SteveD Posted March 22, 2003 Share Posted March 22, 2003 keep it up blatt's no need to appoligies it makes great reading Quote Link to comment Share on other sites More sharing options...
Jan Coombes Posted March 22, 2003 Share Posted March 22, 2003 I have never been sprinting before (so I may not win my class this year) but as you are only on the track for a short time I would guess GRIP is the key. As for the 13" 15" issue I have to place my vote with the 13", given the 2. The real important thing is getting the car matched to the tyres, I think, it is about 20% of the flex should come tyre wall the rest from the shocks and chassis (look at the big side walls on F1 cars) if you are running a bigger wheel you have a lower profile thus less flex. c******m found this out and teamed up with Avon to make the CR500, but even then the walls are too stiff. You could take your car to company that makes shocks and you can get some made to suit, Richard Ince did this on his R500, and the results were amazing As for me I don’t have that sort of lolly so I am going with A032R this time round, but I think I would have ACB10s if I had the money, more grip and it is a lighter tyre too. Quote Link to comment Share on other sites More sharing options...
timd Posted March 22, 2003 Share Posted March 22, 2003 Good point. The answer is NO..... The 13" tyres I fitted were (in theory at least) a harder compound than what came off. I took off 205-50-15 Yoko A520's all round, with a wear index of 180. I put on Falken 502's 250-60-13 rears, and 185-60-13 fronts with a wear index of 280. A significant difference. Thanks. I did wonder... I would suggest that the significant changes in tyre sizes and profiles would have had just as big an effect on car performance as the changes in compund. Not to mention the change in all up weight that may well have occured at the same time. So I'm afraid that AFAICS your experience does no more to prove the 13" is 'better' than 15" theory than any other. It seems to me that the reasons different people run different tyres are more to do with economics and availability, as Guy suggested. ie List 1As are more readily available in the required makes & models in a 15" and are also better developed due to the mainstream car applications, whereas the opposite is true of List 1Bs which also have the advantage of being significantly cheaper in a 13" size. Just to throw one other point into the pot which seems to have been overlooked so far. The application of the car will also change the requirement of wheelsize. If your car is setup for short sprints then brake cooling is never going to be too much of an issue. However if your car is setup for trackday useage where one day can see the equivalent usage of several years of sprinting, brake temperature can obviously build up a lot more. To counter this you may well have a requirement for larger diameter discs, and a bigger volume of air movement to help cool the brakes. Basically there is no "right" answer, it depends on what you want the car to do and how much you are prepared to spend on it. Quote Link to comment Share on other sites More sharing options...
timd Posted March 22, 2003 Share Posted March 22, 2003 The real important thing is getting the car matched to the tyres, I think, it is about 20% of the flex should come tyre wall the rest from the shocks and chassis (look at the big side walls on F1 cars) if you are running a bigger wheel you have a lower profile thus less flex. Agreed, but... Are you suggesting that F1 cars get 80% of their suspension compliance from their shocks and chassis?? Err, don't think so... Quote Link to comment Share on other sites More sharing options...
Blatman Posted March 22, 2003 Share Posted March 22, 2003 I would suggest that the significant changes in tyre sizes and profiles would have had just as big an effect on car performance as the changes in compund. Not to mention the change in all up weight that may well have occured at the same time.So I'm afraid that AFAICS your experience does no more to prove the 13" is 'better' than 15" theory than any other. Maybe......... The compound of the 13's is definitely harder than the 15's I ran (I put a durometer on them). This would make them less grippy, so I don't see how that is a benefit on it's own. Combined with a weight saving (I saved 28kg's), and the different behaviour of the higher sidewall, I prefer the that set up, and it made ME faster. I haven't tried to PROVE my set up is right is "right", 'cos as you say, there is probably no right answer. What I did want was an answer to a (not so simple, as it turns out) question that came from a proposal from some-one who I thought may have some insight, theory, or higher knowledge on the subject which he may want to share. The statement was If you're on List 1As ( ie roadgoing classes) there is no decent rubber in 13". So if you want to be competitive you'll need 15".No-one ever wins on 13" List 1A tyres anymore. It's not about handling it's about GRIP. My question, BASED ON THAT OBSERVATION, AND THAT OBSERVATION ALONE, WAS Why would a 13" tyre with a wear rating number of, say, 200 have less grip than a 15" tyre with the same wear rating? I was after some insight, and maybe a bit of deductive reasoning, which I got, but apparently failed to understand. However FOR ME, I prefer 13's. If that one thing means I'll never be a winner, so be it. I didn't like the way the car felt on 15's, so I am in no rush to change back. There is also enough evidence from other Se7en drivers to support my theory that a swap from 15's to 13's brings many benefits, although for speed events, it seems that if I want to win on 13's, I may well need to switch classes so that I can run 1B tyres. At no point have I ever said that I am 100% right or anybody else is 100% wrong. I wouldn't do that, unless I was 100% sure of my answer. As with most things speed event related, I have LOTS to learn, so I need to ask LOTS of questions......... Quote Link to comment Share on other sites More sharing options...
