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Old 05-16-2009, 04:41 PM   #1 (permalink)
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Changing wheel size?

Hello all,

On my Astra, I've currently got 175/80/14 tyres on steel rims. I will soon need 2 new front tyres. Should I stick with the same size or should I choose a different size? I imagine I shouldn't be having a smaller overall wheel diameter or it'd increase engine speed at the equivalent speed. Keep in mind, where I live, the roads are full of potholes, however I will be driving on highways 80% of the time and they tend to be well maintained here in the UK. Also, my current wheel covers are fairly aerodynamic and it'd be sad to lose those covers.

Other Astras has the following tyre sizes as standard - Vauxhall usually use unusual rim measurements so it'd be easier to get rims off other Astras rather than trying to find non Vauxhall rims that fits my car, but I will consider other sizes.

165/80/14
175/70/14
185/65/14
185/70/14
185/65/15
195/60/15
205/50/16

Thanks for your time in advance!

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Old 05-16-2009, 09:05 PM   #2 (permalink)
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Personally I would stay with the size you have fitted now if you are happy with the ride handling balance.

If they are stock they will be easier to find and usually cheaper as well and you can keep the aero covers too.

If you go to another size what you gain in extra diameter will probably not offset the costs of purchase and you will need new aero covers as well.

just my opinion.

Pete.
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Old 05-17-2009, 10:00 AM   #3 (permalink)
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A larger overall diameter (see Tire size calculator ) will usually help mileage a bit, but choosing low rolling resistance tires is good for a whole 5%.
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Old 05-17-2009, 10:06 AM   #4 (permalink)
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Yes, but I could choose both larger overall diameter AND low rolling resistance tyres. However, I've found that 175/80/14 is rather large already and trying other sizes would actually decrease the overall diameter.

Now just need to bloody finally decide on which tire to choose...

Thanks for your time!
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Old 05-17-2009, 01:27 PM   #5 (permalink)
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Eddles -

I am happy with my one-size-up-from-stock Continental Contact-Pro tires :

http://ecomodder.com/forum/showthrea...ires-2642.html

I deliberately searched for a tyre that was rated at 51 PSI max, which is the PSI I use.

I would consider getting "two-sizes-up-from-stock" next time, but I would have to weigh that against my taller 5th gear.

Question: Do you have freeways with "rain grooves" in the road? If you do, then the "road wiggle" could become annoying. I only hit that maybe 5% of my commute, but it's not enough to bother me.

CarloSW2
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Old 05-17-2009, 01:52 PM   #6 (permalink)
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Thanks for your comment!

I was pleased to see that that website offers pressure information about various tires, as I really wanted to know which tire could be inflated to 51 PSI. Unfortunately, they don't have the EcoContact 3 The EcoContact ESP on there doesn't come in 175/80/14 while the EcoContact 3 does come in 175/80/14 and I still don't know what pressure that tire can be inflated to. I do hope it can be inflated up to 51 PSI otherwise I'll not be too happy.

We don't have rain grooves - I've never seen those before. However highways do tend to get wear in the slow lane (rightmost lane for you) due to trucks, I think the same as the US, and wider tires are more likely to "tramline" in the wear grooves. I experienced this in my old Vauxhall Nova when I changed from 145/something/14 to 195/60/15. Sometimes the wear is severe enough to make 2 narrow shallow rivers which isn't much fun to drive through.

Anyway. Back on topic. Wouldn't increasing the width of the tire decrease fuel economy due to increased rolling resistance and increased frontal profile? Tires with a size of 185/80/14 are unusual, the selection is rather slim. I can't seen any fuel efficient tire with the 185/80/14 size. Oh well, this is probably why Vauxhall chose the 175/80/14 size when making the ECO4. I could go for an 185/80/15 size but this would require new rims which is easy enough to find, but I won't get a fuel efficient tire in this size and I think I'd be better off sticking with a fuel efficient tire in the 175/80/14 size.

Your thoughts?
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Old 05-17-2009, 08:34 PM   #7 (permalink)
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From what I can determine the series around 65 and above are aimed mostly at the "comfort " end of the market where as the lower profiles are marketed for more "sporty" drivers and for both groups FE seems to be a lesser consideration.

Having the larger width tyres will add to the frontal profile (I thought the Astra had an air deflector just ahead of the front wheels?) but the rolling resistance side of it varies from tyre to tyre so that part is not so clear cut.

I am inclined to go with you suggestion of the 175/80-14 if you are happy with them.

HTH , Pete.
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Old 05-18-2009, 01:01 PM   #8 (permalink)
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Unfortunately the Astra don't have the deflectors. However, other models might have it, so I'll have a look out, see if the others has it and if so, I'll see if I can get some off a scrapped Astra.

Thanks for your advice!

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