Has anybody fitted 19" wheels ?
Discussion
I don't get how changing the rear width would have an affect on the steering and how the front wheels get affected by camber or ruts, especially if they are now wider. You'd expect that to make it worse.
Can anyone explain that in language suitable for a complete idiot like me please?
If it's like for like other than tyre brand at the front, surely that is a major factor?
Can anyone explain that in language suitable for a complete idiot like me please?
If it's like for like other than tyre brand at the front, surely that is a major factor?
Now that this is back on topic, this is an interesting conversation....
I've spent a lot of time playing around with my car to get the handling where I want it and can relate to a lot of this. I have noticed that the rear can have an effect on the steering on ruts / cambers. It manifests itself as almost a mild rear steer effect that means the rear is pulling against the front, if that makes sense?
I've long considered new wheels and the opportunity to have more tyre choice appeals too....
Dave - If you don't mind, could you give more details of your wheels (offsets, width, spacers used, sourcing, etc)? If you'd rather discuss off-line, that' fine! Since fitting the wider fronts, how has the tramlining changed? With the narrower rears, do you find traction to be (more of!) an issue?
Thanks, Mark
I've spent a lot of time playing around with my car to get the handling where I want it and can relate to a lot of this. I have noticed that the rear can have an effect on the steering on ruts / cambers. It manifests itself as almost a mild rear steer effect that means the rear is pulling against the front, if that makes sense?
I've long considered new wheels and the opportunity to have more tyre choice appeals too....
Dave - If you don't mind, could you give more details of your wheels (offsets, width, spacers used, sourcing, etc)? If you'd rather discuss off-line, that' fine! Since fitting the wider fronts, how has the tramlining changed? With the narrower rears, do you find traction to be (more of!) an issue?
Thanks, Mark
deadscoob said:
I don't get how changing the rear width would have an affect on the steering and how the front wheels get affected by camber or ruts, especially if they are now wider. You'd expect that to make it worse.
Can anyone explain that in language suitable for a complete idiot like me please?
If it's like for like other than tyre brand at the front, surely that is a major factor?
I guess its as difficult to explain as why a different make of rubber may do it. Can anyone explain that in language suitable for a complete idiot like me please?
If it's like for like other than tyre brand at the front, surely that is a major factor?
Im off to work but will pick this up again later.
If you're ok Dave, I'd also be interested in the details. My geo is quite aggressive, which is amazing on track, but along with the Kumhos it can be quite exciting on bumpy roads.
Perhaps we could have a meet up and swap wheels to see the immediate difference? Or next time we hook up you take me out in yours?
I'd like to keep the track performance, but a little less skittishness on bumpy roads would be fantastic
Perhaps we could have a meet up and swap wheels to see the immediate difference? Or next time we hook up you take me out in yours?
I'd like to keep the track performance, but a little less skittishness on bumpy roads would be fantastic
If you go for wider fronts, the extra width will need to be on the inside edge, so you effectively move the centre of the contact patch in slightly...this in turn reduces the scrub radius (slightly) and will reduce feedback through the wheel - manifesting itself as a perceived reduction in bump steer at the steering wheel.
Jonny
Jonny
Quite some years ago I fitted large AC Schnitzer wheels to my BMW 540 and shod them with P Zeros. The tramlining was horrendous and my wife had a go at me for ruining the car. Didn't help that I hadn't told her I was doing it together with some body mods!
When the tyres needed replacing I changed to Michelin Pilot Sports and it transformed the car - no tramlining and the steering sharpened up.
After that I changed the tyres to Michelin on my wife's BMW ZM Coupe and the handling again was transformed.
A few years later I again changed to Michelins on my RS6. Guess what, transformed.
I am hoping the pilot sports I have for the Ultima will be just as pleasing when the Ultima gets on the road. From this I glean that tyres can make so much difference!
When the tyres needed replacing I changed to Michelin Pilot Sports and it transformed the car - no tramlining and the steering sharpened up.
After that I changed the tyres to Michelin on my wife's BMW ZM Coupe and the handling again was transformed.
A few years later I again changed to Michelins on my RS6. Guess what, transformed.
I am hoping the pilot sports I have for the Ultima will be just as pleasing when the Ultima gets on the road. From this I glean that tyres can make so much difference!
Storer said:
I also have a set of wheels with track tyres on them and the fronts are 285's so I could try 285 front and 295 rear. As near as damn it the same size.
Could be interesting.
Roll on April!
Paul
The ratio of the widths front:rear with this setup is quite a way from the static weight distribution of the car so intrigued as to how it goesCould be interesting.
Roll on April!
Paul
macgtech said:
Storer said:
I also have a set of wheels with track tyres on them and the fronts are 285's so I could try 285 front and 295 rear. As near as damn it the same size.
