changes of direction and our lumpy surfaces.
If you change the wheel or tyre sizes then you shift the bias towards more comfort away from handling or closer to more solid handling and away from comfort.
Handling expectations are different depending who you are and what experience you have.

So the best wheels and tyre sizes for getting used to the car are the standard ones.
Then learn about what different sizes and profiles do to the handling of the car and decide what you want from it.

The reason for having bigger wheels  on the back of the roadster is the same for any mid-engined rear wheel drive car, your weight and power is back there. You can use the weight and put the power down better and safer with the wider wheels and tyres and the larger diameter allows a profile that is stable (not wobbly). The front wheels are smaller and narrower because they do a different job, smaller allows you to turn the wheels and make use of the lower frontal weight better.

In other words it's all to do with balance.
Spend your time reading through tyres tyres tyres threads and show us your wheels and you'll get a good start in finding what works. The above is only a little bit of the science involved, as much as I can take probably, but reading other peoples' experiences is always helpful ... just remember they will drive differently to you   s:wink: :wink: s:wink:

[Jrichards20]

Sorry, my earlier post was mainly talking about tyres not wheels :s. Completly agree with dj2k21 and Wabbitkilla. I had 16'' all round with same size tyres all round, and it snapped going round a corner and I flew into a high raised kerb (broken suspension) etc etc. I wouldnt say im bad at controlling a car either, thats why I am very wary about chaning how the car was set up. Bad experience. if your going to change without enough research. Dont Drive Fast. Thats my advice  s:) s:)

[trickyD]

But then PFL has 15's all round so is the PFL car set up wrong?

[steve b]

But then PFL has 15's all round so is the PFL car set up wrong?

No, just improved upon.

[jonty]

I'm going to break the mould here and say that the reason Face-lift and PFL are different is a stylistic change, and there's not much else that's gone into it - in an attempt to keep the car current, Toyota fitted a wider tyres which make it look more sporty, and the larger diameter also makes it look a bit more 'dynamic' as they'd say in the styling dept.

On paper the actual driving dynamic will be ever so slightly changed as the extra width gives more grip, but the lower profile stiffer tyre sidewall will take away grip (just like stiffer springs) and so overall it's probably not that different on the road - I've not driven both (only pre) so can't make a direct comparison, but I imagine the condition difference between cars -now they are 6+ years old- is a bigger factor anyway.

[Wabbitkilla]

Err ... plus the gearing of PFL cars had the engine running in the rev range that was known to cause resonant damage while cruising on motorways.
Upping the wheel size meant that cruising revs were moved away from that range, 6th gear was added, and mpgs were improved too.

Stylistically, yes actually I find I prefer the car on 16" wheels and probably has its part to play in Toyotas decision.

[steve b]

Reasoning behind bigger diameter rims on the rear of mid engines cars(it's standard practise on most - or just lower profile tyres) is due to the weight distribution.  Lower profile flex would be exaggerated by the weigh over the rear, the tyres have agreat demand placed on them accelerating out of bends and stiffer sidewall gives better feedback than a taller side wall with more flex.  Think about how people don't like the flexi walls on toyo tr1s, a problem magnified on a taller profile tyre.

[Wabbitkilla]

Lower profile flex would be exaggerated by the weigh over the rear, the tyres have agreat demand placed on them accelerating out of bends and stiffer sidewall gives better feedback than a taller side wall with more flex.  Think about how people don't like the flexi walls on toyo tr1s, a problem magnified on a taller profile tyre.

that is also a good reason   s:) s:)

[trickyD]

But surely they knew this before launching the PFL?
The resonance and gearing sounds like more of a reason to make such a drastic change.
I say drastic because it kind of looks like they got it wrong first time.

[Wabbitkilla]

They didn't admit to the precat issue, so they're not going to jump up and admit a resonance issue.
The resonance issue was only resolved in the last generation of the engine in the FL car, and then properly afterwards in the other cars it was used in.
Remember the engine was designed in America to be a cheap and economical unit. The first time it was stressed and had VVTI fitted was in the generation of cars released with the Gen7 Celica and MK3 MR2, so their testing hadn't shown up the issue prior. It's cheaper to change the wheels on a car than it is to re-work an engine production line.

[trickyD]

Yep, makes sense.
Don't forget the sticky accelerator pedal too!