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Old 06-22-2017, 09:50 PM   #26
John V, outside agitator
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Yeah of course the height matters as well, but in general terms for a car those should hold true . For a kart it's more tuning around the compromise of not having a differential. If you are raising the center of gravity to make a car better, then there is a compromise (differential, ground clearance, bad suspension geometry, etc). Except gravel/sand, because gravel is weird and doesn't act like asphalt.
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hey nice info but one question.. Maybe i missed it but I don't think i saw any reference at all to available travel???? Way a long time ago over on the other side of the country in Sollentuna a very sharp guy named Kent Öhlin was busy developing his first shocks which really became for the start of series production, the best shocks in the world for my sport...moto-cross... back then we were hack+sawing up frames about every 7-8 months making longer and longer travel suspension....and available suspension travel was a key factor.....
What I'm wondering is kinda obvious: If you have 75mm wheel travel it seems its going to be a bolloxed up job if you sprung--and damped it--like a 60s Merikun Sofa..alll other things being equal..
Where does wheel travel fit in your calculations??

Also: where does power? and power vs grip? Powerful car with short gearing and lots of grip is going to want substantially different than some wheezy ol thing..

Or powerful car with short gearing but low grip?? (Ya know sort of like hundreds of guys are out every weekend doing all over the country there...)

Be interested in your thoughts...
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Old 06-27-2017, 02:29 PM   #27
Poik
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Originally Posted by John V, outside agitator View Post
Hej Pojken... Having fun in Göteborg?
hey nice info but one question.. Maybe i missed it but I don't think i saw any reference at all to available travel???? Way a long time ago over on the other side of the country in Sollentuna a very sharp guy named Kent Öhlin was busy developing his first shocks which really became for the start of series production, the best shocks in the world for my sport...moto-cross... back then we were hack+sawing up frames about every 7-8 months making longer and longer travel suspension....and available suspension travel was a key factor.....
What I'm wondering is kinda obvious: If you have 75mm wheel travel it seems its going to be a bolloxed up job if you sprung--and damped it--like a 60s Merikun Sofa..alll other things being equal..
Where does wheel travel fit in your calculations??
Well, wheel travel is more of a compromise of packaging than anything else, which is why I didn't mention it. And we're talking about a 240, so the packaging has already been taken care of. In general, more wheel travel is usually better, but it doesn't do anything if you can't use it, and too much can be bad as well. In the example for the OP's car with the estimated weights and chosen front spring installed with zero preload, at ride height the front suspension will compress about 60mm, or about 57mm of compression of the strut. And that's that for rebound travel, because you can't get any more than that without reducing the spring stiffness. You can lower the spring by adjusting the spring seat so that it rattles around at full droop, and the car will be lower, but you have zero spring stiffness in that part of the stroke, so you won't really be able to generate any forces from the tire with the wheel just hanging there. In that case it doesn't make a whole lot of sense to have 60mm of rebound travel and 120mm of compression because you'll never use that much travel unless you go off a big jump or hit a speed bump at 100mph. So for cars that go off big jumps that could be nice to have to absorb the energy more linearly, but not so much for road cars. It's not going to hurt that much, but it shouldn't be prioritized. It does however give you the ability to use a longer spring aid (bump stop), and that can also allow a more linear rate.

I really don't have much/any experience with motocross, but if you were modifying the bikes for more travel, you would have had to make the springs softer at the same time to take advantage of the increased rebound travel. That would give you better grip just due to less load variation across rough terrain. And bikes don't have lateral load transfer, so the purpose/requirements of wheel travel is a lot different.

Quote:
Also: where does power? and power vs grip? Powerful car with short gearing and lots of grip is going to want substantially different than some wheezy ol thing..

Or powerful car with short gearing but low grip?? (Ya know sort of like hundreds of guys are out every weekend doing all over the country there...)

