Technical Speedometer vs. GPS speed

[lukaszbogacz]

Hey folks!!

In my previous daily (Jeep Grand Cherokee WK2) I've managed to change the tire size in a way that the speedometer and the GPS are showing exactly the same speed. It required to increase the overall size dimension from 30,5" to 32" tire. I really like it.

I was wondering if anyone tried that in a Panda. I know that when you have a stock tire size the difference can be significant. I currently run 195/45r16 and it's around 7km/h lower than the GPS. I think that using the size from Panda Cross (175/65r15 or similar size 24" tire) should improve this.

Is there anybody who tried to increase the tire size and tested which tires will actually fit in the wheel well? for the 16" i want to go for 205/50r16 but not sure if it will be be too wide. Any suggestions will be more that appreciated

 

[bugsymike]

You also have to check the offset of the new wheel re clearance.
There are several websites that can give details of which options work and how the rolling circumferance affects road speed.

 

[Mike1alike]

Your experiment sounds interesting.
Can't help you there, sorry.
But I'm watching it.

 

[bugsymike]

Your experiment sound interesting.
Can't help you there, sorry.
But I'm watching it.

Sometimes only trying to fit the wheel will prove one way or another.
I had a Skoda Scout 4x4 on 17 inch wheels but saw a cheap set of Audi TT wheels that physically went on the studs, but the offset meant the rim even without a tyre hit the suspension.
In the end I went for a slightly wider 17 inch tyre but with a higher profile also and got a comfortable ride, however I did have to fit black Powerflex front wishbone bushes as they controlled the movement of the front wishbones much better than new standard bushes which if braking going into a bend allowed the tyres to "kiss" the edge of the wheel arches.
After fitting I was also pleased to see speedo and GPS matched as speedos tend to be over generous, mind you that does mean no lee way re speed cameras.

 

[Mike1alike]

Sometimes only trying to fit the wheel will prove one way or another.

That's exactly what I was thinking!

 

[lukaszbogacz]

You also have to check the offset of the new wheel re clearance.
There are several websites that can give details of which options work and how the rolling circumferance affects road speed.

Thinking about sticking to factory wheels, not looking to spend too much on this. Currently I have the factory Panda Sport 16 inch rims and also a set of 15 inch steelies. This is what I was able to “measure” using the internet:

I could also get a bit narrower wheel like 185/55r16 and this will be also 24 inch tire with a slight increase of width comparing to the 15 inch one:

No rush on this as I’m currently on All-Season tires which act pretty ok in the cold and wet Polish winter. I want to get this done closer to the summer period.

 

[bugsymike]

There are so many variables all you can really do is try a friends wheels if possible.
Wheel rim width as well as off set can affect how close a tyre gets to the suspension or wheel arch, as well as the tyre profile etc.
I wouldn't go for anything that involves spacers as they put undue strain on mounting bolts/studs and wheel bearing etc.
At the moment if your speedo and GPS don't match you don't no exactly what rolling circumferance you need to be aiming for, so without that as a starting point best tyre width etc. is only a guess.
Another point is what might seem a good choice may make handling horrible in different conditions.

 

[lukaszbogacz]

There are so many variables all you can really do is try a friends wheels if possible.
Wheel rim width as well as off set can affect how close a tyre gets to the suspension or wheel arch, as well as the tyre profile etc.
I wouldn't go for anything that involves spacers as they put undue strain on mounting bolts/studs and wheel bearing etc.
At the moment if your speedo and GPS don't match you don't no exactly what rolling circumferance you need to be aiming for, so without that as a starting point best tyre width etc. is only a guess.
Another point is what might seem a good choice may make handling horrible in different conditions.

For sure what will fit is 175/65r15 since a lot of Pandas have such tires. I know that on this size the overall speed difference between the gauges and the GPS is reduced to 2 km/h. I’m aiming to achieve that with my 16” wheels as well.

 

[bugsymike]

For sure what will fit is 175/65r15 since a lot of Pandas have such tires. I know that on this size the overall speed difference between the gauges and the GPS is reduced to 2 km/h. I’m aiming to achieve that with my 16” wheels as well.

So presumably that will involve a lower profile tyre where you have to compromise between better handling and a harder ride on bumpy roads.

