Lighter wheels?
- Thread starter A2Steve
- Start date
bretti_kivi
Member
Personally, I saw a 15% improvement. Jigsaw reported 20%+ improvement. I dont see this as "hardly noticeable"...
Agreed that 16s are probably the best compromise, probably because this
that extra sidewall gives more protection against potholes than the rubber bands on the 17s!
is also true. But I don't see the "sidewall flex" as an issue, really; if you compare winters vs. summers you're comparing apples and pears - but even doing that, I don't see how you're going to see any benefit whatsoever until serious speeds. Everything else is going to be dampers and springs. Besides, I see a different issue here: a Goodyear F1 tyre will have a stiffer sidewall (probably) than a Goodyear Efficient Grip, because it's intended to be a handing, sporty, performance tyre. Simply saying "any 195/55 will have less stiff sidewalls than 195/50" isn't really enough.
I think you'll find a benefit shifting from the S3 rims to something like those Momo Corses, because you'll drop from 20+kg per corner to closer to 16. I'd estimate a nicer ride, and around 5-10% increase in MPG from that change alone.
Birchall
Dick Chown Award 2016
If that is what you achieved then I can't argue with that, I know you tell it as it is.
But if you look at the "science", the saving in weight in total is not huge and the slightly narrower width is also small.
So in theory the difference in weight is not 20% of the car's weight, more like 2%, so scientifcally that saving cannot be 20% due to just the weight alone.
As for the width, there is an even smaller difference in width and so the drag is not affected to any large extent.
I don't doubt your improvement though, of course, but I would imagine that it was due to other factors.
Improvements in MPG can only be judged after lots of journeys because there are so many influencing factors, varying temperature, varying gradients, driving style etc.
So we can perhaps agree to disagree on this one, but I do agree with the saving, but not the extent of that saving.
I also agree that the 16" wheels are the best compromise (and cosmetics also play a part).
I also agree about the sidewall stiffness.
I just changed from economy (cheap) tyres and the difference in tyre wall stiffness was significant. The Vredestein 215 35 18s are noticeably softer and quieter
Steve B
Birchall
Dick Chown Award 2016
Funnily enough my local tyre fitter was singing the praises of Vredestein recently.
I normally don't, because tyres are rarely exceptional, yes, you get good and bad of course, but these have been the best tyre I have had (on a normal road car that is!). Even better that the Goodyears I had on an earlier set of wheels (same size 215 35 18s).
They are the quietest I have had on an A2 too.
Steve B
fbi
Member
Bret,
Well, I said that my winter tyres are 15" (195's) just to point out that I switch(ed) from 15" to 17" (205's) and 17" to 15" once a year, so my view is not just based on old memories, but on all the swaps I made...
Speaking of memories, my first A2 came with 15" alloys and summer tyres, but narrower (175 = OEM). So, less grip than wider tyres, and flexy sidewalls. Maybe less noticeable because of less grip than 195's.
No serious speed, really. Just a tight bend on a dry road, there is a hell of a difference between 15" and 17" (but in comfort too !)
You are right, there are different range of tyres, and sportier models must have logically stiffer sidewalls.
Steve,
from my experience, the increased weight of the wheels is really noticeable when accelerating and braking. You really "feel" the higher inertia of the wheels.
Re. fuel economy, at steady speed, only the rolling resistance and aerodynamic drag matter. And width is of course a key factor for both. (With the same rubber compound,) a wider tyre will affect fuel economy.
The accelerations with heavier wheels affect also fuel economy.
So the difference in fuel economy depends on the type of journeys...
Ritchtea
Member
in the bike world un-sprung mass (wheels tyres) is big for performance gains, always quoted as every kg saved un-sprung is worth many more times sprung weight.
The handling will also benefit from less inertia.
I'm bias though as a pepperpot adaptor went from 17's to Pp pots. can see the sense in people saying 16's are a good compromise just don't wright off (with tyres) a 5kg per corner un-sprung weight reduction.
The handling will also benefit from less inertia.
I'm bias though as a pepperpot adaptor
went from 17's to Pp pots. can see the sense in people saying 16's are a good compromise just don't wright off (with tyres) a 5kg per corner un-sprung weight reduction.
Birchall
Dick Chown Award 2016
As you say, the sprung / unsprung difference is noticeable as far as handling / suspension reaction, that is for sure.in the bike world un-sprung mass (wheels tyres) is big for performance gains, always quoted as every kg saved un-sprung is worth many more times sprung weight.
The handling will also benefit from less inertia.
I'm bias though as a pepperpot adaptor
I am just not so sue that the economy savings are huge, after all a difference of 20 kilos is the same as a small child. I would hope that having my small grandson in the car would not have a 20% fuel disadvantage?
Steve B
Ritchtea
Member
Steve,
The 20% may not be due to weight alone the combined effects, might be like that of a remap because un-sprung weight effects acceleration, handling and breaking the engine's work load is less??
The 20kgs is un-sprung remember may have the effect of 100kgs sprung? ask the smallest grandson to throw you out and note the fuel saving!?
Lee.
The 20% may not be due to weight alone the combined effects, might be like that of a remap because un-sprung weight effects acceleration, handling and breaking the engine's work load is less??
The 20kgs is un-sprung remember may have the effect of 100kgs sprung? ask the smallest grandson to throw you out and note the fuel saving!?
Lee.
