geofff Posted August 10, 2004 Share Posted August 10, 2004 Hi All, Straight cut gearboxes give you an efficiency gain, correct? But how much? You can also change your gearing and make it closer. Thus making sure you never drop out of your power band. You would change first gear primarily for the run to the first corner (from a circuit perspective) and the other gears you would select to make sure you exit certain corners correctly rather than being inbetween gears? Are my assumptions right so far? I know from an earlier thread how to calculate overall gearing and speed in gears BUT......how do I select my gear ratios for a particular circuit without extensive testing? Is their a resource available anywhere which gives me the information I need? I'm aware I'll probably end up buying a single gear cluster which will be a compromise for all the circuits I'll be racing and that I'll probably have to take the advice of Quaife or Tran-X but I'd like to go into the conversation with a little bit of knowledge. Thanks for any info you can give me. Geoff This is a hell of a lot easier for karts - you only have one ratio & testing is cheap! Quote Link to comment Share on other sites More sharing options...
Blatman Posted August 10, 2004 Share Posted August 10, 2004 First thing is to make sure that you are allowed to alter the gearing in the race series in which you intend to run. You may have to keep standard ratios if that's what the rules state. The only other thing I have an opinion on is the straight cut gears comment. If you can tell the difference in power losses between straight cut and helcal gears, Frank Williams should be leaving Jenson where he is, and be signing you... Quote Link to comment Share on other sites More sharing options...
geofff Posted August 10, 2004 Author Share Posted August 10, 2004 Hi Blatman, I'll double check the regs but I'm pretty sure gearing is free in the BARC series. I always thought straight cut gears were more efficient and the reason road cars had helical was because of the reduced noise and ease of changing gear without crunches. I have no engineering basis for any of this of course. If you can mention it to Frank I'm free tomorrow morning at 8.35 - just after I present my resignation. Ta Geoff Quote Link to comment Share on other sites More sharing options...
Matt Seabrook Posted August 10, 2004 Share Posted August 10, 2004 If you can mention it to Frank I'm free tomorrow morning at 8.35 - just after I present my resignation. Ta Geoff Quote Link to comment Share on other sites More sharing options...
Blatman Posted August 10, 2004 Share Posted August 10, 2004 Straight cut gears are more efficient, but the change quality with a synchro box won't be any different than with helical gears. If a straight cut 'box is crunchy, it'll be suffering the same problems as a helical gear 'box, unless it's a dog box... I maintain though that if you can actually discern the difference from the drivers seat, then you should resign your job forthwith. IMHO, the only difference you'll notice is that your hearing will get worse... Quote Link to comment Share on other sites More sharing options...
Westfieldman Posted August 10, 2004 Share Posted August 10, 2004 WHAT WHAT DID YOU SAY BLATTERS............. Quote Link to comment Share on other sites More sharing options...
Blatman Posted August 10, 2004 Share Posted August 10, 2004 Quote Link to comment Share on other sites More sharing options...
Kev Bamber Posted August 10, 2004 Share Posted August 10, 2004 When buying my gearset I asked Tran-X about the real reasons for straight cut & as Blatters said, they confirmed power loss is negligible for our purposes, the main reason they do it is for ease of manufacture - they are only tooling up for small quantities. As for ratio's - are you circuit racing or Hillclimb/sprinting as I have stong opinions on how the smaller (1600cc) cars should be geared for the latter. Very very roughly, 45 in 1st, then 20mph increments subsequently giving approx 125mph with a 5 speed box. If you do the calc's, you will see the CR box will have to be paired with a short CWP ratio to achieve this. Kev. Quote Link to comment Share on other sites More sharing options...
Blatman Posted August 10, 2004 Share Posted August 10, 2004 Yup. Straight cut gears are one of those n-th degree choices, for use when every last HP counts. Most people buy straight cut gearboxes under the impression that the gears are stronger. They aren't, unless they are made from stronger material than the equivalent helical gear. What straight cut gears don't have is power losses due to the side thrust created by helical gears. As noted though, power loss is tiny, and for our purposes, not really worth considering as the main reason for buying the 'box. However, if you're in a race with identical cars with identical gearboxes save for a straight cut one in your car, it should make the best of the power it has, compared to the rest. Can you drive well enough to find it though? I certainly can't...... yet... Quote Link to comment Share on other sites More sharing options...
geofff Posted August 10, 2004 Author Share Posted August 10, 2004 Hi All, Well it would seem I'm going to save my pennies and stay with the RS2000 box I've already sourced. Kev - I'm circuit racing. Thank You Geoff Quote Link to comment Share on other sites More sharing options...
Blatman Posted August 10, 2004 Share Posted August 10, 2004 Don't forget that the side benefit of buying a straight cut 'box is that it's almost certainly had a re-build, with new bearings and synchros etc etc. If your RS2000 'box hasn't had a recent rebuild, then it may not survive the circuit racing for as long as you may expect... Quote Link to comment Share on other sites More sharing options...
geofff Posted August 10, 2004 Author Share Posted August 10, 2004 Hi Blatman, I'll be doing some testing before I start the season - if I get my A*** into gear and finish the build. If it goes bang I can buy myself out of trouble via a Quaife Clubman box. If not I'll have saved myself enough money for a couple more test days. Ta Geoff Quote Link to comment Share on other sites More sharing options...
Blatman Posted August 10, 2004 Share Posted August 10, 2004 Sounds good to me. Keep some money back for a 'box though, 'cos it's bound to go at the most inconvenient moment. Sods law an' all... Quote Link to comment Share on other sites More sharing options...
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