Spring rates on the Boxer and handling

Tifosiron does, try PMing him. He went with adjustable coil overs. Carobu offers boxer suspension upgrades as well and I think they are a sponsor here.

P.

 

Jim Fuchs has both, tough to get a hold of though.

 

Call Carobu.
They can probably work up what you're looking for.
John

 

Mario, I had Carobu do the suspension work as they also did the PPI. Very satisfied. They replaced the springs, I think with Eibach along with adjustable Konis. I do remember asking that the springs be 15% stiffer than stock. On a rear wheel drive you want the front to be proportionaltely a little stiffer than the rear. My car rode and drove very well. Not well enough to avoid being hit in the rear when stationary, but still quite good.

Do not forget I am in flat and relatively smooth south Florida. And the car looked great lowered.

Call Tate at Carobu.

 

Reviving an old thread...

I'm curious what the actual factory spring rates are. I'm not really sure I have the right math, so please correct me. I came up with 181 lb/in in the front, and 148 lb/in in the rear (x2). I attempted to derive these values from the workshop manual's suspension specs.

Front

- Spring length (no load): 360 mm
- Spring length (static load): 205 mm
- Static load: 500 kg

500 / (360 - 205) = 3.23 kg/mm = 181 lb/in

Rear

- Spring length (no load): 316 mm
- Spring length (static load): 210 mm
- Static load: 280 kg

280 / (316 - 210) = 2.64 kg/mm = 148 lb/in (x2)

Is that right? If so, it seems to align with Carobu's recommendation to use 225 lb/in springs in the front (leave the rear alone?). I don't see many people talking about this, but the front does seem a bit too light.

 

By modern standards thats really soft, and you can feel that in the boxers superb ride once you get rid of 42 psi trx tires.
However if one is going stiffer on springs then the right matching shocks are needed. Form my lotus experience one can go way stiffer on springs if running some superb Ohlins TTX shocks, and BBI 6x TTx would be something like 7-12K..

I think years ago Penske offered shocks for these cars, or at least a few were fitted with them.

Along the same likes to me the biggest issue on the BBi is body lean, so i'd maybe start with roll bars and roll bar bushings.

 

Exactly. I've been talking with Ohlins for a little bit, trying to figure out the right setup. Likely going with TTX36 (or maybe ILX36). You're correct, price is ~$10k for all six. Not cheap, but Ohlins is one of (if not the) best in the world and these are custom built (not some off-the-shelf product). I am hoping to finalize the specs early next week, but spring rates are part of that. I am thinking that I want to keep the rear spring rates the same, but go stiffer in the front.

Side note, I've seen Ohlins on a boxer before, but I believe it was the STJ; which is basically an adjustable and more serviceable version of the Koni – so I don't think the performance would be much different than the stock Koni converted to adjustable.

Reducing body roll from an upgraded torsion bar is a whole other ball of wax. To me, body roll is actually pretty noticeable even when cornering at moderate speeds. I don't think I've come across anyone on the forums talking about it though. I did some preliminary research a while back – looking for a more meaty and adjustable sway bar, but came up dry. Do you know of any? I was hoping the springs and compression settings would help without needing a new sway bar, but that might be wishful thinking.

 

I can only give experience with changes to my lotus track and lotus street car, both now running Ohlins.
The track car is the most illustrative example. That car came with Nitron adjustable. Those shock's with the stock "road/Track) springs always felt either too soft in the rear, or just a click away from being too hard and making the rear feel like a solid axle. We went with Ohlins ttx 36 shocks. Its pretty neat how you can order those shocks built up to your spec, everything from valving to perch heights etc. Mine were built to the same spec lotus was using on their then exige v6 race cars
so there was not guess work there.

I don't remember what e changed in terms of rear spring rates, but I do remember the fronts went from 550 lbs to 650 and we used shorter springs but very high quality ones. The ride was first of all dramatically improved as was roll so that was a win win. We're talking about a car thats pretty much getting banged over track curbs lap by lap, the suspension absorbs better now and feel to have better compliance (car not thrown about as much), yet more control ie not as loose.
That boils down to a quality shock that can provide with stiffer springs better ride, better compliance and better control.

i took a while to figure out the settings though, and there the ohlins online manual was really helpful. there felt to be still an area where the rear was either too stiff leading to premature breakaway, or too soft with a bit too much lean and resultant camber toe changes. We're talking a car running slicks going full tilt through he esses at the Glenn. Reading the manual i realized that what was needed was indeed more compression, but also less rebound so that the inside wheel maintained better contact. lean was reduced and in corner grip went way up. That then led to adjustments to camber and toe etc to take advantage of this. I have yet to touch the roll bars on this car, and according tot he ohlins manual Im probably using the shocks to mask a roll bar deficiency, which ultimately is a dead end in terms of how far you can go, but the car is 1 sec per pap quicker and running less toe and camber tore wear is dramatically improved.

Point is suspension is still part of the dark arts. Ohlins and some stiffer springs will really improve ride and roll if you get it right. Ive read the BB roll bar is fine but one should go to a modern urethane type busing for the roll bars as this will also significantly improve roll control.

if one thinks about it, most cars come with probably $500 shocks, maybe better cars come with 2k shocks, Ohlins TTX at 10k is why most cars don't have them.
in the sport motorcycle world, the same bike with adjustable factory shock and ohlins TTX show similar results. Less harshness , more control. While the Ohlins are adjustable they adjust within the range of the orifices specked, and what spec you'd need for a BBi I have no idea. Theyre also adjustable coil overs so you can play with ride height and rake which probably will show dividends too.

We know that Nick masons BBLM lapped goodwood faster than his f40 same day same driver. So the Bb chassis and suspension has much potential with springs shocks and tires.
Perhaps the most accurate critique I read about the Bb said it was car that fell between too stools, didnt know wheter it was going to be a Ferrari Gt, or a hard core car. You're certainly taking the powertrain in the BBlm direction while also maintaining street civility, thats possible with modern computer controlls O2 sesors etc. Today similar improvements can be achieved in suspension in terms of both ability and civility.

Great project.