paul jacobs Posted December 17, 2012 Share Posted December 17, 2012 Is there a definative way to tell the difference in the two 'quick' racks or even any stampings or markings which would help identify which rack is which please? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted December 17, 2012 Member Share Posted December 17, 2012 Quoting Piers7: AFAIK the standard rack is 1.9 turns lock to lock and the 22% rack is 1.7.Jonathan Link to comment Share on other sites More sharing options...
Damdy-Cash Posted December 18, 2012 Share Posted December 18, 2012 here Cheers Volker Link to comment Share on other sites More sharing options...
Rob Walker Posted December 18, 2012 Share Posted December 18, 2012 If you look at the casting opposite the pinion , the hole is blanked off by an aliuminium disc about 20mm dia ,the 22% rack is identified by a pink disc Link to comment Share on other sites More sharing options...
Willie. Posted December 18, 2012 Share Posted December 18, 2012 There are all sorts of suggestions and no fail safe way that I have come across. In order to solve this, would anyone with a known 22% rack be willing to accurately measure one full turn of the input shaft (Or steering wheel) and measure the length travelled by one of the steering arms (Measured at the inner gator). That should give us an in vs out ratio. Then if someone could do the same for a known 8% rack we will have a surefire way of telling what's what. Just a suggestion. Link to comment Share on other sites More sharing options...
Myles Posted December 18, 2012 Share Posted December 18, 2012 I might be able to measure the22% one tomorrow - weather permitting. Anyone any idea what level of accuracy will be required? I'm guessing that there isn't actually much difference overall...? Link to comment Share on other sites More sharing options...
6speedmanual Posted December 18, 2012 Share Posted December 18, 2012 I will attempt to measure mine at weekend. The faster rack should move 12.96% more. Peter Link to comment Share on other sites More sharing options...
Gavin H Posted December 18, 2012 Share Posted December 18, 2012 May be a stupid question but what does the % stand for or signify? (Just curious as I'm sure it has no bearing on identification...) TIA Link to comment Share on other sites More sharing options...
Willie. Posted December 18, 2012 Share Posted December 18, 2012 Not sure what accuracy would be needed, but I'd guess if the input shaft could be measured to 1 spline tolerance and the steering arm/output to 1/16", it should be more than accurate enough. A pic, if possible, of measuring the steering arm (At the rack body) would help anyone else replicate the measurement. I can't mind what they look like, but I'm imagining undoing the inboard cable tie & pulling the boot back, putting a mark on the inner rack and then using a square ended steel rule against the alloy rack body to measure how far it travels. Apologies for seeming like a lazy dictator, but I've sold my rack now, and nobody knew what it was, so I've nothing to measure ☹️ Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted December 18, 2012 Member Share Posted December 18, 2012 Quoting Gavin H: May be a stupid question but what does the % stand for or signify? (Just curious as I'm sure it has no bearing on identification...)Steering ratio, Wikipedia article... unless it has some special meaning in the world of 7s... Jonathan Link to comment Share on other sites More sharing options...
Area Representative Golf Juliet Tango Posted December 18, 2012 Area Representative Share Posted December 18, 2012 The ratio is quite clear. Quite why Caterham use a %, is a bit of a puzzle. The other puzzle (for me) is why the small difference in ratio becomes such a large difference in the % used in Caterham's figures. Link to comment Share on other sites More sharing options...
Dr Slotter Posted December 18, 2012 Share Posted December 18, 2012 The percentage means the percentage extra reduction relative to the standard rack. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted December 18, 2012 Member Share Posted December 18, 2012 *arrowup* *arrowup*That sounds better than my guess. Jonathan Link to comment Share on other sites More sharing options...
6speedmanual Posted December 18, 2012 Share Posted December 18, 2012 I believe it to be the % increase in rack movement for a given input. The 8% rack has been standard for years'n'years, since the first Caterham dedicated Titan rack. The 22% is the only real quick rack choice. The original "0%" rack would be the old BL Mini derived item. The variations in the different turns lock to lock for the apparently same ratio could be due to different lock stop settings for wide and narrow track, with/without cycle wings. Anyone shed any more light? Peter Link to comment Share on other sites More sharing options...
