Discussion
Hi all,
My current winter car, which is a E320cdi estate of 2004 vintage currently supports 245-45/17.
If I change to 265-40/17 which keeps the rolling radius & diameter etc within 2%, is there anything else I should be concerned about.
I'm due a tyre change and a bit more grip from the barge would be handy. She happily spins the rears with 500nm of of torque.
Please discus the pros and cons.
Iceboy
My current winter car, which is a E320cdi estate of 2004 vintage currently supports 245-45/17.
If I change to 265-40/17 which keeps the rolling radius & diameter etc within 2%, is there anything else I should be concerned about.
I'm due a tyre change and a bit more grip from the barge would be handy. She happily spins the rears with 500nm of of torque.
Please discus the pros and cons.
Iceboy
On the plus side: on a smooth surface your lateral grip will be greater.
On the negative side: the wider contact patch and increased unsprung weight may cause some handling issues on uneven surfaces.
But it might work well if it fits within the dynamic working range of your suspension and geometry.
On the negative side: the wider contact patch and increased unsprung weight may cause some handling issues on uneven surfaces.
But it might work well if it fits within the dynamic working range of your suspension and geometry.
Rovinghawk said:
Friction is a function of weight rather than width. Contact area stays the same (just wider & shorter); are you sure you'll get more grip?
RH
This would be true if tyre grip worked by friction alone rather than chemical bonding and if tyres didn't have structure inside them to stop the contact patch changing shape like a balloon.RH
There is an excellent page of well written but inaccurate and hoplessly over-simplified bilge on the Tyre Bible website, which is not any more accurate than any other bible. I keep seeing bits of it regurgitated all over the internet.
Caulkhead said:
I very much doubt you'll notice any increase in traction with that change of tyre size on a heavy diesel estate. You're more likely to notice a swap to a stickier compound - what brand and type of tyres are currently fitted?
I agree. Also, you can play about with tyre pressures (within sensible limits) to see what gives you the best compromise of grip vs fuel economy.To answer the OP
- you'd need to be mindful of insurance implications to non-standard tyre sizes
- you'd want to make sure a 265 would sit comfortable on your current wheel with (if you advise I can tell you)
- you'd need to ensure there won't be any suspension / arch rubbing due to the wider width, though with a fairly small change I'm sure you won't have a problem
As others have said, you'll get more of a grip difference changing tyre brands than you will tyre sizes.
- you'd need to be mindful of insurance implications to non-standard tyre sizes
- you'd want to make sure a 265 would sit comfortable on your current wheel with (if you advise I can tell you)
- you'd need to ensure there won't be any suspension / arch rubbing due to the wider width, though with a fairly small change I'm sure you won't have a problem
As others have said, you'll get more of a grip difference changing tyre brands than you will tyre sizes.
Rovinghawk said:
doogz said:
The contact area might stay the same, depending on what tyres you fit.
Same weight, same pressure, same contact area.RH
So the structure of the tyre doesn't do anything?
So if I get a car, and reduce the pressure of the tyre to zero, does the contact area become infinite? Or is the situation more complex than that?
Captain Muppet said:
Rovinghawk said:
eg:
1400 lb car.
35 psi tyres
1400/35=40 square inches contact area. No other variables.
RH
Awesome!1400 lb car.
35 psi tyres
1400/35=40 square inches contact area. No other variables.
RH
For a flat tyre: 1400/0 = infinity. If there was a flat tyre anywhere in the universe we'd be able to touch it, all of us, all at once.
That can't be right can it?
IceBoy said:
It is a strange one as the I currently have 245/45-17 all round but some cars have staggered set-up with 265/40-17 at the rear only?
IceBoy
Ignoring the physics bickering for a second, it might be that the previous owner of your car (assuming there was one) fitted the same size all round on staggered wheels, or your car was spec'd with wheels which don't come as staggered.IceBoy
If the tyres are the same all round, but the wheels are staggered, you might be able to tell just by looking at them (assuming you have the same tyres front and back) - if the rear is wider the tyre will look smaller on the wheel, and the front will look comparatively pinched.
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