mark260463 Posted March 25, 2005 Share Posted March 25, 2005 I have just put some MB mags on my R400, replacing the std anthrecite alloys, I have put exactly the same tyres back on (CR 500's). I understand the theory on rotating mass and unsprung weight. However I was amazed at what a difference i noticed, the car seemed to pick up and accelerate much quicker ( 😬)but also bounce around a bit more ( ☹️to start with but after an hours blat I have got used to it). I must admit I did not think I would notice such a difference - Questions:- 1) is it just my imagination or is this normal ? 2) Would the difference be even greater with a lighter tyre (ACB10?) maybe ? Thanks *smile* Mark 20 years with no points then I buy this bloody thing Link to comment Share on other sites More sharing options...
Mark Gregory Posted March 25, 2005 Share Posted March 25, 2005 Mark: I can't really help with your questions on the pros & cons of reducing unsprung weight, other than to say lower is better. But I have a cheeky question, I may be interested in your anthracite wheels if you are thinking of selling. Thanks, Mark Link to comment Share on other sites More sharing options...
Joe 90 Posted March 25, 2005 Share Posted March 25, 2005 Apart from the reduced weight, they will have lower rotational inertia. This means they will "spin up" easier, just like a lightweight flywheel will make an engine rev easier. SEP field working, not spotted in 103,100 miles. Some photos on webshots, updated 25 Jan Link to comment Share on other sites More sharing options...
Nifty Posted March 25, 2005 Share Posted March 25, 2005 I certainly notice the difference with my 1400SS *thumbup* Keep off the straight and narrow 😬 Link to comment Share on other sites More sharing options...
mark260463 Posted March 25, 2005 Author Share Posted March 25, 2005 Mark Good try - but I am hanging on to them for now as a spare set - will let you know if I change my mind. Mark 20 years with no points then I buy this bloody thing Link to comment Share on other sites More sharing options...
Mark Gregory Posted March 25, 2005 Share Posted March 25, 2005 Mark: It's a fair cop, but if you don't ask....etc Link to comment Share on other sites More sharing options...
Rob Walker Posted March 26, 2005 Share Posted March 26, 2005 Mark, The ACB`s are even lighter as they are a crossply construction. Link to comment Share on other sites More sharing options...
anthonym Posted September 22, 2006 Share Posted September 22, 2006 I found this a very interesting comment, about the increased bounce with the lighter mag wheels. I have just ordered 4 of the heavier ally wheels from CC parts to replace 4 mag wheels (one needs repair (one too many slides) and all need x-ray). The single greatest road element that slows me down in the Alps is bumpy road surfaces causing the car to bounce all over everywhere - that and understeer (more like no steer). So I will be very interested to see if the increased weight (approx 2kg per corner) acts like a heavier flywheel - i.e. more inertia keeps me (the car) on a steadier flight path, which of course on the track and normal roads is not a challenge. It-s not so much bump steer as the whole car taking off... given half a chance. Now wheel less as I left my spare wheel set wheel nuts in GB. Anthony R500 Link to comment Share on other sites More sharing options...
irrotational Posted September 22, 2006 Share Posted September 22, 2006 discuss? --- this is a local sig for local people! Link to comment Share on other sites More sharing options...
Unclefester Posted September 22, 2006 Share Posted September 22, 2006 Anthonym....which mags were you using, and do you have the weight? What size are they? Interesting about the extra 'bounce' that's not something I'd have expected...... Blackout!!! 😬 😬here *eek* Link to comment Share on other sites More sharing options...
Mike C. Posted September 22, 2006 Share Posted September 22, 2006 The benefits of unsprung weight savings are often under-estimated. The benefits can be considerable, improving almost all the dynamics - accelaration, braking, steering, ride, etc. It should also enable the wheels to keep in closer contact with the road surface, so there should in fact be less 'bounce'. Gordon Murray, I think, once described it as being equivalent to going for a jog in a pair of wellingtons or a pair of trainers. This is also the main reason buyers of supercars are paying up to £10k for carbon ceramic brakes - even for road use. Mad Manx Link to comment Share on other sites More sharing options...
