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tyre sizes for an auto to improve top speed

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mabbo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mabbo Quote  Post ReplyReply Direct Link To This Post Topic: tyre sizes for an auto to improve top speed
    Posted: 05 Sep 11 at 19:27
hello

i have a 2.1 auto t3 and would like some taller tyres to improve the top speed / lower the rpm whilst on the motorway. 

at the moment it had some 15" penta's with 205/55r15 i think... they might be 50s. i cant remember

ignore the wrong colour door :( 

anyway, would changing to a 205/60 or 65 make much of a difference? how much of a diff would it make to driving around town?

cheers
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve B Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 11 at 19:39
The correct tyre for 15's is either 195/70/15,205/65/15 or 215/65/15 depending on the wheel width?

By fitting any of those size tyres it will only improve your current set up....plus the tyres you're running at present are more than likely car tyres and aren't load rated for a T3.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote chris7ian Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 11 at 19:42
I'm interested in upping the rear tyres on my 2.1 auto too  - how much bigger than stock is feasible?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mabbo Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 11 at 21:53
cheers steve


i thought the standard tyre size is 185r15, which give a overall diameter of 659mm

195/70r15 = 654mm
205/65r15 = 648mm
215/65r15 = 661mm

ill have to check but im sure my tires are 205/55r15 = 607mm so quite a bit smaller than the above. might get them changed to 205/65r15

cheers

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve B Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 11 at 22:00
The T3 standard tyre size is 185R14 which is 654mm.

There's also a tyre calculator in the information section....click on the Brick-Yard logo top left.






Edited by Steve B - 05 Sep 11 at 22:02
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mabbo Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 11 at 22:07
i cant remember the width off the top of my head, ill have to check but iv got a feeling they are 6J
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve B Quote  Post ReplyReply Direct Link To This Post Posted: 05 Sep 11 at 22:25
205's will be fine on 6" or 7" wide alloys.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mabbo Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 11 at 09:54
Just checked, they are 205/50r15 and the wheels are 15x7

my wheels/tyres are 586mm, if 185R14 is 654mm then thats a pretty big difference

ill get them changed at some point :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve B Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 11 at 10:04
I'd say change the rears a.s.a.p as it will help your gearbox as well as your pocket.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote niko Quote  Post ReplyReply Direct Link To This Post Posted: 06 Sep 11 at 13:08
im going to have a tdi engine soon....and may stick with the stock gearbox for a while.
 
my tyres are currently 225 60 16.....what practical difference would 17" wheels make...with maybe a 65 profile.
 
i have seen the calculator to work out diameter.....but what would 20,30 or even 50mm difference make to cruising speed.
 
this stuff is complicated to the unitiatated...
 
i have looked at gearbox codes too without much success....what does the final drive mean in simple terms....what do people go for when they have a refurbed box (aka Aidan T)....
 
any help appreciated
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Post Options Post Options   Thanks (0) Thanks(0)   Quote samuelvincentvella Quote  Post ReplyReply Direct Link To This Post Posted: 09 Jan 12 at 11:49
Nikko and Mabbo
 
I have worked on getting a final drive ring and pinion made up for chaps like us with mopre powerful engines. Stock auto final drives are either 4.09 or 3.27. I have the new 3.27 in my auto with my 2.5 subaru. It has dropped the revs by about 800rpm on the motorway and I'm elated with it.
 
We just put in an order for 60 and most are going to the US, but I kept a few here for UK guys. It'll solve the rpm issues without putting stupid big tyres on the rear.
 
Let me know of youre interested.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote niko Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 12 at 19:52
wish i had known about 6 weeks ago...bit late for me now.
 
but thanks for the tip off.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Diablodub Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 12 at 20:47
Niko with those tyres you speedo will show 52 when doing 70 , 25% drive ratio change , total change in ride height is 68mm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tee3 Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 12 at 21:00
Originally posted by niko niko wrote:

wish i had known about 6 weeks ago...bit late for me now.
 
but thanks for the tip off.

Is yours an Auto? Hows that work with the TDI?



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Post Options Post Options   Thanks (0) Thanks(0)   Quote samuelvincentvella Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 12 at 21:43
Been here for 18 months ;)

http://www.brick-yard.co.uk/forum/auto-rp-group-buy-calling-subaru-auto-owners_topic55350.html
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Post Options Post Options   Thanks (0) Thanks(0)   Quote niko Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 12 at 22:14
Originally posted by Tee3 Tee3 wrote:

Originally posted by niko niko wrote:

wish i had known about 6 weeks ago...bit late for me now.
 
but thanks for the tip off.

Is yours an Auto? Hows that work with the TDI?


 
no..sorry...mines not an auto....excuse my ignorance...does this only work for an auto ?


Edited by niko - 10 Jan 12 at 22:20
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Post Options Post Options   Thanks (0) Thanks(0)   Quote niko Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 12 at 22:22
Originally posted by Diablodub Diablodub wrote:

Niko with those tyres you speedo will show 52 when doing 70 , 25% drive ratio change , total change in ride height is 68mm
 
hi Diablodub..
 
sorry ...dont have a clue what you mean.
which tyres...and which drive ?
 
most of this stuff is complete mumbo jumbo to me ?LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote niko Quote  Post ReplyReply Direct Link To This Post Posted: 10 Jan 12 at 22:26
this is where im at
 
having 215 65 16 tyres fitted on the rear on saturday. (205 65 16 on the front)
 
im pretty happy with my set-up now ...but i know my current tyres are not right ( they are actually 205 55 16 (not 225 like i said months agoEmbarrassed...i was talking pissed up then)
 
i used the calculator and i think im not far over stock. (just about 5%...but about 8% from where i am with my current "small" tyres)
 
therefore the new tyres should only improve things....
i hope this makes some sense.


Edited by niko - 10 Jan 12 at 22:36
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Diablodub Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jan 12 at 06:12
The difference between 185/70/15 and 215/65/16 , actual speed 70 , speedo reading 65.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote niko Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jan 12 at 08:06
Originally posted by Diablodub Diablodub wrote:

The difference between 185/70/15 and 215/65/16 , actual speed 70 , speedo reading 65.

gotcha....thanks for that....
if my fronts are 205 65 16 ...and thats where the speedo takes its reading from ???.will that make it closer to true?
 
cheers
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