Wheel change

MagicSean

I was considering changing my wheels from 18" to 16" as the ones I have are getting damaged a lot on potholes. However a friend of mine posed these questions which I was hoping someone could answer.

1) If you change to a larger wheel size do you get better fuel economy because the car is travelling further for each rotation of the axel?

2) How does the speedometer not be affected by a change in wheel size as the car is now travelling further per rotation.

I have to admit I know very little about car mechanics and haven't a clue how to answer.

mickdw

You must keep the rolling radius the same. So if you get 16" wheels, you will be buying tyres with 25mm higher sidewall compared to those fitted to the 18"
What size tyres do you have at the minute?

MarkR

This may help. As long as you keep the dimensions of the wheels, you shouldn't have any problem.

Wheel size calculator

biko

As to fuel economy, no not likely or at best negligible.
It's more about driving style* than rations of the wheels.


*Aggressive vs Sunday driving. Look into hypermiling for tips on how to increase mileage. Or read this

Gumbo

OP, why not avoid the potholes? or go around them?

ive had 18" on my previous cars and never had any problems at all!

what exactly is going wrong? are you getting blow outs alot?

i suppose it depends on whre your based though.

MagicSean

kceire wrote: »

OP, why not avoid the potholes? or go around them?

ive had 18" on my previous cars and never had any problems at all!

what exactly is going wrong? are you getting blow outs alot?

i suppose it depends on whre your based though.

Try driving from enfield into kilcock. It's like a bomb site. Sometimes it's not always possible to see them or avoid potholes on backroads either. I've had my alloy damaged twice and about six instances where my tyre has bulged.

mickdw

I run 18" with 245/40 tyres & never do any damage driving in poor raods in mayo. I can understand how you would do damage though.

45 profile tyres are about the minimum ratio for poor roads

Seth Brundle

k_mac wrote: »

1) If you change to a larger wheel size do you get better fuel economy because the car is travelling further for each rotation of the axel?

2) How does the speedometer not be affected by a change in wheel size as the car is now travelling further per rotation.

The overall diameter or rolling radius should not change (which should answer #2) so your 18" rims have say 40% profile tyres but the 16" may have a profile of 50% (i.e. you will be moving from low profile tyres to a regular sidewall height.
Also, will the width of the tyre change? Wider tyres could actually increase fuel consumption because there would be more resistance from having a larger surface contact area.
See http://www.carbibles.com/tyre_bible.html

tossy

What car is it? did it come with 18's from the factory? If so 16's may not fit.

johndaman66

k_mac wrote: »

1) If you change to a larger wheel size do you get better fuel economy because the car is travelling further for each rotation of the axel?

That is a myth. On the face of it you would certainly think such is the case but in reality it is not. Do bear in mind that larger wheels will inevitably be heavier also (unless one was spending big bucks on light weight wheels) so more fuel is used in this regard. And it is somewhat different to carrying extra "dead weight" on the vehicle when the weight forms part of the mechanical movement between the engine and the road if you understand what I'm saying. On the other hand if you were to change to a larger diameter lightweight wheel and tyre combination and all other variables were to remain constant I'm sure you would get somewhat better fuel economy but chances are you may never see any savings in cash terms even over the life of a vehicle once you take into consideration the rather high cost of lightweight rims. As you mention also if the overall diameter changes your speedometer/ odometer readings will be incorrect. I am not sure if it possible to re-calibrate speedometer/ odometer but then again suppose virtually anything is possible with money:p

I once changed from 195/65/15 to 215/45/17 on a Vectra. Overall the diameter was pretty much the same...very very little in it if you calculate it out but my fuel economy suffered very dramatically due to the wider tyres. Performance suffered also and can't say I noticed any difference in terms of roadholding.

Nissan doctor

kceire wrote: »

OP, why not avoid the potholes? or go around them?

ive had 18" on my previous cars and never had any problems at all!

what exactly is going wrong? are you getting blow outs alot?

i suppose it depends on whre your based though.

I agree, if you have certain wheels on your car, you adjust your driving style to suit. There is no reason for hitting potholes really especially on a road you drive everyday.

IMO damaging your car on potholes etc means your not paying attention to the road.


Cars are a funny thing, I'm always amazed how people can spend so much of their money on something and then not be carefull how they treat it.

MagicSean

Nissan doctor wrote: »

I agree, if you have certain wheels on your car, you adjust your driving style to suit. There is no reason for hitting potholes really especially on a road you drive everyday.

IMO damaging your car on potholes etc means your not paying attention to the road.


Cars are a funny thing, I'm always amazed how people can spend so much of their money on something and then not be carefull how they treat it.

Thanks for your opinion. I'll keep it in mind. Probably don't get any pothole trouble on your high horse? Unfortunately back roads with no lighting can be a real problem for avoiding potholes. They seem to spring up very fast, as fast as they fill them in. A lot of trucks use the road because there's a quarry nearby.

johndaman66

Nissan doctor wrote: »

I agree, if you have certain wheels on your car, you adjust your driving style to suit. There is no reason for hitting potholes really especially on a road you drive everyday.