Fat Albert Posted March 22, 2003 Share Posted March 22, 2003 The compound of the 13's is definitely harder than the 15's I ran (I put a durometer on them). This would make them less grippy, so I don't see how that is a benefit on it's own. Er.... Not necessarily, Blatman, as I have said earlier it is the co-efficient of friction between the track and the tyre which is affected by the compound, a less durable (by implication, softer) compound may reduce that co-efficient and vice versa. A very silly and extreme illustration of this is the addition of spikes to tyres for driving on ice. Clearly, Guy and the others who race on 15" would not just do so because everybody else does, they would have carried out comparative tests using a scientific approach to determine on their car/suspension what combination of the available wheels/tyres produces the best compromise, wouldn't they? I well remember an F3 Rheims slip streamer when we were all done by JP Jaussaud who fitted 6" wheels, he kept up round the corners only because everyone else was in each others way but was 10-15mph faster on the straight Tyre choice, like everything else in car setup is extremely personal, remember Brundle being unable to drive a Benetton on Schumacher's settings. Carcase construction, weight, temperature stability, sidewall flexibility, etc. all have a bearing on 'feel' as well as requiring 'setup' changes to the car to extract the maximum from each. At least there is a choice, in F1 all the Bridgestone teams choose from Schumacher's table. Finally, Machin, I apologise for my contribution to hi-jacking your thread, for what it's worth, my advice is to spend less on the car and more on practice. There's no point in having the best until you can get the most out of what you've got. Quote Link to comment Share on other sites More sharing options...
Blatman Posted March 23, 2003 Share Posted March 23, 2003 Er.... Not necessarily, Blatman, as I have said earlier it is the co-efficient of friction between the track and the tyre which is affected by the compound, a less durable (by implication, softer) compound may reduce that co-efficient and vice versa. I was also taking in to consideration Guy's earlier point about 13" tyres being 10 years behind their 15" cousins in terms of technology. I don't believe that anyone could argue that compound technology from 10 years ago is comparable with todays technology. On the other hand, I have heard from several sources (except Bridgestone themsleves) that 13" RE720's are identical, compound wise, to the 15" SO2's. I really can't see a tyre manufacturer producing 2 compound types when 1 will do, because it would cost more to produce 2, I would have thought. Or at least, you reduce capacity for new production if you keep old production going. Either way, profits are reduced. So I'm still in a quandry, BUT I stand by my assertion that my 13's have less grip than the 15's, BUT they have other qualities that I like, that help me get around that particular issue. For this year, I hope I have found some tyres that are almost as grippy as the A520's were (IE, a similar wear index), but obviously as they'll be newer anyway, they should grip more. My current tyres are now 4 years old (I got them second hand, 2 years ago, from a chap who used them to sprint a 250+ bhp c******m, so they'd done quite a few heat cycles too), very well used, and quite nasty. Quote Link to comment Share on other sites More sharing options...
Jon Murray Posted March 24, 2003 Share Posted March 24, 2003 Blatters - Have you thought about temporarily going back to 15" rim / tyres or borrowing some for a few laps? That way you could rule out your extra speed being all down to added driver confidence gained through experience. I'm sure it could easily be sorted out in the paddock (although maybe need to borrow cycle wings too ! ) I have seen an awful lot of discussions recently on Blatchat where c******m owners are swopping their 15" Prisoner's to 13" rims and they all say how much more controllable / predicatable the car is as a consequence of the sidewall flex inherent in a 70 series tyre (RE720's). Maybee this is part of the answer to your question, although you know this already Anyway just to fire things up a bit and as an aside, I chatted with Terry Nightingale a few weeks ago about 13" v's 15" debate, his recomendation was simple: 1) On BEC's and cars with less than 200bhp, 13" rules! 2) Cars with more than 200bhp, generally do better on 15". (This isn't a verbatim statement of what he said, so please don't start getting all picky about the word "generally" or anything, but we chatted for about ten minutes on the subject and in a nutshell the two points above sum up my understanding of what I was being told). These results were gained from back to back testing by Terry. Now don't shoot the messenger here lads, these are TN's words of wisdom not mine and, in my opinion I think he know's what he's talking about. Also, Adrian CW won his class in the Speed Series last year on 16" rims, Guy apparantly runs 15" and from what Blatters is saying does rather well (or from what I can see from these messages - he certainly does better than Blatters ). This got me thinking..... It would be very interesting to look at the entire results table from last year's Speed Series and add a column for tyre type / size. Maybe a pattern would start to develop that might provide some empirical data Jon Quote Link to comment Share on other sites More sharing options...
