Page 3 of 3 FirstFirst 123
Results 21 to 29 of 29

Thread: wheel size vs comfort, durability and cost?

  1. #21
    Senior Member
    Join Date
    Apr 2016
    Posts
    621
    Post Thanks / Like
    Quote Originally Posted by wackymatt View Post
    After replacement the small bump handling of the car dramatically improved, before there was a sensation very similar to worn dampers where it felt the front wheels would shake after hitting a small bump at speed. This has been completely eliminated with new wheel bearings.
    wow. I have a noisy front wheel bearing and I was thinking that my front shocks aren't very good. The car skips wide if you hit a bump mid corner

  2. #22
    Senior Member sjc1's Avatar
    Join Date
    Nov 2017
    Location
    Essex
    Posts
    229
    Post Thanks / Like
    Quote Originally Posted by wackymatt View Post
    I replaced my whining diff last year with a 2nd hand unit, had a load of other work done at the same time including new tyres. To cut along story short, after checking/replacing most of the drivetrain & wheels&tyres the source of the body vibration was from the second hand diff. It turns out the diff must have come from a steel bodied car where the tolerances for vibration are larger.

    When the vibration diagnosis was being performed (car on a ramp with back wheels driven at speed by engine) you could clearly see the diff shaking about a bit. The frequency of the vibration narrowed it down to the pinion gear, the vibration was cured by placing counter weights on the prop shaft.

    I had a small vibration through steering that standard wheel balancing alone could not fix. The cause was the brake rotor balance being out. Balancing the wheels on the car fixed this by putting extra compensation weights on the rim.

    During this rather expensive journey I replaced the front wheel bearings, the existing had a high mileage but no usual symptoms that would indicate a problem. After replacement the small bump handling of the car dramatically improved, before there was a sensation very similar to worn dampers where it felt the front wheels would shake after hitting a small bump at speed. This has been completely eliminated with new wheel bearings.
    That’s a really detailed and helpful reply, thank you. I bet there’s a few on here off to check/ replace their wheel bearings... myself included as I have similar symptoms to yours and as described by Dieselnutjob.
    Noble M400, LR Disco 3, Rover 75 V6,Jaguar X350/358 coming... edit.. got one,2007 4.2 LWB with big restoration.

  3. #23
    Senior Member
    Join Date
    Aug 2013
    Posts
    871
    Post Thanks / Like
    Quote Originally Posted by 2woody View Post
    The general principle is that you should have big wheels only if needed to clear the brake pack.

    On an engineering front, bigger wheels are almost completely bad - they weigh considerably more and hence give the suspension more to cope with in terms of unsprung weight, which affects the ride and handling. Bigger wheels also mean less height in the tyre sidewall, which is also bad for handling. Handling is the ability of the car to follow your defined road position, whilst giving decent and reliable feedback - in practice, it relies mostly on the tyre deflection. More deflection through a deeper sidewall = more and better quality feedback to the driver = better handling. Grip really isn't an issue here, as all X350s of whatever spec carry tyres way too wide for the required grip level. Ride comfort also deteriorates with a narrower strip of rubber in play. And then there's reliability - it is much easier to bend a wheel if the tyre profile is low.

    On the flip side, people like the aesthetics of larger wheels (apparently). And this is a marketing thing, usually
    Bigger wheels aren’t always heavier fact ,higher sidewall tyres make steering less responsive and therefore poorer handling characteristics fact ,

  4. #24
    Senior Member
    Join Date
    Oct 2016
    Location
    Northumberland
    Posts
    1,314
    Post Thanks / Like
    Quote Originally Posted by s collins View Post
    Bigger wheels aren’t always heavier fact ,higher sidewall tyres make steering less responsive and therefore poorer handling characteristics fact ,
    I w
    i'll concede that you can get some bigger wheels that can be lighter if you go for forged for example - but generally, the bigger they are, the more they weigh

    But the steering response definitely gets worse with reducing sidewall height. I test vehicles for a living and its one thing that we can measure precisely. Always a car becomes less controllable with reducing sidewall height. The steering can become more immediate, but this is always at a cost of being less responsive. Don't confuse handling with grip here - the two are polar opposites. For a given vehicle, should you increase lateral grip, you are destined to reduce the handling capabilities.

    I've probably bored everyone with this before, but some time ago I ran a test for GM on a car of similar layout and weight to our X350s - we fitted 14, 15, 15, 17 and 18" wheels to it for some lapping with (obviously) reducing sidewall height. All of our ten "random" testers from GM preferred the handling on the 15" wheels and the expert group were also able to get the 15" car round the track faster than the bigger wheel variants.

  5. #25
    Senior Member Partick the Cat's Avatar
    Join Date
    Apr 2013
    Location
    Thornbury, Gloucestershire
    Posts
    1,150
    Post Thanks / Like
    Quote Originally Posted by s collins View Post
    ... higher sidewall tyres make steering less responsive and therefore poorer handling characteristics fact ,
    Sorry but that's not right.

    What woody is referring to is called 'slip angle' (a big mis-nomer because no slipping is taking place). When a car is cornering the front wheels don't quite point in direction that the wheel is travelling, they point slightly further into the turn, ie the wheel runs slightly wide of the direction it's pointing. It's this difference that's called the 'slip angle' and it's an important factor in allowing a front tyre to develop cornering forces before adhesion to the road surface is lost.

