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andyowl
Sr. Member
Posts: 456
New exhaust "straight through" - good sound!
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« Reply #92 on: August 08, 2009, 10:10:09 am » |
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Suspension update, Saturday August 8th.
Well I've fitted the grease nipples to the RH rear suspension after failing to get it to move more than 2.5mm (reduction in the gap under the adjustment cam) using brute force and hammers. Looking at the sectioned trailing arm I am not too hopeful that any grease will get though. The clearance is so small and what was there is filled with ally/steel products of corrosion. I tried to get some PlusGas into the grease nipple but it came out of the side! Wait and see I suppose. I made a heavy duty clamp using two 12mm x 40mm steel bars with M20 studding at each end in an attempt to compress the adjustment cam and reduce the gap. In the end I bent the bars! Even using a "sledge" hammer, in a confined space admittedly, it still didn't shift. Even though I have reduced the clearance under the adjustment cam (I had already opened it by nearly 3 turns on the screw to give a gap of 5.8mm) to 2.6mm the change in ride height is negligible. It is still higher than Grey Baggy! I calculate there is a 1:4 ratio, gap change to ride height change, so I should be looking at a height change of around (5.8-2.6) x 4 = 3.2 x 4 = 12.8mm and that should be measurable even visible!. So I have decided that I will abandon the rear suspension changes until after the Etretat / Le Havre Hill Climb in two weeks time. "Plan B", if waiting for a while doesn't work, is to remove the arm and make a single slit at the forward ends of the casting to try and relieve the clamping forces of the casting around the steel shaft. I am thinking of using a large "U" bolt or two on each leg of the arm to augment the ally strength afterwards although my instinct is that it will not be necessary. Desperate I know but I really do need to lower the rear suspension! To my surprise the front adjusters have not been a problem. They must have been greased at some time. I have not yet worked out the ratio of adjustment to height change. At the moment there is about 30mm of thread available to adjust. I have started to measure "Ride Height" an easier way. I just want it as low as I can without tyre rubbing or grounding on the speed humps in our road! For comparison purposes I have been measuring the distance from the underside of the wheel arch to the ground on the centreline of the wheel. Saves all that stooping or crawling underneath. I would be very interested to know these dimensions on your Bagheeras! I checked our standings in the AutoSolo championship that my motor club (FDMC) are running. There are 10 cars in the Historic Class, 9 of them Healeys or MGBs and one Matra. The Matra is 5th out of 10! How about that? Andy
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andyowl
Sr. Member
Posts: 456
New exhaust "straight through" - good sound!
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« Reply #93 on: August 12, 2009, 10:03:56 am » |
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Tyres and pressures... I just sent this email to Yokohama UK about the pressures they recommend for the A048 tyres I am using. I await a reply.
Dear Simon Clark,
I would very much appreciate your comments and advice on the following set-up.
I am using A048 tyres for MSA National B Sprints and Hillclimbs plus clubman AutoSolos on a 1977 Matra-Simca Bagheera S. This is my first season.
Tyres are run cold or luke-warm, at best, after several runs. See below for further details.
Total weight on the start-line is 1,045kg with a 45/55% front/rear weight distribution i.e.: - total front 470kg and rear 575kg - or per tyre front 235kg and rear 288kg.
Tyre sizes are: F: 185/60 R13 80H R: 205/60 R13 86H based on the tyre width and circumference I have used on another road-going Bagheera for >15 years.
Wheels are 5 1/2" J original Bagheera alloys now with wheel spacers of the maximum MSA will allow i.e. 25mm.
The car is mid-engined 1,442cc with around 85BHP driving the rear wheels. Lefthand drive with full 5 point roll cage.
Could you recommend tyres starting pressures for further experimentation? I presently use 27psig (1.86barg) front and 30 (2.07barg) psig rear. I started with much lower pressures (copying the pressures used on an Alpine-Renault with A048 tyres) but the car handling was very poor. These pressures are around 2psi (0.14bar) higher than those used on the road-going Bagheera with similar width Pirelli tyres.
Understeer has been a problem but using better anti-roll bar mountings (harder bushes and Rose joints on the linkages with "slop" drastically reduced seems to be improving that. Stiffening the ARB itself has not yet been tried due to lack of suppliers.
Tyre temperatures were measured at the Longcross Chertsey Sprint last month after each run (infra-red non-contact meter). - Ambient temp was around 72F/22.2C (I forgot to measure it - sorry). I forgot also to measure the road surface temperature. Weather was cloudy but dry. - I was interested in the temperature variation across the width of each tyre as well as the average tyre temp front and rear. - Temps are measured in Fahrenheit & differences in Rankin degrees as this gives 50% better resolution with a single decimal point display. - Maximum temperature seen (after the second practice run) was 102.4F/39.1C (left rear inner - closest to the exhaust?) with the coldest 87.8F (right front centre). - After the 2nd competitive run (it rained briefly before the start of that run and the track was slightly damp): - the difference across the width of each tyre was: left front = 1.8R, right front = 0.6R, left rear = 2.8R, right rear 1.6R - the average temp on each tyre was: left front = 96.5F, right front = 95.6F, left rear = 92.4F, right rear = 92.0F (This is also the order in which I took the readings. Maybe there is some "cooling down" trend here??) - I regret that I did not check the tyre pressures again at the end of this run nor check the temps or pressures after the 3rd run. - I have all the above on an Excel spread sheet if that would help.
Hoping for your help. The tyres are fantastic and everything I was lead to believe. I will certainly buy them again for next year, unless you have something more suitable for my needs!
Thanks in advance,
Andy Owler
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