Does increase in Rim size really reduce FC DRASTICALLY?

[Ezfaun]

Ask the cyclists why they want thin thin wheel and not fat fat wheel ?

 

Less rolling resistance. But we're talking about larger diameter rims with lower profile tires. Rather than rolling resistance, the main factor is unsprung weight. (I think also affects rolling resistance but not in the sense of friction. More to inertia)

 

[Celicar]

I think a lot depends on whether you are primarily driving in city traffic or expressway. Constant start-stop and mostly in low gear is hugely different from smooth expressway traffic.

[RageX]

you must be a car noobie

 

so when you hear people say FC change a lot after changing to larger rims, you also think their overall diameter also change a lot?????

 

Sometimes it has to? Sorry for my perceived noobishness, just looking at it from the point of view of Physics.

 

If overall diameter is almost identical, tyre width is almost the same, the only effective change would be the weight increase from the larger rims.

 

Will that weight increase be so significant as to affect FC? Then will have to look at the difference in the weight of the rims.

 

BUT using a rough non-scientific calculation - some people claim FC drop from 10km/l to 8km/l - a difference of FC of about 20% - will that be possible just from the weight difference in the rims without a change in the overall diameter or width? I honestly don't know but from the point of view of Physics it seems extremely unlikely to have such a big effect unless there is another explanation.

[VellfireS]

Just want to pose the above question to all the drivers out there, feedback is appreciated.

 

Before I start, let me give some info on my current car. Driving a SUV now. Stock wheels were 235/65 R17.

 

A few months back, the tyres were getting bald and needs a change. I have long been a fan of huge chrome deepdish rims. Since it needed a tyre change, I reckon I will go for the full package.

 

 

After asking around, most of my friends or shop owners will say that 'your FC is going to be super jialat, furthermore with such big rims'.

 

I thought, what the heck, it is not everytime I get to have a car to be able to be fitted with big rims. I went ahead and got a R22 rims with 265/35. The overall diameter is still withn 1% of my stock wheels. I must say, I did not regret my decision. Full chrome with a 3" lips.

 

Before changing wheels, FC was approx 7.8 - 8 km / L.

 

 

After changing rims, I monitored for 2 months and most of the time, it is quite constant.

 

Many who have seen my rims were WOW, your FC must be crazy. I just told them it is ok, still acceptable to me.

 

 

Question to the bros and sis here, be it either you have experience with rims upsizing or you hearsay from others, what do you think my FC is currently.

 

I did not purposely change my driving style before or after, style and attitude still remained the same.

mine did.. used to get 6+..

 

now after up to 20.. 5+ only

[Ezfaun]

 

Sometimes it has to? Sorry for my perceived noobishness, just looking at it from the point of view of Physics.

 

If overall diameter is almost identical, tyre width is almost the same, the only effective change would be the weight increase from the larger rims.

 

Will that weight increase be so significant as to affect FC? Then will have to look at the difference in the weight of the rims.

 

BUT using a rough non-scientific calculation - some people claim FC drop from 10km/l to 8km/l - a difference of FC of about 20% - will that be possible just from the weight difference in the rims without a change in the overall diameter or width? I honestly don't know but from the point of view of Physics it seems extremely unlikely to have such a big effect unless there is another explanation.

 

Yep, changing to heavier rims will greatly affect the moment of inertia at the wheels. It's like putting a heavier flywheel on your engine. It adds to drivetrain loss as it still needs to be turned by the drivetrain. But if you change to bigger but lighter rims, there won't be any significant decrease in fuel economy. Even better is lighter wheels with the same size. The lighter weight and having no increase in the moment arm (diameter) means that there will be less moment of inertia.

 

To answer the TS's question, theoretically, larger diameter rims will impact FC depending on the type of rim you spend on. The larger moment arm needs to be counteracted with a smaller mass so that it doesn't increase the moment of inertia.

[Lattesurf]

Personally I've changed from stock 16" to 18" and down to 17" over the past 5 years on the same car.

 

205/55/16 - stock rims.

Rim weight ~ 10.5kg, tyre weight ~ 10.5kg, total 21kg.

FC generally about 12.5-12.8km/l.

 

225/40/18 - aftermarket rims.

OD increased by about 5.4% from stock.

Rim weight ~ 10kg, tyre weight ~ 10.5kg, total 20.5kg.

FC dipped very slightly to about 12.3-12.5km/l.

 

215/50/17 - aftermarket rims.

OD increased by about 3.9% from stock.

Rim weight ~8kg, tyre weight ~10kg, total 18kg.

FC maintained around 12.5km/l currently.

 

My data looks funny as my FC doesn't seem to decrease significantly through the 2 size changes.

