Date: Tue, 15 May 2001 11:07:30 +0200 From: "James A. Barbour" <jamesnopsamAM.nospam> Subject: Re: RMP to MPH ratio?
Could this be affected by tyre size and / or pressure? in article 3B00214F.F10991A8nopsamsafish.com, Johannes H Andersen at johsnopsamsafish.com wrote on 14/5/01 8:17 pm: > > > Kyle Kontney wrote: >> >> Hello all, >> >> I have two SAAB 900S cars. They have a slight difference and was wondering >> if anyone could tell me if this is adjustable, or if this is normal. Please >> note: these are Automatic, not manual shift, 4-door non-turbo. >> >> The 88 900s gets better gas mileage, and the RPM to MPH is about half >> numerically. For example, if I am traveling at 70 MPH, my RPM is 3500. >> >> My 89 900s has a different ratio. For example, 70 MPH, my RPM is 3800. >> >> So I am wondering if there is something wrong? >> >> What is the acceptable RPM for the speed ratio? >> >> -Kyle >> themoz(at)wi.rr.com > > Hi, the MPH/RPM ratio is fixed, it is determined by top gear ratio, final > drive ratio and wheel size. A higher RPM for a given speed is used in the > automatics to achieve sufficient engine flexibility and driveability, not > necessarily for optimal gas mileage. Hopefully, your auto box is engaging > correctly in top gear for the automatic without slippage or kickdown? > > Johannes
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