 

[Greasytrucker]

My lad had a Mk1 Fabia and we bought a set of Mk1 Octavia wheels 16’ as Octavia wheels were much cheaper than Fabia VRS wheels. The higher profile tyres designed for the Octavia actually made the speedo bang on although we did have to remove a small piece out of one of the rear arches (just one side weirdly) to get them to fit without fouling. When he wore them down we then put the correct size tyres (same as VRS) on the rims and although it obviously put the speedo out slightly again, the handling was so much better!

 

[bugsymike]

My lad had a Mk1 Fabia and we bought a set of Mk1 Octavia wheels 16’ as Octavia wheels were much cheaper than Fabia VRS wheels. The higher profile tyres designed for the Octavia actually made the speedo bang on although we did have to remove a small piece out of one of the rear arches (just one side weirdly) to get them to fit without fouling. When he wore them down we then put the correct size tyres (same as VRS) on the rims and although it obviously put the speedo out slightly again, the handling was so much better!

Another point is the Octavia wheels if they had original tyres may have been designed for a heavier vehicle so less flexible causing handling problems.
When hard up I had a Ford Mondeo and put s/h Ford Transit tyres on it, 185x14, it drove well but less forgiving on a wet bend.
Bearing in mind many cars I drove as an apprentice late 60s were often fitted with remould crossply tyres fitted on six cylinder Fords and Vauxhalls and yet the worst tyres I used were brand new Russian ones in the mid 70s from Moskvich I used on an old Singer Gazelle I was driving, they were free as being a Dealer we used to fit English tyres to make them more sellable???
However the tyre quality was so bad they were moulded eccentric, so slightly like the "clown cars" going up and down as you drove along.
Even the Russian ones on the Lada 1200s, which though marginally better quality certainly helped you brush up on "cadence braking" before the advent of ABS especially diving into a tight bends in the wet whilst out road testing brand new cars after their pre delivery inspections.

 

[Greasytrucker]

Another point is the Octavia wheels if they had original tyres may have been designed for a heavier vehicle so less flexible causing handling problems.
When hard up I had a Ford Mondeo and put s/h Ford Transit tyres on it, 185x14, it drove well but less forgiving on a wet bend.
Bearing in mind many cars I drove as an apprentice late 60s were often fitted with remould crossply tyres fitted on six cylinder Fords and Vauxhalls and yet the worst tyres I used were brand new Russian ones in the mid 70s from Moskvich I used on an old Singer Gazelle I was driving, they were free as being a Dealer we used to fit English tyres to make them more sellable???
However the tyre quality was so bad they were moulded eccentric, so slightly like the "clown cars" going up and down as you drove along.
Even the Russian ones on the Lada 1200s, which though marginally better quality certainly helped you brush up on "cadence braking" before the advent of ABS especially diving into a tight bends in the wet whilst out road testing brand new cars after their pre delivery inspections.

Could have been the fact that the Octavia tyres were over 10 years old as well, bit tough me thinks

 

[bugsymike]

Could have been the fact that the Octavia tyres were over 10 years old as well, bit tough me thinks

But the price was right.

 

[Greasytrucker]

But the price was right.

£120 with 4 tyres each having 5mm+

 

[bugsymike]

£120 with 4 tyres each having 5mm+

Many of my early cars cost less than that, though I fear we are going slightly off topic.

 

[Greasytrucker]

Many of my early cars cost less than that, though I fear we are going slightly off topic.

Off topic on FF? Nah don’t believe it

 

[A3jeroen]

Don't go 2 sizes up. Either 205/45 or 195/50. Not both. And (as shown above) there are internet tools that let you compare sizes.
On my 100HP I had 195/50 instead of 195/45 and that made GPS and cluster almost the same.
There is however a reason why manufacturers choose to have a higher speed in the instrument cluster.

gr J

 

[lukaszbogacz]

Don't go 2 sizes up. Either 205/45 or 195/50. Not both. And (as shown above) there are internet tools that let you compare sizes.
On my 100HP I had 195/50 instead of 195/45 and that made GPS and cluster almost the same.
There is however a reason why manufacturers choose to have a higher speed in the instrument cluster.

gr J

And this was something I was looking for. Thank you.

I'll stick to your recommendation. 195/50r16 is basically a 23.7" tire:

As for the 15" ill get a bit slimmer tire. I think this will be a perfect setup for my need.

Thank you!!