Normans_Ghost Posted September 22, 2006 Share Posted September 22, 2006 Anthony, what arb's have you. best to stiffen front and reduce rear. If you have a rear arb remove it and see if that helps. If it does you may like to then try a stiffer front arb. As for lower is better, not always true. There is an optimum ride height depending on many things but mainly suspension setup. Too low is as bad as too high. Norman Verona, 1989 BDR 220bhp, Reg: B16BDR, Mem No 2166, the full story here You and your seven to The French Blatting Company Limited Link to comment Share on other sites More sharing options...
Paul McKenzie Posted September 22, 2006 Share Posted September 22, 2006 Just gone from 16" HPC wheels with 'Pileup Ditchrunners' to 13" Barnby mags with ACB10's (on 220bhp XE). The weight saving including losing the spare is 35kg *eek* ....not surprisingly the whole experience is transformed...the gearing has dramatically increased the acceleration and the wheels spin on the changes to third and fourth when you're pushing on. It jigs around a bit more, but I'm sure that's just the ACB10's, and on our sh*t roads what can you expect? Paul Link to comment Share on other sites More sharing options...
Unclefester Posted September 22, 2006 Share Posted September 22, 2006 *arrowup*> That's what I'd have reckoned!!! Blackout!!! 😬 😬here *eek* Link to comment Share on other sites More sharing options...
Myles Posted September 23, 2006 Share Posted September 23, 2006 Hmm - but what is doing the bouncing? You've gone from heavy wheels to light and retained the same damping rates etc. As a consequence, are you not over-damped and is this not affecting what is felt in the car? 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7's Equipe™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Paul McKenzie Posted September 23, 2006 Share Posted September 23, 2006 Myles, I stand to be corrected on this, but have we not lost UNSPRUNG weight, hence there should be no effect on the damping 🤔 Paul Link to comment Share on other sites More sharing options...
Myles Posted September 23, 2006 Share Posted September 23, 2006 but have we not lost UNSPRUNG weight, Erm, lighter wheel - less unsprung weight... 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7's Equipe™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Myles Posted September 23, 2006 Share Posted September 23, 2006 Anyway, I stand to be corrected too, but... The sprung mass (body etc.) wants to travel in a straight line (let's ignore cornering and concentrate just on bumps in the road). A light wheel/tyre combo can react more quickly to bumps - a heavy one will react more slowly but will have more momentum to control... The speed at which loads are transmitted to the unsprung mass will affect the ride, won't they? Erm, I wish I had my Racecar Dynamics (or whatever it was called) book to hand... Ho-hum... 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7's Equipe™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Phil Posted September 23, 2006 Share Posted September 23, 2006 As the wheel rides over the bump it is sent upwards requiring the shocks to damp this and the spring to return it to the ground, if you take some of the weight off the wheel this is made easier keeping contact with the road giving better grip, braking, etc. Surely now the shock has less to do and with a great loss of weight from a 16inch wheel to 13inch, the springs are to strong and upsetting the ride making it to hard? I have gone from 5 prisoner wheels to 4 R300/400 15 inch wheels, noticed the difference and well worth the money. Tyres are 195/50/15 toyos. X/FLOW 1700 DD 1990 ROAD USE ONLY..SO FAR Link to comment Share on other sites More sharing options...
Myles Posted September 23, 2006 Share Posted September 23, 2006 Phil - that's the kind of reasoning I was running with... 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7's Equipe™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
anthonym Posted September 23, 2006 Share Posted September 23, 2006 13" Black & Silver R500 "Mike Barnaby" wheel - if that description is right. As to weight.. I gather 2kg less than the new "replacement" alloys I have ordered from CC. (Someone asked my wheel sizes) I reckon I'll miss the mag wheels, but they need testing and its years overdue, now one (rim, not mag centre) is cracked (user error) I can't bring myself to delay longer. Certainly everything I ever read says lower unsprung weight is better, less inertia when hitting bumps etc so suspension has less to do.,, so I suppose the wheel returns to the tarmac faster and that's better handling/more grip. Edited by - anthonym on 23 Sep 2006 18:34:08 Edited by - anthonym on 23 Sep 2006 18:42:56 Link to comment Share on other sites More sharing options...
