WHY do bigger alloys mean worse handling?

[Ed]

2: MR2s have MacPherson Struts. These have terrible camber control under compression which means that the camber varies quite widely when you load a wheel under cornering. Lower profile tyres give less than a stock profile ie 35 profiles say on an 18 will flex less than a 50 series profile. The higher profile helps the tyre maintain a good footrpint on the road when the camber varies when the wheel is under load.

5: With bigger wheels and likely wider tyres there will be more grip, so you can go higher speeds into a corner and all the time you are working the tyre below maximum grip levels you will to a degree be able to go faster, however the aforementioned problem of less progressiveness of lower profile tyres combined with increased sprung weight of bigger wheels and of course not forgetting the propensity for MacPherson struts to cause the camber to go all over the shop means that at the point the car starts to handle (ie just over the maximum limit of grip) everything happens more quickly which makes the car harder to catch. This is most noticeable in the wet only because it is difficult to exceed the grip levels in the dry. Of course what makes it worse in the wet is because of the comparitive lack of grip it ends up feeling like the their is no progressiveness at all in the way in which the tyre lets go, so it makes it difficult to predict. Those that say the car feels like it corners as if on rails are simply talking about roadholding, not handling as they are driving well within the limits of the grip available.

For the most part this post seems to talk about 18`s with standard struts. Now if you have coilovers with full camber adjustment on all four wheels are you saying that the handling is still going to be worse than the standard wheels and that it will still not be as progressive in the way it breaks loose.

[Lauren]

2: MR2s have MacPherson Struts. These have terrible camber control under compression which means that the camber varies quite widely when you load a wheel under cornering. Lower profile tyres give less than a stock profile ie 35 profiles say on an 18 will flex less than a 50 series profile. The higher profile helps the tyre maintain a good footrpint on the road when the camber varies when the wheel is under load.

5: With bigger wheels and likely wider tyres there will be more grip, so you can go higher speeds into a corner and all the time you are working the tyre below maximum grip levels you will to a degree be able to go faster, however the aforementioned problem of less progressiveness of lower profile tyres combined with increased sprung weight of bigger wheels and of course not forgetting the propensity for MacPherson struts to cause the camber to go all over the shop means that at the point the car starts to handle (ie just over the maximum limit of grip) everything happens more quickly which makes the car harder to catch. This is most noticeable in the wet only because it is difficult to exceed the grip levels in the dry. Of course what makes it worse in the wet is because of the comparitive lack of grip it ends up feeling like the their is no progressiveness at all in the way in which the tyre lets go, so it makes it difficult to predict. Those that say the car feels like it corners as if on rails are simply talking about roadholding, not handling as they are driving well within the limits of the grip available.

For the most part this post seems to talk about 18`s with standard struts. Now if you have coilovers with full camber adjustment on all four wheels are you saying that the handling is still going to be worse than the standard wheels and that it will still not be as progressive in the way it breaks loose.

Good point. Well even with coilovers which are much lighter than the struts they replace you still have a MacPherson strut layout, so you will still get the same disadvantages and inherent handling traits. Coilovers can vastly improve things there is no doubt about that, but it relies on them being setup well with the 'right' spring and damper rates. Camber control will not improve though.

[DotNetter]

Just picked up on this thread and the obvious question would be:

"What are the best sized wheel/tyre combination for a mk2 rev1 NA"?

Again, same question would apply to the suspension - if lowering, by how much and what type of kit to use.

I'm a total novice with this stuff but wondered if there was a straightforward answer?

Cheers


Wayne
Mk2 rev1 NA onwer (in case you hadn't guessed)

[ryan]

The reason why smaller wheels with larger profile tyres ie stock sizes ensure optimum handling is for a number of reasons;

4: Bigger wheels mean heavier wheels which increases unsprung weight. However, MacPherson struts have a massive amount of unsprung weight anyway which exemplifies the already mentioned camber control problems, so if you hit a bump mid-corner the car is more likely to 'skip' than say a car with a proper double wishbone setup because there is so much unsprung weight the suspension ie dampers/springs will not react as quickly.

That really does make sense, i've noticed that any undulatin/bumpy road really does upset my tubby, it feels a split second 'behind' to what it should be doing. I put this down to its standard ride height and its heavy 17" wheels, which is still partly the cause I reckon.

[BenF]

Just picked up on this thread and the obvious question would be:

"What are the best sized wheel/tyre combination for a mk2 rev1 NA"?

