75 mph =3600?
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Category: Technical & Model Specific Forums
Forum Name: BMW 3 Series
Forum Discription: This forum will deal with any issues on the BMW 3 Series (E21, E30, E36, E46, E90, E91 & E92)
URL: http://www.bavarian-board.co.uk/forum_posts.asp?TID=6329
Printed Date: 20-May-2024 at 14:18
Topic: 75 mph =3600?
Posted By: 325ism50
Subject: 75 mph =3600?
Date Posted: 17-March-2004 at 02:56
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Wonder why my 2.5L M50TU. 16x7 tyres size is 205\50 3.15 120 kmh\75 mph =3600 rpm how about your? Thanks. ------------- oklah |
Replies:
Posted By: Peter Fenwick
Date Posted: 17-March-2004 at 09:21
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My 328 does around 75 - 80mph at 3000rpm. If you are running on 16" wheels with 205 tyres then you need 55 profile tyres not 50. This would explain the lower gearing of the car. ------------- Entering an age of Austerity and now driving a Focus Diesel. |
Posted By: Sheepmeister
Date Posted: 17-March-2004 at 13:20
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That is the same with my car, and I'm running on 16s with 205/55, I think. Runs at about 3500rpm at 70/80ish... so putting lower profiles on would reduce that? Would that improve fuel consumption?? Sheep |
Posted By: Peter H
Date Posted: 17-March-2004 at 19:29
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Its a combination of profile to width, to keep rolling radius & speedo accuracy. similar if bigger wheel/tyre combinations fitted ie going from 16 inch to 18 inch wheels ------------- Das Wolperdinger AHN-NYUNG-HEE GA-SEH-YO |
Posted By: Peter Fenwick
Date Posted: 18-March-2004 at 09:53
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Sheep, if you are running on 16's then 205/55 or 225/50 are the correct tyre sizes. The profile is a percentage of the tyre width, so for example the profile of a 205/55 is 55% of 205mm = 112.75. Similarly the profile of a 225/50 tyre is = 112.5 ie the same as a 205/50. So you need to keep this profile the same in order to maintain the same rolling radius. Unless of course if you fit bigger or smaller wheels. For smaller wheels you need a bigger profile and for larger wheels a smaller profile. Putting lower profile tyres on the same size wheels will reduce the rolling radius and hence reduce the gearing of the car. This in the long run will probably increase fuel consumption and it will put the speedo out. Also as your car is a four cylinder it may well be slightly lower geared than the 6 cylinder cars anyway. ------------- Entering an age of Austerity and now driving a Focus Diesel. |
Posted By: 325ism50
Date Posted: 20-March-2004 at 15:34
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my car is 2.5L manual box. M50tu engine. ------------- oklah |
Posted By: Peter Fenwick
Date Posted: 22-March-2004 at 09:14
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325ism50. I assume that your car will have the same gearing as mine. Had another look the other day at the revs and mine is 3000 rpm = 80mph. Like I said if you are running 16 inch wheels then 205/50s are the wrong tyres, you need 205/55 or 225/50. ------------- Entering an age of Austerity and now driving a Focus Diesel. |
Posted By: 325ism50
Date Posted: 22-March-2004 at 17:15
I bought the wrong expansive tyre ------------- oklah |