anthonym Posted September 23, 2006 Share Posted September 23, 2006 I just realised arb means anti roll bar: to answer that question I took the car to Hyperion (who built it, very nicely) and they suggested and fitted a thinner front roll bar ...did it make a difference? I don't know. Of course it did, but have I noticed.. now I think about it I think I get less understeer, but a couple of alpine hairpin "no steer" experiences is enough to engender driver improvement pdq. Edited by - anthonym on 23 Sep 2006 18:47:10 Link to comment Share on other sites More sharing options...
Paul McKenzie Posted September 23, 2006 Share Posted September 23, 2006 Phil/Myles, IMHO the shock has the same to do, all you have lost is unsprung weight, which is not the weight carried on the dampers....hence the damping should be unaffected ......think this is going to be a long runner, until someone gets out their book on suspension theory...come back Alan Staniforth, all is forgiven Paul Link to comment Share on other sites More sharing options...
anthonym Posted September 23, 2006 Share Posted September 23, 2006 I have his very book here.. don't know what to look up though.. maybe tomorrow Anthony Faith Manages Link to comment Share on other sites More sharing options...
anthonym Posted September 24, 2006 Share Posted September 24, 2006 it being "tomorrow" I am reading Mr Staniforth's Suspension book chapter about dampers. It seems much of my road experience is based on my car that was built and set up for race track use, being used by me on bumpy alpine roads.. the track settings do not allow for bumps reducing the time the tyres are adhering to the tarmac.. also seems less unsprung weight (ie wheels/disks/tyres etc) means when dampers have less to do they can react faster.. bit like me really.. So with regard to the seed message of this thread: lower unsprung weight, I tentatively suggest some damper tuning to match the reduced weights as they are currently set for heavier duty, presumably assuming more inertia to be managed... etc and for me vice versa when my heavier wheels arrive. It's beginning to seem to me that it's more about tuning the suspension to the weight combinations rather than changing the unsprung weight and saying "oh, it behaves differently". Allan Staniforth suggests that dampers are like hifi: "how much would sir like to spend?" type of thing. So I'm hazarding that heavier wheels could be compensated to some extent (all?) by spending excessive amounts of money on damper technology; or more on wheels and less on dampers..? It seems all the experiences I complain about actually have accepted terms, like for bump dampening we have "walking" and "side hop".. with the aim being to reduce both. I look forward to it. I see on pages 238/9 are flow diagrams for damper adjustments. I have no idea what dampers are on my car. Reference: Allan Staniforth "Competition Car Suspension" ISBN1-85960-644-X £19.99 Reprint 2002 by Haynes. (Oh dear! Here is link to the book on Amazon UK here The price is near £70 quid! Whereas mine actually has £19.99 printed on the back cover and no not confusing it with the edition year.) p.s. I keep talking about the unsprung weight being on the dampers and the above poster says that is wrong: I defer to that view, but use my own until I understand what it really is, which i am looking for right now.,, here we go wiki: http://en.wikipedia.org/wiki/Unsprung_weight here oh dear, from the wiki " A (lighter) wheel which readily moves in response to road bumps will have more grip when tracking over an imperfect road. " VERY interested to read that the benefit of de Dion design is to move the diff weight to the sprung weight side of the equation, makes a lot of sense for a lightweight car like a Seven. Paul M, I am struggling to understand this contention you make above: "all you have lost is unsprung weight, which is not the weight carried on the dampers." Seems to me that's exactly what it is, less workload (weight placed on) demanded of the dampers. if you had said: "all you have lost is sprung weight, (not true anyway.. ) which is not the weight carried on the dampers." I would understand, but you don't so I don't. 🤔 I'm not very sure about this as you can see. Anthony Edited by - anthonym on 24 Sep 2006 16:32:55 Link to comment Share on other sites More sharing options...
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