Again, same question would apply to the suspension - if lowering, by how much and what type of kit to use.

I'm a total novice with this stuff but wondered if there was a straightforward answer?

Cheers


Wayne
Mk2 rev1 NA onwer (in case you hadn't guessed)

For progressive handling on the limit, try 15" rims. The biggest I'd go to preserve the progressiveness of the car on the limit would be 16" rims - I used to use a set for my trackdays.

For compairison, the Roadster uses 15" front and 16" rear rims for 2003-on cars. Trying these on a trackday at Anglesey, I swapped them for 15" front and rear tyres (earier models had them) and I found it made the car much more progressive and fun to slide around.

[DotNetter]

Hi Ben

Thanks for the info.

I currently have a set of rev 2 15" alloys on the car.

The handling is okay and I've been throwing it around the country lanes quite a bit!

I would like something a little larger though (just for the "bling" factor)...although I DON'T want to make the handling worse for the cost of making the car more chaved up

I may look into some 16" rims when the current rubber starts to get low...it looks like it works out cheaper to purchase wheel/tyre packages then to get the rims and dress them yourself.

Cheers


Wayne

[Dave Goodhand]

The tyres are designed to use the sidewall to turn.

Hence when you change to big wheels (which are heavier than air) and low profile tyres you lose the amount of traction they can give at the limit. (Slip angle)

Basically it'll mean if you push your car to the limit on 18s with 35 profile tyres the grip will feel great until a point where it'll throw you off the road with no "known" warning. Whereas a greater sidewall will give you more slip angle and a much more progressive feel whilst on the limit - so you can almost "feel" when the car is going to lose grip etc.

Along with what lauren said about the camber - although if you add wheels and lower your car you really should get everything checked and adjusted accordingly.

I've got 17s on mine with a 45 profile tyre. I seem to prefer this over the 40 profile.. but haven't really ever pushed to what it is capable of, I'll wait for a track day and then comment!

[Speedy]

As Lauren said, the fundamental suspension geometry is designed for a specific wheel/tyre combination. Professional car tuning engineers probably sweated buckets over getting it just right for ride and handling, and then we come along and destroy everything by putting huuuuge wheels on it.

18inches might be big, but it ain't clever

Also, with respect to the 1/4 - bigger wheels effectively increases your gearing, giving you less acceleration (assuming you've increased the whole rolling radius).

[TheRoadWarrior]

Disclamer: I've only used the standard 15"s

...BUT i really dont buy the "18s are rubbish" arguement. 18 doesnt = heavy 'necessarilary'. Obviously they're more expensive, but its possible to have a set of 18s on 35profile that weigh the same or less than the standard set up. Yes wider tyres mean a less progressive breakaway but smaller sidewalls (I.e. 35 compared to 50) should give less flex and therefore better control.

Someone call me a liar

[jonb-]

Right, I can comment better on this now i've used the 18" in anger.

So you know i've driven on

205/45 front 225/45 x 16 rear
205/40 x 17 all round (very briefly)
215/35 x 18 all round

All on a full koni replacement setup (not sure what though as it was on when i got the car) and until i get wider tyres on the rear of the 18's this won't be accurate but my feeling is you can be QUICK on 18"s but NOT FAST... let me explain.

As it's been said before, i seemed to get far more feedback from the 16"s, you could floor it mid corner, feel it starting to break, have a coffee and a snooze, the car will start to steer on the throttle, have another coffee and then start correcting as the backend starts to overtake the frontend. It was much the same on the 17"s bar the back was very light due to narrow width.

As for the 18"s, there seems to be more raw grip there (the newest set of tyres too) and on a single corner under specific conditions i feel they're the QUICKEST of the bunch (once ihave a 235 / 245 on the rear it'll be easy). However, threading down a few of my favourite back roads it just seems so dull, i can't really tell whats under me until it goes from being fun to being scary and you have to get a handful of opposite lock on to catch it which makes you far from fast.

I know i've probably just sprouted out a bunch of crap, but it makes sense in my head (i've done a fair bit of track work in the past).

Bottom line is i love the way the car looks on the 18"s, the mr2 really does work well with big wheels. If i want to go fast i'll jump on my sports bike. I can still have fun on the bigger wheels, just not as much and you have to stay that few percent more away from the limit as catching it is a real bu88er.