Could be interesting.
Roll on April!
Paul
The ratio of the widths front:rear with this setup is quite a way from the static weight distribution of the car so intrigued as to how it goesCould be interesting.
Roll on April!
Paul
The axle weights on the Ultima are 40% front and 60% rear (give or take).
If you are using the 245 fronts on a car with 40% front weight distribution what width should the rears be?
Alternatively, what width should the fronts be if you use 335 rears with a 60% rearward distribution?
Is there a formula that manufacturers use to work these things out?
If you look at Porsche they favour very wide rear tyres versus the fronts on what is a heavily rearward biased weight balance.
McLaren, on the other hand, use a relatively narrow rear tyre on the P1 which is probably a better balanced car.
Who is right (is there a 'right' or 'wrong').
Discuss!
Paul
Just remember one thing, the less Compliance in the tire (Smaller Side wall etc) the more of a Harsh ride you will get, the more nervous it will make the car on normal roads. Nearly all road cars have some compliance in there suspension and or tires, the more you remove the less Road Friendly it may become... For this fact I fitted 17" wheels on my GTR and much preferred driving it than a few 18" wheeled versions I drove, more predictable over a bump etc etc look at the sidewall of any race car LMP or FIA GT they have good 3-4" most no bigger than 18".... But everyone is different and to each there own these are my views and not that of everyone, so ultimately go with what you want....
Storer said:
Little bit of thinking going on here following your comment Johnny.
The axle weights on the Ultima are 40% front and 60% rear (give or take).
If you are using the 245 fronts on a car with 40% front weight distribution what width should the rears be?
Alternatively, what width should the fronts be if you use 335 rears with a 60% rearward distribution?
Is there a formula that manufacturers use to work these things out?
If you look at Porsche they favour very wide rear tyres versus the fronts on what is a heavily rearward biased weight balance.
McLaren, on the other hand, use a relatively narrow rear tyre on the P1 which is probably a better balanced car.
Who is right (is there a 'right' or 'wrong').
Discuss!
Paul
Hi Paul,The axle weights on the Ultima are 40% front and 60% rear (give or take).
If you are using the 245 fronts on a car with 40% front weight distribution what width should the rears be?
Alternatively, what width should the fronts be if you use 335 rears with a 60% rearward distribution?
Is there a formula that manufacturers use to work these things out?
If you look at Porsche they favour very wide rear tyres versus the fronts on what is a heavily rearward biased weight balance.
McLaren, on the other hand, use a relatively narrow rear tyre on the P1 which is probably a better balanced car.
Who is right (is there a 'right' or 'wrong').
Discuss!
Paul
In theory, the ratio of front:rear tyre size should be broadly in line with the front:rear weight distribution. You can then tweak widths to change the handling characteristics...you also need to consider the operating window of the car too in terms of aero loading etc.
The P1 uses 315's at the rear and 245's at the front, and the wheel diameters are slightly larger (20" as opposed to 19" on the front). The width ratios suggest a roughly 40:60 weight distribution. (245/(245+315) = 43%). The Porsche is similar - as you would expect.
Jonny
Hi Jonny (sorry about miss-spelling your name)
Your calculation does suggest that we are using slightly too wide a rear wheel on the Ultima.
You could say we are using too narrow a front wheel instead so my tests should be interesting. Shame I have a variety of tyres on the wheels!
Paul
Your calculation does suggest that we are using slightly too wide a rear wheel on the Ultima.
You could say we are using too narrow a front wheel instead so my tests should be interesting. Shame I have a variety of tyres on the wheels!
Paul
Why? A P1 has incredibly advanced traction control systems, you don't think it would have a 315 tyre without tc do you?
Weight distribution is one thing to get a figure, but driven wheels and traction are surely another.
No fast rwd car with a 50/50 weight distribution has the same section rears as fronts, and that's not simply down to marketing.
Weight distribution is one thing to get a figure, but driven wheels and traction are surely another.
No fast rwd car with a 50/50 weight distribution has the same section rears as fronts, and that's not simply down to marketing.
Storer said:
Hi Jonny (sorry about miss-spelling your name)
Your calculation does suggest that we are using slightly too wide a rear wheel on the Ultima.
You could say we are using too narrow a front wheel instead so my tests should be interesting. Shame I have a variety of tyres on the wheels!
Paul
The formula only gives you a rough ball park and then you can tune the handling with different widths, and again, you need to consider that this is only in the static mode - for more high performance cars you may well be interested in the dynamic case when aero loads are applied, and rear weight transfer under hard acceleration.Your calculation does suggest that we are using slightly too wide a rear wheel on the Ultima.
You could say we are using too narrow a front wheel instead so my tests should be interesting. Shame I have a variety of tyres on the wheels!
Paul
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