Large alloys - what is the point?
Discussion
JR said:
increase the rotating unsprung weight (second moment of inertia)
second moment of inertia applies to rotating mass, it is not relavant that the mass is unsprung. yes they are both negatives for having larger wheels, but are seperate points. it is neither here nor there that the unsprung mass is rotating.
Trommel said:
Very interesting, and agrees with some of the things I've seen with F1 tyres (which may mean I have badly explained myself in my previous post!)The Fisker above may have big wheels, but the styling works around it - with 17" it would look silly.
Consider a Nissan GT-R GT1 - it has to run smaller wheels because of the rules, and they do look quite tiny because the car was styled with much bigger wheels in mind.
doogz said:
wildman0609 said:
second moment of inertia applies to rotating mass, it is not relavant that the mass is unsprung.
yes they are both negatives for having larger wheels, but are seperate points. it is neither here nor there that the unsprung mass is rotating.
Second momemt is useless on it's own, as part of that area is wheel, and part is tyre. A larger wheel/smaller tyre combination may well have a lower I (or whatever you want to call it) value than a smaller wheel + larger tyre combination, but whwen you consider the densities of the 2 materials, that changes things a bit.yes they are both negatives for having larger wheels, but are seperate points. it is neither here nor there that the unsprung mass is rotating.
If we take it as given that you keep the same widths of wheel and tyre then: tyres of the same dia (as in rolling dia or radius) tend to weigh the same - there is less sidewall but more re-inforcement and because this mass is further out from the centre of the wheel the inertia is more for the larger wheel dia tyre. The wheel inertia is always more - not only is it a larger dia but the rim has to span further between spokes meaning either a thicker rim or more (or wider) spokes.
LukeSi said:
Hasbeen said:
If big wheels with ultra low profile tyres were better for handling & traction, don't you think F1 cars would be wearing them?
No, because the rules say they have to have wheels of a certain size otherwise the G-Forces would be too much for the drivers.I,m quite sure that on your average road going car the alloys are purely to compliment the look of the car rather than the way it handles.
I my self run an SE E91 on 16's (albeit looking for a set of good black 17's and I wouldn't go bigger than that and destroy the ride) The ride on the 16's is good, I opted for SE rather then M style set up as the ride on the M style setup and the driving that I do plus my lower back problems would be no good to me at all.Far to harsh ,I know getting old Lol.
The car on 16's doesn't compromise the road handling, the quality boots on it make it stick to the road and I,m pushing 200-210 bhp through the rears (320d remapped) and make it work from time to time.
Occasionly one of my friends comments that I still haven't gotten rid of the small wheels lol..
Black 17's are a work in progress.
A friend at work has an M styled 325i on 18's MV's and the car looks good on them.
Another friend at work has a 318i vert on 19's and it looks ridiculous imo.
At the end of the day it's all down to personal opinion and what individuals want.
A comment earlier on is a valid one - when these cars with big wheels end up in the S/H market the buyers tend to almost die of shock at the price of decent tyres and opt for ditchfinders instead.
I,m pretty sure I,ve seen Corsa's running 18's possibly 19's and Insignias going upto 21 - Diesel sri insignia no less - On 21's !!!! LOL
I my self run an SE E91 on 16's (albeit looking for a set of good black 17's and I wouldn't go bigger than that and destroy the ride) The ride on the 16's is good, I opted for SE rather then M style set up as the ride on the M style setup and the driving that I do plus my lower back problems would be no good to me at all.Far to harsh ,I know getting old Lol.
The car on 16's doesn't compromise the road handling, the quality boots on it make it stick to the road and I,m pushing 200-210 bhp through the rears (320d remapped) and make it work from time to time.
Occasionly one of my friends comments that I still haven't gotten rid of the small wheels lol..
Black 17's are a work in progress.
A friend at work has an M styled 325i on 18's MV's and the car looks good on them.
Another friend at work has a 318i vert on 19's and it looks ridiculous imo.
At the end of the day it's all down to personal opinion and what individuals want.
A comment earlier on is a valid one - when these cars with big wheels end up in the S/H market the buyers tend to almost die of shock at the price of decent tyres and opt for ditchfinders instead.
