Winter wheel & tyre sizes for 2010 Jazz 1.4 Si

[culzean]

Isn't the difference taken up by the alternate specs of tyre, 175 v 185 as oe.
16" will be wider on the road than 15"?

Please do not mix 'winter' and 'summer' tyres this will put the handling in the ditchfinder class, quite skittish!

I agree completely - it is very dangerous to mix winter and summer tyres as the rubber compound and tread pattern and construction are different.  The level of grip on winter tyres is better than summer tyres on colder road surfaces (generally below 7 to 10 deg C) but actually worse on warmer roads.  This is partly due to softer compound, but mainly due to the many extra 'sipes' (intentional cuts) in the tread on winter tyres which affect the stability of the tread blocks during braking - which can increase stopping distance in warmer conditions.

Mixing summer and winter tyres can give extra grip on one end of the car under either warm or cold conditions, as Interlock quite rightly points out - this can de-stabilise the cars handling to a dangerous degree.

[guest5059]

Isn't the difference taken up by the alternate specs of tyre, 175 v 185 as oe.
16" will be wider on the road than 15"?

Please do not mix 'winter' and 'summer' tyres this will put the handling in the ditchfinder class, quite skittish!

I agree completely - it is very dangerous to mix winter and summer tyres as the rubber compound and tread pattern and construction are different.  The level of grip on winter tyres is better than summer tyres on colder road surfaces (generally below 7 to 10 deg C) but actually worse on warmer roads.  This is partly due to softer compound, but mainly due to the many extra 'sipes' (intentional cuts) in the tread on winter tyres which affect the stability of the tread blocks during braking - which can increase stopping distance in warmer conditions.

Mixing summer and winter tyres can give extra grip on one end of the car under either warm or cold conditions, as Interlock quite rightly points out - this can de-stabilise the cars handling to a dangerous degree.

This also applies to anybody that has different makes of tyres whether they are on the front , rear or even on the same axle. Mine are all the same make 175/65 R15 84T summer and M&S. You need to also give the same advise to those that have different makes of tyres ( that will mean different compound , tread and performance )fitted of which there are lots.


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[guest5121]

Hey all,
Our Jazz has got a set of 185/65-15 winter tyres with spikes on oem steelwheels, runs nice and smooth, does not rub and gives you a bit longer gearing so, it should be good for motorway cruising.
We had 175/65-15 on stock alloys for summer, but for 2015 summer plans are going to get set of 16".

[culzean]

Hey all,
Our Jazz has got a set of 185/65-15 winter tyres with spikes on oem steelwheels, runs nice and smooth, does not rub and gives you a bit longer gearing so, it should be good for motorway cruising.
We had 175/65-15 on stock alloys for summer, but for 2015 summer plans are going to get set of 16".

it may have longer gearing but your speedo is now displaying about 7% lower speed than you are actually traveling at,  may result in a speeding ticket one day soon.

[guest3521]

it may have longer gearing but your speedo is now displaying about 7% lower speed than you are actually traveling at,  may result in a speeding ticket one day soon.

I'm not sure where you get 7% from?, the tyre calculator I use gives a difference in diameter of 2.14% and a speed difference of -2.09% (slower), this may differ very slightly with the make of tyre.
In my experience it would make the speedometer read a bit more accurately as they always read too fast from the factory.
FWIW I'm now running 185/65 15 winter tyres, and have not noticed that big a difference, however I will check it against my GPS's and report back.

[VicW]

In my experience it would make the speedometer read a bit more accurately as they always read too fast from the factory.

For what it's worth, on all three of the Jazz's that I have owned the speedometers were very accurate compared with my satnav indicated speeds.

Vic.

[culzean]

http://tire-size-conversion.com/tire-size-comparison/

according to this site the difference between a 15" 185/65  and 15"  175/65 is over 6%

difference between a 15"  185/55 and a 14" 175/65 is basically nothing,  that is why it's OK to fit the 14" 175/65 winter tyres to a Jazz Si etc that normally take 15" 185/55 tyres

[guest4477]

Hi,i must agree with what Vic as said my Sat-nav and speedo are always spot on the same regardless of what speed i am doing,2007 Honda 1.4

[guest3521]

OK, so I've checked my speedo/OBD/gps and the results are as follows, 65mph indicated on speedo, cruise control set, OBD reading 62mph, 63mph on GPS, as a comparison the standard 185/55R16's the OBD and GPS are the same, so yes there is a slight difference, but not enough to make the speedo slow/low.

[stiggysawdust]

As a retired truck driver, I can verify that Tachographs fitted to trucks are very accurate and they always agreed with my GPS.
When the same GPS unit is used in my jazz it always give a different reading to the Jazz speedo.
At an indicated 64 mph the satnav shows 60 mph
At an indicated 43 mph the satnav shows 40 mph. etc.

[guest3521]

As a retired truck driver, I can verify that Tachographs fitted to trucks are very accurate and they always agreed with my GPS.
When the same GPS unit is used in my jazz it always give a different reading to the Jazz speedo.
At an indicated 64 mph the satnav shows 64 mph
At an indicated 43 mph the satnav shows 40 mph. etc.

Interesting, I'm going to try another GPS to cross check my findings.

[culzean]

GPS speed should in theory be the most accurate,  speedometers in vehicles are normally designed to read up to 10% or more 'fast' for obvious reasons,  but cannot read less than the vehicles speed (again for obvious reasons).

http://gpssystems.net/accurate-gpsbased-speedometer/


the speed of revolution of the wheel will be based on the radius between axle and ground,  this depends on tyre size, tyre wear (about 2% between a new and illegal worn tyre),  how hard the tyre is inflated (which is how the tyre deflation works on a Jazz by counting differing rates of ABS pulses* between wheels, the deflating tyre will have a smaller rolling radius and appear to be going faster than the other wheels. (*not brand new Jazz because they now have pressure sensors in valves).

[applicationcen]

My CoPilot sat nav (in my iPhone) and the Road Angel report the same speeds within a very close margin.

Both of them indicate that every car I have used them in is going a few miles slower than the speedomoter of the vehicle says the car is going.

The car speedo reads 70, speed as reported by sat nav and Road Angel 67mph.
50 relates to 48 mph roughly.

[guest3521]

GPS speed should in theory be the most accurate,  speedometers in vehicles are normally designed to read up to 10% or more 'fast' for obvious reasons,  but cannot read less than the vehicles speed (again for obvious reasons).
http://gpssystems.net/accurate-gpsbased-speedometer/
the speed of revolution of the wheel will be based on the radius between axle and ground,  this depends on tyre size, tyre wear (about 2% between a new and illegal worn tyre),  how hard the tyre is inflated (which is how the tyre deflation works on a Jazz by counting differing rates of ABS pulses* between wheels, the deflating tyre will have a smaller rolling radius and appear to be going faster than the other wheels. (*not brand new Jazz because they now have pressure sensors in valves).

I use a GPS speedometer in my classic cars as they aren't as accurate/linear or stable as modern electronic ones.
What erks me is that the OBD MPH reading is spot on (+/-1digit) and that signal is what is coming from the wheel sensors .

[degzi]

If your in the game for decent winter tyres try http://www.nordiccartyres.com

Highly rated winter tyre.