IMO damaging your car on potholes etc means your not paying attention to the road.

Thats grand in theory but in practice its not so easy regardless of how careful you are, especially if you live around this part of the country:rolleyes:

You may well avoid them for some considerable time if you drive on roads you are well used to but most would have reason to be driving a road they are not familiar with from time to time...at least I would. Also roads here detoriate very quickly. Especially during the Summer when sileage is being drawn. If there is rain at the same time a road that is fine one week could be fooked the following week. Its easier than you think to be caught unawares here hit a crater of a hole before you know it!

Nissan doctor

Its nothing to do with being on a high horse, its common driving sense.

Potholes do not appear overnight, you can clearly see where they will form or are likely to form on a road due to its surface and condition. The road has to start cracking etc before the hole will form so when you get onto a road with a surface like this you expect there to be potholes, and start driving accordingly.

If it happens that you only see a pothole at the last minute and you can't avoid it then you still adjust the car by offloading as much weight as possible off the wheel that's it going to hit the hole buy accelerating(lifting weight off the front) or steering slightly left or right(shifting weight off the required wheel) to reduce the impact as much as possible.

I live on a road that is riddled with potholes so badly that even in a 4x4 you have to pick your way along it and I have travelled the length and breath of the country so I'm well aware of the state of the roads!

johndaman66

Nissan doctor wrote: »

Its nothing to do with being on a high horse, its common driving sense.

Potholes do not appear overnight, you can clearly see where they will form or are likely to form on a road due to its surface and condition. The road has to start cracking etc before the hole will form so when you get onto a road with a surface like this you expect there to be potholes, and start driving accordingly.

If it happens that you only see a pothole at the last minute and you can't avoid it then you still adjust the car by offloading as much weight as possible off the wheel that's it going to hit the hole buy accelerating(lifting weight off the front) or steering slightly left or right(shifting weight off the required wheel) to reduce the impact as much as possible.

I live on a road that is riddled with potholes so badly that even in a 4x4 you have to pick your way along it and I have travelled the length and breath of the country so I'm well aware of the state of the roads!

I for one am not saying or otherwise implying you are on a high horse Nissan Doctor and apologies to you if it appeared as such at any stage. I would agree with you to a certain extent and for the very most part you should be able to avoid them on roads you travel everyday but if you do a lot of driving on different poorly surfaced roads that remain here in parts of West Limerick/ North Kerry chances are you will hit a bad pothole sooner or later...particularly roads you wouldn't necessarily be familiar with. I consider myself a careful driver, never had a fault accident in over eight years of driving, do my very best to avoid potholes but sometimes the inevitable happens regardless of how careful and handy I take it. I have sometimes being on poor twisty roads hitting a pothole is the lesser of two evils...for example drive around a bend in a poor narrow twisty road with another vehicle following closely behind, a large tractor comes towards you...what can you do in a situation like that except kill your speed as best you can in the short space and hit the hole really...sometimes you don't have a choice or the alternative is not fantastic!

Nissan doctor

johndaman66 wrote: »

I for one am not saying or otherwise implying you are on a high horse Nissan Doctor and apologies to you if it appeared as such at any stage. I would agree with you to a certain extent and for the very most part you should be able to avoid them on roads you travel everyday but if you do a lot of driving on different poorly surfaced roads that remain here in parts of West Limerick/ North Kerry chances are you will hit a bad pothole sooner or later...particularly roads you wouldn't necessarily be familiar with. I consider myself a careful driver, never had a fault accident in over eight years of driving, do my very best to avoid potholes but sometimes the inevitable happens regardless of how careful and handy I take it. I have sometimes being on poor twisty roads hitting a pothole is the lesser of two evils...for example drive around a bend in a poor narrow twisty road with another vehicle following closely behind, a large tractor comes towards you...what can you do in a situation like that except kill your speed as best you can in the short space and hut the hole really...sometimes you don't have a choice or the alternative is not fantastic!

My high horse comment wasn't aimed at you.

You are of course right, I'm not saying that its possible to avoid every pothole, but the point I'm making is that on a road that will obviously have potholes, I would be driving slow enough or at least with a mind to expecting them.
The way I look on it is that if you have large alloys you have paid for them, and to replace one and a tyre is likley going to cost you 400-500euro if you do damage one. Then factor in the fact that if you have hit your alloy hard enough to damage it, you will have at least knocked your wheel alignment off and at worst put wear and even damage on your shocks/suspension parts so how that wouldn't be on any drivers mind the whole time he is on a bad road is beyond me.

The way I look at it is my alloys(19" with 35 profile tyres) are worth more then any few seconds gained by going faster on the road and I touch wood that in 8 years driving on alloys with low profile tyres all over the country I've never damaged one yet.