How i interpret this is that although larger OD should improve the FC, but the rim+tyre weight plays a big role or rather Inertia weight.

 

When rims are upsized, tyres tend to go lower profile (thinner) but tyre weight stays relatively the same. A 55 profile will weigh very close to a 40 profile tyre of the same brand/model within 2-3inches difference. This means that more weight is located further away from the axle.

 

More weight further from the axle, means more inertia is present and therefore needs more energy to overcome, which indicates poorer FC.

 

But now the OD is increased, which indicates higher RPM and better FC.

 

So these 2 factors combined, sort of evens it out and I still maintain a fairly constant FC since day 1 despite the 3 sets of rims/tyres.

 

 

[Thaiyotakamli]

Wont be more than 1km/l la or else hybrid cars will be fitted with 13" rims

[JaydenSTI]

too many things to consider, size alone not the deciding factor... rolling resistance (tread design), weight of tire/rim (unsprung weight), width of tire, overall diameter, of coz engine size matter as well. smaller size engine will need to produce more work (in term of % of work output comparing before and after) to make ur vehicle move (or to satisfy ur butt feel), thus making foot heavier unconsciously.

 

upsizing rim, to me, a no no for non genuine product, heavy, integrity not certified. tire wise, other then tread design, width and it relative profile, brand is important, at least to me, e.g. Dunlop vs Michelin, same range similar performance, the later anytime for the better comfort (softer side wall, but more progressive feeling in comparison) and less noise, u pay premium for that for sure. Moreover, the Mic last much longer as well and cut through water like a knife even after 15k km on them.

 

my personal experince in upsizing rim, from 17 to 19. The 17 Enkei weigh 11kg each side, while my 19 advan weigh 8kg, the 235/45 Dunlop weigh 11kg while the 245/35 Michelin weigh 9kg. total circumference up close to 5%, but my car felt so damn light on the move and brakes better as well, return me similar FC before and after. Down side, my widened wheel tract (ET55 to ET38) and tire width had numbed the steering respond.

 

If TS is considering a 22 from 17, the cost for the 22 would be skyrocketing, why care about the S$5 extra per 100km traveled distant???? follow ur heart, but know what u want.

[Ladykillerz]

just to share. mine's from 17" to 19" and FC increase from 9.5km/l to 8.5km/l. i don't know any magic but am considering to revert back to 17" though the drive is much better on 19".

[Ronleo]

want to change just change, heck care about FC. Its not as if you are putting in a 20" rim.

Ermm... He's putting 22" rim!!!

[Volvobrick]

If the brake discs are not increased in size at the same time with a BBK, the ultra large rims make them look out of proportion....

[Hamburger]

Ermm... He's putting 22" rim!!!

 

put 22" and still care about FC....diao

[Ronleo]

 

put 22" and still care about FC....diao

Not everyone like u soooo lich drive continental car... ;)

[Hamburger]

Not everyone like u soooo lich drive continental car... ;)

 

bro, mine is lao conti leh,

 

but really its fun to drive with such TC car.

[Woes]

Actually, I'm already driving with the 22" for half a year.

The ride handling definitely feels better. Originally was getting close to 8km/l, now around 7.3km/l.

 

 

My concern is, I have been told before and now that my FC will surely suffer whenever they see my rims. The annoying part is, when I ask them how do they know or why they think so, they will say they have hear from here and there. None of them have actual exp of driving one.

 

I'm not concerned about the FC so much, actually this is my best FC with regards to all previous rides. Some of them are only 5+km/l.

 

My thinking has always been, if you are driving, you definitely need fuel. No matter how the petrol stations increase their price or how we all kbkb, at the end of the day we still need to spend our $$$ on them.

[Woes]

 

bro, mine is lao conti leh,

 

but really its fun to drive with such TC car.

 

I stand with you. My previous 2 cars were all TC. Now driving this family SUV, somehow feels like somewhere is wrong.

 

Really wish to get a TC 7 seater SUV, even better if it comes in manual but looking at the COE now, don't think there's any hope of getting 1. I just cannot imagine myself throwing down 70k for a piece of electronics paper

[Ungtiong]

if stock rim is some heavy cheapo rims on cheapo stock poor fuel efficient tyre then upgrade to forged light weight rims on better tyres with good fuel efficient tyres, the larger rim size may be better in FC or have very minor effect.

[QunZhang]

TBH my FC did suffer a bit, when I upsized from 17" to 18". on 17" is around 9km/l, on 18" is around 8+km/l.

 

But the car certainly feel more planted to the ground, and that is more important for me.

 

Hi Matoonia, I also want to change my 17" to 18". Do you feel any acceleration draggy on 18"? I heard the bigger rims will hamper the accelerations.

Edited January 11, 2019 by QunZhang