6stings
A2OC Donor
in the bike world un-sprung mass (wheels tyres) is big for performance gains, always quoted as every kg saved un-sprung is worth many more times sprung weight.
The handling will also benefit from less inertia.
I'm bias though as a pepperpot adaptor
Maybe in the bike world.
In the car world, less un-sprung weight means more comfort, but the handling can not benefit from that. Less un-sprung weight means less control.
Correct me if I'm wrong.
Birchall
Dick Chown Award 2016
Steve,
The 20% may not be due to weight alone the combined effects, might be like that of a remap because un-sprung weight effects acceleration, handling and breaking the engine's work load is less??
The 20kgs is un-sprung remember may have the effect of 100kgs sprung? ask the smallest grandson to throw you out and note the fuel saving!?
Lee.
Please don't get me wrong, I am trying to figure it out mathematically and I cannot see how something moving up and down (i.e. unsprung) can increase or decrease in weight. It surely only affect the damping (i.e. less weight to move up and dowm) how does that affect the economy?
Surely the MPG is only affected by the weight being carried (including the wheels.
Yes, I can understand a slight effect on accelleration because it has more mass to spin up , but again, mathematically that cannot be a huge difference. your 0 to 60 would not be improved by 20% by fitting a set of wheels 20% lighter? (The total overall weight of the car is only slightly reduced percentage wise.)
So I am hoping that someone can explain why I am wrong so I can correct my logic , not to argue a case., so please don't take any of this personally.
Do we have any mathematicians, scientists on here that could help educate me with some factual logic?
Steve B
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Birchall
Dick Chown Award 2016
Surely it WILL help handling, because a heavier wheel will have more kinetic energy when hitting bumps etc. and so would bounce more?
A lighter wheel would spend more time planted onto the surface due to less bouncing (again, not hugely, but slightly at least) that would help a little when cornering perhaps?
Steve B
Birchall
Dick Chown Award 2016
Yes, I think that in general, in the UK we refer to handling as being related to cornering and track grip etc. especially when turning.
Comfort is another thing altogether and is more related to smooth running over bumps in road use.
Steve B
bretti_kivi
Member
Wikipedia explains it well: https://en.wikipedia.org/wiki/Unsprung_mass
Less unsprung mass means the wheel is more likely to be actually pushed back to the ground by your suspension strut.
I personally run 185/60R15 winters and 195/50R15 summers and feel the massive difference between the sidewalls whenever I change. But it's apples vs. pears, and I'm unconvinced a 205/40R17 on a 7J rim will be any squidgier than a 195/50R15 on a 7J rim.
My numbers are from long term running. I have at least the initial summer change from 17 to 15 and hit 6.6 over 6000km of high-speed running in Europe, down from 7.0 here. That's gone down with the TD Pro Race 1s to around 6.3 long term average. Winter is a different story.
- Bret
Less unsprung mass means the wheel is more likely to be actually pushed back to the ground by your suspension strut.
I personally run 185/60R15 winters and 195/50R15 summers and feel the massive difference between the sidewalls whenever I change. But it's apples vs. pears, and I'm unconvinced a 205/40R17 on a 7J rim will be any squidgier than a 195/50R15 on a 7J rim.
My numbers are from long term running. I have at least the initial summer change from 17 to 15 and hit 6.6 over 6000km of high-speed running in Europe, down from 7.0 here. That's gone down with the TD Pro Race 1s to around 6.3 long term average. Winter is a different story.
- Bret
Birchall
Dick Chown Award 2016
I certainly don't doubt you or your figures, but MPG can vary so much, especially with things like different tyres having different rolling resistance and different tyre pressures when you have swapped them over.
Could it be that the wheels have different tyres and or pressures compared to the others?
Steve B
Could it be that the wheels have different tyres and or pressures compared to the others?
Steve B
bretti_kivi
Member
"Long term" means over the course of several years in the case of the 17"s - they were fitted in Spring 2004 and removed in Summer 2009, and then another five years in the case of teh TDs, bought in 2010 and kept since then. Pressures are similar in both, though the 17" actually had 2.4/2.7 at one point, which is undriveable with the 15s on gravel. They're currently at 2.2 / 2.5 or so. Which is in favour of the 17s....
I drive stuff which is give and take, lots of country roads at 50-60mph, relatively little autobahn except to the airport and back. The improved ride was an additional bonus.
Officially my car has an average on the data tag of 6.3, I think, with S-Line 9-Spoke rims. I have always had 6.9-7.0l/100 during the summer season with 17s.
I am so looking forward to next summer with the light rims and the full B8 pack....
- Bret
I drive stuff which is give and take, lots of country roads at 50-60mph, relatively little autobahn except to the airport and back. The improved ride was an additional bonus.
Officially my car has an average on the data tag of 6.3, I think, with S-Line 9-Spoke rims. I have always had 6.9-7.0l/100 during the summer season with 17s.
I am so looking forward to next summer with the light rims and the full B8 pack....
- Bret
6stings
A2OC Donor
Than I was right. Lower wheel weight means good comfort and not good control/handling.
The fuel economy? I bought a 12 year old car for about £5000, had it fixed for at least £10000 so far, top-insured for £1200 a year, well, how economic should I drive to get even
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bretti_kivi
Member
Improves control, too, because the damper has less to do. It's win-win. The only reason for big wheels in motorsport is the brakes...
- Bret
- Bret