Roadsport06 Posted November 12, 2005 Share Posted November 12, 2005 I have ordered my build for Easter, but would like a lower reving 5th gear for 70mph on the motorway. Do Caterham do this and is it extra? What are peoples views on doing this? The caterham ratios are: CLOSE RATIO 5 SPEED 1st: 3.36:1 2nd: 1.81:1 3rd: 1.26:1 4th: 1.00:1 5th: 0.82:1 Final drive: 3.92:1 How do I work out the engine rev at 70mph? Thanks Link to comment Share on other sites More sharing options...
Mick Day Posted November 12, 2005 Share Posted November 12, 2005 Download this useful gearcalc program here. Does all the maths for you. Link to comment Share on other sites More sharing options...
Roadsport06 Posted November 12, 2005 Author Share Posted November 12, 2005 Cheers, thanks for the gear calc, it saves the hard work!!! Caterham site say they have the standard 3.92 diff and a 3.38 diff ratio. I'd like views on everyday use with a 3.38 compared to a 3.92, would this be a bad move? Link to comment Share on other sites More sharing options...
timbo Posted November 12, 2005 Share Posted November 12, 2005 If your running 14" 185/60 rr tyres (as an example) I make it on a 3.92 diff 84mph at 4000rpm and about 70mph at 3400rpm.. that is totally adaquate...and in my opinion even a little high. (a max speed of 137 at 6500rpm A 3.62 diff would give you 91mph at 4000rpm and 70mph comes up at 3050rpm.... far too high. A max speed of 145mph at 6500rpm Your choice! anxiously waiting for my new 2.3 SV Link to comment Share on other sites More sharing options...
CB Posted November 12, 2005 Share Posted November 12, 2005 There was an interesting thread on gearbox options here BGH though rather than Caterham standard Link to comment Share on other sites More sharing options...
Roadsport06 Posted November 13, 2005 Author Share Posted November 13, 2005 I have been on the gearcalc software and had a look at caterhams final drive options, I think I will go for the 3.38 rather than the standard 3.92 with my k 1.8 (140bhp) as it will certainly help cruising on the motorway. As anyone else been down this route? Any views? Be seeing you Link to comment Share on other sites More sharing options...
Peter Carmichael Posted November 13, 2005 Share Posted November 13, 2005 James, I think you are making a rash decision with the wrong information. It is intended for engines with a more limited rev range than has recently been the case. It has appeared on the pricelist because it is the right diff to get the best out of the 2.3 litre Duratec engines when combined with the six-speed box. A 140 X-power k-series with the five-speed box a 3.92 diff is standard and appropriate. With the six speed box the 3.62 works best. A 3.38 diff with a five speed on a K would be just plain wrong IMO. Link to comment Share on other sites More sharing options...
timbo Posted November 13, 2005 Share Posted November 13, 2005 I do have to second Peter on this one! I doubt there are very few, if any, XR4i type 5 speed K's out there with a 3.38! anxiously waiting for my new 2.3 SV Link to comment Share on other sites More sharing options...
Jason Plato Posted November 13, 2005 Share Posted November 13, 2005 apart from those that *only* get driven on the motorway - in which case a 3.38 is perfect C7 TOP Powered by Hellier Performance 😬 South Wales AO Link to comment Share on other sites More sharing options...
Peter Carmichael Posted November 14, 2005 Share Posted November 14, 2005 Except for having to change down to accelerate... With a 3.38 diff, the car would most likely achieve maximum speed in 3rd gear. By which I mean it would fail to accelerate to the same speed in 4th or 5th. If I remember correctly, most k-series standard and supersport Sevens get ~38mpg on a run even with a 6 speed box with 1:1 top. Link to comment Share on other sites More sharing options...
Mark Durrant Posted November 14, 2005 Share Posted November 14, 2005 Another vote for the 3.92 diff and as Peter says if you fit a 3.38 forget about acceleration . I suggest you go to a local meet and go out in a few diffent cars, a bit difficult at this time of year I know and to show you how popular the 3.38 ratio is I doubt you will find one in a 1.8K. Mark D Su77on Se7ens Link to comment Share on other sites More sharing options...
Fathead Posted November 14, 2005 Share Posted November 14, 2005 sevens are rubbish on the motorway anyway no fun, really noisy and straight with no roundabouts ☹️, I always take an A road even if its longer. Link to comment Share on other sites More sharing options...
Miura Posted November 14, 2005 Share Posted November 14, 2005 James, I run a standard 1.6K configuration (3.92 diff and standard gearbox). At legal speeds on motorway it is fine for cruising (I never remember the actual RPM but it is lower than 4000, the car returns +/- 40 mpg in those conditions) However, acceleration in 5th won't impress you I stand to be corrected but the general conssensus is that the silly short first gear is the main (and only " real "?) problem with the standard set-up. hope this helps ... Link to comment Share on other sites More sharing options...
EFA Posted November 14, 2005 Share Posted November 14, 2005 The only time an R500 beat me in a straight line was when I had a 3.38 diff. Link to comment Share on other sites More sharing options...
Roadsport06 Posted November 14, 2005 Author Share Posted November 14, 2005 Thanks all, I think that the overall view is that Caterham have the final drive just right so I'll stick with that, the only thing that I wish theyd do is make the 5th gear a touch longer. Having said that different ratios for different people, just depends on peoples uses. Link to comment Share on other sites More sharing options...
timbo Posted November 14, 2005 Share Posted November 14, 2005 It took 11 posts to get you to see sense 😬 anxiously waiting for my new 2.3 SV Link to comment Share on other sites More sharing options...
Roadsport06 Posted November 15, 2005 Author Share Posted November 15, 2005 Link to comment Share on other sites More sharing options...
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