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WHY do bigger alloys mean worse handling?
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jonb-




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PostPosted: Sun Aug 07, 2005 9:19 pm    Post subject: WHY do bigger alloys mean worse handling? Reply with quote Reply with quote including images

[Admin] Okay people this topic seems to come up a fair bit, so i've opted to sticky it as there is such a good debate going on within the thread and it covers the subject perfectly.

Right,

Having spun my mk2 and wiped out an alloy (see before and after photos below) i've put on 18's (only size i could get in 24 hours of the alloys i wanted, was after 17's originally).

Now, i've heard it thrown around many forums a bit more tyrewall is better for the handling but no one has ever given me a reason.

For example we've a car with 235/35x18 vs 235/45x16 racing around bands. The only difference i can work out is less damping as there's less air in the tyre (not really the end of the world on track) and less tyrewall flex (which apart from putting heat into the tyre can only be a bad thing).

If someone would enlighten me i'd appreciate it.

As for my motor... before and after. I'm quite pleased with the look (will be even better when i've dropped her a bit more) but am now mortally scared of curbs and everything else that's going to run those wheels.


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TomThumb
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PostPosted: Sun Aug 07, 2005 9:56 pm    Post subject: Reply with quote Reply with quote including images

I heard that 16's are the optimal size for the design of the mr2. for accelleration and handeling.

in theory, you should have aslightley higher top speed, and you accelleration will be a little bit slower. not that you would noticed it.
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Lauren
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PostPosted: Sun Aug 07, 2005 10:15 pm    Post subject: Reply with quote Reply with quote including images

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

1: the cars suspension and handling traits were designed around a given wheel tyre combination.
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.
3: Lower profile tyres have problems maintaining a good footprint of rubber on the road (as mentioned in 2) and lower profile tyres have a stifer sidewall (they have to) so this means that should you exceed the limit of grip that they will break away quicker ie less progressively and you will get less feedback as to when this will happen.
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.
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.

thats basically it. [Wink]
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jonb-




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PostPosted: Mon Aug 08, 2005 7:47 am    Post subject: Reply with quote Reply with quote including images

Impressive answer Lauren, thank you. I'd not thought about camber under cornering.
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jonno




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PostPosted: Mon Aug 08, 2005 8:15 am    Post subject: Reply with quote Reply with quote including images

jonb- wrote:
Impressive answer Lauren, thank you. I'd not thought about camber under cornering.


Most people dont, they only find out when its too late on the road [Smile]

If I had a pound for everyone that came on to this forum and said that they have just put 18's on and the handling is exactly the same as it was before, I would have at least 20 by now!.
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philz
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PostPosted: Mon Aug 08, 2005 8:46 am    Post subject: Reply with quote Reply with quote including images

I think I'll sell my wheels and get a set of 10" minilites with 85 profile rubber, would handle amazingly then.

Might have to take a look at some smaller brakes though, perhaps I could graft on some mini drums instead.
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matt_mr2t




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PostPosted: Mon Aug 08, 2005 9:03 am    Post subject: Reply with quote Reply with quote including images

Yeah but 18's look much better =D>
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Lauren
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PostPosted: Mon Aug 08, 2005 9:43 am    Post subject: Reply with quote Reply with quote including images

matt_mr2t wrote:
Yeah but 18's look much better =D>


In your opinion.. [Wink]

form over function is not my thing. [Razz]
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matt_mr2t




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PostPosted: Mon Aug 08, 2005 9:47 am    Post subject: Reply with quote Reply with quote including images

Still get good 1/4 mile times. Not a fan of driving hard into bends. They do me fine for my driving style.
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Lauren
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PostPosted: Mon Aug 08, 2005 9:57 am    Post subject: Reply with quote Reply with quote including images

matt_mr2t wrote:
Still get good 1/4 mile times. Not a fan of driving hard into bends. They do me fine for my driving style.


Thats cool though obviously only rolling radius is really going to affect 1./4miles, mind you i'm not a fan of 1/4miles.. [Wink]

Thing is though you may find that the 18s contribute to you not wanting to enjoy the cornering capabilities of the car. Just a thought.
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Steve_Rutter




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PostPosted: Mon Aug 08, 2005 10:00 am    Post subject: Reply with quote Reply with quote including images

You'll actually get better 1/4 mile times with smaller wheels, takes a lot less effort to get them turning. You will have slightly taller gear ratios with bigger wheels and thus slightly higher top speed in each gear, but your acceleration will suffer accordingly.
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Frustrated Pilot




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PostPosted: Mon Aug 08, 2005 10:01 am    Post subject: Reply with quote Reply with quote including images

I have 16" alloys.. light weight split rims. they are magnesuim alloy and are a bu99er to look after...

They are 7.5" wide on the front and 8" on the rear. the rubber im using is 205 45 front and 225 45 rear.

Although i have konei shocks nicely set up, i find the handling is Infallible.

I am now looking after my m8's tubby with 17" rims, as he is on holiday.

they are 7.5" wide i think, front and back and have 215, 45 mm rubber on each rim.

I HAVE NEVER BEEN SO SCARED ENTERING CORNERS EVER BEFORE.

even at speeds slower than i would normally drive at.

the handling characteristics are seriously diminished if comparing to my own car. and this tubby has bilsteins.... [Sad]

i was not impressed...

i will also note that the steering is SO HEAVY!!!!!

i need 2 hands to pick up these 17's ..

my 16's only require 4 fingers to lift into position [Mr. Green] [Mr. Green]
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matt_mr2t




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PostPosted: Mon Aug 08, 2005 10:03 am    Post subject: Reply with quote Reply with quote including images

Well I went from 17's to 18's and got lower times.
Although I gained 40bhp from the last time.

I'm not fussed. There is a chance I may get a set of standard wheels for 1/4's one day though.

Lauren, I used to drive a hot hatch. For a while I thought driving hard round the twisties was fun. Then I just thought it was boring and dangerous.
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MartG




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PostPosted: Mon Aug 08, 2005 10:09 am    Post subject: Reply with quote Reply with quote including images

I've got 15"s on mine at the moment ( Mk1 SC ) - they were on when I bought the car - however I'm considering swapping back to a set of the original 14" rims, primarily because of the cr*p ride quality on our British roads.
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philz
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PostPosted: Mon Aug 08, 2005 10:35 am    Post subject: Reply with quote Reply with quote including images

Paul White wrote:
I have 16" alloys.. light weight split rims. they are magnesuim alloy and are a bu99er to look after...

They are 7.5" wide on the front and 8" on the rear. the rubber im using is 205 45 front and 225 45 rear.

Although i have konei shocks nicely set up, i find the handling is Infallible.

I am now looking after my m8's tubby with 17" rims, as he is on holiday.

they are 7.5" wide i think, front and back and have 215, 45 mm rubber on each rim.

I HAVE NEVER BEEN SO SCARED ENTERING CORNERS EVER BEFORE.

even at speeds slower than i would normally drive at.

the handling characteristics are seriously diminished if comparing to my own car. and this tubby has bilsteins.... [Sad]

i was not impressed...

i will also note that the steering is SO HEAVY!!!!!

i need 2 hands to pick up these 17's ..

my 16's only require 4 fingers to lift into position [Mr. Green] [Mr. Green]


Has he had it lowered? Has the geometry been set up correctly? Are his suspension components worn? What brand of tyres is he using? Does he have wider rear tyres than the front?

All things to bare in mind before making a blanket statement about how it must be the 17's that affect his handling.
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Steve_Rutter




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PostPosted: Mon Aug 08, 2005 10:36 am    Post subject: Reply with quote Reply with quote including images

I'd say the reduction in your times had a hell of a lot more to do with the extra 40bhp than the fact that you had 18s on it. You'd get even lower times if you had the 17s on still, lower still if you had standard rims.
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jonno




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PostPosted: Mon Aug 08, 2005 10:42 am    Post subject: Reply with quote Reply with quote including images

matt_mr2t wrote:
Well I went from 17's to 18's and got lower times.
Although I gained 40bhp from the last time.

I'm not fussed. There is a chance I may get a set of standard wheels for 1/4's one day though.

Lauren, I used to drive a hot hatch. For a while I thought driving hard round the twisties was fun. Then I just thought it was boring and dangerous.


Lauren is obviously busy doing something more interesting, so to save her the time...

[url]http://www.bookatrack.co.uk[/url]

Neil.
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matt_mr2t




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PostPosted: Mon Aug 08, 2005 10:51 am    Post subject: Reply with quote Reply with quote including images

I didn't mean the 18's made it faster. I just suggested they dont make it "that" much slower.

And for the record, i have NO interested in taking my car on a track.

I'd take a track car on a track. So if it gets smashed to peices then I have nothing to worry about.
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Lauren
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PostPosted: Mon Aug 08, 2005 11:41 am    Post subject: Reply with quote Reply with quote including images

matt_mr2t wrote:
I didn't mean the 18's made it faster. I just suggested they dont make it "that" much slower.

And for the record, i have NO interested in taking my car on a track.

I'd take a track car on a track. So if it gets smashed to peices then I have nothing to worry about.


Fairy nuff, though actually the risk of an accident on a track day is no doubt a lot lower than you may suppose. Obviously you drive within your limits and you can contain the risks. It certainly is a lot safer than driving at barking speeds on teh roads of course.

I have worked/driven on hundreds of trackdays and in all honesty the number of times i've seen a car completely written off is pretty rare.

i am amazed you got bored with fast cornering and all the myriad of techniques that go with it, but thats fine and each to their own etc.
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matt_mr2t




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PostPosted: Mon Aug 08, 2005 1:18 pm    Post subject: Reply with quote Reply with quote including images

Although I did drive like a bit of a spiv yesterday going after that V6 [Twisted Evil]
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