I remember reading a thread on this some time ago, but I would be interested in other peoples experiences.

I recently swapped the alloys on my 96 turbo to the later style 16"s. The car feels much 'flatter' during cornering, and the grip levels are definately higher (could be the new tyres).

However:

a)steering feel does seem reduced (gyroscopic effect of heavier wheels?)

b)road noise is up

c)tramlines at slow speeds

d)mpg is down (from 290 a tank to 265)

Of coarse, the new wheels do look better!!

Has anyone else seen any of this?

Cheers, Martin

Martin,

a) the whole wheel/tyre mass should be about the same. Plus the overall circumference should be the same - see d)

b) less squashy tyre to absorb the noise!

c) what width are the new tyres? I thought the 15s and 16s were the same width (205) so there shouldn't be a huge difference.

d) what size are the new tyres? If they are the same diamter then this should not be affected.

When I picked up my car on 16s the previous owner had fitted 205/45-16 tyres. And the mpg seemed brilliant - nearly 300 miles to a tank. Swapped them for the proper size (205/50-16) and all was back to reality...

Dave

thanks for your comments

The tyres are the standard size and you are right to say the diameter is the same. I have tried upping pressure to 34psi all round but no real difference (except car felt less planted)

When I fitted them I could feel a weight difference with the 15" wheels, but I have done this on other cars and not noticed any difference in mpg.

The lower profile exagerates the tramlining, I think, because of reduced flex, (which also accounts for the handling benefits).

The only problem is the decrease in mpg when your car does loads of miles every year! I feel this must be the extra weight (or maybe the Bridgestones 'drag' more).

I could comfortably make 290 miles by middle bar of 'E' on gauge. Now its about 265 (I thought I pushed on, but some of you guys must be flying!!)

Cheers, Martin

Martin,

The gyroscopic effect will be increased, because even if the weight and circumference is the same, the mass is distributed further towards the edge and away from the centre with the larger wheels

Interestting that you got more mpg with lower profile and therefore lower gearing, usually you would expect better mpg with the higher gearing

Paul

The tyres are the same diameter (with a couple of mm) for 15 and 16 inch wheels so the gearing is almost the same.
Dave

Dave

Sorry, wasn't very clear, I mean't the differnce between 45 and 50 profile tyres on your 16" wheels

Paul

Hi Paul,

Ok I see now. What I was getting at was that the lower gearing meant that the odometer said I was getting nearly 300 to the tank. Back to the 50s and the correct mileage came up - back to more like 200 to the tank.

dave

PS: since ran the tank empty/near empty a couple of times and I'm now confident o do 260 on a tank with the guage way below the empty mark. I've found that it misfires for a good 8 miles before running out....

So, do you think that because the 16" wheels are a tiny bit bigger in diameter, they rotate
less times for a given distance?

That would mean my trip meter showing a lower reading for a given distance, giving the
illusion of less mpg (also a great way to keep the miles down (20k a year, ouch)

It would also mean my speedo is out, I will check this if I can get my wife to follow me.

Cheers

From memory - 15" tyre sizes are 205/55-15.

Diameters: 15" - 606.5mm
16" - 611.4mm
Or 0.8% larger. But your odometer readings are nearly 10% different. So it must be something else.

Driving style? Attacking those corners faster with the larger better handling wheels...? Air filter clogged? You sure you have the correct tyres?? 205/50-16?

Dave

Do you think a combination of new tyres (+2mm tread) plus higher tyre pressures could account
for the difference?

Cheers

Hi

You are right about 15"s having 205/55. I have also checked my 16"s & I definately have 205/50s on them.

It is interesting how most people (I assume with the larger wheels) report lower fuel consumption than I got with my 15"s. I never had to fill before 290 showed on the trip.

Cheers

Interesting I did the same change last week I also put new tyres on (t1S) and had the geometry all checked/adjusted as well. So I have changed several things at once and the things I have noticed are:
1. Road noise is now intrusive (especially as mine is 5 door)
2. Doesn't tram line any more especially at the 3 mile cross roundabout onto the A33
3. Understeers far worse than the 15's, but this could be the geometry or the tyres.
4. never noticed cats eyes were so big before http://bbs.scoobynet.co.uk/wink.gif

Sheridan,

Cats eyes - you should try the 17s with 215/40 tyres - they're REALLY big with those tyres...

As for the understeering - have you had Prodrive geometry settings done? If not then these make a big difference.

See the FAQ for details.
Dave

The dealer who did my alignment said they would only do the prodrive settings if you had the prodrive suspension. however I am glad I had it done the settings were out anyway.

so has anyone drawn any conclusions? I am starting to wonder if the 15" wheels and the spare cash spent on better tyres might give me the best driving, (although the new alloys look soooo much better) - Then again, I guess I didn't buy it for its looks!

I would definately agree that road noise is worse on 16"s and my car never tramlined at all with the 15"s.

It occurs to me that by the time Subaru made 16"s standard the suspension had been stiffened somewhat. This probably compensates for the extra unsprung weight of the bigger wheels.

Cheers, Martin

Martin,

I'd check out the geometry - go for Prodrive settings and see what difference it makes. If this hasn't been checked then it'll probably be out anyway. It *could* be the lower/stiffer sidewalls casuing it - in which case surely the improved handling is worth the hassle?

Maybe it's your make of tyre? What make did you fit?

Dave

The tyres are the standard Bridgestones (only 1k on them now).

The only real problem is extra fuel cost when you do 700 miles odd a week. I can live with everything else because the car does corner better.

I will check the speedo accuracy this weekend against my other car & let you know if this is the cause.

I probably shouldn't complain too much as 265 miles per tank seems pretty good compared to some.

Cheers, Martin

Just to fill you all in on the latest

- My wife took the car for a while and got 300 miles on a tank - whoops I guess that was me having fun then...

- My dealer told me that the standard fit 16" Bridgestones have a VERY hard sidewall, (they are hard to change apparently). They believe that this increases both road noise AND the tramlining tendency.

-The dealer also suggested that the tramlining can be greatly reduced by adjusting the geometry settings. They have apparently experimented with this and found a setup they feel works best. They also think this reduces tyre wear.

-I can vouch for this reducing tramlining because I just bought a second Impreza (96 5 door) with this setup done. This car is a lot less nervous over bumps than my saloon...

Cheers