[Speedy]

but how do your larger wheels and different profile tyres alter things like the scrub radius, pnumatic trail, etc etc - point is that Toyota made them that size for a reason, Toyotas uber-tuners made it that way, and unless you are an uber engineer yourself, modifying it is probably not going to improve matters.

I'll go get the Carrol Smith books off the shelf if you want to be hosed down with complicated suspension theory...

Bottom line is i love the way the car looks on the 18"s, the mr2 really does work well with big wheels. If i want to go fast i'll jump on my sports bike. I can still have fun on the bigger wheels, just not as much and you have to stay that few percent more away from the limit as catching it is a real bu88er.

Good point there - and of course, bikes go even slower round corners

[jonno]

Disclamer: I've only used the standard 15"s

...BUT i really dont buy the "18s are rubbish" arguement. 18 doesnt = heavy 'necessarilary'. Obviously they're more expensive, but its possible to have a set of 18s on 35profile that weigh the same or less than the standard set up. Yes wider tyres mean a less progressive breakaway but smaller sidewalls (I.e. 35 compared to 50) should give less flex and therefore better control.

Someone call me a liar

The weight of the wheel is only ONE aspect, you also have the lower profile and less flex in the tread face as well as the tread wall. All of this compounds together to make the handling less progressive. Bad camber control is "ok" whilst the sidewall is flexing enough to keep the tread face on the tarmac, once you have bad camber control and a skinny tyre wall though its a different animal.

On the road it wont make that much difference to be honest, at legal speeds the 18's might even feel better!. However, once on track that lack of flex in the sidewall means that you get no warning of the back end starting to let go, you can probably still feel the front understeering everywhere, because the steering starts to go light in your hands but all of a sudden your facing the wrong way coming out of a 3rd gear corner wondering wtf just happened.

I struggled for about 10 months with an MR2 on 18's and its virtually impossible to hold it on the limit, you can get close to the edge but your never quite at 10/10ths - even dropping down to 17's makes a dramatic enough difference on the limit. I must confess to never have driven a turbo on stock 15's, but i have driven an MR2 on circuit with 16/17's and 18's. Overall I prefer 17's but thats probably because I have done more laps on 17's than the others and I am more used to the way they break away

The bottom line is dead simple here guys, if you want take the craners flat then dont run 18's. If you feel the need to waste a mid engined sports car and cruise for totty then 18's are probably what you need, oh and some neons and "phat" stereo .

[Lauren]

Disclamer: I've only used the standard 15"s

...BUT i really dont buy the "18s are rubbish" arguement. 18 doesnt = heavy 'necessarilary'. Obviously they're more expensive, but its possible to have a set of 18s on 35profile that weigh the same or less than the standard set up. Yes wider tyres mean a less progressive breakaway but smaller sidewalls (I.e. 35 compared to 50) should give less flex and therefore better control.

Someone call me a liar

Liar!

feedback is really important when it comes to handling. The other thing that is fundamentally important is progressiveness. Lower profile tyres will provide less feedback because as Dave so eloquently explained the slip angle is narrower and the curve with which the grip levels fall is that much steeper.

The car may react quicker because the sidewalls are so stiff on big wheel/low profile tyre combinations, but the problem is that you need to react that much more quickly to keep it under control. A mid-engined car is that much more sensitive to this than say a front engined rear drive car.

Something else that is fundamental is that we don't muddy the waters by talking about roadholding rather than handling.

roadholding is the amount of grip you have and for the sake of argument lets say its how the car feels when it is operating within its mechanical grip levels of the tyres.. slip angles are not a mega issue at this point..

Handling is what the car starts doing once you start to get within the slip angles of the tyres.. lower profile tyres have a much lower amount of slip they can cope with before they let go compared to higher profile tyres. So a higher profile tyre at least gives you a greater slip angle to play with and means that you have that much more time to react.

Also worth remembering as Alex pointed out that the stock tyre/wheel combo is what the manufacturers spent ages trying to get right. This is critical in a sports car like the MR2, because if it doesn't handle there is no point.

[Lauren]

Right, I can comment better on this now i've used the 18" in anger.

So you know i've driven on

205/45 front 225/45 x 16 rear
205/40 x 17 all round (very briefly)
215/35 x 18 all round

All on a full koni replacement setup (not sure what though as it was on when i got the car) and until i get wider tyres on the rear of the 18's this won't be accurate but my feeling is you can be QUICK on 18"s but NOT FAST... let me explain.