I,m pretty sure I,ve seen Corsa's running 18's possibly 19's and Insignias going upto 21 - Diesel sri insignia no less - On 21's !!!! LOL
Not sure why big wheel fans have to be poseurs, it is possible for someone to enjoy the aesthetics of their own car. Or have we got the usual 'I'm on a motoring forum but think anyone who owns a nice/expensive car is a flash b
d' brigade?
Also, I've seen the Caterham used as an example. Worth bearing in mind that it's arguably the ratio of sprung/unsprung mass that's important, rather than the raw amount of unsprung mass itself. On a light car with spindly suspension (on the front anyway) like a Caterham, the wheels will represent a large proportion of the unsprung mass, and thus a small increase will represent a disproportionate change in unsprung mass, and in turn a disproportionate change in mass:unsprung mass.
On such a simple car it would also exaggerate things like changes to inertia in the steering system which will affect feel and response.
ETA - Despite my job description, feel free to correct me, I've only been doing it a month and I've done more driving than tweaking so far!
d' brigade?Also, I've seen the Caterham used as an example. Worth bearing in mind that it's arguably the ratio of sprung/unsprung mass that's important, rather than the raw amount of unsprung mass itself. On a light car with spindly suspension (on the front anyway) like a Caterham, the wheels will represent a large proportion of the unsprung mass, and thus a small increase will represent a disproportionate change in unsprung mass, and in turn a disproportionate change in mass:unsprung mass.
On such a simple car it would also exaggerate things like changes to inertia in the steering system which will affect feel and response.
ETA - Despite my job description, feel free to correct me, I've only been doing it a month and I've done more driving than tweaking so far!
doogz said:
Which is the more important factor here? Unspring mass, or inertia? Guess it'll depend on the exact sizes of the wheels and tyres in question, and the over-ruling of the 2 factors will be different for different applications.
Why worry about that? They're both worse with larger wheels.The Wookie said:
Also, I've seen the Caterham used as an example. Worth bearing in mind that it's arguably the ratio of sprung/unsprung mass that's important, rather than the raw amount of unsprung mass itself. On a light car with spindly suspension (on the front anyway) like a Caterham, the wheels will represent a large proportion of the unsprung mass, and thus a small increase will represent a disproportionate change in unsprung mass, and in turn a disproportionate change in mass:unsprung mass.
On such a simple car it would also exaggerate things like changes to inertia in the steering system which will affect feel and response.
Yes, the effect would be more noticable on a car like the Cat. That's just to try to illustrate the point.On such a simple car it would also exaggerate things like changes to inertia in the steering system which will affect feel and response.
doogz said:
You make a good point, and obviously the larger the wheel, the heavier it's going to be. But by how much? If we don't consider the inertia side of things, a larger wheel is going to have slightly longer spokes, and the area of the rim itself will be larger by a ratio of the new dia/old dia.
Which is the more important factor here? Unspring mass, or inertia? Guess it'll depend on the exact sizes of the wheels and tyres in question, and the over-ruling of the 2 factors will be different for different applications.
Who you working for BTW? I need to get out of shipbuilding!
In terms of ride, then unsprung mass and inertia are inextricably linked as one effectively creates the other. The unsprung mass is the measurable (or at least calculated) amount, and the inertia is the result which causes the nasties.Which is the more important factor here? Unspring mass, or inertia? Guess it'll depend on the exact sizes of the wheels and tyres in question, and the over-ruling of the 2 factors will be different for different applications.
Who you working for BTW? I need to get out of shipbuilding!
In terms of performance and braking then bigger wheels will almost certainly mean significantly increased rotational inertia, which is never really a good thing, although the effects are pretty limited, particularly at higher speeds.
Ahhh, that would be telling... you might be able to work it out by my location though!
Another consideration from earlier this month:-
JR said:
Rollcage said:
Taken from another forum -
"Well, going from 16" alloys with 195/45 R16 tyres to winter steelies with 175/65 R14 tyres I notice about a 10% difference in fuel consumption.
Given that the rolling radius of both tyres is the same, so gearing pretty much unaffected, would the extra weight of an alloy wheel give worse fuel consumption, and would it be 10% different?
