mad_mike
Member
Registered: 2nd Dec 02
Location: uk, Mansfield
User status: Offline
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will 15" or 17" alloys slow me 1.2 down by a lot?
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Gambit
Member
Registered: 5th Jun 00
Location: Common Sense HQ
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your acceleration will be non existent with 17's!! you still feel a bit of a drop on 15's
but your car is slow as anyhow, so acceleration is already non-existent!
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Blue
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Registered: 24th Feb 03
Location: Sideways
User status: Offline
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Am I not right in thinking that it shouldn't really be affected that much? Yeah, it defo will be with 17's because it's such a big difference but when you go up a size in wheel you come down a size in tyre so - overall the rolling diameter will be near the same on 15's or even 16's
Sure I read it somewhere but then it completely goes against what I thought and what everyone says.
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Icy
Member
Registered: 31st Jan 01
Location: Edinburgh Drives: Mk3 Golf Gti
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ok here my speeds i got on mine
14s top speed on flat 93 downhill 100
15s 90 95
17s 85(usualy under80 tho) 90
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Rover Steve
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Registered: 5th Mar 03
Location: stafford uni
User status: Offline
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had my mates 17's on my car here are the speeds :-
15" - 150mph then off the clock
17" - 150mph then off the clock 
As long as you keep the rolling radius similar, the only thing slowing you is the width of the tyre.
Ste
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Adam_lee
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Registered: 23rd Apr 02
Location: Manchester
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ICY, You recon its slower with 17" wheels on but maybe its no diffrent at all? To effect the car's speed the rolling diameter of the wheel must be longer than the standard and hence your final drive ratios would be slightly effected. On the other hand your clock would say 85 when your doing much more becouse one revolution of the wheel is covering more distance. It probably all balances out.
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Icy
Member
Registered: 31st Jan 01
Location: Edinburgh Drives: Mk3 Golf Gti
User status: Offline
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no coz was drivin with mate on 17s 1,4 16v phoned him at 80mph his was at 80mph too
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Adam_lee
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Registered: 23rd Apr 02
Location: Manchester
User status: Offline
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I find it hard to belive? The only reason the car would be slower is if the wheels are bigger in overall diameter. Otherwise it would make no diffrece to the speed? Soooooo if the wheels are bigger and hence slower, then for every one rotation of your wheel the car now does a greater distance. your spedo would then be out of calibration and you would be doing faster than your clocks say. For each one mile per hour you would be doing one and a bit miles per hour.
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Hillzlo
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Registered: 9th Nov 02
Location: Noitacol
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And what about 18's? Am I stupid for wanting this done?
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Adam_B
Member
Registered: 13th Dec 00
Location: Lancashire
User status: Offline
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Yes. I just put some 17s on mine, enuff bling bling for me 
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MattyB
Member
Registered: 13th Nov 01
Location: 118.5bhp :D
User status: Offline
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1.2 8v on 16s =  i top out at 85 and chew thru fuel
Matt
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IntaCepta
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Registered: 25th Mar 02
Location: Mill Hill East, Greater London
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i got 13" steelies n top out at 100, with 110 downhill. (indicated)
wouldn't the extra weight of the alloys make a difference?
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jm960326
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Registered: 24th Aug 02
Location: Rob Cheshire
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I got a 1.2 8v, 15s on can get 100 in it no probs. Put some 15s on and lower it, it'll look fine.
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MattyB
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Registered: 13th Nov 01
Location: 118.5bhp :D
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yeah with my 15"s it used to be ok....but now
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MikeH
Member
Registered: 3rd Apr 03
User status: Offline
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Ok, it is simple ratios.
If you put a bigger overall diameter on the car your power at the wheel will be reduced but the potential top speed should actually be higher.
Think about two mountain bikes, one has massive wheels and the other has tiny ones, it will be easier to start the small bike off but the one with bigger wheels will likely go faster.
You should be able to calculate the power loss (ignoring and other mechanical losses) with the following equation:
If for arguments sake we say the car is traveling at 100mph and has 90bhp with 13s on.
Under the same conditions with 17s it would be
17/13 * 100mph = 130mph
13/17 * 90bhp = 68bhp
This assumes the outside diameters are 13 and 17 whcih is never actually the case!
The thing is you i've assumed the same conditions and got a top speed of 130mph but the car would probably never get there because it would require too much power.... which is now reduced
I think i have my maths right, its been a while!!!
Mike...
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