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Model specific boards => Golf mk3 => Topic started by: snaps on 14 March 2007, 14:44

Title: 97/p Tyres
Post by: snaps on 14 March 2007, 14:44

on the stock alloys it came with 205/50/15 Ditch Finders  :laugh: i have a set of Eagal F1's that are 195/50/15 on my 1.4 which is parked up, can i swap them im not bothered about the 1.4 as thats not being driven, but will my 97/p be ok, i know the earlyer gti's were fitted with 195's but dont know about the wheels  :undecided:

there the wheels..

(http://www.npuk.net/storage/gti6.jpg)

Title: Re: 97/p Tyres
Post by: patch900 on 14 March 2007, 20:06

No reason why they wont fit, overall rolling radius will be affected slightly but shouldnt alter the speedo

Title: Re: 97/p Tyres
Post by: boneybradley on 15 March 2007, 09:26

I have 195's on the front of mine (due to last owner finding they were much cheaper) and have no problem's

Title: Re: 97/p Tyres
Post by: Len on 15 March 2007, 09:44

Quote from: patch900 on 14 March 2007, 20:06

No reason why they wont fit, overall rolling radius will be affected slightly but shouldnt alter the speedo

No more so than 5mm tread to 1.5mm tread!

Title: Re: 97/p Tyres
Post by: rubjonny on 15 March 2007, 09:54

your speedo will over-read by a tiny ammount, at 59mph, your speedo will say 60mph  :grin:

http://www.miata.net/garage/tirecalcold.html

Title: Re: 97/p Tyres
Post by: patch900 on 15 March 2007, 11:05

Quote from: Len405 on 15 March 2007, 09:44

Quote from: patch900 on 14 March 2007, 20:06

No reason why they wont fit, overall rolling radius will be affected slightly but shouldnt alter the speedo

No more so than 5mm tread to 1.5mm tread!

whenever anyone changes their alloys to say 17" from 15" they will also affect radius and speedo

Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
205/50-15         4.0in  11.5in    23.1in         72.5in        874        0.0%
205/40-17         3.2in  11.7in    23.5in         73.7in        860        1.7%

So the speedo will also be out 1mph with these on

Title: Re: 97/p Tyres
Post by: Len on 15 March 2007, 11:13

What about 215/40 on 17's then patch?

And are you allowing for vehicle weight deflecting the tyre?

Oh and correct tyre pressures?

Title: Re: 97/p Tyres
Post by: rubjonny on 15 March 2007, 11:16

215s would be 3% too slow, use the tire size calc link I posted ;)

Title: Re: 97/p Tyres
Post by: Len on 15 March 2007, 11:23

Wow! I always thought it was the other way around!!!!

So Johnny to your knowledge what revs should I have a t certain speeds?
At 85mph my revs show about 3550/3600 and at 90mph revs show 4080/4100.

Is this a result of my tyre sizes?

Title: Re: 97/p Tyres
Post by: patch900 on 15 March 2007, 11:42

Hi Len,

jonny already posted back, I just used his link to compare. I have always wondered how much it would change the speedo readout.

Nice link jonny, cheers.

Title: Re: 97/p Tyres
Post by: rubjonny on 15 March 2007, 11:47

tire size will also affect things like your top speed, rpm at certain speeds and also accelleration.  With a smaller rolling radius your accelleration will be better, but you will loose out on top speed.

For the sizes we're talkign about here though the difference wont be that noticable.  If you want to see how tire rolling radius affects speed & rpm, check out this gearbox calculator:

http://www.aufg48.dsl.pipex.com/speed-ratio.html

The ratios listed are not 100% accurate, but if you know the gear ratio & FD of your gearbox you can play with different tire sizes and see what happens :)

Title: Re: 97/p Tyres
Post by: Len on 15 March 2007, 11:49

Thanks Jonny will check it out when I know the ratios.