scott beeland Posted March 24, 2003 Share Posted March 24, 2003 Just to spice up the debate I'm gonna alternate between 13" 32r's and 15" toyo T1s during the speed series. I like how it feels on the road on the 32 r's but time will tell Quote Link to comment Share on other sites More sharing options...
machin Posted March 24, 2003 Author Share Posted March 24, 2003 OK......I started this whole thing, but I've been away a couple of days....been busy haven't you?! To answer some people's technical questions:- Correct: A tyre's grip is determined by its compound, temperature and wear (all of these add up and give a value for the coeffiecient of friction), -NOT its width, -the problem is that as you use a tyre the wear on a thinner tyre is greater, and the heat goes up higher (a little improves the coeff and too much decreases it). Now Ferrari's, etc, use really wide tyres and still only get 5000 miles out of them, -they would have the same initial grip if they were thinner but would probably only get 1000 miles from them....and they'd overheat sooner. i.e they're made of a sticker compound. Therefore if you want more grip (i.e you have more power) you want a stickier compound and therefore its best to go for wider tyres so they last a reasonable time, and don't overheat so quick. Its the same deal with brakes.......you can get the same initial grip out of a small pad using the same compound of brake pad as a massive disc/caliper...but the wear on a smaller disc/pad is greater and so is the tendancy to overheat....so the braking performance would be worse. OK? So I'm thinking.....I probably don't need bigger brakes on my westy? I just need some stickier brake pads. Or has anyone else found that their standard brakes overheat (even though we are only talking a short burst for hillclimbing/sprinting?), and therefore I can use the smaller wheels. Basically you only increase the wheel size if you need to have bigger brakes (F1 cars have tiny carbon brakes and therefore don't need the huge wheels they need in Touring cars). ......And you only need bigger brakes if the standard ones overheat....... I have no experience of hillclimbing, so some knowledge is required...do people use the standard brakes or go for bigger (Wilwood do a few sets.....). So as a summary:- Big wheels:- can fit larger brakes Weigh more When fitter with low-profile tyres have less side-wall deflection. Look Better (?) Big Brakes:- Weigh More Overheat less quickly Wear less quickly This problem is made a little more difficult because someone mentioned that you can't get good sticky tyres on 13" rims. I'll be, hopefully, running in the lowest class (A), -so it looks like to get more grip (stickier compound) I will have to go for 15" tyres because of tyre availabilty......but then Blatman uses 13".......therefore can I ask what wheels and tyres Blatman uses (the ones on your avatar look really cool....and don't look like they have massive profiles??) Cheers guys........let the debate continue Machin Quote Link to comment Share on other sites More sharing options...
doomZday Posted March 24, 2003 Share Posted March 24, 2003 For some more interesting tyre opinions, take a look at this. Quote Link to comment Share on other sites More sharing options...
steve wilson Posted March 24, 2003 Share Posted March 24, 2003 For some more interesting tyre opinions, take a look at this. Very interesting Quote Link to comment Share on other sites More sharing options...
steve wilson Posted March 24, 2003 Share Posted March 24, 2003 For some more interesting tyre opinions, take a look at this. Very interesting Quote Link to comment Share on other sites More sharing options...
fordy Posted March 24, 2003 Share Posted March 24, 2003 .but then Blatman uses 13".......therefore can I ask what wheels and tyres Blatman uses (the ones on your avatar look really cool....and don't look like they have massive profiles??) the car in his avtar is his road car - it has 15"s on, his sprint car has 13's Nice havin 2 cars - lucky b*******. cheers Chris Quote Link to comment Share on other sites More sharing options...
BobM Posted March 24, 2003 Share Posted March 24, 2003 Also, Adrian CW won his class in the Speed Series last year on 16" rims, Guy apparantly runs 15" and from what Blatters is saying does rather well (or from what I can see from these messages - he certainly does better than Blatters ). This got me thinking..... It would be very interesting to look at the entire results table from last year's Speed Series and add a column for tyre type / size. Maybe a pattern would start to develop that might provide some empirical data I think this is where this thread is potentially misleading. There are so many variables here that to try to link one variable with someone winning/doing well is a dangerous assumption. If you were to put Michael Schumacher and me in identical cars the only obvious differing factor would be about 12" in height and I bet none of you would accept that as the reason for him going about twice the speed I could manage! The tyres a successful driver uses are merely an association, to prove causation requires you to control out the variables such as car weight/balance, suspension quality/setup, brakes, power:weight ratio etc. Oh yes, and driver ability ... possibly the biggest variable! The only objective test of tyres I've seen was in Evo magazine last year where they used a standard control car (Focus ISTR) with the same setup/wheels and drivers etc and had a series of objective tests such as cornering G on a circular track, lap times round a handling circuit, stopping distances etc. It was at Michelin's testing facility in the south of France IIRC. What was interesting there was that despite similar objective performance the drivers felt some of the tyres 'gave them more confidence'. Quote Link to comment Share on other sites More sharing options...
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