NB the above is getting better fuel consumption on the smaller wheels, as they are lighter.
I'd find it unlikely that the difference in wheel weight would make that much of a difference to fuel economy - would it be more likely to a subconscious change in driver style with winter tyres on?
"Well, going from 16" alloys with 195/45 R16 tyres to winter steelies with 175/65 R14 tyres I notice about a 10% difference in fuel consumption.
Given that the rolling radius of both tyres is the same, so gearing pretty much unaffected, would the extra weight of an alloy wheel give worse fuel consumption, and would it be 10% different?
NB the above is getting better fuel consumption on the smaller wheels, as they are lighter.
I'd find it unlikely that the difference in wheel weight would make that much of a difference to fuel economy - would it be more likely to a subconscious change in driver style with winter tyres on?
Kolbenkopp said:
Car and Driver did an interesting feature on that:
http://www.caranddriver.com/features/10q1/effects_...
http://www.caranddriver.com/features/10q1/effects_...
GaryST220 said:
Ford quite nicely provide fuel consumption figures for their cars with various sized tyres. The extra urban figures for my ST220 is 35.x MPG on 225/40/18, and 38.x MPG on 205/55/16 - on the flip size the urban cycle is negligible. Having used both tyre sizes, I would agree with Ford; the cars also much faster on the 16" alloys.
So 10% is quite feasible. Weight, width, rolling resistance, and drag. Could be around £20 a month for many.doogz said:
I'd imagine the larger brake discs that you're likely to have fitted, the pre-requesite for the larger wheels, may well have more of an effect than the actual increase in inertia of the wheel itself. Or, well, again, depends on the exact dimensions.
If you're fitting (or buying a car which has) larger brakes (maybe fitted by the manufaturer) and those brakes require larger wheels then you've little alternative. FWIW the increase in wheel size is usually the dominant one but as you say it depends on the dims.
Big Rod said:
My first car was a bog standard Cortina. I remember my peers, (who had mainly MKII Escorts), wanting the wheels off Capris because although they were the same pattern, they were wider with a deeper dish. Wider was the way back then and it made sense!!
Sadly it was a co' car and if I was found to have tampered with it there'd have been hell to pay so wheels were out of the question as they'd have been easily noticed.
Unfortunately however, they sprung my replacement car on me one day by surprise and I didn't have time to remove my 'HiPower' Sharp radio/cassette player, craftily hidden speakers and graphic equaliser, rear headrests, electric aerial, Ghia dials, (had a rev' counter!!), and Granada trip computer! <sigh>
Ha ha, those were the days eh?.Sadly it was a co' car and if I was found to have tampered with it there'd have been hell to pay so wheels were out of the question as they'd have been easily noticed.
Unfortunately however, they sprung my replacement car on me one day by surprise and I didn't have time to remove my 'HiPower' Sharp radio/cassette player, craftily hidden speakers and graphic equaliser, rear headrests, electric aerial, Ghia dials, (had a rev' counter!!), and Granada trip computer! <sigh>
S1MMA said:
I hate large wheels on hatchbacks with tiny brakes. Especially older ones with drums on the back, looks cack.
Some of the modern stuff is ok, 18s on Golf GTis etc... I also like big saloons which have moderately sized wheels (18s or 19s for more modern stuff with big arches).
Sports cars are all about the function/form and performance IMO. My car comes on 19s standard, 12" wide at the rear. Brakes are 380mm up front, so need a 19" wheel to fit under:
Lovely car.Some of the modern stuff is ok, 18s on Golf GTis etc... I also like big saloons which have moderately sized wheels (18s or 19s for more modern stuff with big arches).
Sports cars are all about the function/form and performance IMO. My car comes on 19s standard, 12" wide at the rear. Brakes are 380mm up front, so need a 19" wheel to fit under:
Those 6 pots are awesome and have ceramic pistons!
I have a set with 362mm AP racing discs and bespoke brackets + Carbotech XP10 pads.. they will be fitted to my car when my Forged wheels come from Japan.
I have been out in an EVO fitted with this brake set up and they are just amazing! So much pedal feel and braking force on tap.
Unlike the AP racing brake kits, the Porsche caliper is a monobloc design so a lot more rigid.
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