As it's been said before, i seemed to get far more feedback from the 16"s, you could floor it mid corner, feel it starting to break, have a coffee and a snooze, the car will start to steer on the throttle, have another coffee and then start correcting as the backend starts to overtake the frontend. It was much the same on the 17"s bar the back was very light due to narrow width.

As for the 18"s, there seems to be more raw grip there (the newest set of tyres too) and on a single corner under specific conditions i feel they're the QUICKEST of the bunch (once ihave a 235 / 245 on the rear it'll be easy). However, threading down a few of my favourite back roads it just seems so dull, i can't really tell whats under me until it goes from being fun to being scary and you have to get a handful of opposite lock on to catch it which makes you far from fast.

I know i've probably just sprouted out a bunch of crap, but it makes sense in my head (i've done a fair bit of track work in the past).

Bottom line is i love the way the car looks on the 18"s, the mr2 really does work well with big wheels. If i want to go fast i'll jump on my sports bike. I can still have fun on the bigger wheels, just not as much and you have to stay that few percent more away from the limit as catching it is a real bu88er.

Makes sense Jon. If i understand you correctly you say that 16s feel more progressive than 18s, which is exactly as i'd expect.

[Lauren]

Just something else i thought of! I raced an RX8 last year and that has as standard 235/35/18s. That car is far easier to handle than an MR2, no question at all. I guess this is largely down to the suspension setup as it has double wishbones all round, so camber is well controlled at all points and is a known quantity (unlike the MR2). Also it was designed with those wheel and tyre sizes. Obviously it is a front (though 'mid-front') engined rear drive car which also helps. You can hold those at a far greater angle in fact pretty much any angle you please round a corner.

So yes, big wheels and very low profile tyres can work well, but only really if you have a double wishbone setup and if the car was tuned to handle with this setup in mind.

[TheRoadWarrior]

Hurmm. Interesting. So the only solution to controlling camber properly on the 2 is fitting coilovers?

Whats the detrimental effect of the camber varying under compression?

[jonb-]

Just something else i thought of! I raced an RX8 last year and that has as standard 235/35/18s. That car is far easier to handle than an MR2, no question at all. I guess this is largely down to the suspension setup as it has double wishbones all round, so camber is well controlled at all points and is a known quantity (unlike the MR2). Also it was designed with those wheel and tyre sizes. Obviously it is a front (though 'mid-front') engined rear drive car which also helps. You can hold those at a far greater angle in fact pretty much any angle you please round a corner.

So yes, big wheels and very low profile tyres can work well, but only really if you have a double wishbone setup and if the car was tuned to handle with this setup in mind.

Exactly, this is proven by nearly every hypercar i can think of. Low profile can, and does work on a car designed for it. Unfortunately for us, in comparison our 2's suspension setup may as well be a bendy twig.

Lauren, you're a wealth of knowledge and you've made this thread really interesting, thank you.

[aaronjb]

If you feel the need to waste a mid engined sports car and cruise for totty then 18's are probably what you need, oh and some neons and "phat" stereo .

I thought that was what owning a sports car was for? (cruising for totty, that is)

[Lauren]

Hurmm. Interesting. So the only solution to controlling camber properly on the 2 is fitting coilovers?

Whats the detrimental effect of the camber varying under compression?

Nope fitting coilovers will not solve the camber control problem as you will still have MacPherson struts albeit with an adjustable spring platform.

Camber on a MacPherson Strut varies as it goes under compression so the wheel goes from say negative camber toward positive camber and thus the tyre contact to the road is compromised as it no longer holds the tyre flat to the road under hard cornering. Lower profile tyres accentuate this because the sidewall is that much stiffer.

have a look at this to see what i mean:
MacPherson strut:


Not a brilliant drawing i know just pinched it via google, but if you think about it as the suspension compresses because the top point (ie the strut top) is in a fixed position on the chassis the lower arm will go through an arc but the top will stay fixed, so the camber changes a result.

Look at this illustration of a double wishbone:


Because you have another arm much like the lower arm, (called wishbone for obvious reasons) you can see that as the suspension compresses the way the hub is held to the road surface can be held constant or controlled via unequal length wishbones to keep the camber at a known quantity throughout the arc of the suspension movement.

Sorry, is not easy to explain!

Further possibly helpful references:
http://www.answers.com/topic/macpherson-strut
http://www.answers.com/topic/double-wishbone-suspension

[TheRoadWarrior]

OK i get it, thanks for the link. Seems like the 2 is doomed to sit on smaller wheels if you want performance (Which i do )