RAL­LY­ING

Motor Sport News - - Ohlins Dampers -

For ral­ly­ing, the ALR TPX/TTX range is also used. It’s tes­ta­ment to the ef­fec­tive­ness and the ad­justa­bil­ity of this range that it’s suit­able for the dif­fer­ent de­mands of both ral­ly­cross and ral­ly­ing.

“In ral­ly­ing, it’s mainly long-term en­durance you are af­ter,” says Jarl­mark Nafver. “In ral­ly­cross, it’s about be­ing able to hit other cars and not lose the wheels as well as sur­viv­ing the peak loads of the high jumps and the hard land­ings.

“In ral­ly­ing, the peak loads are fairly sim­i­lar from a ground con­tact per­spec­tive, but ob­vi­ously not from con­tact with other cars. In ral­ly­ing you also know more about what the sur­face will be like on a stage com­pared to the con­stant sur­face changes in a short time in ral­ly­cross.”

While Ohlins is not cur­rently at the top level of WRC, a quirk of the man­u­fac­tur­ers cur­rently com­pet­ing, its dampers are on the Peu­geot 208 R5 car cur­rently com­pet­ing in WRC2. In that car, Jose Suarez man­aged to set a top six time over­all on the Monte Carlo Rally, al­beit in dry­ing con­di­tions that favoured his later road po­si­tion.

“The peak loads, say on a jump in Fin­land, would be up around 40-50kn,” says Jarl­mark Nafver. “But it’s when driv­ers make mis­takes that you get the real peak loads if they put the tyre on the in­side of a cor­ner and there’s a 20cm rock in there – that’s when we see sim­i­lar loads to ral­ly­cross. That’s a test of the bend­ing re­sis­tance and the ten­sile strengths. We try to de­sign the damper so that it’s still on the car and it’s the rim that brakes.”

With en­durance also comes a tem­per­a­ture chal­lenge. On a hot rally such as the Acrop­o­lis in Greece, the dampers can face heat up to 120-150C.

In­evitably, at this level the dampers re­quire ser­vice af­ter every event, but there are Ohlins prod­ucts lower down the range with­out so many spe­cial fea­tures that don’t re­quire such fre­quent at­ten­tion.

The top-end TPX damper also has some ad­van­tages over a reg­u­lar damper de­signed to make its per­for­mance more con­sis­tent.

“The TPX is a twin-pis­ton sys­tem, com­pared to our TTX, which is twin­tube damper with two valves in the cylin­der head,” says Jarl­mark Nafver. “So what we’ve es­sen­tially done is in­stead of hav­ing both valves in the cylin­der head, we put them on the pis­ton rods, so it’s ac­tu­ally two pis­tons in­stead of one.

“The work­ing prin­ci­ple for TPX is ex­actly the same as the TTX. You are only build­ing pres­sure up­wards rather than down­wards so the low­est pres­sure in the damper will al­ways be the gas pres­sure. This changes the han­dling of the damper be­cause if you have a reg­u­lar damper where you have a sin­gle pis­ton, you can change the be­hav­iour by chang­ing the gas pres­sure.

“In such a damper, you have a pos­i­tive build-up on the side that’s re­sist­ing, then a neg­a­tive on the back side of the valves, so you need a very high gas pres­sure. On our damper, you don’t have that.”

In­ter­est­ingly, the damper is so sen­si­tive that if you run them in a static dyno, you don’t see much re­sponse on the graph based on ad­just­ments. But the dy­namic change in the real world is far big­ger and can be felt with the driv­ers. This is why Ohlins puts a lot of ef­fort into the re­sponse time of the damper by min­imis­ing the hys­tere­sis – the lag be­tween the in­put and the re­quired re­ac­tive out­put.

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