Going from 60 to 55 profile.

Third Opinion

Third Opinion

Third Opinion

Soldato
Joined
3 Jun 2005
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5,365
Location
West Sussex
My mini suv/crossover uses a strange size of tyre (non XL tyres). They are ridiculously expensive and only have a few tyres available.

It is 80% used totally on road with the odd pretty poor farmers track to deal with.

If I come down a profile from 60 to 55 tyres like halve in price. In fact I could have a set of the old style Goodyear Eagle F1 GSD3's (E marked) fitted for under £250. The cheapest budgets (Nankangs) cost about £280 a set.

Is it legal now and what kind of speedo problems am I like to suffer? The car is chipped anyway for more spirited road driving using the Fiat/Alfa 1.9JTD.

If legal Seems a sensible mod and would improve safety.

I am not worried about gearing as it is 6 speed and feels over geared from about 4th upwards.
 
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It's impossible to say without the rest of the info - size of wheel and width. There are loads of calculators on the internuts on most tyre seller sites to calculate the speed difference. Changing the aspect ratio in itself isn't illegal.
 
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You'll struggle to notice the speedo impact at all but it's worth being aware it's there.

In terms of comfort it's likely that will be reduced a bit but again how much you'll actually notice will be dictated by what the car is like as standard and how good or bad the suspension is.

Personally speaking it'd be a no brainer for me
 
Bear said:
It's impossible to say without the rest of the info - size of wheel and width. There are loads of calculators on the internuts on most tyre seller sites to calculate the speed difference. Changing the aspect ratio in itself isn't illegal.
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Good to hear it is within the law.

The current size is 205/60/16 on an V rating.

I would like to keep the current alloys and go 205/55/16 on a w.

The car has been re-mapped from 120BHp to approximately 155BHP. so tyre upgrade seems safe to me.
 
Third Opinion said:
Good to hear it is within the law.

The current size is 205/60/16 on an V rating.

I would like to keep the current alloys and go 205/55/16 on a w.

The car has been re-mapped from 120BHp to approximately 155BHP. so tyre upgrade seems safe to me.
Click to expand...

It should be fine, it is recommended that you try and keep the difference less than 2.5 to 3% and yours would come to -3.08% so reading 70mph would really be 67.8mph not a big deal really.
 
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Bear said:
It should be fine, it is recommended that you try and keep the difference less than 2.5 to 3% and yours would come to -3.08% so reading 70mph would really be 67.8mph not a big deal really.
Click to expand...

That's assuming his speedometer is already perfectly calibrated, which is unlikely. After fitting 55 profile tyres it could be as bad as -13% out, though it's more likely to be somewhere between those limits in practice.

The engine RPM will also be 3% higher for any given road speed. Ground clearance will be reduced by about 10mm.
 
Third Opinion said:
Good to hear it is within the law.

The current size is 205/60/16 on an V rating.

I would like to keep the current alloys and go 205/55/16 on a w.

The car has been re-mapped from 120BHp to approximately 155BHP. so tyre upgrade seems safe to me.
Click to expand...

What are your tyre options like at 225/55/16? That would be more comparable from a rolling radius point of view and an extra 20mm in width shouldn't cause an issue.
 
Third Opinion said:
My mini suv/crossover uses a strange size of tyre (non XL tyres). They are ridiculously expensive and only have a few tyres available.

It is 80% used totally on road with the odd pretty poor farmers track to deal with.

If I come down a profile from 60 to 55 tyres like halve in price. In fact I could have a set of the old style Goodyear Eagle F1 GSD3's (E marked) fitted for under £250. The cheapest budgets (Nankangs) cost about £280 a set.

Is it legal now and what kind of speedo problems am I like to suffer? The car is chipped anyway for more spirited road driving using the Fiat/Alfa 1.9JTD.

If legal Seems a sensible mod and would improve safety.

I am not worried about gearing as it is 6 speed and feels over geared from about 4th upwards.
Click to expand...
if you drop the aspect ratio down a size then you go up a size in width or diameter. this should give you roughly the same rolling radius as the originals
 
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