Be interested in your thoughts...
I don't really think power comes into play here very much, that's more of getting the balance correct front to rear rather than overall spring and damper level. But with more power it will more easily show the faults in the tuning. FWD/AWD/RWD will need different tuning, just as much as a BMW and a Volvo will need different tuning. Different surfaces like asphalt, gravel, and snow/ice react differently to the overall level though, so generally for gravel you want less spring than on asphalt, and on ice/snow even less, so that you slow down the load transfer. The guidelines I gave are good estimates to get in the ballpark and will satisfy 95% of the people on here. To get better than that you would have to do actual tuning of the damper components, which I think very few people on here have the time/energy/skill to do.
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Last edited by Poik; 06-29-2017 at 04:47 PM.. Reason: Correction.
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Old 12-14-2017, 08:36 PM   #28
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It has been a long time since I last wrote the things I promised in this thread. I have not taken all the measurements I would like yet (corner weights left to do), but I don’t have easy access to such scales. Anyway, will do it soon, as I may have found a solution.

I have however gathered some info, and made some progress with an excel file – calculator, which is also not finished. HERE IT IS

First of all, I found some info from the KONI dealership about the yellow shock absorbers, which for some reason they keep it “confidential”. So here they are:

Part #86-411245 Sport (front) = serviceable

@0,33 m/s -> Rebound = 950N , Bump = 700N
@0,13 m/s -> Rebound = 510N , Bump = 480N

Part # 26-1129 Sport (rear) = NOT serviceable

@0,33 m/s -> Rebound = 2200N , Bump = 1150N
@0,13 m/s -> Rebound = 1050N , Bump = 700N

I feel that these are the maximum values ie when adjusted to the hardest setting. I did ask for clarification, but I got no answer. At least this is a start.

I was also told that these dumpers are not linearly adjusted if you pass the middle setting.

Maybe some of you who followed my project know that I had my old (red) KONIs revalved to yellows. Well, as I found out this was a general assumption, since many kind (numbers – called 3,5,6 etc) of valves are available and I have no idea which were installed, and generally the red KONIs have different type of manufacturing compared to the yellows. For example a yellow with valve no3 is much stiffer than a red with valve 5!! Also my red, were just oil, while the yellows are gas-oil filled. Reds of this type are no longer available and they were front and rear serviceable, since they had no gas.

Since I intended to use the revalved reds with Ben’s coilover stuff, I had them tested at the dyno, and got some interesting results:

Front – soft setting – all left:

@ 50mm/s -> Rebound = -100N , Bump = 261N
@ 100mm/s -> Rebound = -116N, Bump = 452N
@ 150mm/s -> Rebound = -316N, Bump = 581N

Front – hard setting – all right:

@ 50mm/s -> Rebound = -268N , Bump = 214N
@ 100mm/s -> Rebound = -379N, Bump = 353N
@ 150mm/s -> Rebound = -467N, Bump = 467N

Rear – soft setting – all left:

@ 50mm/s -> Rebound = -471N , Bump = 241N
@ 100mm/s -> Rebound = -709N, Bump = 267N
@ 150mm/s -> Rebound = -837N, Bump = 287N
@ 200mm/s -> Rebound = -960N, Bump = 303N
@ 250mm/s -> Rebound = -1089N, Bump = 312N

Rear – medium setting – middle:

@ 50mm/s -> Rebound = -579N, Bump = 184N
@ 100mm/s -> Rebound = -941N, Bump = 223N
@ 150mm/s -> Rebound = -1097N, Bump = 247N
@ 200mm/s -> Rebound = -1275N, Bump = 263N
@ 250mm/s -> Rebound = -1486N, Bump = 275N

Rear – hard setting – all right:

@ 50mm/s -> Rebound = -734N, Bump = 160N
@ 100mm/s -> Rebound = -1195N, Bump = 220N
@ 150mm/s -> Rebound = -1378N, Bump = 231N

Also attaching the measurement sheets, just in case I wrote something wrong, or if someone wants to see more details.

FRONT MEASUREMENTS and REAR MEASUREMENTS

Next step is to complete my excel file with POIK's equations. Hopefully i will have more done soon
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Old 08-27-2020, 08:16 AM   #29
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What an excellent thread.
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Old 08-29-2020, 08:42 PM   #30
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Yep. Don’t know how i missed it, except i might have been on a road trip.
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