Area Representative Golf Juliet Tango Posted December 18, 2012 Area Representative Share Posted December 18, 2012 OK, I understand the calculation but it is so obscure that it is pretty much obfuscation. Surely, stating the true steering ratio would, in fact, just give accurate information? After all, few of us know what the point of reference feels like. I don't know which rack I have in either car but I know how different they feel, although they both go around corners pretty well they do do it differently. Hard to describe (and there are so many other influences there, different engine weight, different wheel diameter, different tyre width, different track width and more) Edited by - Golf Juliet Tango on 19 Dec 2012 08:15:55 Link to comment Share on other sites More sharing options...
Mankee Posted December 18, 2012 Share Posted December 18, 2012 I found some information from a previous post of mine which gives a bit of reasoning to the percentage thing: A steel-cased rack (from a Mini?) is 2.25 turns lock-to-lock An 8% quicker rack 2.07 turns lock-to-lock A 22% quicker rack 1.75 turns lock-to-lock But, as noted by Peter, track and cyle wings/flares might bugger up some of these figures. Link to comment Share on other sites More sharing options...
6speedmanual Posted December 19, 2012 Share Posted December 19, 2012 Not sure that I've ever seen steering rack ratio quoted as x:y as in a final drive ratio. As the rack is straight ratio of turns in to turn out is not applicable. Ratio of linear movement in to linear movement out would be ok and would also take account of the steering wheel diameter. All the other factors mentioned (GJT) are what make the forces which have to be overcome by the input effort by the driver. The real biggies once underway and cornering are the self aligning forces from the tyres and the geometry of the suspension. Peter Link to comment Share on other sites More sharing options...
Dr Slotter Posted December 19, 2012 Share Posted December 19, 2012 'Academically' speaking, and ignoring things like Ackermann geometry, it is the ratio between the angle turned by the steering wheel and the resulting angle turned by the wheels. e.g. A motorcycle/bicycle has a steering ratio of 1:1 A sports car of some description would have a steering ratio somewhere in the range of 8:1 (something like a Seven) to 12:1 (something like a sports saloon) A typical passenger car would have about 20:1 Bigger stuff (buses/lorries etc.) is as much as you like! Some numbers... A standard Caterham rack (as described by Mankee in this thread) would generate about 100° of wheel angle for 2.25 turns (i.e 810° of steering wheel rotation), 810:100 = 8.1:1 A '8%' rack, 2.07 turns (745°) = 745:100 = 7.45:1 and 8 - (8 x 0.08) = 7.36 A '22%' rack, 1.75 turns (630°) = 630:100 = 6.3:1 and 8 - (8 x 0.22) = 6.24 Link to comment Share on other sites More sharing options...
6speedmanual Posted December 19, 2012 Share Posted December 19, 2012 Slotter Interesting. Not seen that before but an interesting comparator. Regarding your three calcs, they assume that all three racks gice the same turning angle of the wheel. As disussed above, we know there are several variations in lock-stop settings to cater for different track width, wings, etc. Peter Link to comment Share on other sites More sharing options...
Dr Slotter Posted December 19, 2012 Share Posted December 19, 2012 That doesn't have an effect on the ratio though, just the absolute limits of both the angles constrained by that ratio. Link to comment Share on other sites More sharing options...
6speedmanual Posted December 19, 2012 Share Posted December 19, 2012 Yebu' Your calculation assumes 100deg of wheel turn in all cases and the turns lock (stop) to lock (stop) quoted in an earlier post. If the lock-stops are set differently, the wheels will turn different amoumts. As succinctly put by Mankee, this will "bugger up" the figures. Peter Link to comment Share on other sites More sharing options...
Dr Slotter Posted December 19, 2012 Share Posted December 19, 2012 If the stops restrict the wheels moving, they will restrict the movement of the steering wheel by the same amount. e.g. if the 100° is restricted by the stops and actually should be 110°, the steering wheel would need/be able to turn 2.47 turns, as for a given rack, the ratio will be constant. That assumes the rack is of fixed ratio, not variable of course. Link to comment Share on other sites More sharing options...
6speedmanual Posted December 20, 2012 Share Posted December 20, 2012 True. But we don't know if all the stop settings are the same on the 3 examples given. Link to comment Share on other sites More sharing options...
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