    The tyre is able to do this because the inner and outer sidewalls are able to deform differently and allow the tyre's 'footprint' on the road to twist slightly relative to the line of the wheel. The wider the tyre, ie the further apart the sidewalls, the smaller the slip angle of the sidewalls for a given sidewall deformation. Likewise the deformation also increases (or maximum slip angle decreases) as the height of the sidewall decreases. Both effects act to limit the amount of slip angle that can develop before adhesion is lost and the tyre skids.

    The effect of this is to act the opposite was to the other, simpler, effect that a larger are footprint (wider tyre) gives better grip ... there's a trade-off between them, and there is an optimum point between the two effects.

    What woody is pointing out is that visual fashion has taken many cars into this 'too-stiff-sidewall' zone.

    This argument holds far less for the rear wheels where the slip angle effect is far, far, smaller. That's why rear tyres can be, and often are, wider than the front (steering) wheels.
    Last edited by Partick the Cat; 12-09-19 at 11:26.
    "The jaguar is a compact and well-muscled animal." (Wikipedia on Panthera Onca)
    2008 XJ Sovereign 2.7 Tdvi,
    LWB, Sunroof, 19" Polaris, Botanical Green
    2008 Hyundai Getz 1.4
    Previous: 2004 Hyundai Getz; 1990 Merc 190E 2.6; 1987 Nissan Prairie ... 1954 Mk-C 197cc Bond Minicar

  6. #26
    Senior Member
    Join Date
    Apr 2016
    Posts
    621
    Post Thanks / Like
    I notice that wheels in the original brochure for the first X350s were 18" Dynamics, so I guess that an 18" is what the car was designed to have.

    Personally I quite like the forgiving nature of older cars with narrow and high profile tyres. More modern cars with more grip seem to snap away from gripping to totally out of control very quickly and unless you are an experienced track driver or something then maybe it all happens too quickly. I guess that if you have practiced driving a car very quickly then you will already know what's its going to do on the limit and you'll be ready for it. I haven't done that in my X350 as I am a bit too frightened of crashing it and so I don't really know what it will do on the limit. My guess is that things happen somewhat more suddenly on 20s than 18s.

  7. #27
    Senior Member
    Join Date
    Jan 2016
    Posts
    143
    Post Thanks / Like
    I'm still using the 17" Elegance wheels - they somehow suit the cars and there are plenty of all season tires to choose from.

    The Nokian weatherproofs which I have on now have done 47,000 miles but show some cracks now. Will try Hankooks next, though the Nokians where super comfortable and super quit, especially in rain.

  8. #28
    Senior Member
    Join Date
    Aug 2013
    Posts
    871
    Post Thanks / Like
    Quote Originally Posted by Partick the Cat View Post
    Sorry but that's not right.

    What woody is referring to is called 'slip angle' (a big mis-nomer because no slipping is taking place). When a car is cornering the front wheels don't quite point in direction that the wheel is travelling, they point slightly further into the turn, ie the wheel runs slightly wide of the direction it's pointing. It's this difference that's called the 'slip angle' and it's an important factor in allowing a front tyre to develop cornering forces before adhesion to the road surface is lost.

    The tyre is able to do this because the inner and outer sidewalls are able to deform differently and allow the tyre's 'footprint' on the road to twist slightly relative to the line of the wheel. The wider the tyre, ie the further apart the sidewalls, the smaller the slip angle of the sidewalls for a given sidewall deformation. Likewise the deformation also increases (or maximum slip angle decreases) as the height of the sidewall decreases. Both effects act to limit the amount of slip angle that can develop before adhesion is lost and the tyre skids.

    The effect of this is to act the opposite was to the other, simpler, effect that a larger are footprint (wider tyre) gives better grip ... there's a trade-off between them, and there is an optimum point between the two effects.

    What woody is pointing out is that visual fashion has taken many cars into this 'too-stiff-sidewall' zone.

    This argument holds far less for the rear wheels where the slip angle effect is far, far, smaller. That's why rear tyres can be, and often are, wider than the front (steering) wheels.
    sidewall flex creates under steer through flexing Patrick therefore reducing sidewall flex improves steering feedback ,response and improved cornering ability.
    if you can’t dazzle with brilliance baffle with bull excrement

  9. #29
    Senior Member
    Join Date
    Oct 2016
    Location
    Northumberland
    Posts
    1,314
    Post Thanks / Like
    Quote Originally Posted by Partick the Cat View Post
    The effect of this is to act the opposite was to the other, simpler, effect that a larger are footprint (wider tyre) gives better grip ... there's a trade-off between them, and there is an optimum point between the two effects.

    What woody is pointing out is that visual fashion has taken many cars into this 'too-stiff-sidewall' zone.

    This argument holds far less for the rear wheels where the slip angle effect is far, far, smaller. That's why rear tyres can be, and often are, wider than the front (steering) wheels.
    Yup - that's pretty spot on.

    Controllability and handling both increase with increasing tyre slip. As an absurd example, I have a set of crossplies that I bring out on special occasions when I'm teaching track-day driving. Ultimate cornering speed is of course diminished, but you can absolutely make the car to which they're fitted point in any direction that you want with only the throttle - the absolute definition of handling.

    Don't forget that slip is a 360 degree thing - a tyre has available slip angle to use in cornering, braking and lateral directions. Just driving at a constant speed in a straight line puts all of the tyres into some slip. That's why we all drive rear-wheel-drive - so that more of the available slip is used at the rear by relieving the front wheels of traction.

    Unfortunately, I'm not going to get the chance to drive my X350 on the 18" wheels it was designed with (always the sweetest handling version), as it's only 19's that will clear the brakes. In any case, 19" wheels and 255-section tyres are way into the overkill zone for a car of this weight

Page 3 of 3 FirstFirst 123

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •