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Discussion Starter #1
Having just changed my tyres from 16" to 17", I am still learning how to control the wayward actions of those 225/45/17 on anything other than perfect roads. My first observation is how much the tyres prefer to follow any uneven tarmac problems or groves in the road. Quite a handfull to keep the car straight.
The streets of London have been dug up so many times, few are excempt from severe uneven ride. The back streets are just out of bounds for me now...

Anyone got any tips for me on how to safely handle these situation?
 

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Classic trade-off situation going on here. The relative lack of sidewall flex here makes the car react much more directly and precisely to the steering wheel, but the flipside is it will be less tolerant to ruts, off-cambered roads, tramlining, et cetera.
In most cases, this will be amplified by the oversized wheel/tyre combination being rather heavier than the original - the tiny bit of weight that is saved in the sidewall dimensions of the tyre (mostly offset by going to a wider size and/or sturdier construction that comes with a higher speed index, anyways) isn't by far enough to compensate for the added weight of a larger rim (as an aside, with the current trend to 20" or even bigger rims, tyre fitters aren't allowed to lift them themselves by work inspection anymore, so the new generation of tyrefitting/balancing machines often comewith a hydraulic lift...). You don't want to have an unsprung weight too high in relation to the weight of the total vehicle or it'll be a case of the tail wagging the dog...

Solution - depends on what car we're talking about. For 9000's 17" should be about spot on and I would investigate compensating for the difference by getting springs that are specifically made to work with seventeens (eg Abbott). In the case of a Classic 900, I would stich with sixteens and a rather narrower tyre profile (it's not only Abbott who maintain 195/50/16 is the ideal size for that car as regards overall road handling!.
 

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Oh, now I remember - yours is a 9-3, right? 17" Should be OK then, but in your case I think now that the sidewalls don't flex as much anymore the forces are transmitted to other parts that can/will give, and what you are experiencing are the deficiencies of the 9-3 front supension - more to the point the rubber donut dividing the front suspension lower member in two halves, and the lack of proper steering rack fixation. In addition to my former point about springs, I'd look at the corresponding parts from Abbott's VRK.
 

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Discussion Starter #4
Thanks for that Eric.
Het zit zo: I have fitted the steering clamp from Abbott, so the steering is at least a lot more controllable now. My dampers and springs are the same as on the Viggen (as are those groved brake pads).

But I like that comment you made about the tail wagging the dog . I do indeed sometime get that feeling under me that the back wheels are going all over the place, whilst I am trying to keep the front wheels in a straight line. And with that engine of mine producing so much power with no noticeable turbo lag, hell has no fury like...

Could tyre pressure experimentation help me in any way?
 

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Hi all! With this reply I would like to breathe new life into this topic as I experienced the same "problems" on by 9-3. I've the double 3-spoke 17 inchers from the late Aero models, a VRK and Koni adjustables fitted on my MY98 2.0 Turbo but still felt a bit uncomfortable with the behaviour described by StanleyB. To convince myself about these feelings I borrowed a set of 16 inch wheels from my fathers 9-3 Anniversary without any mods, and yes after a couple of days driving on these I'm sure... this combination drives a lot better
so I'm almost convinced to change my 17 inch wheels for a new set of 16 inch's, UNLESS someone here can give me a hint regarding an alternative solution for this problem... So, does tirepressure affect this significantly? should I consider different springs? maybe different tires?? I currently have Pirelli P6000, while I know from my fathers 9-5 Aero that with Michelin Pilot Primacy he didn't have the actual problem at all, while his new P-Zero's have (only when they're cold)...

I would be very happy to have some tips as I really like the looks of the 17 inch wheels
 

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Stanley, Have you checked the pressure in your tyres. I have a 9-3 Aero running on 17" wheels, I also have the steering clamp and the rest of the bits and pieces from the Viggen rescue kit fitted. During the winter up here, I let the pressure in the tyres down to 25 psi, to give me better grip on the snow and ice, but that made the car tramline on the slightest imperfection in the road. That didn't bother me through the winter, as I was never going that fast, but now that the better weather is here, I have put the tyres back up to 38 psi, and the tram lining has all but disappeared. I'm sure the manual recommends even higher temperatures for high speed cruising with a full load in the car, so these pressures are no problem.
Neil
 

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I have a similar experience with my 9-3. However, my car has 205/55-15 tires on it and I get it too. I have Bridgestone S03PPs and they like to follow every little bump in the road and therefore require more input to keep the car tracking where I would like it. My winter tires do not do this. I think the problem is more a facor of the tire type and its grip level than anything else.
 

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My '94 900T also did this when I first bought it - quite alarming compared to my 9000T - a check on the tyre pressures (I use standard 33psi on 205/55/16)and the tracking done made quite a difference but my front tyres were also worn and I changed them to Pirelli P6000's - I think the new tyres helped also - not necessarily Pirelli's but I think the front becomes a bit more twitchy on worn tyres. I still get torque steer when accelerating with the streering off centre and especially if I hit a small bump - nearly ended up on the pavement the other day - but the car does not follow white lines some much now. Hope to fit a VRK at some point in the future.
 
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